Nervous System

Nervous System Cell types of

Neural tissue Neurons Neuroglial cells

Divisions of the Nervous System

Central Nervous System Brain Spinal cord

Peripheral Nervous System Peripheral nerves

Cranial nerves Spinal nerves

Divisions of Peripheral Nervous System Sensory Division

Picks up sensory information and delivers it to the CNS

Motor Division Carries information to muscles and glands Divisions of the Motor Division

Somatic – carries information to skeletal muscle Autonomic – carries information to smooth

muscle, cardiac muscle, and glands.

Divisions Nervous System

Functions of Nervous system Sensory Function

Sensory receptors gather information

Information is carried to the CNS

Integrative Function Sensory information

used to create Sensations Memory Thoughts Decisions

Motor Function Decisions are acted

upon Impulses are carried

to effectors

Neuron Structure

Myelination of Axons White Matter

Contains myelinated axons

Gray Matter Contains

unmyelinated structures

Cell bodies, dendrites

Classification of Neurons Bipolar

Two processes Eyes, ears,

nose Unipolar

One process Ganglia

Multipolar Many

processes Most neurons

of CNS

Classification of Neurons Sensory Neurons

Afferent Carry impulse to CNS Most are unipolar Some are bipolar

Interneurons Link neurons Multipolar In CNS

Motor Neurons Multipolar Carry impulses

away from CNS Carry impulses to

effectors

Types of Neuroglial Cells Schwann Cells

Peripheral nervous system

Myelinating cell Oligodendrocytes

CNS Myelinating cell

Microglia CNS Phagocytic cell

Astrocytes CNS Scar tissue Mop up excess ions, etc Induce synapse formation Connect neurons to blood

vessels Ependyma

CNS Ciliated Line central canal of spinal

cord Line ventricles of brain

Types of Neuroglial Cells

Regeneration of A Nerve Axon

Resting Membrane Potential Inside is negative relative to the outside Polarized membrane Due to distribution of ions Na+/K+ pump

Potential Changes At rest membrane

is polarized Threshold stimulus

reached Sodium channels

open and membrane depolarizes

Potassium leaves cytoplasm and membrane repolarizes

Local Potential Changes Occur on membranes of dendrites and cell bodies Caused by various stimuli

Chemicals Temperature changes Mechanical forces

If membrane potential becomes more negative, it has hyperpolarized

If membrane potential becomes more positive, it has depolarized

Graded (see paragraph under potential changes) Summation can lead to threshold stimulus that starts

an action potential

Action Potentials Nerve impulse Occur on axons All-or-none Refractory period

Absolute – time when threshold stimulus does not start another action potential

Relative – time when stronger threshold stimulus can start another action potential

Action Potentials

Impulse ConductionEVENTS LEADING TO THE CONDUCTION OF A NERVE IMPULSE

1. Neuron membrane maintains resting potential.2. Threshold stimulus is received.3. Sodium channels in the trigger zone of the neuron open.4. Sodium ions diffuse inward, depolarizing the membrane.5. Potassium channels in the membrane open.6. Potassium ions diffuse outward, repolarizing the

membrane. 7. The resulting action potential causes a local bioelectric

current that stimulates adjacent portions of the membrane.8. A wave of action potentials travels the length of the axon as

a nerve impulse.

Saltatory Conduction

The Synapse Nerve impulses pass from neuron to neuron at

synapses

Synaptic Transmission Neurotransmitters

are released when impulse reaches synaptic knob.

Synaptic Potentials EPSP

Excitatory postsynaptic potential Graded Depolarizes membrane of postsynaptic neuron Action potential of postsynaptic neuron becomes more

likely IPSP

Inhibitory postsynaptic potential Graded Hyperpolarizes membrane of postsynaptic neuron Action potential of postsynaptic neuron becomes less

likely

Summation of EPSPs and IPSPs EPSPs and IPSPs are added together in a process called summation

More EPSPs lead to greater probability of action potential

Neurotransmitters

Impulse Processing Neuronal Pools

Groups of interneurons that make synaptic connections with each other

Interneurons work together to peform a common function

Each pool receives input from other neurons Each pool generates output to other neurons

