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L14 - descending pathways Flashcards

1
Q

which tracts are descending

A

lateral corticospinal
ventral corticospinal
extrapyramidal tracts

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2
Q

types of neurones involved in descending pathways

A

upper
lower
interneuron

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3
Q

origin of UMN

A

cerebral and subcortical structures (basal ganglia and other centres in the brainstem)

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4
Q

origin of LMN

A

brainstem and spinal cord (ventral grey horn)

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5
Q

role of interneuron

A
  • Provides opportunities for motor neurones to be modified

- important in reflex arcs

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6
Q

what type of neurones are LMN

A

peripheral nerves

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7
Q

where do LMN terminate

A

motor end plates / neuromuscular junctions

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8
Q

how to LMN exit the spinal cord

A
  • cell bodies take origin in the ventral grey horn
  • exit via the ventral route
  • efferent
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9
Q

pyramidal tracts

A

descending pathways pass through pyramids in the medulla

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10
Q

corticobulbar/corticonuclear

A

descending pathways which originate in the cortex and stop at the cranial nerve nuclei

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11
Q

corticonuclear pathway - facial nerve

A
  • cerebral cortex
  • precentral gyrus
  • internal capsule
  • brainstem / spinal cord at a specific nucleus associated with a cranial nerve
  • UMN innervates muscles of face and makes contact with cell body of LMN
  • LMB leaves brainstem via facial nerve
  • innervate muscles of facial expression
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12
Q

where to UMN and LMN synapse (lateral corticospinal tract)

A

contralateral ventral grey horn

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13
Q

corticospinal pathway

A
  • UMN travels down spinal cord
  • via pyramids in medulla
  • enter corticospinal tracts
  • descend in the lateral white column of the spinal cord
  • at level of muscle, they jump into the ventral grey horn to synapse with LMN
  • LMN uses peripheral spinal nerve to send axons and innervate the specific skeletal muscle
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14
Q

location of anterior limb of IC

A

between head of caudate and lentiform nucleus

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15
Q

location of posterior limb of iC

A

between thalamus and lentiform nucleus

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16
Q

location of fibres of corticospinal tract in IC

A

Face = GENU

Arms, trunk, legs = POSTERIOR LIMB

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17
Q

innervation of IC

A

deep perforating arteries

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18
Q

brainstem path of descending fibres

A
  • start in cortex
  • funnel down via post. limb of IC
  • continuous with cerebral peduncles in midbrain
  • travel through ventral pons
  • regroup in the medulla and majority of them cross at the decussation of pyramids to travel contralaterally
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19
Q

what % of fibres cross at decussation of pyramids

A

85%

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20
Q

what type of innervation does the anterior corticospinal tract provide

A

bilateral

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21
Q

what type of innervation does the posterior corticospinal tract provide

A

contralateral

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22
Q

what happens to the 15% of fibres which do not cross at the level of the pyramids

A
  • descend ipsilaterally down the spinal cord
  • some join the anterior corticospinal tract and supply muscles
  • some cross and contact the LMN at the level of the muscle
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23
Q

function of anterior corticospinal tract

A

axial musculature

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24
Q

function of lateral corticospinal tract

A

limb musculature

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25
Q

where do UMN and LMN synapse in anterior corticospinal tract pathway

A

inspilateral ventral grey horn

26
Q

mechanisms of LMN lesions

A

peripheral nerve injury

infection

27
Q

consequences of LMN lesions

A
  • flaccid paralysis of muscles involved
  • diminished or absent tendon reflexes at level of lesion
  • muscle wasting
  • muscle weakness
  • hypotonia
  • fasciculation/fibrillation
28
Q

hyporeflexia

A

diminished tendon reflexes

29
Q

areflexia

A

absent tendon reflexes

30
Q

hypotonia

A

decreased muscle tone

31
Q

fasciculation

A

spontaneous muscle twitches

32
Q

fibrillaiton

A

rapid spontaneous muscle contractions

33
Q

UMN injury

A

due to lesion to cerebral hemisphere or as they descend to lateral white column of the spinal cord or corticospinal tract

