Sensory Receptors And Perception Flashcards
What are receptors that respond to stimulus within the body?
What aRe the four major types?
Interoreceptors
- Proprioceptors
- Visceroreceptors
- Chemoreceptors
- Baroreceptors
What are receptors that respond to stimuli from the outside environment?
What are four examples?
Exteroreceptors
- Cutaneous sense
- Vision
- Olfaction
- Hearing
What does a proprioceptor respond to?
Movement or change in position
What does a visceroreceptor respond to?
Stretching of internal organs or muscular contraction
What does a chemoreceptor respond to?
Changes in the chemical environment
What do baroreceptors respond to?
Changes on pressure
What is the difference between sensation and perception?
What do people in a coma have?
Sensation is the conscious and unconscious awareness of external or internal stimuli
Perception is the conscious awareness AND interpretation of sensation
People in comas have sensation without perception
What is meant by modality?
The specific type of sensation (vibration and thermal pain)
What is transduction?
The conversion of one form of energy to another (light to electrical signal that can be processed in the visual cortex)
What is conduction?
The propagation of a signal to a distant site in the nervous system.
When a receptor potential reaches a threshold at the trigger zone, the receptor can initiate one or more nerve impulses
Why does a sensory exam of light touch yield incomplete information?
Because touch is carried in both small and large fibers
What are the three major components of the somatic sensory system?
- A subsystem for detection of mechanical stimuli such as touch vibration and pressure
- Subsystem for sensation of position
- Subsystem for painful stimuli and temperature
How do peripheral nevers vary in myelin content, diameter, and speed of conduction?
Large diameter fibers are heavily myelinated and conducted impulse quickly (50 m/sec or faster)
What kind of stimuli is transmitted by large caliber fibers?
Mechanical stimuli and somatic motor axons
What signals are transmitted by unmyelinated fibers?
What is the speed of transmission and diameter?
pain and temperature Slow transmission (few m/sec) and small diameter
What is the morphology, sensory modality and conduction for a Ia fiber?
Large myelinated
Proprioception (muscle spindle)
Fast (90m/sec)
What is the morphology, sensory modality and conduction for an Abeta fiber? (type II)
Large myelinated
Vibration pressure touch and stretch
50 m/sec
What is the morphology, sensory modality and conduction speed for an Adelta fiber? (type III)
Small myelinated
Touch, cold, pain
20 m/sec
What is the morphology, sensory modality and conduction speed for a B fiber?
Small myelinated
Autonomics
10 m/sec
What is the morphology, sensory modality and conduction speed for a C fiber? (type IV)
Small unmyelinated
Temperature, pain, itch
1m/sec
What is the difference between type Ia and type Ib fibers?
Ia- sensory afferent for muscle spindle (muscle stretch)
Ib- sensory afferent for Golgi tendon organs (muscle tension)
Both are proprioceptive fibers
A process that affects large, myelinated sensory fibers (Ia) will be associated with what presentation?
The absence of a deep tendon reflex
A monosynaptic deep tendon reflex does what?
A polysynaptic deep tendon reflex does what?
Mono- excites motor agonists
Poly- inhibits motor antagonists
What is tabes dorsalis?
What fibers are selectively damaged by it?
What does this cause?
Syphilis
Large, myelinated fibers
This makes sensory ataxia (due to affected deep tendon reflex) and loss of joint position sense
If large myelinated sensory fibers are damaged, why are people more sensitive to pain?
Because the large fibers suppress painful stimuli.
Which sensory fibers are activated at the lowest threshold ?
The larger the fiber, the lower the threshold for activation so if you stimulate the large fibers with non-painful electrical currents, it can suppress pain.
Where do cell bodies of sensory neurons lie?
What type of neuron is it?
Outside of the spinal cord in the dorsal root ganglion.
These are bipolar neurons with two long axons.
Where does large fiber sensation enter the spinal cord?
What senses are carried by these large fibers?
Where do they travel and synapse?
Medial part of the dorsal root and ascend in the ipsilateral dorsal column.
