Sensory Receptors Flashcards
sensory receptors code for ____,_____ and ______
intensity (stimulus strength), duration (temporal aspects of stimulus) and location (the spatial distribution of the stimulus)
mechanoreceptors open in response to _____ resulting in _____
stretch, depolarization of mechanosensory neurons
pain are mechanosensation are ______
separate pathways
pain pathways:
cross over in the spinal cord and move upward to the caudal medulla
label this diagram:
a: dorsal root ganglion cells
b: mechanosensory afferent fiber
c: pain and temp afferent fiber
d: receptor ending
somatosensory afferents _____ from the ____ to CNS
convery info, skin surface, CNS
what transmits sensation from the head to CNS?
trigeminal nerve (CN V)
sensory info from the rest of the body is relayed by ____ pairs of afferent and efferent spinal nerves
31
the spinal nerves are:
Cervical nerves (8)
Thoracic nerves (12)
Lumbar nerves (5)
Sacral nerves (5)
Coccygeal nerves (1)
dermatome:
a region innervated by a single pair of spinal or cranial nerves.
sensory nerves project to the _____ and _______ in the parietal lobe
primary somatosensory (S1), secondary somatosensory cortex (S2)
secondary sensory order neurons from the _____ integrate in the _____ at the:
somatosensory cortex, thalamus, Ventral posterior medial nucleus (VPM) and Ventral posterior lateral nucleus (VPL)
the medial lemniscal pathway deals with…
sensation from the dorsal column (upper and lower body)
MPL: lower body:
enters spinal cord, then synapses at the gracile nucleus.
MPL: upper body:
enters spinal cord, then synapses at the cuneate nucleus.
both the gracile and cuneate nucleus are in the ______; this is where _______
caudal medulla, crossing over occurs
Where does the sensory information from the Medial Lemniscal Pathway terminate in the brain?
Terminates in the ventral posterior lateral nucleus of the thalamus before projecting to the primary somatosensory cortex.
How is sensory information from the upper and lower body organized in the somatosensory cortex?
terminates in different places of the somatosensory cortex, maintaining somatotopic organization
trigeminal lemniscal pathway deals with..
sensation from the face
TLP: sensory afferents enter the ____ in the midbrain, and the _____
nucleus of the trigeminal complex, crosses over
TLP: on the contralateral side, info rises until it ____ at the _____
synapses, ventral posterior medial nucleus of the thalamus
TLP: from here, neurons project to the _____
primary somatosensory cortex
T/F: sensory receptors are distrivuted evenly throughout the body
false, the amount of receptors present correlates with sensivity
what does lateral inhibition increase?
acuity
what does convergence do?
decreases acuity but increases sensitivity
the representation of the body is not _____ in the _______.
proportional, somatosensory cortex
neurons in the _____ form _______ columns
somatosensory cortex, functionally distinct
what streams are present in each column?
for rapidly-adapting and slowly-adapting afferents.
what can the proportion of the somatosensory cortex devoted to a body part be increased by?
further activity
what can it be decreased by?
lack of activity/amputation.
what does chronic two photon imaging reveal?
neural connectivity at the level of single synapses is affected by sensory deprivation from stroke
What stimulus features can be encoded by neurons in the Secondary Somatosensory Cortex/Area 2?
orientation and direction
when does optimum firing occur in secondary somatosensory cortex neurons?
occurs when an object is in a certain orientation and direction
how is optimum firing occuring with a certain direction acheived?
as higher-order neurons combine the receptive fields from multiple excitatory and inhibitory neurons.
Under what conditions will a neuron in the secondary somatosensory cortex fire?
