The Nervous System Chapter 10 A&P

(Central Nervous System) B. Brain disorders 2. Dementia

syndrome that includes progressive loss of memory, shortened attention span, per- sonality changes, reduced intellectual capacity, and motor control deficit a. Alzheimer disease (AD)—brain disorder of the middle and late adult years characterized by dementia b. Huntington disease (HD)—inherited disorder characterized by chorea (purposeless move- ment) progressing to severe dementia c. HIV (also causes AIDS) can infect neurons and thus cause dementia

(Nerve Impulses) B. Mechanism

1. At rest, the neuron's membrane is slightly posi- tive on the outside—polarized—from a slight excess of Na on the outside 2. A stimulus triggers the opening of Na channels in the plasma membrane of the neuron 3. Inward movement of Na depolarizes the mem- brane by making the inside more positive than the outside at the stimulated point; this depolar- ization is a nerve impulse (action potential) 4. The stimulated section of membrane immedi- ately repolarizes, but by that time the depolariza- tion has already triggered the next section of membrane to depolarize, thus propagating a wave of electrical disturbances (depolarizations) all the way down the membrane

(Autonomic Nervous System) A. Functional anatomy

1. Autonomic nervous system—motor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue; regulates the body's automatic, or involuntary, functions 2. Autonomic neurons—preganglionic autonomic neurons conduct from spinal cord or brainstem to an autonomic ganglion; postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue 3. Autonomic or visceral effectors—tissues to which autonomic neurons conduct impulses (that is, cardiac and smooth muscle and glandular epi- thelial tissue) 4. Composed of two divisions—the sympathetic system and the parasympathetic system

(Autonomic Nervous System) E.Autonomic neurotransmitters

1. Cholinergic fibers—preganglionic axons of para- sympathetic and sympathetic systems and parasympathetic postganglionic axons release acetylcholine 2. Adrenergic bers—axons of sympathetic postganglionic neurons release norepinephrine (noradrenaline)

(Central Nervous System) C. Spinal cord

1. Columns of white matter, composed of bundles of myelinated nerve bers, form the outer portion of the H-shaped core of the spinal cord; bundles of axons called tracts 2. Interior composed of gray matter made up mainly of neuron dendrites and cell bodies 3. Spinal cord tracts provide two-way conduction paths—ascending and descending 4. Spinal cord functions as the primary center for all spinal cord re exes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain

(Cells of the Nervous System) A. Neurons

1. Consist of three parts a. Cell body of neuron—main part b. Dendrites—branching projections that conduct impulses to cell body of neuron c. Axon—elongated projection that conducts impulses away from cell body of neuron 2. Neurons classi ed according to function, or direction of impulse a. Sensory neurons: conduct impulses to the spinal cord and brain; also called afferent neurons b. Motor neurons: conduct impulses away from brain and spinal cord to muscles and glands; also called efferent neurons c. Interneurons: conduct impulses from sensory neurons to motor neurons or among a network of interneurons; also called central or connecting neurons

(Autonomic Nervous System) B. Autonomic conduction paths

1. Consist of two-neuron relays (that is, preganglionic neurons from the central nervous system to autonomic ganglia, synapses, postganglionic neurons from ganglia to visceral effectors) 2. In contrast, somatic motor neurons conduct all the way from the CNS to somatic effectors with no intervening synapses

(Central Nervous System) D. Coverings and uid spaces of the brain and spinal cord

1. Coverings a. Cranial bones and vertebrae b. Cerebral and spinal meninges (1) Dura mater—tough outer membrane (2) Arachnoid mater—cobweblike middle layer (3) Pia mater—delicate inner layer; adheres to CNS tissue 2. Fluid spaces a. Subarachnoid spaces of meninges b. Central canal inside cord c. Ventricles in brain

(Autonomic Nervous System) C. Sympathetic nervous systems

1. Dendrites and cell bodies of sympathetic pregan- glionic neurons are located in the gray matter of the thoracic and upper lumbar segments of the spinal cord 2. Axons leave the spinal cord in the anterior roots of spinal nerves, extend to sympathetic, or collat- eral, ganglia and synapse with several postgan- glionic neurons whose axons extend to spinal or autonomic nerves to terminate in visceral effectors 3. A chain of sympathetic ganglia is in front of and at each side of the spinal column 4. Functions of the sympathetic nervous system a. Serves as the emergency or stress system, con- trolling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are triggered b. Group of changes induced by sympathetic control is called the flight-or- fight response