Proprioception, Vibration, stretch, pressure
The first synapse is with the nucleus gracilis or cuneatus in the medulla.
Where do small fibers enter the spinal cord?
What sensations are these?
Where do they travel and synapse?
They enter in the lateral division of the dorsal root and ascend in the dorsal horn a level or two (lissaurs tract) before synapsing with w a secondary neuron in the substantia gelatinosa.
Pain and temperature
The secondary neuron from the substantia gelatinosa crosses and ascends in the anterolateral part of white matter on the contralateral side of the sensation (Spinothalamic tract)
What are some examples of small fiber neuropathies?
What do they result in the loss of?
Diabetes, amyloidosis, HIV
Results in the loss of pinprick and thermal sensation
Reflexes will be normal
What type of nerve innervates hair cells?
Are they fast or slow adapting?
What is the structure of a hair cell receptor?
Adelta and Abeta so they detect movement and light touch
They are fast-adapting which means that they discharge briefly after the hair is bent or returns to a normal position but will not continue to fire if the hair stays bent.
The hair cell receptor is a nerve terminal parallel to the hair that is sandwiched between two Schwann cells
What type of fibers are in pacinian corpuscles?
Are pacinian corpuscles fast or slow adapting?
What do they sense?
What is the structure?
Where are they found?
How do you assess the integrity of pacinian corpuscles in the skin?
Abeta fibers
Fast-adapting
Minimal skin distortion and can follow stimuli oscillating at high rates (up to 500Hz)
They are in subcutaneous tissue and are laminated corpuscles with a central naked axon (or axons)
They are found in subcutaneous tissue, ligaments, joint capsules, pleura, peritoneum, nipples, genitalia
Assess with bedside vibratory test (tuning fork)
What types of fibers are in meissners corpuscles?
Are the fibers fast adapting or slow adapting?
What do they measure?
What is the structure?
Where are they found?
How are they tested?
Abeta
Fast-adapting
They measure low frequency oscillations up to 40Hz (flutter-feeling of repetitive movement), light touch, dynamic pressure, two point discrimination
Laminated corpuscle with several nerve fibers intertwined in the lamellae
They are found in the superficial dermal papillae (Esp in fingers, palm, plantar surface of feet)
With a cotton wisp.
What type of fibers are in merkel cells? Are they fast or slow adapting? What do they sense? What is the structure? Where are they located?
Abeta
Slow-adapting (initial rapid burst followed by a sustained rate of discharge relative to the degree of skin indentation)
Respond to light static pressure, discriminate shapes, edges, textures
The structure is a tactile cell, naked axon, and Schwann cell
Found in hairless skin like fingertips and lips and external genitalia. Also found in hair follicles
What is the major role of proprioceptors?
Provide info about static limb position and kinesthesia (sense of movement)
What is kinesthesia?
Sense of movement
Where are proprioceptors located?
What do their afferents allow the CNS to do?
Muscles, tendons, joint capsules, ligaments
The afferents allow the CNS to calibrate output to the muscle based on info from the muscles, joints and tendons and comparison of discharges from the agonist and antagonist muscles
What type of fiber is in muscle spindles?
What is the main function of the muscle spindle?
What does it do to the agonist muscle which it increases signal?
Large diameter type Ia fibers that provide info about the muscle length and stretch
It excites the agonist when it increases
What type of fibers are in the Golgi tendon organs?
What is the major function of the Golgi tendon organ?
What does it do to the agonist muscle if it’s signal is large?
Type Ib fibers that measure tension.
When tension is high, the agonist is inhibited.
Where do afferent fibers from muscle spindles make connections?
What type of connections?
Muscle spindles make excitatory monosynaptic connections with alpha motor neurons in the respective muscle
They also make inhibitory polysynaptic connections with the motor neurons that innervate the muscle antagonist
What are the synapses for Golgi tendon afferents?
Interneurons in the spinal cord that inhibit the motor neurons innervating the muscle of origin and excite the antagonist
What is the Romberg sign?
