Najeeb Neuro Flashcards Preview

Block 6: Neuro > Najeeb Neuro > Flashcards

Flashcards in Najeeb Neuro Deck (372):
1

What are tracts?

Bundles of axons of neurons in the CNS (white matter)

2

What name are given to bundles of axons that connect the anterior part with the posterior part of the brain?

Association fibres

3

What name are given to bundles of axons that connect right and left sides of the brain?

Commissures

4

Give an example of a white matter commissure in the brain

Corpus callosum

5

What are neurological receptors?

Biological transducers - convert one type of energy to another (i.e., mechanical stimulus to Aps)

6

Motor neurons exit the spinal cord _____, whilst sensory informatio is taken into the ___ horn

Ventrally, dorsal

7

The ventral and dorsal root of the spinal cord combine to form the spinal _____, which then divides into an anterior and posterior _____

Trunk; ramus

8

The anterior ramus of a spinal nerve innervates structures in which part of the body?

Anterolateral wall of the body

9

The dorsal ramus of a spinal nerve innervates structures in which part of the body?

Back of the body

10

Dorsal columns of the spinal column are also known what what other name?

Dorsal funiculus

11

Which is the only white matter column that sends ONLY ascending tracts?

Dorsal columns (funiliculi)

12

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)

13

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

14

The dorsal root ganglion contains which neural structure?

Cell body of first order neuron (first in chain of sensory system)

15

Within the dorsal column, sensations from the lower body are located ____, while caudal structures are added in ____

Medially, laterally

16

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.

17

All sensory fibres from the lower limb that enter the dorsal column (up to level of C6) make a special medial ascending bundle called ____?

Facisculus Gracillis

18

All sensory fibres from the upper limb, abdomen and thorax that enter the dorsal column make a special lateral ascending bundle called _____?

Fasisculus Cuneatous

19

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)

20

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)

21

Dorsal columns carry sensory information from which side of the body?

The same side as the column (i.e., information does not cross)

22

What is the name of the bundle of fibres connecting medulla with cerebellum?

Inferior cerebellar peduncle

23

The fibres from the dorsal columns terminate in which nuclei?

Nucleus gracillis and nucleus cuneatous/cuneate in lower medulla

24

The cell bodies present in the nucleus cuneatous and gracillis are what sort of neurons?

Second order (first order was in dorsal root ganglion)

25

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

26

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

27

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)

28

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

29

What is the name given to axons/fibres in the CNS that form a circular bundle? What if they form a flattened bundle?

Fasisculus; lemniscus

30

Where do the second order neurons of the medial lemniscus system (dorsal ascending system) terminate?

In the thalamus

31

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)

32

VPL nucleus receives what sort of information?

Most of the sensation from most of the body (touch, pain ,temperature, position)

33

VPM nucleus receives what sort of information?

Sensation from taste fibres and head/neck fibres

34

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

35

In which nucleus do the third order neurons of the dorsal ascending system originate?

VPL of the thalamus

36

Which nuclei are present on the lateral sides of the thalami?

Lentiform nuclei

37

Which arc-shaped nucleus stretches over the thalami and connects to the lentiform nucleus?

Caudate nucleus

38

Between the thalamus and lentiform nucleus is which white matter bundle?

Internal capsule

39

In between the right and left thalami is which fluid-filled cavity?

Third ventricle

40

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)

41

From which structure does the corona radiata originate?

Posterior limb of the internal capsule

42

What are the receptors in the skin for pain and temperature?

Free nerve endings for pain and thernal receptors for temperature sense

43

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

44

The thermal sensory pathway follows the same pattern as which other pathway?

Pain pathway

45

What is the stimulus for fast pain?

Mechanical or thermal pain (usually from the skin)

46

What is the stimulus for slow pain?

Mechanical or thermal pain, and chemical pain (can be from skin or deeper structures)

47

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)

48

Which 2 chemical substances cannot cause pain, but can reduce the threshold for pain if present in tissue?

Substance P and prostaglandins

49

The first order neurons for the pain (and temperature) pathway have their cell bodies in which location?

Dorsal root ganglion

50

First order neurons in the pain pathway terminate in which location?

In the substantia gelatinosa in the dorsal grey horn of the spinal cord

51

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.

52

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

53

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

54

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

55

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.

Lower; upper

56

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.

57

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

58

The tectum is part of which brain strcture?

posterior midbrain

59

What is the name of the swellings on the posterior midbrain?

