22.1 NS: Reflexive and voluntary activation of muscle

Question 1

What is the difference between signs and symptoms?

What is a syndrome?

Answer 1

Signs: things we can observe

Symptoms: things people report

Syndrome: Symptoms in clusters with signs

Question 2

What is a motor pool?

Answer 2

A muscle that is innervated with 100-1000s of motor neurons

Question 3

What is a motor unit?

Answer 3

One motor neuron that innervates several fibres

Question 4

What does Henneman’s size principle describe?

Answer 4

The order of muscle recruitment is:
Small MNs first
Large, fast twitch fibres last

Question 5

How are NMJs different to most synapses?

Answer 5

There is 1:1 linkage (for impulse and twitch)

Question 6

What happens in myasthaenia gravis?

Answer 6

ACh R’ on the muscles is blocked and the safety margin is eroded

Question 7

What is a fibrillation? How does this occur?

Answer 7

Tiny contraction caused by a single muscle cell

increased ACh R’ expression

Question 8

What is a fasiculation?

Answer 8

A group of muscle fibres contracting involuntarily (spontaneous due to degeneration)

Question 9

What is the difference between when muscles are deinnervated vs. inactivity?

Answer 9

Deinnervation: atrophy and shrinkage (irreversible)

Inactivity: shrinkage (reversible)

Question 10

What do spindles and golgi tendons sense?

Answer 10

Spindles: stretch (intrafusal)
Golgi: force

Question 11

What is the monosynaptic stretch reflex?

Answer 11

A negative feedback loop that results in contraction due to disturbance (e.g. tendon hammer)

Question 12

What is the difference between a LMN and UMN lesion?

Answer 12

LMN: Weakness/paralysis, decreased tone/reflexes, atrophy

UMN: Weakness, spasticity, increased tone/reflexes, Babinski, loss of fine/voluntary movements

Question 13

Where do axons in the lateral white matter vs. the medial white matter come from?

Answer 13

Lateral: motor cortex
Medial: brainstem

Question 14

Topographically, how are muscles mapped in the CNS?

Answer 14

Motor neurons for proximal muscle are in the midline (distal muscles are more lateral)

Question 15

Which tract is responsible for voluntary movement? Where do these fibres cross?

Answer 15

Lateral cortico-spinal tract crosses at the medulla

Question 16

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

Answer 16

Less inhibition, so motoneurons exhibit hyper-excitability