THE SENSES

1
THE SENSES

• Chapter 32

2

• A. Sensory Receptors
• Neurons or specialized epithelial cells that
  detect, transduce, and amplify specific stimuli.

3

• Sensory receptors can signal the brain about
  strength of the stimulus.
• As strength increases...
• number of action potentials generated per unit
  time increases.
• a greater number of sensory neurons are
  activated.
• Many sensory receptors experience sensory
  adaptation.

4

• Types of Sensory Receptors
• Thermoreceptors - detect heat cold
• Pain receptors (nociceptors) - detect chemicals
  released from injured cells
• Electroreceptors - detect electrical fields
• Chemoreceptors - detect chemicals
• Photoreceptors - detect light energy
• Mechanoreceptors - detect mechanical energy
  (touch, pressure, vibration)

5

• B. Chemoreception
• Ability to detect respond to specific chemicals
  in the environment enables organism to smell
  /or taste.
• 1. Invertebrate Chemoreception
• Taste receptors located on
• head of flatworms
• tentacles of octopuses
• mouthparts, legs antennae of many arthropods

6

• Smell receptors located on antennae of many
  insects.

Male silkworm moth Bombyx mori
Sensory hairs on antennae detect pheromones
released by female
7

• 2. Vertebrate Chemoreception
• Human Olfaction (smell)
• Olfactory epithelium located in roof of nasal
  cavity.

Epithelium contains ciliated olfactory receptor
cells (specialized neurons) support cells.
8

• Olfactory pathway odor molecules stimulate
  receptor cells ? olfactory bulb ? olfactory tract
  ? olfactory cortex of frontal lobes.

9

• Human Gustation (taste)
• Sensory receptor organs for taste are taste buds
  located primarily on surface of tongue.

Taste buds respond to 4 primary tastes sweet,
sour, salty bitter.
10
Each taste bud contains 50-150 taste receptor
cells replaced every 3 days.

• Gustatory pathway taste molecules stimulate
  receptor cells ? gustatory nerves ? gustatory
  cortex of parietal lobes.

11

• C. Photoreception
• Ability to detect respond to light.
• All photoreceptors contain pigment molecules
  (usually rhodopsin).
• 1. Invertebrate Photoreception
• Three basic types of eyes
• Eye cups

Distinguish light intensity direction. Ex.
planaria
12

• compound eyes (multiple-lens eyes)

Composed of ommatidia. Form images (mosaic)
detect movement. Ex. insects, crayfish, crabs

• single-lens eyes

Work like a camera. Form distinct images detect
movement. Ex. cephalopods
13

• 2. Vertebrate Photoreception
• Vertebrates have single-lens eyes similar to
  those of cephalopods.
• Eye is composed of 3 distinct layers

14

• Sclera (outermost layer)
• tough connective tissue layer (white of the eye)
  protects inner structures.
• anterior portion of sclera (cornea) is
  transparent admits light.

15

• Choroid (middle layer)
• contains blood vessels (provides nourishment) a
  dark pigment (absorbs light, preventing
  reflection).
• anterior portion of choroid forms
• ciliary body - contains ciliary muscles that
  change shape of lens.
• iris - regulates amount of light entering eye
  opening in center is pupil.

16

• Retina (innermost layer)

• composed of photoreceptors (rods cones),
  bipolar cells ganglion cells.

• fovea centralis - region containing cones, but no
  rods.
• blind spot - region lacking photoreceptors.

Blind spot
17
(No Transcript)
18

• Pathway of light entering eye cornea ? aqueous
  humor ? pupil ? lens ? vitreous humor ? rods
  cones of retina

19
Pathway of visual impulses to brain
rods cones ? bipolar cells ? ganglion cells ?
optic nerve ?
lateral geniculate nuclei ? visual cortex of
occipital lobes.

• Note
• impulses from lateral regions of retinas sent to
  LGN on same side.
• impulses from medial regions cross over at optic
  chiasma enter LGN on opposite side.

20

• D. Mechanoreception
• Ability to detect respond to various forms of
  mechanical energy (touch, pressure, motion
  sound).
• 1. Invertebrate Mechanoreception
• setae - hairlike structures at bases of antennae
  vibrate in response to sound.
• Common in insects.

21

• tympanal organs - thin membranes stretched over
  an air-filled chamber (resonance chamber)
  membrane vibrates in response to sound.
• Common in insects.
• statocysts - fluid-filled sacs containing sensory
  hairs statoliths (tiny mineral particles)
  movement of statoliths helps organism orient with
  respect to gravity.
• Common in jellyfishes, snails, squids,
  crayfishes earthworms.

22

• 2. Vertebrate Mechanoreception
• Hearing
• Mechanoreceptors responding to sound waves are
  located in the ear.
• Human ear is divided into 3 regions
• Outer ear
• pinna (fleshy portion)
• auditory canal (ear canal)
• Tympanic membrane (eardrum) separates outer
  middle ears.

23

• Middle ear - air filled chamber.
• eustachian tube (auditory tube)
• 3 tiny bones (malleus, incus stapes)
• Oval round windows separate middle inner ears.

• Inner ear - fluid filled chamber.
• semicircular canals vestibule
• cochlea

24

• Cochlea contains
• vestibular canal
• tympanic canal
• cochlear canal - contains vibration sensitive
  hair cells.

Pathway of sound waves auditory canal ?
tympanic membrane ? malleus ? incus ? stapes ?
oval window ? vestibular canal ? basilar membrane
? hair cells ? cochlear (auditory) nerve ?
thalamus ? auditory cortex of temporal lobes
25

• Hearing impairments
• Conductive deafness - blocked transmission of
  sound through middle ear.
• Causes excess earwax, ruptured eardrum, middle
  ear infections, fusion of ear bones.
• Sensory (neural) deafness - damage to neural
  structures.
• Causes damage to hair cells, degeneration of
  cochlear nerve, auditory cortex tumors.
• Tinnitus - ringing or clicking sound in ears.
• Causes nerve degeneration, middle or inner ear
  infections, some medications.

26

• Equilibrium Balance
• Regulated by mechanoreceptors in semicircular
  canals vestibule.

Vestibule
Vestibular nerve
27

• Semicircular canals - detect rotational movement
  of head.

• Ampullae - enlarged bases of semicircular canals
  each contains a cupula.
• Cupula - gel-like mass embedded with hair cells.

Equilibrium Pathway rotation of head moves
fluid in one or more semicircular canals ? fluid
displaces cupula ? hair cells ? vestibular nerve
? reflex centers in brain stem cerebellum.
28

• Vestibule (utricle saccule) - detects position
  of head with respect to gravity linear
  movement.
• utricle saccule contain a jelly-like fluid
  embedded with hair cells
• otoliths (calcium carbonate granules) float on
  top of fluid.

Hair cells are oriented vertically in utricle.
Hair cells are oriented horizontally in saccule.
29
Vestibule
Vestibular nerve

• Equilibrium Pathway linear movement displaces
  otoliths ? hair cells ? vestibular nerve ? reflex
  centers in brain stem cerebellum.

30

• Touch
• Mechanoreceptors responding to touch are
  concentrated in the skin of many vertebrates.

• Pacinian corpuscles - respond to firm pressure.
• Meissners corpuscles - respond to light touch.
• Free nerve endings - respond to touch, pressure
  pain.