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Somatic and Special Senses

Somatic and Special Senses
5 groups of sensory receptors:
1.) Chemoreceptors- stimulated by changes in chemical concentration.
2.) Pain receptors- Stimulated by tissue damage.
3.) Thermoreceptors- Stimulated by changes in temperature.
4.) Mechanorecptors- Stimulated by changes in pressure or movemment in fluids.
5.) Photoreceptors- Stimulated by light energy.
All nerve impluses coming from these 5 types of sensory receptors are alike.
The resulting sensation depends on the region of the brain recieving it. (Pg. 227)
Projection- The brain projects thr sensation back to its source.
Sensory Adaptation- When receptors recieve a continuous stimulation they adapt by slowing the rate of impluses sent to the Central Nervous System, eventually it will stop sending signals. (unless stimulus is increased)
Somatic Senses:
1.) Touch & Pressure
a. Free ends of sensory nerve fibers- found mostly in epithelial tissure. (touch & pressure)
b.Meissner’s corpuscles- Are very sensitive to touch. Numerous in hairless portions of skin. (lips, fingertips, palms, soles, nipples, external genitals.)
c. Pacinian corpuscles- stimulated by heavy/deep pressure.  Found in deeper subcutaneous tissue, tendons, & ligaments.
2.) Thermoreceptors
a. Heat receptors- sensitive to temperatures 77 F- 113 F, above 113 F they are triggered. (Feel burn)
b. Cold receptors- sensitive to temperatures 50 F - 68 F, below 50 F then pain receptors are triggered. Both slow rapid adaptation (feel freezing)
3.)Pain receptors (have protective function)
a. Widely distributed throughout skin and internal tissue. Nerve tissue in the brain lack receptors.
b. Pain recptors have poor sensory adaptation. One impluse may continue to send stimulation for some time.
c. Pain seems to be caused by stimulation of mechanorecptors--- decreased blood flow--- low tissue O2 concentration--- accumulation of pain- stimulating chemical. (ex. Muscle cramp pg.254)
d. Referred pain- sometimes with visceral pain--- the pain you feel may come from another place. ( ex. Pain from the heart may be transfered to the left shoulder or inside the left arm. Pg. 254, see pgs. 254-256)
4. Smell (pg. 256)
Olfactory receptors are stimluated by chemicals dissolved in water. (chemorecptors.)
Olfactory organs are in the upper parts of the nasal cavity.
The chemicals that stimulates this oragan enter the nose as a gas and it must dissolve in the fluid around the olfactory recptors. Once stimulates inpulses travell along the olfactory nerves to the olfactory bulbs--- the impulse is than sent along the olfactory tracts to the cerebrum for interpetation.
5.) Sense of taste
Taste buds consist of a group of taste cells. It is round in shape with a taste pore  on it, tiny taste hairs emerge from the pores. ( it is thought that these hairs are the sensitive part of the buds.)
-The buds are found on the tongue surface and some on the roof of the mouth and walls of the pharynx.
-Buds are chemoreceptors, so to taste a certain chemical it needs to be dissolved in saliva.
4 primary taste sensations:
1.) Sweet- (sugar) tip of tongue.
2.) Sour- (vinegar) sides of the tongue.
3.) Salty- (salt) outer edge of the tongue
4.) Bitter- (caffeine) back of the tongue.
- Flavors involve odor, texture, temperature, and chemicals present (spices), and of course the 4 types of tast areas.
6.) Hearing: Ear- external, middle, and inner ear. Functions in hearing and equilibrium.
External ear: Auricle- big flap on side of head.
External auditory meatus- tube to eardrum.
Tympanic membrane- eardrum
*- The auricle picks up sound waves it travels down the External auditory meatus and causes the eardrum to reproduce the vibratons of the sound wave source.
Middle Ear:
Tympanic cavity- an air-filled space seperating the external and inner ear.
It has 3 small bones attached to its walls by small ligaments--- they form a bridge between the tympanic membrane and the inner ear.
* They are responsible for getting the vibrations from eardrum-> inner ear.
Bones- 1.) malleus (hammer) is attached to the wall of ear drum.
2.) Incus (anvil) middle bone.
3.) Stapes (sturrip) is attached to the oart of the inner ear called the oval window.
*Thes 3 bones are collectively called auditory ossicles. The ossicles actually increase the force of the vibrations.
Eustachian- Connects middle war and throat. Keeps pressure equal on each side of the ear drum.
Inner Ear: Consists of tubes and chambers called labyrinth are found within the temporal bone.
The osseous labyrinth is the bony outer canal. The membranes labyrinth is the tube within the osseous labyrinth. The fluid between the labyrinth is the perilymph. The fluid within the membranous labyrinth is the endolymph.
-The labyrinth makes up the cochlea, (Hearing) and the semicircular canals. (Equilibrium)
The membranous labyrinth (cochleur duct) of the cochlea has a chamber above it (Scala vestibuli) and a chamber below it (Scala tympani). Note the membranes, vestibular membrane and basilar membrane, that seperate the membranous labyrinth from these chambers.
The basilar membrane is made up of thousands of elastic fibers of various length.
*Vibrations from the ossicles will come into the inner ear though the oval window--- go through the perilymph--- throught the vestubular membrane and enter the cochlear duct (membranous labyrinth). Her the vibrations cause movements in the basilar membranes.
