Flashcards in Najeeb Neuro Deck (372):
What are tracts?
Bundles of axons of neurons in the CNS (white matter)
What name are given to bundles of axons that connect the anterior part with the posterior part of the brain?
What name are given to bundles of axons that connect right and left sides of the brain?
Give an example of a white matter commissure in the brain
What are neurological receptors?
Biological transducers - convert one type of energy to another (i.e., mechanical stimulus to Aps)
Motor neurons exit the spinal cord _____, whilst sensory informatio is taken into the ___ horn
The ventral and dorsal root of the spinal cord combine to form the spinal _____, which then divides into an anterior and posterior _____
The anterior ramus of a spinal nerve innervates structures in which part of the body?
Anterolateral wall of the body
The dorsal ramus of a spinal nerve innervates structures in which part of the body?
Back of the body
Dorsal columns of the spinal column are also known what what other name?
Which is the only white matter column that sends ONLY ascending tracts?
Dorsal columns (funiliculi)
Which ascending tracts of the spinal cord are most modern/advanced? What sort of information do they carry?
Dorsal columns. More heavily myelinated than anterolateral tracts, so carries faster information > very fine touch, proprioception, vibration and position and is highly specialised (rather than crude temperature, pain, etc. in anterolateral tracts)
List 4 types of receptors that transmit information regarding fine touch, proprioception, pressures, vibrations into the ascending dorsal tract
Meissner receptors, Pacinian receptors, goldi tendon organs and muscle spindles
The dorsal root ganglion contains which neural structure?
Cell body of first order neuron (first in chain of sensory system)
Within the dorsal column, sensations from the lower body are located ____, while caudal structures are added in ____
If there is a lesion impinging on the medial part of dorsal tract of the spinal cord, sensations from which structures will be lost? What if the lesion were affecting the lateral part of the dorsal tract only?
Those from the lower limbs (as lowest structures are carried most medially). If the lesion were in the lateral part of the dorsal tract, upper limb sensation would be lost.
All sensory fibres from the lower limb that enter the dorsal column (up to level of C6) make a special medial ascending bundle called ____?
All sensory fibres from the upper limb, abdomen and thorax that enter the dorsal column make a special lateral ascending bundle called _____?
If a section of the spinal cord is viewed from the level of L1, comment on which dorsal column bundles will be seen
Only 1 fasisculus gracillis on each side (no fasisculis cutaneous at this point because it only carries sensation from the upper limbs)
The dorsal columns are made up of the ____ processes of which neurons?
Central processes of first order neurons whose cell bodies lie in the dorsal root ganglion (and whose peripheral processes bring sensory information into the spinal cord)
Dorsal columns carry sensory information from which side of the body?
The same side as the column (i.e., information does not cross)
What is the name of the bundle of fibres connecting medulla with cerebellum?
Inferior cerebellar peduncle
The fibres from the dorsal columns terminate in which nuclei?
Nucleus gracillis and nucleus cuneatous/cuneate in lower medulla
The cell bodies present in the nucleus cuneatous and gracillis are what sort of neurons?
Second order (first order was in dorsal root ganglion)
Describe the trajectory of axons from the cell bodies of second order neurons in the nucleus graccilis and cuneatous
Cross to contralateral side at level of nuclei (in lower medulla) and move upward
What is the name given to the fibres from the nucleus gracillis and cuneatous that cross in the lower medulla before moving upward?
Internal arcuate fibres
What is the name given to the ascending group of second order neurons of the nucleus graccilis and cuneatous, after they have decussated in the lower medulla?
Medial lemniscus (there is a right and left - and each carries sensory information from the opposite side of the body)
The dorsal column medial lemniscus system is comprised of which structures?
Fasisculus graccilis and cuneatous, nuclei gracillis and cuneatous, internal arcuate fibres and right/left medial lemnisci
What is the name given to axons/fibres in the CNS that form a circular bundle? What if they form a flattened bundle?
Where do the second order neurons of the medial lemniscus system (dorsal ascending system) terminate?
In the thalamus
If sections of the brainstem are taken, comment on where the medial lemnisci will be seen and why
Upper medulla and passing through pons and midbrain. Will not be seen in lower medulla, as this is where the fibres from the second order neurons are decussating before forming the ascending medial lemnisci (right and left)
VPL nucleus receives what sort of information?
Most of the sensation from most of the body (touch, pain ,temperature, position)
VPM nucleus receives what sort of information?
Sensation from taste fibres and head/neck fibres
The second-order neurons in the medial lemnisci reach the thalamus and terminate in which nucleus?
VPL (ventroposterolateral): second order neurons terminate and third order neurons originate here
In which nucleus do the third order neurons of the dorsal ascending system originate?
VPL of the thalamus
Which nuclei are present on the lateral sides of the thalami?
Which arc-shaped nucleus stretches over the thalami and connects to the lentiform nucleus?
Between the thalamus and lentiform nucleus is which white matter bundle?
In between the right and left thalami is which fluid-filled cavity?
Third order neurons from the dorsal column sensory system originate from VPN of the thalamus and travel upward through which structure? What happens to these fibres once they pass through the capsule?
Posterior limb of internal capsule. After passing through, fibres radiate outward to cerebral cortex (corona radiata) and eventually connect to cortex in post central gyrus (sensory cortex)
From which structure does the corona radiata originate?
Posterior limb of the internal capsule
What are the receptors in the skin for pain and temperature?
Free nerve endings for pain and thernal receptors for temperature sense
The pain pathway has which 2 distinct fibre types carrying information to the CNS?
A delta (sharp/fast pain) and C fibre (dull, diffuse pain) pathways
The thermal sensory pathway follows the same pattern as which other pathway?
What is the stimulus for fast pain?
Mechanical or thermal pain (usually from the skin)
What is the stimulus for slow pain?
Mechanical or thermal pain, and chemical pain (can be from skin or deeper structures)
Which chemical substances originate from tissue damage and can stimulate the nerve endings for pain?
5-HT, histamine, bradykinin, acids (and potassium from injured cells)
Which 2 chemical substances cannot cause pain, but can reduce the threshold for pain if present in tissue?
Substance P and prostaglandins
The first order neurons for the pain (and temperature) pathway have their cell bodies in which location?
Dorsal root ganglion
First order neurons in the pain pathway terminate in which location?
In the substantia gelatinosa in the dorsal grey horn of the spinal cord
Describe the origin and pathway of second order neurons in the pain (and temp) pathway (anterolateral pathway)
Originate in the substantia gelatinosa in the dorsal horn of the spinal cord and cross to the contralateral side at the same level of the spinal cord.
As sensory pain/temp fibres enter the spinal cord, they give off which branches to form which tract?
Ascending and descending branches, which form their own local vertical tract (dorsolateral tract of Lissauer) within the spinal cord
The dorsolateral tract of Lissauer is made up of what structures?
Ascending and decending branches of first order neuron central prcesses as they enter into the spinal cord
Cell bodies of the second order neurons fom the pain/temp (anterolateral) pathway exist where?
Within the dorsal horn of the spinal cord (at the level of entry) in the substantial gelatinosa
The lateral part of the lateral spinothalamic tract carries pain and temperature information from the ____ lower part of the body, and the medial part of the tract carries information from the _____ part of the body.
Describe the path that the second order neurons of the pain/thermal pathway take
Originate in substantial gelatinosa and decussate the spinal cord the the level of entry before ascending as the lateral spinothalamic tract.
