Exam 2: Muscle Physiology

motor unit cell

one motor neuron controlling many fibers; innervates muscle fibers; sends a signal to contract all muscle fibers within the unit

muscle twitch

contraction of an entire muscle in response to a stimulus that causes an action potential in one or more muscle fibers; 3 phases: latent period (time between stimulus and muscle response), contraction period, relaxation period

graded muscle responses

variations in muscle contractions in response to different stimuli; frequency, strength and change in stimulation leading to different degrees of contraction

stimulus frequency

rate at which stimulus are delivered to muscle or neuron; impacts force and duration of muscle contractions

stimulus strength

intensity or magnitude of stimulus like voltage or amplitude of electrical signal; rated to strength of neural stimulation affecting muscle contraction

motor unit summation

recruitment; activation of additional motor unit to increase force of muscle contraction based on intensity of stimulus; using all motor units

treppe

physiological state of the muscle affects how much work can be done; gradual increase in calcium availability and muscle responsiveness

sources of ATP for muscle metabolism

adenylate kinase; creatine kinase; anaerobic cellular respiration; aerobic cellular respiration

adenylate kinase

short burst energy demand; AMP + ATP = 2 ADP

creatine kinase

15 seconds of maximal contraction; direct phosphorylation causes rapid ATP generation from creatine phosphate as it donates phosphate to ADP; creatine restored to creatine phosphate during muscle inactivity

anaerobic cellular respiration

30-40 seconds max contraction; used glucose; 1 glucose yields net 2 ADP; pyruvic acid converted to lactic acid; oxygen debt

aerobic cellular respiration

minutes to hours of max contraction; uses carbohydrates (pyruvic acid), proteins, lipids; produces net 36 ATP; most useful

First Class Lever

seesaw; effort, fulcrum, load; may or may not have a mechanical advantage

Second Class Lever

wheelbarrow; fulcrum, load, effort; always has a mechanical advantage

Third Class Lever

lift; fulcrum, effort, load; no mechanical advantage; rapid movement

fulcrum

fixed pivot point where a movement occurs; joint

effort

force applied to move a body part; muscle contraction

load / resistance

weight or resistance that must be overcome or moved; weight of body part or external object

how are contractions regulated at the neuromuscular junction?

acetylcholinesterase terminates acetylcholine activity by breaking it down into acetate and choline, which prevents continuous stimulation; calcium ions are transported back to the sarcoplasmic reticulum, causing muscle fibers to relax; sodium leaves, membrane potential is reset