The organ of Corti holds the hearing recptors on the upper surface of the basilar membrane. Their receptor cells are hair-like & arranged in rows. There is a tectorial membran that is attached to the bony shelf of the cochlea. It hangs down over the top of these hairy receptors.
*When the elastic fibers of the basilar membran vibrate it causes the hairy receptor cells to rub against the tectorial membrane in the orgam of Corti. Sensory impulses are sent out--- it  moves through the cochlear nerve to the temporal lobes of the cerebrum wher it is interpreted.
7.) Sense of equilibrium:
Static equilibrium- keeping head and body stable when we are motionless.
Inside the vestibule the membranous labyrinth expands into two chambers the utricle and saccule.
The anterior wall of the utricle has a structure called a macula. It contains hair cells that project into jelly-like material containing grains of calcium carbonate (otoliths)--- These increase the wt. of the jelly mass. When the head is tilted the mass sags causing the hairs to be bent--- impulses are sent to the brain via the vestibulocochlear nerve. Brain responds by sending motor impulses to skeletal muscles.
Dynamic equilibrium- Aids in balance while body is in motion. Each semicircular canal ends with a swelling called an ampulla. This is where their sensory organs are, called Crista ampullaris. This organ has hairs that extend into a dome shaped gelatinous mass (Cupula).
When we turn our head rapidly the fluid in the canals remains stationary. The cupula bends in opposite direction of head movement. Hairs also bend--- impulse is sent to cerebellum & interpeted.
8.) Sight:
Eye- Main organ
accessory organs:
Eyelid- 4 layers- skin, muscle, connective tissue, conjunctiva (mucus membrane).
Lacrimal glands- continuously secretes tears, they move across the eye and are collected by a superior and inferior canaliculi-> flows to the lacrimal sac than to the nasal cavity. (nose runs when you cry)
Function: Keeps eye moist/lubricated contains lysozyme, an antibacteriant.
-Note the 6 extrinsic muscles and how they move the eye. (pg. 278 chart 102)
Eye: Its wall has 3 layers.
            1) Outer Fibruos Tunic:
Anterior portion is transparent (cornea).  Contains few cells and no blood vessels.  The rest of the O.F.T. is the sclera/white part of the eye.  (Protection and muscle attachment) The optic nerve passes through it in the back of the eye.
            2) Middle Vascular Tunic:
Largely made up of the choroid coat.  It contains many blood vessels, supplying                   nourishment to surrounding tissues.  Also contains pigment producing melanocytes - - -the melanin absorbs excess light keeping the inside of the eye dark. 
*Ciliary body- anterior part of M.V.T forms the internal ring around the eye.
*Lens- Made up of epithelial cells.  It is held into position by suspensory ligaments               that extend from the ciliary processes of the ciliary body. *The contraction and relaxation of the ciliary muscles controls the focus of the eye.*Iris- Muscular diaphram/ colored portion.  The ciliary ody secretes a fluid aqueous humor that fills the Anterior cavity (posterior and anterior chambers)  of the iris.  It helps maintain shape and provides nourishment.  The circular and radial muscles of the iris regulates the amount of light let in.
            3)Inner Nervous Tunic:
Is continuous with the retina, (has vivid receptors), and continuous with the optic nerve.  In the center of the retina is a yellowish spot, macula lutea, which has a depression called Fovea Centralis (Where sharpest vision)  The optic nerve disk of the retina is where the nerves leave the eye (optic nerve), blood vessels enter /  leave here also.  When there is no receptor cells in the optic disk it is called the blind spot.
*When we see something it is either giving off or reflecting light.
*When we focus our eyes we have to bend light waves.  (Refraction)
*The image formed on the retina is upside down and reversed.  (Left to Right)  Our visual cortex corrects this and and we see things in the proper position. (glasses/ reverse image-story)
*Light waves are refracted primarily by the cornea and the lens.  Images from 20+ feet have light waves traveling in nearly parallel lines.  These waves are focused on the retina when the lens is at rest or flattened.  In close images, the focus point is behind the retina--lens must be thinkened by contracting the ciliary muscles. (We increase the refracting power.) 
Visual receptors: (Modified nuerons)
            *Rods- long thin projections at terminal end.  Much more sensitive then cones.  Allow us to see in dim light (no color)
            *Cones- detect color.  Give us a sharp image.  Area of sharpest vision contains only cones. (fovea centralis.)
**Both rods and cones have light sensitive pigments that decompose when light is present. **
Rods- Rhodopsin (visual purple) is broken down into scotopsin (colorless protien) and retinene (yellowish substance).  When Rhodopsin breaks down it releases energy - which causes nerve stimulation.  In bright light almost all Rhopdopsin is broken down...rod sensitivity is reduced.  In dim light Rhodopsin is regenerated from sctopsin abd retinene faster then it is broken down.  (Uses ATP)
Cones: Pigment composed of retinene and another protien.  Are 3 different protiens and 3 different types os cones, each having one of these protiens:
            1)Erythrolabe- sensitive to red
            2) Chlorolabe- sensitive to green
            3) Cyanolabe- sensitive to blue.
Color we can see depends on the cone or the set of cones stimulated.  (Compare to red, green, blue ink in a color printer for computer.)


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