10.1 - Structural & Functional Organization of Muscles

three types of muscle

skeletal, cardiac, and smooth muscle

fundamental purpose of muscle

to convert the chemical energy of ATP into the mechanical energy of motion

six functions of muscles

movement, stability, control of body openings and passages, heat production, hormone secretion, and glycemic control

movement (function of muscle)

muscles enable us to move from place to place, move individual body parts, move body contents, and serve various roles in communication

stability (function of muscle)

muscles maintain posture by preventing unwanted movements and stabilize joints by maintaining tension on tendons and bones

antigravity muscles

muscles that resist the pull of gravity and prevent us from falling or slumping over, at least part of the time

control of body openings and passages (function of muscle)

muscles are involved in the mouth for speech and food intake, eyelid and pupil to regulate the admission of light into the eye, internal muscular rings to control the movement of materials within the body, and urethra and anus to control waste elimination

heat production/thermogenesis (function of muscle)

the skeletal muscles produce 20 to 30% of the body’s heat at rest and up to 85% during exercise

hormone secretion (function of muscle)

exercised muscles secrete hormones called myokines that stimulate glucose synthesis by the liver and the breakdown of visceral fat

glycemic control (function of muscle)

the skeletal muscles absorb, store, and use a large share of one’s glucose and play a highly significant role in stabilizing its blood concentration

muscular system

refers only to skeletal muscles

myology

study of skeletal muscles

skeletal muscles consist of…

muscular tissue, connective tissue, nerves, and blood vessels

connective tissue components of skeletal muscles (small/deep -> large/superficial)

endomysium, perimysium, epimysium, and fascia

endomysium

thin sleeve of loose connective tissue that surrounds each muscle fiber

endomysium (function)

creates room for blood capillaries and nerve fibers to reach every muscle fiber, ensuring that no muscle cell is without stimulation and nourishment; provides the extracellular chemical environment for the muscle fiber and its associated nerve ending

excitation of a muscle fiber

based on the exchange of calcium, sodium, and potassium ions between the endomysial tissue and the nerve and muscle fibers

perimysium

thicker connective tissue sheath that wraps muscle fibers together in bundles called fascicles

fascicles

bundles of 20 to 60 muscle fibers visible to the naked eye as parallel strands

perimysium (function)

carries the larger nerves and blood vessels as well as stretch receptors called muscle spindles

epimysium

fibrous sheath that surrounds the entire muscle

epimysium (outer surface)

grades into the fascia

epimysium (inner surface)

issues projections between the fascicles to form the perimysium

fascia

sheet of connective tissue that separates neighboring muscles or muscle groups from each other and from the subcutaneous tissue

fascia (function)

packages groups of functionally related muscles into muscle compartments; stands between the muscles and the overlying hypodermis and skin

fusiform muscles

relatively strong muscles thick in the middle, with fascicles converging on each tapered end

fusiform muscles (example)

biceps brachii of the arm, gastrocnemius of the calf

muscle strength is proportional to…

the diameter of a muscle at its thickest point

parallel muscles

muscles with a fairly uniform width and parallel fascicles that can span long distances, shorten more than other muscle types, and produce less force

parallel muscles (example)

elongated straps (rectus abdominis of the abdomen, sartorius of the thigh, and zygomaticus major of the face), squarish quadrilateral muscles (masseter of the jaw)

triangular muscles (convergent muscles)

relatively strong, fan-shaped muscles broad at one end with fascicles converging on the other, narrower end

triangular muscles (example)

pectoralis major in the chest, temporalis on the side of the head

pennate muscles

feather-shaped muscles whose fascicles insert obliquely on a tendon that runs the length of the muscle

three types of pennate muscles

unipennate, bipennate, and multipennate muscles

unipennate muscles

pennate muscles in which fascicles approach the tendon from one side

unipennate muscles (example)

palmar interosseous muscles of the hand, semimembranosus of the thigh

bipennate muscles

pennate muscles in which fascicles approach the tendon from both sides

bipennate muscles (example)

rectus femoris of the thigh

multipennate muscles

pennate muscles shaped like a bunch of feathers with their quills converging on a single point

multipennate muscles (example)

deltoid of the shoulder

pennate muscles (force)

generate more force than the preceding types because they fit more muscle fibers into a given length of muscle

circular muscles (sphincters)

muscles that have fascicles in rings around certain body openings and passages that constrict when the muscles contract

circular muscles (example)

orbicularis oculi of the eyelid, external urethral and anal sphincters

smooth muscle sphincters

pyloric valve at the passage from the stomach to the small intestine, some sphincters of the urinary tract and anal canal

intermuscular septa

particularly thick fasciae that tightly bind muscles

seven types of muscles

fusiform, parallel, triangular, unipennate, bipennate, multipennate, and circular muscles

muscles can insert on a…

bone, fascia or tendon of another muscle, or collagen fibers of the dermis

two types of muscle attachment to bones

direct and indirect attachments

direct attachment (fleshy attachment)

attachment with so little separation between muscle and bone that the muscular tissue seems to emerge directly from the bone; in reality, it stops slightly short of the bone and the gap between them is spanned by collagen fibers

indirect attachment

attachment in which the muscle ends visibly short of its bony destination, and the gap is bridged by a tendon

direct attachment (example)

brachialis and lateral head of the triceps brachii

indirect attachment (example)

two ends of the biceps brachii

aponeurosis

tendon that forms a broad sheet located beneath the scalp or associated with certain abdominal, lumbar, hand, or foot muscles

aponeurosis (example)

the palmaris longus passes through the wrist and expands into a fanlike palmar aponeurosis beneath the skin of the palm

retinaculum

band of connective tissue under which a group of tendons from separate muscles passes

retinaculum (example)

the tendons of several forearm muscles pass through the surface of each wrist on their way to the hand

origin

muscle attachment at the stationary end of a bone

insertion

muscle attachment at the moving end of a bone

intrinsic muscle

any muscle contained entirely within a region of interest

extrinsic muscle

muscle that acts upon a designated region, but arises from another region

action

effect produced by a muscle, whether to produce or prevent a movement

four categories of muscle action

prime mover, synergist, antagonist, and fixator

prime mover (agonist)

muscle that produces most of the force during a particular joint action

synergist

muscle that aids the prime mover through producing more power, stabilizing a joint and restricting rotation, or modifying the direction of a movement to specify the action of the prime mover

antagonist

muscle that opposes the prime mover by limiting its speed or range and preventing excessive movement, joint injury, and inappropriate actions

antagonistic pair

pair of muscles that act on opposite sides of a joint

fixator

muscle that prevents a bone from moving

innervation

nerve that supplies a given muscle with stimulation

two groups of nerves

spinal and cranial nerves

spinal nerves

nerves that arise from the spinal cord, emerge through the intervertebral foramina, and supply branches to muscles below the neck

spinal nerves (branching)

immediately after emerging from an intervertebral foramen, each spinal nerve branches into a posterior and anterior ramus

plexus

web-like network of spinal nerves adjacent to the vertebral column

cranial nerves

total of 12 nerves that arise from the base of the brain, emerge through the skull foramina, and innervate muscles of the head and neck