Session 3/4: PNS and Sensory Receptors Flashcards
<p>In order to understand the exact location on the body of a sensation, the position the body was in when the stimulus was applied and the position of the body as it reacts to the stimulus requires what? (3)</p>
<p>1. Understanding of nerve pathways 2. Physiology of how a sensation (stimulus) is encoded 3. How we perceive the sensation at a conscious level.</p>
<p>What is sensation?</p>
<p>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. </p>
<p>What processes are included in sensation? (4)</p>
<p>1. Sensory transduction
2. Receptor potential summation
3. Action potential generation
4. Neural processes that integrate signals centrally by either facilitation (depolarization) or inhibition (hyperpolarization)</p>
<p>What is sensory transduction?</p>
<p>Theconversion of asensory stimulus from one form to another.</p>
<p>What is receptor potential summation?</p>
<p>The summation of the individual actions of ligand-gated ion channel proteins, and decrease over time and space. They do not typically involve voltage-gated sodium and potassium channels.</p>
<p>What is perception?</p>
<p>The process where the CNS receives and interprets sensations based on present experiences, the present state of the internal and external environment, and memory of similar situations.</p>
<p>True or False. Perception occurs to various degrees of refinement. </p>
<p>True.</p>
<p>In what areas of the brain does perception occur and at what level?</p>
<p>1. Thalamus
2. Basal ganglia (movement, inter/intrapersonal space)
3. Cerebellum (unconsciousness)
4. Cortex (conscious)</p>
<p>What level of perception occurs in the basal ganglia?</p>
<p>Movement, intra- and interpersonal space.</p>
<p>What levelof perception occurs in the cerebellum?</p>
<p>Unconsciousness.</p>
<p>What level of perception occurs in the cortex?</p>
<p>Consciousness.</p>
<p>True or False. All receptors are sensitive ONLY to changes in stimulus, not prolonged stimulation.</p>
<p>False. Receptors may be sensitive only to changes in stimulus, OR in prolonged stimulation.</p>
<p>Intensity of a stimulus is related to what? (2)</p>
<p>1. Size of the receptor potential
| 2. Number of receptors activated.</p>
<p>Without a cortex, perceptions are incomplete or skewed from the normal, which can cause what? (4)</p>
<p>1. lack of localization 2. loss of sensation (anasthesia) 3. increased sensitivity (hyperesthesia) 4. abnormal sensation, tingling (parasthesia)</p>
<p>Howdoes sensory transductionoccur?</p>
<p>The energy of a stimulus triggers Na+, K+ and Cl- channels to open, allowing ion movement, such that a local potential difference occurs. This potential change is local and spreads only a few millimeters as it decays.</p>
<p>What types of stimulus energy can undergo sensory transduction? (3)</p>
<p>1. mechanical
2. chemical
3. light</p>
<p>What is the threshold for stimulation?</p>
<p>The amount of stimulus energy it takes to cause a local receptor potential. </p>
<p>What is the threshold for stimulation dependent on?</p>
<p>The physical properties of the receptor itself. </p>
<p>Explain the difference between low and high thresholds for stimulation.Give examples of each.</p>
<p>A low threshold for stimulation only requires a small stimulus to cause a local receptor potential, whereas a high threshold requires a larget stimulus for a local receptor potential.</p>
<p>1. Low threshold: Meissner's corpsucle (low freq vibration triggers)</p>
<p>2. High threshold: Ruffini ending (large amt ofskin stretch or joint movement triggers)</p>
<p>What is threshold for perception?</p>
<p>The lowest stimulus intensity necessary for perception of stimulus. </p>
<p>Threshold for perception is usually the same as the receptor threshold, but may be modified by \_\_\_\_\_\_\_\_ and \_\_\_\_\_\_\_\_\_\_.</p>
<p>Context</p>
<p>Experience</p>
<p>What is adaptation?</p>
<p>The duration for which the receptor potential is generated to the stimulus. </p>
<p>What determines adaptation?</p>
<p>The morphology of the receptor. Occurs when the receptor is continuously stimulated.</p>
<p>What is a rapidly adapting receptor potential? Give an example.</p>
<p>Action potentials are only generated at the onset and offset of the stimulus.
Example: Pacinian corpuscle receptor potential. </p>
<p>What is a slowly adapting receptor potential? Give an example. </p>
<p>Slowly adapting receptor potentials continue to signal throughout the duration of the stimulus.
