visceral sensation
somatic sensation
somatesthetic
proprioceptive
special senses
vision
hearing
taste
smell
uses of sensory input
control of efferent output
reticular formation and cortical arousal and consciousness
stored for future reference
perception: the conscious interpretion of the external world
limited receptor modalities
differential processing of input
manipulation of input to produce altered “reality”
receptors have differential sensitivities to various stimuli
stimulus modality
transduction
adequate stimulus and the law of specific nerve energies
first proposed by Johannes Peter Müller in 1826
modified by work of Lord Edgar Douglas Adrian
Roger Sperry’s research
receptor types
photoreceptors
rods
cones
mechanoreceptors
in glabrous skin
Pacinian corpuscles: deep pressure & high-frequency vibration
Meissner’s corpuscles: light touch, low-frequency vibration
Merkel’s discs: light touch, low-frequency vibration
Ruffini corpuscles: deep pressure
in hairy skin
root hair plexus: deformation
cochlea
hair cells: deformation
thermoreceptors
heat
TRPV1: hot ( >42°C )
capsaicin & camphor
TRPV2: painfully hot ( >52°C )
TRPV3: warm ( >31°C )
TRPV4: tepid ( >25°C )
cold
TRPM8: cool ( <28°C )
menthol
TRPA1: cold ( <18°C )
also found in hair cells
chemoreceptors
distance
olfactory receptors in olfactory system
pheromone receptors in vomeronasal organ
direct
taste buds
pH receptors in carotid & aortic bodies
nociceptors
compound sensations: wetness
altered membrane permeability of receptors results in graded receptor potential
causes
mechanical stimulation
chemical signals
temperature
electromagnetic radiation
increased intensity of stimulus results in increased receptor potential
increased receptor potential results in increased frequency of action potentials
adaptation
tonic receptors: slow adapting
proprioceptors
nociceptors
phasic receptors: fast adapting
off response: transmits a signal when the stimulus is released
somatosensory pathways
destinies of afferent information
reflex arc
ascending pathway
labeled lines
decoding the stimulus
stimulus modality
receptor type
ascending pathway
stimulus location
location of activated receptor field
pathway to somatesthetic cortex
stimulus intensity
frequency of action potentials
number of activated receptors
activation of sensory pathway
phantom pain
acuity is influenced by receptor field size
somatesthetic cortical homunculus
protective mechanism
motivated behavioral responses
emotional responses
subjective interpretation
categories of pain receptors
mechanical nociceptors
thermal nociceptors
polymodal nociceptors
free nerve endings
sensitization by prostaglandins
types of pain
acute pain
chronic pain
cutaneous pain
somatic pain
visceral pain
neuropathic pain
pathways
fast pain pathway
myelinated Aδ (A-delta) fiber
responds to mechanical or temperature stimuli in pain realm
transmits at 5–30 m/sec
uses glutamate as neurotransmitter in dorsal horn with AMPAa receptors
terminates on lamina I (lamina marginalis) of dorsal horns
second-order neurons cross over and pass upwards in contralateral anterolateral columns
terminate in ventrobasal complex of thalamus
third-order neurons relay to cerebral cortex
localization due to stimulation of adjacent tactile receptors
slow pain pathway
unmyelinated C fiber
transmits at 0.4–1.0 m/sec
bradykinin sensitizes nociceptor peripheral terminals
capsaicin blocks C-fiber conduction
terminate on laminae II & III (substantia gelatinosa) of dorsal horns
second-order neuron terminates in lamina V
third-order neurons join fibers from fast pathway, cross over and pass upwards in contralateral anterolateral columns
terminate mostly in brainstem
neurotransmitters
glutamate
uses AMPAa & NMDAb receptors
AMPAa receptors
generate action potentials in dorsal horn cells
transmission of pain message to higher centers
NMDAb receptors
only open after prolonged depolarization
activate ascending pathways
Ca2+ entry into dorsal horn cells
induces hyperexcitability
substance P
naked mole rats lack substance P, and thus do not feel painful stimuli
an 11-amino acid peptide
uses the NK1 (neurokinin-1) receptor
activates ascending pathways
somatosensory cortex
thalamus
reticular formation
axon reflex [perpheral movement of afferent APs] and substance P release ↑ inflammation
analgesia
periaqueductal gray matter and reticular formation in midbrain
descending analgesic system
blocking substance P release from afferent synaptic terminal
opiate receptors for β-endorphin, enkephalins, and dynorphin
| Questions for thought | ||
|---|---|---|
| 1. | Differentiate between tonic and phasic receptors. Give examples. | |
| 2. | Describe at least four types of tactile receptors in the skin, giving a concise functionality for each. | |
| 3. | What is meant by proprioception? Give examples of the princple proprioceptive structures and how each serves its function. | |
| 4. | Is our perception of reality true? Discuss. | |
| 5. | Gladys had to have her left arm amputated after a construction site accident. She reports to you that she occasionally has a tingling sensation in the fingers of her left hand. Do you tell her she should see a psychiatrist? How would you explain her phenomenon to her? | |
| 6. | Explain how we determine the meaning and location of a somatoesthetic sensation. | |
| 7. | What is pain? How is visceral pain different from somatic pain? | |
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[ Anatomy & Physiology 1 syllabus ][
Anatomy & Physiology 2 syllabus ] [ Page created 1999-07-29 ][ Last updated 2011-02-10 ] [ Questions about this lecture? E-mail me ] |