Reflexive and Voluntary Activation of Muscle

Question 1

What are some signs of faulty motor control?

Answer 1

Paralysis
Weaknss
Stiffness
Increased reactivity
Ticks, twitches, and jerks
Fibrillations and fasciculations
Loss of coordination and smoothness
Loss of effectiveness of movements

Question 2

Define motor signs

Answer 2

Observable/measurable motor abnormalities/
Presence of abnormalities/
Absence of normal motor actions

Question 3

Define motor symptoms

Answer 3

Problems of motor function reported by patients

Question 4

Define motor syndromes

Answer 4

Associated/clustered signs and symptoms

Question 5

Where are motor neurons found?

Answer 5

Ventral part of spinal cord

Brainstem

Question 6

What is a motor pool?

Answer 6

Cluster of motor neurons in spinal cord innervating a muscle group

Question 7

What are the characteristics of a motor neuron?

Answer 7

Large
Cholinergic
Fast conducting

Question 8

Where do motor neurons synapse with muscle?

Answer 8

At neuromuscular junction (NMJ)

Question 9

What is the ratio of motor neurons to muscle fibres?

Answer 9

1:many

Question 10

What is a motor unit?

Answer 10

Motor neuron + all muscle fibres it innervates

Question 11

Are motor units all the same size?

Answer 11

No

Question 12

How much force is applied when 25% of a motor pool is activated? Why?

Answer 12

5% of force because smaller motor units recruited first

Question 13

How is the force applied by a muscle increased?

Answer 13

Larger and larger motor units recruited

Question 14

What kind of fibres are those that are first activated?

Answer 14

Slow - don’t fatigue over long periods of time

Question 15

What kind of fibres are activated after slow fibres?

Answer 15

Fast fatigue-resistant

Question 16

What kind of fibres are activated last?

Answer 16

Fast fatiguable

Question 17

What is the neurotransmitter released at the NMJ?

Answer 17

ACh

Question 18

What is a fibrillation?

Answer 18

Tiny contraction caused by activity of single muscle cell

Question 19

What can fibrillations be due to?

Answer 19

Hypersensitivity

Increased AChR expression - including extra-junctional

Question 20

What is a fasciculation?

Answer 20

Groups of muscle fibres contracting involuntarily

Can be measured on surface

Question 21

What does long-term denervation cause?

Answer 21

Atrophy and degeneration of muscle

Question 22

When can atrophy occur?

Answer 22

In catabolic states

• Diabetes
• Cushing’s disease

Question 23

What will complete denervation lead to?

Answer 23

Progressive irreversible muscle loss

Question 24

When at rest, are muscles inactive?

Answer 24

No, have resting tone

Question 25

What do muscle spindles do?

Answer 25

Report back on length of muscle

Question 26

Are muscle spindles in series or parallel with muscle?

Answer 26

Parallel

Question 27

How do muscles spindles work?

Answer 27

The longer a muscle stretches > more activity in these stretch receptors

Question 28

What do Golgi tendon organs do?

Answer 28

Report back on amount of force transmitted through tendon?

Question 29

Are Golgi tendon organs in series or parallel with muscle?

Answer 29

In series

Question 30

What is the role of muscle spindles in the monosynaptic reflex?

Answer 30

Activate motor neurons of same muscle | Returns muscle to original state after stretch detected

Question 31

What are the signs of lower motor neuron lesions?

Answer 31

``` Weakness/paralysis Decreased superficial reflexes Hypoactive deep reflexes Decreased tone Fasciculations and fibrillations Severe muscle atrophy ```

Question 32

What are the three main types of input onto lower motor neurons?

Answer 32

``` Sensory input from muscles Secondary information from interneurons - Most of input Input from brain - Come from various regions - Most don't make direct synaptic contact but via interneurons ```

Question 33

What are the two groups of descending pathways in the spinal cord?

Answer 33

Lateral | Ventromedial

Question 34

What tracts are in the lateral part of the spinal cord?

Answer 34

Corticospinal tract | Rubrospinal tract

Question 35

Where does the corticospinal tract come from?

Answer 35

Cerebral cortex

Question 36

What is the corticospinal tract sometimes called?

Answer 36

Lateral corticospinal tract

Question 37

Do the corticospinal and rubrospinal tracts overlap?

Answer 37

Yes

Question 38

Where does the rubrospinal tract come from?

Answer 38

Red nucleus in brainstem

Question 39

Which tracts are in the ventromedial part of the spinal cord?

Answer 39

Tectospinal tract Vestibulospinal tract Pontine and medullary reticulospinal tracts

Question 40

Where does the tectospinal tract come from?

Answer 40

Superior colliculus

Question 41

What else is the tectospinal tract called?

Answer 41

Colliculospinal tract

Question 42

Where does the vestibulospinal tract come from?

Answer 42

Vestibular nuclei in brainstem

Question 43

What are the two reticulospinal tracts?

Answer 43

Pontine | Medullary

Question 44

Which reticulospinal tract is more lateral?

Answer 44

Medullary

Question 45

Where are the motor neurons for distal muscles in the ventral horns?

Answer 45

More lateral

Question 46

Why is it important that the motor neurons for distal muscles are more lateral?

Answer 46

Lateral descending tracts make most connections with lateral motor neurons > control more distal muscles Because distal muscles involve more voluntary control

Question 47

Where are the motor neurons for proximal muscles in the ventral horns?

Answer 47

More medial

Question 48

Why is it important that the motor neurons for proximal muscles are more medial?

Answer 48

Ventromedial descending tracts make most connections with medial motor neurons > control more medial muscles Because medial muscles involve more involuntary control

Question 49

What does corticobulbar tract refer to>

Answer 49

Cerebral inputs to motor nuclei in brainstem | Cerebral inputs to LMNs in brainstem (cranial nerves)

Question 50

Where does the corticospinal tract decussate?

Answer 50

Medullary pyramids

Question 51

How much of the descending projections from the cerebral cortex decussate at the medullary pyramids?

Answer 51

90%

Question 52

Where do the 10% of descending projections from the cerebral cortex that don't decussate in the brainstem travel?

Answer 52

In ventromedial pathway

Question 53

Which ventromedial pathways don't decussate?

Answer 53

Vestibulospinal tract | Reticulospinal tract

Question 54

Which ventromedial pathways decussate, and where?

Answer 54

Colliculospinal tract | Decussates immediately

Question 55

What kinds of connections do ventromedial tracts have in the spinal cord?

Answer 55

Synapse with interneurons that spread information ipsilaterally and contralaterally

Question 56

What kinds of connections do ventromedial tracts have in the spinal cord?

Answer 56

Synapse with interneurons that spread information ipsilaterally and contralaterally

Question 57

What happens when the brain can no longer influence the spinal cord?

Answer 57

Spinal locomotor circuits can't be activated Most of inputs from brain inhibitory > now hyper-excitable Spinal reflex circuits become oversensitive and muscle tone above normal levels

Question 58

What is spinal shock?

Answer 58

After lesion when spinal cord doesn't really respond Variable Unknown pathophysiology

Question 59

What are upper motor neuron lesion signs?

Answer 59

``` Weakness Spasticity - Increased tone - Hyperactive deep reflexes - Clonus Babinski's sign Loss of fine voluntary movements ```

Question 60

What is clonus?

Answer 60

Rhythmic response to stimulus for long time after stimulus gone