Sense organs

Olfactory sensory (smell)

Region: mucous membrane of nasal cavity

Like related to degree for olfaction

development of sense of smell varies by species

sensitivity to smell probably decrease w/ time

cells of the olfactory membrane:

olfactory receptors: bipolar neurons w/ cilia or olfactory hairs

supporting cells: columnar epithelium

Basal cells= stem cells

replace receptors monthly

olfactory glands: produce mucus

Both epithelium and glands innervated

Adaptation and odor thresholds

adaptation= decreasing sensitivity

olfactory adaptation is rapid, 50% in 1 second, complete in 1 minute

low threshold, only a few molecules need to be present

Olfactory sensory perception

one odor at a time

emotional and autonomic behaviors

memory recall, more detailed in humans

olfactory pheromones

detectable olfactory chemicals that cause change in animals behavior

chemicals secreted by 1 animal that influences the behavior of another animal

mode of communication

purpose of pheromones: making trails or boundaries, recognizing individuals from the same herd or nest, marking location of food source, emitting alarms

Gustation sensory (taste)

taste requires dissolving of substances

receptors: taste cells

4 basic taste stimuli: sour, bitter, sweet, and salty

anatomy of taste buds

an oval body consisting of 50 receptors cells surrounded by supporting cells

a single gustatory hair projects upward through the taste pore

basal cells develop into new receptor cells every 10 days

physiology of taste

complete adaption in 1-5 minutes

mechanism:

dissolved substance contact gustatory hairs

receptor potential results in neurotransmitter release

nerve impulse formed in 1st order neuron

Visual sensory

Eye

eyelashes help protect from foreign objects, perspiration and sunlight

Sebaceous glands are found at base of eyelashes

palpebral fissure is gap between the eyelids

Tunic (layers) of eyeball:

Fibrous Tunic (outer layer)

Vascular tunic (middle layer)

Nervous tunic (inner layer)

transparent

helps focus light (refraction)

3 layers and nourished by tears and aqueous humor

Sclera: white of the eye

dense irregular CT layer, collage, and fibroblasts

provide shape and support

at the junction of the sclera and cornea is an opening (scleral venous sinus)

posteriorly pierced by optic nerve

Choroid and ciliary body

choroid: pigmented epithelial cells and blood vessels, provide nutrients to retina, and black pigment in melanocytes absorb scattered light

ciliary body: consist of ciliary processes and ciliary muscle, which the muscle alters shape of lens

Iris and pupil: colored portion of eye

hole in center is pupil

function is to regulate amount of light entering eye

muscles of the Iris

constrictor papillae are innervated by parasympathetic fibers while dilator papillae are innervated by sympathetic

response varies w/ different levels of light

lens

lens held in place by suspensory ligaments

focuses light on fovea

The retina

Posterior 3/4 of eyeball

optic disc

Rods- photoreceptors associated w/ black and white vision

sensitive to light

120 million rod cells

distributed along periphery

Cones: photreceptors associated w/ color vision

functions best during day vision

fovea of macula lutea

Pathway of nerve signal in retina

  1. light penetrates retina
  1. rods and cones transduce light into action potentials
  1. rods and cones excite bipolar cells
  1. bipolar excite ganglion cells
  1. axons of ganglion cells form optic nerve leaving the eyeball
  1. to thalamus and then the primary visual cortex

major processes of image formation

  1. refraction of light by cornea and lens
  1. accommodation of the lens, changing shape of lens so that the light is focused
  1. constriction of the pupil, less light enters the eye

Refraction: bending of light as it passes from 1 substance into a 2nd substance w/ a different density

convex lens refract light rays towards each other

lens of eye is convex on both surfaces

Auditory sensory (sound)

Anatomy of the ear:

external: collection of sound

pinna: elastic cartilage covered skin

external auditory canal: tube of cartilage and bone leading into temporal bone

tympanic membrane (eardrum)

middle- air filled cavity in the temporal bone

inner

series of fluid filled membranous sacs and canals

contains mechanoreceptors (hair cells)

3 ear ossicles: malleus, incus, stapes

auditory tube leads to nasopharynx

Bony labyrinth: set of tubelike cavities in temporal bone

cochlea

3 fluid filled channels: scala vestibuli, scala tympani, and cochlear duct

Tubular structure of the cochlea

  1. stapes pushes on fluid of scala vestibuli at oval window
  1. at helicotrema, vibration moves into scala tympani
  1. fluid vibration dissipated at round window which bulges
  1. the central structure is vibrated (cochlear duct)

Sound waves

vibrating object causes compression of air around it= sound waves

frequency of a sound vibration is pitch

greater intensity of vibration, the louder the sound measured in decibels

Physiology of hearing:

  1. Pinna collects sound waves
  1. eardrum vibrates
  1. ossicles vibrate since malleus attached to eardrum
  1. stapes pushes on oval window producing fluid pressure waves in scala vestibuli and tympani
  1. pressure fluctuations inside cochlear duct move the hair cells against the tectorial membrane
  1. Microvilli are bent producing receptor potentials

Physiology of equilibrium (balance):

static equilibrium:

Dynamic equilibrium:

Maintain the position of the body relative to the force of gravity

maintains body position during sudden movement of any type rotation, deceleration or acceleration

macula receptors w/in saccule and utricle

crista receptors w/in ampulla of semicircular ducts