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The General & Special Senses
Chapter 17
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
Mechanoreceptors
• Respond to pressure & touch– Tactile receptors– Baroreceptors– Proprioreceptors– Thermoreceptors
Tactile Receptors• Found in the dermis
Baroreceptors• Monitor changes in pressure
Chemoreceptors• Detect chemicals in solution
– Blood composition
The Special Senses
Olfaction (the nose)• Olfactory receptors
– Can detect at least 50 different primary smells
– Located in the epithelium of roof of nasal cavity
Olfactory Receptors
• 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
Gustation (the tongue)
• Taste receptors are in the taste buds
• 4 primary tastes– Sweet, sour, salty,
bitter• Located in papillae on
the surface of the tongue• Contain the gustatory
receptors– Molecules dissolve in
saliva
Pathway of Gustatory Sense
• 3 cranial nerves relay sensory impulses to the cerebral cortex– Facial,
glossopharyngeal, vagus
– All pass through the medulla & thalamus
Equilibrium & Hearing (the ear)
• External ear– The auricle directs sound waves into the external
auditory meatus to the tympanic membrane
The Middle Ear• Located in the temporal bone• Contains the auditory ossicles
– Malleus
– Incus– stapes
• Connected to throat by the eustachian tube
The Inner Ear
• Located in the temporal bone• Separated from the middle ear by the oval window
The Inner Ear
• 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
• Saccule & utricle– Semicircular canals
• Each has an ampulla
– Cochlea contains• Organ of Corti
The Utricle & Saccule
• Detects static position• Hair cells are
embedded in a gelatinous material
Otoliths at Work• Otoliths are
balanced on top of gelatinous material– Slide when head
tips
– Bend hairs
– Generates nerve impulse
The Semicircular Canals• Detect 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 head– Bends the hairs – Creates nerve
impulses
Semicircular Canals at Work
The Cochlea
• Divided into 3 tunnels by the vestibular and basilar membranes– Scala vestibuli ends
in the oval window– Cochlear duct
contains the organ of Corti
– Scala tympani ends in the round window
Cochlear Chambers
The Organ of Corti
• Consists of hair cells on the basilar membrane
• Tips of hairs touch the tectorial membrane
• Basement membrane vibrates– Hair cells bend
– Sends a nerve impulse
Pathway of Auditory Sense
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
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
Structure of the Eye – 3 Tunics
• Fibrous tunic
– Includes cornea & sclera• Vascular tunic
– Includes choroid coat, ciliary body, lens, iris & pupil
• Neural tunic (retina)– Contains photoreceptors
• Rods & cones– Includes optic disc,
macula lutea & fovea centralis
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-22c
Photo of Posterior Eye
The Cavities of the Eye
• The lens separates the interior of the eye into 2 cavities– Anterior cavity
• Contains aqueous humor
• Glaucoma
– Posterior cavity
• Contains vitreous humor
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
The Retina
• Cones allow for sharp color vision in bright light– Contain pigments– Macula lutea – Fovea centralis
• Rods provide for vision in dim light– Contain the pigment
rhodopsin– Most dense at
periphery of retina
Pathway of Vision Sense
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