34
Q

initial affects of UMN injury

A
  • Flaccid paralysis of opposite limbs

- Loss of tendon reflexes

35
Q

long term affects of UMN

A
  • increased spinal reflex below lesion
  • loss of fine motor control
  • hypotonia
36
Q

why would axial muscle groups be spared is there was an UMN injury

A
  • Axial muscles are supplied bilaterlal
  • If you have an UPM lesion on one side, it does not matter so much as the other side takes over and innervates the muscles
37
Q

how to test presence of pathological reflexes

A

Babinski sign

38
Q

Babinski sign

A
  • stroke sole of foot with sharp object from front to back
  • normal plantar response = toes curl down
  • extensor plantar response = toes fan
39
Q

innervation of LMN in corticonuclear pathway

A

largely bilateral

- fibres from RHS of precentral gyrus innervate muscles in both RHS and LHS of face

40
Q

why are UMN or corticouclear pathways not as severe as corticospinal pathways (on the whole)

A

innervation if bilateral

injury to one will be okay as other side can still innervate it

41
Q

which cranial nerves do not receive bilateral innervation

A

7

12

42
Q

CN7 - facial nerve innervation

A
  • only upper facial nucleus receives bilateral innervation

- lower facial nucleus is supplies contralaterally

43
Q

CN12 - hypoglossal innervation

A

only innervated contralaterally

44
Q

facial colliculus

A

Due to the abducens nucleus, behind which we find the arching fibres / internal genu of the facial nerve

45
Q

corticonuclear input to facial motor nuclei - UPPER FACIAL NUCLEUS

A
  • UMN sends axon via the genu of IC
  • UMN sends bilateral projections to both sides of upper facial nucleus
  • synapses with LMN in upper facial nucleus and innervates both sides of upper face
46
Q

corticonuclear input to facial motor nuclei - LOWER FACIAL NUCLEUS

A
  • lower face region of pre-central gyrus sends UPM to the contralateral lower facial nucleus
  • LMN supplies lower quadrant of contralateral side of face
47
Q

injury to RHS IC genu presentation

A
  • upper face okay due to bilateral innervation

- lower left side of face is weak

48
Q

what has happened if there is a weak lower and a weak upper face

A

Bell’s Palsy

indicates damage to facial nerve itself or lower LM lesion

49
Q

lesion to left hypoglossal nerve, which way does the tongue deviate

A

to the left

50
Q

lesion to RHS CN12 fibres in cortex / IC

A

tongue deviates to left

as left hypoglossal nerve not receiving innervation

51
Q

UMN lesion fo CN12

A

deviation to contralateral side of lesion

52
Q

LMN lesion for CN12

A

peripheral hypoglossal nerve itself is paralysed

53
Q

pathway for CN12

A
  • UMN from pre-central gyrus supplies contralateral hypoglossal nuclei
  • LMN travel via hypoglossal nerve to intrinsic muscles of tongur
54
Q

examples of subcortical structures which play a role in fine tuning information

A
  • basal ganglia
  • tectum, red nucleus
  • reticular formation
  • vestibular system
55
Q

extrapyramidal pathways

A

subcortical structures which play a role in fine tuning information which do not originate in the cortex

56
Q

reticulospinal pathway

A
  • reticular formation to spinal cord

- voluntary movement. breathing/ consciousness

57
Q

reticular formation

A

pons and medulla

58
Q

vestibulospinal pathway

A
  • vestibular nuclei to spinal cord

- controls posture

59
Q

rubrospinal pathway

A
  • red nucleus to spinal cord

- controls muscle tone

60
Q

location of red nucleus

A

midbrain (tectum)

61
Q

location of vestibular nucleis

A

pons and rostral medulla

62
Q

location of anterior corticospinal tract

A

ventral white column (compared to other tracts which are beside the white column)

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