Superior and inferior colliculus (= tectum)

60

The tectum of the midbrain is made up of which 2 strucutres?

Superior and inferior colliculus

61

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

62

What is the spinotectal pathway responsible for?

Spinovisual reflexes

63

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)

64

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)

65

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

66

Slow pain fibres intensely stimulate the _____ _____ before terminating the the VPL nucleus and internal lamina nucleus of the thalamus

Reticular formation

67

What is the reticular formation?

Mixture of grey and white matter entending throughout the brainstem

68

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

69

The reticular formation has heavy connections with which nuclei of the thalamus?

Internal lamina nucleus/intra lamina nucleus

70

All ascending sensory pathways give collaterals to which structure of the brainstem?

Reticular formation

71

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)

72

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

73

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)

74

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

75

Some pain fibres are connected with which nucleus, which is responsible for the emotional response to pain?

Cingulate gyrus

76

The cingulate gyrus is concerned with what information?

Emotion (and emotional response to pain)

77

Some slow pain fibres travel to which part fo the cortex, which is responsible for autonomic responses to pain?

Insula cortex

78

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.

79

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

80

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

81

What substances are released by the descending analgesia system in the spinal cord to reduce pain?

Enkephalins and endorphins (morphine-like)

82

Comment generally on areas where fibres from the descending analgesic fibres come from

Periventricular area, periaqueductal area and other midline nuclei in the brainstem

83

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

84

What are the 2 main spinocerebellar pathways?

1. Dorsal spinocerebellar pathway (cuneocerebellar pathway included) 2.

85

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

86

Information from which 3 receptor types contributes to the dorsal spinocerebellar pathway?

Goldi tendon organs, muscle spindles and pressure receptors

87

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)

88

The pons is connected to the cerebellum via what strcutures?

Middle cerebellar peduncles

89

The midbrain is connected to the cerebellum via what strcutures?

Superior cerebellar peduncles

90

What are peduncles?

Bundles of white matter which connect the brain stem with the cerebellum

91

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

92

Clark's nucleus receives information from which parts of the body? What about the accessory cuneate nucleus?

Trunk and lower limb; upper limb sensory

93

What is the cuneocerebellar pathway?

Counter-part of dorsal spinocerebellar pathway but providing informationf rom the upper limbs via the accessory cutaneous nucleus

94

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

95

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.

96

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)

97

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

98

What sort of information is carried by the spino-olivary pathway?

Prioprioception, touch, pressure and sense of position (movement and posture)

99

Briefly describe the spino-reticular pathway

Enters spinal cord and ascends directly upward to the reticular formation

100

What name is given to the cortex located in the precentral gyrus?

Primary motor cortex = M1

101

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

102

What is the supplementary motor area responsible for?

Bilateral primitive movement planning, such as primitive movement of hips and axial skeleton

103

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

104

Which area in the pre-motor cortex is responsible for programming patterns and neurons in the primary motor area for meaningful speech

Broca's area

105

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

106

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)

107

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

108

Above Broca's area is which part of the pre-motor area concerned with eye movement?

Frontal eye field

109

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)

110

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

111

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)

112

Describe the important areas in the pre-motor cortex, from most lateral

Brocas area, frontal eye fields, neck movement, hand movement

113

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)

114

The cerebral motor cortex contains how many layers of neurons?

6

115

In which layer of the cerebral cortex are the cell bodies of the neurons that contribute to the corticospinal tracts?

5th layer/lamina

116

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

117

Cells of Batz directly stimulate which motor neurons?

Alpha lower motor neurons

118

All decending fibres in the corticospinal region pass firstly through the _____ ____, and then converge in the ________

Corona radiata; posterior limb of internal capsule

119

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)

120

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

121

Which structures lie beneath the cerebral adqueduct and are known to be implicated in Parkinson's disease?

Substantia nigra

122

What is the name given to the area of the midbrain that lies between the substantia nigra and the tectum?

Tegmentum

123

What is the name given to the area of the midbrain between the substantia nigra and cerebral peduncles, where the corticospinal tracts pass thorugh?

Crus cerebri

124

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

125

What is the name given to the white matter fibres connecting the brainstem to the cerebrum?

Cerebral peduncles

126

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

127

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

128

The pyramids of the medulla are made from what stuctures?

Fibres from coricospinal motor tracts

129

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.

