Compendium Review Chapter 14

Equilibrium

Anatomy of Ear

Astigmatic Eye

Structure and Function of Retina

Damaged Rod Cells of Eye

Anatomy of Eye

Smell

Taste

Pain Receptor in Skin

I. Sensory Receptors and Sensations
II. Proprioceptors and Cutaneous Receptors
III. Senses of Taste and Smell
IV. Sense of Vision
V. Sense of Hearing
VI. Sense of Equilibrium

I. Sensory Receptors and Sensations
A. Sensory Receptors: Special dendrites that detect certain types of stimuli.
- Extroceptors: Sensory receptors that detect stimuli from outside the body (result in taste, smell, vision, hearing and equilibrium.)
- Interoreceptors: Receive stimuli from inside the body. (Ex. Pressoreceptors respond to changes in blood pressure.) Directly involved in homeostasis; regulated by a negative feedback mechanism.
B. Types of Sensory Receptors: 4 Categories
1b. Chemoreceptors: Respond to chemical substances in immediate area. (taste and smell, and various other organs sensitive to internal stimuli.)
2b. Pain Receptors: Type of chemoreceptor. Naked dendrites that respond to chemicals released by damaged tissue. Protective- alert us of danger.
(Insert Pain Receptor in Skin picture / fig.cox.miami.edu / http://fig.cox.miami.edu/~cmallery/150/neuro/senses.htm)
3b. Photoreceptors: Respond to light energy. (Eyes) Stimulation results in color vision.
4b. Mechanoreceptors: Stimulated by mechanical forces, which often result in pressure of some sort. (hearing, balance)
5b. Thermoreceptors: Located in hypothalamus and skin. Stimulated by changes in temperature. (warm receptors- temps rise. cold receptors- temps fall.) (Mader 274)
C. How Sensation Occurs:
- Sensory receptors respond to stimulus from body or environment.
- These receptor cells trigger action potential in connecting sensory neurons.
- Spinal cord and/or brain interpret and analyze information.
(Frolich PowerPoint Slide 24), and initiate motor response. (Mader 275)
1c. Sensation: The conscious perception of stimuli.
2c. Review: Sensory receptors are first element in reflex arc. Reflex actions become known to us only when sensory info reaches the brain. The brain then integrates this info with other info from other sensory receptors.
3c. All sensory receptors initiate nerve impulses, and the resulting sensation depends on which part of the brain receives the impulse.
4c. Integration: The summing up of signals. Occurs BEFORE sensory receptors initiate the nerve impulse.
5c. Sensory Adaptation: A type of integration. A decrease in response to stimulus. (When you get "used" to a smell, etc.) (Mader 275)
II. Proprioceptors and Cutaneous Receptors
A. Sensory Receptors: 3 types
- Proprioceptors: Mechanoreceptors involved in reflex actions that maintain muscle tone, equilibrium, and posture. They detect the degree of muscle relaxation, stretch of tendons, and movement of ligaments. (Mader 276) More simply put, "Proprioception—gives body position by sensing muscle tension." (Frolich PowerPoint Slide 27)
B. Cutaneous Receptors: Skin is composed of two layers, the epidermis and dermis.
1b. Dermis contains cutaneous receptors: Causes skin to be sensitive to the touch, pressure, pain, and termperature.
2b. There are three types of cutaneous receptors that are sensitive to fine touch: Meissner corpuscles, Merkel disks, and root hear plexus.
3b. Two types of cutaneous receptors sensitive to pressure: Pacinian corpuscles and Ruffini endings.
4b. Temperature Receptors: Free nerve endings in the epidermis.
C. Pain Receptors: Internal organs have pain receptors, as do the skin. Sensitive to chemicals released by damaged tissues.
1c. Referred Pain: Occurs when pain receptors are stimulated from the skin as well as the internal organs. (Mader 277)
III. Senses of Taste and Smell
A. Taste and Smell are chemical receptors because the receptors are sensitive to molecules in the food we eat and air we breathe.
1a. Bear chemoreceptors: Plasma membrane receptors that bind to particular molecules. Two Types:
