Muscle Morphology and Mechanics

Question 1

What shape is the pectoralis major?

Answer 1

Convergent

Question 2

What shape is the deltoid?

Answer 2

Multipennate

Question 3

What shape is the biceps brachii?

Answer 3

Fusiform

Question 4

Describe fasciculation and a disease where it becomes pathological.

Answer 4

Muscle twitching. Normal to have it slightly.

Pathological when excessive e.g. motor neuron disease

Question 5

Describe isotonic muscle contraction

Answer 5

Equal force, muscle changes in length to move the load.
Can be concentric: muscle shortens, e.g. to lift the load in the hand.
Or eccentric: muscle exerts force while being extended e.g. walking downhill. Linked to delayed onset muscle soreness.

Question 6

Describe isomeric muscle contraction

Answer 6

Constant length, variable extention.
e.g. hand grip
Has a profound effect on blood pressure

Question 7

Describe the difference between slow and fast twitch muscle fibres.

Answer 7

Slow - many mitochondria so not fatigueable

Fast - fewer mitochondria

Question 8

What is proprioception? Give a drug that can interfere with it.

Answer 8

Feedback control of movement, awareness of self.
Muscle spindles tell the brain about force and stretch. They are specialised muscle fibres with associated nerve endings, enclosed in a capsule.
Alcohol interferes with it.

Question 9

What is one motor unit?

Answer 9

A muscle fibre and the fibre it innervates. Signal molecules.

Question 10

Give an example of signal molecules used between the nerve end and muscle which is not a neurotransmitter.

Answer 10

Neurotropins e.g. neurotropin 3
Cytokines e.g. cardiotrophin-1
Insulin-like growth factor e.g. ILGF-1

Question 11

Where in the brain are motor control centres for the muscles found?

Answer 11

Cerebrum

Question 12

Describe hypotonia and give a disease which can cause it.

Answer 12

Loss of muscle tone.
Cerebral/spinal neural shock
Lesions of the cerebellum
Motor nerve lesions: polyneuritis
Primary degeneration of muscles: myopathy

Question 13

Describe excitation-contraction coupling

Answer 13

Action potential travels down t-tubules, activating the sarcoplasmic reticulum to release calcium ions.

Question 14

Describe spatial summation

Answer 14

More motor neurons are activated so more muscle fibres are recruited to develop an increased force.
Reflex pathway from muscle spindles, joint receptors and golgi tendon organs. Have a role in recruitment.

Question 15

Describe temporal summation

Answer 15

Contraction depends on the frequency of stimuli.

Question 16

What is electromyography used for?

Answer 16

In diagnosis of diseases disrupting muscle contraction, such as motor neuron disease.
Electrodes are places above or in the muscle to see if contraction and electrical signals match.

Question 17

What happens to calcium in muscle cells after contraction?

Answer 17

Most is pumped back into the sarcoplasmic reticulum, some binds calmodulin.

Question 18

State sources of energy for ATP that allows myosin head detachment from actin.

Answer 18

Stores, creatine phosphate, glycolysis, oxidative phosphorylation

Question 19

What causes muscle cramp?

Answer 19

Lactate build up

Question 20

What is peripheral fatigue?

Answer 20

A depletion of muscle glycogen which occurs within one minute if there is interrupted blood flow.

Question 21

Describe contracture

Answer 21

A state of continuous contraction. Due to depletion of ATP as myosin heads are unable to detach.
E.g. rigor mortis