General and Special Senses

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I. General Senses

A. Classification of Receptors According to Stimulus Type Detected

1. Nociceptors -

Referred pain

2. Thermoreceptors

3. Mechanoreceptors

a. Tactile (touch) receptors

1. Meissner's corpuscles

2. Pacinian corpuscles

b. Baroreceptors/pressoreceptors (ex.: stretch receptors) -

c. Proprioceptors (ex.: tendon organs and muscle spindles) - 

4. Chemoreceptors (ex: carotid & aortic bodies, olfaction; gustation) -

5. Photoreceptors (vision)

B. Receptor Potentials (how sensory receptors send info to sensory neurons; a type of graded potential)

1. Generator potential - if strong enough (or sent at higher frequencies), causes the sensory neuron to reach threshold; the action potential that results is projected to the appropriate area of the cerebral cortex 

2. Sensory Adaptation - a reduction in sensitivity to a constant stimulus

II. Special Senses

A. Olfaction

1. Chemoreceptors
2. Olfactory organ

a. Olfactory epithelium
b. Olfactory receptors 
c. Basal cells - stem cells
d. Requirements for substances to be "smelled"

1.  Enter as a gas
2.  Water and lipid-soluble substance diffuse in mucus
3.  "Odorant" molecules bind to receptors (odorant-binding proteins)

3. Olfactory nerve pathways

a. Olfactory organ
b. Olfactory bulb (synapse)
c. Olfactory tract
d. [Some fibers] to limbic system and hypothalamus
e. [Some fibers] to primary olfactory cortex 
*Note:  Olfaction is the only sensory pathway that does not synapse in the thalamus on its way back to the cerebral cortex*

B. Gustation

1. Taste buds -
2. Gustatory cells
3. Cranial nerves involved with gustation and parts of oral cavity served by each:

a. VII
b. IX
c. X

5. Gustatory pathway:  Taste buds --> Cranial nerves VII, IX and X --> Medulla oblongata     --> Thalamus --> Parietal lobe (Postcentral gyrus) 

6. Primary taste sensations and locations on the tongue:

a.
b.
c.
d.
e.
f.

C.  Vision (some anatomy is not listed, but may be referred to during class)

1. Extrinsic Eye Muscles

a. Superior Rectus -
b. Inferior Rectus -
c. Medial Rectus -
d. Inferior Oblique -
e. Lateral Rectus -
f. Superior Oblique -

2. Layers of the Eye

a. Fibrous Tunic

1. Sclera -
2. Cornea -

b. Vascular Tunic (Uvea)

1. Choroid -
2. Ciliary body (smooth muscle)

a. Ciliary muscles
b. Ciliary processes

3. Iris

a. Inner circular smooth muscle -
b. Outer radial smooth muscle -

4. Pupil -

c. Neural Tunic (Retina)

1. Pigmented layer -
2. Neural layer

a. Rods and Cones (receptor cells)
b. Bipolar cells
c. Ganglion cells

3. Optic disk (blind spot)
4. Macula lutea
5. Fovea centralis -

3. Internal Chambers and Fluids

a. Anterior Cavity

1. Aqueous humor -
2. Canal of Schlemm (scleral venous sinus) -
3. Glaucoma -

b. Posterior Cavity

1. Vitreous body -

4. Lens

a. Capsule -
b. Suspensory ligaments
c. Ciliary processes
d. Cataracts -

5. Physiology of Vision

A. Light Refraction

1. Properties of light

a. Objects either give off light or reflect light
b. Light may be refracted (bent)

1. Convergence - light rays come together

2. Divergence - light rays bend away from a central point

2. Cornea (75% of refraction) > aqueous humor > lens > vitreous humor

3. Light converges on the retina (image is upside down and reversed left to right)

4. Accommodation -

B. Refraction Disorders

1. Presbyopia (far-sightedness of age) -
2. Myopia (near-sightedness)

a. Eyeball characteristics:
b. Light focuses in front of the retina

3. Hyperopia (far-sightedness)

a. Eyeball characteristics:
b. Light focuses behind the retina

4. Emmetropia - normal vision
5.  Astigmatism -

C. Visual Receptors

1. Rods

a. Very sensitive to light
b. Responsible for night vision
c. Produce colorless images that are not very sharp/clear
d. Pigment = Rhodopsin

2. Cones

a. Stimulated by bright light
b. Three different kinds of cones (red, blue, and green)
c. Produce very sharp, colorful images
d. Fovea centralis

D. Visual Pigments

1. Rods contain Rhodopsin

When Rhodopsin absorbs light, the following occurs:

Rhodopsin (light) ---> opsin (protein) + retinal (from Vitamin A)

2. Cones contain retinal and opsins as well but respond to red, green or blue wavelengths of light

3. Breakdown of pigments leads to generation of a receptor potential

4. Bright light decomposes the rhodopsin in the rods, so we see in color

5. Dark-adapted eyes

a. Rhodopsin is NOT decomposed
b. Takes time to occur, but activation of the rods occurs (think of entering a darkened movie theatre)

6. Light-adapted eyes

a. Light sensitivity decreases because rhodopsin is decomposed
b. Cones are activated

7. Color vision

a. Wavelength of light:  remember ROY G. BIV (700-400 nm)
b. Overlap of cone sensitivity
c. Color-blindness -

E. Stereoscopic Vision

1. Distance, depth, height and width of objects
2. Dependent upon binocular vision

III. Visual Nerve Pathways

A. Optic nerves
B. Optic chiasma (medial retinal fibers cross over)
C. Optic tract
D. Thalamus and Superior Colliculi of Midbrain
E. Optic radiations
F. Occipital lobe (visual cortex)

D. Equilibrium and Hearing

1. Structure of Ear - Outer Ear:

a. Auricle (pinna)
b. External auditory meatus (ceruminus glands)
c. Tympanum (tympanic membrane) -

2. Structure of Ear - Middle Ear:

a. Ossicles

1. Malleus
2. Incus
3. Stapes

b. Oval window (superior)
c. Round window (inferior)
d. Auditory (Eustachian) tube
e. Tympanic reflex (Tensor tympani and Stapedius muscles)
f. Otitis media

3. Structure of Ear - Inner Ear:

a. Bony (osseus) labyrinth
b. Perilymph
c. Membranous labyrinth
d. Endolymph
e. Semicircular canals

1. Ampulla
2. Crista ampullaris

f. Vestibule

1. Utricle (superior)
2. Saccule (inferior)

g. Cochlea

1. Cochlear duct (Scala media)
2. Organ of Corti
3. Scala Vestibuli
4. Scala Tympani
5. Vestibular membrane
6. Basilar membrane
7. Helicotrema
8. Tectorial membrane

4. Mechanism of Hearing (see Table 9-2 in Martini)

a.  Transmission of sound to inner ear

b.  Resonance of the Basilar membrane

c.  Excitation of hair cells of organ of Corti (begin nerve pathway)

d.  Cochlear nerve

e.  Vestibulocochlear nerve

f.  Cochlear nucleus of medulla

g.  Inferior colliculi

h.  Thalamus

i.  Auditory Cortex

5. Homeostatic Imbalances of Hearing

a. Deafness

1. Conduction deafness
2. Sensorineural deafness

b. Tinnitus -

c. Meniere's Disease -

Last Updated 11/14/07

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