L12: Muscle Physiology

skeletal muscle tissue

attached to bone and skin, striated, voluntary, contract rapidly, fatigue easily, powerful, require nervous system sitmulation

cardiac muscle

only in heart, bulk in heart walls, striated, can contract without nervous system stimulation, involuntary (ANS control), subject to modulation form endocrine system

intercalated discs

structures that connect cardiac muscle cells to each other

smooth muscle tissue

in walls of hollow organs (e.g. stomach, uringary bladder, blood vessels and airways AKA bronchioles), not striated, can contract without nervous system stimulation, subject to modulation by endocrine system, involuntary (ANS control)

branching chains of cell, uni or binucleate; striated

what's the histology (cell shape and appearance) of cardiac muscle?

single, very long cylindrical multi, multinucleate cells with obvious striations

what's the histology of skeletal muscle?

single, fusiform, uninucleate, no striations

what's the histology of smooth muscle?

excitability

ability to receive and response to stimuli

contractibility

ability to shorten forcibly when stimulated

extensibility

ability to be stretched

elasticity

ability to recoil to resting length

movement of bones or fluids, maintaining posture and body position, stabilizing joints, heat generation

what are the 4 important functions of the muscle?

40%

skeletal muscle make up how many percent of body weight?

flexion

move bones closer together

extension

moves bones away from each other

biceps

when you bend your arm at the elbow, what muscle is the flexor?

triceps

when you extend your arm at the elbow, what muscle is the extension?

tendon

attach muscle to bone

ligaments

attach bone to bone

muscle cell (myocyte)

a long, tubular cell with a large number of mitochondria

fascicle

muscle fibers are sheathed in connective tissue with groups adjacent muscle fibers bundled together into units

collagen, elastic fibers, nerves, and blood vessels

what is found between fascicles?

sarcolemma

cell membrane of a muscle fiber

sarcoplasm

cytoplasm of a muscle fiber

sarcoplasmic reticulum

specialized endoplasmic reticulum of muscle cells

myofibrils

densely packed, rod-like elements that make up 80% of cell volume; determine how thick your muscles are

make more myofibril

how does your muscle cell regenerate when you "destroy your muscle to regenerate them" when you're working out?

wrapped around each myofibril

where is the sarcoplasmic reticulum?

store Ca 2+

what's the purpose of sarcoplasmic reticulum?

Ca 2+ ATPase

Enzyme facilitating Ca 2+ uptake in sarcoplasmic reticulum.

t-tubules

extension of sarcolemma that associate with ends (terminal cisternae) of sarcoplasmic reticulum

terminal cisternae

enlarged areas of the sarcoplasmic reticulum surrounding the transverse tubules.

increase surface area

how does t-tubules allow action potential to move from cell surface into interior of fiber?

allow action potential to move from cell surface into interior of fiber

what's the purpose of t-tubules?

myosin and actin

what proteins in the myofibril are contractile?

contractile proteins

myosin and actin

tropomyosin and troponin

what proteins in the myofibril are regulatory?

regulatory proteins

tropomyosin and troponin

titin and nebulin

what proteins in the myofibril are accessory?

accessory proteins

titin and nebulin

myosin

motor protein with ability to create movement

protein chains that intertwine to form a long tail and a pair of tadpole like heads

describe the appearance of a myosin?

thick filament

the thick myosin strands and their multiple heads projecting from the center of the sarcomere toward, but not all to way to, the Z-discs

actin

protein that makes up the thin filaments

g-actin

a globular subunit of F actin with an active site for binding a myosin head

f-actin

a fibrous protein made of a long chain of G actin molecules twisted into a helix; main protein of the thin myofilament

bounded to

where is troponin and tropomyosin in terms of actin?

myosin crossbridge

connects parallel thin and thick filaments

titin

a protein that positions the myosin filament to maintain equal spacing between actin filaments; stabilizes position of thick filament and its elasticity returns stretched muscles to their resting length

nebulin

an elastic protein lying along the thin filament and attaches to a z disk but doesn't extend to the M line

thick

titin is to what filament as nebulin is to thin filament

thin

titin is to thick filament as nebulin is to what filament

z disks

zigzag protein structures that serve as the attachment site for thin filaments; equivalent to m line for the thin filament

i band

lightest color bands of sarcomere and represent a region occupied by only thin filaments

a band

darkest sarcomere band and encompasses entire length of a thick filament; thick and thin filament overlap at outer edges

