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The Nervous System: Physiology > Functional Hierarchy of the Motor System > Flashcards

Functional Hierarchy of the Motor System Flashcards

1
Q

What allows direct control of muscle

A

Motor neurones in the spinal cord

in the final common path

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2
Q

Where doe reflex occur

A

Autonomously at each segmental spinal levels

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3
Q

Where does input to trunk and limbs arise from

A

Vestibulospinal and reticulospinal tracts

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4
Q

What is the function of the basal ganglia in the motor system

A

Gating proper initiation of movement

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5
Q

What is the function of the cerebellum in motor system

A

Sensory motor coordination of ongoing movement

-refinement

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6
Q

What is the function of the cerebral cortex in the motor system

A

Planning, initiating and directing voluntary movements

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7
Q

What is the function of brainstem in the motor system

A

Controls spinal reflexes and integrates them into higher order reflexes controlling posture and balance

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8
Q

What controls the brainstem nuclei and stimulates voluntary movement

A

Cerebral cortex
(motor cortex, premotor and supplementary motor areas)

Basal ganglia

Cerebellum

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9
Q

What four system control movement

A

Descending control pathway (motor cortex and brainstem)

Basal ganglia

Cerebellum

Local spinal cord and brainstem circuits

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10
Q

Where are the Lower motor neurones found and what is their function

A

at spinal levels directly innervate muscles to initiate reflex and voluntary movements

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11
Q

What is the result of lower motor neurones lesions

A

Flaccid paralysis

muscle atrophy - as no longer metabolically active

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12
Q

What is the function of the upper motor neurones

A

synapse with multiple lower circuit neurones to regulate  motoneurone activity

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13
Q

Where are upper motor neurones located

A

Brainstem or cortex

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14
Q

What do the upper motor neurones from the cortex control

A

Spatiotemporal skilled movement

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15
Q

Lesion is upper motor neurones in the cortex causes

A

Spasticity, some paralysis, may be transient

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16
Q

Lesion specifically in the brainstems posture -regulating pathway causes

A

Spastic paralysis

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17
Q

Lesion in the Corticospinal tract (cortex) result in

A

weakness (paresis), rather than paralysis

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18
Q

What does it mean that there is a spatial map of the body musculature in the spinal cord

A

Muscles closer to the trunk (shoulders) are more medial motor neurones and muscle located further away from the trunk (fingers) are lateral motor neurones

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19
Q

How does body musculature in the spinal cord refer to arms and legs

A

Medio-laterally

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20
Q

How does the spinal cord receive descending input

A

via neurons in the brainstem AND direct cortical input via Corticospinal / Pyramidal tract.

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21
Q

How does ascending sensory input enter the spinal cord

A

at any level and in the from of proprioceptors, touch, pain etc

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22
Q

Why and How does the sensory input reach brainstem

A

via the vestibular system to inform about balance

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23
Q

What occurs when sensory input is at the level of the cortex

A

We make movements in response to visual, olfactory, auditory, emotional, intellectual cues

24
Q

If their is damage to sensory input at spinal level what can occur

A

paralysis as if the motoneurones themselves had been damaged

25
Q

What is the affect of sensory neuropathy

A

Loose all proprioception (lost sense of body in time and space and motor control so effectively paralysed)

26
Q

How does sensory neuropathy occur

A

autoimmune attack on sensory neurones in the dorsal root ganglia cause loss of large myelinated fibres

27
Q

What occurs in the stretch reflex

A

Initial stimulus causes the muscle to stretch and stimulates muscle spindles

afferent Impulses from muscle spindle acting as stretch receptor travel to spinal cord via dorsal route

efferent/motor impulses leave via ventral route and travel to to alpha motor neuones leading to contraction of the stretched muscle resulting in extension

whilst efferent impulses travel to antagonist muscle and cause relation
(= reciprocal inhibition)

28
Q 
What is the crucial cord segment in the 
biceps jerk 
tricep jerk 
patellar tendon 
Achilles tendon reflex
A

C6
C7
L4
S1

29
Q

What is the significance of testing reflexes

A

Helps to detect level of spinal cord damage

Impaired reflexes indicate areas of nerve damage

30
Q

In spinal cord damages where can reflects be evoked

A

Above spinal cord damage

31
Q

How do you avoid voluntary influencing of reflex response

A

Distract patient

32
Q

What occurs in the process of the flexor (withdrawal) reflex

A

Uses information from pain receptors (nociceptors) in skin, muscle and joint and through a polysynaptic and protective process to withdraw body away from painful stimulus and toward the body

