Download Ch 9 Sensory System

Ch 9 Sensory System
In order to maintain
homeostasis (ie stable internal
environment), it is necessary
to detect changes in the
external environment and
react appropriately.
Several sensory systems exist
that detect external changes
rapidly. These systems
include: the somatosensory
(touch, pressure, pain etc)
system, visual system,
auditory and vestibular
system, olfactory (smell)
system, and gustatory (taste)
system.
A major objective of this
section is to look at how
events in the outside
environment are detected,
converted to action potentials,
travel to the brain, and
become consciously
perceived.
• Sensations or senses are
categorized into 2 types
1. General senses = receptors widely
scattered throughout body and detect
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touch
pressure
temperature
pain
vibration
itch
proprioception (position of limbs/muscle
sense
• Sensations or senses
2. Special senses = receptors
are housed in specialized
organs
• ear = hearing & equilibrium
• eye = vision
• tongue = taste
• nose = olfaction (smell)
• Sensory Receptors
• detect internal & external
changes (stimuli)
• they are specialized cells or
sensory neurons (dendrites or
dendritic processes)
• Sensory information from
receptors are relayed to the
CNS
neurons
• CNS interprets information &
conveys a sensation or sense
back to original area
Types of Sensory Receptors
• Receptor types can be associated with
both the general and special senses
• Pain receptors (nociceptors) = detect
tissue damage
• Mechanoreceptors = detect changes in or
distortions of cell membranes, respond to
mechanical stimuli such as stretching or
bending of receptors, or movement
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Touch
Pressure
Hearing
Equilibrium
• General Senses:
• Touch, pressure receptors
• Examples
proprioceptors = tendons &
muscles (muscle spindle)
baroreceptors = stretch
receptors
Touch, pressure
• mechanoreceptors
• quickly adapts
Examples
fine touch & pressure = Merkels
& Meissner’s corpuscles
deep pressure = pacinian
corpuscles
• Other Types of Sensory Receptors
• Thermoreceptors = detect changes
in temperature (hot & cold)
• Photoreceptors = changes in light
(vision)
• Chemoreceptors = changes in
chemical composition (taste &
smell)
Chemoreceptors
•respond to chemicals 
odor molecules
• in blood vessels detect
blood pH, O2 and CO2
• Receptor Characteristics
• Sensory adaptation = ability
of a receptor to adapt
(reduce its sensitivity) to a
constant stimulus
Olfaction and touch
adapt quickly to a
constant stimuli
Pain
• common in skin, joints,
bones, blood vessels, eye(s)
• few in deep tissue, viscera
(in fact very dull)
• none in the brain
•doesn’t adapt or does so
slowly!
Pain
• referred pain = the
perception of pain coming
from parts of body not
actually stimulated
−common with viscera pain
receptors = often dull
− Ex. Heart, Gallbladder, or
Bladder
Temp.
• located in:
− skin, eye(s), muscles, liver,
hypothalamus
• cold receptors 3-4x more
numerous
• quickly adapts
Transduction
Transduction (2 viewpoints)
• Takes external stimuli and converts
it into an electrical signals (done in
the lab)
• Takes environmental information
(environmental stimuli) from the
periphery and turns it into the
language the brain understands 
Action Potentials
Environmental Stimuli
Primary Somatosensory
Cortex
Once sensory
information
reaches the
brain through
specific nerve
tracts, it travels
to the primary
somatosensory
cortex, which is
located in the
parietal lobe on
the postcentral
gyrus behind
the central
sulcus.
Homunculus
Somatosensory
cortex is arranged
in a topographical
manner on the
postcentral gyrus.
This area of the
brain is called the
somatosensory
homunculus. It
receives sensory
information from
each part of the
body