chapter 12,13,14

medial lemniscus

A white matter tract that originates in the gracile and cuneate nuclei of the medulla oblongata and extends to the thalamus on the same side; sensory axons in this tract conduct nerve impulses for the sensations of proprioception, fine touch, vibration, hearing, and equilibrium

chemcial protection

CSF provides an optimal chemical environment for accurate neuronal signaling. Even slight changes in the ionic composition of CSF within the brain can seriously disrupt production of action potentials and postsynaptic potentials.

mechanical protection

CSF serves as a shock-absorbing medium that protects the delicate tissues of the brain and spinal cord from jolts that would otherwise cause them to hit the bony walls of the cranial cavity and vertebral canal. The fluid also buoys the brain so that it "floats" in the cranial cavity.

Neuroglia

Cells of the nervous system that perform various supportive functions. The neuroglia of the central nervous system are the astrocytes, oligodendrocytes, microglia, and ependymal cells; neuroglia of the peripheral nervous system include Schwann cells and satellite cells. Also called glia

direct motor pathways

Collections of upper motor neurons with cell bodies in the motor cortex that project axons into the spinal cord, where they synapse with lower motor neurons or interneurons in the anterior horns. lateral corticospinal, anterior corticospinal, and corticobulbar tratcs

Complete transection of spinal cord

Complete loss of all sensory modalities below level of lesion; associated with motor paralysis and loss of sphincter control

retrograde

Fast axonal transport that occurs in a retrograde (backward) direction moves membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled.

reflex

Fast response to a change (stimulus) in the internal or external environment that attempts to restore homeostasis. Involuntary

satellite cells

Flat neuroglial cells that surround cell bodies of peripheral nervous system ganglia to provide structural support and regulate the exchange of material between a neuronal cell body and interstitial fluid.

Hyperpolarizing phase

Following the repolarizing phase there may be an after-hyperpolarizing phase, during which the membrane potential temporarily becomes more negative than the resting level. The after-hyperpolarizing phase occurs when the voltage-gated K+ channels remain open after the repolarizing phase ends.

Axonsomatic

From axon to cell body

nerve fiber

General term for any process (axon or dendrite) projecting from the cell body of a neuron.

Columns

Group of white matter tracts in the spinal cord (1) anterior (ventral) white columns, (2) posterior (dorsal) white columns, and (3) lateral white columns (Figure 13.3). Each column in turn contains distinct bundles of axons having a common origin or destination and carrying similar information.

cardiovascular center

Groups of neurons scattered within the medulla oblongata that regulate heart rate, force of contraction, and blood vessel diameter.

precentral gyrus

Gyrus of cerebral cortex located immediately anterior to the central sulcus; contains the primary motor area.

postcentral gyrus

Gyrus of cerebral cortex located immediately posterior to the central sulcus; contains the primary somatosensory area.

Epinephrine

Hormone secreted by the adrenal medulla that produces actions similar to those that result from sympathetic stimulation. Also called adrenaline

threshold stimulus

However, an action potential will occur in response to a threshold stimulus, a stimulus that is just strong enough to depolarize the membrane to threshold.

all-or-none principle

If a stimulus depolarizes a neuron to threshold, the neuron fires at its maximum voltage (all); if threshold is not reached, the neuron does not fire at all (none). Given above threshold, stronger stimuli do not produce stronger action potentials.

cranial reflex

If integration occurs in the brainstem rather than the spinal cord, the reflex is called a cranial reflex. An example is the tracking movements of your eyes as you read this sentence.

neuritis

Inflammation of one or several nerves that may result from irritation to the nerve produced by direct blows, bone fractures, contusions, or penetrating injuries. Additional causes include infections, vitamin deficiency (usually thiamine), and poisons such as carbon monoxide, carbon tetrachloride, heavy metals, and some drugs.

Meningitis

Inflammation of the meninges due to an infection, usually caused by a bacterium or virus. Symptoms include fever, headache, stiff neck, vomiting, confusion, lethargy, and drowsiness. Bacterial meningitis is much more serious and is treated with antibiotics. Viral meningitis has no specific treatment. Bacterial meningitis may be fatal if not treated promptly; viral meningitis usually resolves on its own in 1-2 weeks. A vaccine is available to help protect against some types of bacterial meningitis.

myelitis

Inflammation of the spinal cord.

epidural block

Injection of an anesthetic drug into the epidural space, the space between the dura mater and the vertebral column, in order to cause a temporary loss of sensation. Such injections in the lower lumbar region are used to control pain during childbirth.

association areas

Large cortical regions on the lateral surfaces of the occipital, parietal, and temporal lobes and on the frontal lobes anterior to the motor areas connected by many motor and sensory axons to other parts of the cortex; concerned with motor patterns, memory, concepts of word-hearing and word-seeing, reasoning, will, judgment, and personality traits.

nerve block

Loss of sensation in a region due to injection of a local anesthetic; an example is local dental anesthesia.

Facial (VII) nerves

Nuclei in the pons receive sensory impulses for taste and provide motor impulses to regulate secretion of saliva and tears and contraction of muscles of facial expression via the facial nerves.

Vestibulocochlear (VIII) nerves

Nuclei in the pons receive sensory impulses from and provide motor impulses to the vestibular apparatus via the vestibulocochlear nerves. These nerves convey impulses related to balance and equilibrium.

Reticular Activating System (RAS)

A portion of the reticular formation that has many ascending connections with the cerebral cortex; when this area of the brainstem is active, nerve impulses pass to the thalamus and widespread areas of the cerebral cortex, resulting in generalized alertness or arousal from sleep.

olive

A prominent oval mass on each lateral surface of the superior part of the medulla oblongata.

tendon (Golgi tendon) organs

A proprioceptive receptor, sensitive to changes in muscle tension and force of contraction, found chiefly near the junctions of tendons and muscles.

sensory areas

A region of the cerebral cortex concerned with the interpretation of sensory impulses.

primary motor area

A region of the cerebral cortex in the precentral gyrus of the frontal lobe of the cerebrum that controls specific muscles or groups of muscles.

primary somatosensory area

A region of the cerebral cortex posterior to the central sulcus in the postcentral gyrus of the parietal lobe of the cerebrum that localizes exactly the points of the body where somatic sensations originate.

rami

A short distance after passing through its intervertebral foramen, a spinal nerve divides into several branche

third ventricle

A slitlike cavity between the right and left halves of the thalamus and between the lateral ventricles of the brain.

Fascicles

A small bundle or cluster, especially of nerve or muscle fibers (cells).

falx cerebelli

A small triangular process of the dura mater attached to the occipital bone in the posterior cranial fossa and projecting inward between the two cerebellar hemispheres.

Nodes of Ranvier

A space along a myelinated axon between the individual Schwann cells that form the myelin sheath and the neurolemma

subarachnoid space

A space between the arachnoid mater and the pia mater that surrounds the brain and spinal cord and through which cerebrospinal fluid circulates.

subdural space

A space between the dura mater and the arachnoid mater of the brain and spinal cord that contains a small amount of fluid.

epidural space

A space between the spinal dura mater and the vertebral canal, containing areolar connective tissue and a plexus of veins.

sleep

A state of partial unconsciousness from which a person can be aroused; associated with a low level of activity in the reticular activating system.

consciousness

A state of wakefulness in which an individual is fully alert, aware, and oriented, partly as a result of feedback between the cerebral cortex and reticular activating system.

muscle action potential

A stimulating impulse that propagates along the sarcolemma and transverse tubules; in skeletal muscle, it is generated by acetylcholine, which increases the permeability of the sarcolemma to cations, especially sodium ions (Na−).

muscle tone

A sustained, partial contraction of portions of a skeletal or smooth muscle in response to activation of stretch receptors or a baseline level of action potentials in the innervating motor neurons.

