The General & Special Senses Chapter 18

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

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 Phantom pain 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 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

Olfactory Receptors

Olfactory Receptors

Taste receptors are in the taste buds 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

Taste Areas of the Tongue

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 Cochlea 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

Consists of hair cells on a basement membrane 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

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

Vision (the eye) Accessory structures Eyelids protect the eye Conjunctiva lines the eyelid Lacrimal gland produces tears Extrinsic muscles move the eyeball

The Eye

Consists of 3 tunics (layers) 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

The lens separates the interior of the eye into 2 cavities 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

Contains many blood vessels & nerves 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

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

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

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 Myopia Hyperopia Presbyopia Astigmatism