Chapter 13

Question 1

Common signs of lower motor neuron lesions

Answer 1

Decreased or absent reflexes
Flaccid paralysis
Atrophy

Question 2

Low motor neurons convey

Answer 2

Signals to extrafusal and intrafusal skeletal muscle fibers

Question 3

Cell bodies of spinal LMN are located in

Answer 3

Ventral horn

Question 4

Motor pools

Answer 4

A cluster of Cell bodies whose axons project to a single muscle

Question 5

Medially located motor pools

Answer 5

Innervate axial and proximal muscles

Question 6

Laterally located motor pools

Answer 6

Innervate distal muscles

Question 7

Anteriorly located motor pools

Answer 7

Innervate extensors

Question 8

Posterior motor pools

Answer 8

Innervate flexors

Question 9

Myotome

Answer 9

A group of muscles innervated by a single spinal nerve

Question 10

Two types of motor neurons

Answer 10

Alpha and gamma

Question 11

Alpha motor neurons

Answer 11

Have large cell bodies and large myelinated axons
Project to extrafusal skeletal muscle

Question 12

Gamma motor neurons

Answer 12

Have medium sized myelinated axons
Project to intrafusal fibers in the muscle spindle

Question 13

Alpha-gamma coactivation 

Answer 13

When the CNS wants a muscle to contract, signals are sent to alpha motor neurons, and also instructs gamma motor neurons to contract intrafusal fibers when the extrafusal muscle fibers actively contract

Question 14

Motor unit

Answer 14

An alpha motor neuron and the muscle fibers it innervates

Question 15

Motor units are classified as

Answer 15

Slow twitch, or fast twitch

Question 16

Slow twitch muscle fibers

Answer 16

Innervated by smaller in diameter, slower conducting alpha motor neurons

Question 17

Fast twitch muscle fibers

Answer 17

Innervated by larger diameter, faster conducting alpha motor neurons

Question 18

Reciprocal inhibition

Answer 18

The inhibition of antagonist muscles during agonist contraction
Avoids cocontraction, one gets stimulated/excited, one gets inhibited

Question 19

Reflexes involve

Answer 19

A receptor, an afferent limb, a synapse, an efferent limb, and an effector

Question 20

Spinal reflexes require

Answer 20

Sensory receptors, primary afferents, synapses between primary afferents and LMNs, and muscles

Question 21

Phasic stretch reflex / Deep Tendon Reflex / Myotatic Reflex

Answer 21

Muscle contraction in response to quick stretch
Tapping the knee reflex

Question 22

Withdrawal reflex / cutaneous reflex

Answer 22

Person steps on tack → lower limb flexs automatically lifting the foot before person is consciously aware of the pain
Circuitry in spinal cord

Question 23

Muscle spindle output

Answer 23

Not linearly related to changes in muscle length or rate of change in length
Modified by sensitivity adjustments and by recent movements and contractions the muscle has undergone

Question 24

Contracture

Answer 24

The adaptive shortening of a muscle-tendon unit
Prolonged immobility causes contracture, muscle loses elasticity and thickens
Loss of sarcomeres

Question 25

Spontaneous involuntary muscle contraction include

Answer 25

Muscle cramps
Fasciculations
Myoclonus
Tremors
Fibrillations
Abnormal movements

Question 26

Fasciculations

Answer 26

Quick twitches of all muscle fibers in a single motor unit
Eyelid twitch

Question 27

Myoclonus

Answer 27

Brief involuntary contraction of a muscle or group of muscles
Hiccups or muscle jerks

Question 28

Fibrillations

Answer 28

Random, spontaneous, brief contractions of single muscle fibers snot visible on the surface of the skin and are always pathologic
Detectable by EMG (electromyography)

Question 29

Muscle atrophy

Answer 29

The loss of muscle bulk

Question 30

Disuse atrophy

Answer 30

Results from lack of muscle use

Question 31

Neurogenic atrophy

Answer 31

Caused by damage to the nervous system

Question 32

Hypotonia

Answer 32

Abnormally low muscular resistance to passive stretch
Occurs with decreased LMN input

Question 33

Flaccidity

Answer 33

Total lack of muscle tone
Occurs with complete LMN lesions

Question 34

Poliovirus

Answer 34

Infection that affects only LMNs
Selectively invades lower motor neuron cell bodies and destroys some of them denervating muscle fibers

Question 35

Postpolio syndrome

Answer 35

Occurs years after illness
Due to overextended surviving neurons not being able to support the abnormal number of axonal branches, causing some distal branches to die
Symptoms include increased muscle weakness, joint and muscle pain, fatigue and breathing problems