Convergence Neuron receives input from

several neurons Incoming impulses represent

information from different types of sensory receptors

Allows nervous system to collect, process, and respond to information

Makes it possible for a neuron to sum impulses from different sources

Divergence One neuron sends

impulses to several neurons

Can amplify an impulse

Impulse from a single neuron is CNS may be amplified to activate enough motor units needed for muscle contraction

Clinical Application Multiple Sclerosis Symptoms

Blurred vision Numb legs or arms Can lead to paralysis

Treatments No cure Bone marrow transplant Interferon (anti-viral drug) hormones

Causes Myelin destroyed in various parts of CNS Hard scars (scleroses) form Nerve impulses blocked Muscles do not receive innervation May be related to a virus

Meninges of the Spinal Cord Meninges

Membranes surrounding CNS Protect CNS Three layers

Dura mater – outer, tough Arachnoid mater – weblike Pia mater – inner, delicate

Meninges of the Spinal Cord

Spinal Cord Structure Extends foramen

magnum to 2nd lumbar vertebra.

Cross Section of Spinal Cord

Spinal Cord Functions Center for spinal reflexes Conduit for nerve impulses to and from the

brain

Reflex Arcs Reflexes – automatic, subconscious responses

to stimuli

Knee-jerk Reflex Helps maintain posture

Withdrawal Reflex Protective

Crossed-Extensor Reflex Flexor muscles contract Flexor muscles on opposite side inhibited Extensor muscles on opposite side contract

for balance

Tracts of the Spinal Cord Ascending tracts conduct sensory impulses

to the brain Descending tracts conduct motor impulses

from the brain to motor neurons reaching muscles and glands.

Ascending Tracts

Fasciculus cuneatus Lateral spinothalamic

Brain Functions

interprets sensations determines perception stores memory reasoning makes decisions coordinates muscular

movements regulates visceral activities determines personality

Major Parts cerebrum

two cerebellar hemispheres

diencephalon brain stem cerebellum

Structure of Cerebrum corpus callosum

connects hemispheres convolutions

bumps or gyri sulci

grooves longitudinal fissure

separates hemispheres transverse fissure

separates cerebrum from cerebellum

Lobes of Cerebrum

Frontal Parietal Temporal Occipital Insula

Functions of Cerebrum

interpretation initiating voluntary movements storing memory retrieving memory reasoning center for intelligence and personality

Functional Regions of Cerebral Cortex Cerebral Cortex – thin layer of gray matter

that constitutes the outermost portion of cerebrum; contains 75% of all neurons in nervous system

Motor Areas Primary Motor Areas

frontal lobes control voluntary muscles

Broca’s Area anterior to primary motor cortex usually in one hemisphere controls muscles needed for speech

Frontal Eye Field above Broca’s area controls voluntary movements of eyes and eyelids

Motor Areas

Sensory Areas Cutaneous Sensory Area

parietal lobe interprets sensations on skin

Visual Area occipital lobe interprets vision

Auditory Area temporal lobe interprets hearing

Sensory Areas

Association Areas regions of cortex that are not primary motor or

primary sensory areas widespread throughout the cerebral cortex analyze and interpret sensory experiences provide memory, reasoning, verbalization,

judgment, emotions

Association Areas Frontal Lobe Association

Areas concentrating planning problem solving judging

Parietal Lobe Association Areas understanding speech using words to express

thought

Temporal Lobe Association Areas remember visual scenes remember music remember complex

patterns Occipital Lobe

Association Areas combine visual images

with other sensory experiences

Hemisphere Dominance Dominant hemisphere

controls speech writing reading verbal skills analytical skills computational skills

In over 90% of population, left hemisphere is dominant

Nondominant hemisphere controls nonverbal tasks motor tasks understanding and

interpreting musical and visual patterns

provides emotional and intuitive thought processes

Memory Short Term

working memory closed circuit circuit is stimulated

over and over when impulse flow

stops, memory disappears

Long Term changes structure and

function of neurons enhanced synaptic

transmission

Basal Nuclei masses of gray

matter deep w/in cerebral

hemispheres caudate nucleus,

putamen, globus pallidus

produce dopamine control certain

muscular activities

Diencephalon between cerebral hemispheres and brainstem surrounds third ventricle thalamus hypothalamus optic tracts optic chiasm infundibulum posterior pituitary mammillary bodies pineal gland

