Download Afferent

Chapter 6
The Peripheral Nervous System:
Afferent Division & Special Senses
V edit. Pg. 185-232
VI edit. Pg. 181-231
VI edit. Pg. 183-235
Organization of the Nervous System
Neuronal Circuit
© Brooks/Cole - Thomson Learning
Sensory Receptors
Devices capable of detecting and measuring a particular physical
parameter
A)
B)
C)
D)
Chemoreceptors: mediate sense of smell and taste
Pain receptors: sensitive to tissue damage
Thermoreceptors: detect changes in temperature
Mechanoreceptors (propioreceptors, baroreceptors,
stretch receptors): sense changes in pressure,
tension, movement
E) Photoreceptors: mediate sense of vision
Information conveyed by these receptors is processed
in the brain as a sensation (perception)
Sensory Receptors
Somatic Senses
Special Senses
Sensory receptors
associated with:
Sensory receptors
associated with:
Skin
Joints
Muscles
Viscera
Smell
Taste
Hearing/Equilibrium
Vision
Sensory Transmission:
Receptor Potential
Sensory Transmission:
Generator Potential
Sensory Transmission:
Sensory transmission is graded: the strongest the
stimulus, the more action potentials are generated (or
depolarizing responses)
From Neuron to Brain, IV Ed.
The larger the receptor potentials , the
greater the frequency of action
potentials
Adaptation
Ability of a receptor to limit its response despite
continuous stimulation
Tonic receptors
Phasic receptors
Adaptation in Somatic Senses
Touch and pressure
Receptors: Free nerve
endings, Meissner‘s
corpuscle, Pacinian
corpuscle
Temperature
Pain
Receptors: Free nerve
endings receptors divided
into cold receptors (10-20
degrees) and warm
receptors (25-45
degrees)
Receptors: Free nerve
ending receptorsVisceral pain
receptors, Cutaneous
pain receptors
Meissner‘s corpuscle:
found in hairless parts of
skin near epidermis.
Mediate sense of light
touch and texture
sensations.
Pacinian corpuscle: found
in dermis. Mediate crude
touch and vibrations
Undergo Adaptation
Divided into: fast
conducting,
myelinated A-delta
receptors mediating
sharp pain and slow
conducting,
unmyelinated C-type
receptors mediating
chronic pain and
visceral pain
Undergo Adaptation
No adaptation
Adaptation in Special Senses
Smell
Olfactory receptors
in nasal cavity
Undergo Adaptation
Taste
Hearing
Taste buds receptors in
Hair cells in inner
tongue, cheek, roof of the ear
mouth, walls of pharynx
Sense sweet, bitter, sour
and salty tastes
Sense low and high
frequencies sounds
Undergo Adaptation
No adaptation
Eye Anatomy
© Brooks/Cole - Thomson Learning
Structure of the Eye
Outer
Middle
Inner Tunica
Cornea
Sclera
Ciliary body
Iris
Lens
Choroid coat
Retina
A) Cornea: Transparent layer
of connective tissue with
very few cells. It contains
little blood supply but a
significant nerve
innervation
B) Cornea continues with
sclera on back of the eye
A) Iris: Layer of connective
tissue and smooth muscle
cells. Amount of melatonin
in iris determines eye color
B) Divide the anterior cavity
into an anterior chamber
and a posterior chamber
containing aqueous humor
C) Function: regulate the
amount of light coming
into the eye
Control of Pupillary Size
A) Lens: Transparent layer of
connective tissue/dead cells with
few cells and a lot of intercellular
material. Accumulation of opaque
fibers causes cataract
B) Lens are attached to suspensory
ligaments that are attached to
ciliary body
C) Function: focus/accommodation
D) The anterior chamber between
the cornea and the lens is filled
with the aqueous humor secreted
by the ciliary body
E) Accumulation of aqueous humor
cause glaucoma
A convex lens concentrates all light
rays into the focal point
Function of the Lens
Focus of light rays on the retina
Disorders associated with the lens: cataracts, stigmatism, myopia
(nearsightedness), heperopia (farsightedness)
Control of the
thickness of the
lens can be used
to focus the light
rays coming from
distant or close
objects
A) Lens: Transparent layer of
connective tissue/dead cells with
few cells and a lot of intercellular
material. Accumulation of opaque
fibers causes cataract
B) Lens are attached to suspensory
ligaments that are attached to
ciliary body
C) Function: focus/accommodation
D) The anterior chamber between
the cornea and the lens is filled
with the aqueous humor secreted
by the ciliary body
E) Accumulation of aqueous humor
cause glaucoma
Lens and Ciliary Body
Accommodation:
Ability to change the
shape of the lens to
focus an object in
the retina
Far-light sources
require a flat lens
Near-light sources
require a rounded
lens
Accommodation:
Ability to change the
shape of the lens to
focus an object in
the retina
Far-light sources
require a flat lens
Near-light sources
require a rounded
lens
Accommodation
Close Object
Distant Object
Ciliary muscle contract
(+ Parasympathetic NS)
Ciliary muscle relax
(+ Sympathetic NS)
Suspensory ligaments
relax
Suspensory ligaments
contract
Thick (round) lens
Thin (flat) lens
Eye Anatomy-Retina
© Brooks/Cole - Thomson Learning
Retinal Structure
Photoreceptors
The retina contains two kind of photoreceptors: cones and rods.
