Flashcards in Brain and spinal cord Deck (131):
Describe the tendon stretch reflex (myotatic reflex).
When the muscle is stretched, this causes the intrafusal fibres of the muscle spindle to increase in length, which causes the 1a afferent to stimulate the alpha motor neurone (monosynaptic reflex) and gamma motor neurone in the spinal cord. The alpha motor neurone causes the extrafusal muscle fibres to contract, and the gamma motor neurone causes the intrafusal muscle fibres to contract so the muscle spindle stays sensitive. There is also reciprocal inhibition (via an inhibitory interneurone) of the antagonist muscle.
Describe the inverse stretch reflex
The muscle is over-stretched, which causes the collagen fibrils of the golgi tendon organ to come close together so the 1b afferent is stimulated. The 1b afferent activates inhibitory interneurones in the spinal cord, which inhibit the alpha motor neurone so that the muscle relaxes. There is also reciprocal contraction of the antagonist muscle.
What is the flexor withdrawal/crossed extensor reflex?
You step on a tac. Cutaneous nociceptors are stimulated and stimulate an interneurone in the spinal cord which activated the alpha motor neurone of the flexor in the affected leg (so you remove your foot from the tac), and the extensor in the other leg (so you don't fall over). At the same time there is reciprocal inhibition of the antagonist muscles on both sides.
What are the neurotransmitters for nociception?
Glutamte and Substance P.
What do Aalpha fibres carry?
What do Abeta fibres carry?
What do Adelta fibres carry?
What do C fibres carry?
What is Gate theory?
If the Aalpha and Abeta fibres from the injured area are stimulated, they activate an inhibitory interneurone which prevents the C fibre activating the projection neurone, so the painful stimulus is suppressed.
What is hyperalgesia?
A state where there is a heightened pain response to a stimulus that would normally cause pain (lowered pain threshold).
What is allodynia?
A person experiences pain from a stimulus that would not normally cause pain (e.g light touch).
What causes Huntingdon's disease?
A mutation on chromosome 4 which means the output neurones of the striatum are lost so the globes pallidus external segment can't be inhibited and the cortical motor areas are overstimulated. This means there are excessive uncontrollable jerky movements (chorea).
It is treated pharmacologically by depleting dopamine.
What causes hemiballismus?
Damage to the subthalamus nucleus which causes rapid, flinging, violent movements of limbs on only one side.
What is the name of the white matter in the cerebellum?
What are the two major functions of the cerebellum?
Comparative functions - detecting motor error (difference between intended movement and actual movement).
Motor memory - storing learned movements (implicit memory).
Name the three major divisions of the cerebellum.
Spinocerebellum (vermis and medial bits), cerebrocerebellum (lateral bits of lobes), vestibulocerebellum (nodulo-floccular lobe).
What are the functions of the cerebrocerebellum?
Receive inputs from the cerebral cortex, regulate highly skilled movements involving complex sequence of movements (speech).
What are the functions of the spinocerebellum?
Receive direct input from the spinal cord. Lateral part involved in movements of the distal muscles (limbs). Central part (vermis) involved in movement of the axial muscles (trunk).
Which cerebellar peduncle is entirely efferent?
Which cerebellar peduncle is entirely afferent?
Which cerebellar peduncle is a mix of efferent and afferent?
Where does the cerebellum get motor inputs?
Contralaterally from the cerebral hemisphere to the pontine nuclei, then through the transverse fibres of the pons and the middle cerebellar peduncles.
Where does the cerebellum get its sensory inputs?
Proprioception from muscle spindles, vestibular nuclei, visual and auditory inputs, ipsilaterally entering the cerebellum through the inferior cerebellar peduncle.
Where does the cerebellum receive inputs from modulation on timing, learning and memory.
The inferior olive in the medulla, conveying information to the contralateral cerebellar hemisphere through the inferior cerebellar peduncle.
Where do the deep cerebellar nuclei send information?
Contralaterally through the superior cerebellar peduncle to the thalamus and the cerebral cortex.
What are the functions of the vestibulocerebellum?
Receiving nuclei from the vestibular nuclei in the brainstem, involved in movements controlling posture and balance, and eye movements.
Which of the deep cerebellar nuclei does the vestibulocerebellum send information to?
Fastigial nucleus or direct to the spinal cord.
Which of the deep cerebellar nuclei does the spinocerebellum (lateral) send information to?
Interposed (and fastigial) nucleus.
Which of the deep cerebellar nuclei does the spinocerebellum (vermis) send information to?
Which of the deep cerebellar nuclei does the cerebrocerebellum send information to?
Name the three layers of the cerebellar cortex.
Granule layer, Purkinje layer, molecular layer.
What are the input cells of the cerebellar cortex?
Climbing fibre (input from inferior olive).
Mossy fibre (from all other inputs).
What are the output cells of the cerebellar cortex?
