sensory and perception (sight and hearing) 7-3-11

8/6/2019 Sensory and Perception (Sight and Hearing) 7-3-11

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SENSORY & PERCEPTION:Si ht and Hearin

Read RAVEN Chapter 45, pg 915, Sensory system


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Learning objectives Describe thepathway of sensory information

Describe the types of receptor cellsand theirfunctions

EYE Describe the structureand thefocusing mechanismof the human eye Explain thepathway of lightin the human eye Describe the structureof the human retina

Explain thefunctions of the different cell typespresent in the human retina EAR

Describe the structure of the human ear Explain the functions of the OUTER-, MIDDLE- and INNER ear Explain the structure and transduction of the cochlea Describe the structure of VESTIBULAR APPARATUS > utricle, saccule and

semi-circular canals Compare the structure and function of the saccule and utriclewith that of the

semicircular canals in maintaining equilibrium

Outline the roles of vestibular apparatus in maintaining body equilibrium


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Pathway of sensory information.The types of receptor cells and their functions

Sight The human eye

Subtopic

Hearing The human ear


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basic of nervous system Membrane potential

Diff betw the electrical charges (voltage) inside and outside the cell

Resting potential Membrane potential of a cell that is not sending nerve impulses

Depolarized A stimulus> membrane potential> LESS negative than the resting

potential> region of the membrane Hyperpolarized

Membrane potential becomes MORE negative than resting potential

Hyperpolarization is inhibitory, decreases the ability of neuron to generate a

neural impulse An action potential (nerve impulse)

Is generated when the voltage is greater than the threshold level, >-55mV

Is an all-or-none response, either it occurs or it does not

No variation exists in the strength of a single impulse


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In general sense, RECEPTOR?? (recall chapter: Transport across cell membrane, Bio1) A membrane protein that changes shape when it binds a

specific hormone or neurotransmitter

In neurobiology, sensory receptor?? A specialized receptor cells, typical of a neuron OR

specialized cells in close contact with neuron ,

depolarizations or hyperpolarizations) in response to specificstimuli

Receptor potential is a graded response, magnitude of changedepends on the energy of stimulus

Freq of receptor potentials is how the brain determines theintensity of a stimulus

Receptor potential = graded response, like postsynaptic potential---EPSP/IPSP, X Actionpotential (all or none response)

Sensory neuron = a.k.a. afferent neuron (carry info toward CNS)


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Graded potential

Is a depolarization OR hyperpolarizationthat varies depending on the strength of

the stimulus


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A simple sensory pathway: Sensory processing

Reception: sensory receptor (extremely sensitive) receivingspecificstimuli from external (Exteroreceptors-heat, light, pressure,chemicals) and internal (Interoreceptors-blood pressure, body position)

Transduction: conversion of aphysical or chemical stimulus to voltagechange in the membrane potential (receptor potential is a graded

otentials ma nitude chan e accordin to the stren th of the

stimulus Transmission: Sensory information is transmitted through the

nervous system in the form of impulse, or action potentialsNote: Processing (integration) of sensory information occur as soon as the

information is received Perception:When action potentials reached the brain via sensory

neurons, perception (such as colours, smells, sound and tastes)constructed in the brain, by comparing present sensoryexperience with our memories of past experiences.


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A simple sensory pathway

Reception> Transduction> Transmission> Perception

SENSORY CELLSNEURON BRAIN

Sensory input is integrated at many levels

Sensory integration begins (1) in the receptor itself, integrated by summation (add up)

(2) Also, in spinal cord and brain


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Impulses from sensory receptor differ

Total no. of sensory neurons transmitting the signal

Specific neurons transmitting action potential & their target

Number action potentials transmitted by a given neuron

Freq of the action potentials transmitted by each neuron

. .intensity between the gentle rustling of leaves anda clap of thunder??

