Flashcards in Neurology Deck (511):
How many cranial nerves are there?
What is the brainstem?
The part of the CNS, exclusive of the cerebellum, that lies between the cerebrum and the spinal cord
What is not bilateral in the brainstem?
The pineal gland
What is bells-palsy?
Face drooping, post-infection
Why do we have contralateral function? Where does it originate?
There is crossing over of 95% of nerves in the pyramidal decussation
Where are the sensory and motor nuclei located in the brainstem?
Sensory nuclei are lateral and motor nuclei are medial
What is one of the first areas to be damaged in Parkinson's disease?
Where are transverse fibres located in the brainstem?
What does the pons provide the floor of?
The fourth ventricle
At what point does the brainstem start to look like spinal cord?
In the lower medulla
What are the symptoms of lateral medullary syndrome?
Ipsilateral cerebellar ataxia (same side loss of control of body movements)
Ipsilateral loss of pain/ thermal sense (face)
Horner's syndrome (drooping eyelid; loss of sympathetic tone to the head and neck)
Hoarseness, difficulty swallowing
Contralateral loss of pain/ thermal sense (trunk and limbs)
How much of the body's cardiac output is used by the brain?
How much of the body's O₂ consumption is used by the brain?
How much of the body's liver glucose is used by the brain?
Where does the brain's blood supply come from?
Internal carotid arteries
Where does the vertebral artery originate?
From the subclavian artery
What do the vertebral arteries join to form?
The basilar artery
What is the only unpaired artery in the circle of Willis?
The anterior communicating artery
In what vessel does all blood drained from the brain end up?
The internal jugular vein
What is a stroke?
A rapidly developing focal disturbance of brain function of presumed vascular origin and of >24 hours duration
What is the main cause of stroke? (and percentage occurrence)
What is a transient ischaemic attack?
A rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours.
Often the precursor to a stroke
What is infarction?
Degenerative changes which occur in tissue following occlusion of an artery
What is cerebral ischaemia?
Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not quickly restored. Hypoxia is a component of ischaemia
What are the possible causes of occlusions?
Formation of a blood clot (thrombus)
Plugging of a small vessel by material carried from larger vessel (e.g. thrombi from the heart or atherosclerotic debris from the internal carotid)
What are the main risk factors for stroke?
What does the middle cerebral artery supply?
Most of the lateral aspect of the brain
What does the anterior cerebral artery supply?
Supplies the frontal lobe all the way back to the parietal-occipital fissure
What would occlusions of the anterior cerebral artery cause?
Paralysis of the contralateral leg > arm, face
Disturbance of intellect, executive function and judgement (abulia)
Loss of appropriate social behaviour
What would occlusion of the middle cerebral artery cause?
A "classic stroke"
Contralateral hemiplegia: arm > leg
Contralateral hemisensory (loss of sensation) deficits
Hemianopia (blindness over half the field of vision)
Aphasia (confuses similar sounding words) (L-sided lesion)
What would occlusion of the posterior cerebral artery cause?
- Homonymous hemianopia
- Visual agnosia (Loss of ability to recognise things)
What are the different types of haemorrhagic stroke? (4)
What commonly causes an extradural stroke? When are you likely to present?
Trauma, rupture of the vessels supplying the dura- shows immediate effects
What commonly causes a subdural stroke? When are you likely to present?
Trauma- shows delayed effects
What commonly causes a subarachnoid stroke?
What commonly causes an intracerebral stroke?
What type of haemorrhage results from a venous bleed and can take hours to present?
A subdural haemorrhage
If a patient has a sudden onset of stroke symptoms what does this suggest as the cause?
An occlusion of a vessel
A patient presents with sudden developed right-sided weakness and language dysfunction. They can understand verbal commands but cannot move their right arm and leg when asked to do so. What artery has become occluded?
Middle vertebral artery
If a patient presents with stroke symptoms that worsen over time what does this suggest is the cause?
Insufficient oxygen delivery to the brain causing function to become significantly impaired occurs when blood flow is reduced by how much?
More than 50%
If cerebral blood flow is interrupted unconsciousness will result after how long?
What is syncope?
If blood glucose concentrations fall below what level unconsciousness, coma and death will result?
Total cerebral blood flow is autoregulated between what mean arterial blood pressures?
How does the stretch-sensitive cerebral vascular smooth muscle respond to high and low blood pressure?
High BP: Contracts
Low BP: Relaxes
What happens if the blood pressure increases above the autoregulated range? What pressure is this?
If the blood pressure increases above 160 mmHg increased flow can lead to swelling of brain tissue, which is not accommodated by the closed cranium. This increases intracranial pressure - dangerous!
What controls the local regulation of cerebral blood flow?
What neural factors regulate local cerebral blood flow?
1) Sympathetic nerve stimulation (at high BP)
2) Parasympathetic (facial nerve) stimulation
3) Central cortical neurones
4) Dopaminergic neurones
What are pericytes?
A form of brain macrophage with diverse activities. They have important functions in maintaining capillary integrity and function.
Peripheral vessels have sparse pericyte coverage, while BBB capillaries have dense pericyte coverage
e.g. immune function, transport properties, contractile
What parts of the brain are innervated by dopaminergic neurones? What do they do?
Innervate penetrating arterioles and pericytes around capillaries
May participate in the diversion of cerebral blood to areas of high activity
May cause contraction of pericytes via aminergic and serotoninergic receptors
How does sympathetic nerve stimulation regulate local cerebral blood flow?
Produces vasoconstriction; probably only when arterial blood pressure is high
How does parasympathetic nerve stimulation regulate local cerebral blood flow?
Produces slight vasodilation
How do central cortical neurones contribute to the regulation of cerebral blood flow?
Release a variety of vasoconstrictor neurotransmitters such as catecholamines
What chemical factors influence the regulation of cerebral blood flow, causing vasodilation?
CO₂, pH, NO, K⁺, adenosine, anoxia and others
What produces CSF?
What is the normal volume of CSF?
What are the functions of CSF?
Protection (physical and chemical)
Nutrition of neurones
Transport of molecules
How do blood-brain barrier capillaries prevent solute and fluid leak across the capillary wall?
They have extensive tight junctions at the endothelial cell-cell contacts
What kind of molecules can cross the blood-brain barrier? Give examples. How are they removed from the CNS?
Lipophilic molecules (e.g. O₂, CO₂, alcohol and anaesthetics)
Removed directly via diffusion down concentration gradients
What are the circumventricular organs? What are these areas usually involved in? Give example of areas with these properties
Areas in the brain, close to the ventricles, that lack the blood-brain barrier properties. Their capillaries are fenestrated.
These areas of the brain are generally involved in secreting into the circulation, or where the plasma needs to be sampled
e.g. the posterior pituitary and median eminence secrete hormones; area postrema samples the plasma for toxins and will induce vomiting
Why did the old-fashioned H1 blockers make patients feel drowsy? How do the second generation antihistmaines prevent this?
They are hydrophobic and could cross the BBB. Histamine is important in wakefulness and alertness, so these antihistamines made people feel drowsy. Now used as sedatives.
Second generation antihistamines are polar and therefore do not readily cross the BBB
How does the BBB affect the use of dopamine in the treatment of Parkinson's disease?
A key therapy in Parkinson's disease is pharmacologically raising the level of dopamine in the brain. Dopamine cannot cross the BBB so L-DOPA must be used instead as it can cross the BBB via an amino acid transporter, to then be converted to dopamine in the brain.
Circulating L-DOPA is also converted to dopamine peripherally, so very little is able to access the brain. L-DOPA must be co-administered with the DOPA decarboxylase inhibitor Carbidopa, which cannot cross the BBB, so does not affect the conversion in the brain
What are the two major parts of the diencephalon?
What is the thalamus?
A collection of several large nuclei that serve as synaptic relay stations between the cerebral cortex and the rest of the CNS
It is an important integrating centre for most inputs to the cortex
Key role in:
- general arousal
- focussed attention
Divided into right and left thalamus by the third ventricle connected by the intermediate mass. Ipsilateral connections with the two hemispheres (no interaction across the midline)
What is the ventral lateral nucleus connected to? What is it's function?
Connected with the motor corticles (primary, premotor and supplementary)
Helps to function in coordination and planning of movement, and in learning movement
What is the ventral anterior nucleus connected to? What is it's function?
Connected with the motor corticles (primary, premotor and supplementary)
Helps to function in planning movement, and initiates wanted movement and inhibits unwanted movement
What is the ventral posterolateral nucleus connected to? What is it's function?
Connected with the primary somatosensory cortex for the body
It sends touch and proprioceptive information to the primary somatosensory cortex from the body
What is the ventral posteromedial nucleus connected to? What is it's function?
Connected with the primary somatosensory cortex for the head
It sends touch and proprioceptive information to the primary somatosensory cortex from the head
What is the lateral geniculate nucleus connected to? What is it's function?
Connected with the visual system, sending information to the primary visual cortex in the occipital lobe
What is the medial geniculate nucleus connected to? What is it's function?
Connected with the auditory system, acting as a key auditory relay between the inferior colliculus of the midbrain and the primary auditory cortex
What do the anterior, lateral dorsal and dorsomedial association nuclei connect to?
Parts of the limbic system
(cingulate and prefrontal cortex)
What do the lateral posterior and pulvinar association nuclei connect to?
