PNS and Sensory Receptors Flashcards
what is sensation
the process where sensory receptors receive information from both the internal and external environment and encode the information for transmission to various areas of the nervous system
sensation includes what processes?
sensory transduction
receptor potential summation
action potential generation
neural processes that integrate signals centrally by either facilitation (polarization) or inhibition (hyperpolarization)
what is perception
the process where the CNS receives and interprets the sensation based on
- present experiences
- present state of the internal and external environment
- memory of similar situations
where does perception and its refinement occur?
thalamus
basal ganglia
cerebellum
cortex
perception at the cortical level is usually considered…
conscious perception
perception at the level of the cerebellum is considered…
unconscious perception
how may the basal ganglia be involved in perception
unconscious representations of movement experiences
perception of inter- and intrapersonal space
without the cortex, perceptions are…
incomplete or skewed from the normal which may include lack of localization, anesthesia, or hyperesthesia, paresthesia
what is sensory transduction
changing the energy of a stimulus into a neural energy
sensory transduction
- what type of energy can it be
- how does it produce a change
energy may be mechanical, chemical, light
how
-produces a change in the receptor membrane such that a local potential difference occurs
-i.e. Na+, K+, and Cl- channels open to allow ion movement
this potential change is local and spreads only a few millimeters as it decays
what is the “threshold for stimulation”
amount of stimulus energy it takes to cause a local receptor potential
threshold depends on receptor
what is the “threshold for perception”
lowest stimulus intensity necessary for perception of stimulus
usually the same as receptor threshold, but may be modified by context and experience
what is adaptation
the duration for which the receptor potential is generated to the stimulus
adaptation is determined by…
-examples
morphology of the receptor
eg. Pacinian corpuscle receptor potential is RAPIDLY adapting and thus a generator potential is only generated when the stimulus comes on or off
-APs will only be generated at onset and offset of stimulus
Ruffini corpuscles are slowly adapting and continue to signal throughout the duration of the stimulus
quality - specificity coding
-how does our nervous system discern different types of sensation via the receptors?
receptors are specialized by their morphology to respond to only one type of stimulus
stimulus intensity
- directly related to…
- what happens once the stimulus intensity is determined
size of the receptor potential
number of receptors activated
after stimulus is coded, it is transferred to the generation of an AP and coded by the frequency of AP and the number of discharge fibers
as a stimulus intensity increases, what happens to the
- AP frequency
- AP amplitude
- AP speed
only frequency changes (increases)
what is a receptive field
area surrounding the receptor that when stimulated excited or inhibits the firing of a particular cell
where is the concentration of receptive fields the greatest
tips of fingers and tongue
-smallest receptor fields
-most sensitive parts of the body
as you move proximally, receptive field size increases and density of receptors decreases
what is a dermatome
area of the body surface contributing sensory input to one dorsal root
two concepts related to somatotopic organization of the CNS
lateral inhibition
orderal mapping of sensations from body surface onto CNS areas
what is lateral inhibition
-function
excitatory discharge is greatest at center of receptive field, and is inhibitory at the periphery
serves to sharpen peak of activity within the brain
where does lateral inhibition occur
first in the dorsal column nuclei
then at subsequent synapses in the CNS
also present in visual system
lateral inhibition function in the visual system
serves to enhance distinction between two stimuli and aids in recognition of pattern and contour
what areas are responsible for orderly mapping of sensation from body surface onto CNS areas
dorsal column nuclei
thalamus
somatosensory cortex
(termed the sensory homunculus)
the areas with the largest receptor density will have the largest…
cortical receptive field
some cells in the sensory cortex respond to specific…
orientation, movement, and shape of stimulus
what are different ways of classifying sensory receptors
according to stimulus location
according to sensory system
according to stimulus energy
sensory receptor classificiation based on stimulus location
exteroceptors
-stimuli from the external environment
proprioceptors
-position of body segments relative to each other and position of body and head in space
interoceptors
-signal body events such as blood glucose level and blood pressure
sensory receptor classificiation based on sensory system
somatic -tactile, joint, muscle, tendon, thermal, pain visual vestibular auditory olfactory gustatory
sensory receptor classification according to stimulus energy
mechanoreceptors -touch/pressure, proprioception, air waves chemoreceptors -taste, smell, blood gas level nocipeptors -damaging stimuli thermoreceptors -heat and cold photoreceptors -light
sensory fiber types
Ia (A-alpha) Ib (A-alpha) II (A-beta) III (Adelta) IV (C)
Ia sensory fibers
- diameter (um)
- conduction velocity m/s
- receptors innervated
12-20 um
70-120 m/s
receptors
-primary afferents of muscle spindle
Ib sensory fibers
- diameter (um)
- conduction velocity m/s
- receptors innervated
12-20
70-120
receptors
-golgi tendon organ
type II sensory fibers
- diameter (um)
- conduction velocity m/s
- receptors innervated
5-14 um 30-70 receptors -secondary afferents of muscle spindle -touch -pressure -vibration
type III sensory fibers
- diameter (um)
- conduction velocity m/s
- receptors innervated
2-7 12-30 receptors -touch and pressure -pain and temperature (cold)
type IV sensory fibers
- diameter (um)
- conduction velocity m/s
- receptors innervated
0.5-1
0.5-2
receptors
-pain and temperature (warm)
-unmyelinated fibers
conduction velocity
-effect of size
small diameter fibers are slower because they provide more resistance to flow of current and have less insulation from myelin
which fibers are small diameter?
