Honors Anatomy & Physiology - Muscular System Vocab

will add more words as we progress

A Band

Situated on either side of the H Zone of a muscle sarcomere (the area were contraction and relaxation of the muscle occurs, where sarcomeres overlap during muscle movements).

Involuntary muscle

a muscle that contracts without conscious control (ex: smooth and cardiac)

Transverse (T) tubule

extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells

Fascicle

a group of muscle fibers that is “bundled” as a unit within the whole muscle

Tropomyosin-troponin complex

Regulates skeletal muscle by blocking the myosin binding site of actin in the absence of Ca²⁺

Acetylcholine

Chief neurotransmitter of the parasympathetic nervous system, the part of the autonomic nervous system. This can stimulate a response or block a response and thus can have excitatory of inhbitory effects.

Isometric Contraction

a muscle contraction without motion. Used to stabilize a joint, such as when a weight is held at waist level neither raising nor lowering it.

Sarcomere

The basic contractile unit of muscle fiber. Each one is composed of two main protein filaments--actin and myosin—which are the active structures responsible for muscular contraction. 

Acetylcholinesterase

An enzyme found in the synapse between nerve cells and muscle cells. It springs into action soon after a signal is passed, breaking down the acetylcholine. This effectively stops the signal, allowing the pieces to be recycled and rebuilt into new neurotransmitters for the next message.

Latent period

A short delay (1-2 msec) from the time when the action potential reaches the muscle until tension can be observed in the muscle.

Sarcoplasm

The cytoplasm of striated muscle cells. 

Actin

Protein that is an important contributor to the contractile property of muscle and other cells

Length-tension relationship

In general, as muscles shorten, they are able to generate greater amounts of tension. However, shortening a muscle beyond a certain point will not longer generate any increases in tension.

Sarcoplasmic reticulum

Specialized smooth endoplasmic reticulum that is important in transmitting the electrical impulse as well as in the storage of calcium ions. 

Aerobic metabolism

Occurs when the body produces energy (in the form of ATP) using oxygen. Fats and carbohydrates are the main fuels in aerobic metabolism.

Motor end plate

A chemical synapse between the terminal part of the motor neuron and the target muscle.

Sliding filament theory

The explanation for how muscles contract to produce force. The actin and myosin filaments within the sarcomeres of muscle fibers bind to create cross-bridges and slide past one another, creating a contraction.

Anaerobic metabolism

ATP production without oxygen (or in the absence of oxygen), occurs by direct phosphate transfer from molecules such as glycolytic intermediates or creatine phosphate (CrP), to ADP forming ATP. Glucose is its only fuel. 

Motor neuron

A neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon projects to the spinal cord or outside of the spinal cord to control muscles and glands.

Skeletal muscle

The functions of skeletal muscle include producing movement, maintaining body posture, controlling body temperature, and stabilizing joints.

Aponeurosis

A thin sheath of connective tissue that helps connect your muscles to your bones. These are similar to tendons, but is a thin sheet of connective tissue. 

Motor unit

The combination of an individual motor neuron and all of the muscle fibers that it innervates.

Spatial summation

Signals coming from multiple simultaneous inputs.

Asynchronous firing of motor units

One contracts and then, a fraction of a second later, another contracts before the first has time to relax, and then another fires and so on. This allows for smooth muscle contraction. 

Multiunit smooth muscle

Differs from single-unit in that each smooth-muscle cell receives its synaptic input. This gives it much finer control. It is found in the airways of the lungs, large arteries, and ciliary muscles of the eyes.

Striations

Repeating A and I bands of the proteins actin and myosin that are present along the length of myofibrils. 

Muscle Fiber

Each skeletal muscle fiber is a single cylindrical muscle cell. An individual skeletal muscle may be made up of hundreds or thousands of these bundled together and wrapped in a connective tissue covering.

Synaptic cleft

A small gap between the axon terminal of the presynaptic neuron and the membrane of the postsynaptic cell.

Cardiac muscle

Makes up the thick middle layer of the heart. It is one of three types of muscle in the body, along with skeletal and smooth muscle.