Diencephalon Thalamus

gateway for sensory impulses heading to cerebral cortex

receives all sensory impulses (except smell) channels impulses to appropriate part of cerebral

cortex for interpretation Hypothalamus

maintains homeostasis by regulating visceral activities

links nervous and endocrine systems

Limbic System Consists of

portions of frontal lobe portions of temporal lobe hypothalamus thalamus basal nuclei other deep nuclei

Functions controls emotions produces feelings interpret sensory impulses

Brain Stem Three Parts

Midbrain Pons Medulla

Oblongata

Midbrain between diencephalon

and pons contains bundles of

fibers that join lower parts of brainstem and spinal cord with higher part of brain

cerebral aqueduct cerebral peduncles –

bundles of nerve fibers corpora quadrigemina –

centers for visual and auditory reflexes

Pons rounded bulge on underside of brainstem between medulla oblongata and midbrain helps regulate rate and depth of breathing relays nerve impulses to and from medulla

oblongata and cerebellum

Medulla Oblongata enlarged continuation of

spinal cord conducts ascending and

descending impulses between brain and spinal cord

contains cardiac, vasomotor, and respiratory control centers

contains various nonvital reflex control centers (coughing, sneezing, vomiting)

Reticular Formation complex network of nerve

fibers scattered throughout the brain stem

extends into the diencephalon

connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum

filters incoming sensory information

arouses cerebral cortex into state of wakefulness

Types of Sleep Slow Wave

person is tired decreasing activity of reticular system restful dreamless reduced blood pressure and respiratory rate ranges from light to heavy alternates with REM sleep

Rapid Eye Movement (REM) some areas of brain active heart and respiratory rates irregular dreaming occurs

Cerebellum inferior to occipital lobes posterior to pons and medulla oblongata two hemispheres vermis connects hemispheres cerebellar cortex – gray matter arbor vitae – white matter cerebellar peduncles – nerve fiber tracts dentate nucleus – largest nucleus in cerebellum integrates sensory information concerning position of

body parts coordinates skeletal muscle activity maintains posture

Cerebellum

Peripheral Nervous System Cranial nerves arising from the brain

Somatic fibers connecting to the skin and skeletal muscles

Autonomic fibers connecting to viscera Spinal nerves arising from the spinal

cord Somatic fibers connecting to the skin and

skeletal muscles Autonomic fibers connecting to viscera

Structure of a Peripheral Nerve

Nerve Fiber Classification Sensory Nerves – conduct impulses into CNS Motor Nerves – conduct impulses to muscles or glands Mixed Nerves – contain both sensory nerve fibers and

motor nerve fibers; most nerves General somatic efferent fibers

carry motor impulses from CNS to skeletal muscles General somatic afferent fibers

carry sensory impulses to CNS from skin and skeletal muscles

General visceral efferent fibers carry motor impulses away from CNS to smooth

muscles and glands General visceral afferent fibers

carry sensory impulses to CNS from blood vessels and internal organs

Nerve Fiber Classification Special somatic efferent fibers

carry motor impulses from brain to muscles used in chewing, swallowing, speaking, and forming facial expressions

Special visceral afferent fibers carry sensory impulses to brain from olfactory and

taste receptors Special somatic afferent fibers

carry sensory impulses to brain from receptors of sight, hearing, and equilibrium

Cranial Nerves

Spinal Nerves

mixed nerves 31 pairs

8 cervical (C1 to C8) 12 thoracic (T1 to T12) 5 lumbar (L1 to L5) 5 sacral (S1 to S5) 1 coccygeal (Co)

Spinal Nerves Dorsal root

axons of sensory neurons in the dorsal root ganglion

Dorsal root ganglion cell bodies of sensory neurons

Ventral root axons of motor neurons whose cell bodies are in

spinal cord Spinal nerve

union of ventral root and dorsal root

Spinal Nerves

Dermatome An area of skin that the sensory nerve fibers

of a particular spinal nerve innervate

Autonomic Nervous System functions without conscious effort controls visceral activities regulates smooth muscle, cardiac muscle,

and glands efferent fibers typically lead to ganglia outside

CNS Two Divisions

sympathetic – prepares body for fight or flight situations

parasympathetic – prepares body for resting and digesting activities

Autonomic Nerve Fibers all are motor (efferent) preganglionic fibers

axons of preganglionic neurons

neuron cell bodies in CNS

postganglionic fibers axons of postganglionic

neurons neuron cell bodies in

ganglia

Sympathetic Division thoracolumbar divison – location of

preganglionic neurons preganglionic fibers leave spinal nerves

through white rami and enter paravertebral ganglia

paraverterbral ganglia and fibers that connect them make up the sympathetic trunk

