Muscles

skeletal muscle

• type of muscle tissue

• has muscle fibers

• longest muscle cells

• striated

• voluntary control

• very adaptable

• multinucleated

cardiac muscle

• type of muscle tissue

• striated

• involuntary control

smooth muscle

• type of muscle tissue

• has muscle fibers

• found in walls of visceral organs

• force fluids and other substances through internal body channels

• involuntary control

epimysium

outer covering of dense irregular connective tissue that surrounds the entire muscle

perimysium

fibrous connective tissue that surrounds each fascicle

fascicle

group of muscle fibers

endomysium

wispy sheath of connective tissue that surrounds each individual muscle fiber

direct/fleshy attachments

attachment type where the epimysium of a muscle is fused to periosteum of bone or perichondrium of cartilage

indirect attachments

attachment type where the muscle’s connective tissue wrappings extend beyond the muscle either as a ropelike tendon or sheet like aponeurosis

sarcolemma

plasma membrane of muscle fibers

sarcoplasm

cytoplasm of a muscle cell that contains large amounts of glycosomes and myoglobin

glycosomes

granules of stored glycogen that provide glucose during muscle cell activity

myoglobin

red pigment that stores oxygen

myofibrils

cylindrical structure that spans entire length of muscle fiber; striated; made of myofilaments

myofilaments

protein filaments found in myofibrils

thin filament

filament composed primarily of actin

thick filament

filament composed primarily of myosin

sarcomere

organized repeating contractile units

H band

part of the sarcomere; lighter region on either side of the midline, contains only thick filaments

M line

part of the sarcomere; connects central portion of each thick filament

A band

part of the sarcomere; dense region of the sarcomere that contains thick filaments

I band

part of the sarcomere; contains thin filaments only, extends from A band to A band between sarcomeres

Z line

part of the sarcomere; marks the boundary between adjacent sarcomeres

cross bridge

linking of thick and thin filaments during contraction

G actin

active sites on actin where myosin head attaches during contraction

F actin

long actin filaments in thin filaments

tropomyosin

rod shaped protein that spirals around actin core of thin filament; blocks myosin binding sites in a relaxed muscle fiber

troponin

globular complex in thin filament that binds calcium ions

elastic filament

composed of titin; helps muscle spring back into shape after stretching and helps muscle resist excess stretching

titin

giant protein in elastic filaments; extends from Z disc to the thick filament and then runs within the thick filament to attach to M line

sarcoplasmic reticulum

elaborate smooth ER; interconnecting tubules surround each myofibril; regulates Ca2+

terminal cisterns

form larger, perpendicular cross channels at A band-I band junctions; paired

T tubules

elongated tubule of sarcolemma at each A band-I band junction; conduct impulses to the deepest muscle cell regions

triads

successive groupings of a terminal cistern, T tubule, and another terminal cistern

sliding filament model of contraction

idea that during contraction, the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree

excitation-contraction coupling

sequence of events by which transmission of an action potential along the sarcolemma causes myofilaments to slide

somatic motor neurons

nerve cells that activate muscle fibers

neuromuscular junction/end plate

axon terminal sent to single muscle fiber

synaptic cleft

space between axon and muscle fiber

acetylcholine

neurotransmitter released by motor neurons

acetylcholinesterase

enzyme that degrades ACh in the synaptic cleft

provide more surface area for more ACh receptors

junctional folds in the sarcolemma of the muscle fiber serve what purpose?

myasthenia gravis

autoimmune disease characterized by ptosis, difficulty swallowing and talking, and generalized muscle weakness due to a shortage of ACh receptors

ATP

what drives cross bridge detachment?

