Transcript Somatic and Special Senses

Somatic and Special Senses
Anatomy and Physiology
The Pathway
• Sensory receptor gets stimulated
• Triggers a nerve impulse (wave of
depolarization)
• Impulse sent to the brain
• You feel a sensation
• Sensation: a feeling that occurs when brain
interprets electrical impulses
Sensory receptors stimulated by
different and specific things
• Chemoreceptors:
chemicals
• Pain receptors: tissue
damage
• Thermoreceptors:
temperature change
• Mechanoreceptors:
pressure or movement
• Photoreceptors: light
Chemoreceptors
• Taste
• Smell
• CO2 and O2 levels in
the blood
Pain Receptors
• Consist of free nerve
endings
• Widely distributed in
the skin
• Not so accurate in the
viscera
• No pain receptors in
the brain
Referred Pain
• Feels as though the
pain is coming from
somewhere else
• Example: a person
might feel pain in the
left arm during a heart
attack
• Several body parts use
the same nerve
pathways
Thermoreceptors
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Two kinds:
Heat receptors
Cold receptors
Hot and cold extremes
also stimulate pain
receptors
Mechanoreceptors
• Pressure or movement
• Free nerve endings
• Meissner’s corpuscles
are sensitive to light
touch
• Pacinian corpuscles
are sensitive to heavy
pressure
Meissner’s
corpuscle
Pacinian
corpuscle
Photoreceptors
• Sensitive to light
• Only found in the eye
• Rods and Cones
Sensory Adaptation
• When receptors
continue to be
stimulated, they stop
sending the nerve
impulse
• Particularly noticeable
with smell
• Pain receptors adapt
poorly, if at all
What makes one sensation
different from another?
• All nerve impulses are
the same
• They are simply
waves of
depolarization—
electrical signals
• Depends on which
area of the brain
receives the impulse
Sense of Smell
• Chemoreceptors
• Chemicals dissolved
in liquid stimulate
them
• “Olfactory” is
associated with smell
• Smell and taste
function together
Olfactory Receptors
• Olfactory organs in the upper part of the nasal cavity
contain the olfactory receptors
• The receptors are surrounded by columnar epithelial
cells
• Cilia cover the dendrite ends
Olfactory Receptors
Olfactory Receptors
The nerve pathway
• Receptors send
impulses to neurons in
the olfactory bulb
• Olfactory nerve tracts
take the impulse from
the bulb to temporal
and frontal lobes
• Brain interprets the
receptor combinations
as an odor
The Brain Areas
Not everyone can smell!
• 2 million people in the
U.S. have no sense of
smell
• This condition is
called anosmia
• Usually due to damage
in the olfactory nerves,
but could also be
frontal lobe damage
Sense of Taste
• Chemoreceptors
• Receptors are in the
taste buds
• Taste buds are part of
tiny elevations
(bumps) on the tongue
called papillae
Taste buds are in the folds of the
papillae
papilla
Taste bud
Taste Buds
The Four Taste Sensations
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Sweet
Sour
Salty
Bitter
Taste can be a
combination of
these
The Pathway
• Taste receptors send
nerve impulses along
three cranial nerves
into the medulla
oblongata
• From there it goes to
the thalamus (relay
center) to the parietal
lobe
Hearing
• Involves
mechanoreceptors
• Vibration stimulates
the tiny hairs
mechanically
• Chain reaction sends
the vibrations to the
inner ear
Hearing
• Ear is divided into
three sections: outer,
middle, and inner
• Outer ear consists of
auricle (pinna),
external auditory canal
(meatus), up to the
eardrum (tympanic
membrane)
Hearing
• Function of the auricle
is to gather sound
waves into the ear
• Sound waves travel
through the external
auditory canal
• Sound waves vibrate
the eardrum
Hearing
• In the middle ear,
there are three bones
called ossicles.
• They are lined up end
to end.
• The vibrating eardrum
causes the first bone to
vibrate, then the
second, then the third.
Hearing
• The first bone is the malleus (hammer), then the
incus (anvil), then the stapes (stirrup)
Hearing
• The stirrup pushes on
another membrane
called the oval
window
• This is the entrance
into the inner ear
• “Real” hearing takes
place in the inner ear
Hearing
• The oval window is
smaller than the
tympanic eardrum
(eardrum)
• So there is more force
per unit area, resulting
in amplification of the
vibrations
Hearing
• Oval window is
touching the cochlea,
the real organ of
hearing
• Chochlea is snail
shaped
• Inside the cochlea is
the Organ of Corti,
which contains the
actual hearing
receptors
Hearing
• The actual hearing
receptors are hair cells
inside the cochlea
• The hair cells are attached
to membranes. When the
membranes vibrate, the
hair cells are bent.
• This triggers the attached
neuron to depolarize,
sending the impulse to the
temporal lobe of the brain
Hearing
• Different frequencies
of sound waves
vibrate different parts
of the membrane.
• This causes different
neurons to be
stimulated, allowing
us to hear different
sounds
Loss of Hearing
• In older people, the
membranes become
less flexible
• Could be damage to
the auditory nerve or
the cochlea
• Loud noises or music
can speed up the loss
of hearing
Ear Infections
• Common in young children
• Auditory tube connects the throat with the middle
ear
• Cold, sore throat, infection may spread into ear
Normal
eardrum
Infected eardrum
Balance and Equilibrium
• Inner ear also controls
balance and
equilibrium
• Static equilibrium
senses the position of
the head and posture
when the body is still
• Dynamic equilibrium
involves moving
Balance and Equilibrium
• Static equilibrium is
controlled by the
vestibule, a structure
located between the
cochlea and the
semicircular canals.
Vestibule
Balance and Equilibrium
• In the vestibule, hairs of
sensory neurons stick up
into a gel material.
Moving the head forward,
backward, or to one side
stimulates the hair cells.
They send a nerve impulse
to the brain. The brain
controls muscles to
maintain balance.
Balance and Equilibrium
Balance and Equilibrium
• Dynamic equilibrium is
controlled by the
semicircular canals
• The three semicircular
canals are at right angles
to each other, making
them in different planes
• Contain hair cells
(receptors) and fluid
• When body moves, the
canals move, but the fluid
stays stationary, bending
the hairs
The hair cells (sensory
neurons, send impulses
to the brain. The brain
interprets and adjusts to
maintain balance.
Seasick
Balance and Equilibrium
Vertigo: a
sensation of
dizziness
You are not
moving, but
your eyes send a
message that
you are.
Causes: inner ear infection, or in roller coasters, motion
sickness, receptors and brain cannot compensate for
abnormal movements
Balance and Equilibrium
• Other structures help
in maintaining
equilibrium. Special
mechanorecptors
called proprioceptors
detect body position.
The eyes also send
information about
body position.