Muscular Tissue: Intro & Anatomy

myology

study of the muscular system

movement, communication, stability, support, temperature regulation

what are the 5 functions of muscle?

excitability

muscle responds to stimulus (chemical messengers, stretching, etc.)

contractility

muscles shorten (contract) when stimulated

extensibility

muscle stretches between contractions

elasticity

muscle stretches and recoils (returns to resting length)

excitability, contractility, extensibility, elasticity

what are the four characteristics of muscle tissue?

flexes

when the bicep contracts, the tricep ______ and the forearm flexes

when the bicep ______, the tricep contracts and the forearm extends

skeletal, cardiac, smooth

what are the three types of muscle tissue?

skeletal

located in the skeleton, voluntary, striated, cylindrical, and multinucleate

cardiac

located in the heart, involuntary, striated, branched, one nucleus/cell

smooth

located in the walls of hollow organs, involuntary, non-striated, tapered, one nucleus/cell

muscle tissue

only contains cells + ECM

muscle organ

contains cells + ECM (tissue), blood vessels, nerves, and connective tissue

myofiber

smallest level of muscle anatomy, aka muscle cell, muscle fiber

muscle fascicle

bundle of muscle fibers (myofibers)

muscle

bundle of fascicles (organ)

endomysium

connective tissue wrapping, wraps around each myofiber

perimysium

connective tissue wrapping, bundles myofibers into fascicles

epimysium

connective tissue wrapping, surrounds entire muscle (organ)

sarcolemma

plasma membrane

sarcoplasm

cytoplasm/internal space, occupied mostly by myofibrils, glycogen (storage form of glucose), myoglobin (O₂ binding protein)

many

muscle cells have ____ mitochondria in order to make a lot of ATP for movement

sarcoplasmic reticulum

smooth ER, terminal cisterns, transverse (T) tubules, “triad”, major role is to regulate intracellular Ca⁺² levels

smooth ER

forms networks around myofibrils

terminal cisterns

dilated portions of SR running from one side of myofiber to other

transverse (T) tubules

between two terminal cisterns, infoldings of sarcolemma

triad

2 terminal cisterns + 1 T-tubule

myofibrils

bundles of parallel myofilaments (proteins), thick, thin, and elastic filaments

thick filament

bundle of myosin molecules, tail binds molecules together, head binds to ATP and actin (important for muscle contraction)

thin filament

2 intertwined strands of actin, fibrous actin (F actin) = chain of monomers called globular actin (G actin), tropomyosin and troponin

tropomyosin

blocks active sites so no muscle contraction can happen (where myosin will bind)

troponin

Ca-binding protein on tropomyosin

elastic filament

made of titin, anchors thick filament, allow for stretch and recoil

sarcomere

contractile unit of a muscle fiber, myofilaments are organized into this, made up of thick, thin, and elastic filaments

contract

when myofibrils ________, the entire cell shortens, pulls on tendon, which pulls on the bone creating movement

shorten

when a muscle contracts, the sarcomeres _______

Z

one sarcomere is the region between two _ discs

Z disc

border between 2 sarcomeres; anchors thin (actin) and elastic (titin) filaments

M line

bisects H band; links thick (myosin) filaments to each other

H band

ONLY thick filaments; disappears when sarcomere shortens (i.e., muscle contracts)

A band

length of a thick filament; partially overlapped by thin filaments

I band

distance between two adjacent A bands; bisected by Z disc; made of thin and elastic filaments (no thick filaments)

dark

the A band appears ____ because thick and thin filaments overlap

light

the I band appears _____ because it does not have thick filaments

sliding filament model

actin myofilaments slide over myosin to shorten sarcomeres → contraction!

actin and myosin do not change length

in fully contracted muscle: H band disappears, I band narrows, and there is no change to the A band