3_Peripheral Nervous System 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 from transmission to various areas of the nervous system.
What is perception?
The process where the central nervous system receives and interprets the sensations based on present experiences; the present state of the internal and external environment, and memory of similar situations
Where does perception occur in various degrees of refinement?
Thalamus, basal ganglia, cerebellum and cortex
What is perception at the cortical level usually considered?
conscious perception
Unconscious perception is considered?
perception at the level of the cerebellum
The basal ganglia may be involved in unconscious representations of movement experiences, but also is involved with:
perception of inter- and intra-personal space
Without a cortex, perceptions are incomplete or skewed from the ___________________________________________.
normal which may include lack of localization, anesthesia or hyperesthesia, parasthesia.
What is sensory transduction?
changing the energy of a stimulus into a neural energy.
A stimulus energy can be ________, _________ and ____________.
mechanical, chemical and light
A stimulus energy produces a change in the receptor membrane such that a ________________________
a local potential difference occurs (in other words, NA+, K+ and CI- channels open to allow ion movement).
The local potential change is local and spreads _________________________.
only a few millimeters as it decays.
What is threshold for stimulation?
The amount of stimulus energy it takes to cause a local receptor potential and depends on the physical properties of the receptor itself.
What does it mean that some receptors have low thresholds?
it takes only a small stimulus to cause a local receptor potential.
Give an example of a receptor with a low threshold:
Meissner’s corpuscle - low frequency vibration
What does mean that some receptors have high thresholds?
it takes a larger stimulus to cause a local receptor potential.
Give an example of a receptor with a high threshold:
Ruffini endings - skin stretch, joint movement
What is the threshold for perception?
The lowest stimulus intensity necessary for perception of stimulus.
Threshold for perception is usually the same as the receptor threshold, however it may be modified by:
context and experience.
What is adaptation?
The duration for which the receptor potential is generated to the stimulus.
What determines adaptation?
The morphology of the receptor, e.g. Pacinian corpuscle receptor potential is rapidly adapting and thus a generator potential is only generated when the stimulus comes on or off.
Action potentials will only be generated at _______ and _______ of the stimulus
onset and offset
Ruffini corpuscles are slowly adapting and continue to signal ______________________.
throughout the duration of the stimulus.
How many types of stimuli are receptors specialized to respond to?
Receptors are specialized by their morphology to respond to only one type of stimulus.
What was the opposing theory about coding?
Patterns of stimuli similar to “Morse codes”, signaled they type of stimulus.
What is the intensity of a stimulus directly related to?
the size of the receptor potential and the # of receptors activated.
The intensity of a stimulus is transferred to the generation of an action potential and coded by ____________________ and _____________________.
the frequency of AP and the number of discharge fibers.
The stronger the stimulus =>
the greater the size of the receptor potentials (depolarization)
the greater the size of the receptor potentials (depolarization) =>
the greater the number of receptors being activated.
the greater the number of receptors being activated =>
the greater summation of the depolarizing events and thus the increased frequency of action potentials.
True of False: Only the frequency of the action potentials is changing, not the amplitude or the speed with which the action potentials are traveling.
True.
Location is understood as:
signaled by firing a specific group of neurons activated by the stimulus
Receptive fields are surrounding the receptor, then when stimulated ________________________________.
excites or inhibits the firing of a particular cell.
What anatomical structures/ regions have the smallest receptive fields?
The fingers and the tongue.
The fingers and tongue have the smallest receptors and receptive fields AND:
the largest number of receptive fields per area (these areas are the most sensitive in the parts of the body).
Moving proximally, receptive field size ________ and density of receptors _______, and sensitivity _______.
size increases
density decreases
sensitivity decreases
What are dermatomes?
Areas of the body surface contributing sensory input to one dorsal root.
Excitatory discharge is greatest at center of receptive field and is inhibitory at the periphery in :
Lateral inhibition.
What does lateral inhibition serve to do?
sharpen peak activity within the brain.
Where does lateral inhibition first occur? Where does it occur secondarily?
In dorsal column nuclei and then at subsequent synapses in the CNS
Other than the dorsal column nuclei, where else does lateral inhibition take place?
present in the visual system
Lateral inhibition serves to enhance distinction b/n 2 stimuli and:
aids in recognition of pattern and contour.
What will areas with the largest receptor density also hae?
The largest cortical receptive field.
True or false: There are no cells in the sensory cortex that respond to specific orientation, movement and shape of stimulus.
False, There ARE cells in the sensory cortex that respond to specific orientation, movement and shape of stimulus.
