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Lecture 6

PSYC 212 Lecture Notes - Lecture 6: Homunculus, Ejaculation, Posterior Column

Course Code
PSYC 212
Reza Farivar

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Lecture 06 - Pain, Orgasm and Enteric
Sensations: “The bad, the good and the ugly”
Free nerve endings
oC-fibers and A δ (delta) fibers
oSlow and fast pain signals
oPain vs. nociception
Sharp pain : A delta fibers
Slower pathway, more sensitive to chemical irritants,
including things in your blood as well: C- fibers
Myelinated fibers that carry mechanoreceptor signals: A
alpha & A beta (touch stimulates inhibitory interneurons in the
spinal cord via A alpha dna A beta fiber activation)
oAnterolateral pathway
Different from mechanoreceptor signal pathway
Big difference is that cell bodies in DRG, the axons
terminate in the ventral portion of the spine instead.
Therefore its immediate, so automatic, reflexive.
Allows for pain aversion reflex.
Referred pain:
oA lot of the DRG that combine the pain receptors don’t just
combine them from skin but also from the
Controlling pain
oChange in criterion? Or change in sensitivity?
Change in sensitivity by top down control
oGate control theory of pain (Happens in spine)
Signal from somatosensory fiber
And signal from pain fiber
Pain exerts influence on itself, if you only have c fiber
than.. brain can exert excitatory influence on inhibitory
neuron, instead of directly inhibiting it.
About to touch something that is hot, excite the
inhibitory interneuron, in turn reducing activity of
projection neuron, thus reducing sensation to pain.
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Sexual stimulation And Orgasm
A: clitoris
In the clitoris:
oSome of the same mechanoreceptors seen in other skin, but a
high presence of FA1 and FA2 type mechanoreceptors
oFree nerve endings: axons exiting their myelin sheath.
Sensitive to thermal variations and pain
oSome specialized sensors:
Krause-Finger’s corpuscles (Thermoreceptor for cold)
oSensitivity increases as blood flow to the clitoris increases,
because of increased mechanical tension
oIn the clitoral hood and labia minora
Similar to the clitoris but far less dense
oAs the stimulation increases, so does the blood flow there,
meaning that sensation increases.
Mechanoreceptors in the penis:
oFast adaptive neurons increase in tip of penis
oHigh slow adaptive at the tip in contrast to the very few FA
oRemoval of sensory afferents in animals results in loss of
proper mounting orientation
SA receptors on the penis: intromission guides?
Pudendal Nerve
oCarries sensory and motor signals from genitals and anus
oDorsal penile nerve and dorsal clitoral nerve carry sensory
signals to the pudendal nerve
oSummation of sensory signals are believed to take place in
the spine, and upon reaching threshold, hypogastric nerve is
stimulated, resulting in emission and ejaculation in males and
climax in females.
oClimax does not require brain, but rather muscle contraction.
Enteric sensation (The gut)
Most afferents leaving the gut are multi-modal – not pure perfect
mechanoreceptors, respond to chemical content of food you’re
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