1Sensory ReceptorsSensations -- Action potentials that reach the brain via sensory neuronsPerceptions - the brains interpretation of sensations

Sensory reception - the detection of the energy of a stimulus by receptors in sensory cells

Sensory receptors specialized neurons or epithelial cells that respond to specific or generalized stimuli

What is stimulus?

Sensory Receptors Exteroreceptors detect stimuli outside the body

e.g. heat, light, pressure, chemicals

Interoreceptors - detect stimuli within the body, e.g. blood pressure (baroreceptors), body position (proprioreceptors: muscle spindles + tendon organs)

All stimuli represent Energy

Convert stimuli into membrane potentials and transmit signals to nervous system.

General Receptors or Special Receptors

General receptors -- throughout skin Or body: muscle spindles and tendon organs

Special Sense Receptors Given location(s) where stimuli are detected Taste buds, nasal cavity Eyes and ears

Figure 49.3 Sensory receptors in human skin

ThermoreceptorsHot or cold

PressureLight touch or deep pressure

Pain nocioreceptors

Sensory Receptors

Functions of Sensory Receptors1. Transduction 2. Amplification 3. Transmission 4. Integration

Sensory Receptors1. Sensory Transduction

Conversion of stimulus energy into membrane potential of receptor cell

Begins by a change in membrane permeabilityresults in graded change in membrane potential

RECEPTOR POTENTIAL

Is graded: proportional to strength of stimulus can be due to change in ion permeability :

1. as gated ion channels respond to receptor molecule(a ligand binds to)

2. or due to actual stretching of membrane in response to pressure.

2Sensory Receptors

2. Amplification - strengthening of a stimulus too weak to be carried into nervous system

Direct - Complex organ, ear: sound waves magnified 20X

Part of transduction in eye: 100,000X of action potential in signal to brain from eye, vs. few photons of light energy trigger process

Sensory Receptors

3. Transmission - conducting impulses to CNS

Some cases, pain receptor, is a sensory neuron that conducts signal

other receptors transmit chemical signals (neurotransmitters) across a synapse to a sensory neuron

Stimulus does not turn on/off production of action potential but controls the frequency with which they are generated can detect a change in stimulus intensity,not just presence or abscence of stimuli

Sensory Receptors

4. Integration - processing of information > begins immediately

integration via summation of graded potentials

Sensory adaptation specific type integration Decreased responsiveness to continued stimulation

Receptors are selective determine what signals sent to CNS otherwise would feel every heartbeat

Integration occurs at every level of nervous system cellular integration is only 1st step

Types of Receptors - type of energy transduced

1. Mechanoreceptors - mechanical energy: pressure, touch, stretch, motion, sound

2. Nocioreceptors - pain (mechanical or heat energy) 3. Thermoreceptors - temperature: heat or cold4. Chemoreceptors - general or specific chemical molecule

binds to site on membrane receptor protein

5. Electromagnetic receptors - electromagnetic energy (elec. Mag. spectrum) light, electricity, magnetism

6. Photoreceptors -- special kind of E.M.R. organized into eyes

Hearing and EquilibriumHuman ear: outer ear, middle ear, and inner ear

Outer ear pinna captures sound waves and

Auditory canal -- collects sound waves transfers to middle ear through tympanic membrane (eardrum)

Ossicles small bones in middle ear: malleus, incus & stapes

Vibrations of the ossicles help amplify and transmit energy to inner ear: to cochlea, snail through oval window.

Middle ear also has Eustachian tubes -- connect to nasal pharynx, allow equalizing pressure with external environment

Figure 49.17 Structure and function of the human ear

Organ of Corti has hair cells

3Figure 49.4 Mechanoreception by a hair cell

Hearing and Equilibrium Inner ear:

2 parts: cochlea and semicircular canals

1. cochlea 2 canals Vestibular and Tympanic, filled with fluid

Basilar membrane has Organ of Corticontains hair cells are actual receptor cells of ear

Sound waves are pressure waves transmitted through this series of structures.

Depolarization increases neurotransmitter release and frequency of action potential in adjacent sensory neuron.

Hearing and Equilibrium

Volume is determined by amplitude of sound wave (wave height) how loud

Pitch is determined by frequency of sound wave: (wave length) low or high sounds (base or treble)

Basilar membrane is not uniform all along its length but is stiff at proximal end and flexible at distal end. Each region is sensitive to a particular frequency of vibration.

> Perception of pitch depends on neural mapping in specific auditory areas of brain.

Human Hearing range: 20 Hz to 20,000 Hz.

Figure 49.18 How the cochlea distinguishes pitch

Hearing and Equilibrium

Inner ear: Semicircular canals 3 channels in inner ear responsible for

detecting body position & balance; equilibrium

hair cells respond to changes in movement with respect to gravity & position of the head.

Figure 49.19 Organs of balance in the inner ear

Semicircular Canals

4Figure 49.20 The lateral line system in a fish

ChemoreceptionPerceptions of smell and taste are interrelated

Receptor function is very similar: (no distinction in animals that inhabit an aqueous environment.)

