Sensory System

CHAPTER 13

JOE PISTACK MS/ED

Sensory System

Sensory SystemSenses:

Seeing

Hearing

Feeling

Tasting

Allows us to experience the world.

We experience the world through our senses.

Allows us to keep track of what is happening in our bodies.

Acts as a danger signal when we come in contact with a harmful stimulus.

Cells that detect stimuliReceptor-a specialized area of a sensory neuron that detects a specific stimulus.

Ex. Receptors in the eye respond to light.

Ex. Receptors in the tongue respond to chemicals in food.

Five types of sensory receptors:

Chemoreceptors-stimulated by changes in chemicals such as H+, calcium and food. Ex. Taste and smell.

Pain receptors or nociceptors -stimulated by tissue damage or distention. Ex. Pain.

Thermoreceptors -receptors stimulated by changes in temperature. Ex. Heat and cold

Receptors (continued)

Mechanoreceptors-receptors stimulated by changes in pressure or movement of body fluids.

Ex. Hearing and equilibrium.

Photoreceptors-receptors stimulated by light.

Ex. Sight.

SensationThe conscious awareness of incoming sensory information.Ex. “Ouch”-indicates that you are aware of a painful stimulus.

Four components of a sensation:

(1) Stimulus-light will stimulate sight. Absence of light, you cannot see.

(2) Receptor-light waves stimulate photoreceptors in the eye producing a nerve impulse.

(3) Sensory nerve-the nerve impulse is conducted to the occipital lobe of the brain.

Sensation (continued)

Two characteristics of sensation are:

ProjectionAdaptation

Projection-the process by which the brain, after receiving a sensation, refers that sensation back to its source. Ex. Pain

Adaptation-adapting to the stimulus. Ex. When you enter a room with a strong odor, it may be overwhelming at first and then become less noticeable. Sensory receptors adapt.

Two Groups of Senses

General senses: called general or somatic.

Widely distributed throughout the body.

Include: PainTouchPressure TemperatureProprioception

Special senses:

Localized within a particular organ in the head.

Include:TasteSmellSightHearingBalance

Five Special Senses

Five special senses:SmellTasteSightHearingbalance

Pain

Pain-receptors for pain, called nociceptors consist of free nerve endings that are stimulated by tissue damage.

Pain receptors are widely distributed throughout the skin, the visceral organs, and other internal tissues.

Pain

Serves a protective function, it motivates the person to remove its cause.

Patient’s with diminished pain response are at risk .

Diabetic patients have a decreased pain sensation due to nerve damage. They are unable to feel pain in lower extremities. They require meticulous foot care.

Referred Pain

Referred Pain-when pain feels as if it is coming from an area other than the site where it originates.

Ex. Heart pain radiates down arm.

Analgesics-drugs to relieve pain.

Pain Triggers

Three pain triggers:

(1) Tissue injury promotes the release of certain chemicals that stimulate pain receptors.

(2) A deficiency of oxygen stimulates pain receptors.

(3) Pain may be experienced when tissues are stretched or deformed.

Mechanoreceptors

Touch receptors or tactile receptors are found mostly in the skin.

They allow us to feel.

Particularly numerous in the lips, fingers, toes, tongue, and external genitalia.

Located in the skin, subcutaneous tissue, and deep tissue.

Thermoreceptors

Two types of thermoreceptors are heat and cold.

Found in free nerve endings, and specialized sensory cells beneath the skin.

Cold receptors are stimulated between 50 and 76 degrees F and heat receptors are stimulated between 76 and 112 degrees F.

Proprioception

Sense of orientation or position.

Allows you to locate your body part without looking at it.

Plays an important role in maintaining posture and coordinating body movement.

Proprioception

The receptors for proprioception are located in muscles, tendons, and joints.

Proprioceptors are also found in the inner ear, where they function in equilibrium.

The cerebellum receives sensory information from these receptors.

Sense of Smell

Olfaction-sense of smell, associated with the sensory structures located in the upper nose.

Classified as chemoreceptors, stimulated by chemicals that dissolve in the moisture of the nasal tissue.

Sense of Smell

The olfactory receptors are stimulated , the sensory impulses travel along the olfactory nerve

(CN I).

The sensory information is eventually interpreted as smell within the olfactory area of the temporal lobe.

Sense of Taste

The sense of taste is also called the gustatory sense or gustation.

The taste buds are the special organs of taste.

Taste receptors are located in the tongue and are classified as chemoreceptors.

Sense of Taste

Four basic taste sensations:

Sweet-tip of the tongue.

Salty-near the tip of the tongue.

Sour-located in the middle of the tongue.

Bitter-back of the tongue.

Sense of Sight

Vision is one of the most cherished senses.

The eyes are the organs of vision.

Visual accessory organs assist with function and protecting the eye from injury.

Visual Accessory Organs

Visual accessory organs include the:

EyebrowsEyelidsConjunctivaEyelashesLacrimal

apparatusExtrinsic eye

muscles

Visual Accessory OrgansThe eyebrows:

Patches of hair located above the eyes.

