Somatosensory System Flashcards
These cells respond to transient, phasic, or vibratory stimuli; no maintained stimulation; rapidly-adapting
- Meissner corpuscles
- Pacinian corpuscles
- Some hair follicle receptors
These cells respond to tonic events; encode intensity and duration; related to displacement and velocity of stimulus; slowly-adapting
- Merkel cells
- Ruffini corpuscles
- Some hair follicle receptors
Deep tactile mechanoreceptors are:
Pacinian and Ruffini corpuscles
Large diameter fiber types are:
A-beta and A-alpha
Small diameter fiber types are:
A-delta and C
Lesion of the thalamogeniculate arteries of the PCA can cause what?
Loss of blood to VPL and VPM, and therefore loss of all tactile sensation over the contralateral body and head
What is kinesthesia?
Positional awareness information, conveyed via proprioceptive sensory receptors within mm. and joints; serves balance, posture, and limb movement
- Dynamic and static nuclear bag fibers
- Golgi tendon organs via A-alpha fibers
What is stereognosis?
Ability to recognize a 3D object form texture, size, and spatial sensory modalities
What is agnosia?
Loss of ability to recognize objects, sounds, smells, or other sense modalities
Describe the Jaw Jerk Reflex.
- Ruffini endings in jaw, periodontal ligaments send signals to mesencephalic nucleus
- Send input to trigeminal motor nucleus to contract temporalis/masseter
What is complex regional pain syndrome?
Increased sensitization to pain within the body manifesting as chronic pain, often resulting from peripheral nerve damage. Most commonly manifests as back pain.
What is allodynia?
Lowered stimulus threshold for the A-delta fibers, leading to painful sensation to non-painful stimuli
What is hyperesthesia?
Lowered stimulus threshold for the C fibers
How do NSAIDS act?
Inhibit production of prostaglandin from neutrophils and macrophages by inhibiting COX2; PG normally binds nociceptor terminal to elicit a painful sensation
How does a capsaicin receptor inhibitor work?
Inhibition of voltage-gated sodium channel (typically elicits painful sensation during inflammation and in response to heat)
How does a bradykinin receptor inhibitor work?
Inhibition of response to bradykinin released from leukocytes, which binds nociceptor terminal membrane
How does gabapentin (neurontin) work?
Blocks calcium channels on the nociceptor, prohibiting neurotransmitter release in the SC
What is Brown-Sequard Syndrome? What can cause it?
Ipsilateral loss/reduction of discriminative, positional, vibratory sensation at/below level of lesion AND contralateral loss of pain/temp/crude touch two levels down and below AND ipsilateral motor loss
- Occlusion of posterior spinal artery (just for dorsal columns probably)
- Spinal cord hemisection
- Tabes dorsalis (progressive locomotor ataxia, degeneration of posterior columns)
Tabes dorsalis patients often walk in what specific way?
Wide-based stance (lack of proprioceptive sense), placing feet down hard
Lesion of area 1 in primary somatosensory cortex causes:
Deficit in TEXTURE discrimination (functions with 3b for discrimination of moving stimuli)
Lesion of area 2 in primary somatosensory cortex causes:
Loss of size and shape discrimination (astereogenesis); receptive for palpation of shape and curvature of objects
Lesion of area 3b in primary somatosensory cortex causes:
Deficits in both texture and size/shape discrimination - more profound deficits in 3b, indicating that is performs initial processing (which is carried on by 1 and 2)
Lesions is parietal association cortex (5 and 7) will cause:
Agnosia, from loss of contralateral body map –> limb not recognized by the body
What is plasticity, in terms of loss of limb?
Reassignment of brain functions within synaptic regions (after amputation, stroke) –> proximal areas overgrow into lost region
Leads to phantom limb / chronic pain
What is Friedreich ataxia?
Degeneration of spinocerebellar tracts –> lack of coordination during walking or other movements due to lack of cerebellar sensory feedback to regulate the movements (mossy fibers to vermis and paravermal regions)
List a few symptoms of ALS lesions.
Hypesthesia (reduced sensibility), numbness, paresthesia, anesthesia
What is peripheral sensitization?
