Intro to sensory systems Flashcards
What are the five types of receptors (classified by the stimulus)?
- Mechano
- Thermo
- Photo
- Chemo
- Nociceptor
What is perception?
The conscious awareness of stimuli
What is the process of translating a physical stimulus to a nerve impulse?
Sensory transduction
What is receptor potential?
change in the membrane potential produced by a transducer mechanism
True or false: the receptor potential is a graded potential
True
Most receptor potentials are generated how?
Via depolarization of a receptor
How is the rate of receptor potential changed?
Rate at which action potentials are generated increases as receptor potential rises higher above threshold.
If the receptor potential is a hyperpolarization, does it generate an action potential?
No
What is the labeled line principle?
tells you the sensory modality since there is a chain of connected neurons from the sensory receptor which responds to the stimulus to the brain area that perceives the stimulus
How do we know “what” and “where” a stimulus is?
Labeled line principle
What is a receptor field?
the region of tissue (e.g. skin) within which a stimulus can evoke a change in the firing rate of the neuron.
What is an adequate stimulus?
Under normal circumstances, a specific receptor is affected by only one stimulus modality
What is the receptor specificity?
There is only one stimulus that can affect a given receptor
True or false: receptor potential change with the size of the stimulus
True
True or false: action potential changes with the size of the stimulus
False
How do pacinian corpuscles work?
Movement causes Na channels to open. Bigger stimulus = more openings
True or false: wherever along the chain of a receptor is stimulated, it will produce the same sensation
True
What is the pathway in the spinal cord that transmits proprioception and fine touch? Where do these cross in the spinal cord? Where do these project to?
Dorsal columns (fasciculus cuneatus and gracilis)
These cross in the medulla via the nucleus cuneatus and gracilis to project to the VPL nucleus of the thalamus, then the somatosensory cortex
What are the pathways in the spinal cord that transmit pain and crude touch?
Neospinothalamic and paleospinothalamic pathways
Where do the neospinothalamic and paleospinothalamic pathways cross over?
At the level (and 1-2 above/below) they enter via the anterior white commissure.
What is the area that the axons of the neospinothalamic pathway go up and gown in the spinal cord?
Lissauer’s tract
Where are the cell bodies of the primary motor neurons in the dorsal columns and the neo/paleospinothalamic pathways housed?
DRG
What is the law of projection?
in a neuron in a sensory pathway is stimulated, the subject perceives the stimulus as being in the location of the sensory receptor for that pathway
Where is the primary somatosensory cortex?
Behind the central sulcus
Review the homunculus distribution of the sensory cortex if you do not remember
It’s not that bad really…
What is the blood supply to the medial cortex? Lateral?
Medial = anterior cerebral Lateral = middle cerebral
What are the parts of the body that are represented by the medial part of the somatosensory cortex?
Foot, leg, hip, genitals
What are the two ways in which the nervous system codes for stimulus strength?
- Frequency of nerve impulses
2. Number of fibers activated
What is the concept of lateral inhibition?
When a part of a receptor field is stimulated, the receptors in close proximity are inhibited, thus providing more localized stimulus
How does the nervous system code for stimulus duration? (2 different ways)
Maintains continuous signal strength during stimulus
Have on-off signal
True or false: inhibition is just as useful as excitation in the nervous system
True
What causes the adaptation of a sensory receptor?
When a maintained stimulus of constant strength is applied to a receptor, the frequency of the action potentials in the receptor’s sensory nerve decreases over time.
True or false: all receptor use the same mechanism of adaptation to a stimulus
False
What are the non-adapting receptors?
Nociceptors
What is a tonic receptor?
A receptor that does adapt, but does so slowly
How do tonic receptors adapt?
Initial burst of firing when the stimulus is applied, but then slows down
Merkel cell endings are what type of adapting receptors?
Slowly adapting receptors
When are slowly adapting receptors useful?
for giving continuous information about stimulus strength and signaling stimulus duration
When are slowly adapting receptors NOT useful?
not as useful for signaling stimulus duration at low stimulus intensities
Pacinian corpuscles and Meissner’s corpuscles are what type of receptors (slow or fast adapting)?
Fast adapting
What are phasic or rate receptors?
fast adapting receptors
When are fast adapting receptors useful?
useful for signaling beginning and end of stimulus
Can fast receptors signal a change in stimulus intensity? If so, how?
Yes–number of action potentials transmitted related to rate at which change is taking place
What type of receptors are needed to extract dynamic information e.g. velocity and acceleration
Fast adapting
Which type of receptors are useful for sensing when a stimulus begins and ends (fast or slow adapting)?
Fast adapting
What type of receptor is useful for sensing stimulus intensity?
Tonic receptors
What are the four different types of tactile sensation receptors?
- Crude
- Discriminitive
- Pressure
- Flutter/vibration
What type of receptors are utilized for crude touch? How well are these myelinated?