(Nerves) B. Nerve coverings— brous connective tissue

1. Endoneurium—surrounds individual bers within a nerve 2. Perineurium—surrounds a group (fascicle) of nerve bers 3. Epineurium—surrounds the entire nerve

(Cells of the Nervous System) C. Disorders of nervous tissue

1. Multiple sclerosis—characterized by myelin loss in central nerve bers and resulting conduction impairments 2. Tumors a. General name for nervous system tumors is neuroma b. Most neuromas are gliomas, glial tumors c. Multiple neuro bromatosis—characterized by numerous benign tumors

(Peripheral Nervous System) C. Peripheral nerve disorders

1. Neuritis—general term referring to nerve in ammation a. Sciatica is in ammation of the sciatic nerve that innervates the legs b. Neuralgia, or muscle pain, often accompanies neuritis 2. Trigeminal neuralgia—recurring episodes of stabbing pain along one or more branches of the trigeminal ( fth cranial) nerve in the head 3. Bell palsy—paralysis of facial features resulting from damage to the facial (seventh cranial) nerve 4. Herpes zoster, or shingles a. Viral infection caused by chickenpox virus that has invaded the dorsal root ganglion and remained dormant until stress or reduced immunity precipitates an episode of shingles b. Usually affects a single dermatome, producing characteristic painful plaques or vesicles

(Autonomic Nervous System) F. Autonomic nervous system as a whole

1. Regulates the body's automatic functions in ways that maintain or quickly restore homeostasis 2. Many visceral effectors are doubly innervated (that is, they receive bers from parasympathetic and sympathetic divisions and are in uenced in opposite ways by the two divisions)

(Autonomic Nervous System) G.Disorders of the autonomic nervous system

1. Stress-induced disease a. Prolonged or excessive response to stress can disrupt normal functioning throughout the body b. Examples of stress-induced conditions include heart disease, digestive problems, and reduced resistance to disease 2. Neuroblastoma—highly malignant tumor of the sympathetic nervous system, primarily affecting young children

(Autonomic Nervous System) D. Parasympathetic nervous system

1. Structure a. Parasympathetic preganglionic neurons have dendrites and cell bodies in the gray matter of the brainstem and the sacral segments of the spinal cord b. Parasympathetic preganglionic neurons termi- nate in parasympathetic ganglia located in the head and the thoracic and abdominal cavities close to visceral effectors c. Each parasympathetic preganglionic neuron synapses with postganglionic neurons to only one effector 2. Function—dominates control of many visceral effectors under normal, everyday conditions; counterbalances sympathetic function

(Cells of the Nervous System) B. Glia (neuroglia)

1. Support cells, bringing the cells of nervous tissue together structurally and functionally 2. Three main types of connective tissue cells of the CNS (Figure 10-3) a. Astrocytes—star-shaped cells that anchor small blood vessels to neurons b. Microglia—small cells that move in in amed brain tissue carrying on phagocytosis c. Oligodendrocytes—form myelin sheaths on axons in the CNS (Schwann cells form myelin sheaths in PNS only)

(Peripheral Nervous System) B. Spinal nerves

1. Thirty-one pairs—contain dendrites of sensory neurons and axons of motor neurons 2. Conduct impulses necessary for sensations and voluntary movements 3. Dermatome—skin surface area supplied by a single cranial or spinal nerve

(Nerves) A. Nerve—bundle of peripheral axons

1. Tract—bundle of central axons 2. White matter—brain or cord tissue composed primarily of myelinated axons (tracts) 3. Gray matter—brain or cord tissue composed pri- marily of cell bodies and unmyelinated fibers

(Peripheral Nervous System) A. Cranial nerves

1. Twelve pairs—attached to undersurface of the brain 2. Connect brain with the neck and structures in the thorax and abdomen

How many pairs of spinal nerves are connected to the spinal cord? a. 23 b. 13 c. 31 d. 32

