Glossary: The Nervous System

abducens nerve
sixth cranial nerve; responsible for contraction of one of the extraocular muscles
action potential
change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers
arachnoid mater
middle layer of the meninges named for the spider-web–like trabeculae that extend between it and the pia mater
astrocyte
glial cell type of the CNS that provides support for neurons and maintains the blood-brain barrier
autonomic nervous system (ANS)functional division of the nervous system that is responsible for homeostatic reflexes that coordinate control of cardiac and smooth muscle, as well as glandular tissue
axon
single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a target cell
axon terminal
end of the axon, where there are usually several branches extending toward the target cell
blood-brain barrier (BBB)
physiological barrier between the circulatory system and the central nervous system that establishes a privileged blood supply, restricting the flow of substances into the CNS
brain
the large organ of the central nervous system composed of white and gray matter, contained within the cranium and continuous with the spinal cord
Broca’s area
region of the frontal lobe associated with the motor commands necessary for speech production and located only in the cerebral hemisphere responsible for language production, which is the left side in approximately 95 percent of the population
Brodmann’s areas
mapping of regions of the cerebral cortex based on microscopic anatomy that relates specific areas to functional differences, as described by Brodmann in the early 1900s
brain stem
region of the adult brain that includes the midbrain, pons, and medulla oblongata and develops from the mesencephalon, metencephalon, and myelencephalon of the embryonic brain
cauda equina
bundle of spinal nerve roots that descend from the lower spinal cord below the first lumbar vertebra and lie within the vertebral cavity; has the appearance of a horse’s tail
central canal
hollow space within the spinal cord that is the remnant of the center of the neural tube
central nervous system (CNS)
anatomical division of the nervous system located within the cranial and vertebral cavities, namely the brain and spinal cord
cerebellum
region of the adult brain connected primarily to the pons that developed from the metencephalon (along with the pons) and is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord
cerebral cortex
outer gray matter covering the forebrain, marked by wrinkles and folds known as gyri and sulci
cerebral hemisphere
one half of the bilaterally symmetrical cerebrum
cerebrospinal fluid (CSF)
circulatory medium within the CNS that is produced by ependymal cells in the choroid plexus filtering the blood
cerebrum
region of the adult brain that develops from the telencephalon and is responsible for higher neurological functions such as memory, emotion, and consciousness
cervical plexus
nerve plexus associated with the upper cervical spinal nerves
choroid plexus
specialized structures containing ependymal cells lining blood capillaries that filter blood to produce CSF in the four ventricles of the brain
continuous conduction
slow propagation of an action potential along an unmyelinated axon owing to voltage-gated Na+ channels located along the entire length of the cell membrane
corpus callosum
large white matter structure that connects the right and left cerebral hemispheres
cranial nerve
one of twelve nerves connected to the brain that are responsible for sensory or motor functions of the head and neck
dendrite
one of many branchlike processes that extends from the neuron cell body and functions as a contact for incoming signals (synapses) from other neurons or sensory cells
depolarization
change in a cell membrane potential from rest toward zero
diencephalon
region of the adult brain that retains its name from embryonic development and includes the thalamus and hypothalamus
dura mater
tough, fibrous, outer layer of the meninges that is attached to the inner surface of the cranium and vertebral column and surrounds the entire CNS
endoneurium
innermost layer of connective tissue that surrounds individual axons within a nerve
ependymal cell
glial cell type in the CNS responsible for producing cerebrospinal fluid
epineurium
outermost layer of connective tissue that surrounds an entire nerve
excitable membrane
cell membrane that regulates the movement of ions so that an electrical signal can be generated
facial nerve
seventh cranial nerve; responsible for contraction of the facial muscles and for part of the sense of taste, as well as causing saliva production
fascicle
small bundles of nerve or muscle fibers enclosed by connective tissue
foramen magnum
large opening in the occipital bone of the skull through which the spinal cord emerges and the vertebral arteries enter the cranium
frontal lobe
region of the cerebral cortex directly beneath the frontal bone of the cranium
glial cell
one of the various types of neural tissue cells responsible for maintenance of the tissue, and largely responsible for supporting neurons
glossopharyngeal nerve
ninth cranial nerve; responsible for contraction of muscles in the tongue and throat and for part of the sense of taste, as well as causing saliva production
graded potential
change in the membrane potential that varies in size, depending on the size of the stimulus that elicits it
gyrus
ridge formed by convolutions on the surface of the cerebrum or cerebellum
hippocampus
gray matter deep in the temporal lobe that is very important for long-term memory formation
hypoglossal nerve
twelfth cranial nerve; responsible for contraction of muscles of the tongue
hypothalamus
major region of the diencephalon that is responsible for coordinating autonomic and endocrine control of homeostasis
integration
nervous system function that combines sensory perceptions and higher cognitive functions (memories, learning, emotion, etc.) to produce a response
ligand-gated channels
another name for an ionotropic receptor for which a neurotransmitter is the ligand
limbic system
most associated with emotional behavior and memory formation
lumbar plexus
nerve plexus associated with the lumbar spinal nerves
lumbar puncture
