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TCN A&P ch. 7
The Nervous System
167
Anatomy
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03/13/2012

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Term
Action Potentials
Definition
The electrical signals used for long-distance communication in the nervous system.
Term
Absolute Refractory period
Definition
The period during which the neuron is functionally unable to generate a second spike, occurring early in the period of repolarization and afterhyperpolarization.
Term
Activation gate
Definition
Senses the transmembrane potential and can be opened by depolarization.
Term
Afferent axons
Definition
Carry information towards the CNS.
Term
Adrenaline
Definition
The main form of catecholamine released by the adult adrenal. Also called epinephrine.
Term
Acetylcholine
Definition
The chemical transmitter used by the preganglionic cells.
Term
Adrenal Medullae
Definition
Endocrine glands that could be thought of as modified sympathetic ganglia.
Term
Abducens
Definition
The cranial nerve that innervates the muscle that abducts the eye.
Term
Anterior horns
Definition
Central gray matter is shaped like a capital H and the horns are the arms of the H that project anteriorly.
Term
Anterior spinocerebellar tracts
Definition
Located within the spinocerebellar pathway, carrying information from muscle and joint receptors to the cerebellum.
Term
Anterior comissure
Definition
Smaller and less important fiber tracts that connect corresponding parts of the right and left halves of the CNS.
Term
Agonists
Definition
Substances similar enough to the legitimate transmitter to activate the receptor.
Term
Arachnoid mater
Definition
One of three membranes of connective tissue that surround the whole CNS, located between the dura mater and pia mater.
Term
Alpha-Adrenergic receptors
Definition
Receptors for norepinephrine and epinephrine.
Term
Arachnoid villi
Definition
Fingerlike projections of the arachnoid that act as valves projecting through the dura into the dural blood sinuses.
Term
Aterhyperpolarization phase
Definition
A period during which the membrane potential is even more inside negative than at rest.
Term
Beta-adrenergic receptors
Definition
Receptors for norepinephrine and epinephrine.
Term
Autonomic nervous system
Definition
That part of the peripheral nervous system that supplies motor innervation to the viscera.
Term
Axon hillock
Definition
A single tubular axon that sprouts from the cell body at a bump. Also called an initial segment.
Term
Basal ganglia
Definition
Now called basal nuclei, these are islands of neuronal cell bodies in the cerebral white matter.
Term
Astrocytes
Definition
A class of glial cells in the CNS that control the composition and volume of the fluid microenvironment that surrounds central neurons.
Term
Axon terminal
Definition
Structures that allow neurons to communicate with each other and with effectors.
Term
Association areas
Definition
In the cerebral cortex, responsible for forming a unified picture of the sensory world, associating key elements of it with the resources of past experience, and formulating complex behaviors.
Term
Axon
Definition
A single tubular structure on the neuron cell body that conducts action potentials.
Term
Cerebral aqueduct
Definition
Connects the third and fourth ventricle, running through the midbrain, dividing it into a dorsal tectum and paired ventral cerebral peduncles.
Term
Cerebrospinal fluid
Definition
Secreted by the choroid plexus, it circulates throughout the ventricles and the subarachnoidal space, providing a liquid cushion that gives some protection to the brain and spinal cord.
Term
Cerebral peduncles
Definition
Structures found in the fourth ventricle.
Term
Chemical synapse
Definition
The most common form of synapse in which the axon terminal releases a specific neurotransmitter chemical that acts on the plasma membrane of the target cell, either to excite or to inhibit electrical activity in the recipient cell.
Term
Central commissure
Definition
The central gray matter is shaped like a capital H. The crossbar of the H is the central commissure.
Term
Central canal
Definition
The central gray matter is shaped like a capital H. The crossbar of the H is the central commissure and contains the hollow central canal.
Term
Caudate nucleus
Definition
Islands of neuronal cell bodies in the cerebral white matter that are involved in the control of movement.
Term
Cerebellum
Definition
Coordinates and smooth body movements, particularly rapid ones.
Term
Commissures
Definition
Fiber tracts that connect corresponding parts of the right and left halves of the CNS.