Compare and contrast the information carried by the lateral spinothalamic and anterior spinothalamic tracts
Lateral carries pain and temperature information, anterior carries information about crude touch
The tectum is part of which brain strcture?
What is the name of the swellings on the posterior midbrain?
Superior and inferior colliculus (= tectum)
The tectum of the midbrain is made up of which 2 strucutres?
Superior and inferior colliculus
Which 3 ascending spinal pathways fuse together in the medulla and then run anatomically as a single bundle up to the thalamus? What is the name of the bundle?
Lateral and anterior spinothalamic tracts and spinotectal tract. Form the spinal lemniscus
What is the spinotectal pathway responsible for?
The medial lemniscus is formed from the ____ tract, whilst the spinal lemniscus is formed from the _____
edial formed form dorsal column system, spinal lemniscus is formed from the anterolateral tract (combination fo anterior and lateral spinothalamic tracts and spinotectal traact)
Where do the anterior and lateral spinothalamic tracts and spinotectal tracts terminate? (after they have fused to form the spinal lemniscus in the medulla)
Anterior and lateral spinothalamic tracts terminate in the VPL nucleus of the thalamus, whilst the spinotectal tract terminates in the superior tectum/colliculus (note that slow/diffuse pain fibres also terminate in the internal thalamic lamina)
Compare and contrast where the fast vs slow pain second order neurons from the pain pathway terminate
Fast pain all terminate in VPL nucleus of the thalamus. Slow/diffuse/dull pain fibres terminate in the VPL as well as the internal.intra lemina nuclei of the thalamus
Slow pain fibres intensely stimulate the _____ _____ before terminating the the VPL nucleus and internal lamina nucleus of the thalamus
What is the reticular formation?
Mixture of grey and white matter entending throughout the brainstem
What is the main function of the reticular formation?
Main switch of the brain: keeps all cerebral cortex active during the day but decreases activity night so no longer has ability to stimulate cortex - regulates sleep/wake cycles
The reticular formation has heavy connections with which nuclei of the thalamus?
Internal lamina nucleus/intra lamina nucleus
All ascending sensory pathways give collaterals to which structure of the brainstem?
What is the clinical significance of ascending slow pain fibres stimulating the reticular formation and intra laminal nucleus of the thalamus?
Painful stimuli from slow fibres irritates reticular formation to keep the CNS on and active to eliminate the source of pain (i.e., can't sleep)
Compare the information passed on to the cortex from sharp pain vs slow/dull pain fibres after passing through their respective nuclei in the thalamus
Fast pain fibres from the VPL nucleus provide the cortex with information about the characteristic and location of the pain. Slow/dull pain fibres from the intra lamina nucleus alert the whole cortex to the pain in general
What is the insula?
A portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal and frontal lobes)
Describe the passageway of the pain pathway after travelling through the thalamus
Pass through poterior limb of internal capsule and fan out to postcentral gyrus
Some pain fibres are connected with which nucleus, which is responsible for the emotional response to pain?
The cingulate gyrus is concerned with what information?
Emotion (and emotional response to pain)
Some slow pain fibres travel to which part fo the cortex, which is responsible for autonomic responses to pain?
Explain why slow pain is diffuse and difficult to localise, while fast pain is easily located
When fast pain fibres enter the spinal cord (from A delta fibres which are myelinated), they synapse immediately with second order neuron before decussating and travelling straight up the lateral spinothalamic tract to the brain. On the other hand, slow pain fibres (C fibres, non myelinated) enter the spinal cord and then synapse with many, many neurons before decussating. In this way, the cortex finds it much more difficult to localise where the dull pain started/came from.
Which NTs are produced by pain nerve endings to stimulate second order neurons in the substantia gelatinos of the spinal cord?
Glutamate and substance P
Explain why massaging/stimulating areas of skin that are not painful can decrease the pain of another area of the body
Gate control theory: some sensory neurons have the ability to give off APs to collateral connector neurons that are connected with the second order neurons of the pain pathway and ican release NTs that inhibit them
What substances are released by the descending analgesia system in the spinal cord to reduce pain?
Enkephalins and endorphins (morphine-like)
Comment generally on areas where fibres from the descending analgesic fibres come from
Periventricular area, periaqueductal area and other midline nuclei in the brainstem
Spinocerebellar pathways carry information from the right side of the body to which side of the cerebellum?
Right - i.e., the spinocerebellar pathways are the only acending pathways that carry ipsilateral information
What are the 2 main spinocerebellar pathways?
1. Dorsal spinocerebellar pathway (cuneocerebellar pathway included) 2.
Describe the dorsal spinocerebellar pathway
Fibres enter dorsal horn spinal cord and terminate in Clark's nucleus, giving rise to second order neurons which turn laterally and enter the white matter lateral column on the ipsilateral side before ascending. They enter the ipsilateral cerebellar cortex via the inferior cerebellar peduncles
Information from which 3 receptor types contributes to the dorsal spinocerebellar pathway?
Goldi tendon organs, muscle spindles and pressure receptors
The cell bodies of the second order neurons of the dorsal spinocerebellar pathway make which vertical nucleus in the spinal cord?
Dorsolateral nucleus of clarke (Clark's nucleus)
The pons is connected to the cerebellum via what strcutures?
Middle cerebellar peduncles
The midbrain is connected to the cerebellum via what strcutures?
Superior cerebellar peduncles
What are peduncles?
Bundles of white matter which connect the brain stem with the cerebellum
The cell bodies of the first order neurons in the dorsal spinocerebellar system exist in which spinal levels. What about Clark's nucleus? What is the significance of this arrangement?
Dorsal root ganglion from C8 to S3. Clark's nucleus extends from C8 to L3 (not to lower lumbar and sacral levels). Therefore fibres which enter through lower levels must first ascend upwards to connect with Clarks nucleus
Clark's nucleus receives information from which parts of the body? What about the accessory cuneate nucleus?
Trunk and lower limb; upper limb sensory
What is the cuneocerebellar pathway?
Counter-part of dorsal spinocerebellar pathway but providing informationf rom the upper limbs via the accessory cutaneous nucleus
What is the most significant difference between the dorsal spinocerebellar pathway and the anterior spinocerebellar pathway?
Second order neurons cross the spinal cord to the contralateral side before ascending
Describe the anterior/ventral spinocerebellar pathway
Enter dorsal spinal cord and synapse, giving rise to second order neurons which decussate at the level of entry to the spinal cord and then ascend. Enter the superior cerebellar peduncle on contralateral side, and then they turn back and re-decussate across the cerebellum so they end up back on the ipsilateral side.
Briefly describe the spinotectal pathway
Enters spinal cord and second order neuron decussates before ascending to the tectum (also joins with anterior and lateral spinothalamic pathways at the level of the medulla)
Briefly describe the spino-olivary pathway
Enters spinal cord second order neuron decussates before ascending to the olive of medulla and then through the inferior cerebellar peduncles into the cerebellum
What sort of information is carried by the spino-olivary pathway?
Prioprioception, touch, pressure and sense of position (movement and posture)
Briefly describe the spino-reticular pathway
Enters spinal cord and ascends directly upward to the reticular formation
What name is given to the cortex located in the precentral gyrus?
Primary motor cortex = M1
What functions is the pre-motor area responsible for?
