The General & Special Senses Chapter 8. Introduction Senses – our perception of what is “out...

The General & Special Senses

Chapter 8

Introduction

• Senses – our perception of what is “out there”

• 2 groups– General senses

• Includes senses that are not specific

• Pass information through spinal nerves

– Special senses• Found within complex sense organs to cerebral

cortex

• Pass information through cranial nerves to cerebral cortex

Receptors

• Sensory receptors are transducers – Change stimuli into electro-chemical impulses – Specific receptors can transduce only certain

types of stimuli

Human Anatomy, 3rd editionPrentice Hall, © 2001

Figure 18-01

Receptors

Interpretation of Sensory Information

• Occurs in cerebral cortex

• Depends on the area of the cerebral cortex that receives the information

Central Processing and Sensory Adaptation

• Sensory adaptation – the loss of sensitivity after continuous stimulation– Occurs in some types of receptors

• Role – prevents brain from being overloaded with unimportant information

Receptors of the General Senses• Pain

– Referred pain

– Phantom pain

• Thermoreceptors detect changes in temperature• Mechanoreceptors respond to pressure & touch• Chemoreceptors detect chemicals in solution

– Blood composition

– (Smell)

– (Taste)

What’s a Dermatome?• A localized area of skin that is has its

sensation via a single nerve from a single nerve root of the spinal cord. Shingles (Herpes zoster virus infection) typically affects one or several isolated dermatomes.

What’s a Dermatome?

From Medical school Halloween partyFrom Textbook


Figure 18-02

Referred Pain

The Special Senses

Olfaction (the nose)

• Olfactory receptors– Can detect at least 50 different primary smell– Located in the roof of nasal cavity– Molecules dissolve in the mucus or lipids of the

epithelium – Olfactory neurons pass through the roof of the

nasal cavity and synapse in the olfactory nerve– Olfactory tracts go directly to the cerebral

cortex


Figure 18-06a

Olfactory Receptors


Figure 18-06b

Olfactory Receptors

Taste (the tongue)

• Taste receptors are in the taste buds– Can detect 4 primary tastes

• Sweet, sour, salty, bitter

– Located in papillae on the surface of the tongue – Taste buds contain the taste receptors– Molecules dissolve in saliva– Cranial nerves relay sensory impulses to the

cerebral cortex


Figure 18-07a

Taste Areas of the Tongue


Figure 18-07b

Taste Buds


Figure 18-07c

Taste Bud

Equilibrium & Hearing (the ear)

• External ear– The auricle directs sound waves into the

external auditory meatus to the tympanic membrane

• Middle ear– Contains the auditory ossicles

• Malleus, incus, stapes

– Connected to throat by the eustachian tube

• Inner ear


Figure 18-09

The Ear


Figure 18-10b

The Middle Ear

The Inner Ear

• Separated from the middle ear by the oval window

• Consists of a series of canals filled with fluid

The Inner Ear

– Semicircular canals• Contains receptors for head position

– Cochlea • Contains the organ of Corti, the organ of hearing


Figure 18-12b

The Inner Ear

The Semicircular Canals

• Detects balance

• Arranged at right angles to each other

• Contain hair cells are embedded in gelatinous material with fluid over it

• Detect movement of the head – Bends the hairs, creating nerve impulses


Figure 18-12c

Hair Cells in the Semicircular Canals

The Organ of Corti

• Detects sound waves

• Consists of hair cells on a basement membrane

• Tips of hairs touch the tectorial membrane

• When the basement membrane vibrates, the hair cells are bent, sending a nerve impulse


Figure 18-16d

Organ of Corti


Figure 18-16e

Organ of Corti

Summary of Hearing

• Sound waves enter the external auditory meatus• Tympanic membrane vibrates• Auditory ossicles vibrate• Oval window vibrates• Fluid in inner ear vibrates• Basement membrane moves• Hairs rub against the tectorial membrane• Nerve impulse is sent along the auditory nerve to

the brain

Diseases of Hearing

• External Otitis, the most common disorder of the outer ear, also know as Swimmer’s ear. The process develops due to loss of the protective cerumen (wax) and excessive moisture in the ear canal.

• Otitis Media is one of the most common diseases of children, due to chronic middle ear infection. Treatments: antibiotics, otomyringotomy (surgical insertion of rigid “ear tubes”).

• Conductive Hearing Loss, usually due to otosclerosis, progressive fixation of the stapes due to aging or disease.

Vision (the eye)

• Accessory structures– Eyelids protect the eye

• Conjunctiva lines the eyelid

• Lacrimal gland produces tears

– Extrinsic muscles move the eyeball


Figure 18-18b

The Eye

Structure of the Eye

• Consists of 3 tunics (layers)– Outer tunic – outermost layer

• Includes the cornea & sclera

– Middle tunic • Includes the choroid coat, ciliary body, and lens,

iris & pupil

– Inner tunic (retina) – inner layer• Contains the rods & cones (photoreceptors)

• Includes the optic disc (blind spot),


Figure 18-20b

The Eye


Figure 18-20a

Tunics of the Eye


Figure 18-22c

Inner Tunic

The Cavities of the Eye

• The lens separates the interior of the eye into 2 cavities– Anterior cavity in front of the lens

• Contains aqueous humor– Glaucoma

– Posterior cavity behind the lens• Contains vitreous humor

Cavities of the Eye


Figure 18-23

The Vascular Tunic

• Contains many blood vessels & nerves

• The iris controls the size of the pupil

• Suspensory ligaments attach the lens to the ciliary body– Controls the shape of the lens

• Allows focusing on near & distant objects

• Cataract


Figure 18-20c

The Pupil

The Retina

• Cones allow for sharp color vision in bright light– 3 types, each with a different pigment

The Retina

• Rods provide for vision in dim light– Most dense at the periphery of the retina– Contain the pigment rhodopsin


Figure 18-22a1

Visual Receptors

Summary of Vision

• Light rays enters through the pupil

• Light rays cross in the lens

• Retina receives reversed & upside down image

• Rods & cones are stimulated

• Optic nerve carries impulse to the brain

Abnormal Vision

• Astigmatism

Occurs when the transparent media of the eye (includes the cornea, crystalline lens) are inconsistently or irregularly shaped. Causes blurred vision at far and near distances.

Abnormal Vision

• Cataracts

A clouding and hardening of all or part of the transparent lens located inside the eye, most often caused by the aging process, UV light exposure, etc.

Abnormal Vision

• Glaucoma

A condition characterized either by increased intraocular pressure- "high blood pressure of the eye" -that can result in damage to the optic nerve and to retinal nerve fibers, or by significant decreased intraocular pressure.

Abnormal Vision• Hyperopia

Farsightedness. A condition in which rays of light are focused behind the retina, so distant objects appear clearer than near ones.

Abnormal Vision

• Presbyopia

Caused by the loss of elasticity in the lens inside the eye as part of the aging process, resulting in a gradual decline in a person’s ability to focus on close objects or to see small print. Virtually everyone is affected after the age of 40.

Abnormal Vision• Myopia

Near sightedness. A condition in which light rays are focused in front of the retina instead of on it, so near objects appear more clear than far ones.

Abnormal Vision• Macular degeration

Common eye age-related disease that causes deterioration of the macula, the central area of the retina, the paper-thin tissue at the back of the eye where light-sensitive cells send visual signals to the brain. Sharp, clear, “straight ahead” vision is processed by the macula.

Abnormal Vision• Retinoblastoma

Malignant tumor of the retina. Inherited form is caused by a genetic abnormality in the Rb gene.

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