awareness of external or internal stimuli.
interpretation of the meaning of sensations.
that do not reach the thalamus and cerebral
cortex: blood pressure and carbon dioxide
– Thermal sensations: warm, cold
– Pain sensations
– Proprioceptive sensations
– Dynamic sensations (movements of limbs and head)
conditions within internal organs.
field of the receptor, which is the body region
where stimulation elicits a response.
energy into electrical energy
The sensory receptor transduces energy in a
stimulus into a graded potential
– Graded potentials vary in amplitude depending
on the strength of the stimulus
– Graded potentials are not propagated
sensory neuron trigger one or more nerve
impulses that propagate toward the central
– Encapsulated Nerve Endings
– Separate Cells
– No structural specialization microscopically
– Pain, thermal, tickle, itch, some touch
– Capsule enhances sensitivity or specificity of the receptor
– Pressure & vibration (lamellated), some touch (Meisner)
specialized, separate cells
– The specialized cell synapses with first-order sensory neuron
– Hearing and equilibrium hair cells (inner ear),
photoreceptors (retina), gustatory receptors (taste buds)
– Receptor potentials
Amplitude of both types of potentials varies
directly with the intensity of the stimulus
– Encapsulated nerve endings
– Receptive part of olfactory receptors
– A sufficiently large generator potential will
generate an action potential.
– Gustatory receptors (taste)
– Photoreceptors (sight)
The sensory receptor is not the first-order neuron
The PSP may in turn trigger one or more nerve
from the first-order neuron. There is a synapse
between the receptor and the first-order neuron.
– Provide information about external environment
– Sight, odor, taste, touch, pressure, vibration, thermal, pain
– Provide information about internal environment
– Impulses usually not consciously perceived
– Provide information about body position, muscle length and tension, position and motion of joints, and equilibrium
stretching of blood vessels and internal organs
which is a decrease in the generator potential
or receptor potential amplitude when exposed
to a stimulus that is applied at a constant
level over a reasonably long term.
– Slowly adapting receptors
– Are specialized for signaling changes in a stimulus
– Examples: touch, pressure, smell
– Continue to trigger nerve impulses as long as the stimulus persists
– Examples: pain receptors, proprioception, chemical composition of the blood
– Pacinian corpuscles
– Ruffini endings
– Hair root plexuses (free dendritic endings)
– Ruffini corpuscles (encapsulated)
over a larger area than touch
It occurs with deformation of deeper tissues
than does touch, hence some of the receptors
for pressure are deeper
– Pacinian corpuscles
repetitive sensory signals from tactile receptors
which detect lower-frequency vibrations
– Lamellated corpuscles (Pacinian corpuscles),
which detect higher-frequency vibrations
nerve endings and lamellated corpuscles.
Thermoreceptors are unspecialized free nerve
endings that respond to absolute and relative
changes of temperature
basale of the epidermis.
that occurs when the receptive field of a cold
receptor is touched by a small probe having a
higher temperature than the skin.
to 118º F).
in every tissue of the body except the brain.
Termed nociceptors, they exhibit very little
– Potassium ions
serve as chemotactic agents for phagocytes. They are formed in blood from inactive precursors
emigration of phagocytes through capillary walls. They are released by damaged cells.
removed occurs because the pain-mediating
Differentiated based on
– Types of nerve fibers that propagate the impulses (hence the speed of propagation)
– Where in the body the particular type of pain can
Propagated along medium-diameter,
myelinated A fibers
Also termed acute, sharp, or pricking pain
Not felt in deeper tissues of the body
– Needle puncture
– Knife cut
second or more after the stimulus is applied
Propagated along small-diameter,
unmyelinated C fibers
Also termed chronic, burning, aching, or
throbbing pain, it may be excruciating
Felt in both the skin, deeper tissues of the
body, and internal organs
Where is slow pain localized?
Slow somatic pain is reasonably well localized, but more diffuse
regions of high sensory input (such as the
skin) and nerve fibers from regions of
normally low sensory input (such as the
internal organs) happen to converge on the
same levels of the spinal cord.
interprets them as pain in the chest and left arm.
Some analgesic drugs block formation of
prostaglandins, which stimulate nociceptors
– Neurons in the brain generate sensations of body awareness, including those neurons that previously received sensory impulses from the missing limb, thereby giving rise to false sensory perceptions
termed proprioceptors, allowing us to know
where our head and limbs are located and
how they are moving even without looking at
Proprioceptors adapt slowly, and then only
slightly, so they provide continuous
information to the brain
– amount of tension on tendons
– position of joints
– relative rates of movement of body parts
– weights of objects
Joint kinesthetic receptors
muscles that participate in stretch reflexes
Their function is to measure muscle length—
how much a muscle is being stretched
muscle will stimulate the muscle spindle
around 3 to 10 specialized muscle
fibers = intrafusal muscle fibers)
intrafusal muscle fibers are enclosed by
a connective tissue capsule = muscle spindle
large-diameter A fibers called alpha motor
alpha motor neurons of that same muscle,
causing contraction of extrafusal fibers.
have numerous muscle spindles (greater density)
– Muscles involved in coarser movements have
fewer (lesser density)
– The small skeletal muscles of the middle ear have very few muscle spindles (at one time, it was
thought they had none)
tendon and a muscle
Tendon organs protect tendons and their
associated muscles from damage due to
They are slowly adapting
capsule of connective tissue.
causing muscle relaxation before the muscle
can be damaged.
– Changes in velocity
– Free nerve endings
– Type II cutaneous mechanoreceptors (Ruffini
(Pacinian) corpuscles in the connective tissue
outside articular capsules
ligaments which are similar to tendon organs