31

Organs and Divisions of the Nervous System

A. Central nervous system (CNS)—brain and spinal cord B. Peripheral nervous system (PNS)—all nerves C. Autonomic nervous system (ANS)

The Synapse

A. De nition—the place where impulses are transmit- ted from one neuron to another (the postsynaptic neuron) B. Synapse made of three structures—synaptic knob, synaptic cleft, and plasma membrane C. Neurotransmitters bind to speci c receptor mole- cules in the membrane of a postsynaptic neuron, opening ion channels and thereby stimulating impulse conduction by the membrane D. Names of neurotransmitters—acetylcholine, cate- cholamines (norepinephrine, dopamine, and sero- tonin), endorphins, enkephalins, nitric oxide (NO), and other compounds E. Parkinson disease (PD)—characterized by abnor- mally low levels of dopamine in motor control areas of the brain; patients usually exhibit involun- tary trembling and muscle rigidity (parkinsonism;

Reflex Arcs

A. Nerve impulses are conducted from receptors to effectors over neuron pathways or re ex arcs; con- duction by a re ex arc results in a re ex (that is, contraction by a muscle or secretion by a gland) B. The simplest re ex arcs are two-neuron arcs— consisting of sensory neurons synapsing in the spinal cord with motor neurons; three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons

Acetylcholine is released by a. sympathetic preganglionic axons. b. parasympathetic preganglionic axons. c. parasympathetic postganglionic axons. d. All of the above release acetylcholine.

All of the above release acetylcholine

These chemicals allow neurons to communicate with each other. a. Neurofibrils b. Neurotransmitters c. Sensory transmitters d. Glial transmitters

Neurotransmitters

Axon terminals of autonomic neurons release either of two neurotransmitters. a. Norepinephrine and acetylcholine b. Norepinephrine and aldosterone c. Norepinephrine and dopamine d. Acetylcholine and aldosterone

Norepinephrine and acetylcholine

Which glia cell produces the myelin that envelopes the nerve fibers of the brain and spinal cord? a. Astrocytes b. Microglia c. Oligodendroglia d. Choroid plexus

Oligodendroglia

The nervous system is divided into which two principal divisions? a. Peripheral and central b. Autonomic and central c. Autonomic and peripheral d. Central and afferent

Peripheral and central

(Central Nervous System) B. Brain disorders 1. Damage to brain tissue

a. Concussion—type of traumatic brain injury (TBI) caused by a jolt to the head and resulting changes in brain chemicals (or even bleeding or swelling) and characterized by changes in thinking, physical symptoms such as nausea, and mood or sleep changes; symptoms may develop months after an injury (postconcus- sion syndrome) b. Cerebrovascular accident (CVA)—hemorrhage from or cessation of blood ow through cere- bral blood vessels; a "stroke" c. Cerebral palsy (CP)—condition in which damage to motor control areas of the brain before, during, or shortly after birth causes paralysis (usually spastic) of one or more limbs

(Central Nervous System) A. Divisions of the brain 1. Brainstem

a. Consists of, named in ascending order, the medulla oblongata, pons, and midbrain b. Structure—white matter with bits of gray matter scattered through it c. Functions (1) All three parts of brainstem are two-way conduction paths (a) Sensory tracts in the brainstem conduct impulses to the higher parts of the brain (b) Motor tracts conduct from the higher parts of the brain to the spinal cord (2) Gray matter areas in the brainstem func- tion as important re ex centers

(Central Nervous System) A. Divisions of the brain 3. Diencephalon

a. Hypothalamus (1) Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter (2) Acts as the major center for controlling the ANS; therefore helps control the function- ing of most internal organs (3) Controls hormone secretion by anterior and posterior pituitary glands; therefore it indirectly helps control hormone secretion by most other endocrine glands (4) Contains centers for controlling appetite, wakefulness, pleasure, etc b. Thalamus (1) Dumbbell-shaped mass of gray matter extending toward each cerebral hemisphere (2) Relays sensory impulses to cerebral cortex sensory areas (3) In some way produces the emotions of pleasantness or unpleasantness associated with sensations c. Pineal gland (pineal body) (1) Small body resembling pine nut behind the thalamus (2) Adjusts output of "timekeeping hormone" melatonin in response to changing levels of external light (sunlight and moonlight)

(Central Nervous System) A. Divisions of the brain 4. Cerebrum

a. Largest part of the human brain b. Outer layer of gray matter is the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons c. Interior of the cerebrum composed mainly of white matter (1) Tracts—nerve bers arranged in bundles (2) Basal nuclei—islands of gray matter regu- late automatic movements and postures d. Functions of the cerebrum—mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements.