procedure used to withdraw CSF from the lower lumbar region of the vertebral column that avoids the risk of damaging CNS tissue because the spinal cord ends at the upper lumbar vertebrae
mechanically gated channel
ion channel that opens when a physical event directly affects the structure of the protein
membrane potential
distribution of charge across the cell membrane, based on the charges of ions
meninges
protective outer coverings of the CNS composed of connective tissue
microglia
glial cell type in the CNS that serves as the resident component of the immune system
midbrain
middle region of the adult brain that develops from the mesencephalon
myelin sheath
lipid-rich layer of insulation that surrounds an axon, formed by oligodendrocytes in the CNS and Schwann cells in the PNS; facilitates the transmission of electrical signals
myelin
lipid-rich insulating substance surrounding the axons of many neurons, allowing for faster transmission of electrical signals
nerve
cord-like bundle of axons located in the peripheral nervous system that transmits sensory input and response output to and from the central nervous system
neuron
neural tissue cell that is primarily responsible for generating and propagating electrical signals into, within, and out of the nervous system
neurotransmitter
chemical signal that is released from the synaptic end bulb of a neuron to cause a change in the target cell
node of Ranvier
gap between two myelinated regions of an axon, allowing for strengthening of the electrical signal as it propagates down the axon
occipital lobe
region of the cerebral cortex directly beneath the occipital bone of the cranium
oculomotor nerve
third cranial nerve; responsible for contraction of four of the extraocular muscles, the muscle in the upper eyelid, and pupillary constriction
olfaction
special sense responsible for smell, which has a unique, direct connection to the cerebrum
olfactory nerve
first cranial nerve; responsible for the sense of smell
oligodendrocyte
glial cell type in the CNS that provides the myelin insulation for axons in tracts
optic nerve
second cranial nerve; responsible for visual sensation
parietal lobe
region of the cerebral cortex directly beneath the parietal bone of the cranium
perineurium
layer of connective tissue surrounding fascicles within a nerve
peripheral nervous system (PNS)
anatomical division of the nervous system that is largely outside the cranial and vertebral cavities, namely all parts except the brain and spinal cord
pia mater
thin, innermost membrane of the meninges that directly covers the surface of the CNS
plexus
network of nerves or nervous tissue
prefrontal lobe
specific region of the frontal lobe anterior to the more specific motor function areas, which can be related to the early planning of movements and intentions to the point of being personality-type functions
premotor area
region of the frontal lobe responsible for planning movements that will be executed through the primary motor cortex
process
in cells, an extension of a cell body; in the case of neurons, this includes the axon and dendrites
propagation
movement of an action potential along the length of an axon
proprioception
general sensory perceptions providing information about location and movement of body parts; the “sense of the self”
repolarization
return of the membrane potential to its normally negative voltage at the end of the action potential
resting membrane potential
the difference in voltage measured across a cell membrane under steady-state conditions, typically -70 mV
reticular formation
diffuse region of gray matter throughout the brain stem that regulates sleep, wakefulness, and states of consciousness
sacral plexus
nerve plexus associated with the lower lumbar and sacral spinal nerves
saltatory conduction
quick propagation of the action potential along a myelinated axon owing to voltage-gated Na+ channels being present only at the nodes of Ranvier
satellite cell
glial cell type in the PNS that provides support for neurons in the ganglia
Schwann cell
glial cell type in the PNS that provides the myelin insulation for axons in nerves
sensation
nervous system function that receives information from the environment and translates it into the electrical signals of nervous tissue
somatic nervous system (SNS)
functional division of the nervous system that is concerned with conscious perception, voluntary movement, and skeletal muscle reflexes
spinal cord
organ of the central nervous system found within the vertebral cavity and connected with the periphery through spinal nerves; mediates reflex behaviors
spinal accessory nerve
eleventh cranial nerve; responsible for contraction of neck muscles
spinal nerve
one of 31 nerves connected to the spinal cord
stimulus
an event in the external or internal environment that registers as activity in a sensory neuron
subarachnoid space
space between the arachnoid mater and pia mater that contains CSF and the fibrous connections of the arachnoid trabeculae
sulcus
groove formed by convolutions in the surface of the cerebral cortex
synapse
narrow junction across which a chemical signal passes from neuron to the next, initiating a new electrical signal in the target cell
synaptic cleft
small gap between cells in a chemical synapse where neurotransmitter diffuses from the presynaptic element to the postsynaptic element
synaptic end bulb
swelling at the end of an axon where neurotransmitter molecules are released onto a target cell across a synapse
temporal lobe
region of the cerebral cortex directly beneath the temporal bone of the cranium
thalamus
major region of the diencephalon that is responsible for relaying information between the cerebrum and the hindbrain, spinal cord, and periphery
threshold
membrane voltage at which an action potential is initiated
trigeminal nerve
fifth cranial nerve; responsible for cutaneous sensation of the face and contraction of the muscles of mastication
trochlear nerve
fourth cranial nerve; responsible for contraction of one of the extraocular muscles
vagus nerve
tenth cranial nerve; responsible for the autonomic control of organs in the thoracic and upper abdominal cavities
ventricles
remnants of the hollow center of the neural tube that are spaces for cerebrospinal fluid to circulate through the brain
vestibulocochlear nerve
eighth cranial nerve; responsible for the sensations of hearing and balance