The Senses Chapter 29
Dec 25, 2015
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
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