Connect with the association cortex at the parieto-temporo-occipital junction and the prefrontal cortex
What are intralaminar nuclei? What are they part of? Where do they receive input from?
Small nuclei embedded in the lamina dividing the thalamus
They form part of the reticular activating system; responsible for the control of the level of arousal of the brain by modulating the level of activity of the cerebral cortex
They receive inputs from the reticular formation of the brainstem, and then project diffusely throughout the cortex
What nuclei receive inputs from the reticular formation of the brainstem?
What is the structure of the reticular nucleus?
A fine sheet of neurotissue that lies over the lateral surface of the thalamus like a net (has good access to other thalamic nuclei, but no direct connections with the cerebral cortex)
What is thalamic syndrome? What causes it?
Caused by cerebrovascular events (e.g. strokes)
Results in contralateral hemianaesthesia, burning or aching sensations on one-half of the body, often accompanied by mood swings. Sensation if reduced, exaggerated or altered and there is emotional disturbance (e.g. depression)
Where is the hypothalamus located?
Below and anterior to the thalamus
Posterior to the optic chiasm and pituitary infundibulum
What do the paraventricular nucleus and supraoptic nucleus contain?
Contains oxytocin and vasopressin neurones which project into the posterior pituitary
Contains neurones which regulate ACTH and TSH secretion from the anterior pituitary, as well as gastric reflexes, maternal behaviour, blood pressure, feeding, immune responses and temperature
How does the hypothalamus coordinate homeostatic mechanisms?
1) The autonomic nervous system
(via connections with the brainstem and spinal cord)
2) The endocrine system
(via the pituitary)
3) Controlling behaviour
(via connections with forebrain structures)
What forebrain structures are associated with the hypothalamus?
Limbic system (hippocampus, amygdala, cingulate cortex, septal nuclei)
What is the hypothalamus responsive to? (7)
2) Olfactory stimuli
4) Neural information
5) Autonomic inputs
6) Blood-bourne stimuli
(like leptin, ghrelin, angiotensin, insulin, pituitary hormones, cytokines etc)
What behaviours does the hypothalamus control?
1) Eating/drinking behaviours
via appetite sensors
3) Sexual behaviour
4) Circadian rhythm
controlled by light-sensitive nuclei
What are the cranial nerves?
1) Olfactory nerve
2) Optic nerve
3) Occulomotor nerve
4) Troclear nerve
5) Trigeminal nerve (V1, V2 and V3)
6) Abducent nerve
7) Facial nerve
8) Vestibulococclear nerve
9) Glossopharyngeal nerve
10) Vagus nerve
11) Accessory nerve
12) Hypoglossal nerve
What foramen does each cranial nerve exit the skull from?
1) Cribriform plate of the ethmoid bone
2) Optic Canal
3/4/6) Superior orbital fissure
5) V1- Superior orbital fissure
V2- Foramen rotundum
V3- Foramen ovale
7) Internal acoustic meatus to stylomastoid foramen
8) Internal acoustic meatus
9/10/11) Jugular foramen
12) Hypoglossal canal
Which nerve is the only one to exit dorsally?
Which cortical areas are supplied by the middle cerebral artery?
Primary motor cortex for face
Primary motor cortex for arm
Primary somatosensory cortex for arm
Primary auditory cortex
Which cortical areas are supplied by the anterior cerebral artery?
Primary motor cortex for foot
Which cortical areas are supplied by the posterior cerebral artery?
Primary cerebral artery
What are the differences in size and shape between C5 and L5 vertebrae?
C5 is larger and more oval-shaped
What are the differences in the proportion of white to grey matter between C5 and L5 vertebrae?
Greater proportion of white matter at C5 as all descending and ascending tracts must pass through this area
What is the cuneate fasciculus? What is the difference between this in the C5 and L5 vertebrae?
Touch and proprioception from upper limb
Present in C5 but not in L5
What anatomical feature distinguishes the thoracic sections from other levels of the cord?
The presence of the intermediolateral column, which contains the cell bodies of the preganglionic sympathetic neurones
What are Betz cells? How does their structure support their function?
Upper motor neurones
They have a large cell body to support their long projection axons down to the ventral horn of the spinal cord
What is the distinguishing feature of layer 1 of the cerebral cortex?
It has very few neurones, just fibres and glial cells
What is the role os mechanoreceptors?
- light touch
- joint position
- muscle length
- muscle tension
What defines a tickle?
Relatively mild stimulation caused by something moving across the skin. May be pleasurable
Wher can tickling occur?
At areas of the body with naked unmyelinated afferent nerve fibres
What defines an itch?
An annoying local mechanical stimulation or chemical agent (e.g. histamine, kinins)
Relieved by scratching- stimulation of large nerve fibres overwhelms spinal transmission (closes the Gate)
Occurs in neuropathy, renal failure, dermatitis
What receptor is responsible for the cool feeling you get when eating mint?
What it Trpv1 receptor sensitive to?
Activated by >42°C, <17°C and chilli
Causes the burning feeling in extremem cold
What results from the loss of function mutation NaV1.7?
Born with an inability to feel pain- very rare
What is the nociceptor stimulus threshold? Is it the same in every individual?
The weakest stimulus required to elicit a specific response or reflex
Varies in relation to anatomical location, and inter-individual differences (low/high pain threshold)
What determines the stimulus intensity?
- Frequency of action potentials generated
- Number of separate receptors activated
What is recruitment of sensory neurones?
Where adjacent sensory neurones are activated when stimulus intensity increases
What is lateral inhibition of neurones? Where is it mediated?
Where activation of one neural unit inhibits another. Allows pin-point accuracy in localisation of the stimulus
Mediated by interneurones within the dorsal horn of the spinal cord
What is two-point discrimination of neurones? Where is greatest and poorest?
The ability to detect that tewo stimuli are distinct from one another.
Weakest in the back (65mm)
Strongest in the fingers (2mm)
What is neural adaptation?
If a stimulus of constant strength is maintained for a period of time the frequency of action potentials diminishes
What type of receptor responds rapidly to neural adaptation?
What type of receptor responds slowly to neural adaptation?
What are the different nerve fibre types and their function?
α- Proprioception, somatic motor
β- Touch, pressure
γ- Motor to muscle spindle
δ- Pain, cold, touch
What is the function of C-type nerve fibres
Dorsal root- Pain, temperature, mechanoception
Sympathetic- Postganglionic sympathetic
What is the Cortical Homunculus?
A map of the body within the brain
Which nerve fibre transmits painful stimuli?
Where is the dorsal root ganglion?
In the posterior spinal nerve root
Which of the following is not an example of a mechanoreceptor?
- Dermal plexus
- Pacinian corpuscle
- Papillary plexus
- Ruffini ending
- Lissauer's corpuscle
Where do pain and temperature pathways decussate?
In the spinal cord
Where do touch and proprioception pathways decussate?
In the brainstem
Wha is the Gate Control Theory?
A non-painful stimulus can inhibit transmission of a painful stimulus
What are the different types of pain? (6)
What is the WHO analgesic ladder for cancer pain relief?
1) Paracetamol, aspirin and ibuprofen
2) Codeine and tramadol
What is myalgia? What are the features of this type of pain?
Describe somatic pain. What are the features?
A type of nociceptor pain that is well localised (affects the skin).
What are dermatomes?
A section of the skin which corresponds to a nerve root from the spinal cord
Describe visceral pain.
Viscera have low-density of sensory innervation. Characteristically midline pain at level of the sternum/epigastrium.
Pain may be referred. Requires a multimodal treatment
What is hyperalgesia?
Increased pain from a stimulus that normally provokes pain
Hypersensitivity to pain
What is the wind-up phenomenon?
Where repetitive stimulation of wide dynamic range neurones induces increased evoked response and post-discharge with each stimulus
Describe neuropathic pain?
Pain in an area of neurological dysfunction. Has poor response to normal analgesic drugs. Can last after the area has healed completely
- electric shock
What criteria is used to diagnose Complex Regional Pain Syndrome?
IASP Budapest criteria
What is Complex Regional Pin Syndrome?
Severe form of neuropathic pain with neurogenic inflammation
Overexpression of nociceptive endings
Treated with medication and spinal cord stimulation
What causes phantom limb pain?
Remapping of the cortical homunculus. Areas lying near to the area which controls the amputated limb begin to stimulate phantom limb pain
What drugs are used to treat neuropathic pain?
Topical (e.g. Capsaicin)
How do capsaicin patches work to treat neuropathic pain?
Capsaicin binds to TRPV1 receptor on nerve endings allowing influx of calcium. Capsaicin has direct toxicity to mitochondria, which reduces the number of nerve endings
Nociceptive impulses are transmitted by which nerve fibres?
A-δ and C
What is allodynia?
Pain due to a stimulus that does not normally provoke pain
Functionally, what are the three areas of the cerebral cortex? Describe their function.
- receive sensory information from the thalamus and include primary visual, primary auditory and primary somatosensory cortex
- concerned with motor control. Include the primary motor cortex (M1: executes voluntary movements) and the motor association cortex (which selects voluntary movements). Also motor functions have been described for the posterior parietal cortex and dorsolateral prefrontal cortex
- include Brocke's and Wernicke's area. Function to produce a meaninful perceptual experience fo the world, enabling us to interact effectively and carry out abstract thinking and language
What is hierarchical organisation?