Perform a protective role.

Keep perspiration out of eyes and shade eyes from glaring sunlight.

Participate in facial expression as in the “raised eyebrow look”.

Visual Accessory Organs

Eyelids:Also called palpebrae.Protect the eyes.Prevent the entrance

of foreign objects.Wash tears over the

surface of the eye.The medial inner

canthus and the lateral outer canthus are the corners of the eye where the upper and lower eyelids meet.

Visual Accessory Organs

Skeletal muscle opens and closes the eyelids.

The muscle that opens the eyelid is called the levator palpebrae superioris,

(levator means to raise, like an elevator).

The muscle that closes the eyelid is the obicularis oculi.

Visual Accessory Organs

Conjunctiva-thin mucous membrane that lines the inner surface of the eyelid.

The conjunctiva also folds back to cover a portion of the sclera (discussed later) on the anterior surface of the eyeball and is called the white of the eye.

Visual Accessory Organs

The conjunctiva secretes a substance that moistens the surface of the eye.

The anterior surface of the eye must be kept moist or it will ulcerate and scar.

The conjunctiva is very vascular.

Visual Accessory Organs

The “Bloodshot” appearance of the eyes is caused when the blood vessels dilate.

Eye drops that get the red out, cause the blood vessels of the conjunctiva to constrict.

Conjunctivitis-”pink eye”

inflammation of the conjunctiva caused by a bacterial infection.

Visual Accessory OrgansEyelashes:

Line the edges of the eyelid and help to trap dust.

Touching the eyelash stimulates blinking.

Sty or hordeolum -infection of the hair follicle caused by staph.

Visual Accessory Organs

Lacrimal Apparatus:

Composed of the lacrimal gland and a series of ducts called tear ducts.

The lacrimal gland is located in the upper lateral part of the orbit and secretes tears which flow across the surface toward the nose.

Visual Accessory Organs

Tears drain through small openings called lacrimal puncta and then into the lacrimal sac and nasolacrimal ducts.

The nasolacrimal ducts eventually empty into the nasal cavity.

Visual Accessory Organs

Normal tears flow to the back of the throat and are swallowed.

Increase in tears, as in crying, nose begins to run.

Tears perform several functions, moisten, lubricate and cleanse the surface of the eye.

Tears contain losozyme which helps destroy pathogens and prevent infection

The EyeballHas a spherical shape

and is approximately ¾ to 1 inch in diameter.

Most of the eyeball sits within the bony orbital cavity of the skull, partially surrounded by a layer of orbital fat.

Composed of three layers: sclera, choroid, and the retina.

The Sclera

The outermost layer.

Made up of tough, fibrous, connective tissue that covers most of the eyeball.

Helps contain the contents of the eye.

Shapes the eye and is the site of attachment for extrinsic muscles.

The Cornea

Cornea-transparent extension of the sclera.

Covers the area over the iris.

Cornea is avascular and transparent, light rays can go through this structure.

Called the window of the eye

The Cornea

The cornea has a rich supply of nerve fibers ,

sensitive to touch.

Corneal reflex-protective function, if the surface of the cornea is touched lightly, causes blinking.

The ChoroidThe Choroid is the middle

layer of the eye located between the retina and the sclera.

Highly vascular.

Attached to the innermost layer of the retina.

Extends toward the front of the eyeball to form the ciliary body.

The Choroid

The ciliary body secretes a fluid called the aqueous humor.

Gives rise to the ciliary muscles.

Iris-most anterior portion of the choroid, the colored portion of the eye.

The Pupil

Pupil-opening or hole in the middle of the iris.

Pupil size is regulated by two sets of intrinsic muscles located in the iris.

Iris regulates the amount of light entering the eye.

The Retina

Innermost layer of the eyeball.

Nervous layer containing visual receptors which are sensitive to light, called photoreceptors.

Two types of photoreceptors are rods and cones.

The Retina

Rods, scattered throughout but most abundant along periphery.

Cones, most abundant in the central portion of the retina.

Fovea centralis area that contains the highest concentration of cones.

The RetinaThe Optic Nerve forms

where the neurons of the retina converge in a small circular area in the back of the eye called the optic disc.

Because there are no photoreceptors there, images formed there are not seen by the brain. This area is called the “Blind Spot”

The Eye

Cavities of the Eye

Anterior CavityLocated between the

Lens and CorneaFilled with Aqueous

HumorAqueous Humor helps

maintain shape of anterior eye and nourishes the cornea

Posterior CavityLarger and located

between the Lens and Retina

Filled with Vitreous Humor

Vitreous Humor pushes on the retina creating good contact with the Choroid ensuring a rich supply of oxygenated blood

Eye Muscles

Extrinsic eye muscles:

Skeletal muscles.

Located outside the eye.

Move the eyeball in various directions.

Eyes move together in a coordinated way.

