The General & Special Senses Chapter 8. Introduction Senses – our perception of what is “out...
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Transcript of The General & Special Senses Chapter 8. Introduction Senses – our perception of what is “out...
The General & Special Senses
Chapter 8
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
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-01
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)
What’s a Dermatome?• A localized area of skin that is has its
sensation via a single nerve from a single nerve root of the spinal cord. Shingles (Herpes zoster virus infection) typically affects one or several isolated dermatomes.
What’s a Dermatome?
From Medical school Halloween partyFrom Textbook
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-02
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
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-06a
Olfactory Receptors
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-06b
Olfactory Receptors
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
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-07a
Taste Areas of the Tongue
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-07b
Taste Buds
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-07c
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
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-09
The Ear
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-10b
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• Contains receptors for head position
– Cochlea • Contains the organ of Corti, the organ of hearing
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-12b
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
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-12c
Hair Cells in the Semicircular Canals
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
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-16d
Organ of Corti
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-16e
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
Diseases of Hearing
• External Otitis, the most common disorder of the outer ear, also know as Swimmer’s ear. The process develops due to loss of the protective cerumen (wax) and excessive moisture in the ear canal.
• Otitis Media is one of the most common diseases of children, due to chronic middle ear infection. Treatments: antibiotics, otomyringotomy (surgical insertion of rigid “ear tubes”).
• Conductive Hearing Loss, usually due to otosclerosis, progressive fixation of the stapes due to aging or disease.
Vision (the eye)
• Accessory structures– Eyelids protect the eye
• Conjunctiva lines the eyelid
• Lacrimal gland produces tears
– Extrinsic muscles move the eyeball
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-18b
The Eye
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),
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-20b
The Eye
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-20a
Tunics of the Eye
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-22c
Inner Tunic
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
Human Anatomy, 3rd editionPrentice Hall, © 2001
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 focusing on near & distant objects
• Cataract
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-20c
The Pupil
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
Human Anatomy, 3rd editionPrentice Hall, © 2001
Figure 18-22a1
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
• Astigmatism
Occurs when the transparent media of the eye (includes the cornea, crystalline lens) are inconsistently or irregularly shaped. Causes blurred vision at far and near distances.
Abnormal Vision
• Cataracts
A clouding and hardening of all or part of the transparent lens located inside the eye, most often caused by the aging process, UV light exposure, etc.
Abnormal Vision
• Glaucoma
A condition characterized either by increased intraocular pressure- "high blood pressure of the eye" -that can result in damage to the optic nerve and to retinal nerve fibers, or by significant decreased intraocular pressure.
Abnormal Vision• Hyperopia
Farsightedness. A condition in which rays of light are focused behind the retina, so distant objects appear clearer than near ones.
Abnormal Vision
• Presbyopia
Caused by the loss of elasticity in the lens inside the eye as part of the aging process, resulting in a gradual decline in a person’s ability to focus on close objects or to see small print. Virtually everyone is affected after the age of 40.
Abnormal Vision• Myopia
Near sightedness. A condition in which light rays are focused in front of the retina instead of on it, so near objects appear more clear than far ones.
Abnormal Vision• Macular degeration
Common eye age-related disease that causes deterioration of the macula, the central area of the retina, the paper-thin tissue at the back of the eye where light-sensitive cells send visual signals to the brain. Sharp, clear, “straight ahead” vision is processed by the macula.
Abnormal Vision• Retinoblastoma
Malignant tumor of the retina. Inherited form is caused by a genetic abnormality in the Rb gene.