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Sem 4 - Nervous System > Motor System > Flashcards

Motor System Flashcards

1
Q

What are the types of motor neurones?

A

Upper motor neurones

Lower motor neurones

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2
Q

Where is the cell body of upper motor neurones located?

A

Cell body and axon are found in the primary motor cortex in the pre-central gyrus of the frontal lobe

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3
Q

Where does the axon of all upper motor neurones travel?

A

Descends in the corona radiata and internal capsule

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4
Q

What is the corona radiata?

A

White matter structure formed by many upper motor neurone axons running together

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5
Q

What happens to the corona radiata?

A

Becomes condensed into the internal capsule

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6
Q

Where is the internal capsule located?

A

The thalamus is medial to it

The lentiform nucleus is lateral to it

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7
Q

Where does the axon of upper motor neurones supplying the trunk and limbs travel?

A

After the internal capsule, it descends down the medullary pyramids

At the end of the medullary pyramids, it decussates

Descends down the spinal cord in the lateral corticospinal tract

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8
Q

What forms the lateral corticospinal tract?

A

Upper motor neurone axons in the spinal cord

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9
Q

Where is the lateral corticospinal tract located?

A

Lateral funiculus of spinal cord

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10
Q

What does the upper motor neurone axon do in the lateral corticospinal tract?

A

Synapses onto lower motor neurone or inhibitory interneurone

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11
Q

Where does the upper motor neurone synapse onto the inhibitory neurone or the lower motor neurone in the corticospinal tract?

A

In the ventral horn of the grey matter of the spinal cord

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12
Q

What is the function of upper motor neurones in the corticospinal tract?

A

Stimulate lower motor neurones

Or stimulate inhibitory interneurones

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13
Q

What do inhibitory interneurones do?

A

Synapse onto lower motor neurones

Inhibit them

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14
Q

Are lower motor neurones excited more or inhibited more by upper motor neurones and inhibitory interneurones?

A

Inhibited more

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15
Q

Where does the axon of upper motor neurones supplying the head and neck travel?

A

After the internal capsule, it travels to motor nuclei in the brainstem

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16
Q

What are brainstem motor nuclei?

A

Continuation of ventral horn of grey matter of spinal cord

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17
Q

How is the facial nerve motor nucleus organised?

A

Split into two
One half corresponding to upper face
Other half corresponding to lower face

18
Q

How do upper motor neurones innervate the facial nerve motor nucleus?

A

Upper motor neurones supplying the upper half of the face innervate both facial nerve motor nuclei i.e. both right and left sides

Upper motor neurones supplying the lower half of the face innervate the contralateral facial nerve motor nucleus i.e. opposite side

19
Q

What are the motor abnormalities with damage to upper motor neurones from the right side of the brain supplying the face?

A

Upper half of face is normal due to innervation by upper motor neurones from left side of brain

Lower half of face on right side is normal due to innervation by upper motor neurones from left side of brain

Lower half of face on left side is weak or paralysed due to loss of innervation by upper motor neurones from right side of brain

20
Q

What causes upper motor neurone damage?

A

CNS lesions only

21
Q

What are the signs and symptoms of damage to upper motor neurones?

A

Weakness

Hypertonia, increased muscle tone

Hyper-reflexia, enhanced reflexes

Extensor plantar reflex called Babinski sign (note this is normal in babies)

22
Q

Why does damage to upper motor neurones cause hypertonia?

A

Loss of overall inhibitory effect on lower motor neurones

Increased activity of lower motor neurones

23
Q

Why does damage to upper motor neurones cause hyper-reflexia?

A

Loss of overall inhibitory effect on lower motor neurones

More excitable lower motor neurones

24
Q

How long do the signs and symptoms of damage to upper motor neurones take to develop? Why?

A

After a few days or a week

Due to spinal shock

25
Q

What is spinal shock?

A

Refers to how loss of innervation of lower motor neurones initially decreases their activity and excitability, this is spinal shock

But afterwards, their activity and excitability increases to above normal levels

26
Q

What does spinal shock give similar signs and symptoms to?

A

Lower motor neurone lesion

27
Q

Where is the cell body of lower motor neurones located?

A

For lower motor neurones supplying the trunk and limbs, ventral horn of grey matter of spinal cord

For lower motor neurones supplying the head and neck, brainstem motor nuclei

28
Q

Where does the axon of lower motor neurones travel?

A

For lower motor neurones supplying the trunk and limbs, in peripheral nerves

For lower motor neurones supplying the head and neck, in cranial nerves

29
Q

What is the function of lower motor neurones?

A

Stimulate muscles to contract

30
Q

What types of neurones are involved in a spinal reflex?

A

Primary sensory neurone

Lower motor neurone

Inhibitory interneurone

31
Q

What stimulates the patellar reflex arc?

A

Stretch of the quadriceps muscle stimulates muscle spindles in it

32
Q

What carries sensory information from muscle spindles to the spinal cord in the patellar reflex arc?

A

Primary sensory neurones

33
Q

What do primary sensory neurones involved in the patellar reflex arc do in the spinal cord?

A

Synapse onto lower motor neurones supplying the quadriceps muscle and stimulate them

Synapse onto inhibitory interneurones supplying the hamstring muscle and stimulate them

34
Q

What does stimulating the lower motor neurones in the patellar reflex arc do?

A

Stimulates the quadriceps muscle to contract

35
Q

What does stimulating the inhibitory interneurone in the patellar reflex arc do?

A

Inhibits lower motor neurone supplying hamstring muscle

Prevents hamstring muscle contracting and opposing the quadriceps muscle

36
Q

What is the purpose of deep tendon reflexes?

A

Maintain posture

37
Q

What causes damage to lower motor neurones?

A

CNS lesions damage the cell body and proximal axon

PNS lesions damage the axon

38
Q

What are the signs and symptoms of lower motor neurone damage?

A

Weakness

Hypotonia, decreased muscle tone

Areflexia, absence of deep tendon reflexes

Fasciculation, uncoordinated muscle contraction

Wasting

39
Q

Why does damage to lower motor neurones cause wasting?

A

Loss of trophic factors secreted from from the lower motor neurone onto the muscle membrane

40
Q

How long does wasting take to occur with lower motor neurone damage?

A

Weeks to months

Sem 4 - Nervous System (25 decks)

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