If excitatory input is preceded by a lot of inhibitory input, or if there is simultaneous inhibitory and excitatory input, the cell won’t fire.**
The cell fires only if the stimulus moves in a certain direction in the receptive field.
types of sensory afferents
muscle spindles, golgi tendon organs, touch receptors, myelinated free nerve endings, and unmyelinated free nerve endings
muscle spindles:
(1a, A-alpha): for proprioception; large & myelinated (fastest)
golgi tendon organs:
(1b, A-alpha): for proprioception; large and myelinated (fastest)
touch receptors
(II, A-beta): Merkel, Meissner, Pacinian, and Ruffini cells.
myelinated free nerve endings
(III, A-delta): for pain, temperature.
unmyelinated free nerve endings
(IV, C): pain, temperature, itch; slowest.
name the encapsulated skin receptors
meisnner corpuscle, ruffini corpuscle, pacinian corpuscle
name the non-encapsulated skin receptors
merkel cell-neurite complex, free nerve endings
meisnner corpuscle
responds to pressure and grip
- Small receptive fields
- Rapidly-adapting
- A-beta afferents
ruffini corpuscle
responds to stretching and proprioception
- Large receptive fields
- Slowly-adapting
- A-beta afferents
pacinian corpuscle
respond to vibration
- Large receptive fields
- Rapidly-adapting
- A-beta afferents
merkel cell-neurite complex
responds to form and texture.
- Small receptive fields (high spatial acuity)
- Slowly adapting
- A-beta afferents
*semi-neuron; doesn’t fire, only amplifies responses
label this diagram:
a: free nerve endings
b: meissner
c: merkel cell-neurite complex (touch dome)
d: ruffino corpuscle
e: pacinian corpuscle
for each type of stimuli….
these receptors code for different aspects
stimulus features are encoded by the ___ and ____ of receptor that is activated
type and location
What is the primary objective of microneurography?
measure sensory activity
How does microneurography record sensory activity?
Implant fine electrodes into the skin towards nerves.
Record action potentials.
How does microneurography avoid nerve damage?
Use thin electrodes (200 microns in diameter).
label this diagram:
a: stimulus
b: merkel - SA
c: meissner - RA
d: ruffini - SA
e: pacinian - RA
f- small receptive
g: large receptive fields
cre recombinase
cuts genes at loxP sites
by using a specific promoter to drive Cre expression….
you can delete a certain gene to create a tissue-specific knockout.
cre/lox system
You can also cross it with a strain with a stop-cassette preceded target gene, to get expression of the target gene in only a certain type of cell.
proprioception
Sensing “oneself” and where parts of our body are in 3-dimensional space
what 3 mechanoreceptors are involved in proprioception
Muscle spindles
Golgi tendon organs
Ruffini endings (in joints)
in proprioception, muscle spindles contain
2 types of contracile fibers
what are the two types of contractile fibers?
extrafusal and intrafusal fibers
extrafusal fibers
make up the bulk of the muscle.
- Force-generating, innervated by alpha motor neurons
intrafusal fibers
are involved in detecting changes in muscle length.
- Are arranged in parallel.
- Two kinds: Nuclear “chain” fibers, Nuclear “bags” fibers
T/F intrafusal fibers are present in all fibers
false, they are not, mostly in smaller muscles where you need fine proprioception
most muscle contain ____ and ____
2-3 bag and 4-6 chain fibers
Nuclear bag fibers (NBFs):
- Type Ia afferents
- Phasic (code for dynamic information)
- Form annulospiral synapses.
Nuclear chain fibers (NCFs):
- Type II afferents
- Tonic (code for static information)
- Form flower-spray synapses
Gamma motor fibers (GMFs):
- Code for both dynamic and static information.
- Work to adjust the tension on the central part of the intrafusal muscle in order to keep Ia afferents near threshold, which helps it effectively encode for dynamic information.
muscle spindles drive _____ tendon reflexes
knee jerk/patellar
what happens when the muscle spindle detects a stretch of the quad?
the sensory neuron signals to a alpha motor neuron to extend the antagonistic hamstring muscle.
to maintain a load, an ____ helps to ____ antagonisitc muscles to maintain resistance
interneuron, inhibit
golgi tendon organs detect…
muscle tension, but are insensitive to passive stretch that would activate muscle spindles
how are golgi tendon organs arranged?
in series with extra fusal muscles
golgi tendon organs contain _____
slowly adapting Ib afferents
what is the primary function of golgi tendon organs in muscle regulation?
maintain steady muscle tone
how do GTOs respond to an expectionally heavy load on muscles?