Sympathetic Division

Sympathetic Division postganglionic fibers extend

from sympathetic ganglia to visceral organs

postganglionic fibers usually pass through gray rami and return to a spinal nerve before proceeding to an effector

preganglionic fibers to adrenal medulla do not synapse with postganglionic neurons

Sympathetic Division

Sympathetic Division

Parasympathetic Division craniosacral division

– location of preganglionic neurons

ganglia are near or within various organs

short postganlionic fibers

preganglionic fibers of the head in III, VII, and IX

preganglionic fibers of thorax and abdomen in X

Parasympathetic Division

Control of Autonomic Activity

Controlled largely by CNS Medulla oblongata regulates cardiac,

vasomotor and respiratory activities Hypothalamus regulates visceral functions Limbic system and cerebral cortex control

emotional responses

Life-Span Changes Brain cells begin to die before birth Over average lifetime, brain shrinks 10% Most cell death occurs in temporal lobes By age 90, frontal lobe has lost half its neurons Number of dendritic branches decreases Decreased levels of neurotransmitters Fading memory Slowed responses and reflexes Changes increase risk of falling Sleep problems common

Clinical ApplicationCerebral Injuries & Abnormalities

Concussion brain jarred against

cranium loss of

consciousness temporary loss of

memory mental cloudiness headache recovery usually

complete

Cerebrovascular Accident stroke sudden interruption in blood

flow brain tissues die

Cerebral Palsy motor impairment at birth caused by blocked cerebral

blood vessels during development

seizues learning disabilities

Somatic and Special Senses

Sensory Receptors specialized cells or multicellular structures

that collect information stimulate neurons to send impulses along

sensory fibers to the brain

Receptor Types Chemoreceptors

respond to changes in chemical concentrations Pain receptors

respond to tissue damage Thermoreceptors

respond to changes in temperature Mechanoreceptors

respond to mechanical forces Photoreceptors

respond to light

Sensory Impulses stimulation of receptor causes local change in its

membrane a graded electrical current is generated that reflects

intensity of stimulation if receptor is part of a neuron, the membrane

potential may generate an action potential if receptor is not part of a neuron, the receptor

potential must be transferred to a neuron to trigger an actin potential

peripheral nerves transmit impulses to CNS Sensation

feeling that occurs when brain interprets sensory impulse

Sensory Adaptation adjustment of sensory receptors from

continuous stimulation stronger stimulus required to activate

receptors smell receptors undergo sensory adaptation

Somatic Senses senses associated with skin, muscles, joints,

and viscera three groups

exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain

proprioceptive senses – senses associated with changes in muscles and tendons

visceroceptive senses – senses associated with changes in viscera

Touch and Pressure Senses Free nerve endings

common in epithelial tissues

detect touch and pressure

Meissner’s corpuscles abundant in hairless

portions of skin detect light touch

Pacinian corpuscles common in deeper

subcutaneous tissues, tendons, and ligaments

detect heavy pressure

Touch and Pressure Senses

Temperature Senses Warm receptors

sensitive to temperatures above 25oC (77o F) unresponsive to temperature above 45oC (113oF)

Cold receptors sensitive to temperature between 10oC (50oF)

and 20oC (68oF) Pain receptors

respond to temperatures below 10oC respond to temperatures above 45oC

Sense of Pain free nerve endings widely distributed nervous tissue of brain lacks pain receptors stimulated by tissue damage, chemical,