130

Describe the location of the pyramidal decussation of the corticospinal tract

Junction of medulla and spinal cord

131

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)

132

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

133

The fibres from the lateral corticospinal tract are concerned with what types of movements?

Skilled and voluntary movements (especially fine movements in the hands)

134

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

135

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

136

What is a lower motor neuron?

Neurons coming out of CNS (brainstem or spinal cord) and connecting to NMJs

137

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

138

List the types of neurons that leave the CNS

Preganglionic parasympathetic, preganglionic sympathetic and lower motor neurons (connecting to NMJs)

139

What is the name given to the tract that sends descending fibres to stimulate lower motor neurons of the brainstem?

Corticoneuclear fibres

140

Corticonuclear fibres are synonymous with which other tract?

Corticospinal tract

141

Those corticonuclear fibres that are specifically connected with lower motor neurons in medulla are called ____?

Corticobulbar fibres

142

The superior and inferior colliculi are specifically concerned with which reflexes?

Superficial = Visual reflexes; Inferior = Auditory reflexes

143

Lower motor neurons receive input from which descending tracts?

Corticospinal (or corticonuclear in the brainstem), tectospinalÉ

144

Fibres that decending from the red nucleus and cross before descending on the contralateral side are part of what tract?

Rubrospinal tract

145

List the 5 descending tracts that originate from subcortical areas

Tectospinal, reticulospinal, rubrospinal, vestibulospinal, olivospinal tracts

146

What is the name of the nuclei present at the junction between the medulla and the pons?

Vestibular nuclear complex

147

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

148

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)

149

Extensor musles are also known by what other name?

Anti-gravity muscles

150

Which pathway (and assistant pathway) is responsible for providing input to the extensor muscles?

Vestibulospinal (and assisted by pontine reticulospinal)

151

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)

152

Which pathway (and assistant pathway) is responsible for providing input to the flexor muscles?

Rubrospinal and assisted by medullary reticulospinal

153

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

154

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

155

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)

156

Which tract is assistant to the rubrospinal tract in controling flexor muscle tone?

Medullary-reticulospinal tract (from medullary reticular nuclei)

157

Sympathetic fibres originate in the ____ part of the hypothalamus, whilst parasympathetic fibres originate in the ____ part

Posterior; anterior

158

Sympathetic fibres from the posterior part of the hypothalamus descend down the spinal tract and stimulate pre-ganglionic sympathetic neurons in which spinal levels?

T1-L2

159

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

160

Parasympathetic outflow is from which cranial nerves?

3, 7, 9 and 10 (III, VII, IX and X)

161

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)

162

Which fibres of a muscle are connected to Golgi tendons?

Extrafusal

163

Alpha motor neurons connect the anterior horn of the spinal cord with which muscle fibres?

Extrafusal fibres

164

Alpha motor neurons release which neurotransmitter at the NMJ?

Cholinergic fibres (NT is ACh)

165

What sort of receptors are present at the NMJ and allow binding of the NT released by alpha motor neurons?

Nicotinic receptors (for ACh)

166

Nicotinic receptors at the NMJ are coupled with what sort of channels?

Cationic channels

167

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)

168

The sensitivity of muscle contraction is dependent on what?

Muscle spindles (degree of stretch sensed by afferent neurons and relayed to spinal cord)

169

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

170

Gamma motor neurons give motor supply to what part of the muscle?

Spindle

171

Alpha motor neurons supply ______ muscle fibres, whilst gamma motor neurons supply ______ muscle fibres

Extrafusal; intrafusal

172

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

173

What sort of fibres take stretch information from muscle spindles toward the spinal cord?

Ia

174

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

175

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

176

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)

177

When are golgi tendon organs stimulated?

When there is too much tension on the muscle and it threatens the integrity of the locomotor system

178

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

179

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)

180

Which spinal nerve supplies the biceps?

Musculoskeletal

181

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)

182

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)

183

Which 2 factors lead to atrophy of muscle?

1. Trophic action (denervation) 2. Disuse

184

Maintenance of tone of a muscle is primary dependent on acitivty of?

Gamma motor neuron

185

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)

186

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

187

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

188

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

189

Which is the only cranial nerve which exists from the back of the CNS?

CN IV (trochlear)

190

The pineal gland is located at the back of which ventricle?

3rd

191

CN V (trigeminal) exits the brainstem at what location?