Planning the motor activity (programming) - i.e., where the body is located in space and what program must be executed to complete a particular movement (therefore all proprioceptive information passes to this area) - basically decides which neurons in the primary motor area need to be stimulated to carry out the movement
What is the supplementary motor area responsible for?
Bilateral primitive movement planning, such as primitive movement of hips and axial skeleton
Why is the primary motor cortex unable to function without the pre-motor area?
Because the pre-motor area decides what program must be carried out and stimuluates specific neurons in the primary area as required. I.e., the primary area cannot make decisions and needs the input from the pre-motor area, which has made the plan
Which area in the pre-motor cortex is responsible for programming patterns and neurons in the primary motor area for meaningful speech
Describe, in terms of neuroanatomy, why a baby can make sounds but not meaningful words
Speech area (Broca's area) of pre-motor cortex is not functional yet
Suppose a patient has had a stroke, and knows what he wants to say but cannot make meaningful words. What part of the area is liklely to have damaged?
Speech area (Broca's area) of pre-motor cortex (i.e., nothing is wrong with the neurons in the primary motor cortex that work the required muscles, but damage to the pre-motor area means that no program can be given to the primary area)
Describe the difference in outcome if the primary motor cortex was stimulated, vs if the pre-motor area was stimulated
Primary motor area would elicit random movements of some muscles, but stimulation of the pre-motor area would result in whole patterns of pre-programmed movement
Above Broca's area is which part of the pre-motor area concerned with eye movement?
Frontal eye field
What is the purpose of the frontal eye field in the pre-motor area?
Plan how eyes should be deviated and to what degree (stimulation on one side of the field will result in conjugate eye movement toward the opposite side)
Explain why a tumour in the pre-motor area may cause the eyes to deviate toward the contralateral side (i.e., away from the tumour) initially, but then cause the eyes to swing back toward the tumour after some time
Tumour irritating front eye field in pre-motor side causes neurons to overperform/hyperfunction. At a point where the tumour actually destroys the eye field, it is unable to program the eyes to look toward the contralateral side. However, the eye field on the other side (not affected by the tumour) is now unbalanced, so the eyes deviate toward the tumour
List the areas of the motor homunculus, from lateral to medial (within the primary motor cortex)
Pharynx, tongue, facial expression etc (speech - large area), head and neck, hand (large area), shoulder through to foot (most medially)
Describe the important areas in the pre-motor cortex, from most lateral
Brocas area, frontal eye fields, neck movement, hand movement
Where do the fibres of the descending corticospinal tracts found?
30% from primary motor area, 30% from supplementary + pre-motor area and 40% from sensory cortex (post central gyrus)
The cerebral motor cortex contains how many layers of neurons?
In which layer of the cerebral cortex are the cell bodies of the neurons that contribute to the corticospinal tracts?
What is the name of the large neuronal cell bodies that are present ONLY in the primary motor cortex? What is special about these neurons?
Cells of Batz: very large cells with very thick and heavily myelinated descending axons
Cells of Batz directly stimulate which motor neurons?
Alpha lower motor neurons
All decending fibres in the corticospinal region pass firstly through the _____ ____, and then converge in the ________
Corona radiata; posterior limb of internal capsule
Explain why a small lesion or infarct near/on the posterior limb of the internal capsule can destroy so much motor activity in the cerebrum and even lead to hemiplegia
Due to arrangement of motor fibres being so compact - i.e., lots of information in a small space as they pass through the posterior limb of the internal capsule. This posterior limb is supplied only by 1 small artery, which can commonly become blocked in old age > many fibres destroyed > equivalent of destroying all cerebral cortex > all motor movements on the contralateral side become impaired > hemiplegia (note that sensory information travelling upward would also be affected, so sensation on the contralateral side would also be impaired)
Describe the passage of the corticospinal tract fibes after passing through the internal capsule until they reach the midbrain
Pass through midbrain and converge on central 3/5ths of crus cerebri. Pass through pons and are scattered/dispersed (due to density of pontine nuclei and corticopontine/corticocerebellar fibres). Once they have reached the medulla, the re-converge to pass through the pyramids
Which structures lie beneath the cerebral adqueduct and are known to be implicated in Parkinson's disease?
What is the name given to the area of the midbrain that lies between the substantia nigra and the tectum?
What is the name given to the area of the midbrain between the substantia nigra and cerebral peduncles, where the corticospinal tracts pass thorugh?
How many segments of the crus cerebri are there? Through which sections do the corticospinal tracts pass through?
5; tracts pass thorugh central 3/5ths
What is the name given to the white matter fibres connecting the brainstem to the cerebrum?
What are pontine nuclei and what are they responsible for?
Groups of grey matter/cell bodies surround by white matter in the pons. Special fibres from the cortex terminate on these nuclei (corticopontine fibres), and from here, fibres travel through medial cerebellar peduncle into the cerebellum to give constant updates about body position
Explain why a small lesion near the corticospinal tracts as they pass throught he internal capsule is worse than a small lesion affecting the motor fibres in the pons
Because the tract is densely packed in the cerebrum but all the fibres become scattered in the pons
The pyramids of the medulla are made from what stuctures?
Fibres from coricospinal motor tracts
Describe the passage of the corticospinal tract once they have passed through the pyramids of the medulla
At the lower end of the pyramid, 90% of fibres cross and continue to descend in the contralateral side of the spinal cord (pyramidal decussation) while 10% remain on the ipsilateral side. The fibres that have crossed continue to descend through the spinal cord as the lateral corticospinal tracts, whilst the uncrossed 10% of fibres from each side run to form the anterior corticospinal tract. The lateral tracts continue down and synapse onto motor neurons in the lateral ventral horn (or via interneurons). The anterior tract fibres decussate in the spinal cord and synapse onto medial ventral horn.
Describe the location of the pyramidal decussation of the corticospinal tract
Junction of medulla and spinal cord
Describe the resultant effects on the motor system if there is a lesion above vs a lesions below the pyramidal decussion
Lesions above the decussation result in contralateral motor dysfunction, while lesions below the decussation produce motor deficits on the ipsilateral side (as the lesion is occuring after the decussation has occurred)
The fibres from the anterior corticospinal tract are concerned with what types of movements? Where does this information originate from in the cortex?
Primitive movements of the trunk/axial skeleton. Information comes from supplementary motor area
The fibres from the lateral corticospinal tract are concerned with what types of movements?
Skilled and voluntary movements (especially fine movements in the hands)
Compare the points of decussation for the anterior vs lateral corticospinal tracts
Lateral tract decussates in the pyramidal decussation (90% of fibres), and anterior (remaining 10%) decussate at the level of the spinal cord for which they are needed
List all of the areas that the corticospinal tract sends collateral information to on its descending pathway through the brain and brainstem
Feeds back to cortex, to basal ganglia (lentiform nucleus), red nucleus, vestibular nuclei and olivary nuclei
What is a lower motor neuron?
Neurons coming out of CNS (brainstem or spinal cord) and connecting to NMJs
What is an upper motor neuron?
Group of all neurons that originate at high cortical level and decend to lower motor neurons (directly or indirectly) to moderate the activity of the LMN
List the types of neurons that leave the CNS
Preganglionic parasympathetic, preganglionic sympathetic and lower motor neurons (connecting to NMJs)
What is the name given to the tract that sends descending fibres to stimulate lower motor neurons of the brainstem?