=ipsilateral flexion in response to pain

33
Q

What is activated by the nociceptive fibres that controls all the flexor muscle of the affected limb

A

activate interneurones in spinal cord segment which in turn activates α motoneurones

34
Q

In the flexor withdrawal reflex if you withdraw the limb and do nothing else, you would fall over, so what additional process occurs to prevent this

A

The Contralateral limb extends - maintain an upright postures by extending the limb to bear body weight

35
Q

How does the contralateral limb extend

A

By excitatory interneurones crossing the spinal cord

36
Q

What is the affects of increase sensory AP from nociceptors

A

Increases activity of the flexor muscle of the affected part

Inhibits the antagonist extensors

Excite contralateral extensors

Inhibit contralateral flexors

37
Q

How does sensory information ascend to the brain

A

Via the contralateral spinothalamic tract

38
Q

What is the two reasons the flexor crossed extensor reflex far slower than the stretch reflex

A

The process has several interneurones in the pathways each with a small synaptic delay (slow down process)

Nociceptive fibres have smaller smaller than muscle spindle afferents (conduct more slowly)

39
Q

What occurs in the golgi tendon reflex

A

There is an excessive load on muscle, activates GTO reflex
Neurones from golgi tendon organ flies, motor neurone is inhibited causing the muscle to relax and release the load in an aim to protect the arm

40
Q

How do you maintain contraction of the GOT reflex if you are holding something important and heavy

A

Reflexes are over-ridden consciously

by Descending voluntary excitation of motoneurones overriding the inhibition from the GTOs

41
Q

Where does a motor neurones receive its synpases

A

Many are from descending cortical excitatory and inhibitory inputs, with continual integration of EPSPs and IPSPs

42
Q

How is the stretch reflex over-ridden

A

strong descending inhibition hyperpolarizes α-motoneurones and the stretch reflex can not be evoked.

43
Q

Where do the muscle spindles get their motor innervation

A

Gamma motor neurones innervating both poles of the intrafusal pathway and maintain spindles sensitivity t stretch

44
Q

What occurs with high gamma motoprneruone activation of spindle fibres

A

Muscles become extremely resistant to stretch and become spastic

45
Q

What is the clinical relevance of the stretch reflex

A

reflexes can be evoked above, but not below given level may localise a problem eg. segmental trauma to the spine.

46
Q

Why does a more painful stimulus give a larger response

A

Due to facilitation which increases the effects of sensory inputs

47
Q

How do pain fibres input facilitate the action of muscle spindles

A

By maintaining the alpha motor neurones in a more depolarised state

48
Q

What can mild cutaneous stimulation provoke (give an example)

A

Flexor reflex

eg mild stoking of the sole of your foot causes plantar flexion - downward curling of big toe)

49
Q

What is it called when the toe extends and doesn’t flex (fans up and out)

A

Babinskis sign

50
Q

What is the cause of Babinskis sign

A

Damage or disruption to the Corticospinal tract (upper motor leison) meaning their is an imbalance between extensor and flexor reflexes

51
Q

Where else is babinskis sign seen in

A

Seen in children < 1 year old motor system not fully developed

After epileptic seizures - transient cortical function disruption

52
Q

What is the affect does spinal transection (complete tear of spinal cord) have on the function of higher centres in maintaining normal reflexes

A

immediate sensory and autonomic effects - loss of sensation;
loss of bowel, bladder and sexual regulation

53
Q

What Occurs in spinal shock

A

Loss of supraspinal excitation (no control from higher centres)

hyporeflexia, as all reflexes below the point of injury
are not evoked

This lasts 2-6 weeks - then gradual return of reflexes

54
Q

What is the second stage of symptoms seen after spinal shock

A

Reflexes return

Reflexes are exaggerated = hyperflexia

  • Light touch provokes powerful withdrawl
  • extensor reflex support body weight briefly

Clonus

55
Q

Define clonus

A

stretch causes oscillatory muscle contraction/relaxation

The Nervous System: Physiology (15 decks)

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