mechanical forces, or extremes in temperature

do not adapt Visceral Pain

may exhibit referred pain not well localized

Referred Pain may occur due to sensory impulses from two

regions following a common nerve pathway to brain

Pain Nerve Fibers Acute pain fibers

thin, myelinated conduct impulses

rapidly associated with

sharp pain well localized

Chronic pain fibers thin, unmyelinated conduct impulses

more slowly associated with dull,

aching pain difficult to pinpoint

Regulation of Pain Impulses Thalamus

allows person to be aware of pain

Cerebral Cortex judges intensity of pain locates source or pain produces motor

response to pain produces emotions to

pain

Pain Inhibiting Substances enkephalins serotonin endorphins

Stretch Receptors

proprioceptors send information to CNS concerning

lengths and tensions of muscles 2 main kinds of stretch receptors

muscle spindles – in skeletal muscles Golgi tendon organs – in tendons

Stretch Receptors

Special Senses

sensory receptors are within large, complex sensory organs in the head

smell in olfactory organs taste in taste buds hearing and equilibrium in ears sight in eyes

Smell

Olfactory Receptors chemoreceptors respond to chemicals dissolved in liquids

Olfactory Organs contain olfactory receptors and supporting

epithelial cells cover parts of nasal cavity, superior nasal

conchae, and a portion of the nasal septum

Olfactory Receptors

Olfactory Nerve Pathways

Once olfactory receptors are stimulated, nerve impulses travel through olfactory nerves to olfactory bulbs to olfactory tracts to limbic system (for emotions) and olfactory cortex

(for interpretation)

Taste

Taste Buds organs of taste located on papillae of tongue, roof of mouth,

linings of cheeks and walls of pharynx Taste Receptors

chemoreceptors taste cells – modified epithelial cells that function

as receptors taste hairs –microvilli that protrude from taste

cells; sensitive parts of taste cells

Taste Receptors

Taste Sensations

Four Primary Taste Sensations sweet – stimulated by carbohydrates sour – stimulated by acids salty – stimulated by salts bitter – stimulated by many organic compound

Spicy foods activate pain receptors

Taste Nerve Pathways

Sensory impulses from taste receptors travel along cranial nerves to medulla oblongata to thalamus to gustatory cortex (for interpretation)

Hearing

Ear – organ of hearing 3 Sections

External Middle Inner

External Ear auricle

collects sounds waves external auditory meatus

lined with ceruminous glands carries sound to tympanic

membrane terminates with tympanic

membrane tympanic membrane

vibrates in response to sound waves

Middle Ear tympanic cavity air-filled space in

temporal bone auditory ossicles

vibrate in response to tympanic membrane

malleus, incus, and stapes oval window

opening in wall of tympanic cavity

stapes vibrates against it to move fluids in inner ear

Auditory Tube eustachian

tube connects

middle ear to throat

helps maintain equal pressure on both sides of tympanic membrane

usually closed by valve-like flaps in throat

Inner Ear complex system of

labyrinths osseous labyrinth

bony canal in temporal bone

filled with perilymph membranous

labyrinth tube within osseous

labyrinth filled with

endolymph

Inner Ear 3 Parts of Labyrinths

cochlea functions in hearing

semicircular canals functions in equilibrium

vestibule functions in equilibrium

Cochlea Scala vestibuli

upper compartment leads from oval

window to apex of spiral

part of bony labyrinth Scala tympani

lower compartment extends from apex of

the cochlea to round window

part of bony labyrinth

Cochlea Cochlear duct

portion of membranous labyrinth in cochlea

Vestibular membrane separates cochlear

duct from scala vestibuli

Basilar membrane separates cochlear

duct from scala tympani

Organ of Corti group of hearing

receptor cells (hair cells) on upper surface of

basilar membrane different frequencies of

vibration move different parts of basilar membrane

particular sound frequencies cause hairs of receptor cells to bend

nerve impulse generated

Organ of Corti

Auditory Nerve Pathways

Summary of the Generation of Sensory Impulses from the Ear

Equilibrium

Static Equilibrium vestibule sense position of head when body is not moving

Dynamic Equilibrium semicircular canals sense rotation and movement of head and body