Muscle Tone (tonus)

The natural and continuous slight contraction of a muscle that gives resistance to passive stretching during relaxation. 

Synaptic knob

Also called a bouton, its a relay point at the tip of a transmitting neuron in the brain. 

Glycogen

The stored form of glucose that’s made up of many connected glucose molecules.

Twitch contraction

The contractile response of a single muscle fiber to a single stimulus from a motor neuron.

Glycogen-lactic acid system

Uses glucose stored in the muscles as glycogen during anaerobic metabolism to produce energy quickly. Lactic acid is produced as an end product. 

Visceral (single-unit) smooth muscle

Produces slow, steady contractions that allow substances, such as food in the digestive tract, to move through the body.

I Band

It is called the light band that contains only the thin filament (actin).

Recruitment

Measure of how many motor neurons are activated in a particular muscle. The higher this is the stronger the muscle contraction will be. 

Voluntary muscle

Skeletal muscles of the body that attach to bones and control movement of the limbs, head, neck, and body under conscious control.

Incomplete tetany

When the muscle fibers do not completely relax before the next stimulus because they are being stimulated at a fast rate; however there is a partial relaxation of the muscle fibers between the twitches. 

Innervation

The distribution or supply of nerves to a part.

Refractory period

A state of recovery that occurs after a neuron has fired an action potential. During this period, another action potential cannot be easily produced.

Wave summation

Occurs when stimulations are delivered to a muscle fiber faster than it is able to completely relax.

Intercalated discs

Gap junctions that link adjacent cardiac muscles so that electrical impulses can travel between cells and causes to contract almost simultaneously.

Relaxation phase Z line

The Z-lines are closer during contraction because actin and myosin interaction generates cross-bridges, which slide myofilaments over each other. During relaxation, myosin and actin detach and the Z-lines slide back apart. 

Agonist (prime mover)

These muscles cause the movement to occur. They are the muscles that are primarily responsible for generating the movement.

Gracilis

A slender superficial muscle of the inner thigh.

Semimembranosus

A muscle within the posterior compartment of the thigh

Antagonist

These muscles act in opposition to the movement generated by the agonists and are responsible for returning a limb to its initial position.

Hamstrings

Any one of the three posterior thigh muscles in between the hip and the knee (from medial to lateral: semimembranosus, semitendinosus, and biceps femoris).

Semitendinosus

One of the three muscles that make up the hamstrings muscle group, and it is located at the posterior and medial aspect of the thigh. This is named due to it having a long tendon of insertion. 

Belly

The widest part of a muscle

Insertion

The place where one end of a muscle is attached to the freely moving bone of its joint. 

Serratus anteiror

Very thin and covers the side of the ribcage. Also called the “boxer” muscle.

Biceps brachii

Commonly known as the biceps, is a large, thick muscle on the ventral portion of the upper arm. 

Latissimus dorsi

A broad, flat muscle occupying most of the lower posterior thorax. The muscle’s primary function is to move the upper extremity, but it is also considered an accessory muscle of respiration.

Sternocleidomastoids

Each of a pair of long muscles that connect the sternum, clavicle, and mastoid process of the temporal bone and serve to turn and nod the head.

Biceps femoris

A muscle of posterior compartment of the thigh, and lies in the posterolateral aspect. 

Complete tetany

The stimulus frequency is so high that the relaxation phase disappears completely, contractions become continuous.

Myocyte

A muscle cell.

Synaptic vesicle

Small, electron-lucent vesicles that are clustered at presynaptic terminals. They store neurotransmitters and release them by calcium-trigged exocytosis

Conductivity

Ability to cross space in between neurons.

Myofibril

A cylindrical bundle of contractile filaments within the skeletal muscle cell. The myofibrils are composed of individual contractile proteins called myofilaments. 

Temporal summation

The effects of impulses received at the same place can add up if the impulses are received in close temporal succession.

Contractility

The ability of muscle cells to forcefully shorten.

Myofilament

Threadlike structures that comprise the myofibril inside the muscle cell. There are two main types: thin and thick. In skeletal muscle, they are arranged in a repeating pattern of light and dark bands. 