Number of neurons transmitting action potentialsFrequency of the action potential


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Sensory Adaptation: sensory receptors adapt to stimuli

Sensory adaptation If the stimulus continues at the same intensity, a sustained

stimulus

decrease in fre uenc of action otentials in a sensor neuron

even when stimulus is maintained (receptor sensitivitydecreases, lower freq of receptor potential)

OR decrease of the number of neurotransmitter from apresynaptic terminal, if series of action potential still persist

F: Enables one to discriminate between unimportantbackground stimuli that can be ignored and new, importantstimuli requires attention

EXCEPTION, receptors for pain and cold


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Types of sensory receptors Classified based on the type of stimulus to which they respond

FIVE types: (1) Mechanoreceptors,

,

(3) Electromagnetic receptors,

(4) Thermoreceptors and

(5) Pain receptors


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Mechanoreceptors

Receptors in the (1) skin (respond to touch, pressure), stretchreceptors in many (2) internal organs, position sensors in the (3)

joints and receptors in the (4) inner ear (detect sound)(1) SKIN:

several types of mechanoreceptor neurons, dendrite produces a receptorotential when its membrane is stretchor ressed

Dendrites (touch receptors) are free nerve endings, produce sensations ofitching or tickling, pain, touch, temperature

Other receptors enclosed in the connective tissue, Pacinian corpuscle (touchand deep pressure; E.g. vibration or a sharp poke!); Meissners corpuscle(touch and light pressure, conc in hairless skin); Merkels disc (touch)

Density of mechanoreceptors in skin varies (fingertips!!, lips)

(2) INTERNAL ORGANS

In many hollow organs (stomach, intestine, rectum and urinary bladder)

Signal fullness by responding to stretch


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Ruffini corpuscle(heat, pressure)

Free nerve endings(pain)

HairMeissner corpuscle(touch, pressure)

Merkel disc(touch, pressure)

Epider

mis

Fig. 42-4a, p. 899

Dermis

S

ubcutaneous

tissue

Pacinian corpuscle(deep pressure,

touch)Hair follicle receptor(hair displacement)


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3. Ruffini

corpuscle

2. Meissnercorpuscle

1. Merkle

cell

4. Paciniancorpuscle

Free nerve

ending

1. Merkle Cell 2. Meissner Corpuscle

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

3. Ruffini Corpuscle

Tonic receptors locatednear the surface of the

skin that are sensitiveto touch pressure and

duration.

Tonic receptors locatednear the surface of the

skin that are sensitiveto touch pressure and

duration.

Receptors sensitive tofine touch, concentratedin hairless skin.

4. Pacinian Corpuscle

Pressure-sensitive

receptors deep belowthe skin in the

subcutaneous tissue.


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Pacinian corpuscle,

Fig. 42-4b, p. 899

receptor


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(4) Other mechanoreceptor sensemovement of hairs

E.g.

Cats and rodent: at the base of their whiskers

Deflection of the whiskers triggers action potential,provide detailed information of nearby objects


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Mechanoreceptors

(3) JOINTS

Proprioceptors: Allow animal toperceive body orientation andpositions of its parts

ypes

(i) Muscle spindles; detect musclemovement

(ii) Golgi tendon organs, tension in

contracting muscles and in tendons

(iii)Joint receptors, detect movement ofligaments


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Nerve

Biceps extension

causes it to stretch

Specializedmuscle fibers(spindle fibers)


Skeletal muscle

Motor neurons

Sensory neurons

MUSCLESPINDLES,

Stretch receptorembedded within

skeletal muscleStretching of the muscle

elongates the spindle fibers,stimulates sensory dentriticending wrapped around them


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Chemoreceptors Receptors that transmit information about total

solute [ c ] or individuals types of molecules

E.g. in human brain, osmoreceptors,

etect c anges n so ute c o t e oo , st mu atethirst when osmolarity increases

Receptors for specific molecules:

Glucose, oxygen, carbon dioxide and amino acids


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Electromagnetic receptors Detect various forms of electromagnetic energy

Visible light, electricity, magnetism Photoreceptors (eyes)

Infrared receptors (snakes)

Detect body heat of prey


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Electroreceptors

Some fishes generates electrical current; to locate prey thatdisturb those current

Platypus has electroreceptors on its bill, detect electric fieldsby the muscle of crustacean, frogs, small fish

Electromagnetic receptors

mportant n commun cat on, recogn z ng a potent a mate,male and female have diff. freq. of electrical charges

Electromagnetic receptors Many animals use Earths magnetic field, migratory birds and

sea turtles navigate by magnetic fields Iron-containing mineral magnetite found in the skulls of

vertebrates (salmon, pigeon, sea turtles and humans), in theabdomen of bees, in the teeth of the molluscs, in certainprotists and prokaryotes


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Thermoreceptors

Detect heat and cold

Location

External changes---SKIN: Ruffini nerve ending,

Internal changes----- themoreceptor cells in the

hypothalamus


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Thermoreceptors: heat and cold

