Muscle Classification and Function

Muscle Classification

• Three types of muscles exist:
  • Cardiac muscle tissue is located in the heart.
  • Smooth muscle tissue is found in the walls of visceral organs and blood vessels.
  • Skeletal muscle tissue is within skeletal muscles.
  • Skeletal muscle makes up approximately 40% to 45% of total body weight.

Skeletal Muscle Characteristics

• Skeletal and cardiac muscle appear striated under a microscope, while smooth muscle does not.
• Skeletal muscle is under voluntary control.
• Smooth and cardiac muscle are not under voluntary control.
• A skeletal muscle connects to two bones, crossing the joint between them.
• Most skeletal muscles connect to two bones, but some connect to more than two, or to soft tissue instead of bone.
• Muscle contraction pulls on bony attachments, causing movement.

Muscle Function

• Skeletal muscles are the primary movers of the human body.
• Humans have 640 skeletal muscles, ranging in size and shape from the stapedius in the middle ear to the gluteus maximus.
• Muscles are positioned across joints and connected to bony levers.
• Specific muscles are adapted for appropriate range, direction, and force to meet needs.
• Functions of skeletal muscles include:
  • Producing movement
  • Stabilizing joints
  • Shaping body segments
  • Maintaining posture
  • Forming supportive walls

Muscular Fascia

• Muscular/deep fascia is the tough fibrous connective tissue that structurally organizes muscles.
• Collagen fibers are the major component, with elastin fibers present in smaller amounts.
• Fascia is consistently composed of collagen, but regions receive specific names based on location.
• Endomysium surrounds individual muscle fibers.
• Perimysium surrounds groups of muscle fibers, creating fascicles.
• Epimysium surrounds the entire muscle.
• Fascia blends, continuing beyond the muscle to connect it to bones.
• Fascial attachments transfer muscle contraction force to bones.

Muscle Fiber Interior

• Muscles are composed of fibers.
• Inner structures include nerves, blood vessels, and the sarcolemma, and various parts of the cytoplasm.
• Fibrous attachments, like tendons, connect muscles to bones.

Skeletal Muscle Properties

• Irritability: The muscle's ability to respond to stimuli.
• Contractility: The muscle's ability to produce tension between its ends.
• Relaxation: The opposite of contraction, releasing tension.
• Distensibility: The muscle's ability to stretch or lengthen up to a physiological limit without damage.
• Elasticity: The muscle's ability to return to its original length after stretching, as long as it hasn't been overstretched.

Muscle Classification

• 2 ways to classify muscles:
  • By myoglobin content
    • Red: contain more red fibers and are responsible for slow, sustained movements. - An example is anti-gravity muscles.
    • White: contain more white fibers and are responsible for rapid, short-duration movements.
  • By contractile activity
    • Tonic: low-level, prolonged contractions for posture maintenance.
    • Phasic: rapid, powerful contractions, involved in movement.
  • By the orientation of the pull to the joint structure: - Anterior vs. posterior - Possible axes of motion
  • By the number of joints crossed
    • One joint muscle
    • Two joint muscle
    • Multi-joint muscle

Explore the three types of muscles in the human body: cardiac, smooth, and skeletal. Understand their characteristics, control mechanisms, and roles in movement. This quiz covers essential information about muscle anatomy and physiology.