Cones mediate color vision (day vision), are less sensitive to light
but have the highest acuity (sharpness)
Optic Disk and Macula Lutea
Fovea-depression in
the retina where light
strike the cones
directly
Optic disc (Blind spot)site where optic nerve
leaves and blood
vessels enter the eye)
Macula-area
with highest
number of
cones
Structure of Photoreceptors
Rods
Cones
Active at night
Active at daylight
Absorb all
visible
wavelengths
Absorb light of a
particular
wavelength
(red, green, blue)
More sensitive
to light
Less sensitive
Lowest acuity
Highest acuity
Contain the
photopigment
rhodopsin
Contain the
photopigment
iodopsin
Rods Photopigment
Rhodopsin = Opsin + retinene
http://www.blackwellpublishing.com/matthews/rhodopsin.html
Dark
Phototransduction
(process of
converting the light
stimuli into
electrical signals)
High concentration
of cyclic GMP
Na+ channels open
in outer segment
Takes
place
in
outer
segment
Membrane
depolarization
Takes
place
in
retina
(Spreads to
synaptic terminal)
Opens Ca2+ channels
in synaptic terminal
Release of inhibitory
transmitter
(inhibition)
Bipolar cells inhibited
No action potential
in cell ganglion cell
No action potential
propagation to
Takes
place
in
synaptic
terminal
Light
(Absorption of
light)
Activation of photopigment
Activation of transducin
Takes
pace
in
outer
segment
(Through a
cascade of
reaction)
Decrease in cyclic GMP
Closure of Na+ channels
in outer segment
Membrane hyperpolarization
(theto
receptor
(Continue
the nextpotential)
page)
(Spreads to
synaptic terminal)
Takes
pace
in
synaptic
terminal
Closure of Ca2+ channels
in synaptic terminal
Release of inhibitory
transmitter
(Removal of inhibition)
Bipolar cells disinhibited
(or, in effect, exited)
Graded potential change
in bipolar cell
(If of sufficient magnitude
to bring ganglion cell to
threshold)
Action potential in
ganglion cell
Propagation of action potential to
visual cortex in the occipital lobe
of the brain visual perception
http://www.physpharm.fmd.uwo.ca/undergrad/medsweb/L1Eye/Eye.swf
Takes
place
in
retina
Light Adaptation
Adaptation of photoreceptor sensitivity to light
At low levels of illumination
photoreceptors are more
sensitive to light. Sensitivity
decreases as the level of
illumination increases
Sensitivity is regulated by calcium
ions. Ca2+ ions decrease
activity of guanylate cyclase
(make less cGMP) and
decrease receptor affinity for
cGMP
Color Vision
Photopigments in Cones
Color Blindness
Occurs as the result of losing a particular type of cone
Visual Inversion
At the beginning of visual processing the image projected into the
retina is upside down and backward because of bending of the
light rays
Visual Pathway
http://www.sumanasinc.com/webcontent/anisamples/neurobiology/visualpathways.html
Binocular Vision
Originate because overlapping visual fields from
both eyes at the same time
Visual Pathway
Photoreceptors (Retina)
Optic nerve
Thalamus
Cortex (Occipital lobe, Primary visual cortex)
Vision (visual sensation)
Ear Anatomy
© Brooks/Cole - Thomson Learning
Ear
External
Pinna
External auditory
meatus
Tympanic
membrane
Middle
Inner Ear
Ossicles
Cochlea
Middle ear cavity Vestibular apparatus
Auditory tube
Sound wave
Air vibrations generated by alternating areas of
high and low pressure of air molecules
Sound wave: Can a sound wave be generated in a
vacuum?