Exteroceptors are:
stimuli from the external EN
Proprioceptors are:
position of body segments relative to each other and position of body and head in space
Interoceptors are:
signal body events such as blood glucose level and blood pressure
Somatic sensory system includes what 6 categories?
1) tactile
2) joint
3) muscle
4) tendon
5) thermal
6) pain
When you turn your head, endolymph maintains its initial position while your head moves around it, effectively moving the endolymph backwards inside the canals –> bending cilia –> starting transduction. The above process occurs in the:
vestibular system
touch/pressure, proprioception, air wave are:
mechanoreceptors
taste, smell, blood gas level, are:
chemoreceptors
damaging stimuli (painful), are:
nociceptors
head and cold are:
thermoreceptors
light is a:
photoreceptor
Sensory Ia (A-a) fibers innvervate ______________ receptors.
primary afferents of muscle spindle
Sensory Ib (A-a) fibers innvervate ______________ receptors.
golgi tendon organ
Sensory II (A-B) fibers innvervate ______________ receptors.
Secondary afferents of muscle spindle, touch, pressure, and vibration
Sensory III (A-d) fibers innvervate ______________ receptors.
touch and pressure, pain and temperature
Sensory IV (C) fibers innvervate ______________ receptors.
pain and temperature, unmyelinated fibers
small diameter fibers are slower because they provide more resistance to flow of current and have less insulation from myelin; this describes?
conduction veloctiy
small diameter fibers have lower amplitude because potential change across the membrane is smaller. Can distinguish smaller diameter from large diameter fibers by size of EMG amplitude; this describes?
amplitude of action potential
small diameter fibers have a higher threshold “0” stimulation because they offer more resistance to current flow. C fibers will require higher intensity of e-stim to activate; this describes?
threshold for stimulus
Motor Alpha (Aa) fibers are:
motor neurons innervating extrafusal muscle fibers
Motor Gamma (Ay) fibers are:
Motor neuron innervating intrafusal muscle fiber
Motor Preganglionic ANS (B) fibers are:
lightly myelinated
Motor Preganglionic ANS (C) fibers are:
unmyelinated
Merkel’s disc fiber type:
slowly adapting, type I
Ruffini ending fiber type:
slowly adapting type II
Meissner’s corpuscle fiber type:
Rapidly adapting type I
Pacinian corpuscle fiber type:
rapidly adapting type II
Merkel’s stimulus:
deformation of skin
Ruffini stimulus:
skin stretch; joint movement
Meissner’s stimulus:
rapid skin displacement
Pacinian stimulus:
mechanical transients; vibration
Merkel’s receptive field size:
small ; 1 F: 3-4 complexes
Ruffini receptive field size:
larger; 1 F: 1R
meissner’s receptive field size:
small; 1 F: 15-20 R
Pacinian receptive field size:
large; 1F: 1 R
Joint mechanoreceptors Type I structure:
Encapsulated, “ruffini-like”
Joint mechanoreceptors Type II structure:
Encapsulated: “paciniform”
Joint mechanoreceptors Type III structure:
Encapsulated: “GTO-like”
Joint mechanoreceptors Type IV structure:
free nerve endings
Joint mechanoreceptors Type I Location:
ligaments, joint capsule, proximal joints
Joint mechanoreceptors Type II Location:
synovial junction of joint capsule, fat pads of joint, distal joints
Joint mechanoreceptors Type III Location:
ligaments, all joints of the body
Joint mechanoreceptors Type IV Location:
joint capsule, ligaments, periosteum, synovial lining, fat pads
Joint mechanoreceptors Type I Response:
mechano / slow adapting / low threshold/ active during movement & rest
Joint mechanoreceptors Type II Response:
mechano/ rapidly adapting, low threshold, active @ beginning and end of movement
Joint mechanoreceptors Type III Response:
mechano/ slow adapting, high threshold, active @ extremes of range and with longitudinal traction
Joint mechanoreceptors Type IV Response:
pain receptor, slow adapting, high threshold, active w/ extreme mechanical force or chemical irritation
Joint mechanoreceptors Type I Function:
contributes to regulation of postural muscle tone, kinesthesia, regulation of muscle tone during movement
Joint mechanoreceptors Type II Function:
provides information about beginning and end of joint movement, may help “boost” muscle tone at beginning of movement to overcome inertia
Joint mechanoreceptors Type III Function:
responds to sudden joint movements and may cause reflex muscle contraction to limit further movement.
Joint mechanoreceptors Type IV Function:
may contribute to a flexion reflex, or to a co-contraction pattern around a joint to prevent further movement
What are muscle spindles?
specialized muscle fibers containing contractile elements.
