The Senses

Chapter 29

Sensory Input• All senses trigger the same TYPE of action

potential– Distinction occurs in activated brain area

• The brain detects sensations and interprets them– Action potentials from sensory receptors– Greater stimuli = higher frequency of AP’s

• Brain constructs perceptions from integrating sensations with other information– Neuronal communication involving multiple brain

areas

The Working Brain

Sensory Receptor Types• Nociceptors

– Respond to excess heat, pressure, or chemicals

– Tissue damage– All parts of the body but brain

• Thermoreceptors– Temperature of skin and blood– Maintains homeostasis via the

hypothalamus• Photoreceptors

– Light absorbing pigments– Light detection

Sensory Receptor TypesMechanoreceptors Chemoreceptors• Touch, pressure, & vibrations• Bend or stretch PM of

receptor cell = changing permeability– Stretch receptors – position of

body parts– Hair cells - sound waves and

H2O movements

• Chemicals in the internal & external environment– O2 in arterioles– Osmoreceptors - changes in

[blood solute]– Pheromone detection

Sensory Adaptation

• Sensory receptors become less responsive– Fewer action potentials

• Limits reactions to normal background stimuli– Shower or hot tub temperature– Odors over time

The Evolving Eye• Invertebrates

– Eye cups: light intensity and direction only– Simple eye: light dark, some distance and

color– Compound eye: form mosaic images

• Multiple photoreceptors w/own eye• Acute motion detectors and color vision

• Vertebrates (Cephalopods too)– Single-lens eye: b&w, color, motion, image

formation• Amount of light entering the pupil is regulated by

an iris• Passes through a lens which focuses light on the

retina– Upside down and inverted– Rods, cones, and fovea

• 3D images from 2 eyes

Single–Lens Eye• Changes lens shape to focus

light onto retina– Squid and fish have rigid eyes so

use muscle movement– Mammals use ciliary muscles

• Humors maintain shape and carry nutrients– Blockage of ducts = glaucoma

• Tears only in humans– Excess solution for eye moisture– Drains to nose

• Conjunctivitis

Correcting Vision• Vision tests measure visual acuity or ability to

distinguish fine detail– 20/20 is normal – chart read at 20 feet– 20/10 is better than normal – at 20 feet, read as if at 10

feet– 20/50 is worse than normal – at 20 feet, read as if at 50

feet• Visual problems are often focusing problems– Nearsightedness: can’t focus at distances, eye longer– Farsightedness: can’t focus close, eye shorter– Astigmatism: blurred vision from misshaped lens

• LASIK reshapes cornea to change focusing ability

• 3 main regions• Eardrum separates outer and middle

– Sound pressure moves ear drum to move ossicles in inner ear amplify

• Eustacian tube equalizes pressure b/w middle ear and atmosphere (‘pop’)

• Cochlea houses the hearing organ• Semicircular canals for balance

Gross Anatomy of the Ear

Cochlea• Organ of Corti is the hearing organ

– Contains hair cells embedded in a basilar membrane

• Tectorial membrane bends hairs as basilar membrane moves• Sensory neurons to auditory nerve

Semicircular Canals

• Proprioception and movement– 3, 1 in each plane of movement

• Head mov’ts change fluid direction– AP frequency change– Sudden stop causes dizziness b/c fluid still moves– Brain interprets and commands skeletal muscles

• Motion sickness– Feel, but don’t see movement– Brain think drugs = vomiting

Olfaction• Olfactory receptors detect

airborne molecules– Upper portion of nasal cavity– Impulses to olfactory bulb– Cilia from tips in mucous to

detect substances• Odorants bind to specific

receptors that trigger membrane changes

• Cause action potentials• Humans can detect 1000’s

of odors– Animals can detect more,

sensation is more important

Taste

• Taste buds detect molecules in solution• Four familiar and 1 other taste

– Sweet: organics– Sour: acids– Salty: inorganics– Bitter: caffiene, nicotine, aspirin– Umami –meats, cheeses, and protein-rich

foods (MSG)• Each receptor responsive to a particular

type of substance– Many ‘tastes’ are really smell (head colds)– Spicy foods are pain response