Kaplan MCAT Biology Chapter 4: The Nervous System

Neuron

a cell that conducts electrical impulses; the functional unit of the nervous system

Soma

portion of a neuron where the nucleus, endoplasmic reticulum, and ribosomes are located (aka cell body)

Dendrite

the portion of a neuron that receives stimuli and conveys them toward the cell body

Axon hillock

transition point between the cell body and the axon of a neuron; the site of action potential initiation

Action potential

an abrupt change in the membrane potential of a nerve caused by changes in membrane ionic permeability; results in conduction of an impulse down the axon

Axon

the long fiber of a neuron; conducts impulses away from the cell body toward the synapse

Myelin

the white, lipid-containing material surrounding the axons of many neurons in the central and peripheral nervous systems

Oligodendrocyte

a myelin-producing cell in the central nervous system

Schwann cell

a myelin-producing cell in the peripheral nervous system

Nodes of Ranvier

points on a myelinated axon that are not covered by myelin

Nerve terminal

the end of the axon from which neurotransmitter molecules are released; also called a synaptic bouton

Neurotransmitter

a chemical agent released into the synaptic cleft by the synaptic bouton of a neuron; binds to receptor sites on postsynaptic neurons or effector membranes to alter activity

Synaptic cleft

the small space into which the terminal portion of the axon releases neurotransmitters, which bind to the dendrites of the adjacent (postsynaptic) neuron

Mixed nerve

a nerve carrying both afferent (sensory) and efferent (motor) fibers

Efferent neuron

a neuron that transmits nervous impulses from the central nervous system to an effector (aka motor neuron)

Afferent neuron

a neuron that picks up impulses from sensory receptors and transmits them toward the central nervous system (aka sensory neuron)

Glial cells

support cells for neurons; responsible for functions such as holding neurons in place, supplying neurons with oxygen and nutrients, insulating neurons from other neurons, destroying pathogens, and removing dead neurons (aka neuroglia)

Astrocytes

neuroglia which nourish neurons and form the blood-brain barrier, which controls the transmission of solutes from the bloodstream into nervous tissue

Ependymal cells

neuroglia which line the ventricles of the brain and produce cerebrospinal fluid

Microglia

phagocytic cells that ingest and break down waste products and pathogens in the CNS

Resting potential

the electrical potential of a cell at rest, approximately -70 mV in most excitable cells

Depolarization

raising the membrane potential, Vm, from its resting potential, making the neuron more likely to fire an action potential

Hyperpolarization

lowering of membrane potential from its resting potential, making the neuron less likely to fire an action potential

Threshold

the lowest magnitude of stimulus strength (depolarization) that will induce a response; in the range of -55 to -40 mV in a neuron

Summation

process that occurs when the postsynaptic neuron or target organ requires stimulation from multiple presynaptic neurons in order to respond to stimulus; may be spatial or temporal

Temporal summation

the integration of multiple signals during a relatively short period of time in a postsynaptic neuron

Spatial summation

the integration of both the number and location of incoming signals in a postsynaptic neuron

Refractory period

the period of time following an action potential during which the neuron is incapable of depolarization

Absolute refractory period

the period of time following an action potential during which no amount of stimulation can cause another action potential to occur

Relative refractory period

the period of time following an action potential during which there must be greater than normal stimulation to cause an action potentizl

Impulse propagation

the movement of an action potential down an axon, resulting in neurotransmitter release at the synaptic bouton and transmission of the impulse to the target neuron/organ

Saltatory conduction

the process by which an electrical signal jumps across the nodes of Ranvier to travel down the axon

Effector

an organ, muscle, or gland used by an organism to respond to a stimulus; a postsynaptic target other than a neuron

Acetylcholine

a neurotransmitter found throughout the nervous system (somatic motor neurons, preganglionic parasympathetic and sympathetic nerves, and postganglionic parasympathetic neurons); metabolized by acetylchoinesterase

Interneuron

a neuron that has its cell body and nerve terminals confined to one specific area and is often involved in spinal reflexes; most numerous neuron type

White matter

the portion of the central nervous system consisting primarily of myelinated axons

Gray matter

any region in the central nervous system that consists largely of neuron cell bodies, dendrites, and synapses

Peripheral nervous system

a division of the nervous system consisting of all neurons outside the central nervous system, including sensory and motor neurons; subdivided into somatic and autonomic nervous systems

Somatic nervous system

a subdivision of the peripheral nervous system that governs all voluntary actions

Autonomic nervous system

a subdivision of the peripheral nervous system responsible for involuntary activities, which is further subdivided into the parasympathetic and sympathetic nervous systems

Ganglion

a mass of neuron cell bodies outside the central nervous system

Parasympathetic nervous system

the subdivision of the autonomic nervous system involved in rest and homeostasis; generally antagonistic to the sympathetic nervous system

Sympathetic nervous system

the subdivision of the autonomic nervous system that produces the "fight-or-flight" response; activated by stress

Reflex

an involuntary nervous pathway consisting of sensory neurons, interneurons, motor neurons, and effectors; occurs in response to a specific stimulus

Monosynaptic reflex arc

a reflex pathway having only one synapse between the sensory neuron that receives the stimulus and the motor neuron that responds to it

Polysynaptic reflex arc

a reflex pathway that involves at least one interneuron between the sensory and motor neurons