Divergence

A synaptic arrangement in which the synaptic end bulbs of one presynaptic neuron terminate on several postsynaptic neurons.

convergence

A synaptic arrangement in which the synaptic end bulbs of several presynaptic neurons terminate on one postsynaptic neuron. The medial movement of the two eyeballs so that both are directed toward a near object being viewed in order to produce a single image.

cauda equina

A tail-like array of roots of spinal nerves at the inferior end of the spinal cord.

neural plate

A thickening of ectoderm, induced by the notochord, that forms early in the third week of development and represents the beginning of the development of the nervous system

delirium

A transient disorder of abnormal cognition and disordered attention accompanied by disturbances of the sleep-wake cycle and psychomotor behavior (hyperactivity or hypoactivity of movements and speech). Also called acute confusional state (ACS).

tentorium cerebelli

A transverse shelf of dura mater that forms a partition between the occipital lobe of the cerebral hemispheres and the cerebellum and that covers the cerebellum.

insula

A triangular area of the cerebral cortex that lies deep within the lateral cerebral fissue, under the parietal, frontal, and temporal lobes

superior sagittal sinus

A venous sinus located in the midline just dorsal to the corpus callosum, between the two cerebral hemispheres.

ciliary ganglion

A very small parasympathetic ganglion with preganglionic axons from the oculomotor (III) nerve and postganglionic axons that carry nerve impulses to the ciliary muscle and the sphincter muscle of the iris.

nerve action potential

A wave of depolarization and repolarization that self-propagates along the plasma membrane of a neuron.

inhibitory postsynaptic potential (IPSP)

A hyperpolarizing postsynaptic potential is termed an inhibitory postsynaptic potential (IPSP).

internal capsule

A large tract of projection fibers lateral to the thalamus that is the major connection between the cerebral cortex and the brainstem and spinal cord; contains axons of sensory neurons carrying auditory, visual, and somatic sensory signals to the cerebral cortex plus axons of motor neurons descending from the cerebral cortex to the thalamus, subthalamus, brainstem, and spinal cord.

Thalamus

A large, oval structure located bilaterally on either side of the third ventricle, consisting of two masses of gray matter organized into nuclei; main relay center for sensory impulses ascending to the cerebral cortex.

olifactory bulb

A mass of gray matter containing cell bodies of neurons that form synapses with neurons of the olfactory (I) nerve, lying inferior to the frontal lobe of the cerebrum on either side of the crista galli of the ethmoid bone.

spinal cord

A mass of nerve tissue located in the vertebral canal from which 31 pairs of spinal nerves originate.

central canal

A microscopic tube running the length of the spinal cord in the gray commissure.

gray commissure

A narrow strip of gray matter connecting the two lateral gray masses within the spinal cord.

interventricular foramina

A narrow, oval opening through which the lateral ventricles of the brain communicate with the third ventricle.

Neurons

A nerve cell, consisting of a cell body, dendrites, and an axon.

intercostal nerves

A nerve supplying a muscle located between the ribs. Also called thoracic nerve

cervical plexus

A network formed by nerve axons from the ventral rami of the first four cervical nerves and receiving gray rami communicantes from the superior cervical ganglion.

lumbar plexus

A network formed by the anterior (ventral) branches of spinal nerves L1 through L4.

sacral plexus

A network formed by the ventral branches of spinal nerves L4 through S3.

nervous system

A network of billions of neurons and even more neuroglia that is organized into two main divisions.

plexus

A network of nerves, veins, or lymphatic vessels

reticular formation

A network of small groups of neuronal cell bodies scattered among bundles of axons (mixed gray and white matter) beginning in the medulla oblongata and extending superiorly through the central part of the brainstem.

Astrocytes

A neuroglial cell having a star shape that participates in brain development and the metabolism of neurotransmitters, helps form the blood-brain barrier, helps maintain the proper balance of K+ for generation of nerve impulses, and provides a link between neurons and blood vessels.

Schwann cell

A neuroglial cell of the peripheral nervous system that forms the myelin sheath and neurolemma around a nerve axon by wrapping around the axon in a jelly-roll fashion.

Oligodendrocytes

A neuroglial cell that supports neurons and produces a myelin sheath around axons of neurons of the central nervous system.

presynaptic neuron

A neuron that propagates nerve impulses toward a synapse.

neurosecretory cells

A neuron that secretes a hypothalamic releasing hormone or inhibiting hormone into blood capillaries of the hypothalamus; a neuron that secretes oxytocin or antidiuretic hormone into blood capillaries of the posterior pituitary.

Dendrites

A neuronal process that carries electrical signals, usually graded potentials, toward the cell body.

Acetylcholine

A neurotransmitter liberated by many peripheral nervous system neurons and some central nervous system neurons. It is excitatory at neuromuscular junctions but inhibitory at some other synapses.

Diencephalon

A part of the brain consisting of the thalamus, hypothalamus, and epithalamus.

pontine respiratory group

A part of the medullary rhythmicity center in the pons that sends stimulatory nerve impulses to the inspiratory area that activate and prolong inhalation and inhibit exhalation.

spinal shock

A period from several days to several weeks following transection of the spinal cord that is characterized by the abolition of all reflex activity.

neurologist

A physician skilled in the diagnosis and treatment of disease of the nervous system.

pyramids

A pointed or cone-shaped structure. One of two roughly triangular structures on the anterior aspect of the medulla oblongata composed of the largest motor tracts that run from the cerebral cortex to the spinal cord. A triangular structure in the renal medulla.

tendon reflex

A polysynaptic, ipsilateral reflex that protects tendons and their associated muscles from damage that might be brought about by excessive tension. The receptors involved are called tendon organs.

hypothalamus

A portion of the diencephalon, lying beneath the thalamus and forming the floor and part of the wall of the third ventricle.

cranial nerves

One of 12 pairs of nerves that leave the brain; pass through foramina in the skull; and supply sensory and motor neurons to the head, neck, part of the trunk, and viscera of the thorax and abdomen. Each is designated by a Roman numeral and a name.

cerebral peduncles

One of a pair of nerve axon bundles located on the anterior surface of the midbrain, conducting nerve impulses between the pons and the cerebral hemispheres.

Nuerotransmitters

One of a variety of molecules within axon terminals that are released into the synaptic cleft in response to a nerve impulse and that change the membrane potential of the postsynaptic neuron.

spinal nerves

One of the 31 pairs of nerves that originate on the spinal cord from posterior and anterior roots

spinal nerves

One of the 31 pairs of nerves that originate on the spinal cord from posterior and anterior roots.

gyri

One of the folds of the cerebral cortex of the brain. Plural is gyri. Also called a convolution.

median aperture

One of the three openings in the roof of the fourth ventricle through which cerebrospinal fluid enters the subarachnoid space of the brain and cord.

parasympathetic nervous system

One of the two subdivisions of the autonomic nervous system, having cell bodies of preganglionic neurons in nuclei in the brain stem and in the lateral gray horn of the sacral portion of the spinal cord; primarily concerned with activities that conserve and restore body energy.

sympathetic nervous system

One of the two subdivisions of the autonomic nervous system, having cell bodies of preganglionic neurons in the lateral gray columns of the thoracic segment and the first two or three lumbar segments of the spinal cord; primarily concerned with processes involving the expenditure of energy.