muscle tension

force exerted by a contracting muscle on an object

load

weight of object to be moved

isometric

contraction where muscle tension is developed but the load is not moved

isotonic

contraction where the muscle length changes and moves a load and thin filaments slide

motor unit

one motor neuron and all the muscle fibers it innervates

small

fine motor control muscles have ______ motor units

muscle twitch

motor unit’s response to a single action potential

myogram

recording of contractile activity of a muscle

latent period

phase of twitch myogram where first few milliseconds following stimulation when excitation-contraction coupling is occurring; no response is shown

period of contraction

phase of twitch myogram where cross bridges are active, the tracing rises to a peak, lasts 10-100ms

period of relaxation

phase of twitch myogram where tracing returns to a baseline, final phase, 10-100ms

temporal summation

second contraction occurs before muscle has completely relaxed meaning the muscle is already partially contracted and force generated is larger

unfused/incomplete tetanus

sustained but quivering contraction

fused/complete tetanus

plateau of muscle contractions that occurs when muscle tension reaches a maximum amount and all evidence of relaxation disappears

maximal stimulus

strongest stimulus that increases contractile force; point at which all muscle’s motor units are recruited

size principle

idea that motor units within the smallest muscle fibers are activated first, then larger ones as needed

concentric contractions

contraction type where muscle shortens and does work

eccentric contractions

contraction type where the muscle generates force as it lengthens

muscle tone

phenomenon of even relaxed muscles always being slightly contracted; does not produce active movements but helps stabilize joints and maintain posture

direct phosphorylation of ADP

15 second phase of muscle metabolism; readily reversible coupled reaction

creatine phosphate + ADP → creatinine + ATP

creatine phosphate

unique high energy molecule stored in muscles used to regenerate ATP

anaerobic pathway

30-40 second phase of muscle metabolism; more ATP is generated by breaking down glucose from the blood or glycogen stored in muscles; produces pyruvic acid which is converted to lactic acid

glycolysis

process of breaking down sugars

aerobic respiration

95% of ATP for muscle activity; hours long phase of muscle metabolism; occurs in mitochondria, requires oxygen, series of chemical reactions

aerobic endurance

length of time a muscle can continue to contract using aerobic pathways

anaerobic threshold

point at which muscle metabolism converts to anaerobic glycolysis

heat

most of the energy released during a muscle contraction is given off as what?

no

is smooth muscle multinucleate?

longitudinal layer

layer of smooth muscle where muscle fibers run parallel to the long axis of the organ and contraction causes organ dilation and shortening

circular layer

layer of smooth muscle where muscle fibers run circumference of organ and contraction causes constriction of the lumen and elongation of the organ

peristalsis

process of alternation between longitudinal and circular layers of smooth muscle to produce contraction/relaxation that mixes contents and propels contents through organ pathways

varicosities

bulbous swellings of ANS fibers that innervate smooth muscle

no

does smooth muscle have neuromuscular junctions?

diffuse junctions

wide synaptic cleft that varicosities release neurotransmitter into

no

does smooth muscle have t tubules?

caveolae

pouchlike infoldings that sequester bits of ECF containing a high concentration of Ca2+ close to the membrane

less, myosin heads along their entire length

what makes the thick filaments different in smooth muscle from skeletal muscle?

calmodulin

acts as calcium binding site in smooth muscle instead of troponin

dense bodies

cytoplasmic structures that act as anchoring joints for thin filaments and provide an attachment site for intermediate filaments that resist tension in smooth muscle

slow, synchronized

describe smooth muscle contraction

gap junctions

electrical connections that synchronize smooth muscle

pacemaker cells

set pace of contraction for an entire muscle sheet in smooth muscle

latch state

occurs when smooth muscle myofilaments attach together during prolonged contractions, may be maintained even after myosin is dephosphorylated

smooth muscle tone

moderate degree of contraction maintained in small arterioles and other visceral organs routinely

aerobic pathways

what kind of muscle metabolism does smooth muscle utilize?

stress-relaxation response

allows a hollow organ to fill or expand slowly to accommodate a greater volume without causing strong contractions that would expel its contents

unitary smooth muscle/visceral muscle

• type of smooth muscle

• cells are arranged in opposing sheets

• innervated by the ANS

• electrically coupled via gap junctions

• contract as a unit

• respond to chemical stimuli

multi-unit smooth muscle

• type of smooth muscle

• rarely have gap junctions and spontaneous depolarizations

• muscle fibers are structurally independent of one another

• richly supplied with nerve endings

• involve recruitment