Structure of the Ear
endolymph
perilymph
Hearing
Pinna directs sound wave toward ear canal
Sound wave hits tympanic membrane
Tympanic membrane vibrations are
transmitted to the malleus
(amplification)
Stapes convert vibrations into fluid
movements in the cochlea
Tympanic Reflex
Outward
movement
Inward
movement
Organ of Corti contains hair cells-the sensor
for hearing
Hair cells in organ of Corti transform fluid
movements into electrical signals
http://www.blackwellpublishing.com/matthews/ear.html
High frequency sounds (tone or pitch) are
detected at the base of the cochlea.
Low frequency sounds are detected at the tip of
the cochlea
=high energy
Stiff basilar membrane
=low energy
Flexible basilar membrane
http://www.spacehike.com/multiwavelength.html
Inner hair cells transform mechanical waves into
an electrical signals
Auditory
nerve
Sound waves
Vibration of
tympanic membrane
Vibration of
middle ear bones
Vibration of
oval window
Fluid movement
within cochlea
Vibration of
round window
Vibration of
basilar membrane
Dissipation of
energy (no
sound
perception)
In ear
(continue to next slide)
Bending of hairs of receptor
hair cells of organ of Corti
as basilar membrane movement displaces these hairs
in relation to overlying
tectorial membrane in which
the hairs and embedded
Graded potential changes
(receptor potential) in
receptor cells
Changes in rate of action
potentials generated in
auditory nerve
Propagation of action
potentials to auditory cortex
in temporal lobe of brain for
sound perception
Vestibular apparatus
Vestibular apparatus
Semicircular canals
Otolith organs
Utricle
Saccule
Function: sense rotational
acceleration of the head
(angular movement)
Function: sense linear
movements of the head
and position of the head
relative to gravity
Hair cells in the ampulla transform fluid
movements into electrical signals
Endolymph
Structure of the Ampulla in Semicircular
Canal
Acceleration of the head causes movement
of the endolymph and bending of the cupula
on the opposite direction
Utricle and saccule contain the otolith organ
to sense changes in linear acceleration
Hair cells in otolith organs
Kinocilium
Stereocilia
Otoliths (or ear stones)
Gelatinous
layer
Hair cells
Supporting
cells
Sensory
nerve fibers
Activation of hair cells in utricle and saccule
by changes in head position and linear
acceleration
Gravitational
force
Figure 6.43b
Page 225
Slide 70
Movement of head will
change weight distribution of
otolith due to gravity,
resulting in bending of hair
cells
Figure 6.43c
Page 225
Slide 71
When there is a linear
movement of head, otolith
will try to lag behind due to
inertia, resulting in bending
of hair cells
Hearing/Balance Pathway
Hair cells (Organ of Corti/Otolith
organs/Ampulla)
(Auditory N.
Vestibulocholear N.)
Medulla Oblongata
Cortex (Temporal lobe)
SENSATION OF HEARING & BALANCE
Hearing/Equilibrium Senses
Hearing
Static Equilibrium Dynamic Equilibrium
(linear movements (angular movements
of the head)
of the head)
Functional organ:
Cochlea
Otolith organs: Utricle
and Saccule
Semicircular canals
Hair cells located
in: Organ of Corti
in Cochlea
Base of Utricle and
Saccule
Ampulla
Hair cells undergo
deformation from
tectorial
membrane
Hair cells undergo
deformation from
otolith (calcium
carbonate crystal or
ear stones)
Hair cells undergo
deformation from
cupulla