Purkinje cells (have large cell bodies in the Purkinje layer, and highly branched dendrites in molecular layer).
What are the interneurones in the cerebellar cortex?
Granule cells (branch into parallel fibres in the molecular layer).
Also basket cells, stellate cells, Golgi cells.
Where do granule cells receive input?
Mossy fibres synapsing with granule cell bodies in the granule layer.
Which fibres modify the outputs of the Purkinje cell, by altering the effectiveness of the parallel inputs to the Purkinje cell, and so adjust and correct movements (comparative function).
Climbing fibre from inferior olive in the medulla oblongata.
Where are the mossy fibres carrying input from?
Input from the cerebral cortex via the pontine nuclei and middle cerebellar peduncle. Input from the vestibular nuclei and spinal cord via the inferior cerebellar peduncle.
Which neurotransmitter is produced by Purkinje fibres at the synapse with the deep cerebellar nuclei?
Gamma amino butyric acid (GABA). Purkinje fibres modify movements by inhibiting for learning, memory and timing.
Does damage to the cerebellum lead to movement disorders ipsilaterally or contalaterally?
Ipsilaterally (because that's how the input from the muscle proprioception, vestibular nuclei, auditory + visual, is represented).
What does damage to the vestibulocerebellum lead to?
Disturbances of balance and eye movements.
What does damage to the spinocerebellum lead to?
Central = postural and gait ataxia (wide based with small shuffling movements).
Lateral = upper limb ataxia and dysarthria.
What does damage to the cerebrocerebellum lead to?
Impairment in highly skilled sequences of learned movements.
Damage to cerebellum leads to cerebellar ataxia. What is dyssynergia, dysmetria, days dysdiadochokinesis, intention tremor, ataxic dysarthria?
Dyssynergia = loss of synergistic multi-joint movement, so joints have to be moved one at a time.
Dysmetria = inability to judge distances, so movements overshoot.
Dysdiadochokinesis = inability to perform rapid alternating movements.
Intention tremor = shaking when trying to move but no tremor when at rest.
Ataxic dysarthria = slurred speech.
Which part of the cerebellum does alcohol particularly degenerate?
Anterior cerebellum - affecting movements of the lower limbs especially (so wide staggering gait, but little impairment of hands or arms).
Where do you find medium spiny neurones?
In the striatum.
What are the chief symptoms of Parkinson's?
TRAP - tremor, rigidity, akinesia, postural problems.
Which cells are lost in Parkinson's?
Dopaminergic neurones of substantia nigra.
How much dopamine needs to be depleted before symptoms of Parkinson's will appear?
What type of disorder is Parkinson's?
Hypokinetic movement disorder.
Why is levodopa, not dopamine, used to treat Parkinson's?
Levodopa can cross the blood-brain barrier.
Which basal ganglia pathway is responsible for most of the symptoms of Parkinson's?
Which enzyme breaks down dopamine?
Dopa decarboxylase. An inhibitor for this enzyme is given with levodopa to Parkinson's patients to decrease the breakdown in the circulation and increase the amount making it across the blood-brain barrier.
Which enzyme isn't found in dopaminergic neurones and why?
Dopamine beta-hydroxylase. So noradrenaline isn't produced.
What are the two major metabolites of dopamine?
Dopamine is broken down into dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA).
Name the three dopamine pathways in the CNS and their main functions.
Nigrostriatal - motor control.
Mesolimbic/mesocortical - behavioural effects, emotion, drug-induced reward system.
Tuberohypophyseal - endocrine functions, the hypothalamus and its control of pituitary functions.
What is an autonomic ganglion?
The cell body of the post-ganglion of neurone.
What types of fibres are preganglionic and postganglionic neurones?
Preganglionic = myelinated cholinergic neurones.
Postganglionic = unmyelinated, usually cholinergic or adrenergic.
Name the three types of autonomic ganglion.
Paravertebral (sympathetic trunk), prevertebral (e.g for splanchnic nerves), terminal.
What is dual innervation?
An organ receives nerves from both the parasympathetic and sympathetic division.
Which spinal nerves contribute to the sympathetic splanchnic nerves?
Greater = 5 to 9
Lesser = 10 to 11
Least = 12
Name the principle transmitters in the ANS, and what type of receptor is found in the autonomic ganglion.
Acetylcholine and noradrenaline.
What type of receptor is found at parasympathetic postganglionic synapses, and sympathetic postganglionic synapses on sweat glands?
What type of receptor is found at sympathetic postganglionic synapses.
Where is noradrenaline released?
Locus coeruleus in the pons
Where is serotonin released?
Raphe nuclei in the midline
Where is dopamine released?
Ventral tegmental nuclei in the midbrain
Where is acetylcholine released?
Cholinergic nuclei in the basal forebrain and in the dorsolateral pons
What are the 3 physiological divisions of the nervous system?
