Question

Anatomy Tutorial: Muscles pt. 2

Answer 1

\({\bf{Terminology:}}\)
- motor unit: one motor neuron and the muscle fibers it innervates
- muscle twitch: one contraction in response to one stimulus
- recruitment: steady increase in tension caused by increasing number of active motor units
- muscle tone: resting tension
- muscle spindles: control muscle tone
- hypertrophy: increase in muscle size (not due to cell division/tumors, etc.)
- atrophy: decrease in muscle size

\({\bf{Fast~Twitch/~Slow~Twitch:}}\)
fast:
- white (think white lightning)
- dense myofibrils
- glycogen
- few mitochondria
- large
- anaerobic metabolism
- high tension
- carbs are main source of energy

slow:
- red (think of a stop sign, which you have to slow down and stop)
- small
- slower to exhaust
- aerobic metabolism (red blood cells/myoglobin)
- more mitochondria
- low tension
- high myoglobin
- high capillary supply
- can use carbs, fats, protein as energy

Answer 2

\({\bf{Muscle~Organizations:}}\)


- parallel: fibers run along longitudinal axis, ex: brachii radialis
- convergent: muscles meet at a central tendon/ralphe, ex: pectoralis
- pennate: muscles are attached to a tendon and branch off diagonally (unipennate, bipennate, multipennate), ex: extensor digitorum. to remember the name, it looks like a feather "pen"nate
- sphincter: muscles are arranged in a circle, ex: orbicularis oris

Answer 3

Adapted from Human Anatomy, Martini, et. al. 9th edition