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ANATOMY SEM 3 > B3 - ascending and descending pathways of spinal and cranial nerves > Flashcards

B3 - ascending and descending pathways of spinal and cranial nerves Flashcards

1
Q

how is grey matter arranged in the spinal cord?

A

ventral, dorsal and lateral horns

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2
Q

what do the ventral horns contain?

A

nerve cell bodies of motor neurones

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3
Q

what do the dorsal horns contain?

A

nerve cell bodies of sensory neurones

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4
Q

what do the lateral horns contain?

A

the cell bodies of preganglionic sympathetic neurones

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5
Q

where are lateral horns present?

A

in thoracic and upper lumbar segments

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6
Q

what is the name given to the organisation of grey matter?

A

rex laminae

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7
Q

what does white matter consist of?

A

ascending and descending nerve fibres — contains the myelinated axons of nerve fibres that are passing to and from the brain

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8
Q

ascending vs descending tract function

A

ascending = sensory
descending = motor

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9
Q

ascending spinal tracts carry impulses from what types of receptors to the brain? where does this information go?

A

pain, thermal, tactile, muscle and joint receptors — some info reaches a conscious level (cerebral cortex) whereas some only reaches subconscious centres (eg. the cerebellum)

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10
Q

describe the sequence of 3 neurones between the peripheral receptor and the cerebral cortex

A
  1. the 1st ORDER NEURONE/primary afferent neurone enters the spinal cord through the DORSAL root of a spinal nerve and its cell body lies in a dorsal root ganglion. main fibre remains IPSILATERAL and it SYNAPSES on 2nd order neurone
  2. the 2nd ORDER NEURONE has its cell body in the cord or medulla oblongata. its axon DECUSSATES to the opposite side of the CNS and ASCENDS to the THALAMUS, where it terminates upon the 3rd neurone
  3. the 3rd ORDER NEURONE has its cell body in the thalamus. its axon passes to the SOMATOSENSORY CORTEX in the parietal lobe of the ipsilateral cerebral hemisphere
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11
Q

what are the 2 main ascending tracts?

A

the dorsal columns and spinothalamic tracts

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12
Q

what sort of information does the lateral spinothalamic tract carry?

A

pain and temperature

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13
Q

what sort of information does the ventral spinothalamic tract carry?

A

non-discriminative touch and pressure

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14
Q

what sort of information do the dorsal columns carry?

A

discriminative touch, vibration, proprioception

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15
Q

what 2 dorsal columns are there? what is the difference between them?

A
  • fasciculus gracilis (info from LOWER limbs)
  • fasciculus cuneatus (info from UPPER limbs)
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16
Q

what is a fasiculus?

A

bundle of fibres

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17
Q

what does the spinothalamic tract contain?

A

2nd order neurones

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18
Q

the 2nd order neurones in the spinothalamic tract decussate to the opposite side of the spinal cord by passing through what?

A

ventral white commissure

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19
Q

axons ascend in the ________ spinothalamic tract?

A

contralateral

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20
Q

what do axons pass in in the spinothalamic tract?

A

spinal lemniscus

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21
Q

where do most fibres of the spinothalamic tract terminate? what happens here?

A

in the ventral posterior nucleus of the thalamus — contact 3rd order thalamocortical neurones that project to the somatosensory cortex

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22
Q

what do lesions of the spinothalamic tract lead to?

A

impairment of pain, temperature, touch and pressure sensitivity on the contralateral side

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23
Q

what are located in the dorsal root ganglia?

A

nerve cell bodies of 1st order neurones

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24
Q

axons of the dorsal columns ascend in the ______ dorsal column to the medulla?

A

ipsilateral

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25
Q

where do the axons of the fasciculus gracilis and cuneatus terminate?

A

nucleus gracilis and cuneatus

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26
Q

where do axons of 2nd order neurones in the dorsal columns decussate?

A

medulla

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27
Q

what do the axons of the dorsal columns ascend in and where do they terminate?

