Functional Organisation of the Spinal Cord

Question 1

What are the functional roles of the spinal cord?

Answer 1

segmental reflexes, intersegmental reflexes, pattern generators, transmission of somatosensory information, relay of descending motor control, relay of descending autonomic commands

Question 2

What type of neurons are in the dorsal horn?

Answer 2

sensory

Question 3

What type of neurons are in the ventral horn?

Answer 3

motor

Question 4

What type of information is sent via the anterolateral tract?

Answer 4

nociception

Question 5

Where are the descending motor tracts located in the spinal cord?

Answer 5

lateral

Question 6

Where are the motor neurons for distal muscles located in the spinal cord?

Answer 6

laterally

Question 7

What is a motor unit?

Answer 7

the muscle fibres innervated by one motor neuron

Question 8

What is a motor neuron pool?

Answer 8

a collection of motor neurons that all innervate one muscle

Question 9

What is the function of muscle spindles?

Answer 9

to detect muscle stretch

Question 10

What is the fucntion of tendon organs?

Answer 10

to detect muscle force

Question 11

Describe the monosynaptic stretch reflex

Answer 11

when the muscle is stretched the spindle detects it and send an action potential via the dorsal root to the spinal cord and make an excitatory connection with the muscle to contract in response to the stretch and via an inhibitory interneuron makes the antagonistic muscle relax

Question 12

Describe the tendon organ reflex

Answer 12

when the tendon organs detect an increase in force they signal to the spinal cord via an inhibitory interneuron to decrease contraction of that muscle and signal via an excitatory interneuron to increase contraction of the antagonist muscle

Question 13

Describe the cross extensor reflex

Answer 13

when one limb steps on something sharp it triggers a reflex withdrawl response (flexion) but at the same time the animal needs to stay balanced on the other limbs so intersegmental reflexes work to increase extension in the other limbs

Question 14

What is a lower motor neuron?

Answer 14

a neuron that innervates a muscle

Question 15

What is an upper motor neuron?

Answer 15

a neuron that affects the excitability of the lower motor neuron - may be in the cortex, basal ganglia, brainstem or spinal cord

Question 16

Are most motor interneurons excitatory or inhibitory?

Answer 16

inhibitory

Question 17

What is the result of a lesion in the descending motor pathway?

Answer 17

there is a loss of inhibition resulting in increased muscle tone and exaggerated tendon reflexes

Question 18

How would you localise a descending motor pathway lesion?

Answer 18

test monosynaptic stretch reflexes at different levels