Chapter 12

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Chapter 12

NERVE ENDINGS

FREE NERVE ENDING

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SPECIAL RECEPTOR CELL

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RECEPTOR TYPES

 CHEMORECEPTORS  NOCICEPTORS  THERMORECEPTORS  MECHNORECEPTORS  PHOTORECEPTORS

CHEMORECEPTORS

 CHEMICAL CONCENTRATIONS  SMELL, TASTE

MECHANORECEPTORS

 DETECT CHANGES OF PRESSURE, MOVEMENT,  TYPES: – PROPRIOCEPTORS – BARORECEPTORS – STRETCH RECEPTORS

1 Peri-trichal

(around hair follicle)

“TOUCH” -

hair displacement

RECEPTOR MODALITIES 3 Merkel cell 2 Free endings TOUCH TOUCH COLD PAIN 4 Meissner’s corpuscle 6

Ruffini corpuscle

CT DISPLACEMENT *

wberesford.hsc.wvu.edu

Pacinian corpuscle 5 TOUCH VIBRATION Meisner’s corpuscle

* slowly adapting

PACINIAN CORPUSCLE

d-mis-web.ana.bris.ac.uk

MEISNER’S CORPUSCLE

d-mis-web.ana.bris.ac.uk

BARORECEPTOR

.cvphysiology.com

STRETCH RECEPTORS

users.rcn.com/jkimball.ma.ultranet/BiologyPages

PROPRIOCEPTORS

 CHANGE IN LENGTH OF MUSCLE, MUSCLE TENSION  PRESSURE  GRAVITY http://courses.washington.edu/conj/bess/spindle/proprioceptors.html

THERMORECEPTORS

 TEMPERATURE CHANGE  HEAT: RUFFINI’S END ORGAN  LOSS OF HEAT: KRAUSE CELL

 COLD

KRAUSE CELLS

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 HEAT

RUFFINI’S END ORGAN

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NOCICEPTORS

 PAIN  TISSUE DAMAGE DUE TO: EXCESSIVE MECHANICAL, ELECTRICAL, THERMAL, OR CHEMICAL ENERGY  FREE NERVE ENDING

NOCICEPTORS

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PHOTRECEPTORS

 LIGHT  RODS AND CONES

<> .webvision.med.utah.edu

PAIN PATHWAYS

 ACUTE PAIN/ FAST PAIN: – THIN, MYELINATED FIBERS, Aδ FIBERS – 6-30 M/SEC, DETECTED WITHIN A TENTH OF A SECOND – SHARP, PRICKLING PAIN – MECHANICAL AND THERMAL PAIN

PAIN PATHWAYS

 CHRONIC PAIN – THIN, UNMYELINATED C FIBERS – 0.5 TO 2 METERS/SEC – ACHING, THROBING, BURNING PAIN – CHEMICAL PAIN

SEROTONIN

digital-fx.ca/cme/neuro

PULMONARY AND CARDIAC STRETCH RECEPTORS .lib.mcg.edu

MUSCLE SPINDLE

.lib.mcg.edu

MUSCLE SPINDLE

 NEAR JUNCTIONS WITH TENDONS – INTRAFUSAL FIBERS: MODIFIED SKELETAL MUSCLE FIBERS – COVERED BY A CONNECTIVE TISSUE SHEATH – CENTER: NONSTRIATED WITH A DENDRITE WRAPPED AROUND IT

MUSCLE SPINDLE FUNCTION

– STRIATED PORTIONS CONTARACT: SPINDLE RELAXES – WHOLE MUSCLE RELAXES: SPINDLE STRETCHES AND SENDS IMPULSE TO SPINAL CORD TO MOTOR NEURON TO MUSCLE – MUSCLE CONTRACTS AND OPPOSES GRAVITATIONAL PULL: STRETCH REFLEX

GOLGI TENDON ORGAN

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GOLGI TENDON ORGAN

 IN TENDONS; CLOSE TO MUSCLE ATTACHMENT – CONNECTED TO A SET OF SKELETAL MUSCLE FIBERS – HIGH THRESHOLD – STIMULATED BY INCREASED TENSION

GOLGI TENDON ORGAN FUNCTION – STIMULATED BY INCREASED TENSION – INHIBITS CONTRACTION OF MUSCLES – OPPOSITE OF STRETCH REFLEX – HELPS MAINTAIN POSTURE – PROTECTS AGAINST MUSCLE ATTACHMENTS BEING PULLED AWAY FROM INSERTIONS

SPECIAL SENSES

 RECEPTOR: – INDIVIDUAL CELL OR AN EYE OR AN EAR  MEMBRANE RECEPTOR: – PROTEIN ON PLASMA MEMBRANE

SMELL

 OLFACTORY RECEPTORS FOUND IN THE OLFACTORY EPITHELIUM OF NASAL CAVITY: CHEMORECEPTORS  1000 GENES CODE FOR THE RECEPTORS  A RECEPTOR CELL HAS ONLY ONE TYPE OF RECEPTOR WHICH CAN ONLY DETECT A FEW NUMBER OF ODORS

