Sensory SystemsCh. 39

6 Billion Worlds• Perception awareness of external

and internal environments– Every person’s perception of

everything is a little unique– We all vary in our sensory receptors,

pathway processing, and application of stimuli

• Sensory receptors cells designed to pick up stimulus within a receptive field (type and strength)

• Stimuli can trigger a receptor potential which, when strong enough, will start an action potential along an afferent neuron (sensory transduction)

The Big Five• Most animals posses 5 types of

sensory receptors:1) Mechanoreceptors detect

pressure and body movement; ears2) Photoreceptors detect light; eyes3) Chemoreceptors detect specific

chemicals; taste buds4) Thermoreceptors detect

temperature; skin5) Nociceptors detect damage;

everywhere• Humans have about 15-20 senses:

– Gravity, acceleration, balance, pH, O2

and CO2 levels, time, etc…

Magnitude and Adaptation • Regardless of the sensory

receptor, all action potentials are the same size. How do we measure the strength of a stimulus?– Frequency of action potentials;

faster = stronger– Number of neurons stimulated;

more= stronger• All sensory nerves, except

nociceptors, will learn to ignore a stimulus if it remains at a constant strength for enough time (sensory adaptation) – Reason background noise is ignored

or why you cant feel your clothing

Real Quick….• Next Wednesday you will do a lab to test your

sensory neurons• You will attempt to test how well they function

under different stimuli and explain why they may fail you

• As part of this lab I want each of you to design your own test to run

• By Tuesday, design a sensory test your lab group will do and submit a brief outline

• On Wednesday, make sure to bring the material needed to run your experiment. Bring extra material so other groups may also try your idea!

Mechanoreceptors: Touch• Touch receptors are located

throughout the entire body• The higher the density of

receptors the more sensitive an area is– What are the most sensitive parts

of the body?– Fingers, lips, and tongue

• 2-Point Test test sensitivity by measuring how far way two pins have to be for you to feel both independently

• Hair follicles free nerve ends wrap around our body hair and react to movement of the hairs

Mechanoreceptors: Balance• 2 Resources:1) Proprioceptors sensory

neurons in muscle tissue that tell the brain about body position– Measure stretching,

contractions, and increasing pressure

– Golgi tendon organs monitor stretching of muscles at attachments to bones (tendons)

Mechanoreceptors: Balance2) Vestibular apparatus 3 semicircular canals inside your ear that measure gravity and body movement

– Ampulla (end of tube) is filled with sterocilia (sensitive hairs) and fluid (endolymph)

– Movement in the head moves the fluid which pushes the hairs

– Tubes follow X, Y, and Z axis to give us 3D feedback

• Utricle and Saccule area of hair cells with CaCO3 stones (otoliths) on tope– Pressure of otoliths tell us if we are

upright

The Secret of Sound• Sound changes in air

pressure caused by vibrations– Pitch depends on frequency– Amplitude (loudness)

depends on size of change• Humans 20-20,000 hertz• Not all creatures hear

through “ears”– Many invertebrates hear

through skin– Insects hearing through

exoskeleton or hair cells

Mechanoreceptors: Hearing• Human ear is made of 3 parts:1) Outer ear part we can see;

pinna (ear) funnels sounds into the auditory channel– Pressure pulls and pushes

tympanic membrane (ear drum)2) Middle ear air-filled cavity with three of our smallest bones which transfer tympanic vibrations to oval window (membrane of the inner ear)

– Malleus hammer– Incus anvil– Stapes stirrup

Mechanoreceptors: Hearing3) Inner ear fluid-filled cochlea (3.5 cm spiraled tube) transfer oval window vibrations into neuron impulses

– Organ of Corti (spiral organ) contains sensory hair cells which react to fluid vibrations

– Basilar membrane anchor for hair cells; wide at base and thinner at tip (oval window)• Thin area vibrates at high

frequencies• Wide area vibrates at low

frequencies

• All hair cells send signals along cochlear nerve to the brain

The Mystical Eye• Ocellus simplest eye; detects

lights but depolarizing when photopigments (retinal, made from vitamin A) absorb light

• Compound eye thousands of units (ommatidia) focus light through transparent cells (cornea); great at detecting movement

• Single-lens eye lens (cornea) focuses lights while muscles in pupil change its size (small in bright; large in dim); iris blocks light not hitting lens; retina react to light at the back of the eye– Accommodation changing lens to

focus on objects

Photoreception: Sight• Human eye similar to single-lens

eye; clear fluids (aqueous and vitreous humor) fill spaces in eyes and carry nutrients to cells

• Why not blood vessels?– Limit our vision

• Photoreceptors:1) Rods rod shaped; specialized for

low light; black and white; respond to a single photon of light

2) Cones cone shaped; specialized for wavelengths (color); less sensitive than rods

• Ciliary body muscle tissue changes shape of lens (not pupil) to focus on objects