The pit organ (sense organ)

of a viper, located betweeneye and nostril Locate their prey

Detect the heat from

endothermic animal asinfrared radiation, up to adistance of 1 to 2 meter

Mosquitoes and otherblood-sucking arthropods(ticks or mites) Locate an endothermic host

Pit vipers and boas use thermoreceptors to

locate their prey


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Pain receptors

Extreme pressure, temperature, certain chemicals can damageanimal tissues

To detect stimuli that reflects such harmful conditions animals

Leprosy or Hansens disease, tissue damage results because of the

warning system of pain has fallen silent

rely on nocireceptors (Latin: nocere, hurt) The capsaicin receptor, act as thermoreceptor, is also a

nocireceptor

Nocireceptor highest density in skin, some associate in other

organs E.g. Damage tissues produce prostaglandins (a local regulators of

inflammation), increase nocireceptor sensitivity to noxious stimuli

Painkiller (aspirin and ibuprofen) reduce pain by inhibiting the

synthesis of prostaglandin


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HUMAN EYES

Position of the eyes: in font of the headTo allow both eyes to focus on the same object, overlap

information

BINOCULAR VISION:Three-d images, judging distance & in depth perception


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Anatomy of the human eye Conjunctiva

Transparent mucous membrane covering the anterior portion of the sclera & the

inner surface of eyelids, NOT on the cornea F: Lubricates and protect the eyes

When infected, called conjunctivitis

Is the transparent, curved front of the eye, helps to converge the light rays F: bends the light rays, can be brought to a focus

Defects of corneal curvature: astigmatism

Sclera (forms the white of the eye)

Is an opaque (not transparent, not transmitting light), fibrous, protectiveouter structure

F: Provides attachment surfaces of eye muscles, helps maintain the rigidityof the eyeball


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Astigmatism


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Choroid F: Has a network of b.v, supply nutrients to the cells and remove waste

products

F: Pigmentedthat makes the retina appear black,preventing reflection of lightwithin the eyeball

Anatomy of the human eye

A layer ofsensory neuronsandphotoreceptors(rod and cone cells) F: Contains relay neurons and sensory neurons that pass impulses > the

optic nerve > part of the brain that controls vision

Lens

A transparent, flexible, curved structure Biconvex crystal-like structure

Held in place by a suspensory ligament attached to the ciliary body

F:To focus incoming light rays onto the retina with its refractive

properties


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Iris Is a pigmented muscular, consisting of an INNER ring of

circular muscle (IC) and an OUTER layer of radial muscle(OR)

F: Function to help control the amount of light entering the


Too much light, would damaged the retina

Pupil

A pinhole in the middle of the iris where light is allowed tocontinue its passage

F: Regulates the size of the light opening Bright light: it is constricted

Dim light: it is dilated


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Ciliary body F: Secretes the aqueous humour, exits through canal of Schlemm Excessive fluid pressure: Glaucoma, cause blindness Has suspensory ligaments, hold the lens in place Contains ciliary muscles, enable the lens to change shape during

accommodation ocusin on near and distant ob ects


Aqueous humour (Anterior chamber) Fluid filled region in frontof the lens, Similar to blood plasma Provides nutrients for the lens and cornea Reabsorbed into venous blood Blocked drainage, risk factor for the disease, glaucoma (degeneration of the

optic nerve) F: Maintain the shape of the anterior chamber of the eyeball

Vitreous humour (Posterior chamber) Fluid filled region behindthe lens, Lasts a lifetime and is not replaced

F: Maintain the shape of the posterior chamber of the eyeball

Copyright The McGraw-Hill Companies Inc Permission required for reproduction or display


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Opticnerve

Vein

Artery

Iris

Cornea

Lens

Suspensory

ligament

Pupil

Copyright The McGraw Hill Companies, Inc. Permission required for reproduction or display.

32

Retina

Lens

Suspensory ligament

Sclera

Ciliary muscle

Ciliary muscle


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Choroid

RetinaSuspensoryligaments

Sclera

Iris

Anteriorcavity

LensPathwayof

Fig. 42-18, p. 911

light

Pupil OpticnerveCornea

ConjunctivaBlind

spotCiliarybody

Ciliary muscleCiliary process

Retinalarteries

and veins

Posteriorcavity Vitreous

body

Fovea


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The conjunctiva is a thin membrane that covers the surface of the inner eyelidand the white part of the eyeball.

