Sensory Receptors Flashcards
What is known as the process where sensory receptors receive information from both the internal and external environment and encode the information for transmission to various area of the nervous system?
Sensation
What is known as the process where the CNS receives and interprets the sensations based on present experiences, the present state of the internal and external environment, and memory of similar situations?
Perception
What type of perception occurs at the cortical level?
conscious perception
What type of perception occurs at the cerebellum level?
unconscious perception
The basal ganglia is involved in what type of perceptions?
the basal ganglia is involved in unconscious representations of movement experiences, but also involved with perceptions of inter- and intrapersonal space
What is known as changing the energy of a stimulus into a neural energy?
sensory transduction
The stimulus energy causes what to change in the receptor membrane during sensory transduction?
The stimulus energy (mechanical, chemical, light) produces a change in the receptor membrane (aka local potential difference). Na+, K+, and Cl- channels open to allow ion movement. This potential change is local and spreads only a few mm as it decays.
What is known as the amount of stimulus energy it takes to cause a local receptor potential?
Threshold for stimulation
True or false: Threshold for stimulation depends on the physical properties of the receptor?
True
What is known as the lowest stimulus intensity necessary for perception of stimulus?
Threshold of perception
– usually the same as receptor threshold, but may be modified by context and experience
What is known as the duration for which the receptor potential is generated to the stimulus?
Adaptation
True or False: Adaptation of a receptor is NOT determined by the morphology of the receptor?
FALSE - Speed of adaptation is determined by the morphology of the receptor
What type of adapting receptors end signaling before stimulus is removed and tell when the stimulus was applied?
Rapidly adapting receptors
What type of adapting receptors continue signaling for the duration of the stimulus and tells us how long the stimulus lasted?
Slowly adapting receptors
– action potentials are repeated through length of the stimulus duration
What type of sensory information coding refers to the receptors being specialized by their morphology to respond to only one type of stimulus?
Specificity Coding (Quality)
The intensity of a stimulus is directly related to the ______ of the receptor potential and the _______ of receptors activated.
size; number
The intensity of a stimulus is transferred to the generation of an AP and coded by what two things?
the frequency of AP and the number of discharge fibers
The _______ the stimulus, the _______ the size of the receptor potentials (depolarization), the ______ the number of receptors being activated, the ________ summation of the depolarizing events and thus the ________ frequency of APs.
stronger greater greater greater increased
Only the _________ of APs is changing, NOT the _______ of the _______ with which the APs are traveling.
frequency
amplitude
speed
What is known as the area surrounding the receptor that when stimulated excites or inhibits the firing of a particular cell?
Receptive field
What parts of the body have the smallest receptive fields and the largest number of receptive fields per area, making them the most sensitive parts of the body?
tips of the fingers and the tongue
As you move proximally, receptive field size ______ and density of receptors _______, as does the sensitivity.
Increase; decrease
What is known as the area of the body surface contributing sensory input to one dorsal root?
Dermatomes
What is known as excitatory discharge being greatest at the center of the receptive field and inhibitory at the periphery?
lateral inhibition
– serves to enhance distinction between two stimuli and aids in recognition of pattern and contour
The areas with the _______ receptor density will have the _______ cortical receptive fields.
largest; largest
What type of receptors are stimulated by the external environment?
Exteroreceptors
What type of receptors are stimulated by position of body segments relative to each other and position of body and head in space?
Proprioceptors
What type of receptors signal body events such as blood glucose level and blood pressure?
Interoceptors
Sensory receptors are classified by what three categories?
1) stimulus location
2) sensory system
3) stimulus energy
What are the 6 categories of the sensory system classification?
1) somatic - tactile, joint, muscle, tendon, thermal, pain
2) visual
3) vestibular
4) auditory
5) olfactory
6) gustatory
What type of receptors responds to touch/pressure, proprioception, and air waves?
Mechanoreceptors
What type of receptor responds to taste, smell, blood gas level?
Chemoreceptors
What type of receptor responds to damaging stimuli (pain)?
Nociceptors
What type of receptor responds to heat and cold?
Thermoreceptors
What type of receptor responds to light?
Photoreceptors
What type of sensory fibers have large diameter axons with increased levels of myelin?
Encapsulated fibers: Ia, Ib, II
What type of sensory fibers have small diameter axons with decreased to no myelin?
Non-encapsulated fibers: III, IV
What sensory fibers have a large axon diameter (12-20 micrometers), a fast conduction velocity (70-120 m/s) and innervate primary afferent receptors of the muscle spindle?