Rods and Cones• 120 million rods and 6 million

cones• Fovea area at back of the eye

where the lens focuses light; high conc. Of cones

• Peripheral vision input from area outside fovea; high conc. rods

• Photoreception:1) Outer membrane discs react to

light2) Internal segment processes cells

activity3) Axon of cell absorbs/releases

glutamate to start impulse

Rods and Rhodopsin• Rhodopsin retinal

protein in rods; part of G-protein pathway– Inactive (cis-form)

releases glutamate into synapse

– Active (trans-form) deceases glutamate release by closing Na+

channels and hyperpolarizing the cell

• Rods work opposite of regular neurons; stimulation decreases neurotransmitter release

Vision and The Retina• 6 types of neurons make of the retina:1 and 2) Rods and Cones3) Bipolar cells send impulse from rods/cones to ganglion cells4) Ganglion cells receive info from all over the retina and form optic nerve (blind spot)5) Horizontal cells receive input laterally along excitation point6) Amacrine cells send lateral information on to ganglions from bipolar cells• Lateral inhibition horizontal/amacine

cells inhibit impulses outside area of light on retina; allow better detph

Cones and Color Vision• Most mammals have only 2

types of cones but humans/primates have 3

• Each type has a different photopsins (retinal + opsin proteins)

1) S-type 445nm (blue light)2) M-type 535nm (green light)3) L-type 570nm (red light)• All three have ranges that

overlap so all visible light can be detected

Our Wonderful 3D World• 3D space comes from our

brains receiving 2 sets of visual stimulus (2 eyes)

• Optic chiasm part of image from left and right eye are shared but slightly different positions – Test this by altering which eye

is open• Communication between

each hemisphere in the brain allows the merging of the data to make 3D images

• The greater the difference between data, the closer the object appears and the more 3D it is

Chemoreceptors: Taste • Taste is a crucial survival tool• Organisms taste through their

mouth, feet, antenna, or even their whole body

• Analyzing the chemical make of the material tells the organism the possible benefits or dangers of consuming it

• 5 basic tastes:1) Sweet sugars2) Salty salts3) Sour acids4) Bitter bases and toxins5) Umami protein (glutamate)

The Buds• Taste in many mammals comes

from the tongue moist, enzyme recreating muscular tissue

• Taste buds (papillae) chemoreceptors for the 5 tastes; react to specific chemicals

• Salivary glands release a watery enzyme solution; used to help break down material and dissolve particles to be tasted

• Taste leads to emotional responses due to connections with the limbic system

Chemoreceptors: Smell• Sent is a powerful

communication method in many species– Small amount of particles are

needed to get reactions– Easily dispersed by the wind

• Pheromone communication through sent in insects/animals– Dead ants release a pheromone

that tells other ants to remove its body

– If pheromone sprayed on live ant, he will be kicked out of the colony (thought to be dead)

The Olfactory• Smell in humans is detected by

olfactory bulbs in our nose• Directly linked to the brain…why?

– Most mammals their nose comes first; faster the nose response the safer they are

• Sensory hairs covered in mucus (help dissolve particles in air) react to different classes of chemicals

• Taste and smell have a strong connection; often the smell of something is close to how you will taste it

• Smell is our first memory maker; babies remember the smell of their parents months before their voice, touch, or even face

Nociceptors: Temperature• Thermoreceptors detect

temperature in the environment and the body– Tool: infrared pit organs in

snakes; find blood for mosquitoes

– Safety: reflex protects us from damaging tissue

– Homeostasis: hypothalamus regulates body temp.; causes sweating or shivering

• Most mammals organize temps into groups from 8oC

to 52oC

Nociceptors: Pain• Nociceptors are located

throughout the entire body except the brain

• Natural defense against tissue damage; pain stops our desire to continue a destructive act

• 2 types of pain:1) Glutamate-releasing cells

sharp pain in specific areas2) Substance-P releasing cells

dull aching pain over a general area

• Endorphins natural painkillers released by the CNS that limit Substance-P reaction

Supersenses: Magnetoreceptors and Electroreceptors

• Magnetoreceptors detect the magnetic field of the Earth/magnetic material– Tool: used by migrating species to

guide them across great distances– Field of the Earth varies in location

but is relatively constant • Electroreceptors detect

electrical fields– Passive Tool: used by sharks to

locate prey in unclear water or under sand

– Active Tool: attack prey with electrical impulse from glands; electric eel

Homework• Suggested Homework:– Test Your Knowledge

• Actual Homework:– Discuss the Concepts #3– Interpret the Data– Due Tuesday

• Essay!!!– Explain a sense that humans do not

possess (not magnetic or electroreception) – Citation and reference pages must be done

correctly or you get a 0!– Due Tuesday

• Test!!– Tuesday; Ch. 17, 37, 38, and 39