GTOs relax muscle to prevent muscle damage
describe the modulation pathway of GTOs in muscle tension
- Ib afferent signals GTO.
- Ib inhibitory interneurons are activated.
- Inhibition of alpha motor neurons.
- Inhibition of muscle contraction.
gamma motor fibers get info from ____ about ____
GTOs, current muscle load
What is the primary function of the dorsal spinocerebellar pathway?
Proprioception (sensation of body position and movement).
Describe the route of proprioceptive input from the lower body in the dorsal spinocerebellar pathway.
Muscle spindles → Clarke’s nucleus → Dorsal spinocerebellar tract → Cerebellum.
Describe the route of proprioceptive input from the upper body in the dorsal spinocerebellar pathway.
Muscle spindles → Ventral posterior nucleus of the thalamus → Cerebellum.
Define nociception.
is the process of perceiving and responding to harmful or potentially damaging stimuli.
where are nociceptor receptors
on free nerve endings that detect painful stimuli
types of nociceptors receptors
thermal, mechanical, polymodal
thermal:
respond to stimuli greater than 45 degrees and less than 5 degrees.
- Thinly myelinated A-delta fibers.
mechanical
respond to intense pressure.
- Thinly myelinated A-delta fibers.
polymodal
respond to thermal, pressure, and chemical stimuli.
- Unmyelinated C fibers
what do transient receptor potential (TRP) channels respond to
painful temperatures
TRPM8:
responds to painful cold stimuli.
TRPB1:
responds to painful hot stimuli.
ASIC
harmful pHs (H+).
P2X/P2Y
detect ATP released from mechanical damage.
NaV 1.7:
genetic defects can impact someone’s ability to feel pain.
mutations w Nav 1.7
can cause people to not feel pain (which is harmful as one can’t sense injury), or can cause hypersensitivity to pain.
capsaicin
a compound in spicy food, has vanilloid groups that activate pain receptor transient receptor potential vanilloid member 1 (TRPV1).
TRPV1 and TRPV2
painful heat
hyperalgesia
increased sensitivity to painful stimuli; this is seen at the site of the injury following a painful stimulus.
an inflammatory ‘soup’ increases..
increases the excitability of peripheral nociceptors referred to as peripheral sensitization.
fast pain:
sharp pain mediated by A-delta small myelinated fibers
a-delta fibers in fast pain
make excitatory glutamatergic synapses onto projection neurons in layers 1-5 of the dorsal horn.
slow pain
dull pain mediated by small, unmyelinated C fibers.
c fibers in slow pain
These C fibers make excitatory glutamatergic synapses onto projection neurons in layer 1 of the dorsal horn
inhibitory interneurons
reside in layer 2 (substantia gelatinosa) of the dorsal horn.
- Release enkephalins to modulate pain transmission.
wide dynamic range of neurons
reside in layer 5 of the dorsal horn. These neurons receive:
- Nociceptive information from the gut via A-delta fibers (referred pain).
- Mechanical touch inputs from the skin via A-beta fibers.
gate theory
in the spinal cord, pain signals can be sent up to the brain to be processed to accentuate the possible perceived pain, or attenuate it at the spinal cord itself.
-> Basically, spinal nerves decide what pain gets through and what doesn’t.
allodynia
an increased sensitivity to benign, usually mechanical stimuli.
One theory claims that the chloride reversal in these projection neurons is changed, with a
downregulation of the KCC2 cotransporter.
This means that sometimes…
GABAergic and glycinergic input from interneurons will become excitatory and stimuli driven by mechanosensitive channels that once served to stop pain will now enhance the pain.
anterolateral spinothalamic pathway
is the discriminative pain pathway.
Nociceptive information synapses on the ______ of the spinal cord, and then crosses over.
ipsilateral side
The input moves _______ up the spinal cord until synapsing on the ________of the thalamus.
contralaterally, ventral posterior lateral nucleus
From here, information projects to the ________ of the cerebrum; information from the upper and lower body synapse at different locations.
primary somatosensory cortex