Corticonuclear fibres are synonymous with which other tract?
Those corticonuclear fibres that are specifically connected with lower motor neurons in medulla are called ____?
The superior and inferior colliculi are specifically concerned with which reflexes?
Superficial = Visual reflexes; Inferior = Auditory reflexes
Lower motor neurons receive input from which descending tracts?
Corticospinal (or corticonuclear in the brainstem), tectospinalÉ
Fibres that decending from the red nucleus and cross before descending on the contralateral side are part of what tract?
List the 5 descending tracts that originate from subcortical areas
Tectospinal, reticulospinal, rubrospinal, vestibulospinal, olivospinal tracts
What is the name of the nuclei present at the junction between the medulla and the pons?
Vestibular nuclear complex
Decending tracts that take information to cranial nerve LMNs come from the _______tract, whilst tracts that take information to the spinal nerves are carried in the _____ tract
Corticonuclear tract; corticospinal tract
What is meant by the pyramidal tracts? Which fibres are included?
Any descending tracts which pass through pyramids of medulla = corticospinal (also called pyramidal tracts) and sometimes the corticonuclear tracts are also included (because origin is the same)
Extensor musles are also known by what other name?
Which pathway (and assistant pathway) is responsible for providing input to the extensor muscles?
Vestibulospinal (and assisted by pontine reticulospinal)
Which pathway is an assisting pathway to the vestibulo spinal pathway? Which nucleus do these fibres come from?
Ponto-reticulospinal (from pontine nucleus in reticular formation)
Which pathway (and assistant pathway) is responsible for providing input to the flexor muscles?
Rubrospinal and assisted by medullary reticulospinal
Describe the vestibulospinal and ponto-reticulo spinal tracts
Begin at vestibular nuclear system and pontine reticular nuclei and decend UNCROSSED to spinal cord anterior white matter to control extensor/anti-gravity muscles
Describe the rubrospinal tract
Begin in red nucleus, cross in the brainstem and descend to the lateral white matter of the spinal cord to control the flexor muscles
What are the 2 main functions of the rubrospinal tract?
1. Enhances flexor tone; 2. Acts an accessory pathway from the cortex to spinal neurons (corticorubral fibres)
Which tract is assistant to the rubrospinal tract in controling flexor muscle tone?
Medullary-reticulospinal tract (from medullary reticular nuclei)
Sympathetic fibres originate in the ____ part of the hypothalamus, whilst parasympathetic fibres originate in the ____ part
Sympathetic fibres from the posterior part of the hypothalamus descend down the spinal tract and stimulate pre-ganglionic sympathetic neurons in which spinal levels?
If there is any interruption to the thoracic sympathetic outflow from fibres suppying T1 and T2, what is the resultant pathology? Why?
Horner's syndrome - because T1 and T2 have some sympathetic supply to head and neck. So if there is damage, there will be ptosis, anhydrosis (lack of sweating), constriction of pupil and other symptoms of Horner's
Parasympathetic outflow is from which cranial nerves?
3, 7, 9 and 10 (III, VII, IX and X)
Comment on where there is/is no parasympathetic outflow from the spinal cord
CN III, VII, IX and X. No parasympathetic outflow from cervical, thoracic or lumbar regions. S2-S4 have parasympathetic outflow (i.e., cranial sacral outflow)
Which fibres of a muscle are connected to Golgi tendons?
Alpha motor neurons connect the anterior horn of the spinal cord with which muscle fibres?
Alpha motor neurons release which neurotransmitter at the NMJ?
Cholinergic fibres (NT is ACh)
What sort of receptors are present at the NMJ and allow binding of the NT released by alpha motor neurons?
Nicotinic receptors (for ACh)
Nicotinic receptors at the NMJ are coupled with what sort of channels?
Very briefly describe the interactino between alpha motor neurons and muscle contraction
AP travels along alpha motor neuron and releases ACh into the NMJ. This binds to nicotinic receptors which are coupled to cationic channels. This causes depolarisation, and AP travels along surface of extrafusal muscle fibres and into T tubules, then they stimulate release of calcium in the cell, which leads to actin-myosin interaction (calcium bids to toponin, which moves toposiosin away so that actin and myosin can interact and contract the muscle)
The sensitivity of muscle contraction is dependent on what?
Muscle spindles (degree of stretch sensed by afferent neurons and relayed to spinal cord)
What will be the result of stimulating muscle spindles?
Stimulates increase in AP traffic in sensory stretch receptor afferents toward the spinal cord > stimulates alpha motor neurons in spinal cord > causes extrafusal muscle fibres to contract
Gamma motor neurons give motor supply to what part of the muscle?
Alpha motor neurons supply ______ muscle fibres, whilst gamma motor neurons supply ______ muscle fibres
If a gamma motor neuron is stimulated, what will be the result?
Contraction of muscle spindles > not enough to contract whole muscle but enough to produce stretch at the end of muscle spindles > more APs thrown toward spinal cord > leads to stimulation of alpha motor neuron > leads to contraction of extrafusal muscle > increased muscle tone
What sort of fibres take stretch information from muscle spindles toward the spinal cord?
Describe the pathway of a deep tendon reflex
Hammer hits tendon > produces brisk, transient stretch on whole muscle > extrafusal fibres stretched > stretches intrafusal fibres > stretch receptors increase information (APs) travelling through Ia fibres to spinal cord/CNS > transient overstimulation of alpha motor neurons > produces increased transient AP traffic to NMJ of the same muscle which was stretched > slightly increase NMJ at a very short time > transient contraction/reflex/jerk
Why is the terminology 'deep tendon reflex' a misnomer?
Because the hitting of the tendon does not target deep golgi tendon organs, but the stretch of the whole muscle
List the 5 things that can be tested in a stretch reflex
1. Intrafusal stretch receptors working 2. Sensory afferent Ia fibres working 3. Integration in spinal cord working 4. Alpha motor neuron transmission working 5. NMJ at the muscle working (i.e., in a particular spinal cord level, that input and output are working)
When are golgi tendon organs stimulated?
When there is too much tension on the muscle and it threatens the integrity of the locomotor system
Explain how golgi tendon organs are responsible for maintaining the integrity of the locomotor system
When there is undue tension on a muscle/tendon (to the point where stress would cause damage), golgi tendon organs (receptors) are stimulated > send APs to spinal cord via Ib fibres > stimulate interneurons in the spinal cord > interneurons release inhibitory NT which act on alpha motor neurons > alpha motor neuron inhibited > muscle relaxes > this is the golgi tendon reflex
Explain the difference between muscle stretch reflex and golgi tendon reflex
Stretch reflex (stimulus = stretch, response = contraction); Golgi tendon reflex (stimulus = tension, response = relaxation). When a muscle spindle is stimulated, the end result is contraction of the muscle. When a goldi tendon organ is stimulated, the end result is relaxation of the muscle (due to inhibition)
Which spinal nerve supplies the biceps?
