Muscular System Structure, Function, and Physiology

Vocabulary flashcards reviewing muscular system functions, anatomical actions, contraction physiology, cellular structures, and lever mechanics.

Twitch

The response of a muscle to a single simulation causing fibers to quickly contract then relax.

Graded muscle Contraction

Variations in the degree of muscle contraction by changing either the frequency or strength of the stimulus.

Summation

Accumulation of effects, such as in a muscle contraction when motor neurons continually fire and keep a muscle stimulated.

Tetanus

When a muscle reaches a ceiling of maximum tension and the muscle contraction is sustained due to high-frequency stimulation.

Recruitment (Motor unit Summation)

The process of getting more and more motor units stimulated by delivering stimuli of increasing voltage.

Threshold Stimulus

The weakest stimulus that is capable of producing a response in an excitable tissue, causing the first observable contraction.

Muscle tone

The slight contraction that even relaxed muscles always have that keeps muscles healthy and ready to respond to stimulation.

Muscle tension

The force exerted by a contracting muscle on an object.

Muscle fatigue

The decline in ability of a muscle to generate force.

Lever

A rigid bar that moves on a fixed point when a force is applied to it (our bones act as levers).

Fulcrum

A fixed point that a lever moves on (our joints act as fulcrums).

Effort

The applied force used to move a resistance (created by a muscle contraction).

Load

A resistance (the insertion bone).

Muscle (Organ Classification)

Each muscle is its own organ because they are composed of skeletal muscle tissue, blood vessels, nerves, and connective tissues.

Muscular System Functions

Main function is movement via contractions, but also contributes to maintaining posture, stabilizing joints, and generating heat.

Muscles of the shoulder

Prime movers in flexion and extension of the humerus, making movement of the arm possible.

Diaphragm

The prime mover for inspiration; contracts and flattens moving downward when we inhale to expand the lungs, and releases upward when we exhale to push air out.

Biceps branchii

Upper limb muscle responsible for flexing the forearm.

Branchialis

Muscle that flexes the forearm and serves as a bridge between the humerus and ulna.

Branchior adialis

Synergist muscle in forearm flexion.

Triceps branchii

Main arm muscle in extension.

Sartorius

Lower limb muscle that helps flex, abduct, and laterally rotate the thigh.

Adductors

Muscles that make up the inner thighs and adduct the femur at the hip joint.

Quadriceps femoris

Major extensors of the knee, critical for jumping, climbing, running, and standing up from being seated.

Hamstrings

Muscles of the posterior thigh that antagonize the quadriceps; prime movers in thigh extension and leg flexion.

Calf muscles

Muscles comprising the gastrocnemius, soleus, and plantaris that produce movement in the ankle, foot, and toes.

Tibialis anterior

Prime mover in dorsiflexion.

Trapezius

Muscle responsible for moving, rotating, and stabilizing the scapulae, extending the head at the neck, and controlling movement of the head and shoulder blades.

Latissimus dorsi

Posterior muscle mainly responsible for arm movements.

Erector Spinae

Muscles running the length of the vertebral column that keep backs straight, allow for side-to-side rotation, and act as prime movers in back extension.

Gluteal muscles

Muscles responsible for hip and thigh movement, ability to maintain good posture, and overall strength.

Epicranius

Head muscle responsible for scolp movement.

Masseter

Prime mover in allowing the jaw to close.

Temporalis

Prime mover in allowing the jaw to close.

Buccinator

Main muscle of the cheek.

Head and neck muscles (Insertion)

Muscles that are unique because they insert into skin or other muscles, rather than bones.

Skeletal muscle tissue

Striated muscle attached to bones that differs from cardiac and smooth muscle because it contracts voluntarily and produces movement.

Muscle fiber

A muscle cell.

Myofibrils

Thread-like bunched structures within muscle cells that contain myofilaments running their length and are subdivided into sacromeres.

Sacromeres

Contractile units of each muscle that are critical for muscle contractions.

Mitochondria (Muscle Cell Role)

Organelles critical for providing energy for muscle contractions.

Myosin

Contractile protein making up thick filaments that grabs and pulls actin.

Actin

Contractile protein making up thin filaments that slides past each other and overlaps.

Muscle Contraction Mechanism

Occurs when heads of myosin filaments grab thinner actin filaments and pull them to slide past each other, causing filaments to overlap more and the sacromere to shorten.

Nervous System Requirement

The requirement that muscle contractions only happen if activated or stimulated by the nervous system.

Acetylcholine

The neurotransmitter that motor neurons use in muscle contractions for signaling.

Increasing Contraction Force

Achieved by increasing the frequency of motor neuron stimulation, increasing the number of motor neurons stimulated, or increasing the size of muscle fibers.