Lesson VIII - The Senses
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Lecture
Unit 8 Questions –
Senses - New 2008
Lab: Human
Senses - Part I
Crossword: Eye
Crossword: Ear
Questions: Senses (Old 1. – 30.)
Questions:
Senses (1. – 49., 2007)
I. Sensation and Perception
1. All information is transmitted as action potentials
2. Eg., Same for sight at sound, yet see or hear as different due to region of
cerebral cortex it is directed to.(Visual cortex or auditory cortex)
3. Nerve impulses conducted along sensory neurons are called sensations
4. Brain interprets sensations giving perceptions.
5. Different parts of the brain trigger different perceptions.
6. Crossing nerves could produce light from pressure, etc.
7. Rubbing eyes (pressure) causes spots of light.
8. Pain in a phantom limb is caused by severed, but still living nerves. Pain
is real and caused by irritation.
II. Sensory Receptors
1. Structures which detect changes in external and internal environment
(stimulii in forms of forms of energy)
2. Usualy modified neurons or epithelial cells.
3. Process broken down to 5 steps:
1. Reception - Ability of
cell to absorb energy of a stimulus. Eg., Cones and rods in eye have membranes
having light absorbing pigment molecule.
2. Transduction - Conversion of stimulus energy to change in membrane
potential of receptor cell. Begin with change in membrane permeability of cell,
called receptor potential. Graded potential.
3. Amplification - Strengthening of stimulus energy, otherwise too weak.
Eg., A.P. conducted from eye is 100,000 times as much energy as photons of
light that triggered it.
4. Transmission - conduction of impulses to CNS. Some receptors
(Pain receptors) are sensory neurons which conduct impulse to CNS.
Others are separate and must transmit across synapses first. Intensity is
changed with frequency of impulses along sensory neurons.
5. Integraton - Processing of information. Happens at all levels. Begins
in receptors, then occurs throughout CNS.
4. Types of receptors can be made on basis of location in 2 broad groups.
1. Exteroreceptors - receive
info from outside world
2. Interoreceptors - Provide info about body's internal environment
5. Another type of categorization is by energy source. 5 types:
1. Mechanoreceptors - Stimulated by physical deformation: pressure, touch, stretch, motion, and sound.
a. Bending or stretchin membrane
increases permeability, resulting in depolarization (receptor potential).
b. Touch is due to receptors that are modifide dendrites of sensory neurons.
c. Muscle spindle or stretch receptor is example of interoreceptor which is
mechanoreceptor.
d. Hair cell is another common mechanoreceptor. (human inner ear).
2. Chemoreceptors - Receptors
are responsive to specific molecules: glucose, oxygen, carbon dioxide, amino
acids, etc. Molecules bind to specific sites and cause change in membrane
permeability.
a. 2 groups of chemoreceptrs show intermediate specificity: gustatory (taste)
and olfactory (smell). They respond to categories of related chemicals: seet,
sour, salt, bitter.
3. Electromagnetic receptors - Detect electromagnetic energy, such as
visible light (photoreceptors).
4. Thermoreceptors - Heat or cold located on skin and in in hypothalamus
to regulate body temperature.
5. Pain receptors - Class of naked dentrites in epidermis of skin called
nociceptors. Different groups of pain receptors respond to excess heat,
pressure, or chemicals from damaged or inflamed tissue.
a. Some chemicals that trigger pain: histamine and acids. Prostaglandins increase pin by sensitizing receptors. Aspirin is enzyme inhibitor which prevents prostaglandins synthesis.
III. Receptors of the skin
Figure: Skin
1. Receptors are really all over the body with certain receptors in higher
concentrations in different parts.
2. Receptors of the skin include touch, pressure, heat cold, and
pain. Each is sensitive to one kind of stimulus. They may be
naked dentrites, like light touch and pain, or wrapped in tissue like heat,
cold, and pressure.
3. Touch receptors may lie close to the surface or deeper in the skin.
They may respond to light touch or stronger touch. Some are wrapped around the
base of hairs.
4. Touch receptors are farthest apart on the back and closer together on
fingertips, toes, and lips; and closest on tip of tongue.
4. Judging size of object is partly determined by number of touch receptors stimulated.
5. Pressure receptors lie deep in skin and respond to firm pressure.
6. Heat receptors respond to warmth (Ke) flowing into the skin.
7. Cold receptors respond to loss of warmth (Ke). In general there are 3
to 4 heat receptors for every cold.
8. Pain receptors respond to all kinds of massive stimulation. Sensation
of pain is the same no matter what is causing it.It may be prickling pain (fast
pain) or burning and aching pain (slow pain).
IV. Vision Figure Eye
1. Each eye is composed of 3 layers: outer- sclera and cornea. Middle -
contains choroid, ciliary body, and iris. Inner - consits of
retina.
2. The sclera or white of eye consists of tough white connective
tissue. Maintains shape of eye and provides attachment for muscles.
3. In front the sclera forms the cornea - transparent layer
through which light enters.
4. Just inside cornea is small chamber (anterior chamber) filled
with aqueous humor. Humor refers to fluid within
body.