Inflammation of the conjunctiva is called conjunctivitis, which makes the white ofthe eye appear red.


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Conjunctiva

Palpebral (eyelid)

conjunctiva The portion that lines the

inner surface of the eyelids ---

-appears shiny pink or red Bulbar conjunctiva

Joins the palpebral portion

and covers the exposed partof the sclera, contains manysmall, normally visible blood

vessels


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Fovea

An area of the retina, opposite the pupil

contains ONLY cone cells

espons e or goo v sua acu y

Defects in fovea: Macular degeneration, you can only seeperiphery

Macula

An elevated region, contains the ganglion and bipolar cells ofthe fovea centralis


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The blind spot

All the nerve impulses generated in the retina travelback to the brain

by way of the axons in the optic nerve

At the point on the retina where the approximately 1million axons converge on the optic nerve,

there are no rods or cones

This spot, called the blind spot, insensitive to light.


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Refraction and Inversion of image

Refraction: bending of light rays that enter the

eye, creates focus Inversion: Image pattern is projected onto the

Q: Why does the image appear to you to be rightside up?


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The bending of the incoming light results in an upside-downimage on the retina, BUT the brain reconstruct the image andperceive the image correctly

Image falling on theretina is inverted and

smaller than the object

A d i


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Accommodation: Ability to change focus for near and far vision bychanging the shape of the lens-is accomplished byciliary muscle,Lens can change its curvature to focus an image

Ciliary muscle relax, border ofchoroid moves away from lens

Pull suspensory ligaments away

Accommodation

Near vision

Far vision

Ciliary muscle contract, pullingborder of choroid toward lens

suspensory ligaments loosen

Lens more ROUND

rom ens

Lens more FLAT

Light passing through it bendsLESS


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Accommodation

Contraction and relaxation of ciliary muscles

changes the tension on the lens When the lens is pulled thin, it bends light less

ur enses are pu e t n w en we ocus t e para erays of light from distant objects

When the lens revert to a fat, convex shape, it

bends light more, when we focus the light rays from near objects


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Accommodation also involveschan es in the u il sizes


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IRIS The amount of light entering the eye

is regulated by the IRIS

Pigmented iris: a ring of smooth muscle, appears as

, ,

Consists of two antagonists sets ofmuscle fibers, (1) circular muscle/innerring and (2) radial muscle/outer ring

To decrease the size of pupil, circularmuscle contract

To increase the size of pupil, radial

muscle contract


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Lens gets more rigid with ageA condition called:

Presbyopia

Loss of accommodation ability

-

things up close.

It affects all of us once we reach our 40s.

Biconvex corrective lenses, for near-vision task

(E.g. Reading)


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Near- & Far-sightedness

are due to abnormal eye shape


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Hyperopia vs Myopia Farsightedness - is called Hyperopia

Produce clear images from distant objects but blurred image fromnear objects

If the eyeball is too short or the lens too flat/ inflexible, Focal point falls behind the retina

Eyeglasses with convex lenses

Nearsightedness - is called Myopia (Children -20 yr old) Produce blurred images from distant objects bur clear images from

near objects

If the eyeball is too longor the lens too spherical,

the image ofdistant objects is brought to a focus in front ofthe retina

Nearby objects can be seen more easily.

Eyeglasses with concave lenses correct this problem by

diverging the light rays before they enter the eye.


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Farsightedness (hyperopia) ~the eye cannot focus on nearby objects.The eye is too short or the cornea is too flat.

A person has hyperopia when light entering the eye is focused (calledthe focal point) behind the retina instead of directly on the retina.


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Photoreceptors: Rods and Cones The human retina contains two types of photoreceptors Photoreceptors, linked to neuron, are located in the retina

(1) Rods sensitive to light (low-intensity of light) but do not distinguish colors function in dim light (dim light vision) , form images in black and white (grayscale)

Use for peripheral vision and (B & W) night vision

(2) Cones function in bright light distinguish colors but are not as sensitive as rods permit high-acuity color vision Colour daylight vision Fovea centralis area of the retina with only cones

NOTE: No photoreceptor cells are at the optic disk, or blind spot


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Distribution of photoreceptors in the retina

The fovea centralis is all cones BUT the

periphery is predominantly rods You have good colour vision in the center of your

