5.b Types of Muscular Tissue

Skeletal Muscle

Act to produce and stop movement under voluntary control; striated

Skeletal Muscle Layers

EPE (mysia)

Epimysium

sheath of dense irregular connective tissue wrapping each muscle

Perimysium

arranges muscle fibers into bundles (fascicles)

Perimysium is common in the

limbs

Endomysium

thin CT layer collagen and reticular fibers that encase each muscle fiber; also found in smooth muscle

1st, ___ in the mysia intertwines with the ___ of a tendon/aponeurosis/fascia

collagen

2nd, Tendon fuses with the ___ coating the bone

periosteum

3rd, ___ created by muscular fiber contraction

tension

Sarcolemma

plasma membrane of skeletal ms. fibers

Sarcoplasm

cytoplasm of skeletal ms. fibers

Sarcoplasmic reticulum

specialized smooth endoplasmic reticulum storing, releasing, retrieving calcium ions

Actin and myosin

contractile myofilaments

Sarcomere

Bundled within the myofibril that runs the entire length of the muscle fiber and attaches to the sarcolemma

Striated Appearance

Actin and myosin arranged in sequential order from one end of the muscle fiber to the other

Troponin and tropomyosin

regulatory proteins

Z-discs/-lines

borders each sarcomere; anchor for actin myofilaments

Actin + troponin-tropomyosin complex

thin filament

Myosin + multiple heads

thick filament

ii. Cardiac Muscle

Highly coordinated wave-like contractions; Striated and organized into sarcomeres

Intercalated discs

part of the sarcolemma and contain gap junctions and desmosomes; connects cardiac muscles

Gap junctions

allow depolarizing current by cations to flow from one cardiac muscle to the next

Desmosome

anchors the ends of cardiac muscle fibers together so the cells do not pull apart during stress of individual fibers contracting

Electric coupling

joining between adjacent cardiac muscle fibers (via gap junctions) that allows quick transmission of action potentials and coordinated contraction of the heart

Syncytium

functional unit of a network of electrically connected cardiac muscles

Pacemaker cells

specialized cardiac ms cells that directly control heart rate (respond to ANS and hormones)

Functional syncytium

wave of contraction initiated by pacemaker cells that allow the heart to work as a unit

Autorhythmicity

self-excitable property of pacemaker cells that enables depolarization to threshold and fires action potentials on their own

Action potentials are longer compared to skeletal muscle due to “___” produced by calcium ion entry through voltage-gated calcium channels in the sarcolemma

plateus

iii. Smooth Muscle

do not have striations; in hollow organs

Smooth Muscles are found in

STOVE

Skin

goosebumps

Tracts

digestive, respiratory, genitaurinary

Organs

hollow; except heart

Vessels

veins, arteries, capillaries

Smooth Muscles are ___-shaped and have a single nucleus

spindle

Dense body

analogous to Z-discs of skeletal and cardiac ms fibers fastened to the sarcolemma and anchors actin, myosin, and thick and thin filaments

Alveoli

membrane indentations that allow calcium ions to be sequestered from the extracellular fluid

Calmodulin

regulatory protein present in smooth ms that replaces the cross-bridge formation function of troponin

Latch-bridges

cross-bridges between myosin and actin that keep thick and thin filaments linked together for a prolonged period without need for ATP (for maintenance of tone)

Varicosities

neurotransmitter-filled bulges along smooth ms axons that release NTs into the synaptic cleft

Smooth Muscle Organization

Single & Multiunits

Single unit

muscle fibers joined by gap junctions so that the muscle contracts as a single unit (in the walls of all visceral organs except the heart); also called visceral muscle; has stress-relaxation response (contraction to respond to filling); produce slow, steady contractions

Multiunit

rarely possess gap junctions; contraction confined to the cell (found in large BVs, respiratory airways, and eyes); triggered by ANS or hormones rather than stretching

Hyperplasia

ability of smooth muscle to produce more cells (e.g. uterine smooth muscle during puberty as a response to increased estrogen levels)

Regeneration

Satellite cells & Pericytes

Satellite cells

stem cells incorporated into muscle cells that help in repairing skeletal muscle cells and facilitate protein synthesis for repair and growth

Fibrosis

scar tissue formed when damaged muscle fibers are not repaired by satellite cells; cannot contract

Pericyte

cells in small BVs that allow smooth ms cells to regenerate and repair more readily than skeletal and cardiac ms