HL Human Physiology Vocabulary 6

Neuron

Any of the impulse-conducting cells that constitute the brain, spinal column, and nerves, consisting of a nucleated cell body with one or more dendrites and a single axon. Also called nerve cell, neurocyte.

Glial cell

A supportive cell in the central nervous system. Unlike neurons, glial cells do not conduct electrical impulses. The glial cells surround neurons and provide support for and insulation between them. Glial cells are the most abundant cell types in the cent

Nerves

Any of the cordlike bundles of nervous tissue made up of myelinated or unmyelinated nerve fibres and held together by a connective tissue sheath through which sensory stimuli and motor impulses pass between the brain or other parts of the central nervous

Central Nervous System

The portion of the vertebrate nervous system consisting of the brain and spinal cord. Also called cerebrospinal axis.

Peripheral Nervous System

The part of the vertebrate nervous system constituting the nerves outside the central nervous system and including the cranial nerves, the spinal nerves, and the sympathetic and parasympathetic nervous systems.

Endocrine system

The bodily system that consists of the endocrine glands and the hormones that they secrete.

Motor Neuron

A neuron that conveys impulses from the central nervous system to a muscle, gland, or other effector tissue.

Sensory Neuron

A neuron conveying information originating from sensory receptors or nerve endings; an afferent neuron may be a general or special sensory neuron.

Relay Neuron

A nerve cell whose axon and dendrite lie entirely within the central nervous system and whose function is to relay impulses within the central nervous system.

Dendrites

Any of the various branched protoplasmic extensions of a nerve cell that conducts impulses from adjacent cells inward toward the cell body. Also called dendritic process, dendron , neurodendrite , neurodendron.

Axon

The usually long process of a nerve fibre that generally conducts impulses away from the body of the nerve cell.

Axon Hillock

The conical area of origin of the axon from the nerve cell body.

Nodes of Ranvier

Narrow gaps between the ends of the segments of myelin that insulate single nerve axons.

Schwann cell

Any of the cells that cover the nerve fibres in the peripheral nervous system and form the myelin sheath. Also called neurilemma, neurilemma cell.

Myelin sheath

The sheath surrounding the axon of myelinated nerve cells, consisting of concentric layers of myelin formed in the peripheral nervous system by the plasma membrane of Schwann cells, and in the central nervous system by the plasma membrane of oligodendrocy

Saltatory conduction

The rapid passage of an electric potential between the nodes of Ranvier in myelinated nerve fibres, rather than along the full length of the membrane.

Axon terminals

The somewhat enlarged, often club-shaped endings by which axons make synaptic contacts with other nerve cells or with effector cells (muscle or gland cells). Axon terminals contain neurotransmitters of various kinds, sometimes more than one. These can be

Synaptic Cleft

The space about 10-20 nm wide between the cell membrane of an axon terminal and of the target cell with which it synapses.

Synaptic vesicles

The small (average diameter, 30 nm), intracellular, membrane-bound vesicles near the presynaptic membrane of a synaptic junction, containing the transmitter substance that, in chemical synapses, mediates the passage of nerve impulses across the junction.

Neurotransmitter

A substance (e.g., norepinephrine, acetylcholine, dopamine) that is released from the axon terminal of a presynaptic neuron on excitation, and that travels across the synaptic cleft to either excite or inhibit the target cell.

Acetylcholine

A white crystalline derivative of choline that is released at the ends of nerve fibres in the somatic and parasympathetic nervous systems and is involved in the transmission of nerve impulses in the body.

Synaptic transmission

The passage of a neural impulse across a synapse from one nerve fibre to another by means of a neurotransmitter.

Resting potential

The membrane potential characteristic of a non-conducting excitable cell, with the inside of the cell more negative than the outside.

Threshold potential

The potential that an excitable cell membrane must reach for an action potential to be initiated.

Action potential

An electrical signal that propagates along the membrane of a neuron or other excitable cell as a non-graded (all-or-none) depolarisation.

Depolarization

A change in a cell's membrane potential such that the inside of the membrane is made less negative relative to the outside. For example, a neuron membrane is depolarised if a stimulus decreases its voltage from the resting potential of -70 mV in the direc

Repolarization

The process whereby the membrane, cell, or fibre, after depolarization, is polarized again, with positive charges on the outer and negative charges on the inner surface.

Refractive period

The short time immediately after an action potential in which the neuron cannot respond to another stimulus, owing to the inactivation of voltage-gated sodium channels.

Nerve Impulse

A wave of physical and chemical excitation that moves along a nerve fibre in response to a stimulus.

Sodium-potassium pump

The enzyme-based mechanism that maintains correct cellular concentrations of sodium and potassium ions by removing excess ions from inside a cell and replacing them with ions from outside the cell.

Presynaptic Neuron

A neuron from the axon terminal of which an electrical impulse is transmitted across a synaptic cleft to the cell body or one or more dendrites of a postsynaptic neuron by the release of a chemical neurotransmitter.

Postsynaptic Neuron

A neuron to the cell body or dendrite of which an electrical impulse is transmitted across a synaptic cleft by the release of a chemical neurotransmitter from the axon terminal of a presynaptic neuron.

Ion Channels

Protein ports in cell membranes that are specific for the passage of sodium, potassium, calcium and chloride ions in solution. Changes in the protein configuration, under the influence of various hormone molecule attachment, intracellular ion or other che

Ligand-gated channels

A protein channel that opens in response to the binding of a molecule (the ligand) to the protein, which causes a conformational change in the protein molecule.