Download Ch. 9 – Sensory Systems Steps of sensation and perception

Ch. 9 – Sensory Systems
Sensory Receptors
•  Structures that detect changes in conditions
inside and outside of body
•  Send that info to CNS in the form of action
potentials
•  Specialized to detect different kinds of stimuli:
–  light, sound, pressure, chemicals, temperature,
etc.
–  In each case, the stimulus triggers the opening or
closing of gated Na+ channels
Steps of
sensation
and
perception
Sensory adaptation
•  Receptors decrease response or stop responding
when they are constantly stimulated
–  “Getting used to” a stimulus
–  E.g. adapting to temperature of a hot bath
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General types of sensory receptors
•  Mechanoreceptors – respond to physical distortion
(stretching, compressing, twisting) of receptor
–  Touch, pressure, vibration, proprioception (body and limb
position), hearing, equilibrium
•  Thermoreceptors – respond to changes in
temperature
•  Photoreceptors – respond to light
–  Vision
•  Chemoreceptors – respond to presence of
chemicals
–  Smell, taste, levels of certain chemicals in body fluids
(e.g. O2, CO2, glucose, etc.)
•  Pain receptors – respond to very strong stimuli
usually resulting from tissue damage
The senses
•  General senses: touch, pressure, vibration,
temperature, proprioception, pain
–  Receptors distributed throughout body and
relatively simple in structure
•  Special senses: vision, hearing, smell, taste,
equilibrium
–  Receptors found in special sense organs only,
tend to be more complex in structure
General sense receptors in the skin
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Vision:
anatomy
of
the eye
Outer Fibrous Layer (1 of 3):
cornea
Forms the outermost
sclera coat of the eye and is
composed of:
• Opaque sclera (posterior)
• Clear cornea (anterior)
The sclera:
protects the eye and
anchors extrinsic muscles
The cornea:
allows light to enter the
eye
Middle Vascular Layer (2 of 3): iris
Choroid
forms the middle coat of the
eye and is composed of:
• Choroid
• Ciliary body
• Iris
The Choroid :
• Blood rich region that prevents
light scatter with pigmentation
pupil
Ciliary body
The ciliary body:
•  The ciliary processes secrete aqueous humor
•  The ciliary muscles control lens shape
The iris:
•  Pigmented region that allows light to pass through the pupil
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Sensory Tunic (3 of 3): retina
Also known as the
retina, forms the
innermost coat of the
eye and is composed of:
-rods
-Cones
-optic Disc (Blind spot)
-fovea
Inner Cavi<es and Fluids Anterior
Segment
(cavity)
The lens separates the
anterior cavity from
the posterior cavity
Posterior cavity:
Lens
Posterior
segment
(cavity)
• Contains vitreous
humor, which is formed
before birth
• This stagnant gel-like
fluid keeps the retina
pressed against the
wall of the eyeball
Cells of the re<na’s neural layer rods: interpret light in shades of grey
Cones: interpret light in shades of red, green, and blue
Bipolar cells: stimulate ganglion cells after receiving signals
from the rods & cones
Ganglion cells: receive signals from bipolar cells and take them
into the brain via the optic nerve (a collection of ganglion
cell axons) 4
Photoreceptors
•  ~ 6 million cones, ~ 120 million rods
•  3 types of cones respond maximally to different wavelengths
(colors) of light:
–  Red, blue, and green cones
–  Brain interprets color based on degree of stimulation of various cone
types
Now you see it…Now you don’t Fovea
Optic
disc
Fovea
centralis
•  Found directly behind
the lens
•  Contains mostly cones
•  For high visual
acuteness
Optic disc•  AKA “blind spot”
•  Where ganglion cell
axons form the optic
nerve to exit the eye
•  No photoreceptors
found here
Hearing:
the nature
of sound
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Anatomy of the ear
The cochlea
The process of hearing
Video
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Organ of Corti: Function
(1) Pressure waves distort
basilar membrane.
(2) triggers vibration of hair
cells against the tectorial
membrane.
(3) Shearing force of the
tectorial membrane
against the hair cells
signals sensory nerve
fibers.
Hearing loss occurs (most often) in a 1:1 with hair cell loss.
Vestibular apparatus
•  Position of
the head
with respect
to gravity
Static equilibrium:
utricle and saccule
of vestibule
Static equilibrium: utricle and saccule
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Dynamic
equilibrium:
semicircular
canals
•  Equilibrium
when the
body or head
is moving
Dynamic equilibrium:
semicircular canals
Smell (olfaction)
•  Chemical sense
•  A rarity: olfactory
receptors (which
are neurons)
replaced ~ every
60 days
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Taste
•  Another chemical sense – closely related to smell
•  Taste cells (which are not neurons) replaced ~ every
10 days!
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