Example: Ruffini corpuscles.</p>
<p>What is quality-specificity coding?</p>
<p>Receptors are specialized by morphology to respond to only one type of stimulus.</p>
<p>What was the opposing theory to specificity coding prior to its proposal in the 1800's?</p>
<p>Patterns of stimuli, similar to "Morse codes", signaled the type of stimulus.</p>
<p>What is frequency and population coding?</p>
<p>The intensity of a stimulus is directly related to the size of the receptor potential and the number of receptors activated.</p>
<p>Choose the best answers.
The stronger the stimulus, the (GREATER/SMALLER) the size of the receptor potentials, the (GREATER/LESSER) the number of receptors being activated, the (GREATER/LESSER) summation of the depolarizing events and thus the increased frequency of action potentials.</p>
<p>Greater
Greater
Greater</p>
<p>True or false.
The amplitude and speed with which the action potentials are traveling can change, but the frequency of action potentials cannot. </p>
<p>False.</p>
<p>What is a receptive field?</p>
<p>The area surrounding the receptor that when stimulated excites or inhibits the firing of a particular cell.</p>
<p>Which areas are considered the most sensitive parts of the body? Why?</p>
<p>The tips of fingers and the tongue.
Most sensitive because they have the smallest receptive fields and the largest number of receptive fields per area. </p>
<p>Choose the best answer.
As you move proximally, receptive field size (INCREASES/DECREASES) and density of receptors (INCREASES/DECREASES), therefore (INCREASING/DECREASING) sensitivity. </p>
<p>1. Increases
2. Decreases
3. Decreases.</p>
<p>What is a dermatome?</p>
<p>An area of the body contributing sensory input to one dorsal root.</p>
<p>What is convergent excitation?</p>
<p>All excited receptors converge onto one cell. </p>
<p>What is somatotropin organization of the CNS? This is more commonly know as the sensory \_\_\_\_\_\_\_\_.</p>
<p>An orderly mapping of sensations from body surface onto CNS area. There is a point-for-point correspondence of an area of the body to a specific point on the CNS.
Knows as the sensory homunculus.</p>
<p>True or false.
In a sensory homunculus, the areas with the largest receptor density will have the largest cortical receptive field.</p>
<p>True.</p>
<p>True or False.
There are cells in the sensory cortex that respond to specific orientation, movement and shape of stimulus.</p>
<p>True</p>
<p>How can sensory receptors be classified?</p>
<p>1. Stimulus location 2. Sensory system 3. Stimulus energy 4. Fiber type (most general classification) </p>
<p>What are exteroceptors?</p>
<p>Sensory receptors that receive stimuli from the external environment.</p>
<p>What are proprioreceptors?</p>
<p>Sensory receptors that position body segments relative to each other and position of body and head in space</p>
<p>What are interoceptors?</p>
<p>Sensory receptors that signal body events such as blood glucose levels and blood pressure. </p>
<p>Sensory receptors can be classified according to their corresponding sensory system. Name these 6 systems.</p>
<p>1. Somatic (tactile, joint, muscle, tendon, thermal, pain)
2. Visual
3. Vestibular
4. Auditory
5. Olfactory
6. Gustatory</p>
<p>Sensory receptors can be classified according to stimulus energy types. Name the 5 of these receptors and the corresponding stimulus energy.</p>
<p>1. Mechanoreceptor- touch/pressure, proprioception, air waves
2. Chemoreceptors- taste, smell, blood gas level
3. Nocireceptors- damaging stimuli (pain)
4. Thermoreceptors- heat and cold
5. Photoreceptors- light</p>
Name the 5 types of sensory fibers.
- Ia (A-α)
- Ib (A-α)
- II (A-β)
- III (Aδ)
- IV (C)
What sensory fiber types have a large diameter?
Ia, Ib, II
What sensory fiber types have a small diameter?
III, IV.
Which diameter fibers have a faster conduction velocity- small or large? Why?
Small diameter fibers are slower because they provide more resistance to flow of current and have less insulation from myelin.
Which sensory fiber types have a fast conduction velocity?
Ia, Ib, II
Which sensory fiber types have a slow conduction velocity?
III, IV
Which sensory fiber types are myelinated?
Ia, Ib, II, III
Which sensory fiber types are unmyelinated?
IV
What type of receptor is innervated by Ia sensory fibers?
Primary afferents of the muscle spindle
What type of receptor is innervated by Ib sensory fibers?
Golgi tendon organ
What type of receptors are innervated by II sensory fibers?
Secondary afferents of muscle spindle
Touch
Pressure
Vibration
What type of receptors are innervated by III sensory fibers?
Touch
Pressure
Pain
Temperature
What type of receptors are innervated by IV sensory fibers?
