Transcript Visual Field - Warren`s Science Page

Sensory Perception: A Summary
AP Biology
Spring 2011
Reception of stimulus
energy
Transduction
of stimulus
energy
Brain response
(sensation or
perception)
 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)
receptors
 Osmoreceptors: 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 tissues
 Many 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 stimulus
 Ex. The pressure exerted by a sock
 Example of how we make use of sensory pathways
 Figure 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 tissues
 Thermoreceptos, mechanorecptors, and pain receptors
 Adapt 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 Krause
 Thermoreceptor, 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 stretches
 Signal 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, tendons
 Superficial 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 enkephalins
 Lower 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 amplified
 Bad sunburn and hot shower
 Referred pain: perception of visceral sensations as
somatic sensations
 Ex. Heart attack
 Makes mistake because of nervous system construction
 Sensory inputs of
skin and certain
internal organs enter
same segments of
spinal cord
 Skin 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 slightly
 If 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 head
 Auditory 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, stirrup
 By 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, cochlea
 Cochlea: pea sized, fluid-filled structure,
transduction of waves of sound into action potentials
occurs here
 Sound waves make stirrup vibrate
 Middle ear bone pushes against oval window
 Transmits 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 vibrate
 Low 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 source
 Use 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 complex
 Light enters dark chamber through pupil
 An 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 cells
 Ciliary 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 fields
 Deals with one kind of visual stimulus: form,
movement, depth, colour texture
 After early processing signals
reach different parts of visual
cortex
 Integration 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