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The Muscular System. Chapter 6. Skeletal Muscle. Bundles of striped muscle cells Attaches to bone Often works in opposition. biceps. triceps. Tendons Attach Muscle to Bone. muscle. tendon. bursae. synovial cavity. TRICEPS BRACHII. Human Skeletal Muscles. BICEPS BRACHII.

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skeletal muscle
Skeletal Muscle
  • Bundles of striped muscle cells
  • Attaches to bone
  • Often works in opposition

biceps

triceps

tendons attach muscle to bone
Tendons Attach Muscle to Bone

muscle

tendon

bursae

synovial

cavity

human skeletal muscles

TRICEPS BRACHII

Human Skeletal Muscles

BICEPS BRACHII

PECTORALIS MAJOR

DELTOID

TRAPEZIUS

SERRATUS ANTERIOR

EXTERNAL OBLIQUE

LATISSIMUS DORSI

RECTUS ABDOMINUS

GLUTEUS MAXIMUS

ADDUCTOR LONGUS

BICEPS FEMORIS

SARTORIUS

QUADRICEPS FEMORIS

GASTROCNEMIUS

TIBIALIS ANTERIOR

skeletal muscle structure
Skeletal Muscle Structure
  • A muscle is made up of muscle cells
  • A muscle fiber is a single muscle cell
  • Each fiber contains many myofibrils

myofibril

sarcomere
Sarcomere

A myofibril is made up of thick and thin filaments arranged in sarcomeres

sarcomere

sarcomere

sarcomere

sarcomere

Z band

Z band

Z band

muscle microfilaments
Muscle Microfilaments

Thin filaments

  • Like two strands of pearls twisted together
  • Pearls are actin
  • Other proteins in grooves in filament

Thick filaments

  • Composed of myosin
  • Each myosin molecule has tail and a double head
sliding filament model
Sliding-Filament Model
  • Myosin heads attach to actin filaments
  • Myosin heads tilt toward the sarcomere center, pulling actin with them
sliding filament model9
Sliding-Filament Model

Sarcomere shortens because the actin filaments are pulled inward, toward the sarcomere center

contraction requires energy
Contraction Requires Energy
  • Muscle cells require huge amounts of ATP energy to power contraction
  • The cells have only a very small store of ATP
  • Three pathways supply ATP to power muscle contraction
atp for contraction
ATP for Contraction

ADP + Pi

Pathway 1

DEPHOSPHORYLATION

CREATINE PHOSPHATE

Relaxation

Contraction

creatine

Pathway 2

AEROBIC RESPIRATION

Pathway 3

GLYCOLYSIS ALONE

glucose from bloodstream and

from glycogen break down in cells

oxygen

nervous system controls contraction
Nervous System Controls Contraction
  • Signals from nervous system travel along spinal cord, down a motor neuron
  • Endings of motor neuron synapse on a muscle cell at a neuromuscular junction
role of calcium in contraction
Role of Calcium in Contraction
  • T tubules in the sarcoplasmic reticulum relay signal
  • Calcium ions are released
troponin and tropomyosin
Troponin and Tropomyosin
  • Lie in groove in actin filament
  • When muscle is relaxed, tropomyosin blocks myosin binding site
  • When troponin binds calcium ions, it changes shape and moves tropomyosin
  • Cross-bridge formation and contraction can now proceed
muscle tension
Muscle Tension
  • Is mechanical force a contracting muscle exerts on an object
  • For a muscle to shorten, muscle tension must exceed the load that opposes it
  • The load may be the weight of an object or gravity’s pull on the muscle
two main types of contraction
Two Main Types of Contraction
  • Isotonic contraction
    • Muscle visibly shortens; moves a load
    • Tension remains constant as the muscle changes length
  • Isometric contraction
    • Muscle does not change length
    • Tension is insufficient to move load
motor unit
Motor Unit
  • One neuron and all the muscle cells that form junctions with its endings
  • When a motor neuron is stimulated, all the muscle cells it supplies are activated to contract simultaneously
  • Each muscle consists of many motor units
twitches and tetanus

peak

relaxation

Twitches and Tetanus

stimulus

contraction starts

time

number of stimuli per second

number of stimuli per second

tetanic

contraction

twitch

repeated stimulation

two types of skeletal muscle
Two Types of Skeletal Muscle
  • Slow, or red, muscle
    • Many capillaries, high myoglobin
    • Contracts fairly slowly
    • Can sustain contraction
  • Fast, or white, muscle
    • Fewer capillaries, less myoglobin
    • Contracts quickly
    • Cannot sustain contraction
muscle fatigue
Muscle Fatigue
  • An inability to maintain muscle tension
  • Occurs after a period of tetanic contraction
  • Different types of muscle show different fatigue patterns