Where high order areas (somatosensory cortex, prefrontal cortex, motor association corticles, basal ganglia, thalamus, primary motor cortex and cerebellum) are involved in the more complex task of programming and planning movements, and coordinating muscle activity.
Lower level areas (brain stem and spinal cord) perform the execution of movement
What are the different areas of the motor cortex?
1) Primary motor cortex (M1)
2) Premotor cortex
3) Supplementary motor area
What is Broadmann's area 4? Where is it located and what is it's function? What cells are found in this area?
The primary motor cortex
Located in the frontal lobe on the precentral gyrus, anterior to the central sulcus
Function: controls (initiates) fine, discrete, precise voluntary movements. Provides the descending signals to execute movements
Contains Betz cells which send their axons down to the spinal cord via the corticospinal tract
What is innervated by the lateral corticospinal tracts?
Where do these axons decussate?
Innervates arms and legs
Decussates in the pyramidal decussations (medulla)
What is innervated by the anterior corticospinal tracts? Where do these axons decussate?
Innervates muscles of the front, back and proximal part of the limbs
Decussates in the spinal cord
What type of signalling is used to transmit signals from the brain all the way to the muscles?
Generation and propagation of an action potential along the axon in electrical
Impulse transmission is chemical mediated by neurotransmitters
What is in Broadmann's area 6? Where are they located and what are their function?
- Located in the frontal lobe anterior to the primary motor cortex
- Involved in planning movements; regulates externally cued movments
Supplementary Motor Area
- Also anterior to the primary motor cortex, but more medial
- Involved in planning complex movements and programming sequencing of movements. Regulates internally driven movements (e.g. speech)
What is located in the Association cortex?
Posterior Parietal Cortex
- ensures movements are targeted accurately to objects in external space
- involved in selection of appropriate movements for a particular course of action
What are the positive and negative signs of an upper motor neuron lesion?
Loss of function (-)
- Paresis: graded weakness of movements
- Paralysis (plegia): complete loss of muscle activity
Increased abnormal motor function (+) (loss of inhibitory descending inputs)
- Spasticity: increased muscle tone
- Hyperreflexia: exaggerated reflexes
- Clonus: abnormal oscillatory muscle contraction
- Babinski's sign
How are the tongue muscles innervated from the descending motor pathway?
Corticobulbar tract from the head region of the motor cortex; synapses with the hypoglossal nerve which innervates the tongue
What is apraxia? What causes this?
A disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movement
Lesion of inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area) can cause apraxia; stroke and dementia are the most common causes
What are the symptoms of a lower motor neuron lesion?
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Fasciculations: damaged motor units produce spontaneous action potential resulting in a visible twitch
Fibrillations: spontaneous twitching of individual muscle fibres, recorded during needle electromyography examination
What are the upper motor neuron signs of motor neuron disease?
- Increased muscle tone (spasticity of limbs and tongue)
- Brisk limbs and jaw reflexes
- Babinski's sign
- Loss of dexterity
What are the lower motor neuron signs of motor neuron disease?
- Muscle wasting
- Tongue fasciculations and wasting
- Nasal speech
What part of the brain controls the execution of movements?
Primary motor cortex
What part of the brain controls the planning of movements?
Premotor cortex and the supplementary motor area
What part of the brain controls the selection and accuracy of movements?
What is the role of side loops in the motor hierarchy?
Brain circuits which "help" the cortical areas to smoothly regulate motor behaviours
What structures form the basal ganglia?
Striatum: caudate and putamen
Globus pallidus externa (GPe) and globus pallidus interna (GPi)
Substantia nigra pars compacta (SNc) and pars reticulata (SNr)
Subthalamic nucleus (STN)
What is the function of the basal ganglia?
- Elaborating associated movements (e.g. swinging the arms when walking, facial expression matching emotions)
- Moderating and coordinating movement (suppressing unwanted movements)
- Performing movements in order
Where does the striatum (in the basal ganglia) send and receive information from?
Receives input from many brain areas
Sends output only to other components of the basal ganglia
What is the pathway of the basal ganglia input and output?
Input from the cortex enter the putamen in the basal ganglia:
- Direct pathway: to the GPi and SNr (involving GABA)
- Indirect pathway: to the GPe via STN (involving GABA)
GPi and SNr are the only output from the basal ganglia with projections to the thalamus, and via the thalamus back to the cortex (supplementary motor area and premotor cortex)
How is the basal ganglia pathway inhibited or excited?
The globus pallidus and the substantia nigra inhibit the thalamus (GABA)
The putamen inhibits GPi and SNr which releases the thalamus from inhibition
The thalamus releases the selected movement through it's projections into the cortex
The correct balance of excitation/inhibition of the thalamus is maintained by the SNc which provides excitatory inputs to the striatum (dopamine)
What are the different classes of syndromes that occur through damage to the basal ganglia?
Hypokinetic: decreased movement
(e.g. Parkinson's disease)
Hyperkinetic: increased movement (Huntington's disease)
What causes Parkinson's disease?
Neuronal degredation of substantia nigra pars compacta causes loss of nigro-strial dopaminergic axons in striatum
>80% loss of dopamine cells
- disruption of the fine balance of excitation and inhibition
- reduction of the excitation motor cortex
What are the main signs of Parkinson's disease?
Bradykinesia- slowness of (small) movements (doing up buttons, handling a knife)
Hypomimic face- expressionless, mask-like (absence of movements that normally animate the face)
Akinesia- difficulty in the initiation of movements because cannot initiate movements internally
Rigidity- Muscle tone increase, causing resistance to externally imposed joint movements
Tremor at rest- Starts in one hand (pill-rolling tremor), with time spreads to other parts of the body
Parkinsonian's gait- walking slow, small steps, shuffling feet, reduced arm swing
Stooped posture- Head and body bent forward and downward
What is Huntington's disease?
Neurodegenerative genetic disorder
Abnormality in chromosome 4. Autosomal dominant
Degeneration of GABAergic neurons in the striatum (caudate first then putamen later)
- disruption of fine balance between inhibition and excitation
- motor cortex gets excessive excitatory input
- motor cortex continuously sends involuntary commands for movements and movement sequences to the muscles
What are the main signs of Huntington's disease?
Choreic movements (chorea): rapid jerky involuntary movements of the body. Hands and face affected first then legs and the rest of the body
- Speech impairment
- Difficulty swallowing
- Unsteady gait
Later on, cognitive decline and dementia
What are the three horizontal lobes of the cerebellum?
What are the three sagital zones of the cerebellum?
What side of the body and cerebral hemisphere is the cerebellum connected to?
SAME side of the body
OPPOSITE cerebral hemisphere
What are the main neurotransmitters in the cerebellum?
What lobe is the vestibulocerebellum? What is the function of this region?
The flocculonodular lobe
- regulation of gait, posture and equilibrium
- coordination of head movements with eye movements
What parts of the cerebellum make up the spinocerebellum? What inputs project into each area?
What is the function of the spinocerebellum?
Spinal afferents from axial portions of the body, trigeminal, visual and auditory inputs
Spinal afferents from the limbs project to the intermediate hemisphere
Coordination of speech
Adjustment of muscle tone
Coordination of limb movements
What part of the cerebellum makes up the cerebrocerebellum? What is the function of this area?
The lateral hemisphere
Coordination of skilled movement
Cognitive function, attention processing of language
What is the function of the cerebellum?
1) Maintenance of balance and posture
2) Coordination of voluntary movements
3) Motor learning
4) Cognitive functions (language)
What causes and results from Vestibulocerebellar Syndrome?
Damage (tumour) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when sitting with eyes open)
What causes and results from Spinocerebellar Syndrome?
Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly the legs, causes abnormal gait and stance (wide-based)
What causes and results from Cerebrocerebellar Syndrome?
Damage affects mainly arms/skilled coordinated movements (tremor) and speech
What are the main signs of cerebellar disorders?
Deficits apparent only on movement
- Ataxia: general impairments in movement, coordination and accuracy
- Dysmetria: inappropriate force and distance for target-direted movements
- Intention tremor: increasingly oscillatorytrajectory of a limb in a target-directed movement
- Dysdiadochokinesia: inability to perform rapidly alternating movements
- Scanning speech: staccato, due to impaired coordination or speech muscles
Give an example of hereditary and acquired cerebellar disorders.
Hereditary- Friederich's Ataxia
Acquired- Multiple Sclerosis
How can the membrane potential of the post synaptic neurone be altered?
1) Made less negative (closer to activation threshold)- an excitatory post synaptic potential (EPSP)
2) Made more negative (further away from activation threshold)- inhibitory post synaptic potential (IPSP)
Graded effects- summation
What is the neuromuscular junction?
A specialised synapse between the motor neurone and the motor end plate, the muscle fibre cell membrane
How is the neuromuscular junction activated?
Action potential arrives at NMJ, Ca²⁺ influx causes ACh release. ACh binds to receptors on the motor end plate.
Ion channel opens- Na⁺ influx causes action potential in muscle fibre
What are miniature end-plate potentials?
Where at rest, individual vesicles release ACh at a very low rate
What are the alpha motor neurones?