Anterolateral side of the pons

192

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

193

Which cranial nerves exit the brainstem at the inferior cerebellar peduncle (from superior to inferior)

CN IX, X and XI (cranial part of XI)

194

Where does CN XII exit the brainstem?

In the medulla between the pyramid and olive

195

What sort of fibres are attached to the cell bodies of neurons in the anterior grey horn of the spinal cord?

General somatic efferents

196

What sort of fibres are attached to the cell bodies of neurons in the posterior grey horn of the spinal cord?

General somatic afferents

197

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)

198

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)

199

Describe the location of the trigeminal sensory ganglion

Posterior-most part of middle cranial fossa at the tip of the temporal bone

200

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

201

The motor root of the trigeminal nerve is responsible for which functions?

Muscles of mastication (NOT connected with ganglion)

202

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)

203

Which is the largest cranial nerve?

Trigeminal

204

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)

205

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

206

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)

207

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

208

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

209

General somatic afferents of the trigeminl system carry what sorts of information?

Fine touch (and 2 point discrimination), pain, temperature and proprioception

210

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

211

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.

212

The external ear is supplied by which 4 nerves?

V, VII, IX, X

213

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

214

What % of CO goes to CNS?

15%

215

Vertebral arteries take orogin from which major blood vessel?

Subclavian

216

Which 2 major systems are responsible for delivering blood to the brain?

Vertebral arteries (basillar/posterior system) and internal carotid arteries (anterior system)

217

Vertebral arteries travel through which foramina?

Foramina of transverse processes of cervical vertebrae

218

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)

219

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)

220

Where do the R and L vertebral arteries meet?

Ponto-medullary junction (i.e., after they have entered through foramen magnum)

221

Once the R and L vertebral arteries meet at the ponto-medullary junction, they move upwards as which large artery?

Basilar artery

222

The basilar artery divides into which terminal branches at the top of the brainstem?

R and L posterior cerebral arteries (PCAs)

223

The right and left posterior cerebral arteries supply which areas of the brain?

Midbrain, posterior part of cerebral hemispheres

224

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

225

What is the origin of the posterior inferior cerebellar artery?

Vertebral arteries

226

How much of the spinal cord is supplied by the anterior spinal artery?

Anterior 2/3 of the spinal cord

227

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

228

Which arteries carry blood toward the spinal cord to reinforce the anterior spinal artery?

Segmental arteries

229

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)

230

What is the origin of the posterior spinal arteries?

Vertebral artery (either directly or indirectly from posterior inferior cerebellar arteries)

231

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

232

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

233

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

234

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

235

What areas are supplied by the posterior inferior cerebellar artery?

Cerebellum and lateral part of medulla

236

Which artery may originate from beginning of basillar artery or from the vertebral artery in other people?

Anterior inferior cerebellar artery

237

What areas are supplied by the anterior inferior cerebellar artery?

Lateral part of pons as well as under side of cerebellum

238

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?

Labyrinthine arteries

239

Which 2 nerves accompany the labyrinthine artery?

Facial nerve and vestibulocochlear nerve (through internal acoustic meatus to supply inner ear)

240

Which arteries originate from the basilar artery just below the level of the occulomotor cranial nerve exit?

Superior cerebellar artery

241

What structures are supplied by the superior cerebellar artery?

Some midbrain and superior cerebellum

242

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

243

Which dural venous sinus is located in the middle cranial fossa? Which important structure runs through this sinus?

Cavernous sinus; internal carotid artery

244

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

245

Which branch of the internal carotid artery passes into the orbital cavity through the optic canal?

Ophthalmic artery

246

Which important branch of the ophthalmic artery supplies the retina?

Central retinal artery

247

What is the origin of the central retinal artery?

Internal carotid artery > ophthalmic artery > central retinal artery

248

Name one of the signs of anterior carotdi circulation failure

Blindness in one eye due to occlusion of central retinal artery

249

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

250

Which arterry forms a connection between the the carotid system and vertebral basillar systems?

Posterior communicating artery

251

What is supplied by the anterior choroidal artery?

Supply choroid plexus of lateral ventricle

252

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

253

The anterior communicating artery forms a connection between which vessels?

R and L anterior cerebral arteries

254

Which structures border the circle of willis?

R and L internal carotid arteries, anterior communicating artery, posterior communicating arteries, posterior cerebral arteries

255

Which structure of the arachnoid mater anchors it to the pia matter?

