Glossary: The Nervous System

abducens nerve: sixth cranial nerve; responsible for contraction of one of the extraocular muscles

alar plate: developmental region of the spinal cord that gives rise to the posterior horn of the gray matter

amygdala: nucleus deep in the temporal lobe of the cerebrum that is related to memory and emotional behavior

anterior column: white matter between the anterior horns of the spinal cord composed of many different groups of axons of both ascending and descending tracts

anterior horn: gray matter of the spinal cord containing multipolar motor neurons, sometimes referred to as the ventral horn

anterior median fissure: deep midline feature of the anterior spinal cord, marking the separation between the right and left sides of the cord

anterior spinal artery: blood vessel from the merged branches of the vertebral arteries that runs along the anterior surface of the spinal cord

arachnoid granulation: outpocket of the arachnoid membrane into the dural sinuses that allows for reabsorption of CSF into the blood

arachnoid mater: middle layer of the meninges named for the spider-web–like trabeculae that extend between it and the pia mater

arachnoid trabeculae: filaments between the arachnoid and pia mater within the subarachnoid space

ascending tract: central nervous system fibers carrying sensory information from the spinal cord or periphery to the brain

axillary nerve: systemic nerve of the arm that arises from the brachial plexus

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

basal forebrain: nuclei of the cerebrum related to modulation of sensory stimuli and attention through broad projections to the cerebral cortex, loss of which is related to Alzheimer’s disease

basal nuclei: nuclei of the cerebrum (with a few components in the upper brain stem and diencephalon) that are responsible for assessing cortical movement commands and comparing them with the general state of the individual through broad modulatory activity of dopamine neurons; largely related to motor functions, as evidenced through the symptoms of Parkinson’s and Huntington’s diseases

basal plate: developmental region of the spinal cord that gives rise to the lateral and anterior horns of gray matter

basilar artery: blood vessel from the merged vertebral arteries that runs along the dorsal surface of the brain stem

brachial plexus: nerve plexus associated with the lower cervical spinal nerves and first thoracic spinal nerve

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

carotid canal: opening in the temporal bone through which the internal carotid artery enters the cranium

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

caudate: nucleus deep in the cerebrum that is part of the basal nuclei; along with the putamen, it is part of the striatum

central canal: hollow space within the spinal cord that is the remnant of the center of the neural tube

central sulcus: surface landmark of the cerebral cortex that marks the boundary between the frontal and parietal lobes

cephalic flexure: curve in midbrain of the embryo that positions the forebrain ventrally

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 aqueduct: connection of the ventricular system between the third and fourth ventricles located in the midbrain

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

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

circle of Willis: unique anatomical arrangement of blood vessels around the base of the brain that maintains perfusion of blood into the brain even if one component of the structure is blocked or narrowed

common carotid artery: blood vessel that branches off the aorta (or the brachiocephalic artery on the right) and supplies blood to the head and neck

corpus callosum: large white matter structure that connects the right and left cerebral hemispheres

cranial nerve ganglion: sensory ganglion of cranial nerves

cranial nerve: one of twelve nerves connected to the brain that are responsible for sensory or motor functions of the head and neck

descending tract: central nervous system fibers carrying motor commands from the brain to the spinal cord or periphery

diencephalon: region of the adult brain that retains its name from embryonic development and includes the thalamus and hypothalamus

direct pathway: connections within the basal nuclei from the striatum to the globus pallidus internal segment and substantia nigra pars reticulata that disinhibit the thalamus to increase cortical control of movement

disinhibition: disynaptic connection in which the first synapse inhibits the second cell, which then stops inhibiting the final target

dorsal (posterior) nerve root: axons entering the posterior horn of the spinal cord

dorsal (posterior) root ganglion: sensory ganglion attached to the posterior nerve root of a spinal nerve

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

dural sinus: any of the venous structures surrounding the brain, enclosed within the dura mater, which drain blood from the CNS to the common venous return of the jugular veins

endoneurium: innermost layer of connective tissue that surrounds individual axons within a nerve

enteric nervous system: peripheral structures, namely ganglia and nerves, that are incorporated into the digestive system organs

enteric plexus: neuronal plexus in the wall of the intestines, which is part of the enteric nervous system

epineurium: outermost layer of connective tissue that surrounds an entire nerve

epithalamus: region of the diecephalon containing the pineal gland

esophageal plexus: neuronal plexus in the wall of the esophagus that is part of the enteric nervous system

extraocular muscles: six skeletal muscles that control eye movement within the orbit

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

femoral nerve: systemic nerve of the anterior leg that arises from the lumbar plexus

fibular nerve: systemic nerve of the posterior leg that begins as part of the sciatic nerve

foramen magnum: large opening in the occipital bone of the skull through which the spinal cord emerges and the vertebral arteries enter the cranium

forebrain: anterior region of the adult brain that develops from the prosencephalon and includes the cerebrum and diencephalon

fourth ventricle: the portion of the ventricular system that is in the region of the brain stem and opens into the subarachnoid space through the median and lateral apertures

frontal eye field: region of the frontal lobe associated with motor commands to orient the eyes toward an object of visual attention

frontal lobe: region of the cerebral cortex directly beneath the frontal bone of the cranium

gastric plexuses: neuronal networks in the wall of the stomach that are part of the enteric nervous system

globus pallidus: nuclei deep in the cerebrum that are part of the basal nuclei and can be divided into the internal and external segments

