Nervous System II

Sensory Function

The SensesThe Senses

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General senses of touch Temperature Pressure Pain

Special senses Smell Taste Sight Hearing Equilibrium

I. General Principles of I. General Principles of SensationSensation

A.A.ReceptorsReceptors 1.Specialized cells that

provide the CNS with information

I. General Principles of I. General Principles of SensationSensation

A.A.ReceptorsReceptors 2. Detect a

stimulus and convert it

into an

action potential

which travels to the CNS

- "transductiontransduction"

3.Classification of Receptors3.Classification of ReceptorsBy type of stimulus detected:By type of stimulus detected:

a. Mechanoreceptors detect mechanical stimuli like pressure, sound waves, or stretching.

b. Thermoreceptors detect temperature changes.

c. Nociceptors detect damage to tissues as pain.

d. Photoreceptors detect photons of light.

e. Chemoreceptors detect chemicals by taste, smell, or within body fluids (like carbon dioxide content of the blood).

I. General Principles of I. General Principles of SensationSensation

B. Classification of B. Classification of senses senses

1.1.General senses:General senses:a.Pain, temperature,

touch, pressure, vibration, proprioception (position sense).

b.relatively simple receptors located all over the body.

I. General Principles of I. General Principles of SensationSensation

B. Classification of sensesB. Classification of senses

2. Special senses:2. Special senses: a.Sight, smell, taste, hearing,

and equilibrium (NOT TOUCH)(NOT TOUCH).. b.relatively

complex receptors located

only in the head

C. Levels of SensationC. Levels of Sensation 1.1. SensationSensation is a conscious or is a conscious or

unconscious awareness of unconscious awareness of external and internal stimuliexternal and internal stimuli

2. 2. PerceptionPerception

thethe interpretation interpretation

of conscious of conscious sensations sensations

C. Levels of SensationC. Levels of Sensation

Do you see an Eskimo or the face of a native american?

C. Levels of SensationC. Levels of Sensation 2. 2. PerceptionPerception

b.Pathways that end in the • spinal cordspinal cord can generate a

reflex actionreflex action • brainstem brainstem generate

complex subconscious subconscious motor reactionsmotor reactions

(ex: medulla reg. Heart rate)

• cerebral cortexcerebral cortex generate perceptionperception of the sensory experience.

D. Components of Sensation D. Components of Sensation 1.1. Stimulation:Stimulation: A A stimulusstimulus capable of capable of

initiating a nerve impulse must be initiating a nerve impulse must be present. present.

2.2. Transduction: Transduction: A sensory receptor A sensory receptor (sense organ) must pick up the (sense organ) must pick up the stimulus andstimulus and transducetransduce it to a nerve it to a nerve impulse impulse

3.3. Conduction:Conduction: along a neural pathway from the receptor to the brain.

4.4. Translation:Translation: A region of the brain or spinal cord must translate the impulse into a sensation.

II. General Senses II. General Senses B. Pain Sensations B. Pain Sensations

1.1.Nociceptors Nociceptors - Pain receptors a.located in superficial

parts of skin, joints, periosteum, and around walls of blood vessels.

b.Are free nerve endings c.excessive stimulation

of any receptor type can elicit pain

II. II. Pain Sensations Pain Sensations “Pain" really occurs in the brain, as does

sight, smell, etc., but we "project" the stimulus back to the receptor(so we think we feel in our hands, and hear in our ears, but that perception occurs in the brain, not at the source).

• Nociceptors are Also known as somatic senses because they arise in widespread receptors in the skin (cutaneous sensations) or prioprioceptive sensations in muscles, tendons, joints and the inner ear.

II. General Senses II. General Senses B. Pain Sensations B. Pain Sensations

2.Major categories of Pain a.based on speed of onset quality

of sensation, and duration. b."Acute" pain is fast, sharp, and

not felt in deeper tissues of the body.

c. "Chronic" pain is slow, gradually increases in intensity, and occurs both in the skin and deeper tissues or in internal organs.

