Central Nervous System (CNS)
the brain and spinal cord
spinal cord
a column of nerves that transmits information between the brain and the peripheral nervous system
peripheral nervous system (PNS)
the parts of the nervous system outside the brain and spinal cord
spinal nerves
major nerves that carry sensory and motor messages in and out of the spinal cord
neuron
a cell in the nervous system that transmits information
nerve
a bundle of neuron axons
cranial nerves
major nerves that leave the brain without passing through the spinal cord
somatic nervous system (SNS)
a network linking the spinal cord with the body and sense organs
autonomic nervous system (ANS)
the collection of axons that carry information to and from internal organs and glands
sympathetic nervous system (sympathetic branch)
the division of the autonomic nervous system that coordinates arousal
parasympathetic nervous system (parasympathetic branch)
the division of the autonomic nervous system that quiets the body and conserves energy
dendrites
neuron fibers that relieve incoming messages
axon
a fiber that carries information away from the cell body of a neuron
axon terminals
bulb-shaped structures at the ends of axons that form synapses with the dendrites and cell bodies of other neurons
resting potential
the electrical charge of an inactive neuron
threshold
in neurons, the point at which a nerve impulse is triggered
action potential
a brief change in a neuron’s electrical charge
ion channels
tiny openings through the axon membrane
negative after-potential
a drop in the electrical charge below the resting potential
myelin sheath
insulating material that covers some axons
saltatory conduction
the process by which action potentials traveling down the axons of neurons coated with myelin jump from gap to gap in the myelin layer
synapse
a microscopic space over which messages pass between two neurons
synaptic transmission
the chemical process that carries information from one neuron to another
neurotransmitter
A chemical that moves information from one nervous-system to another