L12 -Lower motor neurons

Question 1

Is motor control part of the pre or post central gyrus?

Answer 1

Pre

Question 2

Is somatosensory part of the pre or post central gyrus?

Answer 2

Post

Question 3

What does the location of the neuron in the spinal cord (whether its more medial or lateral) tell us about the muscles they act on and the distance of their local circuit neurons? *the same concept applies for dorsal, ventral, longitutinal

Answer 3

MEDIALLY LOCATED - muscles are closer to midline, long-distance local circuit neurons

LATERALLY LOCATED - muscles are located more distally, short-distance local circuit neurons

Question 4

Where are the smallest motor units found

Answer 4

Extraoccular muscles of the eyes (only 3 or 4 fibres)

Question 5

With increased motor unit size, alpha motor neurons exhibit:

Answer 5

Increased: Cell body size, dendritic complexity, axonal diameter, number of axonal branches, short-term EPSP potentiation with repeated activation

Decreased: Input resistance, excitability, 1a EPSP amplitude, PSP decay constant, duration of after - hyperpolarization

Question 6

Input resistance

Answer 6

High input resistance is when you inject a current into a neuron and it stays there.

Low input resistance means current leaks out after injection.

Question 7

What type of motor fibres are recruited for walking and running?

Answer 7

Fast fatigue-resistant

Question 8

What type of motor fibres are recruited for galloping and jumping?

Answer 8

Fast fatigable

Question 9

What are the 3 categories of input

Answer 9

Sensory input from muscle spindles, input from upper motor neurons in the brain, input from spinal interneurons

Question 10

Lower motor neuron

Answer 10

Anything that affects excitability of alpha motor neuron

Question 11

Gamma motor neuron innervates

Answer 11

Intrafusal muscle fibres

Question 12

What level does the stretch reflex (with muscle spindles) occur in

Answer 12

Segemental - doesn’t involve brain stem

Question 13

T/F: Muscle spindles are the only afferent that directly goes to motor neurons

Answer 13

True

Question 14

Function of golgi tendon organs

Answer 14

Force detectors that prevent overstretching of muscles, causing a reflex inhibition of muscles when excessive force is exerted e.g. it excites inhibitory motor neurons of flexor muscle to result in inhibition via distal 1b afferent and excites antagonistic extensor muscle to aid in extension of arm

Question 15

T/F: Muscle spindle primary 1a afferents are the fastest

Answer 15

True

Question 16

Flexion-crossed extension reflex

Answer 16

A reflex found in quadrupeds and humans that occurs when cutaneous afferent fibre from nocieptor is activated.

e.g. stepping on a pin stimulates leg flexes to withdraw leg (flexing) while opposite leg supports it (extension)