Hemisection of spinal cord

Only half the cord is cut (right or left side). Interrupts pain and temperature on the opposite side of the body below the level of injury (contralateral) and discriminative touch and proprioception is lost on the same side of injury (ipsilateral). Motor paralysis is same sided. Called Brown-Sequard Syndrome

2 cells produce myelin sheath

Schwann cells (in the PNS) and oligodendrocytes (in the CNS)

spinothalamic tract

Sensory (ascending) tract that conveys information up the spinal cord to the thalamus for sensations of pain, temperature, crude touch, and deep pressure.

diencephalon

Superior to the brainstem is the diencephalon , which consists of the thalamus, hypothalamus, and epithalamus.

axon terminal

Terminal branches of an axon where synaptic vesicles undergo exocytosis to release neurotransmitter molecules. Also called telodendria

the central nervous system

That portion of the nervous system that consists of the brain and spinal cord.

neural circuits

The CNS contains billions of neurons organized into complicated networks called neural circuits, functional groups of neurons that process specific types of information

mammillary bodies

Two small rounded bodies on the inferior aspect of the hypothalamus that are involved in reflexes related to the sense of smell.

refractory period

The period of time after an action potential begins during which an excitable cell cannot generate another action potential in response to a normal threshold stimulus is called

Neurolemma

The peripheral, nucleated cytoplasmic layer of the Schwann cell. Also called sheath of Schwann

Brainstem

The portion of the brain immediately superior to the spinal cord, made up of the medulla oblongata, pons, and midbrain.

somatic nervous system

The portion of the peripheral nervous system consisting of somatic sensory (afferent) neurons and somatic motor (efferent) neurons. Because its motor responses can be consciously controlled, the action of this part of the PNS is voluntary

posterior column

The posterior column consists of two tracts: the gracile fasciculus and the cuneate fasciculus. The posterior column tracts convey nerve impulses for touch, pressure, vibration, and conscious proprioception (the awareness of the positions and movements of muscles, tendons, and joints).

tectum

The posterior part of the midbrain, called the tectum, contains four rounded elevations

ectoderm

The primary germ layer that gives rise to the nervous system and the epidermis of skin and its derivatives.

motor areas

The region of the cerebral cortex that governs muscular movement, particularly the precentral gyrus of the frontal lobe.

Nissl bodies

The ribosomes are the sites of protein synthesis. Newly synthesized proteins produced by Nissl bodies are used to replace cellular components, as material for growth of neurons, and to regenerate damaged axons in the PNS

The pons also contains nuclei associated with the following four pairs of cranial nerves

Trigeminal (V) nerves, Abducens (VI) nerves, Facial (VII) nerves, Vestibulocochlear (VIII) nerves

roots

Two bundles of axons, called roots, connect each spinal nerve to a segment of the cord by even smaller bundles of axons called rootlets

postsynaptic potential

a type of graded potential. Thus, the presynaptic neuron converts an electrical signal (nerve impulse) into a chemical signal (released neurotransmitter).

upper motor neurons

a type of motor neuron that synapses with a lower motor neuron farther down in the CNS in order to contract a skeletal muscle.

electrical synapse

action potentials (impulses) conduct directly between the plasma membranes of adjacent neurons through structures called gap junctions

Lipofuscin

aging neurons also contain lipofuscin, a pigment that occurs as clumps of yellowish brown granules in the cytoplasm. Lipofuscin is a product of neuronal lysosomes that accumulates as the neuron ages, but does not seem to harm the neuron.

spinal nerves

are associated with the spinal cord and, like all nerves of the peripheral nervous system (PNS), are parallel bundles of axons and their associated neuroglial cells wrapped in several layers of connective tissue. Spinal nerves connect the CNS to sensory receptors, muscles, and glands in all parts of the body. The 31 pairs of spinal nerves are named and numbered according to the region and level of the vertebral column from which they emerge (s

B fibers

are axons with diameters of 2-3 μm. Like A fibers, B fibers are myelinated and exhibit saltatory conduction at speeds up to 15 m/sec (34 mi/hr). B fibers have a somewhat longer absolute refractory period than A fibers. B fibers conduct sensory nerve impulses from the viscera to the brain and spinal cord. They also constitute all of the axons of the autonomic motor neurons that extend from the brain and spinal cord to the ANS relay stations called autonomic ganglia

spinal cord injury

are due to trauma as a result of factors such as automobile accidents, falls, contact sports, diving, and acts of violence.

2 main phases of action potential

depolarization and repolarization

excitatory postsynaptic potential (EPSP)

depolarizing postsynaptic potential is called an excitatory postsynaptic potential (EPSP). Although a single EPSP normally does not initiate a nerve impulse, the postsynaptic cell does become more excitable.

Telencephalon

develops into the cerebrum and lateral ventricles

A neurotransmitter is removed in three ways

diffusion, enzymatic degradation, uptake by cells

gap junctions

each gap junction contains a hundred or so tubular connexons, which act like tunnels to connect the cytosol of the two cells directly

cranial meninges

encircle the brain

ionotropic receptors

is a type of neurotransmitter receptor that contains a neurotransmitter binding site and an ion channel. In other words, the neurotransmitter binding site and the ion channel are components of the same protein.

metabolic receptors

is a type of neurotransmitter receptor that contains a neurotransmitter binding site but lacks an ion channel as part of its structure. However, a metabotropic receptor is coupled to a separate ion channel by a type of membrane protein called a G protein.

anterior median fissure

is a wide groove on the anterior (ventral) side

brain tumor

is an abnormal growth of tissue in the brain that may be malignant or benign. Unlike most other tumors in the body, malignant and benign brain tumors may be equally serious, compressing adjacent tissues and causing a buildup of pressure in the skull.

Shingles

is an acute infection of the peripheral nervous system caused by herpes zoster

action potential

is an electrical signal that propagates (travels) along the surface of the membrane of a neuron. It begins and travels due to the movement of ions (such as sodium and potassium) between interstitial fluid and the inside of a neuron through specific ion channels in its plasma membrane.

transient ischemic attack (TIA)

is an episode of temporary cerebral dysfunction caused by impaired blood flow to part of the brain

nitric oxide

is an important excitatory neurotransmitter secreted in the brain, spinal cord, adrenal glands, and nerves to the penis and has widespread effects throughout the body.

olifactory nerve

is entirely sensory; it contains axons that conduct nerve impulses for olfaction, the sense of smell

diplegia

is paralysis of both upper limbs or both lower limbs

hemiplegia

is paralysis of the upper limb, trunk, and lower limb on one side of the body

spatial summation

is summation of postsynaptic potentials in response to stimuli that occur at different locations in the membrane of a postsynaptic cell at the same time.

temporal summation

is summation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane of the postsynaptic cell but at different times

Cerebrum

is the "seat of intelligence." It provides us with the ability to read, write, and speak; to make calculations and compose music; and to remember the past, plan for the future, and imagine things that have never existed before. The cerebrum consists of an outer cerebral cortex, an internal region of cerebral white matter, and gray matter nuclei deep within the white matter.

relative refractory period

is the period of time during which a second action potential can be initiated, but only by a larger-than-normal stimulus. It coincides with the period when the voltage-gated K+ channels are still open after inactivated Na+ channels have returned to their resting state

Summation

is the process by which graded potentials add together

anterior white commissure

which connects the white matter of the right and left sides of the spinal cord.

reye's syndrome

Occurs after a viral infection, particularly chickenpox or influenza, most often in children or teens who have taken aspirin; characterized by vomiting and brain dysfunction (disorientation, lethargy, and personality changes) that may progress to coma and death.

motor function

Once sensory information is integrated, the nervous system may elicit an appropriate motor response by activating effectors (muscles and glands) through cranial and spinal nerves. Stimulation of the effectors causes muscles to contract and glands to secrete.

12 pairs of cranial nerves

One of 12 pairs of nerves that leave the brain; pass through foramina in the skull; and supply sensory and motor neurons to the head, neck, part of the trunk, and viscera of the thorax and abdomen. Each is designated by a Roman numeral and a name.

Melatonin

A hormone secreted by the pineal gland that helps set the timing of the body's biological clock.

factor that affect the speed of propagation

1. amount of myelination 2. axon diameter 3. temperature

function of the spinal card and spinal nerves

1.The white matter of the spinal cord contains sensory and motor tracts, the "highways" for conduction of sensory nerve impulses toward the brain and motor nerve impulses from the brain toward effector tissues. 2.The spinal cord gray matter is a site for integration (summing) of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). 3.Spinal nerves and the nerves that branch from them connect the CNS to the sensory receptors, muscles, and glands in all parts of the body.

