Ch 12: Nervous System Structure & Function

central nervous system (CNS)

brain and spinal cord

axon

The fibrous process that connects a neuron with its target.

process

extension from neuron

dendrite

process that receives most of the input from other neurons

gray matter

regions of nervous tissue that contain many cell bodies and dendrites

white matter

regions of nervous tissue that contain many axons

nucleus

localized collection of neuron cell bodies in the CNS

ganglion

cluster of neuron cell bodies in the PNS

tract

bundle of axons found in CNS

nerve

bundle of axons found in PNS

somatic nervous system (SNS)

responsible for conscious perception and voluntary motor responses, including reflexes

autonomic nervous system (ANS)

responsible for involuntary control of the body, often pertaining to homeostasis.

enteric nervous system (ENS)

responsible for controlling the smooth muscle and glandular tissue in the digestive system, part of PNS, not dependent on CNS.

synapses

specialized areas of contact where dendrites of one neuron communicate with those of other neurons.

axon hillock

region where the axon emerges from the cell body, the cell body tapers towards the axon fiber

axoplasm

cytoplasm within the axon hillock transitions to a solution of limited components called:

trigger zone

action potentials are generated here, which is a combination of the axon hillock and initial segment

myelin

insulating substance made of glial cells that wraps around many axons

node of ranvier

gaps in myelin sheath surrounding axons, important to how electrical signals are transported down axons.

axon segment

portions of the axon between the nodes of ranvier that are covered in myelin

axon terminal

end of the axon where there are usually several branches extending towards the target cell.

synaptic end bulb

enlargement in the end of each branch of the axon terminal, makes contact with the target cell at the synapse

astrocytes

most abundant neuroglia in CNS, support and brace neurons, anchor them to their nutrient supply

oligodendrocyte

glial cell in CNS, wrap around thicker nerve fibers creating a myelin sheath that insulates the neuron

Microglia

CNS-resident macrophages which engulf and ingest harmful molecules and pathogens, protect the health of neurons and repair damages

ependymal cell

filters blood to make cerebrospinal fluid (CSF)

choroid plexus

structure in ventricles of brain where ependymal cells come in contact with blood vessels

satellite cells

Glial cells of the PNS (sensory and autonomic ganglia), surround cell bodies of neurons

schwann cells

insulate axons with myelin in the PNS, wraps around only one axon segment

threshold

voltage at which a signal is generated

action potential

resulting electrical signal created by the change in voltage of cell membrane from stimulus

propagation

process of the action potential traveling along the axon and into the synaptic end bulbs

thalamus

part of the brain that acts as a relay for sensory information

cerebral cortex

outermost layer of gray matter in the brain, where conscious perception of stimuli begins and is processed and integrated with other sensory stimuli, and a new signal is sent out to create a reaction

precentral gyrus

upper motor neuron of CNS; has an axon that extends all the way down the spinal cord; part of cerebral cortex

nonspecific channel

ion channels that are selective for charge but not for size; only allow positively charged cations through

ligand-gated channel

opens only when a specific ligand binds to the extracellular region of the channel

iontropic receptor

ligand-gated channels allow ions to cross the membrane when the channel is opened by the ligand, changing the charge of the membrane

mechanically gated channel

opens because of a physical distortion of the cell membrane; many channels associated with touch are gated this way.

voltage-gated channel

channel that responds to changes in the electrical charge of the membrane; the inner portion of the membrane is usually negatively charged, when the charge becomes less negative the channel allows ions to cross the membrane.

membrane potential

variations in the electrical state of the cell membrane as relative to the charge outside the cell.

continuous conduction

propagation along an unmyelinated axon

saltatory conduction

propagation across a myelinated axon; faster