Vestibule Utricle

communicates with saccule and membranous portion of semicircular canals

Saccule communicates

with cochlear duct Mucula

hair cells of utricle and saccule

Macula responds to changes in head position bending of hairs results in generation of

nerve impulse

Semicircular Canals three canals at right

angles ampulla

swelling of membranous labyrinth that communicates with the vestibule

crista ampullaris sensory organ of

ampulla hair cells and supporting

cells rapid turns of head or

body stimulate hair cells

Crista Ampullaris

Sight

Visual Accessory Organs eyelids lacrimal apparatus extrinsic eye muscles

Eyelid palpebra composed of four layers

skin muscle connective tissue conjunctiva

orbicularis oculi - closes levator palperbrae

superioris – opens tarsal glands – secrete oil

onto eyelashes conjunctiva – mucous

membrane; lines eyelid and covers portion of eyeball

Lacrimal Apparatus lacrimal gland

lateral to eye secretes tears

canaliculi collect tears

lacrimal sac collects from canaliculi

nasolacrimal duct collects from lacrimal sac empties tears into nasal

cavity

Extrinsic Eye Muscles Superior rectus

rotates eye up and medially

Inferior rectus rotates eye down

and medially Medial rectus

rotates eye medially

Extrinsic Eye Muscles Lateral rectus

rotates eye laterally

Superior oblique rotates eye down

and laterally Inferior oblique

rotates eye up and laterally

Structure of the Eye hollow spherical wall has 3 layers

outer fibrous tunic middle vascular

tunic inner nervous tunic

Outer Tunic Cornea

anterior portion transparent light transmission light refraction

Sclera posterior portion opaque protection

Middle Tunic Iris

anterior portion pigmented controls light intensity

Ciliary body anterior portion pigmented holds lens moves lens for focusing

Choroid coat provides blood supply pigments absorb extra light

Anterior Portion of Eye filled with aqueous humor

Lens transparent biconvex lies behind iris largely composed of lens fibers elastic held in place by suspensory ligaments of ciliary

body

Ciliary Body forms internal ring around front of eye ciliary processes – radiating folds ciliary muscles – contract and relax to move

lens

Accommodation changing of lens shape to view objects

Iris composed of

connective tissue and smooth muscle

pupil is hole in iris dim light stimulates

radial muscles and pupil dilates

bright light stimulates circular muscles and pupil constricts

Aqueous Humor fluid in anterior cavity of eye secreted by epithelium on inner surface of

the ciliary body provides nutrients maintains shape of anterior portion of eye leaves cavity through canal of Schlemm

Inner Tunic retina contains visual receptors continuous with optic nerve ends just behind margin of the ciliary body composed of several layers macula lutea – yellowish spot in retina fovea centralis – center of macula lutea; produces

sharpest vision optic disc – blind spot; contains no visual receptors vitreous humor – thick gel that holds retina flat

against choroid coat

Layers of Retina receptor cells, bipolar cells, and ganglion

cells - provide pathway for impulses triggered by photoreceptors to reach the optic nerve

horizontal cells and amacrine cells – modify impulses

Light Refraction Refraction

bending of light occurs when light waves pass at an oblique angle

into mediums of different densities

Types of Lenses Convex lenses cause light waves to

converge Concave lenses cause light waves to diverge

Focusing On Retina as light enters eye, it is refracted by

convex surface of cornea convex surface of lens

image focused on retina is upside down and reversed from left to right

Visual Receptors

Rods long, thin projections contain light sensitive pigment called rhodopsin hundred times more sensitive to light than cones provide vision in dim light produce colorless vision produce outlines of objects

Cones short, blunt projections contain light sensitive pigments called erythrolabe,

chlorolabe, and cyanolabe provide vision in bright light produce sharp images produce color vision

Rods

Visual Pigments Rhodopsin

light-sensitive pigment in rods

decomposes in presence of light

triggers a complex series of reactions that initiate nerve impulses

impulses travel along optic nerve

Pigments on Cones each set contains different

light-sensitive pigment each set is sensitive to

different wavelengths color perceived depends

on which sets of cones are stimulated

erythrolabe – responds to red

chlorolabe – responds to green

cyanolabe – responds to blue

Stereoscopic Vision provides perception of distance and depth results from formation of two slightly different

retinal images

Visual Pathway

Life-Span Changes Age related hearing loss due to

damage of hair cells in organ of Corti degeneration of nerve pathways to the brain tinnitus

Age-related visual problems include dry eyes floaters (crystals in vitreous humor) loss of elasticity of lens glaucoma cataracts macular degeneration

Clinical Application- Refraction Disorders concave lens corrects

nearsightedness convex lens corrects

farsightedness