The resting membrane potential arises from three major factors

1.Unequal distribution of ions in the ECF and cytosol 2.Inability of most anions to leave the cell 3.Electrogenic nature of the Na+-K+ ATPases.

medulla contains nuclei associated with the following five pairs of cranial nerves

1.Vestibulocochlear (VIII) nerves 2.Glossopharyngeal (IX) nerves 3.Vagus (X) nerves 4.Accessory (XI) nerves (cranial portion) 5.Hypoglossal (XII) nerves

2 main subdivisions of the nervous system

1.central nervous system (brain and spinal cord) 2. peripheral nervous system (all nerves)

blood-brain barrier (BBB)

A barrier consisting of specialized brain capillaries and astrocytes that prevents the passage of materials from the blood to the cerebrospinal fluid and brain.

optic tract

A bundle of axons that carry nerve impulses from the retina of the eye between the optic chiasm and the thalamus.

olfactory tract

A bundle of axons that extends from the olfactory bulb posteriorly to olfactory regions of the cerebral cortex

cerebellar peduncles

A bundle of nerve axons connecting the cerebellum with the brainstem

Tracts

A bundle of nerve axons in the central nervous system

fourth ventricle

A cavity filled with cerebrospinal fluid within the brain lying between the cerebellum and the medulla oblongata and pons.

ventricles

A cavity in the brain filled with cerebrospinal fluid. An inferior chamber of the heart.

lateral ventricles

A cavity within a cerebral hemisphere that communicates with the lateral ventricle in the other cerebral hemisphere and with the third ventricle by way of the interventricular foramen.

Polarized

A cell that exhibits a membrane potential is said to be Most body cells are polarized; the membrane potential varies from +5 mV to −100 mV in different types of cells.

aqueduct of midbrain

A channel through the midbrain connecting the third and fourth ventricles and containing cerebrospinal fluid. Also called the cerebral aqueduct.

arachnoid granulations

A cluster of arachnoid villi is called an

red nuclei

A cluster of cell bodies in the midbrain, occupying a large part of the tectum from which axons extend into the rubroreticular and rubrospinal tracts.

pterygopalatine ganglion

A cluster of cell bodies of parasympathetic postganglionic neurons ending at the lacrimal and nasal glands.

lethargy

A condition of functional sluggishness

pineal gland

A cone-shaped gland located in the roof of the third ventricle that secretes melatonin.

micrcephaly

A congenital condition that involves the development of a small brain and skull and frequently results in mental retardation.

nerve

A cordlike bundle of neuronal axons and/or dendrites and associated connective tissue coursing together outside the central nervous system.

optic chiasm

A crossing point of the two branches of the optic (II) nerve, anterior to the pituitary gland.

neural tube

A developmental abnormality in which the neural tube does not close properly. Examples are spina bifida and anencephaly.

Classification of nerve fibers

A fibers B fibers C fibers

cerebrospinal fluid

A fluid produced by ependymal cells that cover choroid plexuses in the ventricles of the brain; the fluid circulates in the ventricles, the central canal, and the subarachnoid space around the brain and spinal cord.

falx cerebri

A fold of the dura mater extending deep into the longitudinal fissure between the two cerebral hemispheres.

sulci

A groove or depression between parts, especially between the convolutions of the brain. Plural is sulci

Fissures

A groove, fold, or slit that may be normal or abnormal.

posterior (dorsal) root ganglion

A group of cell bodies of sensory neurons and their supporting cells located along the posterior root of a spinal nerve. Also called a dorsal root ganglion.

gracile nucleus

A group of nerve cells in the inferior part of the medulla oblongata in which axons of the gracile fasciculus terminate.

cuneate nucleus

A group of neurons in the inferior part of the medulla oblongata in which axons of the cuneate fasciculus terminate.

Norepinephrine (NE)

A hormone secreted by the adrenal medulla that produces actions similar to those that result from sympathetic stimulation.

white matter

Aggregations or bundles of myelinated and unmyelinated axons located in the brain and spinal cord.

paresthesia

An abnormal sensation such as burning, pricking, tickling, or tingling resulting from a disorder of a sensory nerve.

threshold

An action potential occurs in the membrane of the axon of a neuron when depolarization reaches a certain level termed the threshold (about −55 mV in many neurons). Different neurons may have different thresholds for generation of an action potential, but the threshold in a particular neuron usually is constant. The generation of an action potential depends on whether a particular stimulus is able to bring the membrane potential to threshold

Encephalitis

An acute inflammation of the brain caused by either a direct attack by any of several viruses or an allergic reaction to any of the many viruses that are normally harmless to the central nervous system. If the virus affects the spinal cord as well, the condition is called encephalomyelitis.

fornix

An arch or fold; a tract in the brain made up of association fibers, connecting the hippocampus with the mammillary bodies; a recess around the cervix of the uterus where it protrudes into the vagina.

corpus striatum

An area in the interior of each cerebral hemisphere composed of the lentiform and caudate nuclei.

horns

An area of gray matter (anterior, lateral, or posterior) in the spinal cord

axon hillock

An axon is a long, thin, cylindrical projection that often joins to the cell body at a cone-shaped elevation called the

muscle spindles

An encapsulated proprioceptor in a skeletal muscle, consisting of specialized intrafusal muscle fibers and nerve endings; stimulated by changes in length or tension of muscle fibers.

effector

An organ of the body, either a muscle or a gland, that is innervated by somatic or autonomic motor neurons.

Encephalopathy

Any disorder of the brain.

Stimulus

Any stress that changes a controlled condition; any change in the internal or external environment that excites a sensory receptor, a neuron, or a muscle fiber.

gray matter

Areas in the central nervous system and ganglia containing neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia; Nissl bodies impart a gray color and there is little or no myelin in gray matter.

postsynaptic potential

As ions flow through the opened channels, the voltage across the membrane changes. This change in membrane voltage is a postsynaptic potential.

neuralgia

Attacks of pain along the entire course or a branch of a sensory nerve.

arousal

Awakening from sleep, a response due to stimulation of the reticular activating system (RAS).

mixed nerve

Because the posterior root contains sensory axons and the anterior root contains motor axons, a spinal nerve is classified as a mixed nerve

arachnoid villi

Berrylike tuft of the arachnoid mater that protrudes into the superior sagittal sinus and through which cerebrospinal fluid is reabsorbed into the bloodstream.

Prosopagnosia

Inability to recognize faces, usually caused by damage to the facial recognition area in the inferior temporal lobe of both cerebral hemispheres.

Agnosia

Inability to recognize the significance of sensory stimuli such as sounds, sights, smells, tastes, and touch.

secondary brain vesicles

Both the prosencephalon and rhombencephalon subdivide further, forming secondary brain vesicles.

gliomas

Brain tumors that develop from glial cells

rami communicantes

Branches of a spinal nerve that are components of the autonomic nervous system. Singular is ramus communicans

circulation

CSF is a medium for minor exchange of nutrients and waste products between the blood and adjacent nervous tissue.

Perineurium

Connective tissue wrapping around fascicles in a nerve.

Endoneurium

Connective tissue wrapping around individual nerve axons

primary brain vesicles

Constrictions in this expanded tube soon appear, creating three regions called primary brain vesicles: prosencephalon, mesencephalon, and rhombencephalon

decussation of pyramids

Crossing of the large corticospinal tracts that explains why each side of the brain controls voluntary movements on the opposite side of the body.

Microtubules

Cylindrical protein filament, from 18 to 30 nm in diameter, consisting of the protein tubulin; provides support, structure, and transportation.

axoplasm

Cytoplasm of an axon

Wallerian degeneration

Degeneration of the portion of the axon and myelin sheath of a neuron distal to the site of injury.

Regeneration

Despite this plasticity, mammalian neurons have very limited powers of regeneration, the capability to replicate or repair themselves. In the PNS, damage to dendrites and myelinated axons may be repaired if the cell body remains intact and if the Schwann cells that produce myelination remain active.

cerebrovascular accident (CVA)

Destruction of brain tissue (infarction) resulting from obstruction or rupture of blood vessels that supply the brain. Also called a stroke or brain attack.