The Eye and VisionThe Eye and Vision

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70 percent of all sensory receptors are in the eyes

Each eye has over a million nerve fibers

Protection for the eye

Most of the eye is enclosed in a bony orbit

A cushion of fat surrounds most of the eye

III. Special Senses - III. Special Senses - A. Visual Sensations A. Visual Sensations

1. General a. ophthalmologist doctor who deals exclusively with

parts of the body related to the visual passageways; that is, the eyes, the brain, and the areas around the eye, such as eyelids. An ophthalmologist will inspect the eye for disease, and may perform surgery on the

eyes if necessary. vs.optometrist A person who is

professionally trained and licensed to examine the eyes for visual defects, diagnose problems or impairments, and prescribe corrective lenses or provide other types of treatment.

b.the eyes are the most specialized of all sense organs.

III. Special Senses - III. Special Senses - A. Visual SensationsA. Visual Sensations

2. Accessory2. Accessory Structures of the EyeStructures of the Eye a.a.eyebrows eyebrows

channel sweat;shield from the sun

b.b.Eyelids Eyelids ((aka "palpebrae")• shade eyes from light • moisten and protect eyes

c. Eyelashes c. Eyelashes • protect from foreign objects

III. Special Senses - III. Special Senses - AccessoryAccessory

Structures of the EyeStructures of the Eyed.Canthus is the angular point where

the eyelids meet.e.Caruncle is the fleshy elevation @

the medial canthus; which is the remnant of the “third eye”.

f. Conjunctival sac is the recess @ the junction of the eyelid (palpebrae) & the ocular conjunctivae.

Accessory Structures of Accessory Structures of the Eyethe Eye

Conjunctiva-Conjunctiva- mucous membrane that lines innerpart of the eyelids withtears. Conjunctivitis – inflammation due to infection of the conjunctiva

Accessory Structures of the EyeAccessory Structures of the Eye

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Meibomian glands – modified sebacious glands in the tarsal plates that produce an oily secretion to lubricate the eye

Accessory Structures of the EyeAccessory Structures of the Eye

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Ciliary glands –

modified sweat glands between the eyelashes

Figure 8.1b

Accessory Structures of the EyeAccessory Structures of the Eye

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Lacrimal apparatus

Lacrimal gland – produces lacrimal fluid

Lacrimal canals – drains lacrimal fluid from eyes

Figure 8.1a

Accessory Structures of the EyeAccessory Structures of the Eye

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Lacrimal sac – provides passage of lacrimal fluid towards nasal cavity

Figure 8.1a

Accessory Structures of the EyeAccessory Structures of the Eye

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Nasolacrimal duct – empties lacrimal fluid into the nasal cavity

Figure 8.1a

Function of the Lacrimal ApparatusFunction of the Lacrimal Apparatus

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Properties of lacrimal fluid

Dilute salt solution (tears)

Contains antibodies and lysozyme

Protects, moistens, and lubricates the eye

Empties into the nasal cavity

Crying results from ANS stimulation of the lacrimal apparatus in response to extreme emotion.

Extrinsic Eye MusclesExtrinsic Eye Muscles

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Muscles attach to the outer surface of the eye

Produce eye movements

Figure 8.2

Structure of the EyeStructure of the Eye

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The wall is composed of three tunics

Fibrous tunic – outside layer

Choroid – middle layer

Sensory tunic – inside layer Figure 8.3a

Only about 1/6 of the eyeball is exposed. The orbit contains the eyeball, the extrinsic muscles, nerves, vessels, and a posterior fat pad. The wall of the eyeball can be described in layers known as "tunics".