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

gyrus: ridge formed by convolutions on the surface of the cerebrum or cerebellum

hindbrain: posterior region of the adult brain that develops from the rhombencephalon and includes the pons, medulla oblongata, and 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

indirect pathway: connections within the basal nuclei from the striatum through the globus pallidus external segment and subthalamic nucleus to the globus pallidus internal segment/substantia nigra pars compacta that result in inhibition of the thalamus to decrease cortical control of movement

inferior colliculus: half of the midbrain tectum that is part of the brain stem auditory pathway

inferior olive: nucleus in the medulla that is involved in processing information related to motor control

intercostal nerve: systemic nerve in the thoracic cavity that is found between two ribs

internal carotid artery: branch from the common carotid artery that enters the cranium and supplies blood to the brain

interventricular foramina: openings between the lateral ventricles and third ventricle allowing for the passage of CSF

jugular veins: blood vessels that return “used” blood from the head and neck

kinesthesia: general sensory perception of movement of the body

lateral apertures: pair of openings from the fourth ventricle to the subarachnoid space on either side and between the medulla and cerebellum

lateral column: white matter of the spinal cord between the posterior horn on one side and the axons from the anterior horn on the same side; composed of many different groups of axons, of both ascending and descending tracts, carrying motor commands to and from the brain

lateral horn: region of the spinal cord gray matter in the thoracic, upper lumbar, and sacral regions that is the central component of the sympathetic division of the autonomic nervous system

lateral sulcus: surface landmark of the cerebral cortex that marks the boundary between the temporal lobe and the frontal and parietal lobes

lateral ventricles: portions of the ventricular system that are in the region of the cerebrum

limbic cortex: collection of structures of the cerebral cortex that are involved in emotion, memory, and behavior and are part of the larger limbic system

limbic system: structures at the edge (limit) of the boundary between the forebrain and hindbrain that are most associated with emotional behavior and memory formation

longitudinal fissure: large separation along the midline between the two cerebral hemispheres

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

median aperture: singular opening from the fourth ventricle into the subarachnoid space at the midline between the medulla and cerebellum

median nerve: systemic nerve of the arm, located between the ulnar and radial nerves

meninges: protective outer coverings of the CNS composed of connective tissue

mesencephalon: primary vesicle of the embryonic brain that does not significantly change through the rest of embryonic development and becomes the midbrain

metencephalon: secondary vesicle of the embryonic brain that develops into the pons and the cerebellum

midbrain: middle region of the adult brain that develops from the mesencephalon

myelencephalon: secondary vesicle of the embryonic brain that develops into the medulla

nerve plexus: network of nerves without neuronal cell bodies included

neural crest: tissue that detaches from the edges of the neural groove and migrates through the embryo to develop into peripheral structures of both nervous and non-nervous tissues

neural fold: elevated edge of the neural groove

neural groove: region of the neural plate that folds into the dorsal surface of the embryo and closes off to become the neural tube

neural plate: thickened layer of neuroepithelium that runs longitudinally along the dorsal surface of an embryo and gives rise to nervous system tissue

neural tube: precursor to structures of the central nervous system, formed by the invagination and separation of neuroepithelium

neuraxis: central axis to the nervous system, from the posterior to anterior ends of the neural tube; the inferior tip of the spinal cord to the anterior surface of the cerebrum

occipital lobe: region of the cerebral cortex directly beneath the occipital bone of the cranium

occipital sinuses: dural sinuses along the edge of the occipital lobes of the cerebrum

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

optic nerve: second cranial nerve; responsible for visual sensation

orthostatic reflex: sympathetic function that maintains blood pressure when standing to offset the increased effect of gravity

paravertebral ganglia: autonomic ganglia superior to the sympathetic chain ganglia

parietal lobe: region of the cerebral cortex directly beneath the parietal bone of the cranium

parieto-occipital sulcus: groove in the cerebral cortex representing the border between the parietal and occipital cortices

perineurium: layer of connective tissue surrounding fascicles within a nerve

phrenic nerve: systemic nerve from the cervical plexus that enervates the diaphragm

pia mater: thin, innermost membrane of the meninges that directly covers the surface of the CNS

plexus: network of nerves or nervous tissue

postcentral gyrus: ridge just posterior to the central sulcus, in the parietal lobe, where somatosensory processing initially takes place in the cerebrum

posterior columns: white matter of the spinal cord that lies between the posterior horns of the gray matter, sometimes referred to as the dorsal column; composed of axons of ascending tracts that carry sensory information up to the brain

posterior horn: gray matter region of the spinal cord in which sensory input arrives, sometimes referred to as the dorsal horn

posterior median sulcus: midline feature of the posterior spinal cord, marking the separation between right and left sides of the cord

posterolateral sulcus: feature of the posterior spinal cord marking the entry of posterior nerve roots and the separation between the posterior and lateral columns of the white matter

precentral gyrus: primary motor cortex located in the frontal lobe of the cerebral cortex

