Muscle Structure and Function

Skeletal muscle structure

epimysium

fasicles

perimysium

endomysium

Smooth muscle structure

non-striated

lacks sarcomeres

gap junctions

greater concentration of actin > myosin

Cardiac muscle structure

striated

mononucleated

branched

intercalated discs (gap junctions)

__ attach muscles to bone

tendons

origin/insertion is more movable portion

insertion

what moves toward what between origin/insertion

insertion is pulled towards origin

how do muscles cause bones to move

contracting muscle causes tension on tendons that are attached to bones

what is the agonist muscle

prime mover of any skeletal movement

muscles that act on the same joint to produce opposite actions

antagonists

muscles are divided into columns called

fasicles

which connective tissue surrounds fasicles

perimysium

what surrounds muscle fibers

endomysium

plasma membrane of the muscle cell

sarcolemma

what is unique about muscle cells

multinucleated and striated

components of neuromuscular junction

synaptic ending of motor neuron

muscle fiber

specializations of sarcolemma

where is the motor end plate

on the sarcolemma

neostigmine inhibits __

Ach esterase

what is affected in myasthenia gravis

nicotinic acetylcholine receptors on the postsynaptic membrane

how does curare affect the NMJ

binds to and blocks nicotinic receptors on postsynaptic membrane

which muscle types are striated

skeletal and cardiac

unique features of cardiac muscle

intercalated disc

myofibrils are made of _

myofilaments

myofilaments are composed of _

thick and thin filaments

A band contains

thick filaments (myosin)

which band represents the portion where actin and myosin don’t interact

H band

I band

contains thin filaments

where does actin attach

Z disc

what marks the length of the sarcomere

from 1 Z disc to another

M lines function

structural proteins that anchor myosin during contraction

titin function

attaches myosin to Z disc and contributes to elastic recoil of muscle

each myosin head contains

ATP binding site that acts as an ATPase

what regulates cross bridge attachments in skeletal/cardiac

troponin-troponomyosin

troponomyosin function

blocks the binding sites on ACTIN so myosin cannot bind to it

when is troponomyosin blocking myosin binding sites

during low Ca++ concentrations

Ca++ binds to __ in skeletal/cardiac muscle

troponin

What causes troponomyosin to stop blocking

Ca++ binds to troponin, which causes conformational change in troponomyosin

general storage site for Ca++ in muscle cell

sarcoplasmic reticulum

specific storage site for Ca++ in muscle cell

terminal cisterna of the sarcoplasmic reticulum

whta part of the skeletal muscle is excitable

sarcolemma

what transports APs from the sarcolemma

T tubules

Ca++-ATPase pumps function

pump calcium back into the sarcoplasmic reticulum

is ATP needed for relaxation or contraction

both!

lack of ATP causes increase in muscle tone because

crossbridges never unbind (new ATP not there to cause myosin release of actin)

Ca++ is never pumped back into the sarcoplasmic reticulum

a single rapid contraction and relaxation of muscle fibers is called __

twitch

when does complete tetanus occur

stimulation frequency is so fast that no muscle relaxation occurs

for muscle to shorten, force generated must be __

greater than the load

isometric contraction

muscle length remains constant during force applied during contraction

isotonic contraction

force remains constant, length of the muscle changes

concentric contraction

muscle length shortens

eccentric contaction

muscle length increases because load > force

factors that influence muscle contraction strength

frequency of stimulation

thickness of each muscle fiber

initial length of muscle fiber

energy comes __ for the first 45-90 seconds of exercise

anaerobically

maximum ability of cardiovascular system to transport and utilize oxygen

maximum oxygen uptake

lactate threshold

% of max O2 uptake at which there is a significant rise in blood lactate levels

how does glucose get into muscle cells

GLUT4

source of energy for light exercise

fatty acids

source of energy for moderate exercise

fatty acids and glucose/glycogen

source of energy for heavy exercise

glucose/glycogen

what does the liver do during heavy exercise

increases glyocgenolysis

source of high energy phosphate to regenerate ATP

phosphocreatine/creatine phosphate

which enzyme converts between creatine phosphate and creatine

creatine kinase

what does change between creatine and phosphocreatine produce

ATP/ADP

heavy exercise uses a greater percentage of _ as an energy source

glycogen

why is there a slow decline of oxygen uptake after exercise

oxygen debt

restore cellular energetic stores

O2 needed for anaerobic exercise

types of skeletal muscle fibers

slow twitch

fast twitch

fibers found in slow twitch muscle

Type I

name for type I fibers

slow oxidative/slow twitch

what gives slow twitch fibers red color

myoglobin

types of fast twitch muscle fibers

Type IIX

Type IIA

type of metabolism used by fast glycolytic fibers

anaerobic

effect of endurance training on skeletal muscle

decreased type IIX fibers

increased type IIA fibers

3 categories of muscular dystrophy

structural

metabolic

excitation-contraction coupling

which cells assist during muscle injury

satellite cells

how do satellite cells find injured muscle fibers

chemotaxis

classic indicator of a recently healed muscle fiber

nuclei is closer to the center

what happens to satellite cells with aging

number and function decrease

significance of intercalated discs

allow action potentials to spread throughout cardiac muscle

what joins cardiac muscle together

intercalated discs

what is unique about smooth muscle contraction

lacks troponin/troponomyosin

smooth muscle contraction pathway

Ca++ enters through voltage gated channels in plasma membrane

Ca++ binds calmoudin

Ca/calmoudin complex activates myosin light chain kinase

myosin becomes phosphorylated and active

myosin crossbridges with actin

what causes relaxation of smooth muscle

myosin is dephosphorylated by myosin phosphatase

which type of muscle is myogenic

cardiac and single unit smooth muscle

how is multiunit smooth muscle stimulated

nerve stimulation by ANS

I band marks what space

space between the end of myosin in 1 sarcomere and the beginning of myosin in the next sarcomere (space contains actin)

which bands shrink during muscle contraction

H band

I band

space between Z discs

which way does actin move during contraction

toward the midline

when is myosin able to bind actin

after ATP has been hydrolyzed to ADP and Pi

what happens when myosin binds actin

inorganic phosphate is released —> power stroke

what happens after power stroke

ADP releases from myosin

what causes myosin to unbind from actin

new ATP molecule binds to myosin

AP traveling in the T tubules has what effect

Ca++ gets released from terminal cisternae

type of receptor channel on T tubule

dihydropyridine receptor

receptor channel found on sarcoplasmic reticulum

ryanodine