A. Visual SensationsA. Visual Sensations3. Anatomy of the

Eyeball a. Fibrous Tunic

– outer coat•CorneaCornea

-Anterior, transparent, nonvascular-Refracts light into the eye-Has 5 layers-Very sensitive to pain & touch

A. Visual SensationsA. Visual SensationsCorneaCornea

-Repairs itself easily -The only human tissue that can be transplanted without fear of rejection

A. Visual SensationsA. Visual Sensations3. Anatomy of the

Eyeball a. Fibrous Tunic

• ScleraSclera-white -gives shape and protection

A. The Fibrous TunicA. The Fibrous TunicCornea & Sclera

a. Fibrous Tunic

3. Anatomy of the EyeballVascularTunic-Choroid Layer:

(aka"uvea")

1)1) Middle layerMiddle layer

2)2) Highly Highly vascularizedvascularized

Blood-rich nutritive tunic

Pigment prevents light from scattering

3. Anatomy of the EyeballVascular Tunic-Choroid

Layer

3) 3 parts:3) 3 parts:

choroid, choroid, ciliary ciliary body,irisbody,iris

Modified interiorly into two structures

Cilliary body – smooth muscle

Iris

Pigmented layer that gives eye color

Pupil – rounded opening in the iris

b. Vascular Tunic (aka "uvea") 3) 3 portions3) 3 portions

• The choroidThe choroid

- the darkly-pigmented- absorbs light rays

Suspensor LigamentsSuspensor Ligaments-Attaches the lens to the ciliary body

The Ciliary Body/MuscleThe Ciliary Body/Muscle -Secretes aqueous humor-Alters shape of lens

b. Vascular Tunic

Iris: colored portion that contains the muscle that controls

the size of the pupil.

The Retina: Snot like layer

Sensory Tunic (Retina)Sensory Tunic (Retina)

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Contains receptor cells (photoreceptors) Rods

Cones

Signals pass from photoreceptors via a two-neuron chain Bipolar neurons

Ganglion cells

Signals leave the retina toward the brain through the optic nerve

3. Anatomy of the Eyeballc. Retina (Nervous Tunic)

1)1) Inner layerInner layer

2) function - 2) function - image image formation formation

Neurons of the RetinaNeurons of the Retina

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Figure 8.4

3. Anatomy of the Eyeballc. Retina (Nervous Tunic)

3) Photoreceptor neurons 3) Photoreceptor neurons • Rods- provide vision in dim Rods- provide vision in dim

light & periphal vision; see light & periphal vision; see black & white; most are black & white; most are found towards the edges of found towards the edges of the retina; shapes and the retina; shapes and movementmovement

• Cones– Provide vision in Cones– Provide vision in bright light;densest in the bright light;densest in the center of the retina; see center of the retina; see color & sharpnesscolor & sharpness

Cones are densely concentrated in the central central foveafovea- no rods

Fovea Centralis is a tiny pit in the macula lutea

3. Anatomy of the Eyeballc. Retina (Nervous Tunic)

4)4) Blind spot (optic disc)Blind spot (optic disc)

• where the optic where the optic nerve exits the nerve exits the eye eye

• no no photoreceptors.photoreceptors.

Cone SensitivityCone Sensitivity

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There are three types of cones

Different cones are sensitive to different wavelengths

Color blindness is the result of lack of one cone type

Figure 8.6

LensLens

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Biconvex crystal-like structure

Held in place by a suspensory ligament attached to the ciliary body

Figure 8.3a

3. Anatomy of the Eyeballd. Lens 1)1) nonvascular nonvascular 2)2) changes shape changes shape

to focus light to focus light rays on the rays on the retina retina

3. Anatomy of the Eyeballd. Lens

3)3) cataractscataracts

• a cloudiness that a cloudiness that form in the lens form in the lens of the eyeof the eye

• result of ageing result of ageing and long-term and long-term exposure to exposure to ultraviolet light.ultraviolet light.

Internal Eye Chamber FluidsInternal Eye Chamber Fluids

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Aqueous humor Watery fluid found in chamber between the

lens and cornea Similar to blood plasma Helps maintain intraocular pressure Provides nutrients for the lens and cornea Drains through the canal of Schlemm back

into the blood

e. Interior of Eye1) 1) anterior cavityanterior cavity filled with filled with

thin thin aqueous humoraqueous humor2) 2) Posterior Posterior

cavitycavity filled filled

with with gelatinous gelatinous

vitreous vitreous humor humor (body)(body)

Internal Eye Chamber FluidsInternal Eye Chamber Fluids

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Vitreous humor

Gel-like substance behind the lens

Keeps the eye from collapsing

Lasts a lifetime

and is not replaced

Internal Eye Chamber of CrittersTapetum Ludidium: is a reflective layer, behind the retina of 4 leged animals, that increases the amount of light a critter can see @ night. The Tapetum Lucidium produces the familiar “glowing eyes” of nocturnal animals.

