The General & Special Senses Chapter 8

What are the 5 senses?

Hearing (technical name = Audition) Sight (technical name = Vision) Smell (technical name = Olfaction) Taste (technical name = Gustation) ?

What are the 5 senses? Hearing (technical name = Audition) Sight (technical name = Vision) Smell (technical name = Olfaction) Taste (technical name = Gustation) NOT Touch?

What are the 5 senses? Hearing (technical name = Audition) Sight (technical name = Vision) Smell (technical name = Olfaction) Taste (technical name = Gustation) Balance (technical name = Equilibrium)

Introduction Senses – our perception of what is “out there” 2 groups –General senses Includes senses that are not specific Receptors not specialized or free nerve endings Pass information through spinal nerves –Special senses Highly specialized receptors Found within complex sense organs 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

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 – adjacent nerve sensations such as left arm pain in heart attack –Phantom pain - adjacent nerve sensations such as left arm sensation when left arm has been amputated Thermoreceptors detect changes in temperature Mechanoreceptors respond to pressure & touch Chemoreceptors detect chemicals in solution –Blood composition –(Smell) –(Taste)

Referred Pain

The Special Senses

Olfaction (the nose) Olfactory receptors –Can detect at least 50 different primary smells –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

Olfactory Receptors

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Taste (the tongue) Taste receptors are in the taste buds –Can detect 5 primary tastes Sweet, sour, salty, bitter, umami –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

Taste Areas of the Tongue – traditional but “wrong” watch?v=FSHGucgnvLU &feature=PlayList&p=56 D05189EFBACBB1&ind ex=0&playnext=1 watch?v=lyXA4aNnR3w &feature=PlayList&p=56 D05189EFBACBB1&ind ex=1 watch?v=RIXtM2u-- H8&feature=PlayList&p= 56D05189EFBACBB1&i ndex=3

Modern concept of a taste map Taste researchers have known for many years that these tongue maps are wrong. The maps arose early in the 20th century as a result of a misinterpretation of research reported in the late 1800s, and they have been almost impossible to purge from the literature. In reality, all qualities of taste can be elicited from all the regions of the tongue that contain taste buds. At present, we have no evidence that any kind of spatial segregation of sensitivities contributes to the neural representation of taste quality, although there are some slight differences in sensitivity across the tongue and palate, especially in rodents.

Taste Buds

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

The Ear

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

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

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

Organ of Corti

Summary of Hearing 1.Sound waves enter the external auditory meatus 2.Tympanic membrane vibrates 3.Auditory ossicles vibrate 4.Oval window vibrates 5.Fluid in inner ear vibrates 6.Basement membrane moves 7.Hairs rub against the tectorial membrane 8.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

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),

The Eye

Tunics of the Eye

Inner Tunic through an ophthalmoscope

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

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

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

Visual Receptors be.com/watch?v= f0JpsTgy6ck

Summary of Vision 1.Light rays enters through the pupil 2.Light rays cross in the lens 3.Retina receives reversed & upside down image 4.Rods & cones are stimulated 5.Optic nerve carries impulse to the brain

Visual fields

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.