Somatic (body wall)
Enteric (Meissner/submucosal, Auerbach/myenteric, Dogiel cells that are multipolar and sympathetic)
Where do the plexuses of the enteric nervous system arise?
Around the superior mesenteric artery.
Which type of neurones are unipolar?
Which type of neurones are multipolar?
Which type of neurones are bipolar?
What is the most intimate layer of the meninges which follows all the sulci and gyri, and what does it give rise to in the vertebral foramen which keeps the spinal cord central?
Pia mater -> denticulate ligament
Where is the CSF?
In the sub arachnoid space.
What are the two layers of the dura mater?
Endosteal and meningeal.
What is the difference between the extra-dural space in the skull, and the extra-dural space in the vertebral column?
In the skull it is a potential space, in the vertebral column it is an actual space filled with epidural fat.
What is a spinal segment and how many are there in total?
A section of spinal cord from the start of one set of rootlets to the start of the next. 31 spinal segments in total.
What is carried by the dorsal-columns medial lemniscus tract?
Fine (discriminative) touch, pressure, vibration, conscious proprioception.
Is the dorsal-columns medial lemniscus tract contralateral or ipsilateral?
Contralateral, but the first order neurones run ipsilaterally up the spinal cord, and it is the second order neurones that decussate in the brainstem.
What is the difference between the fasciculus gracilis and fascicles cunneatus?
The fasciculus gracilis is more medial, carries first order neurones from the lower limbs and lower trunk, and synapses with the gracile nucleus in the medulla oblongata.
The fasciculus cunneatus is more lateral, carries first order neurones from the upper limbs and upper trunk, and synapses with the cunneate nucleus in the medulla oblongata.
What is carried by the spinothalamic tract?
Pain, temperature, itch and tickle, crude touch.
Where do the first order neurones of the spinothalamic tract synapse?
In the intermediate grey, the substantia gelatinosa.
Is the spinothalamic tract contralateral or ipsilateral?
Contralateral, the second order neurones decussate in the spinal tract within 2 spinal segments of synapsing with the first order neurone.
As well as the thalamus, where do some of the 2nd order neurones of the spinothalamic tract project?
Reticular formation (so keep us awake and conscious)
What tract do the spinothalamic neurones travel through in the brainstem?
What does the anterior spinothalamic tract carry?
What does the lateral spinothalamic tract carry?
Pain and temperature.
What is carried by the spinocerebellar tract?
Unconscious proprioception to maintain posture and balance.
What is carried by the ventral spinocerebellar tract and does it run ipsilaterally or contralaterally?
Decussates and runs contralaterally up to the cerebellum.
What is carried by the dorsal spinocerebellar tract and does it run ipsilaterally or contralaterally?
Nerve impulses from muscle spindles and Golgi tendon organs etc.
Enters spinal cord at T1 to L2 and 2nd order neurone runs ipsilaterally up spinal cord to the cerebellum.
What is Brown-Séquard syndrome?
Hemisection of the spinal cord which causes...
Ipsilateral hypotonic paresis and anaesthesia, and loss of pain, temperature and crude touch at a sensory level 2 spinal segments below and contralateral to the lesion.
What are the two components of descending tracts?
Upper motor neurones and lower motor neurones.
What are the three ventromedial descending tracts?
What are the three dorsolateral descending tracts?
Which types of muscles is the pontine reticulospinal tract excitatory and inhibitory to?
Excitatory to extensors and inhibitory to flexors.
What is the function of the pontine reticulospinal tract?
It is postural - keeps the trunk straight. It supplies the arm, thigh and trunk, and mediated large movements not fine movements.
It is ipsilateral and polysegmental.
Where does the tectospinal tract receive input from, and what is its function?
Input from superior colliculus (visual tracts) to cervical spinal cord.
It innervates the proximal shoulder girdle and neck muscles, so mediates head turning in response to a stimulus. It is important in orientating (finding your way by looking) and in flinching movements. It is important in ballistic reaching.
What is the function of the vestibulospinal tract, and where does it receive input?
Input from the vestibular system and utricle (organ in inner ear), it is important in balance, excitatory to extensors and prevents Trendelenburg gait. It keeps the trunk upright.
It is polysegmental, ipsilateral, and facilitates quick move,nets to right yourself after a sudden change in body position.
What is the difference between the ventromedial and dorsolateral descending tracts?
The ventromedial are mostly ipsilateral, affect multiple joint movements, mediate posture and balance and innervate the trunk, arm and thigh.
The dorsolateral are mostly contralateral, affect fine movement of individual joints and innervate the forearms, hands, lower legs and feet.
What is caused by a lesion in the ventromedial descending tracts?
Loss of righting (balance) reactions.
Loss of navigational control.
Axial immobility and forward slouching.
No reaching out (ballistic reaching).