Presume there has been a LMN lesion affecting the biceps. After 3 months, comment on the changes seen in the muscle
1. Mass is lost (due to lack of trophic action due to lack of ACh released at NMJ) 2. Power is totally lost 3. Tone reduced = flaccid (gamma motor neurons denervated, resulting in relaxation of msucle spindles > no signal to spinal cord or alpha motor neuron action) 4. Related tendon reflexes are lost (because muscle stretch cannot stimulate the motor reflex) 5. Babinski reflex should be normal (plantar flexion)
Explain why there is more atrophy of muscles in a LMN lesions compared with an UMN lesion
Because in LMN, there is loss of mass due to loss of ACh release at the NMJ, which causes lack of tonicity and muscle atrophy (complete termination of trophic action). In an UMN lesion, the UMN loses inhibitory control of the LMNs, leading to over-firing of the LMN and tonicity of the muscle. There is still atrophy due to lack of use, but not as marked as the atrophy due to neuro degeneration (i.e., there is disuse atrophy but not denervation atrophy)
Which 2 factors lead to atrophy of muscle?
1. Trophic action (denervation) 2. Disuse
Maintenance of tone of a muscle is primary dependent on acitivty of?
Gamma motor neuron
Explain why there is muscle rigitidy in a UMN lesion
UMN lesion = over-firing of LMN > over firing of gamma motor neurons > muscle spindle becomes stretched > give more sensory input to spinal cord > excessive stimulation of alpha motor neurons (i.e., alpha motor neurons are overstimulated by stretch reflex but also via disinhibition of gamma motor neurons)
Explain why there is hyperreflexia in UMN lesions
UMN inhibitory control is lose > gamma and motor neurons over-fire > hammer tap will cause excessive overfiring and excessive stimualtion of alph amotor neurons > produce a lot of ACh and reflex becomes exaggerated
Describe the location of the exit point of CN III (occulomotor) in the brainstem
At the level of the superior colliculus in the front of the midbrain, on the medial side of cerebral peduncle and moves anteriorly
Describe the location of the exit point of CN IV (trochlear) in the brainstem
At the level of the inferior colliculus in the midbrain at the back (this is the only spinal/cranial nerve exiting dorsally) and wraps around to cerebral peduncle more laterally than CN III
Which is the only cranial nerve which exists from the back of the CNS?
CN IV (trochlear)
The pineal gland is located at the back of which ventricle?
CN V (trigeminal) exits the brainstem at what location?
Anterolateral side of the pons
Describe the exit of cranial nerves in the pontine medullary sulcus from medial to lateral
Most medial is CN VI, then VII more laterally and CN VIII
Which cranial nerves exit the brainstem at the inferior cerebellar peduncle (from superior to inferior)
CN IX, X and XI (cranial part of XI)
Where does CN XII exit the brainstem?
In the medulla between the pyramid and olive
What sort of fibres are attached to the cell bodies of neurons in the anterior grey horn of the spinal cord?
General somatic efferents
What sort of fibres are attached to the cell bodies of neurons in the posterior grey horn of the spinal cord?
General somatic afferents
What sort of fibres are attached to the cell bodies of neurons in the transverse grey horn of the spinal cord?
General visceral efferents and general visceral afferents (sensory fibres are more posterior)
Generally speaking, compare the locations of sensory vs motor nuclei in the brainstem
Sensory are more lateral and motor are more medial (results from opening of spinal cord around the central canal to form the 4th ventricle)
Describe the location of the trigeminal sensory ganglion
Posterior-most part of middle cranial fossa at the tip of the temporal bone
Describe the pathway of the sensory root of the trigeminal ganglion
Lateral part of mid-pons > enters CNS at anterilateral part of mid-pontine area
The motor root of the trigeminal nerve is responsible for which functions?
Muscles of mastication (NOT connected with ganglion)
Where does the motor root of the trigeminal nerve exit the skull? Which other structure exits at this point?
Foramen ovale with the mandibular division of the trigeminal nerve (that has originated from the trigeminal ganglion)
Which is the largest cranial nerve?
Where are the trigeminal nuclei located and what are they called?
Midbrain (mesencephalic nucleus), pons (prinicpal sensory pontine nucleus) and floor of medulla to upper spinal cord (spinal nucleus of V)
What are the names of the fibres coming from the trigminal sensory root and projecting to spinal nucleus of the trigeminal nerve?
Trigeminal spinal tract
Fibres from the trigeminal nuclei end up in what structure? What are these ascending fibres called?
Ventro-postero medial nucleus of thalamus; trigeminal lemniscus (or trigeminothalamic tract)
List the 6 components of the trigeminal system
1. Divisions 2. Ganglion 3. Motor and sensory root 4. Tracts (especially spinal) 5. Nuclei 6. lemnisci
Describe the pathway of the trigeminal lemniscus after travelling through the VPM nucleus of the thalamus
Ascend through posterior limb of internal capsule and end up in posterior central gyrus
General somatic afferents of the trigeminl system carry what sorts of information?
Fine touch (and 2 point discrimination), pain, temperature and proprioception
General somatic afferents of the trigeminl system supply which structures?
Half of head, full face, cranial cavity (anterior and medial cranial fossa), eye, nose and paranasal sinuses, oral cavity, anterior 2/3 tongue and external ear
What is very unique about the myelination of the sensory root of the trigeminal system? What is significant about this?
For about 7mm, the part of the trigeminal root connected with the pons, the myelination is provided by oligodendrocytes (which are usually only present within the CNS). Significance is that diseases which affect myelination in CNS can also effect the sensory root of the trigeminal system.
The external ear is supplied by which 4 nerves?
V, VII, IX, X
What motor supply is the trigeminal nerve responsible for?
Muscles of mastication (temporalis, masseter, lateral and medial pterygoids), tensor tympani (pulls ear drum medially), tensor vali palatini, myelohyoid and anterior belly of digastric muscle
What % of CO goes to CNS?
Vertebral arteries take orogin from which major blood vessel?
Which 2 major systems are responsible for delivering blood to the brain?
Vertebral arteries (basillar/posterior system) and internal carotid arteries (anterior system)
Vertebral arteries travel through which foramina?
Foramina of transverse processes of cervical vertebrae
Describe the pathway of the vertebral arteries supplying the brain, from their origin
Originate from subclavian system, travel upwards and medially and pass through foramina of cervical vertebrae transverse processes. Enter cranial cavity through foramen magnum > must pierce dura mater and arachnoid mater to end up in subarachnoid space. R and L meet at ponto medullary junction to become basilar artery, which travels upward before giving off terminal posterior cerebral arteries at the top of the brainstem (just above level of 3rd cranial nerve region)
All major arteries supplying the brain (carotid system, vertebral system and circle of willis) are present in which area?
Subarachnoid space (and floating in CSF)
Where do the R and L vertebral arteries meet?
Ponto-medullary junction (i.e., after they have entered through foramen magnum)
Once the R and L vertebral arteries meet at the ponto-medullary junction, they move upwards as which large artery?
The basilar artery divides into which terminal branches at the top of the brainstem?
R and L posterior cerebral arteries (PCAs)
The right and left posterior cerebral arteries supply which areas of the brain?
Midbrain, posterior part of cerebral hemispheres
Where does the anterior spinal artery originate?
In front of the medulla from the contributary branches of the R and L vertebral arteries. Moves inferio-medially and combine to form anterior spinal artery which descends in the anterior medial fissure of the spinal cord
What is the origin of the posterior inferior cerebellar artery?
How much of the spinal cord is supplied by the anterior spinal artery?
Anterior 2/3 of the spinal cord
If anterior spinal artery is blocked, what will be the result?
Loses blood supply and undergoes infarction to the anterior 2/3 of the spinal cord at that level
Which arteries carry blood toward the spinal cord to reinforce the anterior spinal artery?