Term
Closed state
Definition
An Na+ channel state in which the pore is blocked by an internal activation gate that senses the transmembrane potential and can be opened by depolarization, switching the channel to the open state.
Term
Choroid plexus
Definition
A membrane attached to the roofs of the four ventricles that secretes CSF.
Term
Corpus callosum
Definition
The major commissure.
Term
Convergent
Definition
Several pathways, possibly carrying different types of information, may make synapses on the same neurons.
Term
Cortex
Definition
The bulk of gray matter in the brain.
Term
Cortical dominance
Definition
A critical area located in only one hemisphere.
Term
Depolarization
Definition
Any change in the direction of a less-negative potential.
Term
Diencephalon
Definition
A division of the prosencephalon vesicle, containing the thalamus and hypothalamus regions.
Term
Decussate
Definition
Both sensory and motor pathways cross from one side of the CNS to the other before they enter or leave the brain.
Term
Decremental threshold
Definition
Stimulation of the dendrites results in a local depolarization that decreases in intensity as it travels through the dendrites to the cell body.
Term
Deep cerebellar nuclei
Definition
Embedded within the cerebellum’s core of white matter.
Term
Direct corticospinal pathway
Definition
The pyramidal tracts that carry axons of neurons in the motor cortex that traverse the cord without synapsing until they reach neurons in the spinal segments.
Term
Endoneurium
Definition
Encloses each axon.
Term
Dorsal ramus
Definition
A spinal nerve branch.
Term
dorsal roots
Definition
Each spinal segment has a pair that project from the posterolateral surface on each side.
Term
ependymal cells
Definition
A class of glial cells in the CNS.
Term
efferent axons
Definition
Carry commands to effectors.
Term
Dorsal root ganglion
Definition
Contains the cell bodies of somatic sensory afferents.
Term
Dorsal column pathway
Definition
A pathway located in the posterior funiculus occupies a wedge-shaped sector of the medial posterior cord and carries information about fine touch and pressure sensations.
Term
Extrapyramidal tracts
Definition
Originate in brain stem nuclei that receive input from the basal nuclei and cerebellum, control mainly the muscles of the axial skeleton, and mediate less finely controlled movements of the trunk.
Term
EPSP
Definition
Postsynaptic potentials that increase the likelihood that the postsynaptic cell will initiate an action potential at the axon hillock.
Term
General association area
Definition
Large parts of the temporal, parietal, and occipital lobes that appear to be critical for integrating multiple modes of sensory information into a comprehensive understanding of a situation.
Term
G Protein
Definition
A membrane protein (short for GTP-binding protein) that consists of three subunits designated alpha, beta, and gamma.
Term
Epithalamus
Definition
One of the principal diencephalic structures forming the roof of the third ventricle and containing the pineal gland.
Term
Fourth ventricle
Definition
The hindbrain, connected to the third ventricle by the cerebral aqueduct.
Term
Epineurium
Definition
A sheath that encloses the entire peripheral nerve.
Term
General somatic senses
Definition
A class of the somatic sensory system that includes touch, temperature, and pain that project from the body surface, as well as muscle, tendon, and joint receptors that give information about the position and movement of the body in space.
Term
Gyri (Gyrus)
Definition
Ridges that are created by folding of the cortex as it grows.
Term
Guanylyl cyclase
Definition
Converts guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP).
Term
Gray ramus
Definition
A medial spinal nerve branch that connects the base of each ventral ramus to a corresponding sympathetic chain ganglion, part of the sympathetic branch of the autonomic motor system.
Term
Glia
Definition
The supporting cells of the nervous system.
Term
Gray matter
Definition
The central matter of the spinal cord and much of the cortex.
Term
Glossopharyngeal
Definition
A cranial mixed nerve that serves part of the tongue and throat; carries gustatory afferents from posterior tongue and afferents from the carotid body and carotid sinus that convey information about blood pressure and blood.
Term
Homunculus
Definition
A map of the cortex representing the body surface.
Term
Inferior mesenteric ganglia
Definition
One of four major unpaired prevertebral ganglia located in the abdomen and pelvis.