OLFACTORY RECEPTORS

 THE RECEPTORS HAVE 10-20 CILLIA WHICH STICK INTO THE CAVITY AND ARE THE SENSITIVE AREA  THERE ARE ABOUT 40 RECEPTORS; BIPOLAR NEURONS  ALSO COLUMNAR EPITHELIUM AND MUCOUS CELLS

OLFACTORY RECEPTOR

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OLFACTORY RECEPTOR

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OLFACTORY RECEPTORS

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OLFACTORY RECEPTORS

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OLFACTORY ACTION

 CHEMICALS ENTER AS A GAS  DISSOLVE IN MUCOUS  CHEMICALS BIND TO SPECIFIC MEMBRANE RECEPTORS AND DEPOLARIZE THE NEURON

/users.rcn.com/jkimball.ma.ultranet

faculty.washington.edu

OLFACTORY PATHWAY

   OLFACTORY RECEPTOR IS STIMULATED AND FORMS AN IMPULSE IMPULSE TRAVELS ALONG THE AXON TO THE MITRAL CELLS OF THE OLFACTORY BULB TRAVELS BY OLFACTORY TRACT TO LIMBIC SYSTEM DEEP IN CEREBRAL CORTEX OF TEMPORAL AND FRONTAL LOBES

OLFACTORY PATHWAY CONT.

   IMPULSES FROM THE OLFACTORY RECEPTORS ARE TRANSLATED BY THE BRAIN AS AN OLFACTORY CODE RAPID SENSORY ADAPTATION; 50% IN 1 SECOND, INSENSITIVE WITHIN 1 MINUTE IN DIRECT CONTACT WITH ENVIRONMENT SO OFTEN DESTROYED AND NOT USUALLY REPLACED; COULD LOSE 1%/YEAR

SMELL

 MOST PEOPLE CAN DETECT BETWEEN 3,000 AND 10,000 ODORS

TASTE

    TASTE BUDS CONTAIN GUSTATORY CELLS TASTE BUDS FOUND ON PAPILLAE OF TONGUE, ROOF OF MOUTH, LINING OF CHEEKS, WALLS OF PHARYNX RECEPTORS: MODIFIED EPITHEILIAL CELLS 10,000 TASTE BUDS WITH 50-100 RECEPTOR CELLS EACH

TASTE BUD

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TASTE BUD

TASTE CELL

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TASTE

 TASTE BUD HAS A PORE THAT ALLOWS TASTANTS (CHEMICALS) TO ENTER AND STIMULATE TRANSMEMBRANE RECEPTOR  5 TASTE SENSES: SALTY; SOUR; SWEET; BITTER, UMAMI (GLUTAMIC ACID SALTS)  EACH BUD HAS ALL 5 RECEPTORS

TASTES

     SWEET: – CARBOHYDRATES, SOME INORGANIC SUBSTANCES SOUR: – ACIDS, CONCENTRATION OF HYDROGEN IONS SALT: – IONIZED INORGANIC SALTS, DEPENDS ON TYPE OF CATION BITTER: – MANY ORGANIC SUBSTANCES, INORGANIC SALTS, ALKALOIDS, POISONS UMAMI: – MSG, PARMESAN CHEESE

pubs.acs.org

TASTE PATHWAY

    TASTE RECEPTOR IS STIMULATED; DEPOLARIZING NEURON: FORMING IMPULSE CARRIED BY THREE CRANIAL NERVES; FACIAL NERVE, GLOSSOPHARYNGEAL NERVE AND VAGUS NERVE TO GUSTATORY SYSTEM NEURONS GO TO THE AMYGDALA, HYPOTHALAMUS, AND TO MEDULLA TO THE THALAMUS THALAMUS SENDS TO THE GUSTATORY CORTEX OF THE CEREBRUM AND THE LIMBIC SYSTEM

 FAST ADAPTATION  CELLS REPLACED EVERY THREE DAYS SO DOESN’T DECREASE WITH AGE

TASTE NERVE PATHWAY

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TASTE BUD MAP: MYTH

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FLAVOR

 SMELL, TASTE, TEXTURE, TEMPERATURE

HEARING

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EARDRUM

human-body.net

HEARING

 Humans can hear between 20 to 20,000 decibels, greatest sensitivity at 2,00 to 3,000 vibrations/second  Muscles: – Tensor tympani: holds malleus inward and to wall, involved in tympanic reflex to muffle loud sounds for protection – Stapedius: holds stapes in place

