physiology - chap 12

Whole muscle is divided into columns called

fascicles

Each fascicle is made of many

muscle fibers

muscle fibers =

muscle cells

Muscle fibers are surrounded by the

sarcolemma

what are Muscle fibers are composed of

myofibrils

Myofibrils are composed of

protein filaments

what are protein filaments called

myofilaments

Action potential from neuron stimulates

muscle to contract

Synaptic vesicles at the NMJ contain

acetylcholine

Synaptic vesicles at the NMJ contain acetylcholine that stimulates the production of

an action potential in the postsynaptic membrane

During neuromuscular junction Action potential arrives at NMJ causing which channels to open

voltage-gated Ca2+ channels

during neuromuscular junction Ca2+ stimulates what

Ach release

during muscular junction Ca2+ stimulates Ach release from vesicles, and into what

synaptic cleft

during neuromuscular junction Ach binds to what channels

ligand gated Na+ channels

during muscular junction Ach binds to ligand-gated Na+ channels on postsynaptic membrane, causing channels to

open

during muscular junction Ach unbinds from the channel, which then

closes

during muscular junction Acetylcholinesterase removes what from synaptic cleft

ach

during muscular junction Acetylcholinesterase removes Ach from synaptic cleft by

breaking it down into acetic acid and choline

during muscular junction Choline is brought back to where

presynaptic terminal

during muscular junction Choline is brought back to presynaptic terminal to be recycled to make

Ach

Excitation-Contraction Coupling is a mechanism where

an action potential causes muscle fiber contraction

Sarcolemma

plasma membrane

sarcoplasm

cytoplasm

transverse tubule (t-tubule)

extensions of sarcolemma

sarcoplasmic reticulum

modified er

Terminal cisternae

expanded portions of SR

Action potential from NMJ travels along

sarcolemma of skeletal muscle

Depolarization also travels down where

the t-tubules

Depolarization also travels down the T tubules and

opens voltage-gated Ca2+ channels

Depolarization of T tubules causes

Ca2+ release channels in SR to open

Ca2+ diffuses from

SR in sarcoplasm

Ca2+ binds to

troponin

Ca2+ binds to troponin and This allows

tropomyosin to move, exposing active site of G actin

Myosin heads bind to

active sites forming cross-bridges

In a relaxed muscle Actin and myosin myofilaments

overlap slightly

In contracted muscle Myosin and actin filaments do not

shorten in length

In contracted muscle Z discs are brought closer together because

actin slides past the myosin filaments

During muscle relaxation,Ca2+ moves back into what

sarcoplasmic reticulum

During muscle relaxation, Ca2+ moves back into sarcoplasmic reticulum by which type of transport

active transport

During muscle relaxation Ca2+ moves back into sarcoplasmic reticulum by active transport via

Ca2+-ATPase pumps or out of cell by Ca2+-Na+ cotransport

During muscle relaxation, Ca2+ moves away from

troponin-tropomyosin complex

Muscle Twitch

Muscle contraction in response to a stimulus that causes action potential in one or more muscle fibers

phases of muscle twitch

Lag or latent Contraction Relaxation

Treppe

an increase in the strength of successive contractions

when does treppe occur

muscle rested for prolonged period

Summation

2 or more twitches which build to raise tension

Muscle does not completely

relax before the next stimulus

As the frequency of action potentials increase what happens to the frequency of contraction

increases

Incomplete tetanus

muscle fibers partially relax between contraction

Complete tetanus

no relaxation between contractions

Recruitment

larger motor units are activated when contractions of greater strength are required

Tonus

maintenance of a partially contracted state

Isometric

no change in length but tension increases

Isotonic

change in length but tension constant

Concentric

overcomes opposing resistance and muscle shortens

Eccentric

tension maintained but muscle lengthens

ATP provides immediate energy for

muscle contractions and produced from three sources

Aerobic respiration

Requires oxygen and breaks down glucose to produce ATP, carbon dioxide and water

Creatine phosphate

During resting conditions stores energy to synthesize ATP

Anaerobic respiration

Occurs in absence of oxygen and results in breakdown of glucose to yield ATP and lactic acid

Are Type I fibers (slow twitch) aerobic or anerobic

aerobic

What does it mean for Type I fibers to be highly aerobic

more mitochondria, more fatigue-resistant than fast-twitch

Are type IIx fibers aerobic or anerobic

anaerobic

Type IIa fibers (fast oxidative glycolytic) are

have qualities of both I and IIx

What does it mean for Type IIx fibers (fast twitch) to be highly anaerobic;

respond rapidly to nervous stimulation, fewer and smaller mitochondria than slow-twitch

Muscle spindle apparatus (proprioceptor) what do they monitor

muscle length

Extrafusal fibers

fibers outside of muscle spindle

what are extrafusal fibers innervated by

alpha motor neurons

Intrafusal fibers

fibers inside the muscle spindle

Anulospiral sensory endings

sends information to CNS

what are intrafusal fibers innervated by

gamma motor neurons

Monosynaptic Reflex

Sensory neuron directly synapses with motor neuron in CNS

example of a monosynaptic reflex

knee-jerk reflex

Disynaptic Reflex

two synapses are crossed in the CNS

Golgi tendon organ

monitors muscle tension

Inhibitory reflex regulates muscle

contraction force

Reciprocal Innervation

dual stimulatory and inhibitory activitye

example of reciprocal innervation

Muscle spindle activation causes the agonist to contract AND the antagonist to relax

Crossed-Extensor Reflex

Stimulation will affect also affect the contralateral side

example of crossed-extensor reflex

Stepping on a tack will stimulate muscles to withdraw foot AND also stimulate muscles on the opposite leg to support weight imbalance

Caveolae:

indentations in sarcolemma; may act like T tubules

Dense bodies

instead of Z disks as in skeletal muscle

During smooth muscle contraction Ca2+ binds to what

calmodulin

during smooth muscle contraction Ca2+ binds to calmodulin which regulates

myosin kinase

during smooth muscle contraction what is relaxation caused by

enzyme myosin phosphatase

Myocardial cells

Striated (Sarcomeres), branched, gap junctions

how do myocardial cells behave

as a single unit

myocardial cells automatically produce what

action potentials

myocardial cells have a longer what

duration and longer refractory period