Functional Organization of the Spinal Cord

Question 1

Motor neurons are present in

Answer 1

ventral horns

Question 2

Medial motor neurons innervate

Answer 2

more medial muscle

Question 3

Lateral motor neurons innervate

Answer 3

more distal muscle

Question 4

Each motor neuron innervates

Answer 4

a collection of muscle fibres (2-100+) called a motor unit

Question 5

What is a motor unit?

Answer 5

A motor neuron and the muscle fibres it innervates

Question 6

What is a motor neuron pool?

Answer 6

All the motor neurons that innervate a complete muscle

Question 7

Muscle spindles detect

Answer 7

stretch; muscle length

Question 8

Golgi tendon organs detect

Answer 8

the force of a muscle transmitted through the tendon

Question 9

What is a monosynaptic stretch reflex?

Answer 9

eg knee jerk/tendon jerk; involves a single central synapse

Question 10

In a monosynaptic reflex, what do muscle spindles do?

Answer 10

Activate the AMN of the muscle being stretched to make it contract (oppose the stretch); activate the inhibitory interneuron to the AMN of the antagonist (telling it to relax)

Question 11

In a monosynaptic reflex, what do Golgi tendon organs do?

Answer 11

Activate an inhibitory interneuron to the AMN of the muscle producing too much force to tell it to relax (decrease force); activate an excitatory interneuron to the AMN of the antagonist muscle telling it to contract (increase force)

Question 12

All Golgi tendon organs contact AMNs via

Answer 12

interneurons

Question 13

What are inter-segmental reflexes?

Answer 13

Involving more than one muscle eg bilateral (cross-extensor reflex) and multi-segmental reflexes

Question 14

How does the cross-extensor reflex work?

Answer 14

Stimuli to cutaneous nociceptors sets off a chain of interneuronal connections - causes ipsilateral flexion (w/inhibited extension) to withdraw the limb, and contralateral extension (w/inhibited flexion) to stabilize the body so you don’t fall over

Question 15

Medial interneurons tend to be

Answer 15

bilateral & long; deal with postural control (lots of intersegmental coordination) - many muscles in a large area

Question 16

Lateral interneurons tend to be

Answer 16

ipsilateral & short; deal with complex dextrous movements - coordinating a few (distal) muscles in a small region

Question 17

Lower motor neurons

Answer 17

motor neurons that innervate muscle

Question 18

Upper motor neurons

Answer 18

any neuron that affects the excitability of a lower motor neuron - brainstem, cortex, basal ganglia, etc.

Question 19

Exaggerated reflexes are a sign of

Answer 19

Loss of upper motor neuron control, which is mostly inhibitory; tf reflexes become hyperactive