Free nerve endings (type C unmyelinated fibers)
Do the free nerve endings involved in crude touch have a low threshold or high threshold for stimulation? What is the consequence of this?
Low threshold = high sensitivity
True or false: discriminative touch is carried by both the dorsal lateral and the aternomedial systems?
False–only the dorsal columns
What is the difference between flutter and vibration?
Just frequency–higher = more like vibration
What is the tuning fork utilized for testing vibration sense?
128 hz
Merkel cell fibers are low or high threshold receptors? Where are they found?
Low (highly sensitive)
Found at the base of the epidermis
What is an Iggo dome receptor?
Several merkel discs joined together
What type of fibers innervate Merkels discs? How well are these myelinated?
A-beta fibers–very myelinated
Merkel cells are slow or fast adaptors?
Slow
Which receptors have the highest spatial relationship of all the sensory afferents?
Merkels discs
What are the receptors that play a role in static discrimination of shapes, edges, and textures?
Merkel cells
Ruffini corpuscles sense what?
Joint stretch
Meissner’s corpuscles are rapidly or slowly adapting fibers?
Rapid
Which type of receptors have a very high density in the tips of the fingers?
Meissner’s corpuscles
Where are Meissner’s corpuscles located in the skin?
Just below the epidermis, but closer to the skin than Merkel’s discs
Information from which receptors are probably the basis for the detection of slippage between the skin and an object held in the hand. Responsible for the sensory feedback information needed for the efficient control of grip.
Meissner’s corpuscles
Pacinian corpuscles are slowly or rapidly adapting?
Rapid
Where in the skin are pacinian corpuscles found?
subcutaneous tissue
True or false: pacinian corpuscles adapt more rapidly than Meissner’s
True
Which receptors can detect vibrations transmitted though objects held in the hand thus contributing to skilled tool use?
Pacinian corpuscles
What are the receptors in the base of hairs? What type of fibers are utilized by these receptors?
peritrichial nerve endings–A-delta fibers
Which type of receptor is better at detecting change? Which is better for detecting a long stimulus?
Rapid adapting = good for change
Slow adapting = good for constant stimulus
Itch is sensed by what type of sensors/fibers?
Free nerve endings with C fibers
What part of the body has the least ability to detect two separate points? Best?
Best = hands
Worst = calves
Lack of two point discrimination will indicate damage to what part of the spinal cord?
dorsal columns
What are the receptors involved in proprioception?
a. joint receptors
b. muscle spindles and Golgi tendon organs
c. skin tactile receptors
Joint position proprioception is static or dynamic proprioception?
static
Joint movement proprioception is static or dynamic proprioception?
Dynamic
What is conscious proprioceptions?
Kinesthesia
The DC/ML pathway is responsible for what type of sensation?
fine tactile discriminations, vibratory sense (which is just rapid, repeated touch/pressure) and proprioceptive sense.
What allows for the precise localization of the DC/ML pathways?
Precise localization is possible because the receptors associated
with system can have very small receptive fields
Rhomberg test tests what?
Proprioception
Where is the somatosensory cortex in the cortex of the brain?
Behind the central sulcus
What are the two parts of the homunculus in the medial fissure of the sensory cortex?
Foot and genitals
Where does the DC/ML crossover in the spinal cord?
Caudal medulla
What is graphesthesia?
Ability to recognize figure drawn into hand or onto skin
What is sterognosis?
Ability to recognize 3D objects through touch alone
Neurons in the somatosensory II area show what type of responses?
Attention modulated
(That is, the responses of the neurons in this area to a stimulus depend on whether the subject is paying attention to the stimulus)
What part of the CNS is utilized in graphesthesia?
DC/ML
What is a nerve pressure palsy?
Loss of feeling d/t transient ischemia (“foot falls asleep”)
Why is there a stocking-glove sensory loss?
Leg nerves are longer, and therefore more easily affected by insults
Review Brown_sequard syndrome.
DC/ML will show symptoms of the ipsilateral side of the lesion, since it crosses over in the caudal medulla.
The neospinothalamic/paleospinothalamic (both parts of the spinothalamic system) decussate at the level (or one to two above) of the lesion. (recall the axons in this path from the DRG go up and down in the tract of Lissauer, then cross over in the anterior white commissure).
In Brown-Sequard syndrome, loss or proprioception will by ipsilateral, or contralateral to the side of the lesion. how about pain and temp?
Proprioception ipsilateral
Pain and temp contralateral
What is the order of the speed of fibers?
Aalpha Abeta Agamma Adelta B C C
What are the fibers involved in motor neurons?
A-alpha
What are the fibers involved in GOTs?
A-beta (I-b)
What are the fibers that innervate the muscle spindles?
Ia
What do A-beta fibers innervate?
Muscle spindle endings
What do A-gamma fibers innervate?
Axons of gamma motor neurons
What do A delta fibers innervate?
fast pain, some temp
What do type C fibers innervate?
Free nerve endings