The lower motor neurones of the brainstem and the spinal cord. They innervate the (extrafusal) muscle fibres of the skeletal muscles
Their activation causes muscle contraction
The motor neuron pool contains all alpha motor neurons innervating a single muscle
Where are alpha motor neurones located in the anterior horn in relation to the muscles they innervate?
Flexor muscles- posterior part of the horn (tend movement to the foetal position) e.g. biceps and hamstrings
Extensor muscles- anterior part of the horn (tend movement to straighten the body) e.g. triceps and quadriceps
Distal muscles- lateral part of the horn e.g. muscles of fingers
Proximal part of the horn- medial part of the horm e.g. muscles of the trunk
What is a motor unit?
A single motor neuron together with all the muscle fibres that it innervates
What are the different types of motor neuron? How are they classified?
3 typres classified by the amount of tension generated, speed of contraction and fatigability of the motor unit
- Slow (S, type I)
- Fast, fatigue resistant (FR, type IIA)
- Fast fatiguable (FF, type IIB)
Starts with the smallest diameter cell bodies, smallest dendritic tree, thinnest axon and slowest conduction velocity- gets faster as moving down the groups
What are the two mechanisms by which the brain regulates the force that a single muscle can produce?
What is the recruitment method of regulation of muscle force?
"Size principal"- smaller units are recruited first (these are generally the slow twitch units). As more force is required, more units are recruited
This allows fine control (e.g. when writing), under which low force levels are required
What is the rate coding method of regulation of muscle force?
A motor unit can fire at a range of frequencies. Slow units fire at a lower frequency. As the firing rate increases, the force produced by the unit increases
Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potential
What are neurotrophic factors?
Growth factors which prevent neuronal death and promote growth of neurons after injury
What are the effects of neurotrophic factors on muscle?
Motor unit and fibre characteristics are dependent on the nerve which innervates them. If a fast twitch muscle and a slow muscles are cross innervated the soleus becomes fast and the fast muscle becomes slow
What fibre type changes can occur in muscle? (plasticity of motor units)
Training: Type IIB to IIA (fatiguable to fatigue resistant)
Spinal cord injury/microgravity: Type I to type II
Aging: loss of type I and type II fibres; preferential loss of type II fibres- larger proportion of type I fibres in aged muscle
What is a reflex?
An automatic response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outwards to an effector without reaching the level of consciousness
Magnitude and timing are determined by the intensity and onset of the stimulus
What are the components of a reflex arc?
1) Sensory receptor
2) Sensory neuron
3) Integrating centre
4) Motor neuron
5) Effector (muscle or gland)
What is the mechanism of the monosynaptic reflex?
1) Stretching stimulates sensory receptor (muscle spindle)
2) Sensory neuron excited
3) Within integrating centre (spinal cord) sensory neurone activates motor neuron
4) Motor neuron excited
5) Effector (same muscle) contracts and relieves the stretching
( Motor neuron to antagonistic muscles is inhibited)
What is the mechanism of the flexion withdrawal (polysynaptic) reflexes?
1) Stepping on glass stimulates sensory receptor (dendrites of pain-sensitive neuron)
2) Sensory neuron excited
3) Within integrating centre (spinal cord) sensory neuron activates interneurons in several spinal cord segments
4) Motor neurons excited
5) Effectors (flexor muscles) contract and withdraw leg; other leg extends to maintain balance and upright position
How does supraspinal control influence reflexes?
Higher entres of the CNS exert inhibitory and excitatory regulation upon the stretch reflex.
In normal conditions the inhibitory control dominates
Rigidity and spasticity can result from brain damage giving overactive or tonic stretch reflex
how can higher centres influence reflexes? (5)
1) Activating alpha motor neurons
2) Activating inhibitory interneurons
3) Activating propriospinal neurons
4) Activating gamma motor neurons
5) Activating terminals of afferent fibres.
What higher centres and pathways are involved in supraspinal control of reflexes?
Cortex- corticospinal (fine control of limb movements, body adjustments)
Red nucleus- rubrospinal (automatic movements of arm in response to posture/balance)
Vestibular nuclei- vestibulospinal (altering posture to maintain balance)
Tectum- tectospinal (head movements in response to visual information
What is the gamma reflex loop?
When the joint is extended and the muscle goes slack the spindle is shortened to maintain it's sensitivity
What is hyporeflexia?
below normal or absent reflexes
Mostly associated with lower motor neuron diseases
What is Brown-Séquard syndrome?
Damage to one-half of the spinal cord resulting in ipsilateral paralysis and loss of proprioception and contralateral loss of pain and temperature sensation
What causes jerking movements in a patient who has had a stroke?
Caused by too much glutamate being released. The site of the infarct is an epileptic focus. The levels of ATP cannot be controlled; glutamate is ATP dependent so too much is being released.
Which pathways are affected in Locked In syndrome?
Lesion at the level effecting corticospinal and corticobulbar tracts to spinal and brain stem. The abducens nucleus is effected (lateral eye movement lost)
Below the oculomotor nucleus is intact (vertical eye movement)
Where is the lesion that causes Locked In Syndrome? Why are sensation and consciousness not affected?
Occlusion of the basilar artery which supplies regions in the pons.
Ventral (anterior) brain stem (ascending sensory and reticular formation spared)
Internal carotid artery and circle of Willis supply forebrain and midbrain
What symptoms are seen in a patient with an upper motor neuron lesion?
Increased tone: spasticity and clonus
What symptoms occur in a patient with a lower motor neuron lesion?
Normal or flaccid tone
Reflexes are reduced or absent
Fasciculations and atrophy
Brisk reflexes are indicative of what kind of nervous system lesion?
Upper motor neuron lesion
Tongue wasting is indicative of what kind of nervous system lesion?
Lower motor neuron lesion
If a patient has absent abdominal reflexes while other reflexes are brisk what does this suggest about the affecting lesion?
Lesion is affecting the corticospinal pathway
What is transmitted in the dorsal column pathway? Where does this pathway decussate?
Ascending (sensory) neurones for touch and proprioception are delivered through the CNS to the cortex
Decussates in the brainstem (medulla)
What is transmitted in the spinothalamic pathway? Where does this pathway decussate? Where is the signal transmitted to?
Information about nociception and temperature
Decussated in the spinal cord (after entering) and transmits signals through the spinothalamic tract through the brainstem and midbrain to the thalamus
In the dorsal columns pathway where does information in the gracile fasciculus originate?
Information from the sacral and lumbar regions
In the dorsal columns pathway where does information in the cuneate fasciculus originate?
Information from the thoracic and cervical regions
What is transmitted in the corticospinal pathway? Where does this pathway decussate?
The largest component of the descending motor pathway.
(Important for fine independent movements, mainly of the hands and feet)
This pathway decussated in the pyramids in the medulla
How much of the corticospinal tract decussates in the pyramids? Once they decussate what part of the corticospinal tract do they form?
85% of the tract decussates in the pyramids to form the lateral corticospinal tract
15% remains uncrossed to form the anterior corticospinal tract
What is a fasciculation?
An involuntary abnormal contraction of all muscle fibres on a single muscle unit. It is random and unique to lower motor neuron lesions
Give an example of a pure corticospinal tract disease.
Motor neuron disease
What is paraesthesia?
Altered sensation (e.g. pins and needles)
What is dysarthria?
What is rigidity?
Where the same amount of force has to be applied to both flex and extend a joint
What is spasticity?
The more force the more the rigidity becomes obvious; then it goes away
Why do you not get weakness in Parkinson's disease?
Because it is not a lower motor neurone lesion. It does not involve the pyramidal tract
What areas of the body have better resolution in two point discrimination and what areas have low resolution?
Tongue and finger pads have high resolution
Back has very low resolution
What are the three bones of the ear called?
What role in hearing does the outer ear play?
The outer ear focuses sound on the tympanic membrane and boosts sound pressure
What role in hearing does the middle ear play?
Increases pressure of vibrations by
- focussing vibrations from large surface area (tympanic membrane) to smaller surface area (oval window). The change in surface area means the pressure is increased
- The incus has a flexible joint with the stapes (ossicles use leverage to increase the force on the oval window)
How is the ear protected from loud noises?
The muscles in the middle ear contract to protect the ear from loud noises
- Stapedius muscle
- Tensor tympani muscle
What is the function of the inner ear?
- To transduce vibration into nervous impulses
- Also produces a frequency (or pitch) and intensity (or loudness) analysis of the sound
What are the three compartments of the inner ear?
- Scala vestibuli
- Scala tympani
- Scala media
What fluid is contained in the different compartments in the inner ear?
Scala vestibuli and scala tympani contains perilymph
Scala media contains endolymph
What is the cochlear made of?
What membrane separates the compartments of the cochlear?
What is the structure of the basilar membrane in the ear?
Arranged using the same principle as a xylophone
It is sensitive to different frequencies at different points along it's length
The base is sensitive to high frequencies and is narrow and tight
The apex is sensitive to low frequencies and is wide and loose
What hair cells in the ear contain afferent fibres and which contain efferent fibres?
Inner hair cells contain afferent fibres
Outer hair cells contain efferent fibres
What are the projections from hair cells in the ear called?
What are the concentrations of K⁺ and Na⁺ in the endolymph and perilymph?
