muscle 1 and muscle physiology

how many human muscles are there

over 600

what precent of bodyweight do muscles take up

over half of bodyweight

what are the 3 kinds of muscle

smooth, cardiac, and skeletal

what is the major purpose muscles are specialized for

converting chemical energy into mechanical energy

what kind of muscle does this describe:

has narrow cylindrical fibers non-striated and uninucleate

occurs in walls of internal organs

is voluntary

smooth muscle

what type of muscle does this describe:

has striated, branched, generally uninucleated fibers

occurs in walls of heart

is involuntary

cardiac muscle

what type of muscle does this describe:

has striated, tubular, multinucleated fibers

is usually attached to skeleton

is voluntary

skeletal muscle

what are the functions of skeletal muscle?

body movement: move bones, make facial expressions, speak, breathe, swallow

maintenance of posture: stabilize joints, maintain body position

protection and support: package internal organs and hold them in place

regulating elimination of materials: circular sphincters control passage of material at orifices

heat production: help maintain body tempurature

what are the characteristics of skeletal muscle tissue? also the universal characteristics of muscle

excitability: ability to respond to a stimulus by changing electrical membrane potential

conductivity: involves sending an electrical change down the length of the cell membrane

contractility: exhibited when filaments slide past each other; enables muscle to cause movement

extensibility: ability to be stretched

elasticity: ability to return to original length following a lengthening or shortening

Each skeletal muscle is an _______. With multiple types of tissues working together: skeletal muscle fibers, connective tissue, blood vessels, and nerves.

organ

Muscle fibers bundled within a _____.

fascicle

a whole muscle contains many fascicles

a fascicle consists of many ____. A muscle fiber is a muscle cell.

muscle fibers

what are the 3 concentric layers of wrapping in skeletal muscle?

epimysium, perimysium, and endomysium

what layer of connective tissue concentric wrapping does this describe:

dense irregular connective tissue wrapping whole muscle

epimysium

what layer of connective tissue concentric wrapping does this describe:

dense irregular connective tissue wrapping fascicle

houses many blood vessels and nerves

perimysium

what layer of connective tissue concentric wrapping does this describe:

areolar connective tissue wrapping individual fiber

delicate layer for electrical insulation, capillary support, binding of neighboring cells

endomysium

what two ways can muscles be attached to muscle or bone (or skin to another muscle)

tendon

aponeurosis

tendon

cordlike structure of dense regular connective tissue

aponeurosis

thin flattened sheet of dense irregular tissue

deep fascia

dense irregular connective tissue superficial to the epimysium

sperates individual muscles, binds muscles with similar functions

superficial fascia

areolar and adipose connective tissue superficial to deep fascia

separates muscles from skin

what does this describe:

tendons bridge the gap between muscle ends and bony attachment

collagen of the endo-, peri-, and epimysium continuous

connects into the periosteum and the matrix of the bone

aponeurosis - broad flat sheet (palmar aponeurosis)

retinaculum - connective tissue band that separate tendons from muscles underneath

indirect attachment to bone

what does this describe:

little separation between muscle and bone

muscle seems to immerge directly from bone: margins of brachialis, lateral head of triceps brachii

direct (fleshy) attachment to bone

some muscles insert on the fascia or tendon of another muscle or collagen fibers of the dermis

distal tendon of biceps brachii inserts on the fascia of teh forearm

facial muscles insert in the skin

origin

belly

insertion

origin: bony attachment at stationary end of muscle

belly: thicker, middle region of muscle between origin and insertion

insertion: bony attachment to mobile end of muscle

is skeletal muscle vascularized

yes, has extensive blood vessels that deliver oxygen and nutrients, and remove waste products

is skeletal muscle innervated by somatic neurons

yes

axons of neurons branch, terminate at neuromuscular junctions

can allow for voluntary control of contraction

what are the parts of a muscle cell (fiber)

sarcoplasm (cytoplasm)

multiple nuclei: individual cells are multinucleated

sarcolemma (plasma membrane)

myofibrils

sarcoplasmic reticulum

myofilaments

what part of a muscle cell does this describe:

has typical organelles plus contractile proteins and other specializations

sarcoplasm/cytoplasm

what part of a muscle cell does this descrbe:

has T-tubules (transverse tubules) that extend deep into the cell

sarcolemma and its t-tubules have voltage-gated ion channels that allow for conduction of electrical signalsihas voltage-sensitive calcium channels that are responsive to the electrical signals (action potentials)