,

At night, your vision is best NOT in the center, but

a little bit to the side

Stars look brighter if you dont look directly at them


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Photopigments: Rhodopsin (Rods) andPhotopsins/Iodopsin (Cones)

In both rod and cone cells

Infoldings of plasma membrane form stacks of membranous discs, containphotopigments

Each rod or cone in the vertebrate retina -

(derivative of vit A) bonded to a protein called opsin

Rods the visual pigment, Rhodopsin (Rod-opsin)

Absorption of light by rhodopsinchanges the shape of rhodopsin(cis isomer to trans isomer)

Light activation of rhodopsin is called bleaching

Activated retinal NO longer binds to opsin

If the amount of light decrease abruptly, the bleached rods do not

regain full responsiveness for several minutes


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Absorption of light by retinal

Triggers a signal transduction pathway

NOTE that in rods and cones, the receptor potential is ahyperpolarization, not a depolarization

In the dark, enzymes convert retinal back to cis form, combineswith opsin-form Rhodopsin, sodium channels are open.The rod cell is depolarized and release inhibitoryneurotransmitter Li ht makes rhodo sin

A

change shape,Absorption of lightconverts the cis isomerto trans isomer,

activating a signaltransduction, lead tohyperpolarization and adecrease in inhibitorysignals from rod cells

A B


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DARK- rod and conesare depolarized,continually release

neurotransmitterglutamate, hyperpolarizesthe membrane of bipolar

Dark Responses

Rhodopsin inactive

Na+ channels open

Light Responses

Rhodopsinactive

Na+ channels closed

LIGHT -The bipolar cellsdepolarize, in response tono release of glutamate

when rod hyperpolarize

Rod depolarized

Glutamatereleased

Bipolar cellhyperpolarized

Rod hyperpolarized

No glutamatereleased

Bipolar celldepolarized


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Sensory transduction in photoreceptors

DARK~ Photoreceptor cells depolarize, release

inhibitory neurotransmitter that hyperpolarizesthe bipolar neurons

excitatory neurotransmitter to the ganglion cells thatsignal to the brain

LIGHT~ Photoreceptor cells stop releasing

their inhibitory neurotransmitter to bipolar cells

Bipolar cells depolarize, in turn stimulate theganglion cells, transmit action potentials to the brain


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Cones -three types of cones, visual pigments--Photopsins, respond either to: Blue (455nm), Green (530nm) and Red (625nm) light

Any given cone cell makes only one type of cone pigment

Photopsins formed frm binding of retinal to three distinct

Colour blindness: Defects in the cone pigments arising from mutations in the

opsin genes

An inherited X-linked condition, oft sex linked, 8-10%males are colour blind

Green/red blindness

Blue pigment gene is on chromosome 7


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Neurons of the RetinaNeurons of the Retina

Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings


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R d



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Outer segmentInner segmentSynapticterminal

Rod

Connecting cilium

57

discs

Cone


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Neuronal organization and integration in RETINA

Light has to travel through a number of nerve layerto reach these photoreceptors


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TWO types of lateral interneuron:

Horizontal cells

receive signals from rods andcones

send signals to bipolar cellsBipolar

Photo-receptor cells

Amacrine cells

receive signals from bipolar cells

send signals back to bipolar cellsand ganglion cells

Ganglioncell

cell

Horizontal and amacrine cells integrateinformation across the retina


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Cones: Visual acuityVisual acuity: is a measure of

the detailwe can see

The cones-responsible for high

visual acuity (HIGHRESOLUTION!!)

ONE cone cell synapses onto

ONE bipolar cell, which in turnsynapses onto ONE ganglion

cell


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Rods: Convergence

A ray of light reaching one rod may

NOT be enough to stimulate anaction potential along a pathway

cell So that, enough transmitter

molecules at a synapse reach the

threshold level

SUMMATION, as a result of rodcell teamwork!


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Visual pathway

Light passes through cornea > through aqueoushumour > through lens > through vitreoushumour > image forms on photoreceptor cells

in retina > signal bipolar cells > signal ganglioncells > optic nerve transmits signals to thalamus> integration by visual areas of cerebral cortex


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Integration of visual information begins in the retina

(1) The ganglion cells detect basic informationabout image

(2) Neurons from part of each visual field crossover to the other side of the brain --at theoptic chiasm,

(3) Axons of the optic nerves end in the lateral

geniculate nuclei of the thalamus, send signalto primary visual cortex (in the occipital lobeof the cerebrum)


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Left eye Right eye

Optic nerve

Optic chiasm

Fig. 42-23, p. 915

Optic tract

Lateral geniculatenucleus of thalamus

Occipital lobe

Nocturnal animals have mostly rod vision!!!


