Skeletal Muscles Overview

Study Notes

Endomysium: Delicate connective tissue membrane covering muscle fibers.
Perimysium: Tough connective tissue binding muscle fascicles.
Epimysium: Coarse sheath encompassing the entire muscle.
Tendons or Aponeuroses: The three fibrous components may form tendons or aponeuroses.
Muscle Size, Shape, and Fiber Arrangement:
- Size: Range from minuscule to extensive masses.
- Shape: Diverse shapes, including broad, narrow, long, tapering, short, blunt, triangular, quadrilateral, irregular, flat sheets, or bulky masses.
- Arrangement: Parallel to the long axis, converging to a narrow attachment, oblique, pennate, bipennate, or curved.

Origin: The point of attachment that remains stationary during muscle contraction.
Insertion: The point of attachment that moves during muscle contraction.

Prime Mover: Muscle or group of muscles directly responsible for specific movement.
Antagonist: Muscles directly opposing the prime mover's action, providing precision and control.
Synergists: Muscles contracting simultaneously with prime movers, improving efficiency and movement.
Fixator Muscles: Stabilize joints during movement.

First Class Lever: Fulcrum between the pull and the load. Less common in the human body.
Second Class Lever: Load between the fulcrum and the pull.
Third Class Lever: Pull between the fulcrum and the load. Most common, facilitating rapid and extensive movement.

Naming considerations: Location, function, shape, direction of fibers, number of heads and divisions, point of attachment, and relative size.

Muscles of Facial Expression: Unique attachment to deep skin layers of the face or neck.
Muscles of Mastication: Responsible for chewing movements.
Muscles that Move the Head: Paired muscles on each side of the neck, responsible for head movements.

Muscles of the Thorax: Vital for respiration.
Muscles of the Abdominal Wall: Arranged in three layers with fibers running in different directions, enhancing strength.
Muscles of the Back: Bend and stabilize the back.
Muscles of the Pelvic Floor: Support structures within the pelvic cavity.

Muscles Acting on the Shoulder Girdle: Muscles attaching the upper extremity to the torso, located anteriorly or posteriorly.
Muscles that Move the Upper Arm: Located around the shoulder synovial joint, allowing extensive movement.
Muscles that Move the Forearm: Located proximally to the elbow, attaching to the ulna and radius.
Muscles that Move the Wrist, Hand, and Fingers: Located on the anterior or posterior surfaces of the forearm.

Muscles that Move the Thigh and Lower Leg: Contribute to locomotion and stability.
Muscles that Move the Ankle or Foot:
- Extrinsic Foot Muscles: Located in the leg and exert their actions through tendons attaching to ankle and foot bones, responsible for dorsiflexion, plantar flexion, inversion, and eversion.
- Intrinsic Foot Muscles: Located within the foot, responsible for flexion, extension, abduction, and adduction of toes.

Good Posture: Body alignment that optimizes function and minimizes muscular effort for maintenance.
Posture Maintenance: Muscles exert a continuous pull opposite to gravity. Structures like the nervous system, respiratory, digestive, excretory, and endocrine systems also contribute to posture.

General Functions of Muscles: Movement of the body or parts, heat production, and posture maintenance.

Characteristics of Skeletal Muscle Cells:
- Excitability (Irritability): Ability to respond to stimuli.
- Contractility: Ability to contract, shorten, and produce movement.
- Extensibility: Ability to extend or stretch.