Can still flex elbow and individual digits.
Where does the rubrospinal tract originate and what is its function?
Originates in the red nuclei in the midbrain, supplies the cervical segments (contralateral).
Excitatory to flexors and innervate pectoral girdle. Fix upper arms in the position needed for the fine movements of the lower arms.
What does a lesion in the rubrospinal tract cause?
Impaired distal arm and hand movements and intention tremors.
Where does the corticospinal tract originate?
Primary motor cortex, and run contralaterally.
Where does the corticospinal tract run?
From the primary motor cortex, through the posterior limb of the internal capsule, thought the crus cerebri, over the basilar surface of the pons, through the medullary pyramids.
90% decussate at the base of the medullary pyramids, 10% decussate in the spinal cord.
What is the function of the corticospinal tract?
Voluntary fine motor activity, involving independent flexion of single distal joints.
Above which age are the corticospinal tracts myelinated, and how can you tell?
Fully myelinated above 2 years old. Under two there is an extensor plantar reflex instead of a flexor plantar.
Which corticospinal tract decussates at the bottom of the medullary pyramids, and which decussates in the spinal cord?
Lateral corticospinal tract decussates at the bottom of the medullary pyramids.
Anterior corticospinal tract decussates in the spinal cord.
What effects does a lesion in the dorsolateral descending tracts cause?
Normal walking and navigation.
Normal righting (balance) reactions.
Normal axial posture.
Elbows hang limp.
Only ballistic reaching.
No fine motor control - if you ask the person to flex their fingers they will flex all of them together, not individually.
Where does the hypothalamospinal tract arise and where does it run?
Originates in hypothalamus, projects down to the anterior horn of T1 and synapses with sympathetic nerves.
The sympathetic nerves run up the external carotid artery, supply the sweat glands of the face, the blood vessels of the face, the dilator muscle of the eye pupil, the elevator muscle of the eye.
What are the three symptoms of Horner's syndrome (lesion to the hypothalamospinal tract)?
Miosis - excessively constricted pupil
Ptosis - drooping eyelid
Anhydrosis - dryness of skin on that side of the face because sweat glands are not secreting
What is a pyramidal tract lesion?
A lesion in the internal capsule.
What is the extrapyramidal system?
The basal ganglia and cerebellum, involved in balance, coordination, postural control, reflexes, fine control of movement.
What are the symptoms of an upper motor neurone lesion?
Clonus (sudden hyperextension of wrist/ankle results in opposing beating tremor)
Positive Babinski's (extensor plantar response)
Clasp knife response
What are the symptoms of a lower motor neurone lesion?
Decreased or absent reflexes
Decreased muscle tone (flaccidity)
What are the symptoms of extrapyramidal and cerebellar lesions?
Due to loss of basal ganglia:
Due to loss of cerebellum:
Ipsilateral loss of coordination
Ataxic (cerebellar) gait
What are four causes of upper motor neurone lesions?
Traumatic brain injury
What are 3 causes of lower motor neurone lesions?
Guillian Barre syndrome
Motor neurone disease (amyotropic lateral sclerosis)
What are four causes of extrapyramidal lesions?
Antidopaminergic drugs (e.g metoclopramide, antipsychotics)
Traumatic brain injury to basal ganglia
What are four causes of cerebellar lesions?
In which of upper motor neurone lesions and lower motor neurone lesions are eye movements often spared?
Upper motor neurone lesions.
What is anterior cord syndrome?
Vascular injury at the front of the spinal cord leads to a loss of pain and temperature detection, but preservation of discriminative touch and conscious proprioception (as the dorsal columns are unaffected).
Why does rigour mortis occur in corpses?
ATP is required for muscle relaxation.
What are 3 ways to map the functional activity of the cortex?
1) Surgery - electrode stimulation of each area and observe response produced
2) fMRI - maps changes in blood flow in the brain, proportion of oxyhaemoglobin to deoxyhaemoglobin is measured
3) PET scan - labelled oxygen used to take an "at rest" image which can be subtracted from an image taken whilst performing a task to leave the areas that have been activated, this can be performed a number of times to produce a Mean Difference Image and pinpoint the areas activated
What is the function of the premotor cortex (6)?
What is the function of the prefrontal cortex in movement?
What are the symptoms of raised intracranial pressure?
Headache, vomiting, blurring of vision, drowsiness, papilloedema (swollen optic discs), brainstem dysfunction.
What does damage to the frontal eye field (8) lead to?
The inability to perform conjugate eye movements.
Where is the somatosensory association area and what is its function?
Posterior to the post-central gyrus, allows people to determine the exact shape and texture of an object without looking (supramarginal gyrus - 40)
What is the function of the association visual area (18 + 19)?
Recognising and evaluating what is seen.
What is the function of the frontal eye field (8)?
Controls contraction of the eye muscles to enable voluntary eye movement.