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Cats, raccoons and other nocturnal animals have a high proportion ofrods in retina, an adaptation that gives these animals a night vision

Have a light-reflecting surface behind the retinas in their eyes, which

which help them to see when the light is very dim.

Eyes 'glow' in the beam of

a headlight


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The choroid is a layer of tissue at the back of the eye that contains alarge number ofblood vessels.

"Red eye" usually happens when a flash photograph is taken in dimlight.

In dim light, the pupil is dilated and allows plenty of light to enter the

"red eye in your photograph

eye.

"Red eye" is caused when the choroid reflects the light of the flash.

The pupil does not constrict fast enough to reduce the entering lightand the flash light reflects back out of the eye and is recorded on film.Some cameras use red eye reduction methods: a short burst of light isemitted before the film is exposed. The brief burst of light allows thepupil to constrict and thus reduces "red eye


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Hearing

The sensory organs for hearingandequilibrium are closely associated, in

the human ear

EF


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B C DG

H

I

J

Fig. 42-8a, p. 902

K

L

M

N

A

Auditory bonesSemicircular

l


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Malleus Incus Stapescanals

Oval window

Vestibularnerve

CochlearnerveCochlea

Fig. 42-8a, p. 902

Vestibule

Roundwindow

Tympanicmembrane

Eustachiantube

Auditory canal


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Anatomy of the earThree regions: OUTER,

MIDDLE & INNER ear

(1) OUTER ear

Pinna Auditor canal

(passageway for sound),Tympanic membrane

(eardrum),

F: Collects sound wavesand channels them inward


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(2) MIDDLE ear Called tympanic cavity-filled with air, contains auditory ossicles

Auditory ossicles > Malleus, Incus, Stapes

Malleus (Hammer): 1st

bone attached to the eardrum Incus (Anvil): Middle ear bone

Stapes (Stirrup): Attaches to the oval window

F: Magnifies sound, Conveys sound vibrations to the oval

window

F:To couple sound waves in the air with the pressure wavesconducted through the fluid in the cochlea

Opens into the Eustachian tube, connects with thenasopharynx, Equalizes pressure between the middle ear and

the atmosphere (Enabling you to pop your ears when youchange altitude)


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(3) INNER ear

Oval window, Round window, Cochlea, Vestibularapparatus/organs

-

Two major sensory structuresVestibular apparatus with semicircular canals:

Sensory transducer for our sense ofEquilibrium

Cochlea: Sensory receptor for Hearing


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Vestibular apparatus, contain receptors for equilibrium Vestibular apparatus - saccule, utricle and three semicircular canals

Sensory cells of the saccule and utricle: hairs cells

The receptor cells of saccule and utricle lie in different plane A hair cell: a single kinocilium (true cilium) and many shorter

stereocilia (microvilli; hairlike projections that increase in length from

Hair cells are covered by a gelatinous cupula (/KU-pu-la/) Calcium carbonate ear stones- otoliths (oto=ear; -liths= stones)embedded in the cupula

Pull of gravitycauses the otoliths to press against the stereocilia,

stimulating to initiate impulses Deflection of stereocilia toward the kinocilium depolarizesthe hair cell Deflection in the opposite direction hyperpolarizesthe hair cell

Depending on the direction of movement, the hair cells release more

or less neurotransmitter


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Changes in head position cause the force of gravity to distort the cupula,which in turn distorts the stereocilia of the hair cells.

Hair cells responded by releasing neurotransmitters.

Impulses are transmitted along the vestibulocochlear nerve to the brain


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Linear acceleration: increasin s eed when the

body is moving straight line, sense bysaccule(vertical) and utricle(horizontal), allowing one toknow one position relative to the ground

Angular acceleration: Turning movement, sense bythecircular canals

Semicircular canals



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Cochlea

Vestibular nerve

Kinocilium

StereociliaSensoryneuron

Utricle(horizontalacceleration) Saccule (vertical

acceleration)Gelatinous

Hair cell

Gravitationalforce

79

Otoliths

Hair cells

Signal

Supportingcells

Stationary Movement

a. b.