Pain
Temperature
Which diameter fibers have a higher amplitude of action potential- small or large? Why?
Large diameter fibers have higher amplitude because potential change across the membrane is bigger.
What can an EMG tell you about fiber diameters?
You can distinguish small diameter from large diameter fibers by the size of the EMG amplitude.
Which diameter fibers have a higher threshold for stimulation- small or large? Why?
Small diameter fibers have a higher threshold for stimulation because they offer more resistance to current flow.
Which sensory fiber type will require the highest intensity stimulation to activate?
VI (C)
What are the four types of motor fibers?
- Alpha (A-α)
- Gamma (A-γ)
- Preganglionic ANS fibers (B)
- Postganglionic ANS Fibers (C)
What motor fiber type has a large diameter?
Alpha
What motor fiber types have a small diameter?
Gamma
Preganglionic ANS Postganglionic ANS
What motor fiber types have a fast conduction velocity?
Alpha
What motor fiber types have a slow conduction velocity?
Gamma
Preganglionic ANS Postganglionic ANS
What is the role of alpha motor fibers?
Innervate extrafusal muscle fibers
What is the role of gamma motor fibers?
Innervate intrafusal muscle fibers
What is the difference in myelination between Preganglionic ANS fibers and Postganglionic ANS fibers?
Preganglionic ANS fibers are lightly myelinated, whereas postganglionic fiber are unmyelinated.
Describe a Type 1 receptor.
Structure:
Location:
Response:
Function:
Structure: Encapsulated, “Ruffinilike”
Location: Ligaments, joint capsule, proximal joints
Response: Mechanoreceptors, slow adapting, low threshold, active during movement and at rest
Function: Contributes to regulation of postural muscle tone, kinesthesia, regulation of muscle tone during movement
Describe a Type II receptor.
Structure:
Location:
Response:
Function:
Structure: Encapsulated, “paciniform”
Location: Synovial junction of joint capsule, fat pads of joint, distal joints
Response: Mechanoreceptors, rapidly adapting, low threshold, active at beginning and end of movement
Function: Provide info about beginning/end of joint movement, may help boost muscle tone at beginning of movement to overcome inertia
Describe a Type III receptor.
Structure:
Location:
Response:
Function:
Structure: Encapsulated, “GTOlike”
Location: Ligaments, all joints of the body
Response: Mechanoreceptors, slow-adapting, high-threshold, active at extremes of range and with longitudinal traction
Function: Responds to sudden joint movements and may cause reflex muscle contraction to limit further movement
Describe a Type IV receptor.
Structure:
Location:
Response:
Function:
Structure: Free nerve endings
Location: Joint capsule, ligaments, periosteum, synovial lining, fat pads
Response: Pain receptors, slow-adapting, high-threshold, active with extreme mechanical force or chemical irritation
Function: May contribute to a flexion reflex, or to a contraction pattern around a joint to prevent further movement
What is a muscle spindle?
Special muscle fibers containing contractile elements.
Describe the structure of a muscle spindle.
- Encased in a connective tissue sheath (encapsulated) that is anchored to the endomysium and perimysium that surrounds the fascicles of muscle.
- Run in parallel to extrafusal fibers
What is the purpose of a muscle spindle?
To encode the stretch of a muscle (how it understands movement of the limb)
The contractile fibers within a muscle are referred to as __________
Intrafusal muscle fibers
The fibers that make up the bulk of a muscle are referred to as ________.
extrafusal muscle fibers
True or false. Intrafusal and extrafusal muscle fibers have a typical sarcomere arrangement.
True.
Where are the contractile elements located in extrafusal fibers? How is this different than intrafusal fibers?
In extrafusal fibers, contractile elements are evenly distributed throughout.
In intrafusal fibers, the contractile elements are located at the poles/ends of each fiber.
Describe the contraction of an extrafusal fiber, and how it differs from an intrafusal fiber contraction.
Extrafusal: shortens from the entire length, contracting towards the middle
Intrafusal: Contracts toward the ends, stretching the center part of the fiber.
True or false. Extrafusal and intrafusal fibers are both visible to the naked eye.
False. Only extrafusal fibers can be seen.
What are the two nuclear arrangements of intrafusal fibers found within the muscle spindle?
- Nuclear bag filament
2. Nuclear chain filament.
Describe the nuclear arrangement of a nuclear bag filament.
Nuclei are “clumped” in the middle forming a “bag-like” enlargement of the sarcolemma.
Describe the nuclear arrangement of a nuclear chain filament.
Nuclei arranged linearly in a “chain-like” arrangement.