____________ encases specialized muscle fibers, that is anchored to the endomysium and perimysium that surrounds the fascicles of the muscle
a connective tissue sheath
Contractile fibers within the specialized receptor are _________________.
intrafusual muscle fibers
Extrafusal muscle fibers:
make up the bulk of the muscle
Intrafusal and extrafusal muscle fibers both have:
a typical sacromere arrangement
How many intrafusal muscle fibers are within each muscle spindle?
several
Where are the contractile elements of the intrafusal fibers located?
@ the poles
The fibers are multinucleated, with the nuclei located:
centrally
The first nuclear arrangement of muscle fibers is clumped nuclei:
in the middle forming a “bag like” enlargement of the sarcolemma
The second nuclear arrangement of muscle fibers is with linearly nuclei:
in a “chain-like” arrangement
Do nuclear bag and nuclear chain filaments occur together within each muscle spindle?
yes
how many sensory receptors does each filaments have?
at least 2
Sensory receptors are located either ________________ around the nuclear groups or ______________ near the contractile elements
centrally
peripherally
Primary receptors are
centrally located
secondary receptors are
located peripherally
What is the stimulus during stretch?
mechanical deformation of the afferent ending
_______ endings are highly responsive to rate change of the muscle length, encoding the _________ of the stretch. These are referred to as _______________ .
PRIMARY endings are highly responsive to rate change of the muscle length, encoding the VELOCITY of the stretch. These are referred to as DYNAMIC OR PHASIC ending .
Dynamic or phasic endings AKA:
annulospiral rings
Some seconadry and primary ends responsive to muscle static length are called
static or tonic endings
Theses static (seondary ?) ending AKA:
flower spray endings
Information from primary endings is carried into the CNS by:
Ia fibers
Information from secondary endings is carried by:
type II fibers
Each fiber in the muscle spindle also receives an ending from a ____________ on each contractile component to control__________________________.
y motor neuron
the contraction of each spindle
What does the activation of y motor neurons result in?
Contraction of intrafusal fibers.
What is the contraction of intrafusal fibers used for?
to adjust the sensitivity of each receptor within the muscle spindle
True or False: The adjustment of sensitivity of each receptor within the muscle spindle is the same for dynamic receptors and static receptors.
False: This adjustment is specific and separate to they dynamic receptors and to the static receptors.
What is the purpose of muscle activation?
to prevent “unloading” of the receptor during extrafusal muscle contraction
Motor activation to prevent unloading is accomplished by :
alpha-gamma coactivation
Describe alpha-gamma coactivation:
at the time of a motor neuron firing, the appropriate y motor neurons are also activated
What results from alpha-gamma coactivation?
muscle spindle adjustment that parallels the contraction of the extrafusal muscle fiber
Stimulation of the y motor neurons can take place in situations other than alpha gamma coactivation, resulting in an:
increase in the sensitivity of both the primary and secondary endings.
What influences this y motor neuron activation?
CNS pathways or cutaneous stimulation
What does this y motor neuron activation allow for?
fine-tuning of the spindle as the difficulty of the motor task increases
What are slender capsule encased receptors found at both the origin and insertion of skeletal muscle at the tendonous junction?
golgi tendon organs
How many extrafusal fibers enter the capsule through a funnel like collar?
15-20
Collagen fibers of the epimysium and perimysium of the muscle become braided with the collagen of the _____________.
receptor to the tendon
In the Golgi tendon complex, the receptor is located at the end of the ____ nerve fibers and intertwines within the collagen of the receptor capsule.
Ib
Contraction of the extrafusal fiber causes ________ on the collagen bundles
tension
Tension on collagen bundles compresses the afferent nerve ending, activating a receptor potential, followed by _________________________.
generation of action potential if the stimulus is sufficient.
The GTO is highly sensitive to __________________, and provides continuous feedback
small changes in muscle tension
The GTO has a _______ threshold to tension (resisted muscle stretch) that plays a protective role by inhibiting:
HIGH
a motor neuron activation of the contracting muscle when extremes of range are reached i.e., autogenic inhibition.
Thermal afferents encode:
temperature changes sensed by the skin.
Normal skin temperature is
34oC
What is the primary thermal receptor?
free nerve endings (located in the dermal layer of the skin).
Thermal receptors re continuous with A-d and C fibers, the highest concentration:
located near the midline
Cold afferents respond to temperature changes in the:
10-33oC range
Cold travels over both:
A δ and C fibers.