Endolymph: High K⁺ and low Na⁺
Perilymph: High Na⁺ and low K⁺
How do higher amplitudes of sound affect the hair cells in the ear?
Louder sounds will cause greater deflection of stereocilia and cause K⁺ channel opening
What causes depolarisation of hair cells in the ear?
Upward movement of the basilar membrane displaces stereocilia away from the modiolus
K⁺ channels open allowing K⁺ to enter the endolymph and causing hair cell depolarisation
What causes hyper-polarisation of the ear?
Downward movement of the basilar membrane displaces stereocilia towards modiolus
K⁺ channel closes causing the hair cell to hyperpolarise
What is the central auditory pathway from the cochlear?
Spiral ganglions from each cochlea project via auditory vestibular nerve to the ipsilateral cochlear nuclei (monoaural neurons)
After this point all connections are bilateral
Deafness in one ear due to central causes are caused by what?
Something affecting the cochlear nucleus or nerve VIII
How is hearing organised in the brain?
What level of decibels can humans hear?
0 to 120 dB
What method of investigation is used to evaluate the tympanic membrane?
What is a tuning fork used for in the evaluation of hearing loss? What frequencies do these work at?
Used to differentiate between conductive and sensineural hearing loss.
Routine practices 256Hz, 512Hz and 1024Hz are used (large forks vibrate at a lower frequency
What is the Rinne tuning fork test? What is it used for and what would the result show as?
A Rinne hearing test involves holding the tuning fork vertically in the meatus, then placing the foot plate of the fork on the mastoid bone. It is used to evaluate unilateral conductive hearing loss.
Conductive hearing loss would be louder when placed on the mastoid bone compared to next to the meatus
What is the Weber tuning fork test? What is it used for and what would the result show as?
The Weber tuning fork test is used to differentiate between unilateral conductive and sensorineural hearing loss.
A tuning fork is placed on the top of the head. Normally it will be heard equally on both sides.
In conductive hearing loss it will be heard on the side of the impairment. In sensorineural hearing loss it will be heard on the opposite side of the impairment
What are the methods of assessing hearing?
- Speech audiometry
- Pure tone audiometry
3) Otoacustic emission
What is tympanometry?
An examination used to test the condition of the middle ear and mobility of the tympanic membrane and the conduction bones by creating variations of air pressure in the ear canal
What is spontaneous otoacoustic emission?
Low-intensity sounds called OAEs are produced in a normal cochlea by the outer hair cells as they expand and contract.
Part of the newborn screening program
What are the different types of hearing loss?
1) Conductive hearing loss
2) Sensorineural hearing loss
3) Mixed hearing loss
What defines mild hearing loss (dB)?
A loss of 20-40dB
What defines moderate hearing loss (dB)?
A loss of 40-70dB
What defines severe hearing loss (dB)?
A loss of 70-90dB
What defines profound hearing loss (dB)?
A loss of 90-120(max) dB
What are the possible causes in the outer ear of conductive hearing loss?
What is congenital atresia?
Collapse or closure of the ear canal
May occur in isolation, but typically associated with congenital malformations of the middle ear
What is external otitis?
Swelling and redness of the EAC. Causes pain on mobilisation of the ear and tragus. Can cause systemic symptoms in severe cases
What is exostosis?
Benign bone growth, usually in people with a history of exposure to repeated cold water (divers / surfers)
Usually bilateral with possible extension to the middle ear
Presents with hearing loss, external repeat ear infections and accumulation or ear wax
What are the possible causes in the middle ear of conductive hearing loss?
Acute otitis media
Otitis media with effusion
Chronic otitis media
What is acute otitis media?
Inflammation of the middle ear
What is otitis media with effusion?
Inflammation of the middle ear characterised by the accumulation of fluid
Presents with a history of flu; hearing loss, ear fullness and autophonia
What are the different types of retraction of the tympanic membrane?
What are the different types of perforation of the tympanic membrane?
Inactive and active (inflammation)
What is a cholesteatoma?
Destructive and expanding growth consisting of keratinizing squamous epithelium in the middle ear and/or mastoid process
Serious but treatable ear condition
What is otosclerosis?
Begins as a soft, spongy growth of new bone - may appear anywhere in the middle ear but most often near the oval window
In 90% of cases, there are no symptoms. Otherwise the growth reduces the mobility of the stapes and results in conductive hearing loss
What is the treatment for otosclerosis?
What are the possible causes of sensorineural hearing loss?
Sudden hearing loss
Noise-induced hearing loss
What is presbyacusis?
Loss of hearing associated with aging
Begins in adolescence
It is gradual and symmetric
Men are affected twice as much as women
Often associated with tinnitus
What drugs are considered ototoxic?
Antibiotics: aminoglycosides, tetracyclines
Chemotherapeutic agents: cisplatin, flurocilo
Antimalarials: quinine, chloroquine
What types of infection can cause sensorineural hearing loss?
Bacterial or viral infections that invade the inner ear
Mumps, measles, meingitis, encephalitis, chicken pox, influenza and syphalis
What are the semicircular canals stimulated by?
What are the otolith organs stimulated by?
What are the signals from the semicircular canals and the otolith organs used for?
Control balance reactions
Provide spatial reference for other sensory motor coordinations
Provide compensatory reflexes (Vestibular Ocular Reflex)
Tune cardio-vascular function for reorientations
Serve perception of motion in space
What is the vestibular ocular reflex?
Only eye movement control can stabilise the eyes during high-frequency oscillation.
When the head rotates to the left, the eyes rotate to the right and saccade to the left
VOR operates to maintain the gaze on a selected target
What is the vestibulo-ocular pathway?
Superior and medial neurons project to motor nuclei supplying extraocular muscles
Axons ascend in the MLF and excite the ipsilateral oculomotor (III) nucleus and the contralateral abducens (VI) nucleus
What is vestibular nystagmus?
If there is a vestibular lesion on one side the resting discharge on the opposite side signals to the brain as if the head is turning to that side. The patient experiences illusory spinning to that side and has a nystagmus (as the canal signals drive the eyes in a slow phase movement). Periodically the brainstem generates fast phases (saccades) which drive the eyes back to the centre creating a vestibular nystagmus
What vestibular nerve signals occur when turning the head to the right?
When the head accelerates to the right, the right canals are stimulated by increased firing on the right vestibular nerve. Firing decreases on the left nerve
When the head is stationary what signals act on the vestibular nerve?
The vestibular nerve supports a tonic resting discharge; firing on the right and left nerves equally- because they are opposite they cancel each other out
What is the caloric response? (ear) What is a normal response?
Thermal stimulation of individual horizontal canals of the labyrinth. Temperatures (< 37°C
What caloric response indicates canal paresis?
Small amplitude short duration response to both hot and cold on one side
What caloric response indicates bilateral hypofunction?
Bilateral small short responses
What are the characteristics of acute unilateral vestibular disorder?
Symptoms: Vertigo, ocillopsia, imbalance, nausea, vomiting, abrupt onset
Signs: Nystagmus, pallor, obvious ataxia
Treatment: Steroids + anti-viral (cyclovirs) + anti-emetic for intense 1-2 days, recovery over a week or so
What are the signs of acute vestibular lesion?
Ipsilateral head tilt + skew
What are the sensory receptors of the vestibular system?
Epithelial hair cells
What structure houses the eye? What bone sits superiorly and inferiorly?
The bony orbit
Superiorly: frontal bone
Inferiorly: zygomatic bone
What fills the two chambers of the eye?
Anterior chamber: aqueous humour
Posterior chamber: vitreous humour
What is the specialised part of the retina used for fine vision?
What is the site of blood vessel and nerve attachment in the eye?
What layers make up the tear film?
1) Innermost mucus layer
2) Aqueous layer
3) Outermost lipid layer
What is the content and function of the mucus layer of the tear film?
Mucin is secreted by the conjunctival goblet cells. It coats the cornea and provides a hydrophilic layer that allows for the even distribution of the tear film
What is the content and function of the aqueous layer of the tear film?
Water and proteins are secreted by lacrimal glands. They promote spreading of the tear film, control infectious agents and promotes osmotic regulation
What is the content and function of the lipid layer of the tear film?
Oils are secreted by meibomian glands and provide a hydrophobic barrier
What is a sty (on the eye)?
Infection of the meibomian gland in the eyelid
Which layer in the tear film protects it from rapid evaporation?
The lipid layer
What is the conjunctiva?
The thin transparent tissue that covers the outer surface of the eye
It begins at the outer edge of the cornea, covers the visible part of the eye and lines the inside of the eyelids
It is nourished by tiny blood vessels that are nearly invisible to the naked eye
What are the layers of the coat of the eye?
What are the 5 layers of the cornea? Which layer makes up the majority of the cornea?
2) Bowman's membrane
4) Descemet's membrane
90% of the thickness is taken up by the stroma
What happens if you hydrate the cornea?
Causes oedema of the cornea (as it normally has a low water content- whereas the sclera has high water content)
What is the sclera? What is it made up of?
The white of the eye. It is an opaque, tough layer which consists of irregularly arranged collagen fibres
What are the major constituents of the lens? (eye)
What is the major and secondary refracting structure of the eye?
Major: The cornea
Secondary: The lens
What is the uvea?
The vascular coat of the eye ball which lies between the sclera and the retina
How is the lens attached in the eye?