-large diameter
small
-free nerve endings (Ad, C)
large
-encapsulated nerve endings (Ia, Ib, II)
AP amplitude
-effect of size
small diameter fibers have lower amplitude because potential change across the membrane is smaller
can distinguish size by size of EMG amplitude
threshold for stimulus
-effect of size
small diameter have a higher threshold for stimulation because they offer more resistance to current
-C will require higher intensity
motor fiber types
alpha (A-a)
gamma (A-y)
preganglionic ANS fibers (B)
postganglionic ANS fibers (C)
alpha motor fibers
- diameter (um)
- conduction velocity (m/s)
- role
12-20
15-120
role
-motor neuron innervating extrafusal muscle fiber
gamma motor fibers
- diameter (um)
- conduction velocity (m/s)
- role
2-10
10-45
role
-motor neuron innervating intrafusal muscle fiber
preganglionic ANS fibers (B)
- diameter (um)
- conduction velocity (m/s)
- role
> 3
3-15
role
-lightly myelinated
postganglionic ANS fibers (C)
- diameter (um)
- conduction velocity (m/s)
- role
1
2
unmyelinated
type I joint mechanoreceptors
-structure
structure
-encapsulated “Ruffini-like”
type I joint mechanoreceptors
-location
ligaments
joint capsule
proximal joints
type I joint mechanoreceptors
-response
mechanoreceptors, slow adapting, low threshold
active during movement and at rest
type I joint mechanoreceptors
-function
contributes to regulation of postural muscle tone
kinesthesia
regulation of muscle tone during movement
type II joint mechanoreceptors
-structure
encapsulated “paciniform”
type II joint mechanoreceptors
-location
synovial junction of joint capsule
fat pads of joint
distal joints
type II joint mechanoreceptors
-response
mechanoreceptors, rapidly adapting, low threshold
active at beginning and end of movement
type II joint mechanoreceptors
-function
provides information about beginning and end of joint movement
may help “boost” muscle tone at beginning of movement to overcome inertia
type III joint mechanoreceptors
-structure
encapsulated “GTO-like”
type III joint mechanoreceptors
-location
ligaments
all joint of the body
type III joint mechanoreceptors
-response
mechanoreceptors, slow adapting, high threshold
active at extremes of range and with longitudinal traction
type III joint mechanoreceptors
-function
response to sudden joint movements and may cause reflex muscle contraction to limit further movement
type IV joint mechanoreceptors
-structure
free nerve endings
type IV joint mechanoreceptors
-location
joint capsule ligaments periosteum synovial lining fat pads
type IV joint mechanoreceptors
-response
pain receptor, slow adapting, high threshold
active with extreme mechanical force or chemical irritation
type IV joint mechanoreceptors
-function
may contribute to a flexion reflex, or to a co-contraction pattern around a joint to prevent further movement
thermal afferents
- function
- primary receptor
encode temperature changes sensed by skin (normal skin temperature is 34 C)
primary receptor is the free nerve ending located in the dermal layer of the skin
thermal afferent primary receptors
- continuous with
- location of highest concentration
continuous with A delta and C fibers
highest concentration located near midline
how are thermal afferent receptors classified
response to cold or heat
cold afferents respond to temperature changes in what range
10-33 C
cold travels over what fiber types
A delta and C
heat afferents respond to temperature changes in what range
32-45 C
some respond to 45+
heat afferents travel over what fiber types
C fibers
nociceptors
- location
- free or encapsulated primary receptor nerve ending
location
-dermal layers of the skin
-many deep tissues including muscles and joints
free nerve ending
primary stimulus for nociceptors
mechanical damage to tissue, either by temerature extremes or destruction fo tissue (mechanical, chemical)`
cutaneous nociceptive afferents
-fiber type classification
a delta mechanoreceptive nociceptor
a delta mechanothermal nociceptors
C-polymodal nociceptors
A-delta mechanoreceptive receptors
- characteristic
- primary stimulus