Each filament has at least two sensory receptors located either centrally around the nuclear groups or peripherally near the contractile elements. What are they?
- Primary endings (Ia axon)
2. Secondary endings (II axon)
- What is the histological name of primary endings?
Annulospiral rings.
Primary endings are highly responsive to what?
The rate of change in muscle length. As soon as the change stops, signaling ends (instantaneous response)
What are dynamic or phasic endings? Give an example.
Encode the velocity of a stretch- respond to rate of change. Primary endings in muscle spindles.
What is the role of primary endings?
To encode the velocity of a stretch.
Which is faster- primary or secondary endings?
Primary. Ia axon is faster than II axon.
What is the histological name of secondary endings?
Flower spray endings.
Secondary endings are responsive to what? What is another name for these endings?
Static muscle length.
Also known as static or tonic endings.
What is the role of secondary endings?
Tell us what the new length of muscle is.
What is the stimulus during a stretch?
Mechanical deformation of the afferent ending.
The contractile component of each fiber in a muscle spindle receives what to control its contraction?
An ending from a gamma motor neuron
What occurs when a gamma motor neuron is activated? This can be used to adjust what?
The contraction of intrafusal fibers
Can be used to adjust the sensitivity of each receptor within the muscle spindle.
True or false. Adjustments of sensitivity made by gamma motor neurons is the same for dynamic and static receptors.
False. Adjustments of sensitivity are specific and separate to the dynamic receptors and to the static receptors.
What is the purpose of motor activation of muscle spindles?
To prevent “unloading” of the receptor during extrafusal muscle contraction.
What occurs during alpha-gamma coactivation? What is the result?
At the time of alpha motor neuron firing, appropriate gamma motor neurons are also activated.
Results in muscle spindle adjustment that parallels the contraction of the extrafusal muscle fiber.
How else can gamma motor neurons be stimulated other than by alpha-gamma coactivation? What is the result?
Can be influenced by CNS pathways or cutaneous stimulation.
- Results in an increase in sensitivity of both primary and secondary endings.
- allows for fine-tuning of the spindle as the difficulty of the motor task increases.
What happens with alpha and gamma activation during a muscle elongation?
Inhibit alpha and gamma motor neurons in order to prevent a stretch response.
During muscle elongation and the inhibition of alpha and gamma motor neurons, what part of the spindle stays the same, and what part is stretched?
The center (receptor) part stays the same, so there is no change in sensitivity.
Stretch is kept at the contractile part.
What are golgi tendon organs?
Slender capsule encased receptors found at both the origin and insertion of skeletal muscles at musculo-tendonous junctions.
Describe the structure/ integration of extrafusal fibers with GTOS
Extrafusal fibers enter capsule. Collage fibers of epimysium perimysium become braided with collagen.
Receptor is located a the end of IB nerve fibers and intertwines with the collegen of the receptor capsule.
What occurs with contraction of extrafusal fibers?
- Tension on collagen bundles
- Compressing the afferent nerve ending
- Activating a receptor potential
- Followed by generation of AP if stimulus is sufficient
What is the GTO highly sensitive to? What is the benefit of this?
Small changes in muscle tension,
Benefit is it provides continuous feedback to regulate muscle tension.
GTO has a high threshold to what?
Tension (resisted muscle stretch)
What is autogenic inhibition.
GTO plays a protective role by inhibiting alpha motor neuron activation of the contracting muscle when extremes of range are reached. This is a protective response.
What are the functions of the GTO? (3)
- Measure resistance to limb movement/muscle dynamic
- Provide an ongoing signal coming in- measuring resistance to the movement
- Can inhibit alpha motor neuron (relax muscle), in order to prevent injury to the muscle fibers
True or False. Thermal and nociceptors are encapsulated.
False. Both are nonencapsulated (free nerve endings)
What is normal skin temperature?
34 degrees C
Thermal afferents are responsible for what?
Encoding temperature changes sensed by the skin.
What type of nerve ending (capsulated or nonencapsulated) is found in thermal afferents? Where are they located?
The primary receptor is a free nerve ending.
Located in the dermal layer of the skin.
What fiber innervate thermal receptors? Where is the highest concentration?
Receptors are continuous with A-delta and C fibers, with the highest concentration located near the midline.
How are thermal receptors classified?
By their response to cold or heat (separate receptors, separate responses)
Cold afferents respond to temperatures in what range and travel through what type of sensory fibers?
10-33 degrees celsius.
A-delta and C fibers
Heat afferents respond to temperature changes in what range and travel through what type of fibers?