Segmental arteries move medially toward the spinal cord and divide into which divisions?
Anterior reticular artery (reinforce blood flow in anterior spinal artery) and Posterior reticular artery (reinforce blood flow in 2 posterior spinal arteries)
What is the origin of the posterior spinal arteries?
Vertebral artery (either directly or indirectly from posterior inferior cerebellar arteries)
List 3 major arteries that give segmental arteries to reinforce the blood in the spinal arterial system
1. Deep cervical arteries 2. Intercostal arteries 3. Lumbar arteries
What is the most important artery that provides a segmental artery to reinforce the spinal arteries?
Direct supply from aorta > great medullary artery of ADAM niewicz
Which 2 levels of the spinal cord is the weakest area of blood supply in the territory of anterior spinal artery? Why is this clinically significant?
T4 and L1 (this is because main reinforcing arteries are located just below these points). This is clinically significant because these areas are most likley to develop infarction with reduced blood flow to the anterior spinal artery
Which levels of the spinal cord is the weakest area of blood supply in the territory of the posterior spinal arteries?
T1, 2 and 3
What areas are supplied by the posterior inferior cerebellar artery?
Cerebellum and lateral part of medulla
Which artery may originate from beginning of basillar artery or from the vertebral artery in other people?
Anterior inferior cerebellar artery
What areas are supplied by the anterior inferior cerebellar artery?
Lateral part of pons as well as under side of cerebellum
Which long artery may originate from the basilar artery or from the anterior inferior cerebellar artery in others, and goes to supply the inner ear?
Which 2 nerves accompany the labyrinthine artery?
Facial nerve and vestibulocochlear nerve (through internal acoustic meatus to supply inner ear)
Which arteries originate from the basilar artery just below the level of the occulomotor cranial nerve exit?
Superior cerebellar artery
What structures are supplied by the superior cerebellar artery?
Some midbrain and superior cerebellum
The internal carotid artery enters through the ____ canal, moves forward and then turns upward to exit through the foramen ______, reaching the ____ cranial fossa
Carotid; foramen lacerum; medial
Which dural venous sinus is located in the middle cranial fossa? Which important structure runs through this sinus?
Cavernous sinus; internal carotid artery
Describe the pathway of the internal carotid artery, from it's origin
Originates at common carotid artery (where the division of internal and external carotid arteries occurs at the carotid sinus). Moves upward, enters into carotid canal, moves forward (anterior part of carotid canal opens into the foramen lacerum) and arteries moved through the foramen lacerum, then upwards, pierces the dura mater and enters the cavernous sinus. Then moves upward from here (medial to the anterior clenoid process) and then pierces mater again and comes into subarachnoid space
Which branch of the internal carotid artery passes into the orbital cavity through the optic canal?
Which important branch of the ophthalmic artery supplies the retina?
Central retinal artery
What is the origin of the central retinal artery?
Internal carotid artery > ophthalmic artery > central retinal artery
Name one of the signs of anterior carotdi circulation failure
Blindness in one eye due to occlusion of central retinal artery
Which 2 branches of the internal carotid artery travel backward from the internal carotid artery after it has entered the subarachnoid space?
Posterior communicating artery and anterior choroidal artery
Which arterry forms a connection between the the carotid system and vertebral basillar systems?
Posterior communicating artery
What is supplied by the anterior choroidal artery?
Supply choroid plexus of lateral ventricle
What are the 2 terminal arteries of the internal carotid artery?
After giving off posterior communicating artery, ophthalmic artery and anterior choroidal artery, internal carotid artery divides into 2 terminal branches: lateral terminal branch = middle cerebral artery; and anterior terminal branch = anterior cerebral artery
The anterior communicating artery forms a connection between which vessels?
R and L anterior cerebral arteries
Which structures border the circle of willis?
R and L internal carotid arteries, anterior communicating artery, posterior communicating arteries, posterior cerebral arteries
Which structure of the arachnoid mater anchors it to the pia matter?
Connective tissue reticuli
Which cranial meningeal layer is highly vascular?
Name the 2 layers of the dura mater
Periosteal layer and meningeal layer
What is clinically relevant about the periosteal layer of dura mater?
Periosteal layer can become pathologically separated from the skull bone. Meningeal vessels run through this area (between periosteal and meningeal dura meter), and so haemorrhage can occur.
The periosteal layer of the dura mater is tightly connected to the skull bone except for at which normal anatomical structures?
Venous dural sinuses
Within which 2 layers of the meninges do the meningeal arteries and veins run?
Between the meningeal and periosteal layers of the dura mater
Why does an epidural haemorrhage appear as a 'lens' shape on CT?
Because the ligaments between the sutures in the skull will stop the bleed from pogressing part that point (due to tension), so bleed appears long and thin, with distinct end points at the sutures
Describe the appearance of a subdural haemorrhage on CT
Crescent shape (tracks around the skull between dura and arachnoid mater, with little resistance and little pressure = even distribution)
Rupture of bridging/cerebral veins as they approach the dural sinuses causes what sort of haemorrhage?
Bleeding of meningeal arteries and veins causes what sort of haemorrhage?
What is an aneurysm?
Abnormal, irreversible dilation of arterial wall
Why is subarachnoid haemorrhage so diffuse and widespread?
Because the space is full of CSF, so blood can move easily and throughout entire space
Which form of haemorrhage will result in apperance of RBCs in a LP sample?
Which basal ganglia strucutres are considered to be in the clinical slassification?
Caudate nucleus, lentiform nucleus (putamen + globus pallidus), substantia nigra and subthalami
The globus pallidus is divided into which 2 parts?
1. Globus pallidus interna (medial) 2. Globus pallidus externa (lateral)
Which 3 structures make up the corpus striatum?
Caudate nucleus, putamen and globus pallidus (lentiform nucleus)
Which structures make up the striatum/neostriatum
Caudate nucleus plus only the putamen part of the lentiform nucleus
What are the corticonuclear fibres?
Fibres originating in the cortex that serve motor neurons which are present in the brain stem
Very briefly and simply describe the role of the basal ganglia in motor function planning
Idea of movement occurs in cortex > sends signal to basal ganglia which plans the movement > signal sent back to cortex via the thalamus > stimulates firing of corticospinal and corticonuclear fibres > stimulates muscle contraction
Fibres from cortex stimulate neurons in which basal ganglia first? What are these fibres called?
Neostriatum (mostly putamen); corticostriatal fibres
From the putamen, fibres travel to which basal ganglia structure?
Globus pallidus interna
Fibres from the globus pallidus interna (as part of the direct pathway) travel to which structure to be relayed back to the cortex?
Describe the direct pathway of the basal ganglia and the names of the fibres carrying information between each structure
Fibres from cortex (neocortical fibres) approach putamen > globus pallidus interna (striatopallido-fibres) > thalamus (pallido-thalamic fibres) > back to cortex (thalamo-cortical fibres)
Which fibres of the open basal ganglia pathway are excitatory? What NT do they release?
Neocortical fibres (from cortex to putamen) and thalamocortical fibres (from thalamus back to cortex); NT is glutamate
Which fibres of the open basal ganglia pathway are inhibitory? What NT do they release?