Semicircular


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canals

Membranouslabyrinth

Bonylabyrinth

Cochlear nerve Ampullae

Utricle

Vestibulocochlear

Fig. 42-8b, p. 902

SacculeVestibular nerve

Cochlea

Vestibular apparatus

3 semicircular canals lying in three different plane>Anterior, posterior and lateralHead movement in any direction

> stimulates fluid movement in at least one of the canals

The semicircular canals, arranged in

Each canal has at its base aswelling called an ampulla,


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, g

three spatial planes, detect angularmovements of the head.

Vestibular nerve

g p

containing a cluster of haircells crista (pl:cristae)

Flowof endolymph

Flowof endolymph

When the head changes its rateof rotation, the endolymphpresses against the cupula,bending the hairs.

Cu ula

The utricle and saccule tell the brainwhich way is up and inform it of thebodys position or linear acceleration.

Vestibule

Utricle

Saccule

The hairs of the hair cellsproject into a gelatinous capcalled the cupula.

Body movement

Nervefibers

Hairs

Haircell

Bending of the hairs increasesthe frequency of actionpotentials in sensory neurons indirect proportion to the amount

of rotational acceleration.


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Bonyportion

Membranousportion

Fig. 42-10, p. 904

upu a(pushed to left) Endolymph

flow

CristaBent stereociliaof hair cellsVestibular nerve

Direction of body movement


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Humans are used to movements inthe horizontal lane

But NOT to vertical movement

E.g. motion of an elevator or ship

pitching in a rough sea


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Cochlea, contains receptors for hearingThe cochlea (Latin: snail)

Has two large canals- an UPPERvestibular canal & a LOWERtympanic

Vestibular and tympanic canals contain fluid:perilymph

Cochlear duct: endolymph

Organ of Corti

The organ of Corti lies within themiddle chamber of the cochlea

Physiology of the ear: Hearing


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1. Sound waves are directed towards the tympanic membrane through theauditory canal.

2. They reach the tympanic membrane which vibrates as a result.

3. The ossicle bones then pass on and amplify these vibrations.

4. The membrane of the oval window then vibrates and passes on these.

5. The pressure waves (vibration conducted through the fluid) cause themovements of the fluid perilymph pass through the cochlea

6. The movements of basilar membrane cause the stereocilia of the organ ofcorti rub against the overlying tectorial membrane

6. Physical hair movements result in the ions channels open (in the plasmamembrane of hair cells)> calcium move into hair cells> cause the release ofglutamate (neurotransmitter) > bind to the receptors on the sensory neuron

7. The generation of action potentials which pass along the auditory nerve


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What is the function of themembranous round window??

The round window allows for fluid dis lacement in thecochlea.

EXPLANATION:

Liquids cannot be compressed, the oval window could notcause movement of the fluid in the vestibular canal if there

were no escape valve for the pressure.The round window serves as a pressure valve, bulging outwardas fluid pressure rises in the inner ear.


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Anterior view of thehuman ear

Organ of Corti


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Vestibular canal

Tectorialmembrane

Cochlearduct

Sterocilia

Fig. 42-11c, p. 905

Hair cell

Cochlearnerve

Basilarmembrane

Tympanic canal Fluid vibrations

Pi h L d d li


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Pitch, Loudness and tone quality Sounds differ in pitch, loudness and tone quality (timbre) Pitch (musical notes; the frequency of sound vibrations, vibration per

second), hertz (Hz), Human normal range: 20-20 000 Hz

Low freq vibration: low pitch/low notes near tip of the cochlea High freq: high pitch/high notes near the oval window The brain infers the pitch of a sound from the particular hair cells

ou ness e magn u e o soun v ra ons Soft sound---small vibrations of the tympanic membrane, bones of the middle

ear, oval window, and the basilar membrane, hair bends a little> hair cellproduce small receptor potential, tiny bit neurotransmitter released

Loud Sound---large vibration, greater bending of the hair cells, larger receptorpotential

EXTREMELY loud sounds cld damage the hair cells!!!!!, hearing loss-Rockmusicians, Hair cells in human do not regenerate.

Tone quality (timbre) Many hair cells are stimulated simultaneously, differences in tone quality are

recognized in the pattern of hair cells stimulated


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sensory and perception (sight and hearing) 7-3-11

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