sarcolemma/plasma membrane

what part of a muscle cell does this describe:

hundreds to thousands per cell

bundles of myofilaments enclosed in sarcoplasmic reticulum

myofibrils

what part of a muscle cells does this describe:

internal membrane complex similar to smooth ER

terminal cisternae: blind sacs of sarcoplasmic reticulum; serve as reservoirs for calcium ions; two cisternae with t-tubule inbetween = triad

contains calcium pumps that import calcium; binds to calmodulin and calsequestrin

contains calcium release channels; triggered by electrical signal traveling down T-tubule, calcium released into sarcoplasm

sarcoplasmic reticulum

what part of muscle cells does this describe:

contractile proteins within myofibrils; two types: thick and thin

myofilaments

thick filaments

consist of bundles of many myosin protein molecules; myosin heads point toward ends of the filament

thin filaments

consist of bundles of many myosin protein molecules

twisted strands of F-actin; each F-actin composed of G-actin monomers

G-actin has myosin binding site where myosin heads attach

tropomyosin and troponin are present; regulator proteins

elastic filaments in myofilaments

titin (connectin)

attach thick filament to the z disc

prevent overstretching

at least 7 other accessory proteins

dystrophin is clinically important

describe the organization of a sarcomere

myofilaments arranged in repeating units called sarcomeres

composed of overlapping think and thin filaments

delineated at both ends by z-discs; specialized proteins perpendicular to myofilaments; anchors for thin filaments

the positions of thick and thin filaments gice rise to alternating I-bands and A-bands

what part of the sarcomere does this describe:

light-appearing regions that contain only thin filaments

bisected by Z disc

get smaller when muscle contracts (can disappear with maximal contraction)

I bands

what part of sarcomere does this describe:

dark-appearing region that contains thick filaments and overlapping thin filaments

contains H zone and M line

makes up central region of sarcomere

A band

what does this describe:

central portion of A bad

only thick filaments present; no thin filament overlap

disappears with maximal muscle contraction

H zone

what does this describe:

middle of H zone

protein meshwork structure

attachment site for thick filaments

M line

connectin

extends from z disc to m line

stabilizes thick filaments and has “springlike” properties (passive tension)

dystophin

anchors some myofibrils to carcolemme proteins

abnormalities of this protein cause muscular dystrophy

duchenne muscular dystrophy (DMD): most common type, defective or insufficient dystrophin; sarcolemma damaged during muscle contraction; problems begin early childhood; incurable, patients rarely live to be 30

muscle fibers have abundant ____ for aerobic ATP production

mitochondria

_____ within cells allows storage of oxygen used for aerobic ATP production

myoglobin

____ is stored for when fuel is needed quickly

glycogen

________ ________ can quickly give up its phosphate group to help replenish ATP supply

creatine phosphate

motor unit

a motor neuron and all the muscle fibers it controls

axons of motor neurons from spinal cord or brain innervate numerous muscle fibers

the number of fibers a neuron innervates varies: small motor units have less than 5 to allow for precise control of force output::: large motor units have thousands of muscle fibers to allow for production of large amounts of force but not precise control

fibers of a motor unit are dispersed throughout the muscle, not just in one clustered compartment

synaptic knob

expanded tip of the motor neuron axon

houses syaptic vesicles: small sacs filled with neurotransmitter acetylcholine

has Ca 2+ pumpsin plasma membrane; establish calcium gradient with more outside the neuron

has voltage-gated Ca2+ channels in membrane: Ca2_ flows into cell down conc, gradient if channels open

motor end plate

specialized region of sarcolemma with numerous folds

has many ACh receptors: plamsa membrane protein channels, opened by binding of ACh, allow Na+ entry and K+ exit

synaptic cleft

narrow fluid-filled space

seperates synaptic knob from motor end plate

acetylcholinesterase resides here: enzyme that breaks down ACh molecules

neuromuscular junction

location where motor neuron innervates muscle

usually mid-region of muscle fiber

has the following parts: synaptic know, synaptic cleft, motor end plate

muscle fibers exhibit resting membrane potential (RMP) 

fluid inside cell is negative compared to fluid outside the cell

RMP of muscle cell is about -90mV

RMP established by leak channels and Na+/K+ pumps (voltage-gated channels are closed)