h zone

central region of A band is lighter than the outer edges of A band occupied by thick filaments only

m line

band represents protein that form the attachment stie for thick filaments; equivalent to Z disk for the think filament

stay the same

during muscle contraction, what happens to the A band ? (shorten, extend, or stay the same)

shorten

during muscle contraction, what happens to the I band and H zone ? (shorten, extend, or stay the same)

contraction

creation of tension in a muscle, an active process that require energy input from ATP

muscle tension

the force exerted by a contracting muscle on an object

relaxation

release of tension created by contraction

motor unit

a motor neuron and all the muscle cells it stimulates; when a somatic motor fires an action potential, the muscle fibers in motor unit contract;

multiple

one neuron innervates how many fiber(s) ? (one/multiple)

one

each muscle fiber is innervated by how many neuron(s)? (one/multiple)

neuromuscular junction

point of contact between a motor neuron and a skeletal muscle cell; converts acetylcholine signal from a somatic motor neuron into an electrical signal in the muscle cell

excitation contraction coupling

process in which muscle action potentials initiate calcium signals that in turn activate a contraction-relaxation cycle

contraction relaxation cycle

sliding filament theory of contraction

muscle twitch

simplest contraction resulting from a muscle fiber's response to a single action potential from motor neuron; one contraction-relaxation cycle

sliding filament theory

theory that actin filaments slide toward each other during muscle contraction, while the myosin filaments are still

end plate potential

the depolarizations of skeletal muscle fibers caused by neurotransmitters binding to the postsynaptic membrane in the neuromuscular junction

voltage gated Na+ channels

as action potential travels along the muscle fiber, what opens?

DHP receptor

nonconducting calcium channels in the T-tubule membranes of skeletal muscle cells, which act as voltage sensors in excitation-contraction coupling

DHP and RyR receptors

what two receptors converts electrical signal into a calcium signal

opens RyR Ca 2+ release channels in sarcoplasmic reticulum

once DHP senses an action potential, what does it to the RyR receptor?

Ca 2+ enter cytoplasm and binds to troponin, allowing actin-myosin binding

what happens when RyR Ca 2+ release channels open?

remove calcium from sarcoplasm

how do you end a contraction?

calcium ATPase

pumps Ca 2+ back into the lumen of SR, ending a contraction

sarcomere

contractile unit of a muscle fiber

tropomyosin

in sliding filament theory, when the muscle is relaxed, what is blocking the myosin head from grabbing onto actin?

bind to troponin

in sliding filament theory, what does calcium

troponin moves tropomyosin out of the way allowing myosin head to grab onto actin

in sliding filament theory, once calcium binds to troponin, what happens?

a phosphate bond from ATP breaks to provide energy for the myosin head to pull through the power stroke

how does myosin use ATP in the power stroke?

rigor state

myosin heads are tightly bound to G-actin without ATP

when ADP is released from myosin head

when does the tightest binding between myosin head and actin filament occur?

myosin head releases from actin

when ATP binds to a myosin head, what happens?

myosin hydrolyze ATP, weakly binding to actin

what happens in the myosin head when it's in the cocked position?

rigor mortis

stiffness of the body that sets in several hours after death

lack of ATP, thus myosin heads are forever tightly bound

what's the cause of rigor mortis?

cross bridge formation

activated myosin head binds to actin forming a cross bridge, inorganic phosphate is released, bond between myosin and actin becomes stronger

power stroke

ADP is released and activated myosin head pivots, sliding thin myofilament toward center of sarcomere

cross bridge detachment

when another ATP binds to the myosin head, the link between the myosin head and actin weakens, and myosin head detaches

reactivation of myosin head

ATP is hydrolyzed to ADP and inorganic phosphate. energy released during hydrolysis reactivates myosin head, returning it to cocked position

latent period

short delay between muscle action potential and muscle tension; events of excitation-contraction coupling; no muscle tension

latent period, period of contraction, period of relaxation

what are the 3 phases of muscle twitch?

period of contraction

cross bridge formation; tension increase

period of relaxation

Ca 2+ re-entry into SR; tension declines to zero

summation

if interval of time between action potentials is shortened, the muscle fiber does not have time to relax completely between 2 stimuli, resulting in a forceful contraction

tetanus

if action potentials continue to stimulate muscle fiber repeatedly at short intervals (high frequency), relaxation between contractions diminishes until the muscle fiber achieves a state of maximal contraction

unfused tetanus

fiber relax slightly between stimuli