Understanding Muscle Anatomy and Function

Aug 30, 2024

Human Anatomy and Physiology 1: Muscles Lecture

Professor Mariah Evans

Overview

  • Course: BSC 2085
  • Topic: Muscles
  • Focus: Muscle contraction and the sliding filament theory

Muscle Contraction

Sliding Filament Theory

  • Involves actin (thin filament) and myosin (thick filament) sliding past each other to contract muscles.

Four Actions in Muscle Contraction

  1. Excitation
    • Nerve impulse required
    • Stimulation of voltage-gated calcium channels
  2. Excitation-Contraction Coupling
    • Acetylcholine (ACH) as the neurotransmitter
    • Binds to sarcolemia (muscle cell membrane)
    • Chemically-gated ion channels open
  3. Contraction
    • Actin and myosin form a cross-bridge
    • ATP required for head cocking and power stroke
  4. Relaxation
    • Acetylcholinesterase degrades acetylcholine
    • ATP needed to transport calcium back to sarcoplasmic reticulum

Process of Muscle Contraction

  • Nerve signal stimulates voltage-gated calcium channels.
  • Calcium enters the axon terminal causing the release of acetylcholine.
  • Acetylcholine binds to sarcolemia, opening sodium and potassium channels.
  • This causes an end plate potential (localized change in charge).
  • Action potential propagates down T-tubules, releasing calcium.
  • Calcium binds to troponin, exposing active sites on actin.
  • Myosin heads bind to actin, forming cross-bridges.
  • ATPase breaks down ATP, leading to muscle contraction via power stroke.

Muscle Types

  1. Skeletal Muscle
    • Voluntary, striated, attached to bones
    • Requires nerve impulse
  2. Cardiac Muscle
    • Striated, involuntary
    • Can contract without nerve stimulation
  3. Smooth Muscle
    • Non-striated, involuntary
    • Found in organs like the stomach, bladder

Muscle Tissue Characteristics

  • Excitability: Responds to stimuli
  • Contractility: Can shorten
  • Extensibility: Can stretch
  • Elasticity: Returns to original length after stretching

Functions of Muscle

  • Movement
  • Maintaining posture
  • Stabilizing joints
  • Generating heat

Muscle Structure

  • Epimysium: Covers entire muscle
  • Perimysium: Surrounds fascicles (bundles of muscle fibers)
  • Endomysium: Surrounds individual muscle fibers

Neuromuscular Junction

  • Site where nerve meets muscle
  • Involves acetylcholine crossing synaptic cleft, binding to sarcolemia

Sarcomere

  • Contractile unit of muscle
  • Contains actin and myosin
  • Z-line to Z-line defines a sarcomere

Important Concepts

  • Muscle contraction starts with calcium entering axon terminal
  • Relaxation involves breakdown of acetylcholine and calcium reuptake
  • Understanding muscle physiology is crucial for broader physiology topics

Applications and Examples

  • Pesticides cause spastic paralysis via acetylcholinesterase inhibitors
  • Tetanus (lockjaw) from overstimulation of muscles
  • Muscle relaxants (e.g., Kurari) compete with acetylcholine

Study Tips

  • Review videos and materials provided for a deeper understanding
  • Understanding muscle contraction will aid in understanding other body systems