5. At back of chamber the choroid is the iris. Iris gives eye its
color and adjust to light.
6. Pupil is openening in middle of iris and lets light in.
7. Behind iris is the lense. The cells forming lense contain
special protein called crystalin. Light passes through crystalin
and is bent. Bending allows lense to focus close and distant objects. Muscles
attached to suspensory ligaments stretch lense to change shape.
8. Behind lense is large chamber called posterior chamber filled
with jellylike vitreous humor.
9. Conjuctiva - Membrane that covers sclera and lines eyelids.
10. Palpebrae (eyelids). Folds of skin and muscle.
11. Lacrimal glands: tear ducts.
12. Lacrimal caruncle. fleshy, yellowish projection of tissue
that contains modified sweat and sebaceous glands.
13. Special light sensitive photoreceptors (chemoreceptors) are
arragned in retina at back of eye.
14. Cones are most densely concentrated in central fovea,
small depression. In center of posterior retina and in line with visual axis of
eye.
15. Fovea is area of sharpest vision due to high concentration of
cones.
16. Rods are absent from fovea but increase in density towards outside of
retina. (can see object better at night, without looking directly at it).
17. Light is converted to impulses. 2 kinds of receptors: rods and
cones. Rods are activated in dim light. Cones in bright light.
18. Pigment in receptors is rhodopsin (also called visual
purple). Rods are extreemly sensitive to all colors (wavelengths) but do not
distinguish between them (black and white vision. Many more rods than
cones. 125 million rods and 6.5 million cones.
19. Cones are less sensitive than rods but distinguish color. 3 types of cones:
red, green, yellow. Combination and blending gives all colors.
20. Optic nerve take message to optic lobe (visual cortex).
Point where optic nerve leaves the eye is the blind spot.
21. Vitamin A deficiancy leads to night blindness. Pigment in
rods and cones is decreased.
22. Color blindness is hereditary condition in which there is
less pigment in one or more types of cones is deficient. Red/green is most
common, especially in men.
III. Hearing and Balance Figure
Ear
1.Ear has 2 sensory funtion: hearing and balance, or equilibrium
2. Ear has 3 parts:
a. Outer ear - part that can be seen: pinna
(Auricle) - flap of skin supported by cartilage. Also, a short auditory
canal. Pinna focuses sound. Glands in canal secrete waxy material,
which prevents foreign objects from entering.
b. Middle ear - Stretched across auditory canal is tympanic
membrane (ear drum). Behind eardrum is air filled chamber, containing 3
tiny bones: hammer (malleus) is attached to eardrum, anvil
(incus) connects hammer and stirrup, stirrup (stapes) connects
to oval window. These bones link eardrum with membrane of inner
ear (oval window).
c. Inner ear - Going from middle ear to throat is eustachian
tube, which equalizes pressure of middle ear. Infections may travel
from nose or throat through eustachian tub to middle ear. Cochlea
and semicircular canals are within inner ear. Cochlea
is the organ of hearing. It is snail-shaped fluid-filled cavity. When fluid
vibrates, hair cells lining cochlear move and turn vibrations to nerve
impulses. Organ of Corti (Spiral Organ) is organ of
hearing. It lies on the basilar membrane of the cochlea. These cells line
the length of the cochlea.Receptors are hair cells. Impulses are carried to
brain by acoustic nerve (auditory nerve).
The semicircular canals allows body to maintain balance. There are three interconnect, loop-shaped tubes at right angles to each other. They contain fluid and hairlike projections (ciliated cells) which sense change of body position. Also calcium carbonate and grains of proteins called otoliths (hearing stones). Otoliths rollback and forth and with movement of luid cause hairs, sending impulses to brain.
IV. Taste Figure Taste
1. Suface of tongue is covered by small projections calle d papillae. Within in
papillae are tast receptors (taste buds). Each taste bud has number of sense
cells and opens to furface of tongue through pore. Microvilli extend through
pore.
2. Most taste buds are on tongue; however, also found on roof of mouth, lips,
and throat (especially in children).
3. Four main kinds of tastes: sweet, salty, sour, and bitter. Each taste bud is
particularly sensitive to one taste.
4. Substances must be in solutions to be tasted (chemoreceptors) - many
substances dissolve in saliva.
5. Taste buds tend to be found on specific areas of tongue. See figure. Sour -
sides; Bitter - back; Sweet and salty - front.
6. Most flavor of food comes from smell. Most foods have little tast if you
have a cold or stuffy nose.
V. Smell
1. Olfactory cells are receptors (chemoreceptors) of smell are found
in mucous membrane lining upper nasal cavity. Hve cilia which project into air
cavity.
2. Molecules of gaseous substances enter nose, dissolve in mucus, and stimulate
olfactory receptors.
3. Olfactory receptors are specialized nerve cells. Olfactory nerves
carry impulses to brain.
4. Unlike taste buds, respond to over 50 different odors. Each receptor
responds more to one odor.
5. Continued exposure results in inability to respond to that odor. Like other
parts of ns this is adaptation.
6. More sensitive than taste buds. respond to fewer molecules.