When vision is removed, balance depends on sensory input from proprioceptors.
How are Golgi tendon organs arranged?
How are muscle spindles arranged?
- In series in the tendon to protect from force
2. In parallel to detect the length of muscle
What type of fibers are carried in the thermoreceptors?
Adelta and C fibers
When the skin transiently warms, what fibers are activated and what are silenced?
Warm fibers are activated and cold fibers are silenced.
Are warm and cold fibers fast adapting or slow adapting?
What is the structure of these receptors?
Slow-adapting so they will give sustained discharge related to skin temperature that falls in the physiological range
TRP membrane channels on free nerve endings
What is fast pain in terms or speed, duration, onset?
What type of fibers is this pain carried in?
Immediate, short latency, short duration, well localized.
Adelta
What is slow pain in terms of latency, duration, localization?
What type of fibers carry slow pain?
More diffuse, longer-duration.
Slower C fibers
What is the structure of pain fibers?
Free nerve endings with terminal specialization to cold, heat, or pinch
What do mechanical nocioceptors respond to?
Pinch or pressure but NOT temp or light touch
What do polymodal nocioceptors respond to?
Chemicals applied to skin as well as high intensity mechanical and thermal stimulation
What do visceral pain receptors respond to?
Stretch and distension of visceral organs
Are pain fibers generally fast or slow adapting?
Slow adapting and slow recovering after stimulus but they do NOT discharge continuously in response to maintained stimulation
What is an after-discharge?
After the termination of a painful stimuli, some pain fibers will produce another signal which is the cause of lingering quality of pain
What is sensitization?
Repeated simulations are increasingly effective at generating a response
How do chemoreceptors transduce a signal?
What are examples of chemoreceptor?
- The chemoreceptor detects a stimuli
- This activates a g-protein which activates adenyl cyclase which makes cAMP
- cAMP increases channel conductance depolarizing the membrane
Carotid and aortic bodies which detect oxygen tension in blood
How do mechanoreceptors transduce signal?
What are examples of mechanoreceptors?
- Stretch or tension pulls on a carbohydrate chain anchored to the extra cellular space and membrane cytoskeleton
- This changes the conformation of the channel proteins and changes the conductance producing receptor potential
Pacinian corpuscles and meissners corpuscles, free nerve endings, proprioceptors
What does increasing the stimulus do to action potentials?
Increases the number and frequency of action potentials
What does increasing the duration of a stimuli do to action potentials?
The longer the duration of the stimulus, the longer the train of action potentials generated.
What does increasing the intensity AND duration do to the action potentials?
It increases the frequency, number and train of action potentials.
What is sensory adaptation?
The decline of generator potential with time
What are the slow adapting receptors?
Merkels
Thermal receptors
What are fast adapting receptors?
Hair receptors
Pacinian
Meissners
What areas of the body have the finest two point discrimination?
Fingers, toes, palms, face
Areas of the body that have more discrimination have what distribution of mechanoreceptors?
More dense distribution then less discriminatory regions of the body.
What are receptive fields?
Regions of skin within which tactile stimulus evokes a sensory response
The __________the receptive field, the _________discrimination is.
Smaller, better
OR
Larger, worse
What is a Dermatome?
Do they overlap?
Are all dermatomes the same for all people?
Cutaneous territory innervated by one spinal nerve level (all the receptive fields for one spinal root)
There is considerable overlap of adjacent dermatomes
They are different from person to person
What does the fact that dermatomes overlap tell us about injury to nerve roots?
Just because a nerve root is injured doesn’t mean the person will have complete anesthesia
Where is Dermatome overlap least developed?
For pain and temperature fibers so pinprick will be a good test
- C6
- C8
- T4
- T10
- L5
- S1
- Thumb and first finger
- 4th and fifth finge
- Nipple
- Umbilicus
- Great toe
- Small toe
What are the four major steps for detection to a sensory receptor?
- Detection by sensory organ
- Transduction
- Impulse generation through AP
- Conduction along the axon
What determines the basic properties of the sensory response?
The receptor organ
