The three types of muscle tissue are skeletal, smooth, and cardiac muscle.

Fascia is a layer of dense connective tissue that surrounds and separates each muscle.

Tendons are extensions of connective tissue that fuse to the periosteum of bones, attaching muscles to bones.

Aponeuroses are broad sheets of connective tissue that connect muscles to each other.

The epimysium is the layer of connective tissue that surrounds an entire whole muscle.

The perimysium surrounds individual bundles (fascicles) within a muscle.

The endomysium is the connective tissue layer that covers each individual muscle cell (fiber).

A muscle fiber is a single, long, cylindrical muscle cell.

The sarcolemma is the cell membrane of a muscle fiber.

The sarcoplasm is the cytoplasm of a muscle fiber, containing mitochondria and nuclei.

Myofibrils are parallel structures within the sarcoplasm of a muscle fiber, composed of thick (myosin) and thin (actin) filaments.

Sarcomeres are the basic contractile units of myofibrils, joined end-to-end, extending from one Z line to the next.

I bands are the light bands made of actin filaments anchored to Z lines. A bands are the dark bands made of overlapping thick and thin filaments.

The H zone is in the center of the A band and consists only of myosin filaments.

The M line is in the center of the H zone and contains proteins that hold the myosin filaments in place.

The sarcoplasmic reticulum is the endoplasmic reticulum within a muscle fiber, associated with T tubules and storing calcium.

T tubules are invaginations of the sarcolemma that extend into the muscle fiber and are open to the outside, playing a role in muscle contraction.

The neuromuscular junction is the site where a motor neuron axon terminal meets a muscle fiber, forming a synapse.

The sliding filament model describes how myosin heads attach to actin filaments, pull them, and then detach, causing the sarcomeres to shorten.

ATP provides the energy for the myosin cross-bridges to attach to actin and pull, and is also used to return calcium ions to the sarcoplasmic reticulum for relaxation.

Acetylcholine is the neurotransmitter released by the motor neuron that initiates skeletal muscle contraction.

Oxygen debt is the amount of oxygen required to convert accumulated lactate back into glucose and to resynthesize ATP and creatine phosphate after strenuous exercise.

Muscle fatigue is the loss of a muscle's ability to contract during strenuous exercise, often due to electrolyte imbalances and decreased ATP levels.

A threshold stimulus is the minimum stimulus required to generate an impulse, release calcium ions, activate cross-bridges, and cause a muscle to contract.

A muscle twitch is the response of a single muscle fiber to a single impulse, consisting of a latent period, a contraction period, and a relaxation period.

Summation is the process where a muscle fiber receiving a series of stimuli at increasing frequency reaches a point where it cannot relax completely, and the force of individual twitches combine.

A tetanic contraction is a sustained contraction that lacks any relaxation, resulting from summation.

A motor unit consists of a motor neuron and all the muscle fibers it controls.

Recruitment is the increase in the number of activated motor units within a muscle at higher intensities of stimulation, leading to an increase in contraction strength.

Muscle tone is the continuous state of sustained contraction of a few motor units within a muscle, important for maintaining posture.

The two types of smooth muscle are multiunit smooth muscle and visceral smooth muscle.

Peristalsis is the rhythmic contraction and relaxation of visceral smooth muscle in the walls of hollow organs, responsible for propelling substances through them.

Intercalated discs are complex membrane junctions that join cardiac muscle cells, transmitting the force of contraction and aiding in rapid impulse transmission.

The origin is the immovable end of a muscle, while the insertion is the movable end. Contraction pulls the insertion toward the origin.

The agonist is the prime mover doing the majority of the work. Synergists are helper muscles. Antagonists are opposing muscles.

Skeletal muscles are named based on size, shape, location, action, number of attachments, direction of fibers, or a combination of these factors.

Three muscles of facial expression are the epicranius, orbicularis oculi, and orbicularis oris.

The two main muscles of mastication are the masseter and temporalis.

Two muscles that move the head are the sternocleidomastoid and splenius capitis.

Two muscles that move the pectoral girdle are the trapezius and serratus anterior.

Two muscles that move the arm are the pectoralis major (flexor) and latissimus dorsi (extensor).

Two muscles that move the forearm are the biceps brachii (flexor) and triceps brachii (extensor).

Two muscles that move the hand are the flexor carpi radialis (flexor) and extensor digitorum (extensor).

The four muscles of the abdominal wall are the external oblique, internal oblique, transverse abdominis, and rectus abdominis.

One muscle of the pelvic diaphragm is the levator ani.

Two muscles that move the thigh are the gluteus maximus (posterior group) and adductor longus (adductor).

The hamstring muscles are the biceps femoris, semitendinosus, and semimembranosus.

The quadriceps femoris group is composed of four muscles (rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius) that extend the leg.

Two muscles that perform dorsal flexion of the foot are the tibialis anterior and extensor digitorum longus.

Two muscles that perform plantar flexion of the foot are the gastrocnemius and soleus.