Connective tissue reticuli

256

Which cranial meningeal layer is highly vascular?

Pia mater

257

Name the 2 layers of the dura mater

Periosteal layer and meningeal layer

258

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.

259

The periosteal layer of the dura mater is tightly connected to the skull bone except for at which normal anatomical structures?

Venous dural sinuses

260

Within which 2 layers of the meninges do the meningeal arteries and veins run?

Between the meningeal and periosteal layers of the dura mater

261

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

262

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)

263

Rupture of bridging/cerebral veins as they approach the dural sinuses causes what sort of haemorrhage?

Subdural

264

Bleeding of meningeal arteries and veins causes what sort of haemorrhage?

Epidural

265

What is an aneurysm?

Abnormal, irreversible dilation of arterial wall

266

Why is subarachnoid haemorrhage so diffuse and widespread?

Because the space is full of CSF, so blood can move easily and throughout entire space

267

Which form of haemorrhage will result in apperance of RBCs in a LP sample?

Subarachoid

268

Which basal ganglia strucutres are considered to be in the clinical slassification?

Caudate nucleus, lentiform nucleus (putamen + globus pallidus), substantia nigra and subthalami

269

The globus pallidus is divided into which 2 parts?

1. Globus pallidus interna (medial) 2. Globus pallidus externa (lateral)

270

Which 3 structures make up the corpus striatum?

Caudate nucleus, putamen and globus pallidus (lentiform nucleus)

271

Which structures make up the striatum/neostriatum

Caudate nucleus plus only the putamen part of the lentiform nucleus

272

What are the corticonuclear fibres?

Fibres originating in the cortex that serve motor neurons which are present in the brain stem

273

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

274

Fibres from cortex stimulate neurons in which basal ganglia first? What are these fibres called?

Neostriatum (mostly putamen); corticostriatal fibres

275

From the putamen, fibres travel to which basal ganglia structure?

Globus pallidus interna

276

Fibres from the globus pallidus interna (as part of the direct pathway) travel to which structure to be relayed back to the cortex?

Thalamus

277

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)

278

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

279

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)

280

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

281

The globus pallidus releases the NT _____ onto which nuclei of the thalamus?

GABA; ventroanterior, ventrolateral and dorsomedial nuclei

282

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

283

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

284

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)

285

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)

286

Which pathway of the basal ganglia system is stimulatory only?

Direct pathway

287

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)

288

The caudate nucleus, putamen and globus pallidus are embryonic derivatives of the _____, whilst the substantia nigra and subthalami are derived from the ______

Diencephalon; Mesencephalon

289

Name the 2 parts of the substantia nigra

Pars compacta and pars reticularis

290

Dopamine is released from which part of the substantia nigra?

Pars compacta

291

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

292

What is the result of dopamine released onto D1 vs D2 receptors?

Neurons stimulated; neurons inhibited

293

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.

294

How does the substantia nigra know when to fire dopaminergic information toward the striatum?

Presence of cortico-nigral fibres communicating with cortex

295

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

296

The substantia nigra pars reticularis should be considered functionally similar to which other basal ganglia?

Globus internal pars interna

297

Which neurons in the putamen provide counter-regulation to dopamine in the basal ganglia pathways?

Cholinergic neurons

298

Which neurotransmitter has inhibitory action on the direct basal ganglia pathway? Which are stimulatory?

ACh; glutamate and dopamine

299

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)

300

List the 3 main clinical problems seen in Parkinson's Disease

Hypokinesia (less movements, difficulty initiating movement and less velocity); rigidity; tremor

301

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)

302

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

303

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

304

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

305

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

306

What sort of drugs can cause Parkinson's-like disease?

Dopamine receptor blockers (type of anti-psychotics)

307

The optic nerve is an out-pouching of which embryological structure?

Diencephalon

308

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

309

The optic disc is located on the _____ side of the eye, about 3.5mm from the centre of the ______

Medially; fundus

310

All neuronal fibres in the eye converge toward which structure?

Optic disc

311

The optic disc does not contain what structures?

Light receptors (rods or cones)

312

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.

313

Which yellow-coloured structure can be seen medially to the optic disc in fundoscopy?

Macula lutea

314

The macula lutea has a high concentration of ______ but small concentration of _______

Cones; rods

315

What is significant about the fovea centralis of the macula lutea?

