Activation of Muscles

Question 1

what is the anatomical and functional relationship between motor neurons and muscles

Answer 1

motor neurons are large cholinergic neurons sitting in the ventral region of the spinal cord.

Question 2

One motor neuron may innervates one/several […..] in the muscle. This is called a [….]. They release NT’s onto the fibre{s) at a motor [….].

Answer 2

motor fibres.
Motor Unit.
endplate.

Question 3

A […] describes all the motor neurons involved in the innervation of one skeletal muscle.

A [….] number of motor neurons in a motor pool means the muscles is meant for fine-tuned control, and a […] number of motor units would be present in a muscle with more blunt control.

Answer 3

motor pool.

high
lesser

Question 4

henneman’s size principle describes that for a given percent of motor neuron pool recruited a proportionate amount of [….] will be generated. This represented an [….] curve.

Thus, slow, sustained movements would require a […] % of motor pool to generate a [….] force.

Answer 4

muscle force
exponential.

25% of the motor pool to generate 5% of force.

small/low/reduced
small/low/reduced.
*slow, sustained movements require 25% of motor pool to generate 5% of force.

Question 5

muscle activitations follows an [….] principle. Nerve stimulus must surpass a [….] to activate [….].

Answer 5

all or none.

threshold
muscle twitch

Question 6

at the NMJ, the post synaptic membrane has many […] receptors and has a folded surface to […..]

Answer 6

ACh

Increase surface area for ACh stimulation of the motor end plate membrane.

Question 7

T/F: muscles are rarely inactive and in fact have a resting tone.

Answer 7

TRUE.

maintaining postural control.

Question 8

muscles that remain inactive for long periods of time may express (3):
[….]

Answer 8

1. fibrilation
2. fasciculation
3. long term denervation

Question 9

with inactivity, tiny muscle cells maybe become hypereactive due to upregulation of ACh receptors. Activations are not synaptic and thus not summated. These contractions are called […]

Answer 9

fibrillation

Question 10

with inactivity, a motor unit may be synaptically activated to due to spontaneous activation of a degenerating motor neuron/axon—->involuntary muscle contractions. These contractions are called, […]

Answer 10

fasciculations

*can be measured on the surface.

Question 11

long term denervation may occur in [….] such as in diabetes and cushing’s disease.

Answer 11

catabolic states

Question 12

Motor pools in the spinal cord are clustered in distinct columns of motor neurons extending over multiple spinal cord segments; although, there is significant overlap.

Motor pools that control proximal muscles are generally located […..] to the ventral horn, while those that control distal muscles are located [….].

Motor pools that control flexor muscles are located [….] to the ventral horn while those that control extensor muscles are located [….]

Answer 12

proximal muscles –>medial corticospinal tracts
distal muscles—>lateral corticospinal tracts

flexor muscles–>dorsally
extensor muscles–>ventrally

Question 13

muscle spindles are in parallel with muscles, within the capsule, and relay information RE: […] of the muscle at any one time.

Answer 13

length of the muscle.

via 1A sensory afferents.

Question 14

muscle tendon (golgi tendon organ, GTO), is in series with the muscle and can relay information regarding [……]

Answer 14

how much force is being generated by the muscle.

via 1B afferent neuron.

Question 15

symptoms of Lower Motor Neuron Disease:

• weakness or paralysis
• [….] superficial reflexes
• […] deep reflexes
• […..] tone
• [….] and fibrilations
• severe muscle atrophy

Answer 15

• decreased
• hypoactive deep reflex
• reduced tone (b/c muscle cant be activated by motor neuron)
• fasciculations

Question 16

in the spinal cord, lateral white matter contains axons from the […]

medial white matter contains axons from the […]

Answer 16

motor cortex.

brainstem.

Question 17

the ventromedial pathways of the spinal cord are (4):

Answer 17

tectospinal tract
vestibulospinal tract
pontine reticulospinal tract
medullary reticulospinal tract

Question 18

the lateral pathways of the spinal cord are (2):

Answer 18

corticospinal tract and rubrospinal tract.

Question 19

the corticospinal tract starts in the cerebral cortex (primary motor cortex or pre-motor cortex), sending signals down the white matter of the [….], activating brain stem neurons.

Answer 19

internal capsule

Question 20

in the midbrain the corticospinal tract continues its path ipsilaterally, passing through the [….] to the pons.

Answer 20

cerebral peduncles

Question 21

in the middle pons, the corticospinal tract sends collateral axons off to the [….] , and continues ipsilaterally down the [….] to the medulla.

Answer 21

reticular formation.

pontine fibre bundles.

Question 22

in the middle medulla, the corticospinal tract sends collateral axons off to the [….], and continues ipsilaterally through the […] to the caudal medulla.

Answer 22

reticular formation.

medullary pyramids

Question 23

in the caudal medulla the corticospinal tract goes through the [….] and passes through to the [….]

Answer 23

pyramidal decussation

contralateral side of the spinal cord

Question 24

most of the input from the brain on motor neurons is […] in nature. Thus, in absence of this input, motor neurons become [….]

Answer 24

inhibitory

hyper-excitable.