- sensitized by…
high threshold for stimulation with small receptive areas, 20% that lie within fascial planes
primary stimulus
-sharp pain allowing for discrimination between sharp and dull
sensitized by
-intense heat that results in burn hyperalgesia
A-delta mechanothermal nociceptors
- maximally responsive to…
- responsible for…
maximally responsive to temperature between 45-53 C -also respond to temperatures <20 C receptors are responsible for -first pain from intense thermal stimuli -intense mechanical stimuli
C-polymodal nociceptors
- majority of _____
- what type of nerve ending
- activated buy…
majority of cutaneous receptors (>90%) free nerve endings activated by -thermal (<10 C and >45 C) -mechanical (crush) -chemical (histamine release from tissue damage)
muscle and joint nociceptive afferents
- have what fiber components
- how are these fibers activated
have both A delta and C fiber components
A-delta
-activated by muscle stretch or contraction - ergoceptive
C fibers
-activated by intense mechanical or chemical stimuli - ischemic muscle pain
joint nociceptive afferent receptors (both A-delta and C) are activated by…
- sensitized by
- this develops into a high background firing in the presence of…
activated by intense pressure and movement
sensitized by inflammation
develops into a high background firing in the presence of inflammation
visceral nociceptive afferents
- fiber type
- similar fiber to…
- relay what type of information
- stimulated by…
C fibers similar to C polymodal nociceptors
relay poorly localized and referred information
stimulated by
-twisting
-distention
-inflammation
types of vestibular (and auditory) receptors
hair cells
stereocilia and kinocilia
hair cells
- location
- types
- how are they activated
vestibular apparatus
two types
activated by acceleration of the head by a mechanism knows as mechanoelectrical transduction
-basically a mechanical deflection of stereocilia and kinocilia
stereocilia and kinocilia
- what is the model?
- cliia anchored together by…
gated spring model
cilia are anchored together by a protein link that is attached to (or near) leaky K+ and Ca++ channels, not Na+ as other excitable membranes
stereocilia and kinocilia
- upon deflection
- results in…
upon deflection, channels are modified (opened or closed) to increase or decrease the influx of ions
this mechanical deflection results in an increase or decrease in the release of neurotransmitter (glutamate?) onto the 1st order neuron
structure of receptor apparatus
ampulla of the semicircular canals and macula of the saccule and utricle receptor apparatus (ampulla or macula) is bathed in endolymph, a fluid high in K+ inertial movement of the endolymph results in a corresponding movement of the stereocilia in relation to the kinocilia resulting in an opening or closing of the leaky channels
visual receptor types
-function and location of each
rods and cones rods -more active at times of low light -located at the periphery of the retina cones -most active in bright light -located in the foveal (central) region of the retina
visual receptor are leaky
- similar to…
- result
similar to hair cells of the vestibular system
results in a continual release of neurotransmitter
when visual receptor is activated by light, what happens
it becomes hyperpolarized and results in a decrease in neurotransmitter release
the output of the retina is the…
ganglion cell
prior to the gangion cell of the retina being activated, what happens
a great deal of integration by multiple synapses through bipolar cells, horizontal cells, and maacrine cells
end result of ganglion cell activation
receptive fields are defined for ganglion cells
- large RFs representing peripheral vision
- smaller more precise RFs representing central vision
receptor fields distribution corresponds with the distribution of…
rods and cones respectively
- large RFs correspond with rods
- small RFs correspond with cones
what types of inhibiton are demonstrated using central vision and the activation of cones
surround inhibition
lateral inhibition
