This are specialized cells that provide the CNS with information
about conditions inside or outside the body.
Sensory Receptor Cells
Sensory receptors are specialized to responde to changes in their
environment, this changes are identified as
Stimuli
The translation of a stimulus into an action potential is called
Transduction
General senses start with _________________ , which are _______
endings of _____________________
1- Sensory Receptors
2- Modified Dendritic Endings of sensory neurons
General Senses are found
Throughout the body and monitor most types of general sensory information.
General Senses include:
Pain, temperature, touch,
pressure, vibration and proprioception.
Housed in complex sense organs ___________ senses are found. These
sense organs are composed not only the sensory receptors, but also of
______________ that form its supporting wall, lens, and other
associated structures.
Special Senses nonneural cells
Special Senses include:
Smell (Ofactory) Taste (gustation) Balance
(equilibrium) Hearing Sight (vision)
General Senses and Special Senses need sensory ____________ to
receive the stimuli
receptors
Each receptor is characteristic to a specific sensitivity, which is called
Receptor Specificity.
Which would be the simplest receptors?
Free Dendrites of sensory neurons
Free Dendrites (simplest receptors) may respond to stimuli coming from:
Tissue damage, as a result of chemical stimulation.
Pressure from swelling of the tissue, from fluid
collection. Temperature changes due to increased blood flow
and trauma to tissue.
Stimuli come differently, reason why are classified in different types:
Mechanoreceptors - touch, pressure (include blood
pressure),vibration, and stretch. Thermoreceptor respond to
temperature changes. Photoreceptors respond to light, like
the retina of the eye Chemoreceptors respond to chemicals
in solution Nociceptors responde to potentially damaging
stimuli that result in pain. Example: searing heat, extreme cold,
excessive pressure, inflammatory chemicals
Mechanocoreceptor
Detect physical stimuli which results from the physical distortion of
a cell membrane. This membranes contain mechanically regulated ion
channels whose gates open or close in response to stretchin,
compression, twisting, vibrations, or other distortions.
Thermoreceptor
Are free nerve endings which detect changes in temperature. They are
found in the dermis of the skin, skeletal muscles, the liver and the
hypothalamus. They are phasic receptors.
Monitor changes in presure in the walls of:
blood vessels (aorta, carotid arteries, lungs, vena
cava), the digestive tract, the urinary tract,
and the reproductive tract.
Baroceptor
Monitor body position :
Muscle - muscle spindles Joints - Golgi tendon
organs Movement
Propioceptors
This receptors are which respond to water-soluble and
lipid-soluble substances dissolved in the surrounding fluids.
___________ receptors are the free endings of nociceptors which
may be stimulated by a variety of chemicals.
Chemoreceptors
Chemoreceptors are found within
The _____________ bodies of the internal carotid
arteries. The ______________ bodies of the aortic arch.
In the ___________ and ______________ centers within the brain
stem.
Carotid Aortic Respiratory and Cardiovascular
Center
Complex receptors may be:
Cones and Rods from the Eye retina
The area being monitored by the receptor is called
Receptive Field
The fewer the number of receptors (<receptors) being effected by a stimulus
The greater the ability to localize a stimulus and visa versa
When sensory information arrives in the CNS
It is routed according to the location and nature of the stimulus.
The brain has ________ areas of the ________ concerned with conscious
awareness of sensation.
Sensory Cortex
Sensory areas of the cortex occur in :
Parietal Lobe Insular Lobe Temporal Lobe
Occipital Lobe
The ability of neurons to identify the body region being stimulated
is called
Spatial discrimination
Touch, pressure, pain, temperature, and taste sensation arrive
at the primary sensory cortex (parietal Lobe)
Visual sensations arrive
at the visual region of the cortex ( occipital
lobe) Page 438 and 496
Where visual inerpretation occurs.
Auditory sensations arrive
Hearing receptors in cochlea division; those from equilibrium in
semicircular canals and vestibule form. The two divisions merge to
form vestibulocochlear Nerve, at Temporal Lobe
Olfactory sensations arrive
At the Primary olfactory Cortex at the Temporal Lobe
The neural link between the receptor and the cortical region is called
Labeled Line
CNS interprets sensory information entirely on the basis of the
______ over which it arrives.
Lines
The identity of the active labeled line indicates the ___________ and
________________ of the stimulus
Location Nature
The provider of other information about the strength, duration,
variation and movement of the stimulus is called
Sensory coding
Sensation is
the awareness of changes in the internal and external environment.
Perception is
Conscious interpretation of those stimuli
The feeling of a pebble in your shoe would be
Sensation
The discomfort awareness and how we would respond about this
discomfort from the pebble would be
Perception
The sensory system responsible to serve the body wall and limbs to
receive inputs from exteroceptors, proprioceptors and interoceptors is called
Somatosensory System
What kind of information transmits the somatosensory system
Information about several different sensory modalities or types of sensations.
Exists 3 main levels of neural integration to operate (integrate) in
the somatosensory system (or any sensory):
Receptor Level: sensory receptor Circuit Level:
Processing in ascending pathways Perceptual Level:
processing in cortical sensory areas.
