Sensory Perception: A Summary AP Biology Spring 2011.
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Transcript of Sensory Perception: A Summary AP Biology Spring 2011.
Sensory Perception: A Summary
AP BiologySpring 2011
Stimulus: form of energy that activates receptor endings of a sensory neuron
Sensations: conscious awareness of stimulus Perception: understanding of what a
sensation means
Mechanoreceptors: reseptors stimlate by physical stimuli, such as pressure, touch, stretch, sound, or motion
Thermoreceptors: respond to either heat or cold and help maintain body temperature
Chemoreceptors: detect chemical energy of substances dissolved in a fluid bathing them Gustatory (taste) receptors and olfactory
(smell) receptorsOsmoreceptors: detect changes in the
solute levels of some body fluid
Photoreceptors: detect differences in energy of visible light and UV light
Pain receptors: respond to excess heat, pressure, or specific classes of chemicals released from damaged or inflamed tissuesMany different groups
All sensory receptors transduce stimulus energy into action potentials
Brain assesses each stimuli by which nerve pathways are carrying action potentials, the frequency of action potentials traveling on each axon in the pathway, and the number of axons recruited by the stimulus
Sensory Adaptation: a diminishing response to an ongoing stimulusEx. The pressure exerted by a sock
Example of how we make use of sensory pathwaysFigure 35.2, page 601
Somatic sensations: arise in the cerebrum’s outer layer of gray matter, the cerebral cortex.
Some body parts have more sensory acuity (more neurons)Fingers, thumbs, lips
Sensation of touch, pressure, cold, warmth, and pain
Free Nerve Endings: unmyelinated or thinly myelinated, branched endings of sensory neurons in skin and internal tissuesThermoreceptos, mechanorecptors, and pain
receptorsAdapt slowly to stimualtion Different subpopulations respond to different
stimuli
Encapsulated receptors: detect somatic sesations, 4 types 1. Meissner’s Corpuscle
Fingertips, lips, eyelids, nipples, genitals Adapts very slowly to low-frequency vibrations
2. Bulb of KrauseThermoreceptor, activated at 20 degrees C or lower,
below 10 degrees C contributes to painful freezing sensations
3. Ruffini endings Detect steady touch and pressure, and temp.’s above
45 degrees C 4. Pacinian Corpuscle
Sensitive to fine textures, occurs in dermis, near freely movable joints, and in some internal organs, sensitive to rapid pressure changes brought on by touch and vibrations
Stretch receptors in muscle spindle fibers Increase firing rate as muscle stretchesSignal brain about positions of the body’s
limbs
Pain: perception of a tissue injury
Somatic pain: response to signals from pain receptors in skin, skeletal muscles, joints, tendonsSuperficial somatic pain arises at or near skin
surface , sharp or pricking often does not last long
Deep somatic pain arises deeper in skin or muscles or joints, diffuse and lasts longer
Visceral pain: associated with internal organs Is response to high chemical stimulation,
muscle spasm, muscle fatigue, excessive distension of gut, inadequate blood flow to organs, and other abnormal conditions
Cells injured release chemicals that activate pain receptors
Bradykinins: open floodgates for histamine, prostaglandins, and other participants in inflammatory response
Signals from pain receptors enter spinal cord and cause release of a neuromodulator, substance P, which activates neurons that can signal the sensory cortex
Assess the intensity and type of pain Different signals rouse body and mediate
emotional responses Release natural opiates- endorphins and
enkephalinsLower pain preception
Influence pain tolerance:Emotional states, culture factors, possibly age
(older people handle pain better)Hyperalgesia: intense or long lasting pain
leads to this condition where pain is amplifiedBad sunburn and hot shower
Referred pain: perception of visceral sensations as somatic sensations Ex. Heart attack
Makes mistake because of nervous system constructionSensory inputs of skin and certain internal organs enter same segments of spinal cordSkin encounters more pain than organs, so brain may interpret most sensory input as arriving from skin
Phantom pain: amputees sense presence of a missing body part as if it were still there
Severed sensory nerves continue to respond to the amputation
Brain projects pain back to missing part, past the healed region
Chemoreceptors become activated by binding molecules of a substance that is dissolved in the fluid bathing them
Stimulus triggers signals that travel along nerves through thalamus, signals end in cerebral cortex Perception takes shape and fine tuning
Also reaches limbic system, integrates emotional states and with stored memories
Olfactory Receptors: fire off signals when exposed to water-soluble or volatile (easily vaporized) chemicals