A
  • medial lemniscus
  • terminate in the ventral posterior nucleus of the thalamus
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28
Q

only what fibres exist in the lumbar spine (dorsal columns)?

A

gracilis

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29
Q

what do lesions in the dorsal columns lead to?

A

ataxia and loss of discriminative touch ipsilaterally

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30
Q

what are some causes of dorsal column lesions?

A

tabes dorsalis, vitamin B12 deficiency, multiple sclerosis

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31
Q

name a syndrome that can be caused by a dorsal column lesion?

A

posterior cord syndrome

32
Q

signs and symptoms of posterior cord syndrome? list the causes

A
  • typically present with sensory ataxia, or impaired voluntary movement coordination caused by a lack of proprioception. Sensory ataxia can result in decreased balance, poor coordination, unsteady walking, and frequent falls
  • DAMAGE TO DORSAL COLUMNS — demyelinating disorders (vit B12 def, MS, late syphilis (tabes dorsalis) ), external compression (tumours etc), blockage in posterior spinal artery
33
Q

what do descending pathways contain?

A

motor neurones which bring about muscle contraction

34
Q

what 2 neurones does the basic somatic motor pathway involve?

A

upper and lower motor neurones

35
Q

describe UMNs

A

arise in the primary motor cortex and terminate in the spinal cord or brain stem by synapsing on the LMN

36
Q

describe LMNs

A

nerve cell body located in the ventral horn grey matter in the spinal cord or in specific motor nuclei in the brainstem. terminates on skeletal muscle

37
Q

where is the primary motor cortex?

A

precentral gyrus

38
Q

what is the main descending pathway?

A

corticospinal tract

39
Q

what is another name for the corticospinal tract and why?

A

pyramidal tract because the UMNs decussate on the ventral aspect of the medulla — decussation of the pyramids

40
Q

what are the corticospinal tracts particularly involved in?

A

control of voluntary, discrete, skilled movements, especially those of the distal parts of limbs

41
Q

where are the nerve cell bodies of UMNs located?

A

pyramidal cells of the cerebral cortex

42
Q

what cells gibe rise to the largest diameter corticospinal axons?

A

large Betz cells

43
Q

how do corticospinal axons leave the cerebral hemisphere?

A

by passing through the corona radiata and internal capsule to enter the crus cerebri of the midbrain

44
Q

when do fibres decussate in the corticospinal tracts? what do they enter?

A
  • about 75-90% of fibres decusstae and enter the contralateral lateral corticospinal tract
  • the other 10-25% of pyramidal fibres remain ipsilateral and enter the ventral corticospinal tract - they also decussate near to their termination

ALL DECUSSATE BEFORE THEY SYNAPSE ON LMN

45
Q

what do fibres of the pyramidal tract innervate and control?

A

the contralateral side of the spinal cord and control movement of the contralateral side of the body?

47
Q

what would happen due to a lesion in the primary motor cortex?

A

loss of motor function on opposite side of body

48
Q

what would happen due to a lesion in the lateral spinal cord?

A

motor deficit on ipsilateral side

49
Q

what is hypertonia?

A

increased muscle tone

50
Q

what is hyperreflexia?

A

exaggerated reflexes

51
Q

what is clonus?

A

oscillatory movement — alternating contractions of agonist and antagonist groups

52
Q

where is the trigeminal ganglion?

A

either side of body of sphenoid

53
Q

what carries most sensation from the head and neck?

A

trigeminal nerve = CN V

54
Q

where is the geniculate ganglion?

A

in petrous temporal bone (facial canal)

55
Q

what is the geniculate ganglion?

A

a sensory ganglion of the facial nerve (CN VII) — contains nerve cell bodies of 1st order sensory neurones — taste from anterior 2/3 of tongue

56
Q

1st order neurones of what nerves terminate in the trigeminal nucleus?

A

facial, glossopharyngeal and vagus = CN VII, IX and X

57
Q

what are the 3 sub nuclei of the trigeminal sensory nucleus? what info do they receive?