Term
Initial segment
Definition
A single tubular axon that sprouts from the cell body at a bump. Also called an axon hillock.
Term
Hypoglossal
Definition
The cranial nerve that innervates the muscles of the tongue.
Term
Inferior hypogastric ganglia
Definition
One of four major unpaired prevertebral ganglia located in the abdomen and pelvis.
Term
Hyperpolarization
Definition
Any change in the direction of an even more inside-negative potential.
Term
IPSP
Definition
Postsynaptic potentials that tend to decrease the likelihood that the postsynaptic cell will initiate an action potential at the axon hillock.
Term
Inactivated state
Definition
When the inactivation gate remains closed, the channel cannot be reopened by depolarization.
Term
Inactivation gate
Definition
Once the channel has entered the open state this gate can swing into place and close the channel. While the inactivation gate remains closed, the channel cannot be reopened by depolarization.
Term
Ionotropic receptors
Definition
One type of neurotransmitter receptor that is also an ion channel. Binding of the transmitter to the ionotropic receptor opens the channel, resulting directly in a permeability change.
Term
Internodes
Definition
Regular intervals in which myelinated axons are surrounded by a multilayered sheath formed by glia.
Term
Lateral ventricles
Definition
The paired, C-shaped ventricles within the cerebral hemispheres.
Term
Lateral spinothalamic
Definition
Contains the spinothalamic pathway.
Term
Medulla Oblongata
Definition
A region of the brain stem.
Term
Longitudinal fissure
Definition
Separates the cerebrum into right and left hemispheres.
Term
Interneurons
Definition
Also called association neurons, these are the most numerous neurons that have their processes entirely within the CNS and are involved in processing information for an appropriate response.
Term
Melatonin
Definition
A hormone secreted by the pineal gland that contributes to control of the body’s sleeping-waking cycle.
Term
Mixed nerves
Definition
Nerves that contain both afferent and efferent axons.
Term
Midbrain
Definition
Also known as the mesencephalon, located within the brain stem.
Term
Mesencephalon
Definition
The midbrain portion of the brain stem.
Term
Metabotropic receptor
Definition
A receptor that is coupled to intracellular second messengers by way of G proteins and may be coupled to different second messenger systems in different cell types.
Term
Metencephalon
Definition
The cerebellum and pons portion of brain stem.
Term
Meninges
Definition
The three membranes of connective tissue that surround the whole CNS. The outermost membrane is the tough dura mater. Just deep to the dura mater is the arachnoid mater, and inside that the pia mater.
Term
Microglia
Definition
The cells of the nonspecific immune system rather than true glia cells—they are the form that macrophages take in the brain.
Term
Myelin
Definition
A fatty substance that insulates axons.
Term
Myelencephalon
Definition
The medulla oblongata portion of brain stem.
Term
Nodes of Ranvier
Definition
Sites in a myelinated axon in which the sheath is interrupted at regular intervals, leaving the axonal membrane bare.
Term
Monosynaptic stretch reflex
Definition
The only type of human reflex that is monosynaptic, in which there are no interneurons in the reflex arc and all integration takes place at synapses of the sensory neurons on the motor neurons. A stretch reflex may be evoked by tapping on a muscle or its tendon.
Term
Myelin sheaths
Definition
Surround the dome axons of some central neurons.
Term
Neural tube
Definition
Originates in early development and is formed from a dorsal infolding of ectoderm, the outermost of the three embryonic cell layers.
Term
Monoamine oxidase
Definition
An enzyme that packages for reuse or breaks down any given molecule of recovered norepinephrine.
Term
Nerve fiber
Definition
Long axons found in peripheral nerves that have a thread-like appearance.
Term
Open state
Definition
One of three states a Na+ channel may exist in which the transmembrane potential and can be opened by depolarization.
Term
Oculomotor
Definition
The cranial nerve that contains efferents that innervate four of the six extrinsic eye muscles and parasympathetic fibers that innervate the iris of the eye.
Term
Perineurium
Definition
A wrapping that separates fascicles from one another.