Attached by lens zonules to the cilliary muscles
What is presbyopia?
Deminished function of the lens flattening or contracting to focus on near objects (naturally occurring loss of accommodation
Onset from 40 years of age, with distant vision intact
What is the retina?
A very thin layer of tissue that lines the inner part of the eye, capturing the light rays that enter the eye
What is the macula?
Located roughly in the centre of the retina, temporal to the optic nerve. Is it a small and highly sensitive part of the retina responsible for detailed central vision
How are nutrients and oxygen supplied to the cornea?
Nutrients are supplied by the aqueous humour
Oxygen diffuses through the air to supply the cornea
What is the relationship between blood pressure and aqueous humour?
Not much relationship. The production of the aqueous is not gradient dependent it is energy dependent
Where is aqueous humour produced and drained?
Actively secreted and diffuses out of the epithelial cells of the ciliary body, then flows forwards between the iris and lens and drains through the trabecular meshwork and canal of Schlemm
What is a normal intraocular pressure?
What is glaucoma?
Optic neuropathy with characteristic structure damage to the optic nerve, associated with progressive retinal ganglion cell death, loss of nerve fibres and visual field loss
(Doesn't mention intraocular pressure as this is the only modifiable symptom)
What are the different types of glaucoma? which one is the most common?
1) Primary open angle glaucoma (most common)
2) Closed angle glaucoma (acute or chronic)
What is primary open angle glaucoma caused by?
Trabecular meshwork dysfunction
What is closed angle glaucoma caused by?
Increased pressure pushing the iris/lens complex forwards, blocking the trabecular meshwork. May present with sudden painful red eye with acute drop in vision
Which type of cells in the eye are primarily affected in glaucoma?
Retinal ganglion cells
How do you discriminate between a patient's left and right eye?
If you are looking at the patient's right eye the optic disc will be on the right side
What is the fovea?
The centre of the macula
Where is the macula located?
An avascular spot located temporal to the optic disc
Where causes the optic nerve blind spot?
Where the optic nerve meets the retina there are no light sensitive cells
What is the function of the macula?
A small highly sensitive part of the retina responsible for detailed central vision. It allows us to appreciate detail and perform tasks that require central vision such as reading
What is the most sensitive part of the retina?
What is the concentration of rods and cones in the fovea?
Highest concentration of cones
Low concentration of rods
What is the corresponding anatomical landmark for the physiological blind spot?
How is light captured from the retina?
Light passes into the eye, past the photoreceptors and bounces off the retina then travels back to be detected by neurones in the eye
It is then transformed into an electrical signal and goes to the bipolar cells which (along with horizontal cells) modulate the signal to create an even image
The ganglion cells then send the signal to the brain
What are the two main classes of photoreceptors in the retina?
What is the function of rod photoreceptors?
Longer outer segment with photo-sensitive pigment
100 times more sensitive to light than cones
Slow response to light
Responsible for night vision (scotopic vision)
120 million rods
What is the function of cone photoreceptors?
Less sensitive to light than rods, but faster response
Responsible for day light fine vision and colour vision (photopic vision)
6 million cones
Where do you have the highest concentration of rod photoreceptors?
Number of rods increases up to the area surrounding (but not in) the fovea (blindspot)
20-40 degrees away from the fovea
Where is the highest concentration of cone photoreceptors?
Low concentration which peaks in the fovea
What test is used to test colour perception?
What length of time is required to adapt the rods and cones to darkness?
Cones: 7 minutes
Rods: 30 minutes
How long does it take for the photoreceptors to adapt to light from darkness?
5 minutes by bleaching the photo-pigments
Which is the commonest form of colour vision deficiency in humans?
What happens to light as it is refracted (from one medium to another)?
The velocity of the light changes which changes the path of the light
What type of lens causes the light to be focused to a focal point and what type of lens causes the light to be spread out?
Converging lens focuses to a point
Diverging lens spreads light out
What are the main diopters of the eye?
1) Tear film
What is emmetropia?
When the eye is relaxed and can perfectly focus on an image without any accommodation
What is ametropia?
When there is a refractive error. A mismatch between axial length and refractive power (without accommodation)
What are the different types of ametropia?
1) Myopia (nearsightedness)
2) Hyperopia (farsightedness)
What is myopia? What are the causes?
Where parallel light rays converge at a focal point anterior to the retina. Causes blurred distance vision, squint in an attempt to correct visual acuity, headache
- Excessive long globe (axial myopia): more common
- Excessive refractive power (refractive myopia)
How do you correct myopia?
Use a concave lens (contacts or glasses)
Remove the crystalline lens surgically
What is hyperopia? What are the causes
Parallel rays converge at a focal point posterior to a retina. Causes visual acuity at near tends to blur relatively early. Asthenopic symptoms: eye pain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis, amblyopia (lazy eye > 5D)
- Excessive short globe (axial hyperopia): more common
- Insufficient refractive power (refractive hyperopia)
How is hyperopia corrected?
Use a convex lens or use an intraocular lens
What is astigmatism?
Parallel rays come to focus in 2 focal lines rather than a single focal foint.
Caused by refractive media not being spherical- refract differently along one meridian than along meridian perpendicular to it
>2 focal points (punctiform object is represent as 2 sharply defined lines
What is the circle of least confusion?
The point where your eye tries to focus between two focal points due to meridian lines of differing length, causing an astigmatism
What are the symptoms of astigmatism?
Asthenopic symptoms (headache, eyepain)
Distortion of vision
Head tilting and turning
What is the treatment for astigmatism?
Regular astigmatism: cylinder lenses with or without sperical lenses (convex or concave)
Irregular astigmatism: rigid cylinder lenses, surgery
What occurs to the ciliary muscles during accommodation?
Contraction of the circular ciliary muscles
What is the pathway of a signal from the eye to the visual cortex?
2) Optic nerve
3) Optic chiasm
4) Optic tract
5) Latera Geniculate Nucleus (LGN)
6) Optic radiation
7) Primary visual cortex
[8) Extrastriate cortex]
What are the first order neurons in the retina? And the second and third?
First: Rod and cone retinal photoreceptors
Second: Retinal bipolar cells
Third: Retinal ganglion cells
Why is the receptive field different in different parts of the eye?
In the fovea one cone signals to one bipolar cell which signals to one retinal ganglion cell
Towards the periphery you have a lot of rods signalling a lot of bipolar cells signalling ONE retinal ganglion cell
Explains why you can see clearly in the centre of the eye (fovea) and less so in the periphery of vision
What optic tract will a signal from your right visual field go down?
Left optic tract
A lesion on the right optic nerve prior to the optic chiasm will cause what result?
A loss of all vision from that eye because it is before the optic chiasm
A lesion on the optic chiasm will cause what result?
The medial (nasal) signals from both eyes will be lost which causes temporal vision loss as the vision is inverted
Lateral vision does not decussate so would remain
What is homonymous heminopia?
A loss of half of the field of view due to vision loss temporally in one eye and medial in the other caused by missing information coming from one true side
Frequently occurs in stroke and traumatic brain injury
What is a macula sparing disorder of the visual pathway?
Where a lesion near the back of the brain causes loss of one half of the visual field (homonymous heminopia) but the centre of vision (macula) remains intact as not all of the fibres cross over in the optic chiasm
Area representing the macula receives dual blood supple from posterior cerebral arteries from both sides
What is the most common cause of bitemporal heminopia?
Typically enlargement of the pituitary gland, or a tumour as the pituitary sits under the optic chiasm
Where is the priary visual cortex located?
Along the calcanine sulcus within the occipital lobe
What is the extrastriate cortex?
Area around the primary visual cortex within the occipital lobe. Confers basic visual information, orientation and position into complex visual information
What is the dorsal pathway?
Primary visual cortex to posterior parietal cortex
- Motion detection
- Visual guided action
Damage results in motion blindness
What is the ventral pathway?
Primary visual cortex to infratemporal cortex
- Object representation, face recognition
- Detail fine central vision and colour vision
Damage may result in cerebral achromatopsia
What is a direct and consensual light reflex?
Direct light reflex is where the light is shone into the left eye and the left eye constricts
Consensual light reflex is where the light is shone into the left eye and the right eye constricts
What is a right afferent defect in the light reflex?
No pupil constriction in both eyes when right eye is stimulated but normal constriction in both eyes when left eye is stimulated
e.g. damage to optic nerve
What is a right efferent defect in the light reflex?
No right pupil constriction whether right or left eye is stimulated but left pupil constricts if either pupil is stimulated
e.g. damage tot he right 3rd nerve
What is a unilateral afferent defect in the light reflex?
Different response depending on which eye is stimulated
What is a unilateral efferent defect in the light reflex?
Same unequal response between left and right eye irrespective of which eye is stimulated
In terms of eye movement what is duction?
Eye movement in one eye
In terms of eye movement what is version?
Simultaneous movement of both eyes in the same direction
In terms of eye movement what is vergence?
Simultaneous movement of both eyes in the opposite direction
In terms of eye movement what is convergence?
Simultaneous adduction movement in both eyes when viewing a near object
What are the four straight muscles of the eye?
What are the "non-straight" muscles of the eye?
What muscles of the eye are innervated by cranial nerve III?
What muscles of the eye are innervated by cranial nerve IV?
What muscles are innervated by cranial nerve VI?