Striato-pallido fibres (from putamen to globus pallidus interna) and pallido-thalamic fibres (from globus pallidus interna to thalamus); NT is GABA (and substance P also released)
How is the motor cortex kept inhibited when there is no movement? Explain this phenomenon in terms of the action of the basal ganglia
Globus pallidus interna is actively firing > releases inhibitory GABA on thalamus (ventroanterior, ventrolateral and dorsomedial nuclei of thalamus > keeps thalamo-cortical fibres inhibited > therefore upper motor neurons in motor cortex cannot be stimulated and there is no movement
The globus pallidus releases the NT _____ onto which nuclei of the thalamus?
GABA; ventroanterior, ventrolateral and dorsomedial nuclei
List the 2 ways that GABA causes inhibitory effects
1. Causes influx of chloride into cell > makes cell more negative and hyperpolarised 2. Allows potassium efflux > makes cell more negative and hyperpolarised
Describe what happens in the basal ganglia direct pathway from the beginning of an idea of movement to actual muscle contraction
Corticostriatal fibres stimulated > release glutamate > glutamate binds to receptors and causes cation loading > AP moves down striatal-pallido fibres and releases GABA on pallidal neuron > pallido-thalamic neurons become inhibited (AP is less, less GABA release in thalamus, therefore nothing inhibiting firing) > thalamo-cortico fibres become less inhibited (recall they are normally tonically firing at rest) > thalamo-cortico fibres start firing > stimulates upper lower motor neurons > timulate lower motor neurons > muscle contracts
Describe the pathway of fibres in the indirect basal ganglia system, and comment on which NTs are released by each
Corticostriatal fibres (glutamate) > fibres then go to globus pallidus externus (GABA) > next neuron travels to subthalamus (GABA) > neuron to globus pallidus internus (glutamate) > thalamus (GABA)
Why do we need both a direct and indirect basal ganglia pathway?
For agonist and antagonist movements (i.e., flexors should contract at the same time that extensors relax). Another example is that all the other muscles needed for a movement must be regulated (stabilisation of the shoulder when hand writing)
Which pathway of the basal ganglia system is stimulatory only?
Describe how the indirect pathway in the basal ganglia system works and what the function of this pathway is
Corticostriatal neurons release glutamate > stimulate neuron that travels to globus pallidus externus > release GABA onto neuron that travels to subthalamus > this neuron is inhibited > less GABA is released onto the next neuron situated in the subthalamus > subthalamo-pallidal neuron becomes stimulated and over-fires > release glutamate in globus pallidus interna > neuron travelling to thalamus is stimulated > more GABA released in thalamic nuclei > neuron travelling to cortex becomes inhibited. This then inhibits upper motor neurons that need to be inhibited for movement (i.e., may be the extensors in a certain movement that requires flexors)
The caudate nucleus, putamen and globus pallidus are embryonic derivatives of the _____, whilst the substantia nigra and subthalami are derived from the ______
Name the 2 parts of the substantia nigra
Pars compacta and pars reticularis
Dopamine is released from which part of the substantia nigra?
How does the substantia nigra influence the direct and indirect basal ganglia pathways? What is it's main function?
Dopaminergic neurons in the substantia nigra pars compacta has neurons which travel to the putamen (nigro-striatal fibres) and interacts with neurons of both the direct and indirect pathways (the direct pathway is stimulated whilst the indirect pathway is inhibited) > facilitate the initiation of movement
What is the result of dopamine released onto D1 vs D2 receptors?
Neurons stimulated; neurons inhibited
Explain how dopamine from the substantia nigra pars compacta can both stimulate the direct pathway of the basal ganglia and inhibit the indirect pathway, thereby helping to initiate movement
There are D1 receptors on the direct pathway which cause cationic influx (loading), and D2 receptors on the indirect pathway which cause cation efflux. This means that the D1 receptors are stimulated and D2 receptors are inhibited.
How does the substantia nigra know when to fire dopaminergic information toward the striatum?
Presence of cortico-nigral fibres communicating with cortex
Describe the chain of events that occur in the indirect pathway of the basal ganglia system when dopamine is released on neurons in the putamen
Indirect pathway has D2 receptors > this causes efflux of cations from neuron and inhibition (antagonising effect of corticostriatal fibres in normal indirect pathway without input from substantia nigra) > neuron to globus pallidus external inhibited > next neuron is not receiving inhibition because no GABA has been released > these neurons over fire to the subthalamus and release a lot of GABA > this inhibits glutaminergic neurons from subthalamus to globus pallidus internus > little glutamate released to situmuate pallidal fibres > activity of neuron to thalamus is inhibited > less inhibition of thalamic nuclei > next neuron over fires to stimulate motor cortex
The substantia nigra pars reticularis should be considered functionally similar to which other basal ganglia?
Globus internal pars interna
Which neurons in the putamen provide counter-regulation to dopamine in the basal ganglia pathways?
Which neurotransmitter has inhibitory action on the direct basal ganglia pathway? Which are stimulatory?
ACh; glutamate and dopamine
Give a classic example of a disease in which the direct basal ganglia pathway is affected. How does this manifest?
Parkinson's. Results in difficulty initiating movement and slow movements (bradykinesia or akinasia)
List the 3 main clinical problems seen in Parkinson's Disease
Hypokinesia (less movements, difficulty initiating movement and less velocity); rigidity; tremor
What is the primary problem in Parkinson's disease?
Degeneration of dopaminergic neurons from substantia nigra pars compacta > therefore less dopamine released on basal ganglia direct and indirect pathways in putament (i.e., nigro-striatal fibres)
Describe what happens in the direct basal ganglia pathway in Parkinson's Disease
Release of dopamine on putamen less > less stimulation of D1 receptors in putamen > less GABA released on neurons in globus pallidus > causes neurons heading from GP to thamalus to slightly over-fire GABA > inhibits thalamic cortical fibres > activty then decreased > cortex stimulated less > more difficulty initiating a movement
Describe what happens in the indirect basal ganglia pathway in Parkinson's Disease
Less dopamine > D2 receptors in putamen less stimulated > neurons in putamen less inhibited and over-fire GABA > GABA neuron to subthalamus inhibited > causes over-stimulation of neurons back to GP > release more GABA to thalamus > inhibits next neuron back to cortex > less stimulation of motor cortex
Describe why people with Parkinson's get lead-pipe rigidity
Cortex inhibited via lack of dopamine and subsequent inhibitory effects on basal ganglia direct and indirect pathways > corticoreticular fibres working less > reticular formation over-fires and muscle tone of both flexors and extensors increases
Explain why people with Parkinson's get a rolling tremor
Reverberating circuits in GP externa. When dopamine is less, ACh becomes unchecked and too much > this causes circuits to become fast cycling > causes flexor and extensor muscles to alternate quickly (overcorrection), causing the tremor
What sort of drugs can cause Parkinson's-like disease?
Dopamine receptor blockers (type of anti-psychotics)
The optic nerve is an out-pouching of which embryological structure?
What makes the optic nerve different from peripheral nerves?
Covered by meninges, cannot regenerate, myelin provided by oligodendrocytes, if affected in diseases that only affect CNS, is not affected by diseases of peripheral nerves
The optic disc is located on the _____ side of the eye, about 3.5mm from the centre of the ______
All neuronal fibres in the eye converge toward which structure?
The optic disc does not contain what structures?
Light receptors (rods or cones)
If there is any object falling on the optic disc, why can it not be perceieved? i.e., physiological blind spot
Because the optic disc does not contain any rods or cones.