- Some respond to distant stimuli (olfactory cells), and
- some respond to direct stimuli (taste cells).
B. Taste: Approx. 3,000 taste buds on tongue. 4 primary types:
- Sweet
- Sour
- Salty
- Bitter
1b. The brain receives taste information when molecules bind to receptor proteins of the microvilli, and nerve impulses are generated in sensory nerve fibers that go to the brain. (Mader 278)
(Insert Taste picture / Frolich PowerPoint Slide 29)
C. Sense of Smell: Approx. 80-90% of what we think is taste is actually from the sense of smell.
1c. 10-20 million olfactory cells (which are modified neurons)
are located wihtin the olfactory epithelium in the roof of nasal cavity.
2c. Each olfactory cell ends in a bunch of approx. five olfactory cilia, which haave the receptor proteins for odor molecules.
3c. The brain receives smell information when nerve fibers from like olfactory cells lead to the same neuron in the olfactory bulb, and extension of the brain. An odor has many odor molecules, which activiate a characteristic combination of receptor proteins. Neurons then communicate this ifo via the olfactory tract to the corresponding areas of the cerebral cortex.
4c. Smell actually deteriorates with age! (Mader 278-279)
(Insert Smell picture / Frolich PowerPoint Slide 30)
IV. Sense of Vision
A. Requires work of eyes and brain. Eyes process a good deal of stimuli before nerve impulses are sent to the brain. Still, Approx. 1/3 of cerebral cortex takes part in processing visual info.
B. Anatomy and Physiology of the Eye
1b. Eyeball is an elongated sphere.
- Three layers:
- Layer 1: Sclera: (outer layer)that includes cornea ("window" of the eye).
- Layer 2: Choroid: (middle, thin, dark layer. Absorbs light rays that photoreceptors have not absorbed.) Choroid becomes the iris, which regulates the size of the pupil, the hole in the center of the iris that allows light to enter the eyeball.)
- Ciliary Body: Contains ciliary muscle, to control shape of lens for near and far vision.
- Lens: Attached to ciliary body by ligaments, it divides eye into two compartments.
1. Compartment in front of lens is the anterior compartment. Filled with clear, watery fluid called aqueous humor.
2. Compartment behind lens in the posterior compartment.
- Layer 3: Retina: Located in posterior compartment, filled with clear, gel material called vitreous humor. Also contains rod cells (very sensitive to light, but does not see color) and cone cells (require bright light, sensitive to different wavelengths of light, and can distinguish colors).
- Fovea Centralis: Region of retina where cone cells are dense. Vision is most acute here.
- Sensory fibers from retina form optic nerve, which takes nerve impulses to visual cortex of brain.
C. Function of Lens: Cornea focuses images on retina. Focusing continues as rays go through lens and humors. Image is smaller than object, and is inverted and reversed.
D. Visual Accomodation: Occurs for close vision. Lens rounds up, to bring image to focus on retina.
E. Visual Pathway to Brain: Once light has been focused on photoreceptors in retina, integration occurs in retina, and then nerve impulses begin before the optic nerve transmits them to the brain.
(Insert Anatomy of Eye picture / www.rennard.org / http://www.rennard.org/alife/english/biomintrgb.html)
F. Function of Photoreceptors: These rod and cone cells both have outer segment joined to inner segment by a stalk. Pigment molecules are embedded in membrane of disks in outer segment.
- Rods are sensitive to light- suited for night vision.
- Cones are activated by bright light, and allow us to detect fine detail and color of an object.
(Insert Damaged Rod Cells of Eye picture / www.medicalprogress.org)
G. Function of Retina: Retina has three layers of neurons.
1. Layer closest to choroid has rod cells and cone cells.
2. Middle layer has bipolar cells.
3. Innermost layer has ganglion cells, whose sensory fibers turn into the optic nerve.
