10-27 Ch10 Muscles - XLS GP_CBIO2200 Anatomy and Physiology I Fall 2026

Skeletal muscle

• Attached to bone

• Striated

• Voluntary

Smooth muscle

involuntary

non-striated

Cardiac muscle

loc: heart

striated

cells have irregular branching pattern

Linked by intercalated discs

Excitability

Responsiveness by generating voltage changes

excitiability

Muscles respond to chemicals, physical forces, charge change

Conductivity

• Local charge change triggers wave of change: action potentials traveling down the cell

Contractility

Muscle cells can contract: shorten

Extensibility

Muscle cells can extend: stretch

Elasticity

Muscle cells recoil to original length after stretch

Structural hierarchy of skeletal muscle

• Muscle

• Fascicle

• Muscle fiber

• Myofibril

• Sarcomere

• Myofilaments

Muscle

Organ

• Composed of fascicles

of muscle tissue

• Surrounded by epimysium (layer of

connective tissue)

• Tendons attach it to bone

Fascicle

• Bundle of muscle fibers

• Surrounded by perimysium

(layer of connective tissue

Muscle fiber

• Single muscle cell

• Very long, multiple nuclei

• Nuclei are pushed to

periphery

• Filled with myofibrils

Myofibril

• Bundle of protein myofilaments arranged into

sarcomeres

• Myofilaments: thread-like protein structures made

mostly of the proteins actin, myosin, and titin

Sarcomere

• Segment of myofibril

• Functional unit of muscle fiber

• Contractile unit of muscle fiber- the structure that

contracts

• Myofilament overlap in sarcomeres causes

banded/striated appearance

Myofilaments

• thread-like protein structures

• Form sarcomeres when arranged together bound to Z

discs and M lines

• Three types: Thick, thin, and elastic

Features of skeletal muscle

• Voluntary

• Striated- has visible parallel streaks

• Attached to bone

Connective tissue wrappings

• Endomysium

• Perimysium

• Epimysium

• Endomysium:

around muscle fibers

• Perimysium:

around muscle fascicle

• Epimysium:

around whole muscle

Tendons

• Attach muscle to bone

• Dense regular connective tissue

• Collagen continuous with epimysium,

periosteum of bone

• Collagen stretches and recoils slightly

Muscle fiber:

Skeletal muscle cell

Sarcolemma

• Plasma membrane of muscle fiber