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