Exam 1 - Somatic Sensation Flashcards
How does a neuron respond to a sustained stimulus?
Decreased firing rate over time
hot tub analogy - feels hot for the first few minutes, then our bodies adapt to the temperature
What is another word to describe slow adaptation?
Tonic
What is another word to describe fast adaptation?
Phasic
What do tonic receptors detect?
continuous (sustained) stimulus strength
What do phasic receptors detect?
change in stimulus strength
What is the function of a mechanoreceptor?
They detect mechanical compression or stretching of the receptor/tissues adjacent to receptor
Where are type I mechanoreceptors located?
Outer layers of joint capsul
Which mechanoreceptors have a low threshold (easily fire)?
Type I and Type II
Which mechanoreceptor has tonic effects on lower motor neuron pools?
Type I
What is the difference between type I and type II mechanoreceptor adaptation rates?
Type I - Dynamic & fire with movement; Slowly adapting
Type II - Rapidly adapting, inactive in immobilized joints
Which mechanoreceptor has phasic effects on lower motor neuron pools?
Type II
Which mechanoreceptors are usually myelinated?
Types I-III
Which mechanoreceptor is also a nociceptor?
Type IV
What do Types III & IV have in common?
Very high threshold
What does type III have in common with type I?
Slow adaptation
Which mechanoreceptor is a joint version of a Golgi tendon organ?
Type III
What are the two rapidly adapting tactile receptors?
Meissner’s Corpuscles and Pacinian Corpuscles
Which tactile receptors are slowly adapting?
Merkel’s discs and Ruffini’s end-organ
Which tactile receptors have a small (superficial) receptive field?
Meissner’s and Merkel’s
Which tactile receptors have a large (deep) receptive field?
Pacinian Corpuscle and Ruffini’s end organ
Which tactile receptor is slowly adapting and has a relatively large receptive field?
Ruffini ending
At what temperature are thermoreceptors inactive but nociceptors active?
Below 0 C, above 50 C
When do thermoreceptors discharge spontaneously?
Under normal conditions (wide temp. range)
When do thermoreceptors discharge physically?
When skin temp. changes rapidly
How does the gating theory of pain work?
It involves inhibitory interneurons in the cord that impact nociceptor projection neurons
What inhibits nociceptors in the gating theory of pain?
C fibers (type III) - open the gate and increase nociceptive transmission
What stimulates nociceptors in the gating theory of pain?
A alpha and beta fibers (type I and II) - close the gate and decrease nociceptive transmission
What is secreted by C fibers? What order neuron are they?
First order neuron - secrete substance P and glutamate
What sensations do we feel when C fibers are activated?
Dull burning and aching pain (chemical)
What sensations do we feel when A delta fibers are activated?
Sharp, prickling pain (thermal)
What is the difference between the neo and paleo spinothalamic pathways?
Neo = fast (A delta) Paleo = slow (C fibers)
In type III (A delta) nociceptors, which neurotransmitter is released by first order neurons in the spinal cord?
Glutamate
Lateral inhibition in the somatosensory system is associated with which function?
enhances edges but DOES NOT improve acuity
T/F: A first order neuron when stimulated will both stimulate some 2nd order neurons as well as inhibit other 2nd neurons simultaneously.
True
In a hemisection of the cord, where does a loss of vibration/proprioception occur?
On the ipsilateral side
In a hemisection of the cord, where does analgesia occur?
Contralateral
p.s. Analgesia = inability to perceive temperature/pain
What is the Epicritic pathway in the somatosensory cortex?
Dorsal column-medial lemniscal system (precise objective info)
What is the Protopathic pathway for the somatosensory cortex?
Anterolateral system (spinothalamic) - primitive feeling -
Most vibratory signals are transmitted to the cortex via what pathway?
Dorsal column-medial lemniscal
The anterolateral system transmits which signals/sensations?
Crude touch, nociception, temperature, tickle, itch, sexual sensation
In the somatosensory homunculus, which area of the body would normally have the largest cortical representation?
hands
Where do 1st order neurons synapse in the anterolateral/protopathic pathway?
Dorsal horn of the spinal cord
Where do 1st order neurons synapse in the Dorsal column-medial lemniscal/epicritic pathway?
Brain stem
Where do 2nd order neurons of both pathways cross?
They cross to the other side and ascend, synapsing in the thalamus
Which pathway initiates actions?
Protopathic (anterolateral)
Which pathway modifies actions?
Epicritic (DCML)
Which pathway has fast/large fibers?
Epicritic (DCML)
Which pathway is old phylogenetically?
Protopathic
Where do 1st order neurons reside for both pathways?
