Download Sensory Systems - Blue Valley Schools

Sensory Systems
Cell Structure
• Cells of the sensory and nervous system
derive embryonically from the ectoderm.
• Like epithelial cells, they are polar, having
one end that is specialized for secretion.
• There are a diversity of neurons, sensory,
motor, interneurons, and neuroendocrine
Sensation & Reflex
• Sensory cells and neurons are part of
the peripheral nervous system, while
the central nervous system is
composed of the spinal cord and brain.
• Certain sensory situation demand a
quick response and thus only involve
one interneuron in the spinal cord
without the involvement of the CNS.
Sensory Information
• The relay of stimulus can result in
either excitation or inhibition.
• In the ‘knee jerk’ reflex the quadriceps
is excited and contracts, while the
hamstring is inhibited and relaxes.
Categories of Sensation
• Somatic Senses are those that are
distributed throughout the body (soma).
These include the touch senses of touch,
heat, cold, and pain.
• Special Senses are more localized in
distribution and are associated with a
particular sensory organ – smell (nose),
taste (nose), hearing (ears), and vision
(eyes)
Types of Sensory Receptors
Somatic Senses
• Mechanoreceptors - mechanical energy
• Thermoreceptors - infared energy
• Nociceptors/Pain Receptors - tissue damage
Special Senses
• Chemoreceptors – chemical energy
• Mechanoreceptors - mechanical energy
• Electromagnetic/Photoreceptors – visible
and ultraviolet light
Touch
• The sense of touch is mitigated through
mechano, thermo, and pain receptors.
• Merkel disk receptors, Meissner corpuscles,
Ruffini receptors, and Pancinian corpuscles
are responsible for this sense and are
categorized based on their depth and
responsiveness (superficial or deep, and
slow and rapid firing). Superficial sensory
cells have free endings while deep sensory
cells are encapsulated.
Touch Transduction
• Inhibitory
mechanisms
highlight the
distinction between
highly stimulated
sensory cells and
their neighbors
• This creates greater
discrimination or
acuity.
Taste
• Taste buds have a pore through which fluids
contact the surface of receptor cells. The receptors
end in hair-like extensions containing receptors
that respond to particular chemicals (sweet, souracids, salty, bitter-alkaloids).
Taste Transduction
Smell or Olfaction
• Olfactory receptors are
similar to taste
receptors in having
hair-like ciliated
endings that contain
receptors for water
soluble of volatile
substances.
• The limbic system,
located in the middle of
the cerebral
hemisphere, is
associated in emotion
and memory.
Smell Transduction
Taste Transduction
• Transduction
animation
• Sensory cells
communicate to the
parietal lobe for
integration.
The Ear
• The ear is often
segregated into outer,
middle, inner
components.
• The outer ear is
composed of the pinna
and inner channel.
• The middle ear
contains the eardrum
and ear bones.
• The inner ear is where
the cochlea is found.
The Cochlea
• The cochlea contains fluid
and is bordered by the oval
and round windows.
• Wave of pressure begin in
the vestibular canal and
proceed to tympanic canal.
• The basilar membrane of
the cochlear duct is variable
in its response to different
frequencies.
• When it basal membrane
vibrates relative to the static
tectorial membrane hair
cells in the organ of Corti
are stimulated.
Vestibular Apparatus &
Dynamic Equilibrium
• The vestibular apparatus
senses both dynamic and
static equilibrium.
• It is composed of 3
semicircular canals
positioned in the x, y, and z
planes, each having a
ampulla at its base.
• When the head accelerates
or rotates fluid is displaced
and causes the gelatinous
cupula to move and
stimulate sensory hair cells.
Vestibular Apparatus &
Static Equilibrium
• At the base of the
vestibular apparatus
are bulbs called the
utricle and saccule.
• When you start or stop
moving, movement of
the underlying
membrane causes
stimulation of hairs
cells projecting in to the
less mobile calcium
carbonate otoliths.
Vision
• Photoreceptors are
found in the retina and
include both rods and
cones (color), most
dense at the fovea.
• Both interneurons and
blood capillaries
service the
photoreceptors from
front.
• The interneurons are
transferred through the
optic nerve (blindspot).
The Outer Eye
• The outer eye is formed by the cornea,
aqueous humor, iris, pupil, and the lens and
its ciliary muscles.
• The cornea is the on the outer surface of the
eye and it helps to focus light. Cataracts
occur when there is cloudy vision caused
when transparent lens proteins change such
they no longer transmit light effectively (fried
eggs).
Visual Accommodation
• Visual accommodation occurs through the adjustment of the
lens.
• To focus on distant objects the ciliary muscles relax and allow
the lens to flatten and moving the focal point further back.
• To focus on near objects the ciliary muscles contract and
cause the eye to bulge, shortening the focal point.
The Middle Eye
• The middle portion of the eye is
composed of the liquid vitreous humor.
• In Glaucoma, excess liquid
accumulates in the eye putting
pressure on the eye’s blood vessels so
that they may collapse and no longer
be able to service the retinal neurons.
The Inner Eye:
Sensory Transduction