Special Senses
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Sensory Receptors
– All sensory information is picked up by sensory receptors (_________________________________________
______________________________________________________________)
– Branching tips of dendrites (types of sensory receptors) are called __________________________________
– The area monitored by a single receptor cell is its __________________________________
Sensory Receptors
– All sensory information arrives at the CNS in the form of action potentials in an afferent fiber
• _____________________________________________________________________
– Adaptations can be made to receptors
• An adaptation is a reduction in sensitivity in the presence of a constant stimulus
• Reduces the amount of information arriving at the CNS
The General Senses
– ________________________
– ________________________
– ________________________
– ________________________
– ________________________
– ________________________ (body position)
The Special Senses
– _______________________ (smell)
– _______________________ (taste)
– _______________________
– _______________________ (balance)
– _______________________
General Sensory Receptors
– Pain Receptors (______________________)
• Large receptive field making it hard to pinpoint pain
• Once stimulated, 2 types of axons carry pain sensations:
– _______________________________________________
– _______________________________________________
• Referred pain: the perception of pain coming from parts of the body that are not actually stimulated
– Temperature Receptors (____________________________)
– Chemical Receptors (_____________________________)
• Important chemoreceptors are located in the medulla oblongata, carotid bodies, and aortic bodies
– Mechanoreceptors
• 3 classes:
– __________________________________________________________________________
• 6 of the skin: free nerve endings, root hair plexus, tactile discs, tactile corpuscle,
lamellated corpuscle, and ruffini corpuscles
– __________________________________________________________________________
– __________________________________________________________________________
Special Sensory Reception
– Olfaction (Sense of Smell)
• __________________________
• Paired organs of smell in the roof of the nasal cavity on either side of the nasal septum
– Each consists of an olfactory epithelium containing _____________________________________
• Contain large olfactory glands whose secretions absorb water and forms mucus
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– _____________________________________________________________________________
• Olfactory Pathways
– Axons leaving olfactory epithelium collect into 20+ bundles and penetrate ethmoid bone to reach
olfactory bulbs
• Where 1st synapse occurs
• From bulb, axons travel along olfactory tract to the olfactory cortex in the cerebrum, hypothalamus, and
limbic system
Gustation (Sense of Taste)
• Distributed over the tongue (most important) and adjacent portions of the pharynx and larynx
• ____________________________________________________________________________________
– Protected from mechanical stress (chewing) by papillae
– ______________________________________________________________________________
• Each gustatory cell extends microvilli (taste hairs) into surrounding fluids via an opening
called the taste pore
• ________________________________________________________________
– Greatest sensitivity to sweet/salty are in the front of the tongue and sour/bitter are in the back
• 2 additional tastes (_____________________________) have been discovered in humans
– Umami is a pleasant taste characteristic of beef broth, chicken broth, and parmesan cheese
– Water receptors are especially present in the pharynx and their sensory output is processed in
the hypothalamus
• _________________________________________________________________________________
Vision
• Accessory Structures of the Eye
1. ________________________
• Continuation of the skin
• Protect from dust, debris, and lubricate the eye
• Upper and lower eyelids are connected at the at the _________________________
• Eyelashes are hairs that prevent foreign particles from contacting the eye
• Exocrine glnads:
– Tarsal glands: __________________________________________________
– Lacrimal caruncle: contains glands that produce think secretions that
contribute to the gritty deposits occasionally found after sleeping
2. ________________________
• Shades the eye and prevents perspiration from reaching it
3. ________________________
• An epithelial mucous membrane covering the inner surfaces of the eyelid and the
outer surface of the eye
4. ________________________
• _____________________________________________________________________
_____________________________________________________________________
• The lacrimal gland is located laterally above each eye
• Pathway: _____________________________________________________________
_____________________________________________________________________
5. ________________________
• Inferior/medial/lateral/superior rectus and inferior/superior oblique
• Structure of the Eyeball
– Hollow with its interior divided into 2 cavities: the posterior cavity (___________________________
___________________) and the anterior cavity (__________________________________________)
• Anterior cavity filled with aqueous humor
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The wall of the eye contains 3 distinct layers: the outer fibrous tunic, the intermediate vascular tunic,
and the inner neural tunic
_______________________________
– Provides mechanical support and physical protection, attachment site for eye muscles, and assists in
the focusing process
– Two regions:
• _______________
– “White of the eye”
– Protects and shapes eyeball
– Anchors extrinsic eye muscles
• _______________
– Transparent anterior 1/6 of fibrous layer
– No blood vessels, gets its nutrients and oxygen from tears
______________________________
– Provides route for blood vessels and lymphatic vessels, regulates light entering the eye, secretes and
reabsorbs the aqueous humor, controls the shape of the lens (essential part of focusing)
– Three regions:
• _____________________________
– Posterior portion that separates the fibrous and neural tunics
– Supplies blood, nutrients, and oxygen to all layers of the eyeball
• _____________________________
