Intro to Motor system

Question 1

What type of movement is walking, chewing etc?

Answer 1

Rhythmic motor pattern (subconscious usually)

Question 2

What does the nervous system need to know in order to produce movement? (4)

Answer 2

1. Initial length of the muscle
2. Velocity of muscle length change
3. External loads acting to oppose movement
4. Visual and vestibular info

Question 3

What type of fibers innervate GTOs?

Answer 3

Type Ib afferent

Question 4

What type of fibers innervate muscle spindles?

Answer 4

Type Ia afferent

Question 5

What is feedback control?

Answer 5

use of sensory information during movement to make corrections to the on-going movement.

Question 6

What is feedforward control?

Answer 6

• Sensory information contributes to anticipating the effect of planed movement

Question 7

What is the motor pathway?

Answer 7

Parietal/premotor/supplementary motor cortex to the

Primary motor cortex
Brainstem
Spinal cord

Question 8

What are the two inputs to the thalamus that affect its output to the primary motor cortex?

Answer 8

Basal nuclei

Cerebellum

Question 9

What are the two places that the cerebellum sends information to in the motor pathway?

Answer 9

Brainstem

Thalamus

Question 10

What is the hierarchical organization of the motor control centers?

Answer 10

Cortical areas
Brainstem
Spinal cord

Question 11

What two parts of the brain modify output from the motor cortex?

Answer 11

Basal ganglia

Cerebellum

Question 12

What is the difference between UMNs and LMNs?

Answer 12

UMNs go to a ganglia/nucleus

LMNs symapse on effector muscle

Question 13

What role do gamma motor neurons play in the nervous system?

Answer 13

Innervate intrafusal skeletal muscle fibers, the small muscle fibers within the muscle spindles

Question 14

What are skeltal-fusimotor neurons?

Answer 14

Nerves that innervate both extrafusal and intrafusal muscle fibers: this is sometimes called beta activation

Question 15

Where are LMNs found in the spinal cord?

Answer 15

Anterior horn of the gray matter, with their axons leaving the spinal cord via the ventral root

Question 16

What are alpha motor neurons?

Answer 16

neurons that innervate muscles in the PNS

Question 17

What is a motor neuron pool?

Answer 17

All the neurons that control one muscle

Question 18

What is a motor unit?

Answer 18

one alpha motor neuron plus all the skeletal muscle fibers it innervates

Question 19

What are the four functional components of a motor unit?

Answer 19

• cell body of motor neuron
• axon
• neuromuscular junction
• muscle fibers

Question 20

Where are small motor units used in the body?

Answer 20

Where fine control is needed (oculomotor muscles in the eyes)

Question 21

Where are large motor units used in the body?

Answer 21

In strong muscles that do not need fine control

Question 22

What is the pathogenesis of post-polio syndrome?

Answer 22

surviving motor neurons “adopt orphaned” muscle fibers. This increases stress on these fibers, with repeated remodeling with denervation and reinnervation

Question 23

What produces graded muscle contraction? (there are two options here)

Answer 23

recruitment of more and more muscle units and/or increase the rate at which the alpha motor neuron of each motor unit is firing.

Question 24

What is Henneman’s size principle?

Answer 24

order of recruitment of motor neurons = first recruit small neurons, and then larger neurons, since smaller ones will depolarize first

Question 25

True or false: muscles need constant, low level stimulation. Why?

Answer 25

True, since need muscle protein gene expression

Question 26

What are the symptoms of a LMN lesion?

Answer 26

Atrophy Hypotonia Hyporeflexia Fibrillations/fasciculations

Question 27

What causes the weak reflexes seen in a LMN damage?

Answer 27

Loss of alpha motor neurons to the muscle

Question 28

What are fasciculations?

Answer 28

- visible twitches of muscle that can be seen as ripples under the skin

Question 29

What are fibrillations?

Answer 29

spontaneous activity within single muscle fibers. They are not visible clinically since they are too small to be seen as movement through the skin

Question 30

How do you detect fibrillations of muscle?

Answer 30

Electromyography

Question 31

Fasciculations are a sign of what?

Answer 31

LMN disorder

Question 32

What is the difference in innervation between fasciculations and fibrillations?

Answer 32

Fasciculations are when entire muscle groups are still connected after a lesion, so contract together. Fibrillations are when fibers are not innervated together, thus single fibers twitch

Question 33

What is an injury potential?

Answer 33

Potential generated at site of injury to a motor neuron axon.

Question 34

What happens to muscles that are denervated that causes them to be super sensitive?

Answer 34

Increased number of Ach receptors

Question 35

Flaccid paralysis results when what occurs with the nerves?

Answer 35

Total loss of innervation

Question 36

What is paresis?

Answer 36

paresis refers to partial loss of voluntary contraction or voluntary muscle weakness.

Question 37

Which type of lesion causes flaccid paralysis? Spastic?

Answer 37

``` Flaccid = LMN or initially with UMN Spastic = UMN ```

Question 38

A complete transection of the spinal cord will result in flaccid or spastic paralysis?

Answer 38

Initially flaccid, then spastic

Question 39

What is spinal shock?

Answer 39

the temporary loss of spinal cord reflex activity that occurs below a total (or near total) spinal cord injury.

Question 40

What are the three components/symptoms of spinal shock?

Answer 40

1. Flaccid paralysis 2. Areflexia 3. Loss of autonomic function below level of transection

Question 41

How long do symptoms of spinal shock last? What then?

Answer 41

a few days to weeks Progresses to hyperreflexia

Question 42

Babinski sign it a test for what type of neuron lesion?

Answer 42

UMN

Question 43

What is the MOA of spinal shock syndrome? (3)

Answer 43

Increased blood supply or loss of edema around spinal cord Loss of inhibition of gamma motor neurons

Question 44

What is an UMN?

Answer 44

a neuron in a higher motor area (e.g. motor cortex, premotor cortex, brainstem center) that synapses on a lower motor neuron or on an interneuron which synapses on a lower motor neuron.

Question 45

Spinal cord lesions (e.g. those caused by a broken neck) damage what type of neurons?

Answer 45

LMNs at the site of injury | UMN if spinal tract involved

Question 46

What are the two parts of the spinal cord that produce a multitude of symptoms if transected?

Answer 46

The cervical and lumbar enlargements

Question 47

What is spasticity?

Answer 47

a motor disorder characterized by a velocity- dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex, and is one component of the upper motor neuron syndrome.

Question 48

The oculomotor and trochlear nuclei are UMN or LMNs?

Answer 48

LMNs

Question 49

True or false: there can be LMNs above UMNs in the spinal cord

Answer 49

True, as long as they are not part of the same tract

Question 50

True or false:Damage of the spinal cord can damage both LMNs and UMNs

Answer 50

True

Question 51

True or false: spinal cord lesions always affect all of the descending motor tracts

Answer 51

False--can have only one

Question 52

Upper motor neuron syndrome is what?

Answer 52

When all tracts of UMNs are lesioned

Question 53

DTR are overactive in UMN or LMN lesions?

Answer 53

UMN

Question 54

If a pt presents with both UMN and LMN signs, what should immediately be in your ddx?

Answer 54

ALS

Question 55

What is the pathogenesis of ALS?

Answer 55

Loss of myelination of UMNs and LMN of unknown etiology