Med. Term Ch. 10 The Nervous System - Nerves

Saltatory Conduction

-A means by which action potentials jump from node to node along an axon. -Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of membrane.

Spinal nerves

31 pairs of nerves arising from the spinal cord

Inhibitory postsynaptic potential

A postsynaptic potential that hyperpolarizes the neuronal membrane, making a cell less likely to fire an action potential

action potential

Activated when treshold is reached; causes another type of sodium channel to open. Found along the axon of neuron, especially near "trigger zone"; their opening is what triggers _________ ___________.aka firing off a nerve impluse.

Stimuli

Agent of change (light, sound touch), occurring within or outside the body, that affect nervous system functioning.

Divergence

Branching axon. One neuron sends impulses/Stimulation of many neurons ultimately. Can amplify an impulse. Impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction.

Synaptic potentials

Changes in chemically gated ion channels create local potentials; which enable one neuron to affect another.

Neurotransmitters

Chemicals messengers released by nerves at the end of the nerve cell that stimulate other neurons, muscles, or glands (ex: acetylcholine, norepinephrine, dopamine, seratonin)

Ganglia

Collection of nerve cell bodies found in the peripheral nervous system

Stroma

Connective and supporting tissue of an organ. Glial cells are the stromal tissue of the brain.

Myelin sheath

Covering of white, fatty tissue that surrounds and insulates the axon of a nerve cell. Myelin speeds impulse conduction along axons.

Excitatory Postsynaptic Potential

EPSP, Depolarization in membrane of postsynaptic cell caused by binding of excitatory neurotransmitter from presynaptic receptor; makes it more likely for postsynaptic cell to generate an action potential.lasts for about 15 milliseconds.

Parenchyma

Essential distinguishing tissue of any organ or system. The parenchyma of the nervous system are brain, spinal cord and neurons.

Trigger Zone

Found in a multipolar neuron, first part of the axon, initial segment.

oligodendroglial cell

Glial cell that forms the myelin sheath covering axons.

Ependymal cell

Glial cell that lines membranes within the brain and spinal cord and helps form cerebrospinal fluid.

All-or-None Response

If a neuron respondes at all, it responds completely. A greater intensity of stimulation produces more impulses per sec., not a stronger impulse.

Neuronal Pools

Interneurons. Work together to perform a common function; Each Pool May excite or inhibit. Receive or generates output to other neurons."Learn how to tie your shoes, etc"

Parasympathetic nerve

Involuntary, autonomic nerves that regulate normal body functions such as heart rate, breathing and muscles of the GI tract

Chemically gated

Ion channels that respond to neurotransmitter molecules.

Efferent nerve

Nerve that carries messages away from the CNS; motor nerve

Afferent nerve

Nerve that conducts impulses toward the CNS from the body periphery.

Peripheral nervous system

Nerves outside the brain and spinal cord; cranial, spinal and autonomic nerves.

Autonomic nervous system

Nerves that control the involuntary body functions of muscles, glands and organs.

Central nervous system

Nervous system subdivision that is composed of the brain and spinal cord.

Presynaptic neuron

Neuron carrying an impulse to the synapse; Sender. Neuron that SENDS an AP to the Synapse and Releases a Chemical Signal

postsynaptic

Neuron receiving input

resting potential

One that is not sending impulses or responding to other neurons; has a value of -70 millivolts.

Receptor

Organ that receives a nervous stimulus and passes it on to afferent nerves (ex. skin, ears, eyes, taste buds).

Cell body

Part of the nerve cell that contains the nucleus.

Absolute refractory Period

Part of the refractory period; 1/2,500 of a second axon's voltage-gated sodium channels are not responsive at all; can not be stimulated.

microglial cell

Phagocytic cell that removes waste products from the CNS

Synapse

Space through which a nervous impulse travels between nerve cells or between nerve and muscle or glandular cells.

Neuroglia

Support, insulate, and protect cells.

Vagus nerve

Tenth cranial nerve; its branches reach to the larynx, trachea, bronchi, lungs, aorta, esophagus and stomach. Only cranial nerve that leaves the head.

depolarized

The membrane becomes less negative (more positive) than the resting potential.

Relative Refractory period

The time when the membrane reestablishes its resting potential; Unresponsive to a NORMAL threshold stimulus. However a stimulus of higher than usual intensity may trigger an impulse. -Limits how many action potentials may be generated in a neuron in a given period.

Convergence

Various Sensory Receptors from different Neurons. Can allow for summation of impulses. Allows nervous system to collect, process, and respond to info. Neuron's Axon converge onto one another.

membrane potential

aka transmembrane potential; The potential difference across the cell membrane; measured in millivolts.

Sympathetic nerve

autonomic nerves that influence bodily functions involuntarily in times of stress.

Blood-brain barrier

blood vessels that selectively let certain substances enter the brain tissue and keep other substances out.

Sensory nerve

carries message towards the brain and spinal cord from a receptor (afferent nerve)

motor nerve

carries messages away from the brain and spinal cord to muscles and organs: efferent nerve.

Voltage-gated

ions channels that participate in action potentials.

Plexus

large, interfacing network of nerves (lumbosacral, cervical, brachial)

nerve

macroscopic cord-like collection of fibers (axons and dendrites) that carry electrical impulses.

Dendrite

microscopic branching fiber of a nerve cell that is the first part to receive the nervous impulse.

Axon

microscopic fiber that carries the nervous impulse along a nerve cell.

neuron

nerve cell that carries impulses throughout the body

Sciatic Nerve

nerve extending from the base of the spine down through the thigh, lower leg and foot.

threshold potential

neurons are sufficiently depolarized (less negative or more positive); -55 millivolts

acetylcholine

neurotransmitter released at the ends of nerve cell

glial cell (neurological cell)

supportive and connective nerve cell that does not carry nervous impulses (astrocytes, microglial cells, ependymal cells and oligodendrocytes).

hyperpolarized

the membrane potential becomes more negative than the resting potential.

synaptic transmission

the process through which neurotransmitters are released by one neuron, cross the synaptic gap, and affect adjoining neurons

Cranial nerves

twelve pairs of nerves that carry messages to and from the brain with regard to the head and neck (except the vagus nerve)

astrocyte

type of glial (neuroglial) cell that transports water and salts from capillaries