Motor System

Question 1

What are the types of motor neurones?

Answer 1

Upper motor neurones

Lower motor neurones

Question 2

Where is the cell body of upper motor neurones located?

Answer 2

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

Question 3

Where does the axon of all upper motor neurones travel?

Answer 3

Descends in the corona radiata and internal capsule

Question 4

What is the corona radiata?

Answer 4

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

Question 5

What happens to the corona radiata?

Answer 5

Becomes condensed into the internal capsule

Question 6

Where is the internal capsule located?

Answer 6

The thalamus is medial to it

The lentiform nucleus is lateral to it

Question 7

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

Answer 7

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

Question 8

What forms the lateral corticospinal tract?

Answer 8

Upper motor neurone axons in the spinal cord

Question 9

Where is the lateral corticospinal tract located?

Answer 9

Lateral funiculus of spinal cord

Question 10

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

Answer 10

Synapses onto lower motor neurone or inhibitory interneurone

Question 11

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

Answer 11

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

Question 12

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

Answer 12

Stimulate lower motor neurones

Or stimulate inhibitory interneurones

Question 13

What do inhibitory interneurones do?

Answer 13

Synapse onto lower motor neurones

Inhibit them

Question 14

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

Answer 14

Inhibited more

Question 15

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

Answer 15

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

Question 16

What are brainstem motor nuclei?

Answer 16

Continuation of ventral horn of grey matter of spinal cord

Question 17

How is the facial nerve motor nucleus organised?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

What causes upper motor neurone damage?

Answer 20

CNS lesions only

Question 21

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

Answer 21

Weakness

Hypertonia, increased muscle tone

Hyper-reflexia, enhanced reflexes

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

Question 22

Why does damage to upper motor neurones cause hypertonia?

Answer 22

Loss of overall inhibitory effect on lower motor neurones

Increased activity of lower motor neurones

Question 23

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

Answer 23

Loss of overall inhibitory effect on lower motor neurones

More excitable lower motor neurones

Question 24

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

Answer 24

After a few days or a week

Due to spinal shock

Question 25

What is spinal shock?

Answer 25

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

Question 26

What does spinal shock give similar signs and symptoms to?

Answer 26

Lower motor neurone lesion

Question 27

Where is the cell body of lower motor neurones located?

Answer 27

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

Question 28

Where does the axon of lower motor neurones travel?

Answer 28

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

Question 29

What is the function of lower motor neurones?

Answer 29

Stimulate muscles to contract

Question 30

What types of neurones are involved in a spinal reflex?

Answer 30

Primary sensory neurone Lower motor neurone Inhibitory interneurone

Question 31

What stimulates the patellar reflex arc?

Answer 31

Stretch of the quadriceps muscle stimulates muscle spindles in it

Question 32

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

Answer 32

Primary sensory neurones

Question 33

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

Answer 33

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

Question 34

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

Answer 34

Stimulates the quadriceps muscle to contract

Question 35

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

Answer 35

Inhibits lower motor neurone supplying hamstring muscle | Prevents hamstring muscle contracting and opposing the quadriceps muscle

Question 36

What is the purpose of deep tendon reflexes?

Answer 36

Maintain posture

Question 37

What causes damage to lower motor neurones?

Answer 37

CNS lesions damage the cell body and proximal axon PNS lesions damage the axon

Question 38

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

Answer 38

Weakness Hypotonia, decreased muscle tone Areflexia, absence of deep tendon reflexes Fasciculation, uncoordinated muscle contraction Wasting

Question 39

Why does damage to lower motor neurones cause wasting?

Answer 39

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

Question 40

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

Answer 40

Weeks to months