Alzheimer's disease (AD)

Disabling neurological disorder characterized by dysfunction and death of specific cerebral neurons, resulting in widespread intellectual impairment, personality changes, and fluctuations in alertness

trochlear nerves

Nuclei in the midbrain provide motor impulses that control movements of the eyeball via the trochlear nerves

The sum of all the excitatory and inhibitory effects at any given time determines the effect on the postsynaptic neuron, which may respond in the following ways:

EPSP, nerve impulse, IPSP

cerebellar nuclei

Even deeper, within the white matter, are the cerebellar nuclei, regions of gray matter that give rise to axons carrying impulses from the cerebellum to other brain centers.

synaptic end bulb

Expanded distal end of an axon terminal that contains synaptic vesicles. Also called a synaptic knob.

simple series circuit

In a simple series circuit, a presynaptic neuron stimulates a single postsynaptic neuron. The second neuron then stimulates another, and so on. However, most neural circuits are more complex.

Neurons

In addition to forming the complex processing networks within the brain and spinal cord, neurons also connect all regions of the body to the brain and spinal cord. As highly specialized cells capable of reaching great lengths and making extremely intricate connections with other cells, neurons provide most of the unique functions of the nervous system, such as sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions.

resting membrane potential

In excitable cells, this voltage is termed the resting membrane potential.

parallel after-discharge circuit

In this circuit, a single presynaptic cell stimulates a group of neurons, each of which synapses with a common postsynaptic cell. A differing number of synapses between the first and last neurons imposes varying synaptic delays, so that the last neuron exhibits multiple EPSPs or IPSPs. If the input is excitatory, the postsynaptic neuron then can send out a stream of impulses in quick succession. Parallel after-discharge circuits may be involved in precise activities such as mathematical calculations.

apraxia

Inability to carry out purposeful movements in the absence of paralysis.

synaptic vesicles

Membrane-enclosed sac in a synaptic end bulb that stores neurotransmitters.

brocas speech area

Motor area of the brain in the frontal lobe that translates thoughts into speech. Also called Broca's speech area.

indirect motor pathways

Motor tracts that convey information from the brain down the spinal cord for automatic movements, coordination of body movements with visual stimuli, skeletal muscle tone and posture, and balance. rubrospinal, tectospinal, vestibulospinal, lateral reticulospinal, and medial reticulospinal tracts

myelin sheath

Multilayered lipid and protein covering, formed by Schwann cells and oligodendrocytes, around axons of many peripheral and central nervous system neurons.

oculomotor nerves

Nuclei in the midbrain provide motor impulses that control movements of the eyeball, while accessory oculomotor nuclei provide motor control to the smooth muscles that regulate constriction of the pupil and changes in shape of the lens via the oculomotor nerves.

Abducens (VI) nerves

Nuclei in the pons provide motor impulses that control eyeball movement via the abducens nerves.

Trigeminal (V) nerves

Nuclei in the pons receive sensory impulses for somatic sensations from the head and face and provide motor impulses that govern chewing via the trigeminal nerves.

Neurogila

Neuroglia are smaller cells, but they greatly outnumber neurons—perhaps by as much as 25 times. Neuroglia support, nourish, and protect neurons, and maintain the interstitial fluid that bathes them.

microglial cells

Neuroglial cells that carry on phagocytosis. Also called microglia

endymal cells

Neuroglial cells that cover choroid plexuses and produce cerebrospinal fluid (CSF); they also line the ventricles of the brain and probably assist in the circulation of CSF.

Purkinje cells

Neuron in the cerebellum named for the histologist who first described them.

sensory or afferent division of the PNS

Neurons that carry sensory information from cranial and spinal nerves into the brain and spinal cord or from a lower to a higher level in the spinal cord and brain. Also called afferent neurons.

Interneurons

Neurons whose axons extend only for a short distance and contact nearby neurons in the brain, spinal cord, or a ganglion; they comprise the vast majority of neurons in the body. Also called association neurons.

filum terminale

Non-nervous fibrous tissue of the spinal cord that extends inferiorly from the conus medullaris to the coccyx.

basal nuclei

Paired clusters of gray matter deep in each cerebral hemisphere including the globus pallidus, putamen, and caudate nucleus.

Epithalamus

Part of the diencephalon superior and posterior to the thalamus, comprising the pineal gland and associated structures

dementia

Permanent or progressive general loss of intellectual abilities, including impairment of memory, judgment, and abstract thinking and changes in personality.

continuous conduction

Propagation of an action potential (nerve impulse) in a step-by-step depolarization of each adjacent area of an axon membrane.

circadian rhythm

The pattern of biological activity on a 24-hour cycle, such as the sleep-wake cycle

posterior column-medial lemniscus pathway

Sensory pathways that carry information related to proprioception, fine touch, two-point discrimination, pressure, and vibration. First-order neurons project from the spinal cord to the ipsilateral medulla in the posterior columns (gracile fasciculus and cuneate fasciculus). Second-order neurons project from the medulla to the contralateral thalamus in the medial lemniscus. Third-order neurons project from the thalamus to the somatosensory cortex (postcentral gyrus) on the same side.

sensory function

Sensory receptors detect internal stimuli, such as an increase in blood pressure, or external stimuli (for example, a raindrop landing on your arm). This sensory information is then carried into the brain and spinal cord through cranial and spinal nerves.

suprathreshold stimulus

Several action potentials will form in response to a suprathreshold stimulus, a stimulus that is strong enough to depolarize the membrane above threshold. Each of the action potentials caused by a suprathreshold stimulus has the same amplitude (size) as an action potential caused by a threshold stimulus.

deglutition

The act of swallowing

anterior and posterior lobe

The anterior lobe and posterior lobe govern subconscious aspects of skeletal muscle movements.

Chromatolysis

The breakdown of Nissl bodies into finely granular masses in the cell body of a neuron whose axon has been damaged.

vermis

The central constricted area of the cerebellum that separates the two cerebellar hemispheres.

dermatome

The cutaneous area developed from one embryonic spinal cord segment and receiving most of its sensory innervation from one spinal nerve. An instrument for incising the skin or cutting thin transplants of skin.

Neurofibrils

The cytoskeleton includes both neurofibrils, composed of bundles of intermediate filaments that provide the cell shape and support, and microtubules, which assist in moving materials between the cell body and axon

transverse fissure

The deep cleft that separates the cerebrum from the cerebellum

deglutition center

The deglutition center of the medulla promotes deglutition (swallowing) of a mass of food that has moved from the oral cavity of the mouth into the pharynx (throat)

Synapse

The functional junction between two neurons or between a neuron and an effector, such as a muscle or gland; may be electrical or chemical.

corpus callosum

The great commissure of the brain between the cerebral hemispheres.

pia mater

The innermost of the three meninges (coverings) of the brain and spinal cord.

substantia nigra

The midbrain contains several other nuclei, including the left and right substantia nigra, which are large and darkly pigmented

arachnoid mater

The middle of the three meninges (coverings) of the brain and spinal cord. Also termed the arachnoid.

reflex arc

The most basic conduction pathway through the nervous system, connecting a receptor and an effector and consisting of a receptor, a sensory neuron, an integrating center in the central nervous system, a motor neuron, and an effector. Also called a reflex circuit.

medulla oblongata

The most inferior part of the brainstem. Also termed the medulla.

dura mater

The most superficial of the three spinal meninges is a thick strong layer composed of dense irregular connective tissue. The dura mater forms a sac from the level of the foramen magnum in the occipital bone, where it is continuous with the meningeal dura mater of the brain, to the second sacral vertebra. The dura mater is also continuous with the epineurium, the outer covering of spinal and cranial nerves.

synaptic cleft

The narrow gap at a chemical synapse that separates the axon terminal of one neuron from another neuron or muscle fiber (cell) and across which a neurotransmitter diffuses to affect the postsynaptic cell.

