The General & Special Senses Chapter 18

Introduction Senses – our perception of what is “out there” 2 groups –General senses –Special senses

General Senses Includes senses that are skin or kinesthetic –Temperature, pressure, touch, pain, vibration, proprioception Pass information along the spinal nerves and pathways to the somatosensory cortex

Special Senses Olfaction, gustation, equilibrium, hearing, & vision Found within complex sense organs Pass information along the cranial nerves to specific areas of the cerebral cortex.

Receptors Sensory receptors are transducers –Change stimuli into electro-chemical impulses –Specific receptors can transduce only certain types of stimuli Two general types –Exteroceptors –Interoceptors

Interpretation of Sensory Information Occurs in cerebral cortex Depends on the area of the cerebral cortex that receives the information Also depends on the sequence of neurons carrying the information

Central Processing and Adaptation Adaptation – the loss of sensitivity after continuous stimulation –Tonic receptors are always active –Phasic receptors only relay changes in the conditions they are monitoring Role – prevents brain from being overloaded with unimportant information

Receptors of the General Senses Nociceptors detect pain –Referred pain –Phantom pain Thermoreceptors detect changes in temperature

Referred Pain

Receptors of the General Senses Mechanoreceptors respond to pressure & touch –Tactile receptors are found in the dermis –Baroreceptors monitor changes in pressure –Proprioceptors monitor positions of joints & muscles

Tactile Receptors

Some Enteroreceptors

Receptors of the General Senses Chemoreceptors detect chemicals in solution –Smell –Taste –Blood composition

Chemoreceptors

The Special Senses

Olfaction (the nose) Olfactory receptors –Can detect at least 50 different primary smell –Located in the epithelium of roof of nasal cavity –Molecules dissolve in the mucus or lipids of the epithelium –Olfactory neurons pass through the cribiform plate and synapse in the olfactory bulb –Olfactory tracts go directly to the cerebral cortex

Nasal Cavity

Olfactory Receptors

Gustation (the tongue) Taste receptors are in the taste buds –Can detect 4 primary tastes Sweet, sour, salty, bitter –Located in papillae or bumps on the surface of the tongue (also on the walls of the pharynx & larynx) Taste buds contain the gustatory receptors –Molecules dissolve in saliva –3 cranial nerves relay sensory impulses to the cerebral cortex Facial, glossopharyngeal, vagus All pass through the medulla & thalamus

Tastes on the Tongue

Taste Buds

A Taste Bud

Pathway of Gustatory Sense

Equilibrium & Hearing (the ear) External ear –The auricle directs sound waves into the external auditory meatus to the tympanic membrane Middle ear –Located in the temporal bone –Contains the auditory ossicles Malleus, incus, stapes –Connected to throat by the eustachian tube Inner ear –Located in the temporal bone

The Ear

The Middle Ear

The Inner Ear Separated from the middle ear by the oval window Consists of a series of canals called the bony labyrinth –Lined by a membranous labyrinth filled with endolymph –Perilymph flows between the bony and membranous labyrinth

The Inner Ear The bony labyrinth is divided into 3 areas –Vestibule Contains the saccule & utricle –Involved in static equilibrium –Semicircular canals Each has an ampulla which contains receptors for head position –Cochlea Contains the organ of Corti, the organ of hearing

The Semicircular Canals

The Utricle & Saccule Detects static position Hair cells are embedded in a gelatinous material Otoliths are balanced on top –Slide when the head is tipped –Bend hairs, generating a nerve impulse

The Utricle and Saccule

Otoliths

Otoliths at Work

The Semicircular Canals Detects dynamic balance Arranged at right angles to each other In the ampula, hair cells are embedded in gelatinous material (cupula) with fluid over it Movement of the head bends the hairs, creating nerve impulses

Ampulla

Hair Cell

Semicircular Canals at Work

The Cochlea Divided into 3 tunnels by the vestibular and basilar membranes –Scala vestibuli (top), ends in the oval window –Cochlear duct (middle), contains the organ of Corti –Scala tympani (bottom), ends in the round window

The Cochlea

Cochlear Chambers

The Organ of Corti

Consists of hair cells on the basilar membrane Tips of hairs touch the tectorial membrane When the basement membrane vibrates, the hair cells are bent, sending a nerve impulse

Summary of Hearing Sound waves enter the external auditory meatus Tympanic membrane vibrates Auditory ossicles vibrate Oval window vibrates Perilymph in scala vestibuli & scala tympani moves Basilar membrane moves Hairs rub against the tectorial membrane Nerve impulse is sent along the vestibulocochlear nerve to the brain

Pathway of Auditory Sense

Vision (the eye) Accessory structures –Eyelids protect the eye Conjunctiva lines the eyelid –Lacrimal apparatus Lacrimal gland produces tears Lacrimal canals drain tears into lacrimal sacs Nasolacrimal duct drains into the nasal cavity –Extrinsic muscles move the eyeball

The Eye

Structure of the Eye Consists of 3 tunics (layers) –Fibrous tunic – outermost layer Includes the cornea & sclera –Vascular tunic – middle layer Includes the choroid coat, ciliary body, and lens, iris & pupil –Neural tunic (retina) – inner layer Contains the rods & cones (photoreceptors) Includes the optic disc (blind spot), macula lutea & fovea centralis

The Retina

Sagittal Section of the Eye

Photo of Posterior Eye

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 = pressure from too much aqueous humor Anterior chamber is in front of the iris Posterior chamber is behind the iris –Posterior cavity behind the lens Contains vitreous humor

The 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

The Retina Cones allow for sharp color vision in bright light –3 types, each with a different pigment –The macula lutea contains only cones –Cones are most concentrated in the fovea centralis

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

The Retina

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

Pathway of Vision Sense

Abnormal Vision Myopia Hyperopia Presbyopia Astigmatism