The point of maximal visual accuity (maximum concentration of cones at this point)

316

What is the name given to the very centre of the macula lutea?

Foeva centralis

317

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)

318

What pigment is present in rods?

Rhodopsin

319

What is rhodopsin sensitive to?

Dim light (scotopic/night vision)

320

What pigment is present in cones?

Iodopsin

321

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.

322

What are cones most sensitive to?

Bright light (photopic/day vision)

323

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)

324

Which type of photoreceptor provides colour vision?

Cones

325

Which photoreceptors are more abundant in the human eye?

Rods

326

Which arteries supply the foeva centralis?

None! Simple diffusion is provided from capillaries - this area is avascular

327

The retina contains chains of which 3 types of cells?

Photoreceptors, ganglion cells and bipolar cells

328

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

329

The outer 5 layers of the retina are supplied by?

Simple diffusio of nutrients from choroidal capillaries

330

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

331

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.

332

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 >

333

What forms the optic nerve fibres?

Axons of ganglion cells bundled together

334

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

335

How many layers of the retina exist?

10 (5 inner and 5 outer)

336

Horizontal cells of the retina link which structures?

Connect terminal buttons of rods and cones together horizontally

337

Which cells of the retina connect the outer and inner limiting membrane layers?

Muller cells

338

What is the function of retinal Muller cells?

Modified neuroglial cells of retina connecting outer and inner limiting membranes. Structurally like astrocytes.

339

Which cells of the retina are structurally like astrocytes?

Muller cells

340

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

341

Which NT is released by horizontal cells and amacrine cells of the retina?

GABA (i.e., these cells are inhibitory)

342

In cases of retinal detachment, between which layers does separation most oftenly occur?

Layer 1 (pigment epithelial cells) from layer 2 (photoreceptor layer)

343

The inner 5 layers of the retina are supplied by?

Branches of central retinal artery

344

Name the two divisions of the retina separated vertically through the foeva centralis

Nasal hemi-retina and temporal hemi-retina

345

Name the 4 meridonial divisions of the retina

1. Upper nasal quadrant 2. Lower nasal quadrant 3. Upper temporal quadrant 4. Lower temporal quadrant

346

Name the 3 non-meridonial divisions of the retina

Macula, para-macula area, mono-occular area

347

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

348

What vision will be lost if there is a lesion to the most posterior part of the occipital lobe?

Macula vision

349

What is the condition of unequal pupil size called?

Anisocoria

350

Optic nerves emerge from what part of the eyeball?

Posterior nasal part

351

The optic nerve emerges from the orbit through what structure?

Optic canal

352

From the optic chiasm, optic tract fibres move in what direction?

Posteriorly and laterally

353

Which structures involved in the visual pathway are present on the lateral side of the thalami?

Lateral geniculate bodies

354

After passing though the optic chiasm, the optic nerve becomes the _____?

Optic tract

355

90% of the optic tracts terminate at which structures?

Lateral geniculate bodies of thalami

356

10% of the optic tracts divert into?

The midbrain

357

From the lateral geniculate bodies, fibres take visual information back to the?

Occipital lobes

358

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).

359

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

360

What is the visual field?

An area of the external environemnt that can be seen by one eye (mono-ocular) or both eyes (binocular)

361

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)

362

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

Superior; inferior

363

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)

364

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

365

The cerebellum is embryonically derived from which structure?

Mesencephalon portion of rhomboncephalon (part of the hindbrain)

366

Which lobe of the cerebellum is most primitive? What is the functional significance of this?

Flocculonodular - most primitive functions - balance of head and eyes

367

What is the main function of the anterior lobe of the cerebellum?

Tone

368

What is the main function of the posterior lobe of the cerebellum?

Coordination of movement

369

What is the name given to the longitudinal depression on the posterior surface of the cerebellum?

Vermis

370

Cerebellum controlls functions on the ______ side of the body

Ipsilateral

371

The area just lateral to the vermis of the cerebellum is given what name?

Intermediate zone or para-vermal area

372

What is significant about the vermis and paravermal area of the cerebellum?

They are topographically mapped with the head and neck in the centre and the trunk and limbs are represented more . The trunk and axial body is represented in the actual vermis, whilst the limbs extend into the paravermal area. This is significant because if there is a lesion in the centre of the vermis, the motor control in the trunk will be affected (ataxia od axial muscles) but limbs will be spared