postsynaptic neuron

The nerve cell that is activated by the release of a neurotransmitter from another neuron and carries nerve impulses away from the synapse

Integrative function

The nervous system processes sensory information by analyzing it and making decisions for appropriate responses—an activity known as integration.

medullary respiratory center

The neurons of the respiratory center in the medulla oblongata that control the basic rhythm of respiration.

neurotransmitter receptors

The neurotransmitter molecules diffuse across the synaptic cleft and bind to neurotransmitter receptors in the postsynaptic neuron's plasma membrane. The receptor shown in Figure 12.23

The optic (II) nerve

The optic (II) nerve is entirely sensory and is technically a tract of the brain and not a nerve; it contains axons that conduct nerve impulses for vision (Figure 14.18). In the retina, rods and cones initiate visual signals and relay them to bipolar cells, which transmit the signals to ganglion cells.

dura mater

The outermost of the three meninges (coverings) of the brain and spinal cord.

inital segment

The part of the axon closest to the axon hillock is the initial segment

midbrain

The part of the brain between the pons and the diencephalon. Also called the mesencephalon

Cerebellum

The part of the brain lying posterior to the medulla oblongata and pons; governs balance and coordinates skilled movements.

pons

The part of the brainstem that forms a "bridge" between the medulla oblongata and the midbrain, anterior to the cerebellum.

brain

The part of the central nervous system contained within the cranial cavity

3rd branch of the autonomic nervous system (enteric nervous system)

The part of the nervous system that is embedded in the submucosa and muscularis of the gastrointestinal (GI) tract; governs motility and secretions of the GI tract.

Peripheral Nervous System (PNS)

The part of the nervous system that lies outside the central nervous system, consisting of nerves and ganglia.

propagation

The spread of the action potential down an axon, caused by successive changes in electrical charge along the length of the axon's membrane.

infdibulum

The stalklike structure that attaches the pituitary gland to the hypothalamus of the brain. The funnel-shaped, open, distal end of the uterine (Fallopian) tube.

anterior (ventral) root

The structure composed of axons of motor (efferent) neurons that emerges from the anterior aspect of the spinal cord and extends laterally to join a posterior root, forming a spinal nerve. Also called a ventral root.

posterior (dorsal) root

The structure composed of sensory axons lying between a spinal nerve and the dorsolateral aspect of the spinal cord. Also called the dorsal root.

neurology

The study of the normal functioning and disorders of the nervous system.

cerebral cortex

The surface of the cerebral hemispheres, 2-4 mm thick, consisting of gray matter; arranged in six layers of neuronal cell bodies in most areas.

cerebral cortex

The surface of the cerebral hemispheres, 2-4mm thick, consisting of gray matter; arranged in six layers of neuronal cell bodies in most areas.

conus medullaris

The tapered portion of the spinal cord inferior to the lumbar enlargement.

Cerebrum

The two hemispheres of the forebrain (derived from the telencephalon), making up the largest part of the brain.

Axon

The usually single, long process of a nerve cell that propagates a nerve impulse toward the axon terminals

pontine nuclei

The ventral region of the pons forms a large synaptic relay station consisting of scattered gray centers called

membrane potential

The voltage across a cell's plasma membrane.

vomitting center

The vomiting center of the medulla causes vomiting, the forcible expulsion of the contents of the upper gastrointestinal (GI) tract through the mouth

arbor vitae

The white matter tracts of the cerebellum, which have a treelike appearance when seen in midsagittal section.

meningeal branch

This branch reenters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges.

current

This flow of charged particles

pia mater

This innermost meninx is a thin transparent connective tissue layer that adheres to the surface of the spinal cord and brain. It consists of thin squamous to cuboidal cells within interlacing bundles of collagen fibers and some fine elastic fibers. Within the pia mater are many blood vessels that supply oxygen and nutrients to the spinal cord. Triangular-shaped membranous extensions of the pia mater suspend the spinal cord in the middle of its dural sheath. These extensions, called denticulate ligaments, are thickenings of the pia mater. They project laterally and fuse with the arachnoid mater and inner surface of the dura mater between the anterior and posterior nerve roots of spinal nerves on either side (Figure 13.1a, b). Extending along the entire length of the spinal cord, the denticulate ligaments protect the spinal cord against sudden displacement that could result in shock. Between the arachnoid mater and pia mater is a space, the subarachnoid space, which contains shock-absorbing cerebrospinal fluid.

arachnoid mater

This layer, the middle of the meningeal membranes, is a thin, avascular covering comprised of cells and thin, loosely arranged collagen and elastic fibers. It is called the arachnoid mater because of its spider's web arrangement of delicate collagen fibers and some elastic fibers. It is deep to the dura mater and is continuous through the foramen magnum with the arachnoid mater of the brain. Between the dura mater and the arachnoid mater is a thin subdural space, which contains interstitial fluid.

decremental conduction

This mode of travel by which graded potentials die out as they spread along the membrane is known as decremental conduction. Because they die out within a few millimeters of their point of origin, graded potentials are useful for short-distance communication only.

meninges

Three membranes covering the brain and spinal cord, called the dura mater, arachnoid mater, and pia mater. Singular is meninx

motor tracts

Tracts consisting of axons that carry nerve impulses from the brain are called motor (descending) tracts

stupor

Unresponsiveness from which a patient can be aroused only briefly and only by vigorous and repeated stimulation.

ganglion

Usually, a group of neuronal cell bodies lying outside the central nervous system (CNS). Plural is ganglia.

autonomic nervous system

Visceral sensory (afferent) and visceral motor (efferent) neurons. Autonomic motor neurons, both sympathetic and parasympathetic, conduct nerve impulses from the central nervous system to smooth muscle, cardiac muscle, and glands. So named because this part of the nervous system was thought to be self-governing or spontaneous. involuntary action

spinal reflexes

When integration takes place in the spinal cord gray matter, the reflex is a spinal reflex. An example is the familiar patellar reflex (knee jerk)

depolarizing graded potential

When the response makes the membrane less polarized (inside less negative), it is termed a depolarizing graded potential (Figure 12.14b).

hyperpolarizing graded potential

When the response makes the membrane more polarized (inside more negative), it is termed a hyperpolarizing graded potential

inferior olivary nucleus

Within the olive is the inferior olivary nucleus, which receives input from the cerebral cortex, red nucleus of the midbrain, and spinal cord.

somatic reflexes

You are probably most aware of somatic reflexes, which involve contraction of skeletal muscles.

electrochemical gradient

a concentration (chemical) difference plus an electrical difference. Recall that ions move from areas of higher concentration to areas of lower

coma

a state of unconsciousness from which an individual cannot be aroused. In the lightest stages of coma, brainstem and spinal cord reflexes persist, but in the deepest states even those reflexes are lost, and if respiratory and cardiovascular controls are lost, the patient dies. Drugs such as melatonin affect the RAS by helping to induce sleep, and general anesthetics turn off consciousness via the RAS.

action potentials

allow communication over long distances within the body

cell body

also known as the perikaryon or soma, contains a nucleus surrounded by cytoplasm that includes typical cellular organelles such as lysosomes, mitochondria, and a Golgi complex. Neuronal cell bodies also contain free ribosomes and prominent clusters of rough endoplasmic reticulum, termed Nissl bodies

subthreshold stimulus

an action potential will not occur in response to a subthreshold stimulus, a weak depolarization that cannot bring the membrane potential to threshold.

cerebral hemispheres

and the lateral "wings" or lobes are the cerebellar hemispheres

Neuropeptides

are numerous and widespread in both the CNS and PNS. Neuropeptides bind to metabotropic receptors and have excitatory or inhibitory actions, depending on the type of metabotropic receptor at the synapse. Neuropeptides are formed in the neuron cell body, packaged into vesicles, and transported to axon terminals. Besides their role as neurotransmitters, many neuropeptides serve as hormones that regulate physiological responses elsewhere in the body.

inferior colliculi

are part of the auditory pathway, relaying impulses from the receptors for hearing in the inner ear to the brain. These two nuclei are also reflex centers for the startle reflex, sudden movements of the head, eyes, and trunk that occur when you are surprised by a loud noise such as a gunshot.