A
  • mesencephalic — proprioception
  • chief — touch and pressure
  • spinal — pain and temperature
58
Q

where are the 3 sub nuclei of the trigeminal sensory nucleus?

A
  • mesencephalic = in midbrain
  • chief = pons
  • spinal = extends through medulla into spinal cord
59
Q

what do axons of 2nd order neurones from the trigeminal sensory nucleus do?

A
  • decussate and ascend in the contralateral trigeminal thalamic tract
  • terminate in the VP nucleus of the thalamus
60
Q

what is the name of the motor pathway from motor cortex to motor nuclei of cranial nerves in the brainstem?

A

corticobulbar tract

61
Q

what is a symptom of a hypoglossal nerve lesion?

A

tongue deviation towards the side of weakness

62
Q

how are most cranial nerves innervated? exception?

A

bilaterally — not hypoglossal

63
Q

lesion in CNXII vs other motor CNs?

A
  • lesion in CNXII — one side wouldn’t work as it is contralaterally innervated
  • lesion in bilaterally innervated — no defecit
64
Q

how is the facial nerve different?

A
  • the facial motor nucleus is made up of 2 parts
  • superior part supplies muscles of upper part of face (above eye)
  • inferior part supplies the muscles on the lower half of the face

> upper part of nucleus = bilaterally innervated
lower part of nucleus = contralaterally innervated

65
Q

what is the difference between an UMN lesion and a LMN lesion of the facial nerve?

A

UMN lesion — deficit in lower contralateral half of face (forehead sparing, eg in stroke)

LMN lesion — ipsilateral drooping of face (can’t raise eyebrows)

66
Q

most cranial nerve motor nuclei are bilaterally innervated - what does this mean?

A

they receive innervation from both the contralateral and ipsilateral corticobulbar tracts

67
Q

describe the spinocerebellar tract

A
  • ascending tract
  • carries info from muscle spindles, golgi tendon organs and raw tile receptors to the cerebellum
  • involved in the control of posture and coordination of movement
68
Q

describe the spinoreticulothalamic tract

A
  • ascending tract
  • arises in the spinal cord and ascends to the reticular formation
  • reticulothalamic fibres ascend to the thalamus and synapse with thalamocortical fibres
  • thought to provide a route by which dull aching pain is consciously recognised
69
Q

describe the rubrospinal tract

A
  • descending tract
  • originates from the red nucleus of the midbrain, where fibres then decussate and descend into spinal cord — therefore have a contralateral innervation
  • controls the tone of limb flexor muscles
  • receives afferents from the motor cortex and the cerebellum
  • possibly involved in fine control of hand movements
70
Q

describe the tectospinal tract

A
  • descending tract
  • originates in superior colliculus (receives input from optic nerves)
  • most fibres terminate in the cervical region of the spinal cord
  • it is thought to mediate reflex movements in response to visual stimuli
71
Q

describe the vestibulospinal tract

A
  • descending tract
  • originates in the vestibular nucleus
  • controls extensor muscle tone and is involved in the maintenance of posture
72
Q

describe the reticulospinal tract

A
  • descending tract
  • medial reticulospinal tract — arises from pons, facilitates voluntary movements and increases muscle tone
  • lateral reticulospinal tract — arises from medulla, inhibits voluntary movements and reduces muscle tone
73
Q

what are the cardinal signs of an UMN lesion?

A
  • hypertonia
  • hyperreflexia
  • clonus (involuntary, rhythmic muscle contractions)
  • babinski sign
  • muscle weakness
74
Q

why does tongue deviate to damaged side?

A

overreaction of strong genioglossus muscles

75
Q

upper vs lower lesion tongue protrusion

A

upper = away from lesion
lower = towards lesion

76
Q

what would an UMN lesion in CN VII cause?

A

spastic paralysis in the contralateral lower quadrant of the face

77
Q

what do motor and sensory nuclei in the brainstem contain?

A
  • motor = cell bodies of LMN
  • sensory = 2nd order neurones

ANATOMY SEM 3 (22 decks)

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