Ia (A- alpha)
What sensory fibers have a larger axon diameter (12-20), a fast conduction velocity (70-120 m/s), and innervate receptors of Golgi tendon organs?
Ib (A - alpha)
What sensory fibers have a moderate axon diameter (5-14), a moderate conduction velocity (30-70 m/s), and innervate secondary afferent receptors of the muscle spindle, touch, pressure, and vibration?
II (A - beta)
What sensory fibers have a small axon diameter (2-7), a slow conduction velocity (12-30 m/s), and innervate receptors of touch, pressure, pain, and temperature?
III
What sensory fibers have a small axon diameter (0.5-1), a slow conduction velocity (0.5-2 m/s), and innervate receptors of pain and temperature and unmyelinated fibers?
IV (C)
Small diameter fibers have a _______ conduction velocity. Why?
Slower; because they provide more resistance to flow of current and have less insulation from myelin
Small diameter fibers have ______ amplitude. Why?
Lower; because potential change across the membrane is smaller.
Small diameter fibers have a _______ threshold for stimulation. Why?
Higher: because they offer more resistance to current flow (example: C fibers will require higher intensity of stimulation to activate)
Which motor neuron innervates extrafusal muscle fibers?
Alpha (A-alpha)
Which motor neuron innervates intrfusal muscle fibers?
Gamma (A-gamma)
Which motor fibers have the fastest conduction velocity?
Alpha (A-alpha)
Which motor fibers are lightly myelinated?
preganglionic ANS fibers (B)
Which motor fibers are unmyelinated?
postganglionic ANS fibers (C)
What are the 4 types of cutaneous mechanoreceptors?
1) Meissner’s Corpuscles
2) Pacinian Corpuscles
3) Merkel’s disks
4) Ruffini’s Corpuscles
What nerve fiber type innervates all four cutaneous mechanoreceptors?
Type II (A-beta)
Are cutaneous mechanoreceptors considered high or low threshold?
low-threshold (high sensitivity)
Which cutaneous mechanoreceptor type lies between the dermal papillae just beneath the epidermis, are rapidly adapting and transduces information about the relatively low-frequency vibrations (30–50 Hz) that occur when textured objects are moved across the skin?
Meissner’s Corpuscles
Which cutaneous mechanoreceptor type lie in the subcutaneous layer, are rapidly adapting and provide information primarily about the dynamic qualities of mechanical stimuli?
Pacinian Corpuscles
Which cutaneous mechanoreceptors are slowly adapting?
Merkel disks and Ruffini’s Corpuscles
Which cutaneous mechanoreceptors are rapidly adapting?
Meissner’s Corpuscles and Pacinian Corpuscles
Which cutaneous mechanoreceptor type is located in the epidermis, where they are precisely aligned with the papillae that lie beneath the dermal ridges, and play a major role in the static discrimination of shapes, edges, and rough textures?
Merkel’s disks
Which cutaneous mechanoreceptor type is located deep in the skin, as well as in ligaments and tendons, are particularly sensitive to the cutaneous stretching produced by digit or limb movements, and respond primarily to internally generated stimuli?
Ruffini’s Corpuscles
Where are Type I (encapsulated Ruffini-like) joint mechanoreceptors located?
ligaments, joint capsule, and proximal joints
Type I (encapsulated Ruffini-like) joint mechanoreceptors:
- slow or rapid adapting?
- high or low threshold?
- active when?
- slowly adapting
- low threshold
- active during movement and at rest
Function of Type I (encapsulated Ruffini-like) joint mechanoreceptors?
- regulates postural muscle tone
- kinesthesia (is it moving)
- regulates muscle tone during movement
Where are Type II (encapsulated Paciniform) joint mechanoreceptors located?
synovial junction of joint capsule, fat pads of joint, distal joints
Type II (encapsulated Paciniform) joint mechanoreceptors:
- slow or rapid adapting?
- high or low threshold?
- active when?
- rapidly adapting
- low threshold
- active at beginning and end of movement
Function of Type II (encapsulated Paciniform) joint mechanoreceptors?
- provides information about beginning and end of joint movement
- may help “boost” muscle tone at beginning of movement to overcome inertia
Where are Type III (encapsulated GTO-like) joint mechanoreceptors located?
Ligaments, all joints of the body
Type III (encapsulated GTO-like) joint mechanoreceptors:
- slow or rapid adapting?
- high or low threshold?
- active when?
- slow adapting
- high threshold
- active at extremes of range and with longitudinal traction
Function of Type III (encapsulated GTO-like) joint mechanoreceptors?