Term
Pia mater
Definition
The innermost layer of the meninges that surround the whole CNS.
Term
Oligodendrocytes
Definition
A class of glial cells in the CNS that is responsible for laying down the myelin sheaths that surround the axons of some central neurons.
Term
Paravertebral chain ganglion
Definition
Part of the sympathetic pathway to the effectors.
Term
occipital lobes
Definition
The most caudal lobes that are the site of the primary visual area.
Term
Pineal gland
Definition
The major structure of the epithalamus that is an unpaired, knoblike structure that secretes melatonin.
Term
Polysynaptic Withdrawl reflex
Definition
The reflex arc includes one or more interneurons. The withdrawal reflex is a commonly experienced polysynaptic spinal reflex that results in a generalized flexion of an appendage in response to an aversive stimulus.
Term
Plexi (plexus)
Definition
Interlacing networks formed by the ventral rami of all spinal nerves, with the exception of T2–T12, by joining one another lateral to the vertebral column.
Term
Polarized
Definition
A resting cell’s membrane in which it is charged electrically with a positive and negative pole.
Term
Pituitary gland
Definition
An extremely important element of the endocrine system, projects inferiorly from the hypothalamus.
Term
pons
Definition
A region in the brain stem.
Term
Postcentral gyrus
Definition
The primary somatosensory areas of the cortex.
Term
Posterior spinocerebellar tracts
Definition
Located within the spinocerebellar pathway, carrying information from muscle and joint receptors to the cerebellum.
Term
Postganglionic Neuron
Definition
The second neuron of the autonomic pathways; In the peripheral ganglion, the neuron on which the preganglionic cell’s axon synapses and then projects to an effector in a visceral organ.
Term
Postsynaptic
Definition
In a synaptic transmission, the recipient cell.
Term
Postsynaptic potential (PSP)
Definition
Caused by the binding of transmitter to its receptor initiates a permeability change in the postsynaptic cell.
Term
Posterior horns (Dorsal horns)
Definition
Central gray matter is shaped like a capital H and the horns are the arms of the H that project posteriorly.
Term
Primary brain vesicles
Definition
The prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).
Term
Precentral gyrus
Definition
The primary motor areas of the cortex.
Term
Primary auditory area
Definition
Located in the temporal lobe.
Term
Preganglionic neuron
Definition
The first neuron of the autonomic pathways; its cell body is in the CNS, and its axon projecting to a peripheral autonomic ganglion.
Term
Prosencephalon (forebrain)
Definition
One of three primary brain vesicles.
Term
Prevertebral ganglia
Definition
The point in which a preganglionic axon synapses on a postganglionic neuron that projects to an effector in the abdominal cavity.
Term
Pyramidal tracts
Definition
Carry axons of neurons in the motor cortex that traverse the cord without synapsing until they reach neurons in the spinal segments.
Term
Prefrontal cortex
Definition
Lies rostral to the motor areas of the precentral gyrus, and is important for activities that involve reasoning, complex learning abilities, long-term planning, and judgment and is also involved in mood, emotions, and social behavior.
Term
Rhombencephalon (hindbrain)
Definition
One of the three primary brain vesicles.
Term
Resting potential
Definition
In the resting cell, the plasma membrane is mainly permeable to K+, and the inside-to-outside concentration gradient tends to drive K+ toward the outside of the cell, giving the membrane a slight excess of positive charge on the outside surface of the membrane and a corresponding slight excess of negative charge on the inside.
Term
Reflex arc
Definition
The organization of neurons and effectors, which is the simplest way of organizing the nervous system to achieve an appropriate response.
Term
Rami communicante
Definition
The medial gray ramus and the lateral white ramus that connect the base of each ventral ramus to a corresponding sympathetic chain ganglion, part of the sympathetic branch of the autonomic motor system.
Term
Resting state
Definition
A state in which closed channels could be thought of as available to be opened by depolarization.
Term
Relative refractory period
Definition
A period after the absolute refractory period during which a second action potential can be initiated, but the stimulus must be more intense.
Term
Somatotopy
Definition
The map-like organization of the brain.