Lens AccommodationLens Accommodation

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Light must be focused to a point on the retina for optimal vision

The eye is set for distance vision (over 20 ft away)

The lens must change shape to focus for closer objects

Figure 8.9

A. Visual SensationsA. Visual Sensations4. Vision

a.a.Refraction of Light RaysRefraction of Light Rays

4. Vision

Visual PathwayVisual Pathway

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Photoreceptors of the retina

Optic nerve

Optic nerve crosses at the optic chiasma

Figure 8.11

Visual PathwayVisual Pathway

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Optic tracts

Thalamus (axons form optic radiation)

Visula cortex of the occipital lobe

Figure 8.11

Eye ReflexesEye Reflexes

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Internal muscles are controlled by the autonomic nervous system Bright light causes pupils to constrict

through action of radial and ciliary muscles

Viewing close objects causes accommodation

External muscles control eye movement to follow objects

Viewing close objects causes convergence (eyes moving medially)

5. Vision - Disorders a.a.Glaucoma:Glaucoma: –Results from Results from blockage of blockage of drainaige canalsdrainaige canals

causing increased causing increased

pressure within pressure within

the eyethe eye• Vision loss is caused by Vision loss is caused by

damage to the optic damage to the optic nerve.nerve.

Normal VisionIf one optic nerve is cut, you will completely blind in that eye; but if an optic tract is damaged, you will be partially blind in both eyes.

5. Vision – 5. Vision – DisordersDisorders

b.b.Myopia:Myopia:

• nearsightednearsighted• most common most common

vision problem vision problem

Normal VisionNormal Vision

Nearsighted VisionNearsighted Vision

b. Myopia:b. Myopia:• cornea is cornea is

curved too curved too steeply, or the steeply, or the eye is longer eye is longer than it should than it should bebe

• Light is Light is focused in focused in front of front of retinaretina

Normal VisionNormal Vision

Nearsighted VisionNearsighted Vision

Near Sighted

Correction

6. Vision Disordersc.c.Hyperopia:Hyperopia:

• FarsightedFarsighted• cornea is not cornea is not

curved curved enough, or the enough, or the eye is shorter eye is shorter than normal than normal

• rays focus rays focus behind the behind the retina retina

Normal VisionNormal Vision

Farsighted VisionFarsighted Vision

Far Sighted

Correction

6. Vision Disordersc.c.PresbyopiaPresbyopia

• Result of Result of natural aging natural aging (~ 40 to 45 yrs)(~ 40 to 45 yrs)

• the eye looses the eye looses its ability to its ability to fine focus fine focus

• Results in the Results in the need for need for reading glassesreading glasses

Normal VisionNormal Vision

Farsighted VisionFarsighted Vision

6. Vision Disorderse.e.AstigmatisAstigmatis

m:m: • FarrsighteFarrsighte

dd• An uneven An uneven

curvature curvature of the of the cornea cornea

Normal VisionNormal Vision

AstigmatismAstigmatism

6. Vision Disorderse.e.Astigmatism:Astigmatism:

• Prevents the Prevents the formation of formation of a sharp point a sharp point of focus on of focus on the retina the retina

• Often Often accompanies accompanies myopia and myopia and hyperopiahyperopia

Normal VisionNormal Vision

AstigmatismAstigmatism

The EarThe Ear

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Houses two senses

Hearing

Equilibrium (balance)

Receptors are mechanoreceptors

Different organs house receptors for each sense

Anatomy of the EarAnatomy of the Ear

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The ear is divided into three areas Outer