- responds to sudden joint movements
- may cause reflex muscle contraction to limit further movement
Where are Type IV (free nerve endings) joint mechanoreceptors located?
joint capsule, ligaments, periosteum, synovial lining, fat pads
Type IV (free nerve endings) joint mechanoreceptors:
- slow or rapid adapting?
- high or low threshold?
- active when?
- slow adapting
- high threshold
- active with extreme mechanical force or chemical irritation
Free nerve endings are what kind of receptor?
pain receptor
Function of Type IV (free nerve endings) joint mechanoreceptors?
- may contribute to a flexion reflex, or to a co-contraction pattern around a joint to prevent further movement
What receptor responds to stretch of a muscle and contain contractile elements?
Muscle spindles
What contractile fiber lies within the muscle spindle?
intrafusal muscle fibers
What contractile muscle fiber makes up the bulk of a muscle?
extrafusal muscle fibers
The contractile elements of intrfusal fibers are located where? This allows for what?
located at the poles or ends of each fiber; allowing for elongation of the center of the muscle and not the entire muscle
What are the two nuclear arrangements found within each intrafusal fiber? (multinucleated with all nuclei located centrally)
- nuclear bag –> clumped nuclei in the middle, forming an enlargement of the sarcolemma
- nuclear chain –> nuclei arranged linearly
Each filament has two types of sensory receptors found in the muscle spindle. What are they? And where are they located?
- Primary endings (centrally located)
- Secondary endings (peripherally located)
Which sensory receptor found in the muscle spindle responds to rate of change in the muscle length, encoding the velocity of the stretch?
Primary endings (annulospiral rings)
Which receptors are referred to as dynamic or phasic receptors?
Muscle spindle - primary endings
Which type of muscle spindle receptor is responsive to the muscle static muscle length?
Secondary endings (flower spray endings)
Which receptors are referred to as static or tonic endings?
Muscle spindle - secondary endings and some primary endings
The information from primary endings is carried where?And by what nerve fiber?
into the CNS Ia fibers
The information from secondary endings is carried by what nerve fiber?
type II fibers
Activation of the gamma motor neuron results in the contraction of what type of muscle fiber?
intrafusal fibers
Role of intrafusal fibers?
adjusts the sensitivity of each receptor within the muscle spindle
Purpose of alpha-gamma coactivation?
When the alpha motor neuron fires to trigger the contraction of the extrafusal fiber, the appropriate gamma motor neuron is also activated which causes the intrafusal fiber to contract and prevent “unloading” of the receptor during extrafusal muscle contraction. Overall, it results in muscle spindle adjustment that parallels the contraction of the extrafusal muscle fiber.
Muscle spindles encode the change in what?
length and stretch of a muscle
Stimulation of the gamma motor neuron results in what?
resulting in an increase in the sensitivity of both of the primary and secondary endings - this allows for fine tuning of the spindle as the difficulty of the motor task increases
Stimulation of the gamma motor neuron can be influenced by what?
central nervous system pathways or by cutaneous stimulation
Which receptors are slender capsule encased receptors found at both the origin and insertion of skeletal muscles as musculo-tendonous junctions?
Golgi Tendon Organs
Golgi Tendon Organs are innervated by what type of nerve fiber?
Ib
The GTO is highly sensitive to what?
small changes in muscle tension, providing continuous feedback to regulate muscle tension
What is the protective role of GTO’s?
inhibiting alpha motor neuron activation of the contracting muscle when extremes of range are reached (autogenic inhibition) - protection against damaging resistance that could cause a tear in the muscle
GTO’s tell you what?
the resistance of a particular movement and tells the body whether more muscle activity needs to be recruited or not
GTO’s measure what?
the resistance to limb movement or muscle dynamic or shortening of the muscle
What type of receptor encodes temperature changes sensed by the skin?
Thermal afferents (thermoreceptors)
Where is the primary thermoreceptor located in the body?
the free nerve ending located in the dermal layer of the skin
Thermoreceptors are classified by what?
classified by their response to cold or heat
Cold afferents respond to what temperatures and travel over what nerve fibers?
10-33 degrees Celsius
- fibers A-delta and C (Type III and IV)
Hot afferents respond to what temperatures and travel through what nerve fibers?
32-45 degrees Celsius
- some can respond to temperatures greater than 45 degrees Celsius
- fibers C (Type IV)
What do nociceptors respond to?
pain
Where are nociceptors found in the body?
dermal layers of the skin as well as in many deep tissues including muscles and joints
What other receptor, in addition to nociceptors, respond to pain?
free nerve endings
What is the primary stimulus of nociceptors?
mechanical damage to tissue, either by temperature extremes or destruction of tissue (mechanical, chemical)
What are the three classifications of cutaneous nociceptive afferents?
