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Sensory
Systems
How many different sensory
receptors are hard at work
during a roller coaster ride?
Sensations
• Definition:
– State of
awareness of
internal or
external
conditions of
the body
Tortora
Page 266
Sensations
• Four conditions
for a sensation to
occur:
– Threshold
stimulus.
– A receptor to pick
up the stimulus.
– Conduction of
impulse.
– Translation by
brain into
sensation.
Tortora
Page 266
Sensations
Tortora
Page 266
• Stimulus results
in a generator
potential.
– Depolarization of
receptor
membrane.
– Follows afferent
pathway to
thalamus.
– From thalamus,
action potential
goes to cerebrum
Molecules in food stimulate
generator potentials in taste buds
Sensations
Tortora
Page 266
• 4 Characteristics of a sensation.
– Projection
• “connects” sensation in cerebrum to
correct part of body.
• Example: Brain knows that you just
burned the tip of the pinky
finger on the left hand.
Sensations
Tortora
Page 266
• 4 Characteristics of a sensation.
– Adaptation
• Decrease in sensitivity with continued
non threatening stimulation.
• Example: A person living near the
railroad tracks sleeps
through the passing of the
train
Sensations
Tortora
Page 266
• 4 Characteristics of a sensation.
– Afterimages
• Sensation persists even though stimulus
is removed.
• Exampe: You look at a bright object.
It remains as a vision for a
period of time after looking
away.
Sensations
Tortora
Page 266
• 4 Characteristics of a sensation.
– Modality
• Type of stimulation.
• Example: Vision Vs smell Vs touch
Receptors
• Classification
based on
location:
– Exteroceptors
– Visceroceptors
– Proprioceptors
Tortora
Page 266
Receptors
• Classification
based on type of
stimulus:
–
–
–
–
Mechanoreceptor
Thermoreceptor
Nociceptor
Electromagnetic
receptor
– Chemoreceptor
Tortora
Page 266
Receptors
• Classification
based on type
of
complexity:
– Simple
– Complex
Tortora
Page 266
Accessory Structures
of the Eye
• Eyelids
• Eyebrows
• Lacrimal
apparatus
• Lacrimal gland
• Lacrimal canals.
• Nasolacrimal
duct.
• Role of lysozyme:
antibacterial.
Lacrimal apparatus from Gray’s Anatomy
Structures of
the Eye
• Eye lies
within a
cavity called
the orbit.
Tortora
Page 266-267
Structures of
the Eye
• Muscles that move
the eye:
– Inferior rectus
– Lateral rectus
– Superior rectus
– Medial rectus
– Inferior oblique
– Superior
oblique
Tortora
Page 197
Structures of
the Eye
• Eye has three
layers.
– Fibrous tunic
– Vascular tunic
– Nervous tunic
Tortora
Page 266-267
Structures of
the Eye
• Fibrous tunic
consists of:
– Sclera
– Cornea
– Conjunctiva
Tortora
Page 266-267
Structures of
the Eye
• Vascular
tunic consists
of
– Choroid
– Ciliary body
– iris
Tortora
Page 266-267
Structures of
the Eye
• Nervous tunic
consists of
– Retina
– Rods & cones
– Detached
retina
Tortora
Page 266-267
Structures of
the Eye
• Lens
– Suspensory
ligaments
– cataracts
Tortora
Page 266-267
Structures of
the Eye
• Anterior Cavity
– Anterior
chamber
– Posterior
chamber
– Aqueous humor
– Intraocular
pressure
– Glaucoma
Tortora
Page 266-267
Structures of
the Eye
• Posterior
Cavity
– Filled with
vitreous
humor
Tortora
Page 266-269
Structure of the
Retina
• Retina covers
the choroid
layer.
• Consists of three
zones of neurons
– photoreceptors
– Bipolar
– Ganglion neurons
Tortora
Page 268-269
Photoreceptors
• Modified
dendrites.
• Highly
specialized.
– Rods
– Cones
Tortora
Page 268-269
Photoreceptors
• Modified
dendrites.
• Highly
specialized.
– Cones
– Cones are
concentrated
around the
central fovea.
Tortora
Page 268-269
Visual Pathway
•
•
•
•
Generator
potential is
created by rods
and cones.
Bipolar neurons
Ganglion neurons.
Optic nerve II.
3rd order neuron.
Tortora
Page 268-269
Formation of
Image on Retina
•
•
Four processes
are needed to
form an image on
the retina.
First
–
–
Extrinsic muscles
cause convergence
of eyes on object.
Depth perception.
Tortora
Page 271-272
Formation of
Image on Retina
• Second
– Pupils
constrict so
as to center
the light
entering the
eye.
Tortora
Page 271-272
Formation of
Image on Retina
• Third
– Refraction
(bending of the
light rays)
occurs due to;
•
•
•
•
Cornea
Aqueous humor
Lens
Vitreous humor
Tortora
Page 271-272
Formation of
Image on Retina
• Fourth
– Accomodation
- the lens
changes shape
so as to focus
image on the
retina.
Tortora
Page 271-272
Stimulation of
Photoreceptors
•
•
•
•
•
•
Photopigments are
molecules that change
structure when struck by
light
Small amounts of light
cause rhodopsin to break
down.
Results in opsin and retinal
A.
Starts generator potential.
Reforms quickly.
Daylight overwhelms rods.
Tortora
Page 271-272
Stimulation of
Photoreceptors
•
Three types of cones
–
–
–
•
•
•
•
Red
Green
Blue
Each contains a different
photoreceptor.
All need abundance of light
All break down with intense
light but quickly reform.
Most common form of color
blindness is lack of red or
green cones.
Tortora
Page 271-272