32-45 degrees celsius (some can respond to >45 degrees)
Travel over C fibers
Where are nociceptors found in the body?
Dermal layers of skin
Deep tissues, including muscles and joints
The primary receptor for pain has what type of nerve ending?
Free nerve ending
What is the primary stimulus for nociceptors? Both generally speaking and specifically.
Mechanical damage to tissue. Either by temperature extremes or destruction of tissue (mechanical or chemical)
What receptors are classified as cutaneous nociceptive afferents?
A-delta mechanoreceptive nociceptors, A-delta mechanothermal nociceptors or C-polymodal nociceptors.
A-delta mechano receptive nociceptors are characterized by a (HIGH/LOW) threshold for stimulation with (SMALL/LARGE) receptive areas.
High
Small
Where are 20% of A-d mechanoreceptive nociceptors found?
Within fascial planes
What is the primary stimulus for A-d mechanoreceptive nociceptors? This allows for discrimination between what?
Sharp pain
Allows for discrimination between sharp and dull
What causes sensitization in A-d mechanoreceptive nociceptors? What does this result in?
Intense heat
Burn hyperalgesia
A-delta mechanothermal nociceptors are maximally responsive what temperature range? What other temperatures do they respond to?
Max response at 45-53 degrees.
Also respond to
What receptors are responsible for the first pain from intense thermal stimuli? What other stimuli do they respond to?
A-delta mechanothermal nociceptors.
Also respond to intense mechanical stimuli.
What type of receptor makes up the majority of cutaneous receptors (>90%)?
C-polymodal nociceptors
What type of nerve ending is found in C-polymodal nociceptors?
Free nerve endings
How are C-polymodal nociceptors activated? (3)
- Thermal (45 degrees)
- Mechanical (crush)
- Chemical (histamine release from tissue damage)
True or False. Muscle and Joint nociceptive afferents also have both A-d and C fiber components
True
How are A-d fiber components activated in muscle tissue?
By muscle stretch or contraction (ergoreceptive)
How are C fibers are activated in muscle tissue?
intense mechanical or chemical stimuli (ischemic muscle pain)
How are joint receptors (both A-d and C) activated? How are they sensitized?
By intense pressure and movement.
Sensitized by inflammation
What happens to joint receptors (both A-d and C) in the presence of inflammation
A high background firing rate
What type of fibers are visceral nociceptive afferents? What are they similar to?
C fibers.
Similar to C polymodal nociceptors.
What type of information is relayed by visceral nociceptive afferents?
Poorly localized and referred information.
How our visceral nociceptive afferents stimulated?
twisting, distension and/or inflammation
How many types of hair cells exist in the vestibular apparatus? How are they activated?
Two types.
Both activated by accelaration of the head by a mechanisam know as mechanoelectrical transduction.
What is mechanoelectrical transduction?
A mechanical deflection of steriocilia and kinocilia, also known as the gated spring model.
Describe how stereocilia and kinocilia are anchored together and to cell membranes.
Cilia are anchored together by a protein link.
This protein link is attached to/near leaky K+ and Ca++ channels (not Na+ as other excitable membranes)
Describe the steps involved in mechanoelectrical transduction (gated spring model). (3)
- Deflection of cilia.
- Causes K+ and Ca++ channel modification (opened or closed) to increase or decrease influx of ions.
- Results in an increase or decrease in the release of neurotransmitter (maybe gluatamate) onto the 1st order neuron.
How many types of visual receptors are there? What are they?
Two- rods and cones
When are rods most active?
In low light
Where are rods located?
at the periphery of the retina
When are cones most active?
In bright light
Where are cones located?
in the foveal (central) region of the retina
Visual receptors are leaky, which results in what? This is similar to what other type of cells and system?
Results in the continuous release of neurotransmitter.
Similar to hair cells of the vestibular system.
What happens when visual receptors are activated by light?
The receptor becomes hyperpolarized and results in a decrease in neurotransmitter release.
What is the output of the retina?
The ganglion cells
What occurs before the ganglion cell in the visual system is activated?
Integration takes place by multiple synapses through bipolar, horizontal and amacrine (interneuron) cells.
What is the end result after integration takes place through bipolar, horizontal and amacrine cells?
receptive field definition.
How are large receptive fields defined? What does this correspond to?
For ganglioin cells with large receptive fields represent peripheral vision.
This refers to the location of rods in the periphery.
How are small receptive fields defined? What does this correspond to?
Smaller more precise receptive fields represent central vision.
This corresponds to the location of cones in the center of the retina.
Explain surround and lateral inhibition using central vision and the activation of cones.
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