Muscle Functions: Movement, Stability & Heat

• Muscle functions include movement, stability, control of openings, heat production, and glycemic control.

Movement

• Allows to move from place to place
• Moves body parts and body contents in breathing, circulation, and digestion.
• In communication it includes speech, writing, facial expressions and other nonverbal communications

Stability

• Maintains posture by preventing unwanted movements
• Antigravity muscles prevent from falling over
• Stabilizes joints by maintaining tension

Control of Openings and Passageways

• Sphincters are internal muscular rings that control movement of food, blood, and other materials within the body.

Heat Production

• Skeletal muscles produce as much as 85% of body heat.

Glycemic Control

• Muscles absorb and store glucose which helps regulate blood sugar concentration within a normal range.

• There are about 600 human skeletal muscles.

• They constitute about half of body weight.

• Muscle tissue includes skeletal, cardiac, and smooth.

• Muscles convert chemical energy (ATP) into mechanical energy of motion.

• Myology is the study of the muscular system.

Epimysium

• It is a fibrous sheath surrounding the entire muscle.
• Its outer surface grades into fascia.
• Its inner surface projections form the perimysium.

Fascia

• It's a sheet of connective tissue that separates neighboring muscles or muscle groups, and separates them from the subcutaneous tissue.

Endomysium

• It's a thin sleeve of loose connective tissue around each fiber.
• It allows room for capillaries and nerve fibers.
• Provides a chemical environment for muscle fiber.

Perimusium

• It's a thicker layer of connective tissue that wraps fascicles.

• Fascicles: bundles of muscle fibers wrapped together.

• The perimysium carries nerves, blood vessels, and stretch receptors.

• The strength of a muscle and the direction of its pull are partly determined by the orientation of its fascicles

• Fusiform muscles are thick in the middle and tapered at each end.

• Parallel muscles have uniform width and parallel fascicles.

• Triangular (convergent) muscles are broad at one end and narrow at the other.

• Pennate muscles area feather shaped yielding a lot of torque

• Unipennate muscles have fascicles approaching the tendon from one side.

• Bipennate muscles have fascicles approaching the tendon on both sides.

• Multipennate muscles have bunches of feathers converging to a single point.

• Circular muscles (sphincters) form rings around body openings.

• Muscle compartment: A group of functionally related muscles enclosed by fascia.

• Muscle compartments contain nerves and blood vessels that supply the muscle group.

• Intermuscular septa are very thick fascia that separate one compartment from another.

• In Indirect attachment to bone tendons connect muscle to bone

• Collagen fibers of the endo-, peri-, and epimysium continue into the tendon and from there into periosteum and matrix of bone.

• Aponeurosis is where the tendon is a broad, flat sheet (palmar aponeurosis)

• Retinaculum are connective tissue bands that tendons from separate muscles pass under.

• Direct (fleshy) attachment to bone has little separation between muscle and bone, and the muscle seems to emerge directly from bone.

• Origin is used for the stationary attachment of the muscle.

• Insertion is used for the moving attachment of the muscle.

• Some anatomists prefer non-traditional descriptions of attachments by proximal vs. distal, superior vs. inferior

• Some muscles attach not on bone, but on the fascia or tendon of another muscle or on collagen fibers of the dermis

  • Facial muscles attach to skin

• Intrinsic muscles are entirely contained within a region, such as flexor digitorum brevis in the hand

• Extrinsic muscles act on a designated region, but has one attachment elsewhere.

  • Extrinsic muscles in the forearm attach to the fingers

• Action: effect produced by a muscle to produce or prevent movement

• There are four categories of muscle action, prime more, synergist, antagonist and fixator

Prime Mover (agonist)

• Muscle that produces the most force during a particular joint action

Synergist

• Muscle that aids the prime mover and may contribute additional force
• They modify the direction of movement, or stabilize a nearby joint

Antagonist

• Opposes the prime mover and prevents excessive movement

Antagonistic Pairs

• Muscles that act on opposite sides of a joint

Fixator

• Muscle that prevents movement of bone
• Innervation of a muscle refers to the identity of the nerve that stimulates it
• Knowing innervation enables diagnosis of nerve, spinal cord, and brainstem injuries from muscle tests.
• Spinal nerves arise from the spinal cord.
• Spinal nerves emerge through intervertebral foramina.
• Spinal nerves immediately branch into posterior and anterior rami.
• Spinal nerves innervate muscles below the neck.
• The plexus is a web-like network of spinal nerves adjacent to the vertebral column.
• Cranial nerves arise from the base of the brain.
• They emerge through skull foramina.
• Innervate the muscles of the head and the neck.
• Muscles in system receive about 1.24 L of blood per minute at rest which is one-quarter of the blood pumped by the heart
• During heavy exercise, total cardiac output rises and muscular system’s share is more than three-quarters (11.6 L/min)
• The capillaries branch extensively through the endomysium to reach every muscle fiber.
• The names of muscles comes from Latin
  • Depressor labii inferioris, flexor digiti minimi brevis
  • Tibialis anterior
  • Sternocleidomastoid
• Describes distinctive aspects of the structure, location, or action of a muscle