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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.

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Nervous system1
Nervous System

  • Cell types of Neural tissue

    • Neurons

    • Neuroglial cells

Divisions of the nervous system
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
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.

Functions of nervous system

Sensory Function

Sensory receptors gather information

Information is carried to the CNS

Integrative Function

Sensory information used to create





Motor Function

Decisions are acted upon

Impulses are carried to effectors

Functions of Nervous system

Myelination of axons
Myelination of Axons

  • White Matter

    • Contains myelinated axons

  • Gray Matter

    • Contains unmyelinated structures

    • Cell bodies, dendrites

Classification of neurons
Classification of Neurons

  • Bipolar

    • Two processes

    • Eyes, ears, nose

  • Unipolar

    • One process

    • Ganglia

  • Multipolar

    • Many processes

    • Most neurons of CNS

Classification of neurons1

Sensory Neurons


Carry impulse to CNS

Most are unipolar

Some are bipolar


Link neurons



Motor Neurons


Carry impulses away from CNS

Carry impulses to effectors

Classification of Neurons

Types of neuroglial cells

Schwann Cells

Peripheral nervous system

Myelinating cell



Myelinating cell



Phagocytic cell



Scar tissue

Mop up excess ions, etc

Induce synapse formation

Connect neurons to blood vessels




Line central canal of spinal cord

Line ventricles of brain

Types of Neuroglial Cells

Resting membrane potential
Resting Membrane Potential

  • Inside is negative relative to the outside

  • Polarized membrane

  • Due to distribution of ions

  • Na+/K+ pump

Potential changes
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
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
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

The synapse
The Synapse

  • Nerve impulses pass from neuron to neuron at synapses

Synaptic transmission
Synaptic Transmission

  • Neurotransmitters are released when impulse reaches synaptic knob.

Synaptic potentials
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
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

Impulse processing
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


  • 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


  • 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


Blurred vision

Numb legs or arms

Can lead to paralysis


No cure

Bone marrow transplant

Interferon (anti-viral drug)



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

Clinical ApplicationMultiple Sclerosis

Meninges of the spinal cord
Meninges of the Spinal Cord

  • Meninges

    • Membranes surrounding CNS

    • Protect CNS

    • Three layers

      • Dura mater – outer, tough

      • Arachnoid mater – weblike

      • Pia mater – inner, delicate

Spinal cord structure
Spinal Cord Structure

  • Extends foramen magnum to 2nd lumbar vertebra.

Spinal cord functions
Spinal Cord Functions

  • Center for spinal reflexes

  • Conduit for nerve impulses to and from the brain

Reflex arcs
Reflex Arcs

  • Reflexes – automatic, subconscious responses to stimuli

Knee jerk reflex
Knee-jerk Reflex

  • Helps maintain posture

Withdrawal reflex
Withdrawal Reflex

  • Protective

Crossed extensor reflex
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
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
Ascending Tracts

  • Fasciculus cuneatus

  • Lateral spinothalamic



interprets sensations

determines perception

stores memory


makes decisions

coordinates muscular movements

regulates visceral activities

determines personality

Major Parts


two cerebellar hemispheres


brain stem



Structure of cerebrum
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
Lobes of Cerebrum

  • Frontal

  • Parietal

  • Temporal

  • Occipital

  • Insula

Functions of cerebrum
Functions of Cerebrum

  • interpretation

  • initiating voluntary movements

  • storing memory

  • retrieving memory

  • reasoning

  • center for intelligence and personality

Functional regions of cerebral cortex
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
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

Sensory areas
Sensory Areas

  • Cutaneous Sensory Area

    • parietal lobe

    • interprets sensations on skin

  • Visual Area

    • occipital lobe

    • interprets vision

  • Auditory Area

    • temporal lobe

    • interprets hearing

Association 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 areas1

Frontal Lobe Association Areas



problem solving


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

Association Areas

Hemisphere dominance

Dominant hemisphere controls




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

Hemisphere Dominance


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
Basal Nuclei

  • masses of gray matter

  • deep w/in cerebral hemispheres

  • caudate nucleus, putamen, globus pallidus

  • produce dopamine

  • control certain muscular activities


  • between cerebral hemispheres and brainstem

  • surrounds third ventricle

  • thalamus

  • hypothalamus

  • optic tracts

  • optic chiasm

  • infundibulum

  • posterior pituitary

  • mammillary bodies

  • pineal gland


  • 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
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
Brain Stem