What is third nerve palsy?
Affected eye down and out movement and causes droopy eyelid
Unopposed superior oblique innervated by fourth nerve (down)
Unopposed lateral rectus action innervated by sixth nerve (out)
What is sixth nerve palsy?
Affected eye unable to abduct and deviated inwards
Double vision worsen on gazing to the side of the affected eye
What is vertigo?
The illusion of movement and spatial disorientation, usually rotational or 'true vertigo'
The room is spinning or spinning in their head
Rocking on a boat
What are the different disorders of balance?
Peripheral vestibular disorders
Central vestibular disorders
What does a peripheral vestibular disorder affect? Give examples of this condition.
Labyrinth (semicircular canals) and cranial nerve VIII
e.g. vestibular neuritis, BPPV and Meniere's disease
What does a central vestibular disorder affect? Give examples of this condition
e.g. stroke, MS and tumours
What are the different types of onset/presentation of vestibular disorders?
Give an example of an acute vestibular disorder
Vestibular neuritis (labyrinthitis)
Give an example of an intermittent vestibular disorder
Benign Paroxysmal Positional Vertigo (BPPV)
Give an example of a recurrent vestibular disorder
Give an example of a progressive vestibular disorder
Acoustic neuroma (nerve VIII)
What would happen to the eyes if a patient loses their balance organ on one side?
Other side would become hyperactive so they would develop nystagmus
What is the presentation of vestibular neuritis?
Sudden, unilateral vestibular loss (vertigo, nausea, unsteadiness and nystagmus)
No CNS symptoms or findings
Lasts days to weeks
What are the different types of vestibular projection and their associated symptoms?
Vestibulo-ocular = nystagmus
Vestibulo-spinal = unsteadiness
Vestibulo-autonomic = nausea
Vestibulo-cortical = vertigo
What typically causes an onset of BPPV? How long does it last?
Associated with a change in head position
Lasts for 10 seconds
When performing the Hallpike Manoeuvre if the patient has immediate nystagmus what does this indicate?
It is a central vestibular disorder
When performing the Hallpike Manoeuvre if the patient has a 4-5 second latency then nystagmus what does this indicate?
The patient has benign paroxysmal positional vertigo
What type of disorder causes a vertical nystagmus?
Central vestibular disorder
What manoeuvre tests and treats for nystagmus?
Semont repositioning manoeuvre
What is Meniere's disease?
Build up of endolymphatic pressure (hydrops)
Hearing impaired (Meniere's triad: vertigo, tinnitus and deafness)
Rupture of the membrane causes mixture of endolymph and perilymph which causes a violent sensation of pressure and vertigo which results in a characteristic low frequency hearing loss (1-2kHz)
Unilateral, painful, intense pressure then a roaring tinnitus
What is the classification for diagnosis of Meniere's disease?
Low frequency hearing loss, unilateral loss of balance, associated vertigo, tinnitus, pressure in the affected ear
What is the treatment for Meniere's disease?
Reduce dietary salt
Gentamycin injected into the ear to speed up the destruction of the organ, but causes a 40% chance of hearing loss
First line of treatment: Steroid injection into the ear
How would a recurrent vestibular disorder be diagnosed as migraine?
History of migraine
Migraine symptoms during vertigo attack
Hearing usually spared
Response to treatment
Can mimic vertigo or Meneire's disease
Can have nystagmus in any direction
Once everything else has been excluded can diagnose migraine
What are the different types of central vestibular disorders?
Acute brainstem or cerebellar lesion
Give an example of a central vestibular disorder caused by acute brainstem or cerebellar lesion. What must you enquire about in these patients?
e.g. MS or vascular
Always enquire about brainstem: diplopia, facial numbness and speech
What causes a chronic/progressive central vestibular disorder?
What cells make up the olfactory epithelium?
Bipolar olfactory neurons
What cells in the nose give the epithelium some ability to regenerate?
What is anosmia? What is the most common cause?
Loss of sense of smell
Face trauma is the most common cause
What is the limbic system responsible for?
- Maintainance of homeostasis via activation of visceral effector mechanisms, modulation of pituitary hormone release and initiation of feeding and drinking
- Agonistic (defence and attack) behaviour
- Sexual and reproductive behaviour
- Memory (to previous situations modifies our response)
What is the main output pathway from the hippocampus to the hypothalamus?
What pathway connects the hypothalamus and the anterior nucleus of the thalamus?
What are the functions of the hippocampus? What are the main afferent and efferent connections?
Memory and learning
Afferent: Perforant pathway
What disease targets the limbic system?
What are senile plaques? What disease are they present in?
Lumps of β-protein (a normal physiological protein with unknown function)
Thrown out of cells in Alzheimer's and forms plaques
What part of the brain is affected in early Alzheimer's disease resulting in short-term memory problems?
Hippocampus and entorhinal cortex
What part of the brain is affected in moderate Alzheimer's disease resulting in dressing apraxia?
What part of the brain is affected in late Alzheimer's disease resulting in loss of exectutive skills?
What are the functions of the amygdala? What are the main afferent and efferent connections?
Fear and anxiety. Fight or flight
Afferent: Olfactory cortex, septum, temporal neocortex, hippocampus, brainstem
Efferent: Stria terminalis
What is Kluver-Bucy syndrome? What part of the brain is it associated with?
Bilateral temporal damage
- Loss of fear
- Visual agnosia
Associated with the amygdala
What structures of the brain have been associated with aggression?
- Hypothalamus (particularly anterior)
- Brainstem (periaqueductal grey)
What are the functions of the septum in the brain? What are the main afferent and efferent connections?
Reinforcement and reward
Afferent: Amygdala, olfactory tract, hippocampus, brainstem
Efferent: Stria medularis thalami, hippocampus, hypothalamus
Dopaminergic neurons project forward from the midbrain to the cortex, nucleus accumbens and amygdala via what? What does this result in?
MFB (medial forebrain bundle)
Rewards an experience
What do opioids, nicotine, amphetamines, ethanol and cocaine do in the nucleus accumbens?
Increase dopamine release
Stimulates midbrain neurons, promotes dopamine release or inhibits dopamine reuptake
What is consciousness?
The brain state that enables us to experience the world around us and within one-self
Distinct from automatic behaviours that occur in a rather unconscious manner
It is not equal to being alert or attentive
What part of the brain is associated with the level of alertness/consciousnes?
No single brain region for consciusness
Where does the reticular formation project to in the brain? What does this allow?
The thalamus and the cortex allowing sensory signals to reach cortical sites of conscious awareness such as frontoparietal cortex
What neurones in the reticular formation boost the level of activity in the cerebral cortex (via the thalamus)?
How is the level or arousal monitored?
By recording the activity of neurons
What are the frequency bands and their associated levels of arousal?
Delta (waves <4Hz): sleep
Theta (4-8Hz): drowsiness
Alpha (8-13Hz): Relaxed/eyes closed
Beta (13-30Hz): Normal/waking consciousness
What causes a patient to be in a coma?
1) Damage to the reticular formation/thalamus
2) Massive bilateral cortical insult
e.g. hypoxia, hypoglycaemia, intoxication
What are the different types of coma?
1) Persistant vegetative state
2) Brain death
What causes a persistent vegetative state?
Due to disconnection of cortex from brainstem or widespread cortical damage
What causes a patient to be brain dead?
What is assessed in the Glasgow Coma Scale?
1) Eyes open
2) Verbal responses
3) Motor responses
What is contusion?
A bruise in the brain (haematoma) affecting the capillaries leading to a visible focal spot
What is concussion?
Due to violently shaking the head leaving to microscopic changes in the neuronal tissue affecting the white matter tracts connecting different regions in the cortex
What is visual 'neglect' syndrome?
It is due to frontal-parietal lesions which leads to a state of unawareness of information presented on the contralateral side of the visual space
Particularly right hemisphere
What are the clinical tests to diagnose visual 'neglect' syndrome?
- Hold fingers up to either side of the face, move fingers alternately and ask to identify when fingers are being moved
- Line bisection (mark the middle of a horizontal line)
- Computerised tests (tap all closed circles on a screen)
How do you distinguish hemianopia from visual neglect syndrome?
Hemianopia have normal cortical function but will have a lesion on their optic nerve or optic tract
What is blindsight?
Patients who are perceptually 'blind' of their visual field due to occipital damage can however respond to visual stimuli
What are the behavioural criteria of sleep?
1) Steriotypic or species-specific posture
2) Minimal movement
3) Reduced responsiveness to external stimuli
4) Reversible with stimulation- unlike coma, anesthaesia or death
What is an EEG? What does it measure?
Measures neuron activity in the brain
What is an EOG? What does it measure?
Measures eye movement
What is an EMG? What does it measure?
Measure muscle activity
What are the stages of sleep? What would an EEG, EOG and EMG show in each stage?
Stage 1 and 2 (NREM)
EEG: Brain slows down (theta)
EOG: No eye movement
EMG: Tone reduces
Stage 3 and 4 (NREM)
EEG: Brain gets even slower (delta)
EOG: Not much eye movement
EMG: Even lower muscle tone
Stage 5 (REM)
EEG: Brain activity speeds up (similar to beta in awake)
EOG: Wide eye movements
EMG: Minimal tone (near paralysis)
What would an EEG, EOG and EMG show when awake?