Term
Spike
Definition
When an action potential occurs, the membrane potential changes rapidly from its resting inside-negative value to an inside-positive value (peaking typically in the range of +20 to +50 mV) and just as quickly returns to the resting value.
Term
Schwann cells
Definition
In the PNS, the glial cells responsible for myelinating CNS neurons.
Term
Somatic region
Definition
One region of the PNS that consists of the skeletal muscles and body surface.
Term
Spatial summation
Definition
Multiple synapses located on the same postsynaptic cell.
Term
Spinal nerve
Definition
The major nerves of the spine; there are thirty-one pairs of spinal nerves.
Term
Splanchnic nerve
Definition
A nerve that a preganglionic axon can follow after passing through the chain ganglion without synapsing.
Term
Spinothalamic pathway
Definition
Located in the anterior and lateral spinothalamic tracts, the pathway carries information about coarse touch, temperature, and pain sensations to the primary somatosensory cortex.
Term
Sulci
Definition
Shallow grooves created by folding of the cortex as it grows.
Term
Spinocerebellar pathway
Definition
Carries information from muscle and joint receptors to the cerebellum.
Term
Sympathetic chain ganglia
Definition
A paired series lying parallel to the spinal column on each side and connected to the ventral rami of T1–L1 by rami communicantes.
Term
Spinal reflexes
Definition
The reflex arc does not include brain neurons and is typically limited to one or a few adjacent spinal segments.
Term
Synapses
Definition
The points of close contact between axon terminals and the target cells.
Term
Synaptic cleft
Definition
A narrow space that separates the presynaptic cell and the postsynaptic cell.
Term
Synaptic transmission
Definition
The process of sending information across synapses.
Term
Synaptic fatigue
Definition
Continual use of a particular pathway may result in depletion of the stores of transmitter, decreasing the efficacy of the synapses.
Term
Synaptic vesicles
Definition
A small, membrane-bound vesicles that stores neurotransmitter chemicals in the axon terminal.
Term
Tectum
Definition
The roof of the cerebral aqueduct that runs through the midbrain.
Term
Synaptic delay
Definition
Represents the time required for the presynaptic cell to organize transmitter release, for the transmitter to diffuse to receptors, and for the activated receptors to cause a PSP.
Term
Telencephalon
Definition
In the forebrain, the cerebral cortex and basal nuclei.
Term
Temporal summation
Definition
Several action potentials that arrive one after the other at the same synapse.
Term
Temporal lobe
Definition
The site of the primary auditory area.
Term
Thalamocortical fiber tracts
Definition
Relay information from the somatosensory, visual, auditory, olfactory, and gustatory sensory systems to the primary processing areas in the cortex.
Term
telodendria
Definition
Branches formed at the end of axons, ending in axon terminals.
Term
Upstroke
Definition
A rapid rise in the membrane potential.
Term
Third ventricle
Definition
Located in the center of the diencephalon.
Term
Vagus
Definition
The only cranial nerve to extend beyond the head/neck; innervates larynx and contains afferents and parasympathetic efferents from/to thoracic and abdominal viscera.
Term
Transverse Fissure
Definition
Separates the cerebral hemispheres from the cerebellum.
Term
Trigeminal
Definition
A cranial nerve that contains afferents from the face and innervates masticatory (chewing) muscles.
Term
White matter
Definition
Forming the outer layer of the spinal cord; also the location of the cerebral basal nuclei.
Term
Ventral ramus
Definition
A spinal nerve branch.
Term
Ventral roots
Definition
Each spinal segment has a pair that project from the anterolateral surface.
Term
Ventral horns
Definition
Central gray matter is shaped like a capital H and the horns are the arms of the H that project anteriorly.
Term
Visceral region
Definition
One region of the PNS that consists of the soft internal organs of the digestive system, lungs, heart, and blood vessels, etc.
Term
White ramus
Definition
The lateral branch of the rami communicante that connects the base of each ventral ramus to a corresponding sympathetic chain ganglion.
Term
Ventricles
Definition
A system of four interconnected spaces of the brain filled with cerebrospinal fluid (CSF).
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