Nervous System

Acetylcholine

A neurotransmitter that transmits nerve impulses across the neuromuscular junction.

Action potential

The principal way neurons communicate through brief but large depolarization (-70mV → +30mV); signal over long distances. It is a rapid change in electrical potential across a neuron’s membrane that travels along the axon to transmit a nerve impulse.

Axon

The slender projection of a neuron that generates and conducts electrical impulses; each neuron has only one axon.

Baroreceptors

Pressure-sensitive sensory receptors in blood vessels that detect changes in blood pressure and help maintain homeostasis.

Cerebellum

The part of the brain responsible for coordinating movement, posture, and balance.

Cerebrum

The largest region of the brain, involved in thought, voluntary action, sensation, and reasoning.

Chemoreceptors

Sensory receptors that detect changes in chemical levels such as CO₂, O₂, or pH in blood or tissues.

Dendrites

Branched extensions of the cytoplasm of a neuron that serve as receptive sites.

Depolarization

Reduction in membrane potential so it becomes less negative (-70mV → -50mV) and increases the probability of producing nerve impulses; sodium ions enter the neuron, making the inside of the membrane less negative and initiating an action potential.

Graded potential

A short-lived signal over short distances (membrane potential decreases with distance traveled); a small, localized change in membrane potential whose magnitude depends on the strength of the stimulus; may trigger an action potential if threshold is reached.

Gray matter

Brain and spinal cord tissue that contains neuron cell bodies and is involved in processing and integration of information.

Hyperpolarization

Increase in membrane potential so it becomes more negative (-70mV → -90mV) and decreases the probability of producing nerve impulses; occurs when the inside of the neuron becomes more negative than the resting potential after repolarization.

Hypothalamus

A region of the brain that regulates homeostasis, controlling temperature, hunger, thirst, and linking the nervous and endocrine systems.

Motor unit

A single motor neuron and all the muscle fibers it stimulates, working together for coordinated movement.

Myelin sheath

A whitish, fatty layer that covers axons to increase the speed of electrical impulse transmission; made by Schwann cells.

Neonicotinoids

Synthetic compounds used in insecticides that bind to acetylcholine receptors, but acetylcholinesterase cannot break them down; overstimulate insect neurons through irreversible binding and cause paralysis and death.

Neurons

Specialized nerve cells that conduct messages and transmit electrical and chemical signals in the form of nerve impulses from one part of the body to another.

Neurotransmitter

A chemical messenger released by neurons to transmit signals across synapses to other cells.

Nodes of Ranvier

Gaps between myelin sheaths along an axon that increase the speed of transmission of nerve impulses.

Pituitary gland

The endocrine “master gland” controlled by the hypothalamus; it secretes hormones that regulate other glands and body functions.

Repolarization

Restoration of the resting membrane potential as potassium ions exit the neuron after depolarization.

Schwann cells

Glial cells in the peripheral nervous system that produce the myelin sheath around axons.

Spinal cord

A bundle of nerves running through the vertebral column that transmits signals between the brain and the body and controls reflexes.

Synapse

The junction between two neurons or a neuron and an effector where the transfer of information is mediated.

White matter

Brain and spinal cord tissue containing myelinated axons; responsible for communication between gray matter regions.