Sensory Receptors Flashcards
What do sensory receptors encode?
Intensity: Strength of stimulus
Duration: Length
Location: Spatial distribution
What is a dermatome?
specific segment of skin supplied by a single spinal nerve, when bent over on all fours, human map lines up to have stripes
somatosensory afferents _____ from the _____ to _____
convey information, skin surface, CNS
How do most mechanosensory afferents open their ion channels?
With membrane stretch from mechanosensory stimuli
Spinal cord sections
Spinal cord sections
________ (trigeminal) transmits ______ from ______
cranial nerve V, sensation, head
Somatosensory cortex
area at the front of the parietal lobes that registers and processes body touch and movement sensations, receives inputs from ventral posterior (VP) complex of the thalamus.
What side of the spinal cord does touch go up? Pathway name? where does crossover occur?
Touch sensation ascends ipsilaterally up the medial lemniscal pathway from the gracile tract (lower body) and cuneate tract (upper body), crossover occurs in caudate medulla where it synapses onto internal arcuate fibres.
How is direction selectivity achieved?
It is achieved through multiple cortical inputs to a single Area 2 neuron, where both + and - inputs are simultaneously activated, resulting in a weak response.
How is touch coded at the periphery?
For each type of touch stimulus, there are receptors that code different aspects of the stimuli, with stimulus features encoded by the type and location of receptor activated.
How many pairs of spinal nerves transmit sensation from the rest of the body?
31 pairs of spinal nerves.
How does lateral inhibition increase touch accuity?
Pin prick triggers several receptor neurons, but one more than others, that secondary neuron will then inhibit the surrounding neurons, causing it to be the only one to stimulate a tertiary neuron, thus increasing accuity
How does convergence decrease touch accuity?
Many primary neurons converging onto a single secondary neuron creates a large receptive field. If two stimuli fall within the same field, only one signal goes to the brain.
Homunculus
a maplike representation of regions of the body in the brain, regions are not proportional to size of body part, rather amount of receptors in the body part.
How is the primary somatosensory cortex organized?
Columnar organization based on map of the body. Has slow and fast adapting regions.
slowly adapting
- continue to fire as long as the stimulus is present
- give an absolute sense of stimulus and know it is always there
rapidly adapting
- sense only when the stimulus comes on/off
- good for detecting change
Cortical representation after amputation
Areas beside amputates area will adapt and take over cortical space once designated for the lost appendage.
Orientation sensitive neurons
respond best to movement along a specific axis through a mix of excitatory and inhibitory neurons. Dependent on ratio of excitation/inhibition.
mechanosensory transduction
highly myelinated afferants
- stretch sensitive channels in mebrane
APs generated at nerve ending
pancinian corpuscle
Has layers to detect vibration, in subcutaneous layer, large receptive fields and rapid adaptation, a-beta afferents
Ruffini endings
For skin stretch and proprioception, in dermis, large receptive fields and slow adaptation, a-beta afferents
Meissner corpuscle
For pressure and grip, in dermis, small receptive fields and rapid adaptation.
Merkel cell neurite complex
For form and texture, in epidermis, small receptive fields and slow adaptation.
What afferents do touch receptors use?
a beta afferents
What are Merkel endings?
They are non-encapsulated and encapsulated receptors in the skin that respond to form and texture.
What are the four aspects of sensory stimuli that are coded by sensory receptors?
Intensity, duration, temporal aspects, and location.
What are the four portions of the cortex that make up the somatic sensory cortex?
Frontal, parietal, temporal, and occipital.
What are the two pathways responsible for sensing from the face?
The trigeminal lemniscal pathway and the homunculus pathway.
What are the types of sensory receptors that fall under the category of allcutaneous mechanoreceptors?
Pacinian, Meissner, Ruffini, and Merkel.
What do direction selective neurons do?
They code stimulus features such as direction (where stimuli is moving).
What do orientation selective neurons do?
They code stimulus features such as orientation (angle).
What does photon imaging reveal about neural connectivity?
It reveals that at the level of single synapses, it is affected by sensory deprivation.
What is affected by sensory deprivation at the level of single synapses?
Neural connectivity, as revealed by chronic two-photon imaging.
What is Microneurography?