Z line (disc)

anchor for thin filaments

M line

anchor for thick filaments

A band

dark area; extends length of the thick filaments

I band

light area; think myofilaments only (Z disc is center of I band)

H zone

thick myofilaments only (M line is center of H zone)

sarcomere

funcational unit of skeletal muscle; Z disc to Z disc; aligned end to end within myofibril

what does this describe:

makes up thick myofilaments (~300 myosin molecules per thick myofilament)

rodlike tail & 2 globular heads

heads contain binding sites for actin and ATP

myosin

what does this describe:

makes up thin myofilaments

made of G-actin (polypeptide subunits): contain binding sites for myosin heads; G-actin strung together; 2 twisting strands make up thin myofilaments

actin

what does this describe:

in thin myofilaments

rod-shaped protein that runs along actin

blocks myosin-inding sites on actin when muscle relaxed

tropomyosin

what does this describe:

in thin myofilaments

3 polypeptide subunit complex: 1 subunit boud to actin, 1 subunit bound to tropomyosin, 1 subunit binds Ca2+

troponin

what does this describe:

special type of smooth endoplasmic reticulum

stores and regulates intracellular Ca tha is necessary for contraction

has interconnecting tubules that surround each myofibril

most tubules run longitudinally alonf myofibril

sarcoplasmic reticulum

what forms a traid

sarcoplasmic reticulum: stores and regulates intracellular Ca

terminal cisternae: as each A band/I band junction

T tubules: invaginations of sarcolemma

integral proteins protruding from t-tubule into space between t-tubule and terminal cisternae act as ______ _______.

voltage sensors

integral proteins in terminal cisternae that form ___ channels

Ca

how do muscles contract

1 muscle fiber stimulated by nerve ending: causes change in membrane potential

2 generate and propagate electrical impulse: an electrical impulse has to be generated and propagated along the muscle fibers

3 increase in intracellular Ca: increase in intracellular Ca is the trigger for contraction to occur

it takes both ____ and ____ for contrcation of muslces to occur

nervous and muscular systems

4 major phases of contraction/relaxation

excitation: nerve action potentials→ musclel actions potentials

excitation-contraction coupling: series of events leading to changes in myofilaments

contraction: muscle fiber develops tension and may shorten

relaxation: muscle fiber relaxes and returns to its resting length

voltage (electrical potential)

a difference in electrical charge from one point to another

resting membrane potential

about -90mV

more anions on inside of plasma membrane compared to outside

excess sodium ions (Na+) in the extracellular fluid (ECF)

excess potassium ions (K+) in the intracellular fluid (ICF)

explain the steps of excitation

1: calcium enters at the synaptic knob; nerve signal travels down axon, opens voltage-gated Ca2+ channels, Ca2+ diffuses into synaptic knob, Ca2+ binds to proteins on surface of synaptic vesicles

2: release of ACh from synaptic knob; vesicles merge with cell membrane at synaptic knob: exocytosis; thousands of ACh molecules released from about 300 vesicles

3: binding of ACh at motor end plate; ACh diffuses across celft, binds to receptors, excites fiber

excitation contraction coupling

stimulation of the fiber is coupled with the sliding of filaments

coupling includes the end-plate potential (EPP), muscle action potential, and release of Ca2+ from the sarcoplasmic reticulum

describe end-plate potential (EPP)

ACh receptors are chemically gateed channels that open when ACh binds to them

Na+ diffuses into the cell through the channels, while a little K+ diffueses out

cell membrane breifly becomes less negative at the end-plate region

EPP is local but it does lead to the opening of voltage gated ion channels in the adjacent region of the sarcolemma

describe initiation and propagation of action potential along the sarcolemma and t-tubules

an action potential (AP) is a rapid rise (depolarization) and fall (repolarization) in the charge of the membrane: EPP reaches threshhold by causing nearby voltage-gated channels to open

Na+ diffuses into the cell through voltage-gated channels: cell depolarizes/becomes less negative eventually +30mV; this results in opening of adjacent voltage-gated Na+ channels and more Na+ entry; a chain reaction occurs as a depolarization is propogated down teh membrane and t-tubules

just after Na+ channels open, they close and voltage-gated K+ channels open; K+ diffuses out of the cell; cell repolarizes to -90mV; repolarization is then propogated down the membrane and t-tubules

while the cell is depolarizing and repolarizing it is in a refractory period-unable to respond to another stimulation

describe what happens when AP travels down t-tubules and the release of Ca2+ from sarcoplasmic reticulum

causes voltage-sensitive calcium channels in T-tubule membrane to trigger the opening of calcium release channels in SR terminal cisternae