– Ring of tissue surrounding the lens
– Smooth muscle bundles (__________________) control lens shape
– Ciliary zonule (______________________) holds lens in position
• _____________________________
– The colored part of the eye
– Dialates or contracts changing the size of the pupil (__________________________
_______________________________)
– Eye color is determined by the # of melanocytes and presence of melanin granules
_____________________________
– Delicate two-layered membrane
• Pigmented layer
– ____________________________________
– Stores vitamin A
• Neural layer
– Contains photoreceptors that respond to light, supporting cells and neurons that
process and integrate visual information, and blood vessels that supply the tissues
lining the posterior cavity
The Retina
– Contains several layers of cells:
• The outermost layer contains photoreceptors (cells that detect light)
– 2 types: rods (______________) and cones (_________________)
» Most cones found in region called macula lutea (area where visual images
arrive) at the center of this area (fovea)
• Fovea is the site of sharpest vision and establishes the visual axis
• Bipolar cells
– Synapse with the rods and cones
• Ganglion cells
– Synapse with the bipolar cells to deliver sensory information to the brain
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Lens
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Horizontal and Amacrine cells
– Adjust sensitivity of the retina
The optic disc
• Circular region just medial to the fovea
• No photoreceptors because light striking this area goes unnoticed
– ______________________________________
__________________________________________________________________________________
As light enters the relatively dense lens, the lens provides the extra refraction needed to focus the
light rays from an object toward a specific focal point – the point at which the light rays converge
– Accommodation is the process of focusing an image on the retina by changing the shape of the lens.
The lens either becomes:
• Rounder (______________________________________________________)
• Flattens (______________________________________________________)
– The lens causes the images that reach our retina to be upside down and backward
• Photoreceptors
– Rods and cones
• Rods allow us to see in dim light (fuzzy, indistinct images)
• Cones allow us to see more distinctly in bright light
• We have 3 color cones:
– ___________
– ___________
– ___________
• Color blindness occurs when cones are either absent or nonfunctional
– The most common form is the ability to distinguish between red and green
– _________________________________________
• Photoreceptor Structure
– The structure of rods and cones:
• The outer segment is made of thousands of discs and gives the different photoreceptors their
names
– Discs contain visual pigments
» Derived from the compound rhodopsin (__________________________)
» Rods and each type of cone contain a different form of opsin
• The inner segment contains typical cellular organelles
• Visual Pathway
1. In the visual pathway, the message must cross 2 synapses(__________________________________
_______________________________________) before it moves toward the brain
2. Axons from the entire ganglion cells converge as the 2 optic nerves
3. The 2 nerves meet at the optic chiasm
4. From this point ½ of the nerves continue toward the thalamic nucleus on the same side of the brain
while the other half cross over
Equilibrium (balance) and Hearing
• Anatomy of the Ear
– Three parts of the ear:
1. ____________________________
– Includes the auricle (pinna) which surroundes the entrance to the external acoustic
meatus (ear canal)
» _________________________________________________________________
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Ceruminous glands are along the external acoustic meatus and secrete a waxy material
that helps prevent the entry of foreign objects and insects
– The external acoustic meatus ends at the tympanic membrane (___________) which
separates the inner and middle ear
2. ____________________________
– Air-filled chamber
– Communicates with the superior portion of the pharynx (nasopharynx). This connection
is called the auditory tube (_______________________________________________)
» Enables equilization of pressure on either side of the eardrum
– Contains the auditory ossicles (3 tiny bones together)
» Connect the tympamun with the inner ear
» __________________________________________________
» Act as levers that conduct the vibrations to the inner ear
3. ____________________________
– Provides the senses of hearing and equilibrium
– Protected by a bony labyrinth
» Surrounds and protects the membranous labyrinth
» Subdivided into 3 parts:
• ___________________________________________________________
• ___________________________________________________________
• ___________________________________________________________
– The receptors of the inner ear are the hair cells
» Communicate with sensory neurons by continually releasing small quantities of
neurotransmitters
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Equilibrium
– 2 aspects of equilibrium:
 Dynamic equilibrium
– ________________________________________________________________________
 Static equilibrium
– ________________________________________________________________________
– All equilibrium sensations are provided by hair cells
Hearing
– Receptors of the cochlear duct provide us with the sense of hearing
 The receptor responsible are hair cells similar to those in the vestibule and semicircular canals
 Sound energy is converted in air to pressure pulses which stimulate hair cells along the cochlear
spiral
 _______________________________________________________________________________
 _______________________________________________________________________________
Steps in Hearing
1. Sound waves arrive at the tympanic membrane
2. Movement of the tympanic membrane causes displacement of the auditory ossicles
3. The movement of the stapes at the oval window establishes pressure waves in the preilymph of the
vestibular duct
4. The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct
5. Vibration of the basilar membrane causes vibration of hair cells against the tectorial membrane
6. Information about the region and intensity of stimulation is relayed to the CNS over the cochlear branch
of the cranial nerve VIII