Pain receptors exhibit sensitization following an insult; receptor becomes MORE sensitive (hyperalgesia)
Due to: irritating chemical (capsaicin), inflammatory mediators (bradykinin, prostaglandins), NTs (serotonin, histamine, norepinephrine)
What is primary hyperalgesia?
Occurs in region of damaged skin (receptor sensitization)
What is secondary hyperalgesia?
In the skin bordering the damaged tissue (central sensitization)
Describe central sensitization.
Ongoing input from C and A-delta fibers –> increased receptive field size of posterior horn neurons –> increased response to suprathreshold stimuli, decreased threshold, activation in response to novel inputs (allodynia)
What are pain receptors in muscles?
Receptors of Groups III and IV afferents (excessive m. stretch/contraction)
IV can be stimulated from algesic compound release following muscle injury or ischemia
What are pain receptors for arthritis?
Groups III and IV
What activates visceral pain?
Mechanical distention, ischemia, endogenous compounds (bradykinin, H+, K+)
Anoxia affects ______ fibers first
Larger diameter (DCML deficity)
Local anesthetics preferentially affect _______ fibers first
Smaller diameter fibers; act via blocking sodium channels (analgesia)
Posterior rhizotomy for pain may not be completely effective…why?
Select few C fibers that enter the anterior horn, so some nociceptive fibers may remain after those entering the dorsal horn were sectioned.
Some dermatomes to know - C7: T4,5: T10: L1: L5: S4,5:
C7: index finger T4,5: border of nipple T10: navel L1: pelvic rim L5: big toe S4,5: genitalia and anus
What is shingles?
Viral DRG or trigeminal ganglion latent residence of varicella zoster, periodically exhibiting painful dermatomal skin rash
What is postherpetic neuralgia?
Debilitating recurrent pain following a Herpes Zoster infection (neuropathic pain)
What is the test for ALS function?
Pinpoint application to skin evokes perception of pain (compare distal, proximal)
Diabetes mellitus patients experience distal loss first (stocking-glove sensory loss)
What is the test for DCML function?
1: 2-point discrimination (large to small intervals)
2: 128-Hz tuning fork for testing vibration on bone/tip of finger/toe
What is ALS ischemia?
Blood supply from arterial vasocorona and sulcal branches and anterior spinal a. occlusion –> PATCHY loss of pain/temp/crude touch over contralateral side beginning two levels down
What is a syringomyelia?
Cystic cavitation of central regions of spinal gray matter; impinge on anterior white commissure: ALS loss several segments below lesion
When in C4-5, cape distribution of bilateral ALS
Dull, aching pain from pulp inflammation is conveyed by:
C fibers
Dental hypersensitivity characterized as “sharp” is conveyed by:
A-delta fibers
Inflamed meninges cause many headaches and are supplied by:
CN V
Know the vascular lesions from Exam 1.
Probably all of them. Sorry.
Occlusion of MCA or ACA can cause what?
Loss of sensibility of contralateral region of body, head, face (depending on which artery)
Pain is first to return, then crude touch/thermal, then DCML input (might actually fail to return)
Pain perception and suffering arise from DIFFERENT brain regions!
It’s true.
Neospinothalamic tract is responsible for:
Primary somatosensory = localization
Paleospinothalamic tract is responsible for:
Hypothalamus, limbic system (via RF and PAG) = pain experience/suffering :(
Valium users lack suffering, but can localize pain
Deep Brain Stimulation is used for what?
Treatment of chronic/deafferentation pain; stimulation to somatosensory thalamus, PAG, etc. to activate pain modulation neurons (stimulation-induced analgesia)
Treatment for central pain syndrome?
TENS (Transcutaneous electrical nerve stimulation) - electrical stimulation of DC for retrograde input to spinal cord lamina III for pain suppression
Or, neuroablative procedures (rhizotomy, anterolateral cordotomy, commissural myelotomy, thalamic lesioning)
What is dysrhythmia?
Lack of correct movement timing
What is dysmetria?
Lack of coordinated movements
What is truncal ataxia?
Wide-based gait
What is central pain syndrome?
Often from CNS vascular lesions –> spontaneous paresthesia, dysesthesia, alldoynia, or hyperalgesia (burning, aching, prickling, lacerating, paroxysms, maybe exacerbated by unusual stimuli)
