Anatomy Chapter 6: The Muscular System - Test

Muscle Types

• Three main types: skeletal, cardiac, smooth.

Prefixes Related to Muscles

• myo-: Refers to muscle.
• sarco-: Refers to flesh.
• epi-: Means above, upon, or over.
• iso-: Means equal or the same.
• peri-: Means around.

Skeletal Muscle

• Cells are large, cigar-shaped, and multinucleate.
• Known as striated and voluntary muscle, under conscious control.
• Contracts rapidly upon stimulation.

Connective Tissue in Skeletal Muscle

• Endomysium: Encloses a single muscle fiber.
• Perimysium: Wraps around a fascicle (bundle) of muscle fibers.
• Epimysium: Covers the entire skeletal muscle.

Smooth Muscle

• Lacks striations and is involuntary.
• Located in structures like pupils of eyes and arrector pili muscles.
• Contractions are slow and sustained.

Cardiac Muscle

• Striated and involuntary, found exclusively in heart walls.
• Uninucleate cells interconnect through gap junctions (intercalated discs).

Muscle Functions

• Maintains posture and body position.
• Stabilizes joints.
• Generates heat.

Microscopic Anatomy of Skeletal Muscle

• Sarcolemma: Specialized plasma membrane.
• Myofibrils: Long organelles vital for contraction, exhibit alternating dark (A band) and light (I band) bands.
• Sarcomere: Basic contractile unit; defined by Z discs.

Muscle Fiber Structure

• Composed of sarcolemma and myofibril.

Special Function of Skeletal Muscle

• Contractility: Ability to forcibly shorten in response to a stimulus.

Motor Unit

• Consists of one motor neuron and all skeletal muscle cells it stimulates.

Graded Responses

• Not all muscle fibers are activated simultaneously, allowing for variations in force and shortening.

Energy Sources

• ATP: Primary energy molecule utilized by the body.
• Aerobic Respiration: Requires oxygen; slower but more efficient, used during rest or light exercise.
• Anaerobic Respiration: Fast, less efficient, used during heavy exercise.

Types of Muscle Contractions

• Isotonic Contractions: Muscle shortens and movement occurs.
• Isometric Contractions: Muscle tension increases without shortening.

Resistance Exercise

• Enhances muscle size and strength.

Golden Rules of Skeletal Muscle Activity

• Muscles cross at least one joint.
• Muscle bulk typically lies proximal to the joint they cross.
• Muscles have at least two attachments: origin and insertion.
• Muscles can only pull, never push.
• During contraction, the muscle insertion moves toward its origin.

Types of Body Movements

• Muscles attached at two points; contraction leads to movement across joints.

Origin and Insertion

• Origin: Attachment to an immovable or less movable bone.
• Insertion: Attachment to a movable bone.

Specific Movements

• Flexion: Decreases the joint angle; brings bones closer together.
• Extension: Increases the angle between bones.
• Rotation: Movement of the bone around its longitudinal axis.
• Abduction: Movement of a limb away from the midline.
• Adduction: Movement of a limb toward the midline.
• Circumduction: Combination of flexion, extension, abduction, and adduction, with the proximal end stationary.
• Dorsiflexion: Lifting the foot so its superior surface points to the shin.
• Plantar Flexion: Pointing toes away from the head.
• Inversion: Turning the foot toward the midline.
• Eversion: Turning the foot away from the midline.
• Supination: Palm facing anteriorly.
• Pronation: Palm facing posteriorly with radius and ulna crossing.

Muscle Classifications

• Prime Mover: Muscle with primary responsibility for a specific movement.
• Antagonist: Muscle that opposes or reverses the action of a prime mover.
• Synergist: Muscle that assists the prime mover and reduces unwanted movements.
• Fixator: Specialized synergists that stabilize the origin of the prime mover.

Muscle Characteristics

• Classified by direction of muscle fibers, size, location, number of origins, origin and insertion locations, shape, and action.