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

At what level would you perform a lumbar puncture?

Answer 2

L3-L4 (below termination of the spinal cord)

Question 3

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

Answer 3

lateral

Question 4

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

Answer 4

laterally

Question 5

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

Answer 5

medially

Question 6

What is a motor unit?

Answer 6

group of muscle fibres innervated by a single motor neuron

Question 7

What is a motor neuron pool?

Answer 7

a group of motor neurons that all innervate a single muscle

Question 8

What is the function of muscle spindles? where are they located?

Answer 8

to detect muscle stretch (length), they are intrafusal fibres within muscle fibres

Question 9

What is the function of Golgi tendon organs? where are they located?

Answer 9

to detect muscle force (tension). located in the tendons of skeletal muscles.

Question 10

Describe the monosynaptic stretch reflex (ie knee-jerk)

Answer 10

tendon hammer produces brief stretch on tendon which is detected by the muscle spindle which sends on AP via the dorsal root to the spinal cord where it makes 2 connections:

1. excitatory connection with the motor neuron innervating the extensor muscle
2. with an inhibitory interneuron which synapses with the motor neuron innervating the antagonistic muscle (ie the flexor)

Question 11

Describe the Golgi tendon organ reflex (in response to too much force)

Answer 11

want feedback to decrease force -> tendon organ detects an increase in force so signals via in inhibitory interneuron in the spinal cord to decrease contraction of the muscle under tension and an excitatory interneuron to increase contraction of the antagonistic muscle

Question 12

What is the bilateral/ cross extensor reflex?

Answer 12

an intersegmental reflex ie in response to nociceptive stimuli

Question 13

Describe the bilateral/cross extensor reflex

Answer 13

when one limb steps on something sharp nociceptors mediate a withdrawal reflex (activate flexors and inhibit extensors) and at the same time there is intersegmental reflexes that work to increase extension on the other leg to maintain posture (involves multiple interneurons - ie NOT monosynaptic)

Question 14

Lateral propriospinal interneurons are involved in what?

Answer 14

shorter -> for precision/fine movements ie writing

Question 15

Medial propriospinal interneurons are involved in what?

Answer 15

are longer and involved in action of postural muscles

Question 16

What is a lower motor neuron?

Answer 16

a neuron that innervates a muscle

Question 17

What is an upper motor neuron?

Answer 17

function definition -> any neuron that affects the excitation of a lower motor neuron

Question 18

Are most upper motor interneurons excitatory or inhibitory?

Answer 18

inhibitory -> ie brain is mostly signalling to the spinal cord to do nothing

Question 19

What happens when you have a lesion in the descending motor pathway?

Answer 19

hyperexcitability or the motor neurons below the lesion (increased muscle tone and exaggerated tendon reflexes) -> lost their inhibitory descending control

Question 20

How would you localise a descending motor pathway lesion?

Answer 20

test monosynaptic stretch reflexes at different levels