The Receptor Level starts generating signal - for a
sensation to occur, a stimulus must excite a receptor and action
potential must reach the CNS- Here it is found different types of
Receptor Levels:
Adaptation Phasic Receptor Tonic
Receptor
Adaptation
Is a reduction in the sensitivity of a receptor in the presence of a
constant stimulus.
Not all the sensory receptors exhibit adaptation
Example of Adaptation
When you step into bright sunlight from a darkened room, your eyes
are initially dazzled, but your photoreceptors rapidly adapt, allowing
you to see both bright areas and dark areas in the scene.
Phasic Receptor
Normally inactive. They become temporarily active when
there is a change in the conditions they are monitoring.
Examples
are the lamellar and tactile corpuscles
Tonic Receptors
Provide a sustained response with little or no
adaptation. Examples are Nociceptors and most
Proprioceptors are tonic receptors because of the protective
importance of their information.
Peripheral Adaptation
Occurs when the receptors of sensory neurons alter their levels of
activity. In this situation the receptors respond rapidly at first and
then their activity decreases.
The receptors that respond rapidly at first are called
Fast-acting Receptors
Another name for Tonic Receptors, which are always active and show
little peripheral adaptation is
Slow-adaptation Receptors
Central Adaptation
Occurs whithin the CNS as a result of inhibition of sensory nuclei
along the sensory pathways
Receptors can be divided into groups, according to several schemes:
Exteroceptor Interoceptor Proprioceptor
Exteroceptor
Provide information about the external environment (smell, vision,
hearing, taste, temperature, pain)
Interoceptor
Also called visceroceptor; monitor conditions inside the body (pain,
pressure, hunger, thirst).
Proprioceptor
Like interoceptors, this one respond to internal stimuli.
Receive information concerning body position and movement
(equilibrium).
Occur in skeletal
muscle, tendonds, joints, and ligamentas and in connective tissue
covering a bone and muscle.
A more specific
classification would be according to the nature of the stimulus
which excites the receptor.
Nociceptors
Detect pain due to temperature and physical or chemical damage to the tissue
Types of Pain
Myelinated type A fibers Unmyelinated type C
fibers
Myelinated type A fibers
Carry sensation of FAST PAIN or prickling pain.
an injection or a
deep cut produces this type of pain
2. Unmyelinated type C fibers
Carry sensation of SLOW PAIN Burning and aching
pain
Neurotransmitter
The means by which neurons communicate to process and send messages
to the rest of the body
Neuromodulators
Chemical substances released by a neuron to modulate the
synapsis A chemical messanger released by a neuron that does
not directly cause EPSP or IPSP but instead affect the strength of
synaptic transmision. A neuromodulator may act
presynaptically to influence the synthesis, release, degradation or
repuptake of neurotransmitter. when released, inhibit
activity along pain pathways in the brain.
These compounds, similar to morphine are found in: Limbic System,
Hypothalamus, and Reticular Formation.
_________ bind to the presynaptic membrane and prevent the
release of Substance P, thereby reducing the consciuous perception of pain.
Endorphines and Enkephalins
To moderate Pain transmission in the PNS, Neurotranmitter
____________________ is used.
__________ bind to the presynaptic membrane and prevent the
release of Substance P, Thereby reduce the conscious perception of
pain, although painful stimulus remains.
Substance P Endorphines
There is no "one-receptor-one-function" relationship, but____________________________________
One kind of receptor can respond to several different kinds of
stimuli. Likewise, different types of receptors cn respond to
similar stimuli.
General Senses structures may be
Non-encapsulated (free) Encapsulated
As Non-encapsulated General Senses we find
Free Nerve
Ending of Sensory Neurons - are sensitive to touch
and pressure. These are found between adjacent epidermal cells
and on the corneal
surface of the eye. Modified Free Nerve Ending
( Tactile
(Merkel) Disk - Type 1 Tactile Disk are
specialized epithelial cells found in skin surfaces that lack hair.
They are sensitive to touch when compressed or disturbed
Hair Follicle
Receptor or Root hair Plexus - are the nerve
endings which wrap around the follicle or a hair. When the hair is
displaced, the movement of the follicle distorts the sensory
dendrites and produces action potentials which may be interpreted as
movement of pain.
As an Encapsulated General Senses we find:
Tactile
(Meissner's) Corpuscle - Monitor touch, pressure
and vibrations. Can be free nerve endings to specialized structures.
Meissner's Corpuscle are sensory dendrites which are highly coiled
and interwoven. They are surrounded by modified Schwann Cells and a
fibrous capsule surrounds the entire complex and anchors it with the
dermis. They are most abundant in the eyelids, lips, finertips,
nipples and external genitalia and provide fine touch and pressure,
and low frequency vibration sensations.
Lamellar
(Pacinian) Corpuscle (Lamilated) - are composed
of a single dendritic fiber suroundd by concentric cellular layers.
They are scattered throughout the integument as well as superficial
and deep fascia, joint capsules, the mesenteries and the wall of the
urinary bladder. They are most sensitive to pulsing or
high-frequency vibrating stimuli.
More Encapsulated General Senses are:
Bubous Corpuscle (Ruffini Corpuscle or Type II Tactile disc are
located deep in the skin and are sensitive to pressure and
distortion. They consist of a capsule which contains interwoven
dendrites surrounded by collagen fibers.