1g. Since only rod and cone cells are sensitive tolight, light must penetrate to the back of the retina before they are stimulated. (Mader 282)
2g. Integration occurs when signals pass to bipolar and ganglion cells. They then create the nerve impulses that are taken to the optic nerve to the visual cortex of brain.
H. Blind Spot: Area of no vision. No rods and cones are present where the optic nerve exits the retina.
I. From Retina to Visual Cortex
1i. Optic Chiasma: Optic nerves carry nerve impulses from eyes to optic chiasma, which is x shapted, and formed by the crossing of optic nerve fibers.
2i. Images are "righted" in brain.
(Insert Retina Receptors picture / Frolich PowerPoint Slide 32)
J. Abnormalities of Eye
1j. Color blindness.
2j. Misshapen eyeballs.
3j. Nearsightedness: Can see close objects better than those at a distance. Elongated eyeballs.
4j. Farsighted: Cannot see close objects. Shortened eyeballs.
5j. Astigmatism: Cornea or lens is uneven, and images are funny.
(Mader 284)
(Insert Astigmatic Eye picture / www.daviddarling.info / http://www.daviddarling.info/encyclopedia/A/astigmatism.html)
V. Sense of Hearing
A. Ear has two sensory functions: hearing and balance (equilibrium).
1a. Sensory receptors for both functions are located in inner ear, consisting of hair cells with long microvilli that are sensitive to mechanical stimulation. Mechanoreceptors.
B. Anatomy and Physiology of Ear: Ear has three divisions:
1. Outer Ear: Consists of pinna (external flap) and auditory canal. Secretes ear way, to hellp protect against entrance of foreign materials.
2. Middle Ear: Begins at tympanic membrane (eardrum) and ends at bony wall that has two small openings covered by membranes, called oval window and round window. Ossicles (three small bones) are found between tympanic membrane and oval window.
- Auditory Tube: (eustachian tube) Extends from middle ear to nasopharynx, permitting equalization of air pressure.
3. Inner Ear: Filled with fluid. Has three areas:
- 1. Semicircular canals
- 2. Vestibule (Both of these are concerned with equilibrium.)
- 3. Cochlea: concerned with hearing.
C. Auditory Pathway to Brain: Sound pathway begins with auditory canal, but then hearing requires other parts of the ear, the cochlear nerve and brain.
1c. Through auditory canal and middle ear: Hearing begins when sound waves enter the auditory canal. Sound waves travel by successive vibrations of molecules. Stapes strikes the membrane of oval window, it vibrates, and the pressure is passed to fluid within the cochlea.
2c. From cochlea to auditory cortex: Spiral organ: located in the cochlear canal. Consists of little hair cells and gel material called tectorial membrane.
- Pressure waves move from vestibular canal to tympanic canal.
- Nerve imulses begin in cochlear nerve and travel to brain. (Mader 286-287)
(Insert Anatomy of Ear picture / www2.hawaii.edu / http://www2.hawaii.edu/~heirakuj/ear.htm)
V. Sense of Equilibrium
A. Vestibular nerve takes impulses to brain stem and cerebellum. Through this communication, it helps us achieve equilibrium. Proprioceptors are also necessary.
B. Rotational Equilibrium Pathway:
- Mechanoreceptors in the semicircular canals detect rotational and / or angular movement of the head (rotational equilibrium.)
1b. Ampulla: Base of each of three canals, slightly enlarged.
- Each ampulla responds to head rotation in a different plane of space.
- Brain uses info from hair cells wihin ampulla of semicircular canals to maintain equilibrium through motor output to various skeletal muscles that can right the position of the body.
C. Gravitational Equilibrium Pathway: Mechanoreceptors in utricle and saccule detect movement of head in vertical or horizontal planes (gravitational equilibrium).
- Utricle and saccule are two membranous sacs located in inner ear. (Mader 291)
(Insert Equilibrium picture / Frolich PowerPoint Slide 34)