HEARING

 Auricle funnels sound waves to auditory canal to eardrum  Sound waves changed to vibrations, passed through middle ear bones, stapes magnifies vibrations  Stapes vibrates oval window, vibrations to liquid waves in perilymph

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INNER EAR

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   Vibrations pass from perilymph of scala vestibuli through vestibular membrane to endolymph of scala media and through basilar membrane to perilymph of scala tympani and out to air at round window Organ of Corti has 16,000 hearing receptor cells on surface of basilar membrane in scala media Each receptor cell (epithelial cells) has 4 hair cells with parallel cells of many stereocillia (micro villi) which release neurotransmitters to stimulate associated neuron

CONTINUED

 Specific frequencies vibrate specific subsets of hairs of specific receptor cells (epithelial cells) depolarizes the cell  Calcium enters causing neurotransmitters to be released which stimulate the neuron

INNER EAR

human-body.net

 Labyrinth: – Osseous – Membranous

INNER EAR

Fluids: – Perilymph – Endolymph Parts: – Cochlea – Semicircular canals – Vestibule

AUDITORY NERVE PATHWAYS

 Cochlear branch of Vestibulocochlear cells to auditory neurons, to medulla to midbrain to thalamus to auditory cortices of temporal lobes  Impulse goes to both sides of the cerebrum

 2 senses – Static – Dynamic

EQUILIBRIUM

 Static – In vestibule: membranous labyrinth   Utricle Saccule

STATIC EQUILIBRIUM

 Contain macula: hair cells and supporting cells covered by otolithic membrane with otoliths (calcium carbonate crystals) for increased sensitivity  Head upright: – Utricle hairs vertical – Saccule hairs horizontal

STATIC EQUILIBRIUM

    Hair cells have nerve fiber wrapped around the base Neuron goes to vestibular portion of vestibulocochlear nerve When head moves macula (of one or both) sags due to gravity bending hairs and depolarizing cell Neurotransmitters released stimulating neuron

STATIC EQUILIBRIUM CONT.

 Impulse travels up Vestibulocochlear nerve to midbrain to cerebrum  Cerebrum translates and analyzes impulse and sends appropriate impulse along motor nerves to skeletal muscles to maintain posture

DYNAMIC EQUILIBRIUM

 Macula also involved some: when head or body is thrust forward or backward otolithic membrane lags behind and stimulates hair cells: falling, walking  Semicircular canals – 3: superior & posterior (lateral) – lateral (horizontal) – Body planes

DYNAMIC EQUILIBRIUM

 Semicircular canal ends in swelling= ampulla; communicates with utricle  Ampulla has crista ampullaris containing hair cells in a dome shaped gelatinous mass= cupula  Hair cells have nerve fibers wrapped around the base connected to vestibulocochlear nerve

DYNAMIC EQUILIBRIUM

 Rapid turns of head moves but not the fluid so the cupula of 1 or more semicircular canals bend stimulating the hair cells forming impulse in neuron  Vestibulocochlear nerve carries impulse to cerebellum for interpretation to maintain balance

DYNAMIC EQUILIBRIUM

 Other sensory structures: – Proprioceptors – Eyes  Motion sickness

sirinet.net

Cochlear Implant

http://www.nidcd.nih.gov/health/hearing/pages/coch.aspx

Cochlear Implant Parts

 Microphone  Speech processor: selects and arranges sounds  Transmitter and receiver/stimulator: convert signals to electric  Electrode array: group of electrodes that collects the impulses from the stimulator and sends them to different regions of the auditory nerve

Cochlear Implant continued

 Bypass the part of the ear that is damaged  Directly stimulate auditory nerve  Nerve sends impulses to proper area of brain  Not like normal hearing but allows person to pick up on sounds

SIGHT

EYE PARTS

 Eyelid: Palpebra – 4 layers:  Skin: thinnest  Muscle: orbicularis oculi; levator palpebrae superioris   Connective tissue: tarsal glands Conjunctiva: mucous membrane Lacrimal apparatus: lacrimal gland, superior and inferior canaliculi, lacrimal sac, nasolacrimal duct, nasal cavity

EYE PARTS

   Conjunctiva: glandular cells, lysozyme Extrinsic muscles 3 layers: – Fibrous tunic, vascular tunic, nervous tunic Fibrous: cornea, sclera, Vascular/uveal layer: choroid coat, ciliary body, suspensory ligaments, lens, iris, Nervous tunic: retina, macula lutea, fovea centralis, optic disk, photoreceptors, vitreous humor, vitreous body

en.wikipedia.org

IRIS

    Controlled by circular and radial set of muscles Parasympathetic nerves stimulate the circular muscles to constrict iris (bright light) Sympathetic nerves control stimulate radial muscles to dilate iris Color: very complex, melanin is pigment, genes for blue (recessive), green and brown; no pigment= light blue, also texture, fibrous tissue, blood vessels and selective absorption and reflection of biological compounds

