Muscle Physiology

action potential

nerve impulse

axon terminal

end of axon

neuromuscular junction

point of contact between a motor neuron and a single skeletal muscle fiber

synaptic cleft

space between axon terminal and muscle fiber

synaptic vesicles

hold ACh in the axon terminal

Acetylcholine

neurotransmitter released by axon terminal

motor end plate

highly folded area of the sarcolemma that houses ACh receptors

How is ACh released from the synaptic cleft?

exocytosis

What happens when ACh is released?

ACh receptors depolarize the motor end plate, sodium ions are released into the cell

repolarization

when the sarcolemma is restored to its initial polarized state. A muscle fiber cannot be stimulated until this is complete

"all or none"

a muscle fiber contracts completely or not at all

major functions of skeletal muscle

movement, maintain posture, stabilize joints, generate heat

excitability/irritability

ability to respond to a stimulus

contractility

the ability to shorten when adequately stimulated

extensibility

the ability to be stretched; muscle can be stretched beyond their normal resting length

elasticity

the ability of a muscle fiber to resume its resting length after being stretched

deep fascia

connective tissue that holds a muscle into position; separates it from adjacent muscles

epimysium

layer of connective tissue that surrounds the entire muscle; blends into tendons

perimysium

connective tissue that separates muscle tissue into fascicles

fascicles

group of muscle fibers

endomysium

a sheet of connective tissue that surrounds each muscle fiber

innervated

supplied by nerves

vascular

direct blood supply

sacrolemma

plasma membrane of muscle cell; surrounds myofibers

sarcoplasm

similar to cytoplasm, but contains large amounts of glycogen for energy

sarcoplasmic reticulum

similar to ER of cells; stores and releases calcium on demand when muscles are ready to contract

transverse tubules

channels that carry nerve impulses into a myofiber

mitochondria

muscle cells have many

myofibrils

rod like fibers in muscle cells made of myofilaments

myofilaments

actin and myosin

actin

thin filament, primarily this protein but also contains troponin and tropomyosin

a band

dark appearance, made of primarily thick filaments and some thin filaments

I band

light appearance - thin filaments only

z line

connects each myofibril to the next throughout the width of the muscle fiber

h zone

holds thick filaments together, only visible when the muscle fiber is relaxed

m line

divides an h zone

How can different combinations of muscle fiber contractions give differing responses?

Changing the frequency of muscle stimulation, changing the number of muscle cells stimulated at one time

muscle twitch

a single action potential from a motor neuron producing a contraction of muscle fibers in a motor unit; this does NOT produce significant muscle activity

rapid rate

nerve impulses are delivered at this rate, causing contractions to be summed together

unfused/incomplete tetanus

as simulations become more frequent, muscle contractions get stronger and smoother. The more action potential, the smoother the movement is

fused/complete tetanus

muscle is stimulated so rapidly that no evidence of relaxation is seen. Contractions are smooth and sustained, muscle force depends on the NUMBER of fibers stimulated.

isotonic contractions

myofilaments are able to slide past each other during contractions, the muscle shortens

isometric contractions

tension in the muscle increases, the muscle is unable to shorten

atrophy

muscle wasting away

direct phospholyration

creatine phosphate is found in muscle fibers and as ATP is depleted, interactions between CP and ADP regenerate more ATP in a fraction of second

aerobic respiration

cellular respiration, changing glucose and oxygen into water and carbon dioxide.

anaerobic respiration (glycolysis)

a process in which glucose is broken down in the absence of oxygen, resulting in the formation of 2 ATP molecules and lactic acid

muscle fatigue

Inability of muscle to maintain its strength of contraction or tension; may be related to insufficient oxygen, depletion of glycogen, and/or lactic acid buildup

isometric exercise

exercise in which muscle tension occurs without a significant change in muscle length

isotonic exercise

activity that combines muscle contraction with repeated movement