Dorsal root ganglia
A hemisection of the spinal cord on the right side of T5 that disrupts both ascending and descending projections would create what type of sensory defect below the lesion?
Loss of nociception on the left side, loss of vibration on the right side
T/F: Most nerve cells in the SSC are responsive to only one modality.
True!
E.g. Deep pressure, temperature, nociception, superficial tactile
What are the three types of neurons in Brodman areas 1 & 2 that have complex feature detection capabilities?
- Motion sensitive
- Direction sensitive
- Orientation sensitive
What are direction-sensitive neurons?
Neurons which respond better to movement in one direction than in another
What are orientation-sensitive neurons?
Neurons that respond best to movement along a specific axis
What are motion sensitive neurons?
Neurons which respond well to movement in all directions but not selectively to movement in any one direction
A cortical neuron in Brodman area 2 that fires strongly as a tactile stimulus is drawn across the hand from ulnar to radial but weakly from radial to ulnar is an example of…?
Direction sensitive neuron
What is the major function of anandamide produced by the brain?
Stress induced analgesia
What are the two endogenous cannabinoids produced by the brain?
Anandamide and 2-AG (2-arachidonoylglycerol)
These levels increase during exercise, contributing to ‘runner’s high’
Projections from viscera and projections from the body will share common 2nd order projection neurons in the anterolateral spinothalamic projections. In regards to pain, this is known as…
Referred pain
How can dysfunction of the cervical spine refer pain to the head?
Some C2 projections synapse in the nucleus of CN V (CN V supplies most of head/face, extends down to C2)
What part of the brain will you find BM areas 5 and 7?
Posterior parietal cortex
What type of information does BM area 5 integrate?
Tactile information from mechanoreceptors in skin with proprioceptive input from muscles and joints
Brodman area 7 integrates stereognostic input with what special sense?
Visual
Where does BM area 7 project its fibers?
Motor areas of the frontal lobe
What inputs does BM 7 receive?
visual, tactile, proprioceptive
How is the somatosensory cortex important in movement?
Initiation and guidance
Interneurons in the cord that block nociceptive transmission by 2nd order neurons release what neurotransmitter?
Enkephalin (opioid)
What neurotransmitters are considered an endogenous opioid?
Enkephalin and endorphins
What are the 5 sensations of pain?
Pricking, burning, aching, stinging, soreness
Where do C2 afferents synapse?
DRG (dorsal horn) & CN V nuclei
What is cervical joint dysfunction?
Spill over of signals from cervical joints (C2) to nucleus of CN V
What are the intracranial origins of headache?
Meningitis, Migraine (vasoconstriction/vasodilation), Irritation of Meninges (re: alcohol abuse or constipation)
What are the extracranial origins of headache?
Muscle spasm, eye disorders, cervical joint dysfunction, irritation of nasal passages/sinuses, traction of dura (CN V)
What is spatial summation?
Increasing signal strength transmitted by progressively greater # of fibers
What is temporal summation?
Increasing signal strength by increasing frequency of IPS (impulses/second)
When do we use Erlanger’s system?
Used in motor nerves and skin afferents
When do we use Lloyd’s system?
Used for afferents from receptors in muscle and spinal joints
What is stereognosis?
The ability to perceive form through touch (tests dorsal column-medial lemnicsal system)
What are the 4 types of sensory modalities?
Pressure receptors
Cold receptors (thermo)
Warm receptors (thermo)
Nociceptors
The perception of something wet on your skin is associated with stimulation of which receptors?
Pressure & thermo
The perception of itching on your skin is associated with stimulation of which receptors?
Gentle + nociceptors
The perception of ticklishness on your skin is associated with stimulation of which receptors?
Gentle + pressure receptors
What leads to a continuous intrinsic neuronal discharge?
Leaky membrane to Na+/Ca++
Most neurons are a site of ______ input and a source of _____ output
A. Converging
B. Diverging
Neurons that fire together, wire together
What is synaptic afterdischarge?
Postsynaptic potential lasts for msec (can continue to excite neuron)
What is a reverberatory circuit?
Positive feedback within circuit due to collateral fibers which restimulate itself/neighbor in same circuit
How do we control over-excitation (e.g. seizures) in the brain?
- Fatigue of synapses
- Inhibitory circuits
- Decreasing resting membrane potential
- Long-term changes by down regulation of receptors
Which mechanoreceptor is concentrated in the fingertips and found only in glabrous (non hairy) skin?
Meissner’s corpuscles
Where are Pacinian corpuscles located?
Subcutaneous tissue
Which mechanoreceptor is activated by stretching the skin?
Ruffini end organ
Which mechanoreceptor can sense the curve of an object?
Merkel’s discs