(external) ear

Middle ear

Inner ear

Figure 8.12

III. Special Senses - III. Special Senses - B. Auditory Sensations B. Auditory Sensations

1. Ear Anatomy -

a)a)Outer Ear –Outer Ear – • collect

and funnel sound waves

1. Ear Anatomy -

a)a)Outer Ear –Outer Ear – • consists of

the– auricle auricle

(aka "pinna")

– external auditory canal– tympanic membrane (eardrum)

The External Auditory CanalThe External Auditory Canal

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Narrow chamber in the temporal bone

Lined with skin

Ceruminous (wax) glands are present

Ends at the tympanic membrane

B. Auditory SensationsB. Auditory Sensations 1. Ear Anatomy -

b)b)Middle Ear –Middle Ear – • small, air-filled cavity in the

temporal bone; only involved in the sense of hearing

The Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity

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Two tubes are associated with the inner ear

The opening from the auditory canal is covered by the tympanic membrane

The auditory tube connecting the middle ear with the throat

Allows for equalizing pressure during yawning or swallowing

This tube is otherwise collapsed

B. Middle Ear –B. Middle Ear – • contains the– EustachiaEustachia

n tube n tube functions to equalize pressures on either side of the eardrum – OssiclesOssicles:: malleus, incus, malleus, incus,

stapesstapes– Oval windowOval window and the round round windowwindow

Bones of the Tympanic CavityBones of the Tympanic Cavity

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Three bones span the cavity

Malleus (hammer)

Incus (anvil)

Stapes (stirrip)

Figure 8.12

Bones of the Tympanic CavityBones of the Tympanic Cavity

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Vibrations from eardrum move the malleus

These bones transfer sound to the inner ear

Figure 8.12

Inner Ear or Bony LabyrinthInner Ear or Bony Labyrinth

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Includes sense organs for hearing and balance

Filled with perilymph

Figure 8.12

Inner Ear or Bony LabrynthInner Ear or Bony Labrynth

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A maze of bony chambers within the temporal bone

Cochlea

Vestibule

Semicircular canals

Figure 8.12

B. Auditory SensationsB. Auditory Sensations 1. Ear Anatomy -b)b)Inner Ear –Inner Ear –

• SemicirculSemicircular canals:ar canals: contains contains nerves nerves for for balancebalance

B. Auditory SensationsB. Auditory Sensations 1. Ear Anatomy -

contains receptors for contains receptors for hearinghearing

b)b)Inner Ear –Inner Ear –

• CochleaCochlea

Organs of HearingOrgans of Hearing

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Organ of Corti

Located within the cochlea

Receptors = hair cells on the basilar membrane

Gel-like tectorial membrane is capable of bending hair cells

Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

Organs of HearingOrgans of Hearing

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Figure 8.13

Mechanisms of HearingMechanisms of Hearing

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Vibrations from sound waves move tectorial membrane

Hair cells are bent by the membrane

An action potential starts in the cochlear nerve

Continued stimulation can lead to adaptation

Mechanisms of HearingMechanisms of Hearing

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Figure 8.14

Organs of EquilibriumOrgans of Equilibrium

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Receptor cells are in two structures

Vestibule

Semicircular canals

Figure 8.16a, b

Organs of EquilibriumOrgans of Equilibrium

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Equilibrium has two functional parts

Static equilibrium

Dynamic equilibrium

Figure 8.16a, b

Static EquilibriumStatic Equilibrium

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Maculae – receptors in the vestibule Report on the position of the head

Send information via the vestibular nerve

Anatomy of the maculae Hair cells are embedded in the otolithic

membrane

Otoliths (tiny stones) float in a gel around the hair cells

Movements cause otoliths to bend the hair cells

Function of MaculaeFunction of Maculae

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Figure 8.15

Dynamic EquilibriumDynamic Equilibrium

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Crista ampullaris – receptors in the semicircular canals

Tuft of hair cells

Cupula (gelatinous cap) covers the hair cells

Figure 8.16c

Dynamic EquilibriumDynamic Equilibrium

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Action of angular head movements

