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The General & Special Senses 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 Receptors Figure 18-01 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 Figure 18-02 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 Figure 18-06a Human Anatomy, 3rd edition Prentice Hall, © 2001 Olfactory Receptors Figure 18-06b Taste (the tongue) Taste buds receptors are in the taste – 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 Figure 18-07a Taste Buds Figure 18-07b Taste Bud Figure 18-07c 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 Figure 18-09 Human Anatomy, 3rd edition Prentice Hall, © 2001 The Middle Ear Figure 18-10b 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 hearing the organ of Corti, the organ of The Inner Ear Figure 18-12b 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 Figure 18-12c 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 Figure 18-16d Organ of Corti Figure 18-16e 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 Figure 18-18b 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 Figure 18-20b Tunics of the Eye Figure 18-20a Inner Tunic Figure 18-22c 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 Cataract focusing on near & distant objects The Pupil Figure 18-20c 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 Figure 18-22a1 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