Tendon

A flexible but inelastic cord of strong fibrous collagen tissue attaching a muscle to a bone.

Contraction phase

A single muscle twitch has a latent period, this happens when tension increases. Relaxation phase occurs when tension decreases.

Myoglobin

A protein that’s found in striated muscles, which includes skeletal muscles and heart muscle. Its main function is to supply oxygen to myocytes. 

Elasticity

The ability to recoil or bounce back to the muscle’s original length after being stretched. 

Myosin

A fibrous protein that forms (together with actin) the contractile filaments of muscle cells and is also involved in motion in other types of cells.

Endomysium

The key element that separates single muscle fibers from one another. It allows their autonomous gliding during muscle contraction.

Myosin ATPase

An enzyme that causes ATP hydrolysis which provides energy for actomyosin contraction. 

Epimysium

A sheath of fibrous elastic tissue surrounding a muscle

Neuromuscular Junction

A synaptic connection between the terminal end of a motor nerve and a muscle (skeletal/smooth/cardiac).

Threshold stimulus

The minimum strength required for the stimulus to initiate the response of muscle contraction.

Oxygen debt

The difference between the amount of oxygen needed by the muscles and the actual amount present.

Titin

A molecular spring in muscle cells. This binds calcium at specific sites, thereby increasing its stiffness. 

Extensibility

The ability of a muscle to be stretched. 

Masseter

A muscle which runs through the rear part of the cheek from the temporal bone to the lower jaw on each side and closes the jaw in chewing.

Synergist

Assists the agonist muscle or “primary mover” for a specific action at a joint. This muscle is not the main muscle involved in the action, but works in synergy with the primary muscle.

Deltoid

A large triangular-shaped muscle that lies over the glenohumeral joint and which gives the shoulder its rounded contour. 

Origin (head)

The proximal site that stays more stable and relatively fixed during muscle contraction. The head is a portion at the end of the origin muscle where it fixes to the bone.

Temporalis

A fan-shaped muscle which runs from the side of the skull to the back of the lower jaw and is involved in closing the mouth and chewing.

External abdominal oblique

A muscle of the anterior abdominal wall. It is the largest and most superficial of the flat wall muscles. 

Attachments

Originates from ribs 5-12 and inserts onto the iliac crest and public tubercle.

Pectoralis major

It is a thick, fan-shaped muscle that lies underneath the breast tissue and forms the anterior wall of the axilla.

Tensor fascia lata

A muscle of the proximal anterolateral thigh that lies between the superficial and deep fibers of the iliotibial (IT) band.

Fixator

A muscle which acts as the stabilizer and helps the agonist work effectively of one part of the body during movement of another part. 

Quadriceps femoris

The most voluminous muscle of the human body. This is a hip flexor and a knee extensor.

Tibialis anterior

The largest of four muscles in the anterior compartment of the leg. Its thick muscle belly arises from its proximal attachment at the lateral tibia. 

Gastrocnemius

The chief muscle of the calf of the leg, which flexes the knee and foot. It runs to the Achilles tendon from two heads attached to the femur.

Rectus abdominis

Each of a pair of long flat muscles that is at the front of the abdomen, joining the sternum to the pubis and acting to bend the whole body forward or sideways.

Triceps brachii

A large, thick muscle on the dorsal part of the upper arm. It often appears as the shape of a horseshoe. 

Gluteus maximus

The main extensor muscle of the hip in humans. It is the largest and outermost of the three gluteal muscles.

Rectus femoris

Flexes the hip along the sartorius and iliopsoas and extends the lower leg at the knee, working in conjunction with the other three quadriceps muscles. This antagonizes the hamstring muscles at the knee and the hip.

Vastus medius

One of the four muscles that make up the quadriceps group of muscles. 

Gluteus medius

Located on the lateral aspect of the upper buttock, below the iliac crest.

Sartorius

The longest muscle in the body, spanning both the hip and the knee joints.

Vastus lateralis

A muscle located on the lateral, or outside, part of your thigh. The muscle is one of the four quadriceps muscles and is the largest muscle of that group. 

Perimysium

The sheath of connective tissue surrounding a bundle of muscle fibers.