A fibers

are the largest diameter axons (5-20 μm) and are myelinated. A fibers have a brief absolute refractory period and conduct nerve impulses (action potentials) at speeds of 12 to 130 m/sec (27-290 mi/hr). The axons of sensory neurons that propagate impulses associated with touch, pressure, position of joints, and some thermal and pain sensations are A fibers, as are the axons of motor neurons that conduct impulses to skeletal muscles.

C fibers

are the smallest diameter axons (0.5-1.5 μm) and all are unmyelinated. Nerve impulse propagation along a C fiber ranges from 0.5 to 2 m/sec (1-4 mi/hr). C fibers exhibit the longest absolute refractory periods. These unmyelinated axons conduct some sensory impulses for pain, touch, pressure, heat, and cold from the skin, and pain impulses from the viscera. Autonomic motor fibers that extend from autonomic ganglia to stimulate the heart, smooth muscle, and glands are C fibers. Examples of motor functions of B and C fibers are constricting and dilating the pupils, increasing and decreasing the heart rate, and contracting and relaxing the urinary bladder

graded potential

are used for short-distance communication only

metencephalon

becomes the pons, cerebellum, and upper part of the fourth ventricle

stretch reflex

causes contraction of a skeletal muscle (the effector) in response to stretching of the muscle. This type of reflex occurs via a monosynaptic reflex arc. The reflex can occur by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron. Stretch reflexes can be elicited by tapping on tendons attached to muscles at the elbow, wrist, knee, and ankle joints. An example of a stretch reflex is the patellar reflex (knee jerk)

postsynaptic cell

cell that receives a signal

principle plexuses

cervical, brachial, lumbar, sacral

nuclei

clusters of neuronal cell bodies form functional groups called

cerebellar cortex

consists of gray matter in a series of slender, parallel folds called folia

superior cerebellar peduncle

contain axons that extend from the cerebellum to the red nuclei of the midbrain and to several nuclei of the thalamus. The middle cerebellar peduncles are the largest peduncles; their axons carry impulses for voluntary movements from the pontine nuclei (which receive input from motor areas of the cerebral cortex) into the cerebellum

anterior gray horn

contain somatic motor nuclei, which are clusters of cell bodies of somatic motor neurons that provide nerve impulses for contraction of skeletal muscles.

The motor or efferent division of the PNS

conveys output from the CNS to effectors (muscles and glands). This division is further subdivided into a somatic nervous system and an autonomic nervous system

absolute refractory period

even a very strong stimulus cannot initiate a second action potential. This period coincides with the period of Na+ channel activation and inactivation

ascending sensory axons

f the gracile fasciculus and the cuneate fasciculus, which are two tracts in the posterior columns of the spinal cord, form synapses in these nuclei

Anteograde

fast axonal transport that occurs in an anterograde (forward) direction moves organelles and synaptic vesicles from the cell body to the axon terminals

2 main advantages of electrical synapses

faster communication and synchronization

folia

folds of the cerebellum

Myelencephalon

forms the medulla oblongata and lower part of the fourth ventricle

6 types of neuroglia

four—astrocytes, oligodendrocytes, microglia, and ependymal cells—are found only in the CNS. The remaining two types—Schwann cells and satellite cells—are present in the PNS.

Attention deficit hyperactivity disorder (ADHD)

is a learning disorder characterized by poor or short attention span, a consistent level of hyperactivity, and a level of impulsiveness inappropriate for the child's age. ADHD is believed to affect about 5% of children and is diagnosed 10 times more often in boys than in girls.

posterior median sulcus

is a narrow furrow on the posterior (dorsal) side

unipolar neuron

have dendrites and one axon that are fused together to form a continuous process that emerges from the cell body (Figure 12.3c). These neurons are more appropriately called pseudounipolar neurons because they begin in the embryo as bipolar neurons. During development, the dendrites and axon fuse together and become a single process. The dendrites of most unipolar neurons function as sensory receptors that detect a sensory stimulus such as touch, pressure, pain, or thermal stimuli. The trigger zone for nerve impulses in a unipolar neuron is at the junction of the dendrites and axon

bipolar neurons

have one main dendrite and one axon (Figure 12.3b). They are found in the retina of the eye, the inner ear, and the olfactory area (olfact = to smell) of the brain.

inferior cerebellar peduncles

he inferior cerebellar peduncles consist of (1) axons of the spinocerebellar tracts that carry sensory information into the cerebellum from proprioceptors in the trunk and limbs; (2) axons from the vestibular apparatus of the inner ear and from the vestibular nuclei of the medulla and pons that carry sensory information into the cerebellum from proprioceptors in the head; (3) axons from the inferior olivary nucleus of the medulla that enter the cerebellum and regulate the activity of cerebellar neurons; (4) axons that extend from the cerebellum to the vestibular nuclei of the medulla and pons; and (5) axons that extend from the cerebellum to the reticular formation.

repolarizing phase

he membrane potential is restored to the resting state of −70 mV Then voltage-gated K+ channels open, allowing K+ to flow out, which produces the repolarizing phase.

posterior ramus

he posterior (dorsal) ramus serves the deep muscles and skin of the posterior surface of the trunk

slow axonal transport

he slower system, which moves materials about 1-5 mm per day, is called

reverberating circuit

in this pattern, the incoming impulse stimulates the first neuron, which stimulates the second, which stimulates the third, and so on. Branches from later neurons synapse with earlier ones. This arrangement sends impulses back through the circuit again and again. The output signal may last from a few seconds to many hours, depending on the number of synapses and the arrangement of neurons in the circuit. Inhibitory neurons may turn off a reverberating circuit after a period of time. Among the body responses thought to be the result of output signals from reverberating circuits are breathing, coordinated muscular activities, waking up, and short-term memory.

coughing

involves a long-drawn and deep inhalation and then a strong exhalation that suddenly sends a blast of air through the upper respiratory passages

sneezing

involves spasmodic contraction of breathing muscles that forcefully expel air through the nose and mouth

graded potential

is a small deviation from the resting membrane potential that makes the membrane either more polarized (inside more negative) or less polarized (inside less negative).

lateral gray horn

lateral gray horns, which are present only in thoracic and upper lumbar segments of the spinal cord. The lateral gray horns contain autonomic motor nuclei, which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscle, smooth muscle, and glands.

areflexia

loss of reflexes

cerebrospinal fluid (CSF) three basic functions in helping to maintain homeostasis

mechanical protection, chemical protection, circulation

An axon contains:

mitochondria, microtubules, and neurofibrils

trigger zone

most neurons, nerve impulses arise at the junction of the axon hillock and the initial segment, an area called the trigger zone, from which they travel along the axon to their destination

spinal cord has 2 principal functions in maintaining homeostasis

nerve impulse propagation and integration of information

lumbar enlargement

nerves of pelvis and lower limbs

brachial plexus

network of nerve axons of the anterior rami of spinal nerves C5, C6, C7, C8, and T1. The nerves that emerge from the brachial plexus supply the upper limb.

