Skeletal Muscle System Overview

Introduction to the Skeletal Muscle System

• Focus on skeletal muscle in contrast to smooth muscle.
• Functions of skeletal muscle include:
  • Movement: Enables bodily motion.
  • Posture maintenance: Keeps the body upright.
  • Protection: Shields internal organs.
  • Support: Provides structural support.
  • Regulation of material elimination: Can control elimination through sphincters.

Sphincters and Control

• Explanation of sphincters:
  • Internal sphincter: not under voluntary control.
  • External sphincter: under voluntary control (e.g., bladder control).
• Example situation: Holding in urine during inappropriate times (e.g., teaching, testing).

Heat Production and Thermoregulation

• Skeletal muscles contribute to heat production (thermoregulation).
• Muscle contraction (shivering) is a response to cold.

Characteristics of Skeletal Muscle

Key Vocabulary Terms:

1. Excitability:

   • The capacity to respond to electrical signals.

2. Conductivity:

   • The ability to transmit electrical impulses across a membrane.
   • Difference from excitability: Conductivity involves the movement of the impulse.

3. Contractility:

   • The ability to shorten and generate force (e.g., flexing a bicep).
   • Visible muscle contractions at a macro level and movement of proteins at a cellular level.

4. EMG (Electromyography):

   • Measures electrical activity in skeletal muscles, indicating excitability.

5. Extensibility:

   • The ability of a muscle to stretch.

6. Elasticity:

   • The ability to return to original length after stretching.

Muscle Structure Organization

• Breakdown of skeletal muscle from macro to micro:
  1. Muscle (e.g., bicep): The whole structure.
  2. Fascicle: Bundles of muscle fibers within the muscle.
  3. Muscle Fibers: Individual muscle cells (also called fibers).
  4. Myofibrils: Smaller structures within fibers where muscle contraction occurs.
  5. Myofilaments: The smallest components (actin and myosin), responsible for contraction.

Connective Tissue Layers in Muscle

• Three layers of connective tissue surrounding muscle structures:
  1. Epimysium: Surrounds the entire muscle (outer layer).
  2. Perimysium: Surrounds each fascicle (middle layer).
  3. Endomysium: Surrounds individual muscle fibers (inner layer).

Muscle Attachments

• Two main types of muscle attachment:
  1. Tendon: Connects muscle to bone, typically cylindrical in shape.
  2. Aponeurosis: Connects muscle to muscle or other body parts, flattened or sheet-like in shape.

Tendons vs. Ligaments

• Tendon:
  • Connects muscle to bone.
• Ligament:
  • Connects bone to bone.
  • Important distinction to remember: tendons are used for muscle attachment.

Blood and Nerve Supply to Muscles

• Muscles require a blood supply for oxygen during contraction and to eliminate waste products such as carbon dioxide.
• The necessity for a nerve supply to facilitate muscle contraction and response.