SeeingLight waves enter your

eye, are refracted and focused on the photoreceptors of the retina.

Photoreceptors of the retina translate light impulses, to a nerve impulse, which is then transmitted from the retina, along the optic nerve to the occipital lobe of the brain.

Muscles of the Eye

Strabismus:

Also called cross-eyed.

Eyeballs are not aligned, do not focus on a desired point.

Muscles of the IrisIris contains two

muscles: Radial muscle Circular muscle

Contraction of the radial muscle causes the pupil to dilate.

Contraction of the circular muscle causes pupil to constrict.

Mydriasis

Mydriasis-sympathetic nerve stimulation that causes pupillary dilation.

Mydriatic agents-drugs that cause the pupils to dilate.

Night vision Day vision

Rods respond to dim light.

Provide us with black and white vision.

Deficiency of vitamin A can cause night blindness.

Image produced by the stimulation of cones.

Three types of cones that produce different colors, green, blue and red. Stimulation of combinations of these colors produces different colors.

The Eye

Seeing Not seeing

Light waves enter your eye.

Photoreceptors translate light signal to nerve impulses and then transmitted from retina, along optic nerve to occipital lobe.

Defect along the pathway from the cornea to the brain can interfere with vision.

Ex. Scarred cornea or cloudy lens may block light.

The Eye

Conditions of the Eye

Conditions of the Eye

Glaucoma-increased intraocular pressure may squeeze the blood vessels of the choroid, depriving the retina of adequate blood supply.

Can lead to blindness.

Conditions of the Eye

Detached retina-retina falls away from the choroid and it’s blood supply.

Macular Degeneration

Abilities of the Eye

Accommodation- the ability of the lens to change shape in order to focus on close objects

Presbyopia- the inability of the lens to change shape in order to focus on close objects

Convergence- movement of the eye medially (toward the nose) to stay focused on an object

Photopupillary Reflex- When the pupil of the eye changes size to either limit or increase the amount of light entering the eye

Refraction- the bending of light raysConsensually- what one pupil does…so does

the other

Conditions of the Eye

Diabetic retinopathy-damage of the retinal blood vessels of diabetic patients.

Vessels may develop micro aneurysms which rupture and cause bleeding and scar formation throughout the retina.

The Ear

Ear is divided into three parts:

(1) external ear

(2)middle ear

(3)inner ear

External Ear

Part of the ear you can see.

Composed of the auricle and the external auditory canal.

Auricle or pinna- composed of cartilage covered by a layer of loose fitting skin.

The Ear

Auricle opens into the external auditory canal.

Canal provides a passageway for sound waves to enter the ear.

External auditory is hollowed out of the temporal bone.

The Ear

External auditory canal is about 1 inch long and ½ inch wide and extends to the eardrum (tympanic membrane).

Tympanic membrane separates the external ear from the middle ear.

The Ear

External auditory ear canal is lined with tiny hairs and glands that secrete cerumen.

Hairs help prevent dust and foreign objects from entering the ear.

Objects inserted to remove cerumen may damage the tympanic membrane.

Middle Ear

Small air-filled chamber located between the tympanic membrane at one end and a bony wall at the other end.

Contains: Tympanic membraneThree tiny bones The eustachian tube

Middle Ear

Tympanic membrane is composed of connective tissue and has a rich supply of nerves and blood vessels.

Tympanic membrane vibrates in response to sound waves that enter the ear through the external auditory canal.

Vibration is passed on to tiny bones.

Middle Ear

Middle ear contains the three tiniest bones in the body:

(1)malleus (hammer)(2)Incus (anvil)(3)Stapes (stirrup)

The Ear

If pressure becomes unequal, tympanic membrane bulges.

Membrane streches causing pain. Ex. Pain and pressure in an airplane.

Inner Ear

Consists of an intricate system of tubes hollowed out of the temporal bone called the bony labyrinth.

Inner ear has three parts:

(1) vestibule(2) semicircular

canals(3) cochlea

Inner Ear

Cochlea-snail shaped part of the bony labyrinth.

Inside the cochlea are the receptors for hearing, they are tiny cells that contain tiny hairs and are called the organ of corti.

Hearing

Hearing:Sound waves travel

through the external auditory canal and hit the tympanic membrane.

Vibration causes malleus, incus and stapes to vibrate.

Stapes causes the fluid in the inner ear to move.

This causes the hairs to bend.

Hearing

The bending of the hairs triggers the nerve impulse carried by the cochlear branch of the vestibulocochlear nerve, (CN VIII) to the brain.

Temporal lobe of the cerebrum interprets the impulse as sound.

Equilibrium

Receptors for balance are mechanoreceptors.

Vestibule contains the receptors that provide information about the position of the head at rest.

Semicircular canalas provide information about the position of the body as it moves.

Equilibrium

Receptors sense changing positions of the head.

When position changes the hairs are bent.

Receptor cells send nerve impulses to the brain.

Brain sends the signal to restore balance.