Olfactory receptors -- Sensations of smell. Detect air borne chemicals, relay an electrical impulse via axons of chemoreceptor cells to olfactory bulb

Gustatory receptors -- Sensations of taste. Detection of chemicals in a solution, relay an electrical impulse via sensory neurons to thalamus for sorting, sends on to appropriate higher brain center

Figure 49.x1 Chemoreceptors: Snake tongue Figure 49.2 Sensory transduction by a taste receptor

Gustatory Receptors

Figure 49.24 Olfaction in humans

Olfactory receptors smell

Figure 49.5 Chemoreceptors in an insect: Female silk moth Bombyx morireleasing pheromones; SEM of male Bombyx mori antenna

5Figure 49.9 Structure of the vertebrate eyeVISION in the Vertebrate eye

Human eye can detect wide range colors, images of objects miles away, and respond to only one photon of light.

Sclera white outer layer of connective tissue, covered by conjunctiva except at

Cornea specialized part through which light can penetrate clear Choroid thin pigmented middle layer Iris specialized anterior choroid, muscle, changes size and

limits amount light that enters into eye Pupillary reflex Pupil opening where light enters in and hit lens and then retina Retina innermost layer contains photoreceptor cells

Rod and cones Lens a transparent disc (protein = crystaline) that focuses

light onto the retina

Figure 49.10 Focusing in the mammalian eye

Human eye

Ciliary body produces clear watery fluid (aqueous humor) fills anterior cavity of eye

Vitreous humor jelly-like fluid fills posterior cavity function with aqueous humor as liquid lens

helps focus light onto retina Lens has ability to change shape to focus light. Accommodation when focusing on near object lens

becomes thicker and rounder ciliary muscles contract Retina contains: photoreceptor cells 70% of all sensory

receptors 125 million rod cells & 6 million cone cells. Vision is

hugely important in human perception of environment.

Photopigments in Rod and Cone cells

Rhodopsin is the visual pigment in Rod Cells. Responsible for black and white vision in low light (Compensation for color.)

signal transduction pathway G protein in membrane Photopsins other opsins bound to retinal are responsive to

light energy in cone cells for color vision red, blue, green absorb at different wavelengths

Color blindness: different types Deficiency in or absence of one or more types of photopsin.

More common in males since is x-linked recessive trait.

Figure 49.11 Photoreceptors in the vertebrate retina

Rod cells dim light (b/w vision)

Cones cells color vision

6Bleaching and Regeneration

Retinal - vitamin A derivative + ospin = Rhodopsin Bleaching -- Rhodopsin changes shape as absorbs

light

Light energy isomerizes retinal unbinds from opsin clear = bleached activated

Transducin cascade causes closing of Na+ channel reduces depolarization, leads to hyperpolarization

Rhodopsin regenerates more slowly than photopsins in cone cells.

Figure 49.12 Effect of light on retinal

Bleaching and regeneration Figure 49.13 From light reception to receptor potential: A rod cells signal-transduction pathway

Optic pathway

Rod Cells & Cone cells synapse with bipolar cells , synapse with ganglion cells, help integrate visual stimuli

Vertical path receptor cell > bipolar cell > ganglion > brain. Lateral path horizontal cells & amacrine cells provide integration

leads to lateral inhibition

Horizontal cells inhibit more distant receptors and bipolar cells not receiving stimulus.. Leads to

CONTRAST makes light spot appear lighter & dark spot appear darker. Is repeated by amacrine cells interacting with ganglion cells

Occurs all level visual processing.

Figure 49.15 The vertebrate retina

7Light Stimulus

In Darkness -- partial depolarization causes continual release of glutamate causes Inhibitory Potentials in bipolar cells

Dim light -- small & brief receptor potentials LIGHTTurns off release of glutamate: turns off inhibition Brighter lights -- larger, longer receptor potentials,

less glutamate, inhibition totally removed

Figure 49.14 Effect of light on synapses between rod cells and bipolar cells

Figure 49.15x Photoreceptor cells

Optic Pathway

OPTIC NERVE is formed by axons of ganglion cells transmits sensations from eyes to brain

optic chiasm where two optic nerves meet Crossing

lateral geniculate nuclei of thalamus to primary visual cortex in occipital lobe of cerebrum

Figure 49.16 Neural pathways for vision

Left field of vision in Rt. eye crosses to left

side of Visual cortex

Right field of vision in Lft. Eye crosses to Right

side of visual cortex

Optic Chiasm -Is the crossing point of the

optic nerve fibers

Lateral geniculate nucleus is in THALAMUS

Figure 49.0 Bat locating a moth

8Vision and Hearing problems

Changes occur in eyes and ears that affect ability to see and hear.

Can occur during life or due to mutations

Vision problems

Myopia = nearsightedness Hyperopia = farsightedness Presbyopia gradually decreasing ability to focus on nearby

objects

Vision problems

Myopia = nearsightedness when light rays entering eye focus in front of the

retina, not directly on it. able to see close objects well, but objects in the

distancesuch as highway signs or writing on a chalkboardappear blurred.