  • Three Parts

    • Midbrain

    • Pons

    • Medulla Oblongata


  • 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

Nervous system

  • 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
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
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
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


  • 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

Peripheral nervous system
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

Nerve fiber classification
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 classification1
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

Spinal 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 nerves1
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


  • An area of skin that the sensory nerve fibers of a particular spinal nerve innervate

Autonomic nervous system
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
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
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 division2
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

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
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
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 application cerebral injuries abnormalities


brain jarred against cranium

loss of consciousness

temporary loss of memory

mental cloudiness


recovery usually complete

Cerebrovascular Accident


sudden interruption in blood flow

brain tissues die

Cerebral Palsy

motor impairment at birth

caused by blocked cerebral blood vessels during development


learning disabilities

Clinical ApplicationCerebral Injuries & Abnormalities

Somatic and special senses
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
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
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
Sensory Adaptation

  • adjustment of sensory receptors from continuous stimulation

  • stronger stimulus required to activate receptors

  • smell receptors undergo sensory adaptation

Somatic senses
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
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
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
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

Pain Nerve Fibers

Regulation of pain impulses


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




Regulation of Pain Impulses

Stretch receptors
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

Special senses
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


  • 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 nerve pathways
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 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 sensations
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
Taste Nerve Pathways

  • Sensory impulses from taste receptors travel along

    • cranial nerves to

    • medulla oblongata to

    • thalamus to

    • gustatory cortex (for interpretation)


  • Ear – organ of hearing

  • 3 Sections

    • External

    • Middle

    • Inner

External ear
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
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
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
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 ear1
Inner Ear

  • 3 Parts of Labyrinths

    • cochlea

      • functions in hearing

    • semicircular canals

      • functions in equilibrium

    • vestibule

      • functions in equilibrium


  • 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


  • 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
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


  • Static Equilibrium

    • vestibule

    • sense position of head when body is not moving

  • Dynamic Equilibrium

    • semicircular canals

    • sense rotation and movement of head and body


  • Utricle

    • communicates with saccule and membranous portion of semicircular canals

  • Saccule

    • communicates with cochlear duct

  • Mucula

    • hair cells of utricle and saccule


  • responds to changes in head position

  • bending of hairs results in generation of nerve impulse

Semicircular canals
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


  • Visual Accessory Organs

    • eyelids

    • lacrimal apparatus

    • extrinsic eye muscles


  • 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 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
Extrinsic Eye Muscles

  • Superior rectus

    • rotates eye up and medially

  • Inferior rectus

    • rotates eye down and medially

  • Medial rectus

    • rotates eye medially

Extrinsic eye muscles1
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
Structure of the Eye

  • hollow

  • spherical

  • wall has 3 layers

    • outer fibrous tunic

    • middle vascular tunic

    • inner nervous tunic

Outer tunic
Outer Tunic

  • Cornea

    • anterior portion

    • transparent

    • light transmission

    • light refraction

  • Sclera

    • posterior portion

    • opaque

    • protection

Middle tunic
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
Anterior Portion of Eye

  • filled with aqueous humor

Nervous system

  • transparent

  • biconvex

  • lies behind iris

  • largely composed of lens fibers

  • elastic

  • held in place by suspensory ligaments of ciliary body

Ciliary body
Ciliary Body

  • forms internal ring around front of eye

  • ciliary processes – radiating folds

  • ciliary muscles – contract and relax to move lens


  • changing of lens shape to view objects

Nervous system

  • 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
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
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
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
Light Refraction

  • Refraction

    • bending of light

    • occurs when light waves pass at an oblique angle into mediums of different densities

Types of lenses
Types of Lenses

  • Convex lenses cause light waves to converge

  • Concave lenses cause light waves to diverge

Focusing on retina
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


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


short, blunt projections

contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe

provide vision in bright light

produce sharp images

produce color vision

Visual Receptors

Visual pigments


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

Visual Pigments

Stereoscopic vision
Stereoscopic Vision

  • provides perception of distance and depth

  • results from formation of two slightly different retinal images

Life span changes1
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

Clinical Application- Refraction Disorders