Heat afferents respond to temperature changes in the
32o-45o C range. (However, some can respond to temperatures > 45o C)
Heat afferents are restricted to
C fibers
Nociceptors (pain) occur in both:
the dermal layers of the skin as and many deep tissues including muscles and joints.
The primary receptor for pain is:
a free nerve endings.
The primary stimulus for nociceptors is: ________________.
Either by ____________ or ______________.
mechanical damage to tissue;
Either by temperature extremes or destruction of tissue (mechanical, chemical).
Cutaneous Nociceptive Afferents are classified as:
A-delta (A-δ) mechanoreceptive nociceptors
A-δ mechanothermal nociceptors
or C-polymodal nociceptors.
A-δ mechanoreceptive nociceptors are characterized by having a ______ threshold for stimulation with ______ receptive areas, (___% that lie within fascial planes.)
high
small
20%
For A-δ mechanoreceptive nociceptors the primary stimulus is:
sharp pain allowing for discrimination between sharp and dull.
A-δ mechanoreceptive nociceptors receptors are sensitized by:
intense heat that results in burn hyperalgesia.
A-δ mechanothermal nociceptors are maximally responsive to temperatures between:
45o 53o C, but also respond to temperatures
A-δ mechanothermal nociceptors are responsible for the first pain from ___________ stimuli as well as ___________ stimuli.
intense thermal stimuli
intense mechanical stimuli.
C-polymodal nociceptors are the majority of cutaneous receptors (> 90%) and are:
free nerve endings.
C-polymodal nociceptors are activated by thermal (___________), mechanical (_____) and chemical (________ release from tissue damage).
45o C
crush
histamine
Muscle and Joint Nociceptive Afferents have both
A-δ and C fiber components.
A-δ fiber components (in muscle and joint nociceptive affterents) are activated by:
muscle stretch or contraction – ergoreceptive.
In muscle and joint nociceptive a fferents, C fibers are activated by:
intense mechanical or chemical stimuli – ischemic muscle pain.
Joint receptors (both A-δ and C) are activated by intense ________ and ______, and are sensitized by _____________. This develops into a _________ background firing in the presence of inflammation.
pressure and movement
sensitized by inflammation
a high background
Visceral Nociceptive Afferents are:
C fibers similar to C polymodal nociceptors.
Visceral nociceptive affterents relay poorly localized and _______ information. Stimulated by ________________________________.
referred
twisting, distention and or/inflammation
What are they two types of hairs cells?
Stereocilia and kinocilia
Where do hair cells exist?
vestibular apparatus.
How are hair cells activated?
by acceleration of the head by a mechanism known as mechanoelectrical transduction. (This is basically a mechanical deflection of stereocilia and kinocilia.)
Stereocilia and Kinocilia are a _________ model.
gated spring
The cilia are anchored together by a __________________ that is attached to (or near) leaky ____ and ____ channels, NOT ____.
protein link
leaky K+ and Ca++
NOT Na+
Upon deflection, the channels are modified (opened or closed) to increase or decrease the _________________. This mechanical deflection results in an increase or decrease______________________ onto the ________________________.
influx of ions. increase or decrease in the release of neurotransmitter (glutamate?)
1st order neuron
The structure of the receptor apparatus for the vestibular system include the:
ampulla of the semicircular canals and macula of the saccule and utricle.
The receptor apparatus (ampulla or macula) is bathed in ____________, a fluid high in___.
endolymph
K+
Inertial movement of the endolymph results in a corresponding movement of the: ________ in relation to the _______ resulting in an opening or closing of the ___________.
stereocilia
kinocilia
leaky channels.
What are two types of photoreceptors:
rods and cones.
The rods are:
more active at times of low light and are located at the periphery of the retina.
The cones are:
most active in bright light and are located in the foveal (central) region of the retina.
Photoreceptors are are leaky, similar to hair cells of the vestibular system, resulting in:
a continual release of neurotransmitter.
When the receptor is activated by light, it becomes ___________ and results in a ________ in neurotransmitter release.
hyperpolarized
decreae
What is the output of the retina?
ganglion cell
Prior to the ganglion cell being activated, a great deal of integration takes place by multiple synapses through _____________, ______________, and ________________.
bipolar cells, horizontal cells and amacrine cells
The end result of the integration prior to ganglion cells being activated, is that receptive fields (RF) are defined for ganglion cells with _______ RFs representing __________ vision and _________ more precise RFs representing ___________. This corresponds with the distribution of rods and cones respectively.
large
peripheral
smaller
central vison
Surround Inhibition and Lateral Inhibition are demonstrated using:
central vision and the activation of cones.