(Central Nervous System) B. Brain disorders 3. Seizure disorders

a. Seizure—sudden burst of abnormal neuron activity that results in temporary changes in brain function b. Epilepsy—many forms, all characterized by recurring seizures c. Electroencephalogram—graphic representa- tion of voltage changes in the brain used to evaluate brain activity

(Central Nervous System) A. Divisions of the brain 2. Cerebellum

a. Structure (1) Second largest part of the human brain (2) Gray matter outer layer is thin but highly folded, forming a large surface area for processing information (3) Arbor vitae—internal, treelike network of white matter tracts b. Function (1) Helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain normal postures (2) Variety of additional coordinating effects, assisting the cerebrum and other regions of the brain

A subdivision of the nervous system that regulates involuntary functions is the a. somatic nervous system. b. visceral nervous system. c. central nervous system. d. autonomic nervous system.

autonomic nervous system.

The part of a neuron that transmits impulses away from the cell body is the a. dendrite. b. neurofibril. c.. axon. d. neurilemma.

axon

The second largest part of the brain, located just below the posterior portion of the cerebrum, is the a. midbrain. b. medulla oblongata. c. cortex. d. cerebellum.

cerebellum

Formation of the cerebrospinal fluid occurs in the a. ventricles. b. meninges. c.choroid plexus. d. solar plexus.

choroid plexus.

Nerves that originate from the brain are called a. cranial nerves. b. peripheral nerves. c. afferent nerves. d. spinal nerves.

cranial nerves.

Skin surface area supplied by a single spinal nerve is called a a. dermatome. b. plexus. c. myotome. d. ramus

dermatome

The effect of sympathetic stimulation on the blood vessels in skeletal muscles is a. relaxation. b. constriction. c. dilation. d. no effect

dilation

The limbic system integrates a. consciousness. b. sleep. c. c. d. language.

emotion

The three divisions of the brain that make up the brainstem are the a. medulla oblongata, thalamus, and pons. b. medulla oblongata, thalamus, and midbrain. c. medulla oblongata, midbrain, and pons. d. medulla oblongata, pons, and cerebellum.

medulla oblongata, midbrain, and pons.

This type of glia cell can act as a microbe-eating scavenger a. astrocyte b. microglia c. glioma d. oligodendrocyte

microglia

The white, fatty substance that surrounds an axon is called a. glia. b. Schwann's cells. c. myelin. d. neurilemma.

myelin

Cells that conduct the impulses are called a. glial cells. b. neurons. c. astrocytes. d. Schwann's cells.

neurons

This cranial nerve is responsible for the sense of smell. a. Oculomotor b. Trochlear c. Trigeminal d. Olfactory

olfactory

The autonomic nervous system can be divided into the a. parasympathetic and sympathetic divisions. b. parasympathetic and autonomic divisions. c. sympathetic and autonomic divisions. d. visceral sensory and somatic sensory divisions.

parasympathetic and sympathetic divisions.

The innermost layer of the meninges is the a. pia mater. b. dura mater. c. arachnoid layer. d. choroid plexus.

pia mater

The action potential seems to "jump" from node to node along a myelinated fiber. This type of impulse regeneration is called a. refractory conduction. b. sensory conduction. c. action potential conduction. d. saltatory conduction.

saltatory conduction.

(Nerve Impulses) A. Definition

self-propagating wave of electrical dis- turbance that travels along the surface of a neuron membrane; often called action potentials

The large fluid-filled spaces within the brain are called the a. meninges. b. sulci. c. gyri. d. ventricles.

ventricles

The organs of the nervous system include all of the following except the a. brain. b. vertebrae c. spinal cord. d. nerves.

vertebrae

Bundles of myelinated fibers make up the a. gray matter of the nervous system. b. ganglia. c. white matter of the nervous system. d. motor nerves.

white matter of the nervous system.