Biology 20 - Muscular System

skeletal muscle cells

are striated and tubular, have many nuclei, contract voluntarily, are usually attached to bones of the skeleton

smooth muscle cells

are non-striated, have one nucleus, contract involuntarily, are found in the walls of internal organs

cardiac muscle cells

are striated, tubular, and branched, have one nucleus, contract involuntarily, are found in the walls of the heart

purpose of muscles

contract to: move bones, to push blood around body, to push food through the digestive tract

actin

is a thin filament, long strand of protein

myosin

is a thick myofilament, contains “head”

sliding filament theory

1. When a myofilament contracts, the myosin head moves back toward the backbone

2. Because it is attached to the actin, it pulls the actin along with it

3. Using ATP, the myosin head will release and reposition

4. In this way, the actin is moving step by step along the myosin heads

5. The two myofilaments interact so that the Z lines (anchors for the actin) move closer together (contraction)

hypertrophy

an increase in muscle mass due to an increase in size of individual skeletal muscle fibres (not an increase in number of fibres)

atrophy

reduction in size, tone, and power due to injury or damage to nervous system

muscle fibre

single muscle cell, is responsible for muscle contractions

myoglobin

oxygen-binding pigment (similar to hemoglobin) in a skeletal muscle fibre

sarcolemma

membrane of a muscle fibre

sarcoplasm

cytoplasm of a muscle fibre

sarcoplasmic reticulum

smooth endoplasmic reticulum in a muscle fibre

myofibrils

organized bundles of myofilaments; cylindrical structures, as long as the muscle fibre itself

thick filament

fine myofilament composed of bundles of protein called myosin (about 11 nm in diameter)

thin filament

fine myofilament composed of strands of protein called actin (about 5 nm in diameter)