physiology notes: senses

Senses

1. Transduction: the change of a stimulus into a biochemical event
2. Receptor types:
   1. Chemoreceptors: respond to chemicals (taste buds, olfactory, aortic

bodies and carotid bodies)

2. 2. Photoreceptors: rods and cones in retina
   3. Thermoreceptors: heat and cold
   4. Mechanoreceptors: deforming of receptors; touch, pressure.
   5. Nocioceptors: free nerve endings; pain receptors

3. Tonic receptors: constant rate of firing; slow-adapting

Phasic receptors: burst of activity when stimulated; fast adapting

4. Law of specific nerve energies: sensation produced by the normal stimulus;

Example: Being struck in the eye→burst of light

5. Generator potentials: (receptor); local graded changes (like EPSPs); generate action potentials; if tonic, more action potentials with ↑.

6. Dilation:
   1. Iris of eye with radial muscles: stimulated by postganglionic sympathetic axon→opens in dim light (contraction)
   2. Iris of eye with circular muscle: stimulated by postganglionic

Parasympathetic axons→in bright light.(contraction)

7. Refraction: light moving through a different medium light→cornea→lens→humors produces bending; image will be inverted and

reversed.

8. Accomodation: ability to focus when objects are moved from a distance

Object > 20 feet= lens flattens as ciliary muscle relaxes

Object < 20 feet= lens bulges as ciliary muscle contracts

9. Dark vision: > in rhodopsin in rods
10. Rhodopsin:
    1. Red-blue (purple pigment) consisting of:

Retinene (retinal) from Vitamin A and opsin (protein)

11. Photobleaching:
    1. Retinene has 11-cis form (kinked)
    2. Retinene has all-trans form when hit by photons of light(straight form)
    3. Bleaching→ change in ion permeability of rod cell membrane→nerve

Impulses in ganglion cells

12. Color Vision: Trichromatic theory;

Blue cones: 420 nm; green cones: 530 nm; red cones 560 nm; absorption

spectrum overlaps→ different shades; photopsins, not opsins

13 Retinal cell signaling:

a. Dark: photoreceptors have many Na+ channels open; called dark current

b. Na+ influx causes rod or cone→constant stream of inhibitory neurotransmitters to biplar cell=hyperpolarization.

c. Light: all trans retinene formed→Na+channels close

d. Photoreceptor stops releasing inhibitory neurotransmitter

e. Bipolar cell→action potentials stimulating other cells

14.Neural pathways for photoreception:

12. 1. Bipolar cells→ganglion cells→optic nerve→brain

15. Convergence: when a single bipolar cell synapses with multiple photoreceptor Cells →one ganglion vs. one bipolar cells with one ganglion; this type Gives a smaller visual field (more acute vision)

16. Fovea centralis: area within the macula lutea; contains only cones ; greatest visual acuity in light; sensitivity to low light is poorest.

17. Optic chiasma: crossing over of the medial tracts to opposite sides of the brain

18. Hearing:

a. tympanic membrane: vibrates; attaches to auditory ossicles

b. ossicles (malleus, incus and stapes) attach to oval window of cochlea;

c. oval window: transfers vibrations to cochlea→fluid vibrations

19. Sound transduction:

Cochlea: spiral organ of inner ear with fluid contains basilar membrane with Hair cells; sterocilia contracts tectorial membrane bending hair cells.

20. Hair cell signaling: bending of stereocilia→ion channels in membrane of hair

cells open, depolarizing; > in stereocilia →more neurotransmitter,

increasing action potentials in sensory neuron.

21. Pitch transduction:

Number of sound waves (higher frequency) = high pitch; low frequency=low

Pitch; higher frequency is closer to oval window

22. Volume transduction: louder sound=greater movements of tympanic membrane;

louder volume produces large wave generation in basilar membrane; more

stereocilia to bend.

23. Taste buds: receptors for certain molecules

24. Receptors:

a. Taste (gustation) encapsulated; gustatory hair

1. salty: clustered on the sides: permeable to Na+; Na+ enters→depolarization

2. sour: on sides of tongue; permeable to H+ (sour)

3. sweet: G protein activation; sense organic molecules

4. bitter: back of tongue: G protein

25. Smell: dendritic receptors; axons project into olfactory bulb; G protein activation;

each receptor may activate 50 G-proteins =acute sense of smell in

most mammals.