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

prevertebral ganglia: autonomic ganglia that are anterior to the vertebral column and functionally related to the sympathetic chain ganglia

primary vesicle: initial enlargements of the anterior neural tube during embryonic development that develop into the forebrain, midbrain, and hindbrain

proprioception: general sensory perceptions providing information about location and movement of body parts; the “sense of the self”

prosencephalon: primary vesicle of the embryonic brain that develops into the forebrain, which includes the cerebrum and diencephalon

putamen: nucleus deep in the cerebrum that is part of the basal nuclei; along with the caudate, it is part of the striatum

radial nerve: systemic nerve of the arm, the distal component of which is located near the radial bone

reticular formation: diffuse region of gray matter throughout the brain stem that regulates sleep, wakefulness, and states of consciousness

rhombencephalon: primary vesicle of the embryonic brain that develops into the hindbrain, which includes the pons, cerebellum, and medulla

sacral plexus: nerve plexus associated with the lower lumbar and sacral spinal nerves

saphenous nerve: systemic nerve of the lower anterior leg that is a branch from the femoral nerve

sciatic nerve: systemic nerve from the sacral plexus that is a combination of the tibial and fibular nerves and extends across the hip joint and gluteal region into the upper posterior leg

sciatica: painful condition resulting from inflammation or compression of the sciatic nerve or any of the spinal nerves that contribute to it

secondary vesicle: five vesicles that develop from primary vesicles, continuing the process of differentiation of the embryonic brain

sigmoid sinuses: dural sinuses that drain directly into the jugular veins

somatosensation: general senses related to the body, usually thought of as the senses of touch, which would include pain, temperature, and proprioception

spinal accessory nerve: eleventh cranial nerve; responsible for contraction of neck muscles

spinal nerve: one of 31 nerves connected to the spinal cord

straight sinus: dural sinus that drains blood from the deep center of the brain to collect with the other sinuses

striatum: the caudate and putamen collectively, as part of the basal nuclei, which receive input from the cerebral cortex

subarachnoid space: space between the arachnoid mater and pia mater that contains CSF and the fibrous connections of the arachnoid trabeculae

subcortical nucleus: all the nuclei beneath the cerebral cortex, including the basal nuclei and the basal forebrain

substantia nigra pars compacta: nuclei within the basal nuclei that release dopamine to modulate the function of the striatum; part of the motor pathway

substantia nigra pars reticulata: nuclei within the basal nuclei that serve as an output center of the nuclei; part of the motor pathway

subthalamus: nucleus within the basal nuclei that is part of the indirect pathway

sulcus: groove formed by convolutions in the surface of the cerebral cortex

superior colliculus: half of the midbrain tectum that is responsible for aligning visual, auditory, and somatosensory spatial perceptions

superior sagittal sinus: dural sinus that runs along the top of the longitudinal fissure and drains blood from the majority of the outer cerebrum

sympathetic chain ganglia: autonomic ganglia in a chain along the anterolateral aspect of the vertebral column that are responsible for contributing to homeostatic mechanisms of the autonomic nervous system

systemic nerve: nerve in the periphery distal to a nerve plexus or spinal nerve

tectum: region of the midbrain, thought of as the roof of the cerebral aqueduct, which is subdivided into the inferior and superior colliculi

tegmentum: region of the midbrain, thought of as the floor of the cerebral aqueduct, which continues into the pons and medulla as the floor of the fourth ventricle

telencephalon: secondary vesicle of the embryonic brain that develops into the cerebrum

temporal lobe: region of the cerebral cortex directly beneath the temporal bone of the cranium

terminal ganglion: autonomic ganglia that are near or within the walls of organs that are responsible for contributing to homeostatic mechanisms of the autonomic nervous system

thalamus: major region of the diencephalon that is responsible for relaying information between the cerebrum and the hindbrain, spinal cord, and periphery

third ventricle: portion of the ventricular system that is in the region of the diencephalon

tibial nerve: systemic nerve of the posterior leg that begins as part of the sciatic nerve

transverse sinuses: dural sinuses that drain along either side of the occipital–cerebellar space

trigeminal ganglion: sensory ganglion that contributes sensory fibers to the trigeminal nerve

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

ulnar nerve: systemic nerve of the arm located close to the ulna, a bone of the forearm

vagus nerve: tenth cranial nerve; responsible for the autonomic control of organs in the thoracic and upper abdominal cavities

ventral (anterior) nerve root: axons emerging from the anterior or lateral horns of the spinal cord

ventricles: remnants of the hollow center of the neural tube that are spaces for cerebrospinal fluid to circulate through the brain

vertebral arteries: arteries that ascend along either side of the vertebral column through the transverse foramina of the cervical vertebrae and enter the cranium through the foramen magnum

vestibulocochlear nerve: eighth cranial nerve; responsible for the sensations of hearing and balance