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Chapter 12
NERVE ENDINGS
FREE NERVE
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ENDING
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
“TOUCH” hair follicle)
RECEPTOR MODALITIES
hair displacement
3
Merkel cell
2
Free endings
TOUCH
COLD PAIN
Ruffini
6
corpuscle
Pacinian
corpuscle
CT DISPLACEMENT*
wberesford.hsc.wvu.edu
TOUCH
4 Meissner’s
corpuscle
TOUCH
5
Meisner’s corpuscle
VIBRATION
* 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
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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
KRAUSE CELLS

COLD
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RUFFINI’S END ORGAN

HEAT
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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
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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
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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
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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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sirinet.net
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

sirinet.net
INNER EAR
human-body.net
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
INNER EAR

Labyrinth:
–
–
Osseous
Membranous
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

EQUILIBRIUM

2 senses
– Static
– Dynamic

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

RETINA

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
.stlukeseye.com
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
 40s: lack of accomodation
 50s: 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
?