9 - Muscle and Movement

Question 1

describe the mechanics of synapses reaching a NMJ

Answer 1

• voltage-gated Ca2+ channels open
• Ca2+ enters motor neuron
• ACh exocytosis and diffusion
• ACh-sensitive cation channels open
• Na+ into muscle fibre and K+ goes out
• end-plate membrane depolarises in muscle fibre
• AP causes contraction

Question 2

what regulates muscle contraction?

Answer 2

troponin complex

Question 3

describe how each type of muscle fatigues?

Answer 3

type 1 - doesn’t fatigue
type 2a - eventually fatigues after 8 mins or so
type 2b - rapid fatigue

Question 4

the graduation of muscle force occurs via two mechanisms - what are they?

Answer 4

1. recruitment of motor units
2. firing rate of motor units

Question 5

large motor units are mainly what muscle fibre?

Answer 5

type 2

Question 6

small motor units are mainly what muscle type?

Answer 6

type 1

Question 7

what is the difference between UMN lesions and LMN lesions in terms of:
* muscle strength
* paralysis
* muscle tone
* reflexes

Answer 7

LMN:
* muscle strength - weakness
* paralysis - flaccid
* muscle tone - hypotonia
* reflexes - hyporeflexia

UMN:
* muscle strength - weakness
* paralysis - spastic
* muscle tone - hypertonia
* reflexes - hyperreflexia

Question 8

what is an upper motor neuron?

Answer 8

neuron that originates in cerebral cortex and finishes in brainstem or spinal cord

Question 9

what is a lower motor neuron?

Answer 9

neuron that originates in spinal cord and innervates muscle fibres or glands around the body