Somatic sensation Flashcards
A-alpha fibers
Unconscious propioception
Meissner’s corpuscles nerve fiber and function
A-beta nerve fibers
Dynamic touch (rapidly adapting)
Cool receptor nerve fiber
A-delta
Warm receptor nerve fiber
C fiber
Nociceptors nerve fiber
A-delta (mechanical thermal) = sharp prickling pain
C fibers (Polymodal thermal) = slow burning pain
Nociceptors nerve fiber
A-delta (mechanical thermal) = sharp prickling pain
C fibers (Polymodal thermal) = slow burning pain
Nociceptors nerve fiber
A-delta (mechanical thermal) = sharp prickling pain
C fibers (Polymodal thermal) = slow burning pain
Merkel cell nerve fibers and fxn
A-beta nerve fibers
Static touch (slowly adapting)
Pacinian corpusle nerve fibers and fxn
A-beta nerve fibers
Vibration (RA, rapidly adapting)
Ruffini endings nerve fibers and fxn
A-beta nerve fibers
Skin stretch (SA, slowly adapting) AKA pressure
Pressure and how heavy an object is is felt by…
Ruffini endings
Indentation and grip force is felt by
Merkel cells
Shape/surface is felt by
Meissner corpuscle
Fingertips mechanoreceptor distribution
Best of: Merkel cells, Meissner corpuscles
Remark: Ruffini endings and Pacinian corpuscles have a uniform distribution
The shallower a receptor is, the more __
Sensitivity for responding.
Meissner and Merkel are shallower than Pacinian corpuscles and Ruffini endings.
Grasp & release of objects use __ mechanoreceptors
Meissner
Pacinian
How does our body feel dynamic temperatures?
At sudden colder environments,
1. Cold receptors signals shoot up transiently, and then plateau at a greater frequency than before.
2. Warm receptors are silent (inhibited) transiently and then fire at a lesser frequency than before.
Range of cold fibers
5-40 C
Preferred: 25 C
Range of warm fibers
29-49 C
Peak: 45 C
Fine touch tract
Ventral spinothalamic tract
Astereognosis (Tactile agnosia)
Inability to identify an object by active touch of the hands without other sensory input – lesions of the dorsal column or parietal lobe or parieto-temporo-occipital lobe
Sensory ataxia – Tarbes dorsalis (neurosyphilis), pernicious anemia (vitamin B12 anemia), multiple sclerosis
Romberg’s test
Ask subject to stand erect with feet together – unable to balance even with eyes open = cerebellar ataxia
Ask subject to close his/her eyes (30 sec) – swaying and unable to balance = Romberg’s test positive = sensory ataxia (propioception impairment) or vestibular dysfunction
Pseudoathetosis (Choreaform of distal muscle) confirms severe sensory ataxia induced by lesion of dorsal column or polyneuropathy
Dissociated sensory loss
Syringomyelia – a cyst or cavity (syrinx) forms within the spinal cord – suspended hyp(o)algesia (bilateral loss of sensation in pain and temperature)
Pseudoathetosis
Choreaform of distal muscle
Pseudoathetosis refers to a movement disorder characterised by involuntary, slow, writhing movements resulting from loss of proprioception.
