Muscle anatomy

Question 1

What is a Motor Neuron?

Answer 1

Consists of the axon, the axon hillock and dendrites that activate the a-motor neuron in the skeletal muscle (purves)
(draw motor neuron)

Question 2

Why does the size of the motor neuron differ from muscle to muscle?

Answer 2

due to the amount of control required
eg. in fine motor control, large units are not required
whereas the gastrocnemius and calf contain 2000 muscle fibres to generate ballistic contraction

Question 3

What does a muscle contain?

Answer 3

myofibrils that contain myofilaments (actin and myosin) for contraction
surrounding fibrils in the t-tubules channels known as sarcoplasmic reticulum that contain calcium ions

Question 4

What determines contraction?

Answer 4

frequency of stimulation
CSA and length of muscle
rate which the muscle shortens

Question 5

What are the 3 fibre types?

Answer 5

Type I- slow oxidative fibres
Type 2a- fast, long anerobic
Type 2b- fast, short

Question 6

How are fibre types charachterised?

Answer 6

Enzyme dehydrogenase

gusto genial staining for myosin heavy chains

Question 7

What does a contraction form?

Answer 7

a sarcomere

contains myofilaments, H zone, Z lines, I band and A bands

Question 8

What is the process of muscle contraction?

Answer 8

AP to neuromuscluar junction
stimulate ACH and trigger AP down axon to a motor neuron
this activates sodium potassium pump
t-tubules lead AP to sarcoplasmic reticulum to release calcium ions
calcium now binds to troponin and uncovers binding site, causing modulation of tropomyosin
causes myosin to bind to actin due to power stroke with ATP, this moves Z lines together creating cross bridge cycling of actin and myosin making a contraction

Question 9

What are the types of force contraction?

Answer 9

isometric- produces greatest force
concentric- maximun unloading, shortening, so produces less force but at a fastest velocity
eccentric- the muscle elongates under tension due to an opposing force greater than the muscle generates