EYE PARTS

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RETINA

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PATHWAY

 http://webvision.med.utah.edu/movies/iris edu.mov

RETINA

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FOVEA CENTRALIS

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RETINA

 Photoreceptors  Pigmented epithelium – absorbs light; stores vitamin A  Neurons  Nerve fibers  Limiting membranes

 Retinal neurons – Receptor cells – Bipolar neurons – Ganglion cells – Horizontal cells – Amacrine cells

RETINA

   Macula lutea: fovea centralis Optic disk: optic nerve, central artery and vein Photoreceptors – Rods: 100 million, 100X more sensitive to light, best in dim light, more convergence: less detail, peripheral – Cones: 3 million, color, sharp detail, less convergence, only cones in fovea (no convergence)

VISUAL PIGMENTS

 Rods: rhodospin (Visual purple) – Light: breaks down to opsin & retinal – Opsin activates transducin which activates phosphodiesterase which breaks down cGMP, closes sodium channels, hyperpolarizes neuron, inhibits neurotransmitter release, rods don’t work well – Dim light: rhodopsin regenerated from opsin and retinal so rods work/cones don’t= see gray – Rhodospin is 100,000X more sensitive – Dark adapted – Vitamin A for retinal formation

IODOSPINS

 Light sensitive pigments of cones – Erythrolabe: red light – Chlorolabe: green – Cyanolabe: blue – All 3= white – None= black Color blindness: Green: most common, sex linked (more in males), red weakness: sex linked; Blue: rare, not sex linked= equal in male & female

STEROPSIS

 Distance, depth, height, and width  Eyes are 6-7 cm apart: so superimposed+ 3-D in visual cortex

ELECTROMAGNETIC SPECTRUM

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EYE ANATOMY

.stlukeseye.com

LIGHT PATHWAY

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LIGHT PATHWAY

   Refraction: cornea (75%), lens and liquids Cornea refracts light, iris controls amount, lens focuses and flips image onto retina, photoreceptors form impulse to ganglion cells to optic nerve to optic chiasma, some impulses cross to thalamus via optic radiators to visual cortex of occipital lobes Some impulses to brain stem to control head & eye movement to track moving object; & control movements of both eyes

RETINA

.stlukeseye.com

WAVELENGTHS

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BLUE CONE

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Demonstration of the blind spot

O X

Look at an eye diagram, what causes the blind spot?

Where the optic nerve enters/ no receptor cells Why don’t we see a black dot where the blind spot is?

The brain fills in the space with info from the surrounding area and the other eye

• • • •

Blind spot

It was first thought that the optic nerve entrance should have the greatest visual acuity This hypothesis was disproved in 1660 by Edme Mariotte of France It is located 1.5◦ below the horizon and is about 7.5◦ by 5.5◦ Not found in all animals Why not?

en.wikipedia.org/wiki/File:Foen.wikipedia.org/wiki/File:focus_in_an_eye.svg

The ability to focus on near and distant objects

What is happening? What can be seen correctly?

Near objects Wikipedia.org

Farsightedness/Hyperopia

What is happening? What can be seen correctly?

Far objects

Cortical Implant

 Dr. William Dobelle produced the "Dobelle Eye“ which uses a video camera wired by a computer to platinum electrodes implanted on the visual cortex (brain)

Corneal Transplant

 Just the cornea is transplanted

Pink Eye

 Conjunctivitis/ inflammation of the conjunctiva  Symptoms: itching, burning or stinging, discharge, swelling, watering  Allergic: not contagious  Viral, bacterial: contaigous

Floaters

 Tiny pieces of the eye's gel-like vitreous break loose in the back portion http://www.google.com/imgres?q=eye+floaters&um=1&hl=en&sa=N&rls=com.microsoft:en-us:IE-SearchBox&biw=1024&bih=587&tbm=isch&tbnid=GMLBYEw-M http://www.google.com/imgres?q=eye+floaters&um=

Life Span Changes

 Often first age related change noticed  40 s : lack of accomodation  50 s : smell and taste: anosmia: – Loss of olfactory receptors  60: 25% have significant hearing loss – Damage to hair cells  65-75: 1/3  85: 50% can not hear well: especially high pitches and certain letters

Life Span continued

 – Also presbycusis: degeneration of nerve pathways – Tinnitus: ringing of the ears – Hearing aids Vision declines: – “dry eyes” – Increased floaters – Vitreous humor shrinks and pulls away from retina: flashes – Presbyopia: lens loses elasticity, can’t focus ?

Life span continued

– 70: iris is inelastic and doesn’t let in as much light – Glaucoma: build up of pressure ?

– Aqueous humor: shuts blood vessels ?

– Cataract: lens or capsule becomes opaque ?

– Laser surgery and implant – Macular degeneration: macula cones degenerate – Detached retina: pulls away from choroid coat ?