The cupula stimulates the hair cells

An impulse is sent via the vestibular nerve to the cerebellum

Figure 8.16c

B. Auditory SensationsB. Auditory Sensations 2. Physiology2. Physiology

a)external auditory canal

b)tympanic membrane c)Ossicles amplify the vibration

d)Stapes passes the vibration to the oval window

B. Auditory SensationsB. Auditory Sensations 2. Physiology2. Physiology

d) causes the perilymphperilymph within the inner ear to start moving

e) fluid waves bends "hair cells" of the organ of Corti

f) fluid wave to converted to an electrical impulse and passed tobrain

C. Olfactory Sensations (Smell) C. Olfactory Sensations (Smell) 1. Receptors are in the

superior portion of the nasal cavity

a)a) receptors – receptors – cilia called cilia called

"olfactory hairs" "olfactory hairs"

b)b)Are Are chemoreceptorschemoreceptors

c)c) Smell has 2 Smell has 2 purposes: to detect purposes: to detect potentially potentially harmful/arousing harmful/arousing threats and to threats and to supplement taste.supplement taste.

III. Special Senses - III. Special Senses - C. Olfactory Sensations C. Olfactory Sensations

(Smell)(Smell) 2.2.Substances Substances to be smelled to be smelled must bemust be• VolatileVolatile• Water-Water-

solublesoluble• Lipid Lipid

solublesoluble

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Olfaction – The Sense of SmellOlfaction – The Sense of Smell

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Olfactory receptors are in the roof of the nasal cavity

Neurons with long cilia

Chemicals must be dissolved in mucus for detection

Impulses are transmitted via the olfactory nerve

Interpretation of smells is made in the cortex

Olfactory EpitheliumOlfactory Epithelium

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Figure 8.17

Chemical Senses – Taste and Chemical Senses – Taste and SmellSmell

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Both senses use chemoreceptors

Stimulated by chemicals in solution

Taste has four types of receptors

Smell can differentiate a large range of chemicals

Both senses complement each other and respond to many of the same stimuli

The Sense of TasteThe Sense of Taste

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Taste buds house the receptor organs

Location of taste buds Most are on

the tongue

Soft palate

Cheeks Figure 8.18a, b

III. Special Senses - III. Special Senses - D. Gustatory Sensations D. Gustatory Sensations

(Taste)(Taste)

1.Receptors area)a) gustatory hairsgustatory hairsb)b) Located in Located in

taste taste buds buds on papillae on papillae of of tonguetongue

2.2.Substances to be tasted Substances to be tasted must be in solutionmust be in solution

The Tongue and TasteThe Tongue and Taste

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The tongue is covered with projections called papillae

Filiform papillae – sharp with no taste buds

Fungifiorm papillae – rounded with taste buds

Circumvallate papillae – large papillae with taste buds

Taste buds are found on the sides of papillae

Structure of Taste BudsStructure of Taste Buds

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Gustatory cells are the receptors

Have gustatory hairs (long microvilli)

Hairs are stimulated by chemicals dissolved in saliva

Structure of Taste BudsStructure of Taste Buds

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Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas

Facial nerve

Glossopharyngeal nerve

Vagus nerve

Anatomy of Taste BudsAnatomy of Taste Buds

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Figure 8.18

Taste SensationsTaste Sensations

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Sweet receptors Sugars Saccharine Some amino acids

Sour receptors Acids & Hydrocloric Acid

Bitter receptors Alkaloids, Phenols, & Catechin(flavanols)

Salty receptors Metal ions like Fe, Minerals like Na & K

III. Special Senses - III. Special Senses - D. Gustatory Sensations D. Gustatory Sensations

(Taste) (Taste) 3.Four primary tastes:

sweet, salty, bitter and sour • 10,000 taste buds• Sweet and sour less

sensitive• Bitter most sensisitve

Developmental Aspects of the Developmental Aspects of the Special SensesSpecial Senses

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Formed early in embryonic development

Eyes are outgrowths of the brain

All special senses are functional at birth

That’s All!