People may squint to see distant objects experience eyestrain or, sometimes, headaches.

Eyeglasses or contact lenses can correct myopia. Surgery is another alternative.

Vision problems

Hyperopia = farsightedness, when light rays entering the eye focus behind the retina, not

directly on it.

People with hyperopia are usually able to see distant objects well, but close objects appear blurry.

Hyperopia may cause eyestrain or headaches, especially with reading.

Eyeglasses or contact lenses can correct hyperopia.

Laser vision correction is sometimes possible.

Presbyopia

Eyes gradually decreasing ability to focus on nearby objects. Presbyopia is a normal part of aging and affects virtually

everyone, usually becoming noticeable after age 40.

People typically hold reading materials at arm's length in order to bring the words into focus. may experience headaches or eyestrain while reading, viewing a computer screen;

Presbyopia can be corrected with reading glasses, bifocal or variable focus lenses, or contact lenses. Using bright, direct light when reading is also helpful.

Vision problems

Macular degeneration

Cataracts

Glaucoma

Aniridia

9Macular degeneration

causes dysfunction of the macula, an area in the middle of the retina that makes possible the sharp central vision needed reading, driving, and recognizing faces and colors.

age-related macular degeneration ARMD is the leading cause of visual impairment among older people.

causes blurred, distorted, or dim vision or a blind spot in the center of the visual field.

Macular degeneration Peripheral vision is generally not affected. painless and gradual the affected person at first notices little change.

No cure for macular degeneration, but drug therapy, laser surgery, or other medical treatment may in some cases be able to slow the disease's progression or prevent further vision loss.

People can benefit from the use of various devices for low vision, such as magnifiers, high-intensity lamps, and pocket-sized telescopes.

Cataracts

Condition in which the lens of the eye, (normally clear) becomes cloudy or opaque.

Cataracts generally form slowly and without pain. They can affect one or both eyes.

Over time, a cataract may interfere with vision, causing images to appear blurred or fuzzy and colors to seem faded.

Most cataracts are related to aging; more than 50 percent of all adults by age 80 and are the primary cause of vision loss in people 55 and older.

If cataract interferes with daily activities, surgery is the only effective treatment.

Cataract surgery, which is common, involves removal of the cloudy lens and replacement with an artificial lens.

Glaucoma

Pressure of the fluid inside the eye is too high, resulting in a loss of peripheral vision. If the condition is not diagnosed and treated, the increased

pressure can damage the optic nerve; eventually lead to total blindness.

Vision lost as a result of such damage cannot be restored.A person who has glaucoma may not realize it at first, because the disease often progresses with no symptoms or warning signs.

Early detection through regular eye examination and prompt treatment is essential to prevent vision loss.

Aniridia

Partial or complete absence of the iris of eye.

Rare condition, usually present at birth,

results in impaired vision and sensitivity to light.

At high risk for certain other eye conditions: glaucoma, nystagmus, and cataracts

May benefit from wearing tinted contact lenses or sunglasses, using

magnifiers, and avoiding intense or glaring light.

Causes of hearing loss

Conductive hearing loss

Sensorineural hearing loss

Genetic and/or congenital (present at birth)

Up to 48 % cases, cause remains unknown

10

Conductive hearing loss

interferes with transmission of sound from the outer to the inner ear.

1. middle ear infections (otitis media) 2. collection of fluid in middle ear ("glue ear" in children) 3. blockage of the outer ear (by wax)

4. damage to the eardrum by infection or an injury

5. otosclerosis, the ossicles of the middle ear become immobile because of growth of the surrounding bone

Sensorineural hearing loss p.1 due to damage to the pathway for sound impulses from the hair

cells of the inner ear to the auditory nerve and brain. 1. age-related hearing loss - decline in hearing that many people

experience as they get older 2. acoustic trauma to hair cells (injury caused by loud noise)

3. viral infections of the inner ear (e.g. by viruses such as mumps or measles)

3. Mnire's disease (abnormal pressure in the inner ear) 4. certain drugs, such as aspirin, quinine & some antibiotics, which

can affect the hair cells

Sensorineural hearing loss p.2 due to damage to the pathway for sound impulses from the hair

cells of the inner ear to auditory nerve & brain

5. a benign (non-cancerous) tumor affecting auditory nerve 6. viral infections of the auditory nerve (eg.

mumps or rubella) 7. infections or inflammation of the brain

or brain covering eg. meningitis8. multiple sclerosis 9. a brain tumor 10. a stroke

Deafness in children

Around one in 1000 children are deaf at the age of three.

problems with the birth (including premature birth), number of inherited conditions.

If a pregnant woman gets rubella, the baby is at risk of being born with profound deafness

importance of vaccination against rubella, via MMR vaccine.

Resources

Glossary of eye conditions

American Foundation for the Blind

http://www.afb.org/Section.asp?DocumentID=2139#macular%20degeneration

http://hcd2.bupa.co.uk/fact_sheets/Mosby_factsheets/Hearing_Loss.html

A British health care corporation