Receptor axons lead into one of two olfactory bulbs
In these small brain structures, axons synapse with cells that sort out scent Then, information flows along olfactory tract to cerebrum, where further processed
Use olfactory cues to navigate, find food, communicate
Pheromones: signaling molecules secreted by one individual that change the social behavior of other individuals of its species
Vomeronasal organ: reptiles, most mammals (not primates), cluster of sensory cells that detect pheromones Humans have reduced version
Taste receptors: found on antennae, legs, tentacles, or inside mouth Chemoreceptors
located in our surface of mouth, throat, and upper part of tongue (taste buds)
5 main sensations: sweet, sour, salty, bitter, umani (savory taste)
Vestibular apparatus: one each ear, consist of two sacs (utricle and saccule) along with 3 semicircular canals Sacs and canals interconnect into a continuous,
fluid-filled system where mechanoreceptors are stimulated when you move
Organ of Dynamic Equilibrium: inside bulging semi-circular canal, gelatinous mass which hair cells project Any rotation of head displaces fluid Hydrostatic pressure exerted by moving fluid
shifts gelatinous mass, which bends hair cells Bending causes signals to flow from sensory
neurons to vestibular nerve, which carries signals about motion to brain
Organ of Static Equilibrium: inside each utricle and saccule, send messages to brain about how head is oriented relative to ground Thick membrane rests on hair cells that project
upward from floor of sac Membrane contains mass of crystals, weigh it
down Head upright: weighted membrane presses
down on hair cells, bends them slightlyIf posture changes or speed up or slow down
movement, position of membrane above hair cells will shift
Brain also evaluates input from receptors in skin, joints, tendons
Integration of all information allows control of eye muscles that keep visual fields in focus even with movement
Helps maintain awareness of body’s position and motion in space
Vertigo: sensation that world is moving or spinning around Stroke, inner ear infection, loose particles in
semicircular canals Arises from conflicting sensory inputs
Motion Sickness: from mismatched signals Passengers in a vehicle, confusion of if in
motion (outside vehicle) or stationary (inside vehicle)
Amplitude: loudness (intensity), measure in decibels
Frequency: number of wave cycles per second, more cycles per second higher the frequency and pitch
Water readily transfers vibrations to body tissues
Sound spreads out in air Outer ear: adapted for gathering sounds
from air Pinna: folded flap of cartilage, sheathed in
skin, projects from side of headAuditory canal leads from pinna to middle ear
Middle ear: amplifies and transmits air waves to inner ear Eardrum: thin membrane, vibrates fast in
response to pressure waves Behind drum is air-filled cavity and small
bones: hammer, anvil, stirrupBy interacting bones transmit force of sound
waves from eardrum to a smaller surface (oval window)
Oval window: elastic membrane in front of inner ear
Inner ear: has vestibular apparatus, cochleaCochlea: pea sized, fluid-filled structure,
transduction of waves of sound into action potentials occurs here
Sound waves make stirrup vibrateMiddle ear bone pushes against oval windowTransmits pressure waves to fluid in 2 of 3
cochlear ducts (scala vestibuli and scala tympani)
Waves end at another membrane, round window (bows inward and outward in response)
Third cochlear duct sorts out pressure waves Its basilar membrane wall, is stiff and narrow
near oval window, then broadens and becomes more flexible deeper in coil High pitched sounds make stiff, narrow part of
cochlear duct vibrateLow pitched sounds make flexible part vibrate
Acoustical organ: attached to one surface of basil membrane
Organ of Corti: has arrays of hair cells (acoustical receptor with modified cilia at one end)
Cilia bend when pressure moves basilar membrane
Mechanical energy transduced into action potentials that reach brain
Damage of hairs results in hearing loss
Vision: requires eyes and image perception in brain centers that can interpret patterns of visual stimulation
Eyes: sensory organs that contain a tissue of many densely packed photoreceptors
Photoreceptors: contain pigment molecules that can absorb photon energy, which can be converted to excitation energy in sensory neurons
Ciliary photoreceptors: plasma membrane around the cilium develops into the photosensitive surface Cnidarians, some flatworms, vertebrates
Rhabdomeric photoreceptors: photosensitive surface develops from microvilli around cilium Most flatworms, mollusks, annelids,
arthropods, echinoderms
Photoreceptors dispersed though integument (protective area)
Ocellus: simplest eye, photoreceptors project into these pigmented sports or shallow cups of integument Can determine direction of light sourceUse light as cue for orientation, predators, bio-