Ca2+ interacts with myofilaments triggering contraction

cross-bridge cycling

when Ca2+ binds to troponin, it triggers crossbridge cycling

troponin and tropomyosin move so actin is exposed

cycling continues as long as Ca2+ and ATP are present

results in sarcomere shortening as Z discs move closer together

narrowing or disappearance of H zone and I band

thick and thin filaments remian the same length but slide past each other

4 repeating steps of crossbridge cycling

1: crossbridge formation: myosin head attaches to exposed binding site on actin

2: power stroke: myosin head pulls thin filament toward center of sarcomere; ADP and Pi released

3: release of myosin head: ATP binds to mysoin head casuing its release from actin

4: reset myosin head: ATP split into ADP and Pi by myosin ATPase; provides energy to cock the myosin head

describe steps of sliding filament model of contraction

1 thin filaments slide past thick filaments due to crossbridge formation

2 the I-bands shorten

3 sarcomeres chorten

4 H-zones disappear

5 A-bands move closer together but length is same

events of muscle relaxation

termination of nerve signla and ACh release from motor neuron

hydrolysis of ACh by acetylcholinesterase

closuer of ACh receptor causes cessation of end plate potential

no further action potential generation

closure of calcium channels in sarcoplasmic reticulum

return of Ca 2+ to sarcoplasmic reticulum by pumps

return of troponin to original shape

return of tropomyosin blockade of actin’s myosin binding sites

return of muscle to original position due to elasticity

electrical excitation of a muscle fiber follows all-or-none law

muscle fiber twitches do not

muscle twitch strength is dependent upon:

muscle size

fascicle arrangement

temporal summation

multiple motor unit summation

how stretched muscle was before it was stimulated

temperature of the muscles

lower than normal pH of sarcoplasm

state of hydration of muscle

fatigue

tetanus

spastic paralysis caused by toxin

blocks release of inhibitory neurotransmitter in spinal cord resulting in overstimulation of muscle

vaccination prevents this

botulism

muscular paralysis caused by toxin

prevents release of ACh at synaptic knobs

although toxin ingestion can be fatal, careful injections of it can treat spasticity or can be use for cosmetic purposes

muscle tension

tension is the force generated when a muscle is stimulated to contract

lab experiments measure tension and graph it (myogram)

muscle twitch

a breif contraction to a single stimulus: the minimum voltage that a triggers a twitch is the threshold

what are the periods of a twitch

latent period

contraction period

relaxation period

latent period

time after stimulus but before contraction begins

no change in tension

contraction period

time when tension is increasing

begins as power strokes pull thin filaments

relaxation period

time when tension is decreasing to baseline

begins with release of crossbridges

generally lasts a little longer than contraction period

recruitment or multiple motor unit summation

muscle is stimulated repeatedly

as voltage increase, more units are recruited to contract

it explains how muscles exhibit varying degerees of force: recruit few motor units to lift pencil vs many to life suitcase

above certain voltae, all units are recruited and so maximum contractions occurs regardless of how much higher voltage is

recruitement order is based on size of motor units: small first, large last

wave summation (temporal summation)

if stimulus frequency set at about 20 per second, relaxation is not comlpeted between twitches

contractile forces add up to produce higher tensions

incomplete tetany and tetany

if frequency is increased further, myogram exhibits incomplete tetany: tension increases and twitches partially fuse

if frequency is incresed furtehr still (40-50 per sec) myogram exhibits tetany:tension trace is a smooth line without relaxation

high frequency stimuli lead to fatigue, decrease tension production

muscle tone

resting tension in a muscle

generated by involuntary nervous stimulation of muscle

some motor units stimulated randomly at any time

change continuously so units not fatigued

do not generate enough tension for movement

decreases during deep sleep

isometric contraction

although tension is increased, it is insufficient to overcome resistance

muscle length stays the same

ex: holding a weight while arm doesnt move

isotonic contraction

muscle tension oversomes resistance resulting in movement

tone stays constant, but length changes

concentric contraction

muscle shortens as it contracts

eg: biceps brachii when lifting