Which yellow-coloured structure can be seen medially to the optic disc in fundoscopy?
The macula lutea has a high concentration of ______ but small concentration of _______
What is significant about the fovea centralis of the macula lutea?
The point of maximal visual accuity (maximum concentration of cones at this point)
What is the name given to the very centre of the macula lutea?
Where is the point of maximal visual accuity in the eye? Why?
The foeva centralis of the macular lutea (because this is where the concentration of cones is at it's maximum)
What pigment is present in rods?
What is rhodopsin sensitive to?
Dim light (scotopic/night vision)
What pigment is present in cones?
Describe the location of rods and cones in the eye
Concentration of rods maximal at the periphery of retina and become less more centrally (until there are no rods present in the fovea/macula); Cones are most concentrated at fovea centralis and become less concentrated toward periphery of retina.
What are cones most sensitive to?
Bright light (photopic/day vision)
Describe the quality experienced at night (i.e., in starlight)
Colours not visible - only shades of grey, and shapes more unclear (as these are the functions of the rods in dim light)
Which type of photoreceptor provides colour vision?
Which photoreceptors are more abundant in the human eye?
Which arteries supply the foeva centralis?
None! Simple diffusion is provided from capillaries - this area is avascular
The retina contains chains of which 3 types of cells?
Photoreceptors, ganglion cells and bipolar cells
Layers of retina, from deepest (closest to choroid)
1. Pigment epithelial cell layer 2. Rods and cones (photoreceptors) 3. Outer limiting layer membrane 4. Outer nuclear layer (containing nuclei of photoreceptors) 5. Outer plexiform layer (where photoreceptors synapse with bipolar neurons) 6. Inner nuclear layer (of bipolar cells) 7. Inner plexiform layer (synapses between second and third order neurons) 8. Inner ganglion cell layer 9. Nerve fibre layer (formed by neuronal fibres/central processes of ganlgion cells that will become optic nerve) 10. Inner limiting membrane
The outer 5 layers of the retina are supplied by?
Simple diffusio of nutrients from choroidal capillaries
Why are photoreceptor cells different to most other cells in terms of their response to stimulation (i.e, from light)
When stimulated, rather than depolarising with increased sodiun influx, they depolarise and do not produce APs (but do produce graded local potentials
Describe what happens after photoreceptor cells produce local graded potentials
Electrical information (local graded potentials) passed to bipolar cells via release of neurotransmitter glutamate. Bipolar cells also undergo graded local potentials and transfer stimulation to ganglion cells via glutamate.
Describe what happens when third order ganglion cells are stimulated by glutamate from second order bipolar cells
Processes of ganglion cells bundle together to form optic nerve >
What forms the optic nerve fibres?
Axons of ganglion cells bundled together
Why is the retina considered an 'inverted structure?'
Light passes through transparent layers of retina to first stimulate inner most cells (photoreceptors), which then transfer information back through the outer cell layers to stimulate the optic nerve
How many layers of the retina exist?
10 (5 inner and 5 outer)
Horizontal cells of the retina link which structures?
Connect terminal buttons of rods and cones together horizontally
Which cells of the retina connect the outer and inner limiting membrane layers?
What is the function of retinal Muller cells?
Modified neuroglial cells of retina connecting outer and inner limiting membranes. Structurally like astrocytes.
Which cells of the retina are structurally like astrocytes?
Simply describe the fate of the long processes of ganglion cells of the retina
Bundle together and converge on the optic disc and then all fibres become optic nerve, move in optic tract to reach lateral geniculate body to release neurotransmitter (glutamate) onto the next order neuron
Which NT is released by horizontal cells and amacrine cells of the retina?
GABA (i.e., these cells are inhibitory)
In cases of retinal detachment, between which layers does separation most oftenly occur?
Layer 1 (pigment epithelial cells) from layer 2 (photoreceptor layer)
The inner 5 layers of the retina are supplied by?
Branches of central retinal artery
Name the two divisions of the retina separated vertically through the foeva centralis
Nasal hemi-retina and temporal hemi-retina
Name the 4 meridonial divisions of the retina
1. Upper nasal quadrant 2. Lower nasal quadrant 3. Upper temporal quadrant 4. Lower temporal quadrant
Name the 3 non-meridonial divisions of the retina
Macula, para-macula area, mono-occular area
Describe the relationships between the macula, para-macula area and mono-occular areas of the eye and the area of the occipital cortex mapped by each
Macula maps onto the most posterior part of occipital lobe, para-macula area maps just anteriorly to this, and mono-occular area maps most anteriorly in the occipital lobe
What vision will be lost if there is a lesion to the most posterior part of the occipital lobe?
What is the condition of unequal pupil size called?
Optic nerves emerge from what part of the eyeball?
Posterior nasal part
The optic nerve emerges from the orbit through what structure?
From the optic chiasm, optic tract fibres move in what direction?
Posteriorly and laterally
Which structures involved in the visual pathway are present on the lateral side of the thalami?
Lateral geniculate bodies
After passing though the optic chiasm, the optic nerve becomes the _____?
90% of the optic tracts terminate at which structures?
Lateral geniculate bodies of thalami
10% of the optic tracts divert into?
From the lateral geniculate bodies, fibres take visual information back to the?
Describe the 2 visual pathways originating from the lateral geniculate bodies
1. Upper pathway: most lateral part arcs upwards through parietal lobe and then back to the occipital lobe as the optic radiation (and terminates the the upper part of the calcarine fissure) 2. Lower pathway (loop of Meyer): more medial parts move forward and more laterally through the temporal lobe before arcing back to the occipital lobe (and terminating in the lower part of the calcarine fissure).
What is the loop of Meyer?
The second tract leaving the lateral geniculate body and arcing through the temporal lobe and back around to the lower part of the calcarine fissure in occipital lobe
What is the visual field?
An area of the external environemnt that can be seen by one eye (mono-ocular) or both eyes (binocular)
Information from the right side (assume nasal visual field) of the visual field is formed on which side of the retina?
Left hemi retina (temporal side)
Objects in the inferior visual field are projected onto the ____ part of the retina, whilst objects in the upper field are projected onto the ____ part of retina
Which fibres from the retina decussate at the optic chiasm? Correlate where information passing through these fibres is originating.
Nasal fibres cross in chiasm (i.e., information from an object that has been perceived from the temporal half of the visual field)
Anatomically explain why the right visual field from both eyes is able to project to the opposite left cortex
Right visual field from right eye (temporal) projects onto the nasal hemiretina and crosses to the left occipital lobe via the optic chiasm. The right visual field from the left eye (nasal) projects to the temporal side of the left eye, and these fibres do not cross at the chaism, thus ending up in the left occipital lobe
The cerebellum is embryonically derived from which structure?
Mesencephalon portion of rhomboncephalon (part of the hindbrain)
Which lobe of the cerebellum is most primitive? What is the functional significance of this?
Flocculonodular - most primitive functions - balance of head and eyes
What is the main function of the anterior lobe of the cerebellum?
What is the main function of the posterior lobe of the cerebellum?
Coordination of movement
What is the name given to the longitudinal depression on the posterior surface of the cerebellum?
Cerebellum controlls functions on the ______ side of the body
The area just lateral to the vermis of the cerebellum is given what name?
Intermediate zone or para-vermal area