clocks
Visual Field: part of outside world that eye sees
Eye lens: helps image formation, transparent structure, bends all light rays from a given point in the visual field so they converge onto photoreceptors
Cornea: helps sharpen images, transparent cover that directs light rays onto lens
Simple arthropod eye: one lens for all photoreceptors Spiders
Compound eye: many closely packed rhabdomeric units Some have thousands of units of a sort called
ommatidia, inside each is a photoreceptor with rhabdomeric microvilli; visual pigment rhodopsin, embedded in membrane
Visual mosaic: each unit samples small part of visual field
Crustaceans and insects
Camera eyes: most complexLight enters dark chamber through pupilAn opening in ring of contractile tissue called
iris Behind pupil, lens focus light on retina (tissue
with many photoreceptors) Axons of sensory nerves converge to form optic
tract One tract from each eye extends to brain Cephalopods: octopuses and squids
Wall of eyeball (three layers)
Sensory Tunic (inner layer)
Retina: absorbs, transduces light energy
Fovea: increases visual acuity
Vascular Tunic (middle layer)
Choroid: blood vessels nutritionally support wall cells, pigments prevent light scattering
Ciliary Body: muscles control lens; shape; fine fibers hold lens upright
Iris: adjusting iris controls incoming light
Pupil: serves as enterance for light
Start of optic Nerve: carries signals to brain
Fibrous Tunic (outer layer)
Sclera: protects eye ball (white of eye)
Cornea: focuses light
Interior of eyeball
Lens Focuses light on photoreceptors
Aqueous humor Transmits light, maintains pressure
Vitreous body Transmits light, supports lens and eyeball
Form an inverted, reversed image
When ciliary muscle contracts, lens bulges, bending light rays from a close object so that they become focused on the retina
When muscle relaxes, lens flattens, focusing light rays from a distant object on the retina
Species that move about in night or dimly lit areas need to intercept as much of the available light as possible
Large pupils let in more light Large irises can be dilated more to let in more light
In between retina and choroid is pigmented epithelium
Anchored to epithelium is rod and cone cellsCiliary photoreceptors
Rod and cone cells transduce photon energy into action potentials, messages by which brain cells monitor the visual field
Rod Cells: detect very dim light, basis for coarse perception of movement across visual field Most abundant outside fovea, small circular
region near centre of retina Has rhodopsin pigments Membrane folding and high density of
pigments increases odds of intercepting photons
Cone cells: detect bright light, basis of sharp vision and colour perception
Sense of colour and daytime vision starts when red, green, and blue cone cells, each with different kind of visual pigment, absorb photons
Fovea has greatest density of cone cells Basis of greatest visual acuity (most precise
discrimination between any 2 points in visual field)
Distinct types of sensory neurons lie above rods and cones
These neurons receive, process, and start to integrate signals that arise from transduction of photon energy
Input from about 125 million rods and cones converge on the retinal neurons known as bipolar cells
Humans have 11 types of bipolar neurons- 10 for cones, and 1 for rods
Sort out objects that are lighter than darker ones in visual field’s background
Information also flows laterally among amacrine cells and horizontal cells
Messages converge on 1 million ganglion cells
These are output neurons; axons are start of an optic nerve that carries action potentials to the brain
Before a transduced signal leaves the retina, neurons start integrating and processing it
Humans have 2 optic nerves, 1 from retina in each eye
Each optic nerve delivers signals concerning a stimulus from the left visual field to the right cerebral hemisphere And from right visual field
to left hemisphere
Optic nerve axons end in layered brain region- lateral geniculate nucleus
Each layer has map corresponding to receptive fieldsDeals with one kind of visual stimulus: form,
movement, depth, colour texture After early processing signals reach different parts of visual cortexIntegration organizes action potentials and produces visual sensations
Colour blindness: Cone cells fail to develop
Focusing problems: Astigmatism: unevenly curved corneas, cannot
properly bend all incoming light rays to same focal point
Myopia (nearsightedness): horizontal axis of eyeball is longer than vertical axis, or ciliary muscle responsible for adjusting lens contracts too strongly Outcome: images of distant get focused in front of retina
instead of on it Hyperopia (farsightedness): eyeballs vertical
axis is longer than horizontal Outcome: light rays from closeobjects get focused
behind retina