Human Biology Chapter 7

nerve

A bundle of parallel axons, dendrites, or both from many neurons. It is usually covered with tough connective tissues

neurotransmitter

A chemical released from the axon tip of a neuron that affects the activity of another cell (usually a nerve, muscle, or gland cell) by altering the electrical potential difference across the membrane of the receiving cell.

axon

A long extension from the cell body of a neuron that carries an electrochemical message away from the cells body toward another neuron of effector (muscle or gland). The tips of an axon release a chemical called a neurotransmitter that can affect the activity of the receiving cell. Typically, there is one long axon on a neuron.

sodium-potassium pump

A molecular mechanism in a plasma membrane that uses cellular energy in the form of adenosine triphosphate (ATP) to pump ions against their concentration gradients. Typically, each pump ejects three sodium ions from the cell while bringing in two potassium ions.

sensory neuron

A nerve cell specialized to conduct nerve impulses from the sensory receptors toward the central nervous system.

action potential

A nerve impulse. an electrochemical signal conducted along an axon. A wave of depolarization caused by the inward flow of sodium ions followed by repolarization caused by the outward flow of potassium ions.

motor neuron

A neuron specialized to carry information away from the central nervous system to an effector, either a muscle or a gland.

acetylcholine

A neurotransmitter found in both the central nervous system and the peripheral nervous system. It is the neurotransmitter released at neuromuscular junctions that causes muscle contraction.

dendrite

A process of a neuron specialized to pick up message and transmit them toward the cell body. There are typically many short branching dendrites on a neuron.

ion channel

A protein-lined pore or channel through a plasma membrane through which one type or a few types of ions can pass. nerve cell ion channels are important in the generation and propagation of nerve impulses.

Schwann cell

A type of glial cell in the peripheral nervous system that forms the myelin sheath by wrapping around the system that forms the myelin sheath by wrapping around the axon many times. The myelin sheath insulates axons, increases the speed at which impulses are conducted, and assists in the repair of damage neurons.

interneuron

An association neuron. Neurons located within the central nervous system between sensory and motor neurons that serve to integrate information.

myelin sheath

An insulating layer around axons that nerve impulses over relatively long distances that is composed of multiple wrappings of the plasma membrane of certain glial cells. Outside the brain and spinal cord, Schwann cells form the myelin sheath. It greatly increases the speed at which impulses travel and assists in the repair of damage axons. The Schwann cells that form the myelin sheath are separated from one another by short regions of exposed axon called nodes of Ranvier.

Neuroglial cell

Cells of the nervous system that support, insulate, and protect nerve cells. Also called glial cells.

summation

Combined effects of excitatory and inhibitory effects on a neuron at any given moment that determines whether an action potential is generated.

effector

Lymphocytes that are responsible for the attack on cells or substances not recognized as belonging in the body.

Neuron

Nerve cells involved in intercellular communication. A neuron that affects the activity of another ell (usually a nerve, muscle, or gland cell) by altering the electrical potential difference across the membrane of the receiving cell.

threshold

The degree to which the voltage difference across the plasma membrane of a neuron or other excitable cell must change to trigger an action potential.

refractory period

The interval following an action potential during which a neuron cannot be stimulated to generate another action potential.

synapse

The site of communication between a neuron and another cell, such as another neuron or muscle cell.

saltatory conduction

The type of nerve transmission along a myelinated axon in which the nerve impulse jumps from one node of Ranvier to the next. It greatly increases the speed of nerve conduction.

resting potential

the separation of charge across the plasma membrane of a neuron when the neuron is not transmitting an action potential. It is caused primarily by the unequal distributions of sodium ions, potassium ions, and large negatively charged proteins on either side of the plasma membrane. The resting potential of a neuron is about -70 mV.