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.