EEG: Fast high frequency (beta) activity
EOG: Have eye movement
EMG: Strong tone in muscles
How long is a single sleep cycle?
Between one hour and an hour and a half
When in the night is most of the stage 5 sleep and when is most of the REM sleep?
Most stage 5 sleep at the beginning of the night and most of the REM sleep nearer to the morning
How do heart rate and respiratory rate change through the sleep cycle?
They decrease through the stages of sleep then they increase to a normal level during REM sleep
How is arousal maintained?
Nuclei in the brainstem directly (from the brainstem) or indirectly (from brainstem via the thalamus) modulate the activity in the cerebral cortex
TMN in the hypothalamus also has a similar effect on the cerebral cortex
What two nuclei control the sleep/wake cycle?
VLP: Ventrolateral pre-optic nucleus
LH: Lateral hypothalamic nucleus
How do the VLP nuclei control the sleep/wake cycle?
VLP promotes sleep
They inhibit the activity of the RN and NC nuclei in the brainstem, reducing the amount of activity stimulating the cerebral cortex, causing you to be drowsy
How do the LH nuclei control the sleep/wake cycle?
LH promotes wakefullness
They stimulate the RN and NC nuclei, increasing the amount of activity stimulating the cerebral cortex
When are the VLP nuclei and LH nuclei more active?
VLP more active at night
LH more active in the morning
What is the relationship between VLP nuclei and LH nuclei?
They are mutually antagonistic. One being very active inhibits the action of the other
What part of the brainstem is thought to control REM sleep?
Caudal Pontine Reticular Formation
What nucleus synchronises sleep with falling light level (darkness)? What part of the brain is this found?
Found in the hypothalamus
How does the suprachiasmatic nucleus synchronise sleep with falling light level?
It has an input from the retina from special photosensitive ganglion cells. As light level falls the input activates SCN which then has input to all the nuclei involved in control of the sleep/wake cycle.
How does the SCN affect the pineal gland?
When light level falls the retina input stimulates the SCN which stimulates the pineal gland to secrete melatonin which affects the pituitary
What are the effects of sleep deprivation?
- Sleepiness, irritability
- Performance decrements/ increased risk of errors and accidents
- Concentration/learning difficulties
- Glucose intolerance
- Reduced leptin/increased appetite
- Hallucinations (after long sleep deprivation)
- Death- rats (14-40 days), humans (fatal familial insomnia)
What happens after sleep loss?
1) Reduced latency to sleep onset
2) Increase of slow wave sleep (NREM)
3) Increase of REM sleep (after selective REM sleep deprivation)
What is the function of sleep?
1) Restoration and recovery- but active individuals do not sleep more
2) Energy conservation- 10% drop in BMR, but lying still is just as effective
3) Specific brain functions
What are the functions of dreams?
1) Safety valve for antisocial emotions
2) Disposal of unwanted memories
3) Memory consolidation
- NREM sleep: declarative memory
- REM sleep: procedural memory
What are the causes of chronic insomnia?
1) Physiological (e.g. sleep apnea, chronic pain
2) Brain dysfunction (e.g. depression, fatal familial insomnia, night working
What is the treatment of chronic insomnia?
Most hypnotics enhance GABAergic circuits
What is cataplexy?
When suddenly all the muscles in your body lose their tone and you fall to the ground
What is the genetic cause of narcolepsy?
Orexin deficiency (genetic or autoimmune?)
How can shift work cause sleep disorders?
Night work causes physiological processes to become desynchronised
This can lead to sleep disorders, fatigue and an increased risk of some conditions such as obesity, diabetes and cancer
What structures are located in grey matter? How thick is the grey matter?
Neuronal cell bodies
Glial cells (protects and supports grey matter, maintains homeostasis)
Grey matter is 2-4mm thick
What is contained in white matter?
Myelinated neuronal axons forming white matter tracts
Myelinated pyramidal cell axons, few cell bodies
What are the cortical layers of the grey matter?
I (molecular): Axons and dendrites; few cell bodies
II (external granular): Densely packed stellate cells; a few small pyramidal cells
III (external pyramidal): Loosely packed stellate cells; intermediate-sized pyramidal cells
IV (internal granular): Bands of densely packed stellate cells; no pyramidal cells
V (internal pyramidal): Very large pyramidal cells; a few loosely packed stellate cells
VI (multiform): Pyramidal cells of various sizes, loosely packed stellate cells
What layers of the cortex are responsible for output to the cortex?
Layers II and III
What layers of the cortex are responsible for output to the non-cortex?
Layers V and VI
To subcortical areas
VI mainly sends information to the thalamus
V contains giant Betz cells which projects to other parts of the body, also to brain stem and spinal cord
What layers of the cortex are responsible for input?
Layer IV only
It is then passed to other layers of the cortex
What is connected by association fibres?
Connect areas within the same hemisphere
What are the different types of association fibres? What do they connect?
1) Short association fibres
Fibres which run short distances. Connects two neighbouring gyra together
2) Long association fibres
Connect parts of the cerebral cortex which are located far away from each other
What are the different long association fibres? What do they connect?
1) Superior Longitudinal Fasciculus
(connects frontal and occipital lobe)
2) Arcuate Fasciculus
(connects frontal and temporal lobe)
3) Inferior Longitudinal Fasciculus
(connects temporal and occipital lobe)
4) Uncinate Fasciculus
(connects anterior frontal and temporal lobe)
What fibres connect the left hemisphere to right hemisphere?
What fibres connect the cortex with lower brain structures?
(e.g. thalamus, brain stem and spinal cord)
What are the names of the commissural fibres in the brain?
What is the name of the projection fibres in the brain?
Projection fibres of internal capsule
Where is the primary motor cortex located?
Anterior to the central sulcus in the frontal lobe
Where is the motor association area? What is it's function?
Anterior to the primary motor cortex in the frontal lobe
Main role is higher order processing, helps to plan movement and control movement. Programmes the movement then sends it to the primary motor cortex
Where is the primary somatosensory cortex located? What is it's function?
Located posterior to the central sulcus in the parietal lobe.
It perceives the very basic somatosensory input into the body. Touch, pain temperature, taste
What is the role of the parietal lobe?
Sensory association area
Recognition and interpretation of sensory information from skin, muscles, taste buds
What is the role of the primary visual cortex? Where is it located?
Processing he very basic visual input to the brain.
The most posterior region of the brain
What is the role of the visual association area?
Where is it located?
Used to recognise more detailed structures like colour, shape etc
The remaining occipital lobe, excluding the primary visual cortex
What is the role of the primary auditory cortex?
Where is it located?
Very basic hearing information including speech
Located just below the lateral fissure in the temporal lobe
Where is the auditory association area located? What is it's function?
Located just inferior to the primary auditory cortex in the temporal lobe.
Allows us to comprehend the sound information coming to the primary auditory cortex
What is the role of the prefrontal association area? Where is it located?
Coordinates information from other association areas.
The part of the frontal lobe excluding primary motor cortex and premotor cortex
Apraxia would be a result of a lesion where in the brain?
Motor association area
(difficulty with motor planning to perform voluntary movements and tasks)
Paralysis or paresis would be a result of a lesion where in the brain?
In the primary motor cortex on the contralateral side
Where would a lesion in the brain occur to result in changes in any of the following?
- Decision making
Prefrontal association area
What is Broca's (motor) aphasia?
Impaired speech production but preserved comprehension
Deficits in perception of basic sensory information would be caused by a lesion where in the brain?
Primary sensory cortex
Deficits in interpretation of sensory information would be caused by a lesion where in the brain?
Sensory association area
What is the sensory association area important for?
- Tactile recognition
- Flavour recognition
- Spatial orientation
- Ability to read maps
What is alexia? What causes it?
Deficits in reading due to lesions in the sensory association area
What is agraphia? What causes it?
Deficits in writing due to lesions in the sensory association area
What is acalculia? What causes it?
Deficits in ability to perform calculations due to lesions in the sensory association area
Blindness is caused by a lesion in what area of the brain?
Primary visual cortex
Deficits in the interpretation of visual information is caused by a lesion in what part of the brain?
Visual association area
What is prosopagnosia?
Inability to recognise familiar faces or learn new faces
Deafness is caused by a lesion in what part of the brain? What would a unilateral lesion cause?
Primary auditory cortex
Unilateral lesion would cause partial deafness in both ears
Deficits in the interpretation of auditory information is caused by a lesion in what part of the brain?
Auditory association area
What is Wernicke's (receptive) aphasia
Impaired comprehension but preserved speech production
(what patient says does not make sense)
What is anterograde amnesia? What part of the brain is it associated with?
Inability to form new memories
Associated with the temporal lobe and hippocampus
What is transcranial magnetic stimulation (TMS) used for?
It measures the effects of interference with normal information processing due to electromagnetic stimulation of neurons
What is PET? How does it measure brain activity?
Positron emission tomography
Measured changes in amount of blood flow directly to a brain region following administration of a tracer
What is fMRI? How does it measure brain activity?
Functional magnetic resonance imaging
Measured changed in amount of blood oxygen in a brain region
What hemisphere of the brain is more dominant for language?
What is MAG?
Measured magnetic field generated by the electric currents in the brain
What part of the brain is associated more so with verbal and analytical functions?