Nervous tissue comprises two types of cells

neurons and neuroglia

vestibular nuclei

of the medulla and pons are components of the equilibrium pathway from the inner ear to the brain; they receive sensory information associated with equilibrium from proprioceptors (receptors that provide information regarding body position and movements) in the vestibular apparatus of the inner ear

cochlear nuclei

of the medulla are part of the auditory pathway from the inner ear to the brain; they receive auditory input from the cochlea of the inner ear

gustatory nucleus

of the medulla is part of the gustatory pathway from the tongue to the brain; it receives gustatory input from the taste buds of the tongue

flocculonodular lobe

on the inferior surface contributes to equilibrium and balance.

ligand-gated channels

opens and closes in response to the binding of a ligand (chemical) stimulus. A wide variety of chemical ligands—including neurotransmitters, hormones, and particular ions—can open or close ligand-gated channels. The neurotransmitter acetylcholine, for example, opens cation channels that allow Na+ and Ca2+ to diffuse inward and K+ to diffuse outward (Figure 12.11b). Ligand-gated channels are located in the dendrites of some sensory neurons, such as pain receptors, and in dendrites and cell bodies of interneurons and motor neurons.

voltage gated channels

opens in response to a change in membrane potential (voltage) (Figure 12.11d). Voltage-gated channels participate in the generation and conduction of action potentials in the axons of all types of neurons.

mechanically gated channels

opens or closes in response to mechanical stimulation in the form of vibration (such as sound waves), touch, pressure, or tissue stretching (Figure 12.11c). The force distorts the channel from its resting position, opening the gate. Examples of mechanically-gated channels are those found in auditory receptors in the ears, in receptors that monitor stretching of internal organs, and in touch receptors and pressure receptors in the skin.

sensory neurons

or afferent neurons either contain sensory receptors at their distal ends (dendrites) (see also Figure 12.10) or are located just after sensory receptors that are separate cells. Once an appropriate stimulus activates a sensory receptor, the sensory neuron forms an action potential in its axon and the action potential is conveyed into the CNS through cranial or spinal nerves. Most sensory neurons are unipolar in structure.

motor neurons

or efferent neurons convey action potentials away from the CNS to effectors (muscles and glands) in the periphery (PNS) through cranial or spinal nerves (see also Figure 12.10). Motor neurons are multipolar in structure.

mesencephalon

or midbrain, gives rise to the midbrain and aqueduct of the midbrain (cerebral aqueduct).

poliomyelitis

or simply polio, is caused by a virus called poliovirus. The onset of the disease is marked by fever, severe headache, a stiff neck and back, deep muscle pain and weakness, and loss of certain somatic reflexes. In its most serious form, the virus produces paralysis by destroying cell bodies of motor neurons, specifically those in the anterior horns of the spinal cord and in the nuclei of the cranial nerves. Polio can cause death from respiratory or heart failure if the virus invades neurons in vital centers that control breathing and heart functions in the brainstem

varicosities

others exhibit a string of swollen bumps called

lateral apertures

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

paraplegia

paralysis from the waist down

quadriplegia

paralysis of all four limbs

monoplegia

paralysis of only one limb

blood cerebrospinal fluid barrier

permits certain substances to enter the CSF but excludes others, protecting the brain and spinal cord from potentially harmful blood-borne substances. In contrast to the blood-brain barrier, which is formed mainly by tight junctions of brain capillary endothelial cells, the blood-cerebrospinal fluid barrier is formed by tight junctions of ependymal cells.

Axolemma

plasma membrane of axon

leak channels

randomly alternate between open and closed positions (Figure 12.11a). Typically, plasma membranes have many more potassium ion (K+) leak channels than sodium ion (Na+) leak channels, and the potassium ion leak channels are leakier than the sodium ion leak channels. Thus, the membrane's permeability to K+ is much higher than its permeability to Na+. Leak channels are found in nearly all cells, including the dendrites, cell bodies, and axons of all types of neurons.

sensory receptors

refers to a structure of the nervous system that monitors changes in the external or internal environment. Examples of sensory receptors include touch receptors in the skin, photoreceptors in the eye, and olfactory (smell) receptors in the nose.

effector cell

responds to the impulse at the synapse

hiccupping

s caused by spasmodic contractions of the diaphragm (a muscle of breathing) that ultimately result in the production of a sharp sound on inhalation

posterior gray horn

the posterior (dorsal) gray horns contain axons of incoming sensory neurons as well as cell bodies and axons of interneurons. Recall that cell bodies of sensory neurons are located in the posterior (dorsal) root ganglion of a spinal nerve.

Cerebellum

second only to the cerebrum in size, occupies the inferior and posterior aspects of the cranial cavity. Like the cerebrum, the cerebellum has a highly folded surface that greatly increases the surface area of its outer gray matter cortex, allowing for a greater number of neurons. The cerebellum accounts for about a tenth of the brain mass yet contains nearly half of the neurons in the brain.

sensory tracts

sensory (ascending) tracts consist of axons that conduct nerve impulses toward the brain.

anterior ramus

serves the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk. In addition to posterior and anterior rami, spinal nerves also give off a meningeal branch

axon collaterals

side branches of the axon

Epidermal Growth Factor (EGF)

stimulated cells taken from the brains of adult mice to proliferate into both neurons and astrocytes. Previously, EGF was known to trigger mitosis in a variety of nonneuronal cells and to promote wound healing and tissue regeneration. In 1998, scientists discovered that significant numbers of new neurons do arise in the adult human hippocampus, an area of the brain that is crucial for learning.

ipsilateral reflex

stimulus and response are on the same side of the body

cervical enlargement

supplies nerves to the shoulder and upper limbs

spinal meninges

surround the spinal cord

2 branches of autonomic nervous system

sympathetic and parasympathetic

converging circuit

the postsynaptic neuron receives nerve impulses from several different sources.

Regeneration tube

the Schwann cells on either side of the injured site multiply by mitosis, grow toward each other, and may form a regeneration tube across the injured area (Figure 12.29c). The tube guides growth of a new axon from the proximal area across the injured area into the distal area previously occupied by the original axon.

electrical excitability

the ability to respond to a stimulus and convert it into an action potential

neurogenesis

the birth of new neurons from undifferentiated stem cells—occurs regularly in some animals. For example, new neurons appear and disappear every year in some songbirds. Until recently, the dogma in humans and other primates was "no new neurons" in the adult brain.

Plasticity

the capability to change based on experience. At the level of individual neurons, the changes that can occur include the sprouting of new dendrites, synthesis of new proteins, and changes in synaptic contacts with other neurons.

depolarizing phase

the negative membrane potential becomes less negative, reaches zero, and then becomes positive The first channels that open, the voltage-gated Na+ channels, allow Na+ to rush into the cell, which causes the depolarizing phase.

diverging circuit

the nerve impulse from a single presynaptic neuron causes the stimulation of increasing numbers of cells along the circuit

Epinerium

the superficial connective tissue covering around an entire nerve

synaptic delay

the time required for these processes at a chemical synapse, a synaptic delay of about 0.5 msec, is the reason that chemical synapses relay signals more slowly than electrical synapses.

septum pellucidum

thin membrane that separates lateral ventricles

superior colliculi

two superior elevations, serve as reflex centers for certain visual activities. Through neural circuits from the retina of the eye to the superior colliculi to the extrinsic eye muscles, visual stimuli elicit eye movements for tracking moving images (such as a moving car) and scanning stationary images (as you are doing to read this sentence). The superior colliculi are also responsible for reflexes that govern movements of the head, eyes, and trunk in response to visual stimuli.

lower motor neurons

type of motor neuron that directly supplies skeletal muscle fibers.

multipolar neuron

usually have several dendrites and one axon (Figure 12.3a). Most neurons in the brain and spinal cord are of this type, as well as all motor neurons (described shortly).

Voltage-gated Ca2+ channels

which are present in the membrane of synaptic end bulbs. Because calcium ions are more concentrated in the extracellular fluid, Ca2+ flows inward through the opened channels.

autonomic reflexes

which generally are not consciously perceived. They involve responses of smooth muscle, cardiac muscle, and glands. As you will see in Chapter 15, body functions such as heart rate, digestion, urination, and defecation are controlled by the autonomic nervous system through autonomic reflexes.

Fast axonal transport

which is capable of moving materials a distance of 200-400 mm per day, uses proteins that function as "motors" to move materials along the surfaces of microtubules of the neuron's cytoskeleton.

tentorium cerebelli

which supports the posterior part of the cerebrum, separates the cerebellum from the cerebrum