Sensory Receptors: Tactile, Temperature, Proprioceptive Input Flashcards
Function somatosensory system
Provides information to CNS about the state of the body and its contact with the environment
Function receptors
Transduce mechanical or thermal stimuli (extracellular info into intracellular response)
Where is a receptor potential generated
Distal tips of first order neuron (cell bodies in dorsal root)
Passive potential
Describe first order neurons
Unipolar
Primary neuron
Encode information as APs
What kind of info do APs relay
Info about magnitude and duration
Spinothalamic- Where do first order sensory neurons synapse onto second order neurons
Spinal cord
DCML- Where do first order sensory neurons synapse onto second order neurons
Medulla (brain stem)
Spinothalamic- Where do second order sensory neurons synapse onto third order neurons
Thalamus
DCML- Where do second order sensory neurons synapse onto third order neurons
Thalamus
Where do third order neurons project
Somatosensory cortex (S1)
Name the ascending somatosensory pathways
Dorsal column medial lemniscus DCML
Spinothalamic
What kind of info does dorsal column medial lemniscus propagate
Fine discriminatory touch
Proprioception
What kind of info does spinothalamic propagate
Pain
Temperature
Two Sensory fiber types for skin mechanoreceptor, thermal receptor, nociceptor
III- larger diameter, larger conducting velocity
IV- smaller diameter, smaller conducting velocity
- tactile info and pain, temperature, crude touch
Dermatome
Map for regions of skin sensory neuron responsible for
- specific dorsal root supplies specific cutaneous region
What is found in dorsal and ventral root
Dorsal root- contains sensory neuron (afferent)
Ventral root- contain motor neuron (efferent)
What is found rostral and caudal regarding nerves
Rostral- enters spinal tract
Caudal- afferent limb of reflex arcs
Proof of dermatones
Shingles are found in bands
Name sensory receptor afferents found in glabrous skin
Meissner corpuscles (superficial)
Merkel’s disk (superficial)
Pacinian corpuscles (deeper)
Ruffini endings (deeper)
Name sensory receptor afferents found in hairy skin
Hair and nerve fibers
Free nerve endings
State adaptability and size of receptive field for glabrous skin
Meissner’s corpuscles- fast, small receptive field
Pacinian corpuscles- fast, large receptive field
Merkel’s disk- slow, small receptive field
Ruffini endings- slow, large receptive field
Describe fast receptors
filter steady stimuli
filter slowly changing stimuli
- selectively sensitive to changing stimuli
DCML afferent pathway
First order neuron enters the spinal cord and projects to dorsal column nuclei of medulla
Second order neuron decussate (cross over) at medualla then project to thalamic nuclei
Third order neuron in thalamus and project to S1 (somatosensory cortex)
Name other pathways that project via thalamus
Trigeminal- facial sensation
Spinocerebellar- muscle tone and coordination
Regions of thalamus for 3 specific types of information
VPS- proprioception (DCML)
VPM and VPL- fine touch and vibration (DCML)
VPI- pain and temperature (spinothalamic)
Monkey experiment: What did recording one cortical neuron (in S1) responding to a variety of stimuli identify
There is a favour stimulus for a specific projection pathway
- labeled line coding
- specific directionality preference
- feature extraction
What is feature extraction
Higher order processing in S1 cortical neurons
Specific S1 neurons respond to specific stimuli - all stimuli have a favourable pathway
What does labeled line coding prove
If you provide the same stimulus, you will get the same projection pathway and sent to the same S1 location
What kind of info do III and IV sensory fibers carry
Tactile
- remember different tracts carry these types of info, therefore they don’t have same pathway
Pain
Temperature
Crude touch
Spinothalamic tract pathway
First order neuron enter spinal cord - 2nd order decussate (cross over) - second order neuron in spinal cord - project to third order in VPI thalamus - then S1 (and other areas for emotional responses)
Free nerve endings of nociceptors express what kinds of channels
Chemo, mechano, thermo sensitive ion channels - pain and temperature sensation
Transient receptor potential (TRP) ion channels
What do transient receptor potential ion channels produce? What kinds of things can activate the types
Receptor potential- passive potential can sum to make AP in afferent neuron
TRPV1- heat sensitive (heat temp, wasabi, capsaicin - chilli peppers)
TRPM8- cold sensitive (cold temp, mental)
Both are temp gated- perception of cold or hot
Location S1
Immediately posterior to central sulcus in post central gyrus
State medial to lateral for sensory homunculus and what is heavily innervated
Medial- genitals, feet
Hands at shoulders
Lateral- head, mouth
Big- toes, hands, lips, face
Wilder Penfield
Mapped various brain regions including S1
- developed treatments for epilepsy (electrode to brain to pinpoint what region cause seizure- Montreal technique)
What sensory fiber type carries proprioceptive information from muscle spindles and GTOs
Ia
Ib- GTO
II- smaller diameter, smaller conducting velocity
Where are muscle spindles found and what is their shape
Found in skeletal muscle
Fusiform shaped muscle fibers
Sensory and motor axons
Muscle spindle vs GTO lie in parallel/series with muscle
Muscle spindle- parallel
GTO- series
Function muscle spindles
Detect changes in muscle length
What kind of fibers do muscle spindles have
Nuclear bag fibers
Nuclear chain fibers
Name type of fibers that innervate muscle spindle
Sensory Ia and II
Motor gamma
What is alpha gamma co stimulation
Maintain sensitivity over range of fiber lengths
GTO function
Monitor muscle force
What innervates GTO
Ib afferents sensory
How does GTO measure force
Hooke’s law
Force is proportional to stretch
