the general & special senses - cabrillo collegepdarcey/bio 4/fall 2011/class notes... · the...
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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
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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
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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
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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
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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
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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
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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