1) A-delta mechanoreceptive nociceptors
2) A-delta mechanothermal nociceptors
3) C-polymodal nociceptors
Afferents carry information from ______ to _____?
from the body to the brain
Efferents carry information from _______ to ______?
from the brain to the body
A-delta mechanoreceptive nociceptors have a high or low threshold?
high threshold
A-delta mechanoreceptive nociceptors have what size receptive field?
small receptive field
A-delta mechanoreceptive nociceptors primary stimulus?
sharp pain allowing for discrimination between sharp and dull
A-delta mechanoreceptive nociceptors are sensitized by what?
these receptors are sensitized by intense heat that results in burn hyperalgesia
A-delta mechanothermal nociceptors are maximally responsive to what temperatures?
45-53 degrees Celsius
A-delta mechanothermal nociceptors also respond to what other temperatures?
A-delta mechanothermal nociceptors are responsible for what stimuli?
first pain from intense thermal stimuli as well as intense mechanical stimuli
What receptor type makes up the majority of cutaneous receptors?
C-polymodal nociceptors
What makes up 90% of C-polymodal nociceptors?
free nerve endings
What three stimuli activate C-polymodal nociceptors?
1) thermal ( 45 degrees Celsius)
2) mechanical (crush)
3) chemical (histamine release from tissue damage)
Muscle and joint nociceptive afferents have what two nerve fiber components?
A-delta and C fibers (Type III and IV)
The A-delta fiber components of muscle and joint nociceptive afferents are activated by what?
muscle stretch or contraction - ergoreceptive
The C fiber components of muscle and joint nociceptive afferents are activated by what?
intense mechanical or chemical stimuli - ischemic muscle pain
Joint receptors are activated by what?
intense pressure and movement
Joint receptors are sensitized by what?
inflammation
- develops into a high background firing in the presence of inflammation
Visual nociceptive afferents are what kind of nerve fibers?
C fibers (Type IV)
Visual nociceptive afferents relay what kind of information?
poorly localized and referred information
Visual nociceptive afferents are stimulated by what?
twisting, distention, and/or inflammation
How many types of hair cells exist in the vestibular apparatus?
two types
The two types of hair cells are both activated by what?
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 anchored together by a protein link that is attached to what two ion channels?
leaky K+ and Ca++ channels (NOT Na+)
Mechanical deflection of the cilia results in what?
- the channels are modified (opened or closed) to increase or decrease the influx of ions
- results in an increase or decrease in the release of neurotransmitter onto the 1st order neuron
How does the structure of the vestibular receptor apparatus work?
- bathed in endolymph (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
What are the two main structures of the vestibular apparatus?
- ampulla of the semicircular canals
- macula of the saccula and utricle
What are the two types of photoreceptors?
rods and cones
When are rods most active?
active at times of low light
Where are the rods located?
periphery of the retina
When are cones most active?
active in bright light
Where are the cones located?
in the foveal (central) region of the retina
These visual receptors are ________ (similar to hair cells of the vestibular system) resulting in a continual release of ________.
- leaky
- neurotransmitter
What happens to the visual receptor when it is activated by light?
the visual receptor becomes hyperpolarized and results in a decrease in neurotransmitter release
What is the output of the retina?
the ganglion cell
Prior to the ganglion cell being activated, a great deal of integration takes place by multiple synapses through what three types of cells?
- bipolar cells
- horizontal cells
- amacrine cells
A large receptive field of a ganglion cell represents what type of vision?
peripheral vision
A small receptive field of a ganglion cell represents what type of vision?
central vision
Receptive fields for ganglion cells correspond with what?
the distribution of rods and cones, respectively
Stimulation in the surround results in inhibition or facilitation/excitation?
inhibition
Stimulation in the center results in inhibition or facilitation/excitation?
facilitation/excitation
Which sensory receptor of muscle spindles are innervated by rapidly adapting nerve fibers?
primary endings - Type Ia fibers
Which sensory receptor of muscle spindles are innervated by slowly adapting nerve fibers?
secondary endings - Type II fibers
Nuclear chains excite what sensory receptors of the muscle spindle and are they static or dynamic?
- secondary endings and primary endings
- static
Nuclear bags excite what sensory receptor of the muscle spindle and are they static or dynamic?
- primary endings
- dynamic