Microneurography is a technique based on tungsten needle electrodes which are inserted through the skin and into a nerve.
What is the difference between Merkel and Meissner receptors?
Merkel receptors are slowly adapting (SA) and have small receptive fields, while Meissner receptors are rapidly adapting (RA) and have large receptive fields.
two-point discrimination threshold
method for measuring relative size of receptive fields eg. the threshold is lower for fingers/mouth whereas upper arm is higher
> also there is more receptors in the highest sensitivity areas eg. hands
lateral inhibition increases
acuity (sharpness)
lateral inhibition pathway
stimulus -> primary neuron response is proportional to stimulus strength -> pathway closest to the stimulus inhibits neighbours -> inhibition of lateral neurons enhances perception of stimulus
when you collect from many inputs you lose
acuity (sharpness)
discovery of piezo2
found that mechanically activated currents in merkel cells depend on piezo 2
- knocked out piezo and found no currents
- expressed gene in different cell types
mechanically activated currents in _______ depend on _______
merkel cells, piezo2
Atoh knockout–>
conditionlal knockout that doesnt have merkel and piezo - shows intermediately adapting responses
therefore merkel cells are repsonsible for encoding sustained phase
channel rhodopsin - merkel cells
expressed Chr in merkel cells to directly activate using light and found that by activating merkel cell its enough to create activity in neuron
- must be releasing some chemical (serotonin) to drive response
piezo in touch
most important for increasing sensitivity - amplify responses at low levels
medial lemniscal pathway
touch:
cuneate tract- upper body
gracile tract- lower body
trigeminal lemniscal pathway
information from head
- trigeminal ganglion
density of receptors
non-uniform
- density of receptors correlates to spatial resolution
What is photothrombosis?
Inject dye into bloodstream to visualize flow, can be used to induce ischemic stroke through reactive oxygen species in the blood.
Peri-infarct zone
Area right next to damaged area, involved in cortical map re-wiring.
Tape test for stroke mice
Put tape on paws of control and stroke mice, control mouse took tape off, experimental ignored tape on affected paw.
Ladder test for stroke mice
Assessed control and stroke mice on their paw placements on a horizontal ladder, stroke mice showed less of a grasping response on ladder rungs and more incorrect placements.
What effects did optogenetic stimulation have on stroke mice (4)
- No alteration in blood flow or infarct size
- Formation of new thalamocortical boutons in peri-infarct regions
- Improved recovery of cortical responses/territory involved in forepaw touch
- Accelerated recovery of sensory-motor forepaw function
Proprioception
sensing oneself, where our parts of our body are in dimensional space
there are 3 mechanoreceptors involved
-muscle spindle
-gogli tendon organ
-ruffin endings (in joints)
Extrafusal muscle
-make up the bulk of the muscle
-contractile/generate force
-stimulated by alpha motoneurons
intrafusal muscle fibers
4-10 fibers/spindle in parrallel
-sense stretch (muscle length
-afferent carried by group 1a
-more prominent is muscle groups like eyes and head but less density in legs
what are the two kinds of fibres in intrafusal muscle and how much do muscles usually have?
nuclear ‘chain’ fibre
nuclear ‘bag fibre
-most muscles have 2-3 bag and 4-6 chain
1a afferents
-spiral around the bag fibres for dynamic information
-repsonds to stretch of intrafusal muscle
II afferents
- looks at static information
-nuclear chain fibre
2 types of gamma efferents
-for dynamic and static
-one for bag and one for chain
-they adjust the tension on the central part of the intrafusal muscle but don’t touch the centre
gamma motor neurons/efferents
regulating the contraction of the intrafusal muscle fibers by adjusting the length of the intrafusal muscle fibers
-Dynamic gamma motor neurons regulate the dynamic response of the muscle spindle during changes in muscle length, while static gamma motor neurons maintain the baseline sensitivity of the spindle.
-1a afferents remain close to their threshold for activation
Golgi tendon organs
-proprioceptive sensory receptor that’s in series with extrafusal muscles
-detect tension (load on muscle)
- slowly adapting
-Ib afferents
-insensitive to stretch (which activates spindles)
stretch reflex circuitry -> stretch
-When a muscle is stretched, the muscle spindles are also stretched, leading to the activation of sensory neurons, including the primary (1a) sensory afferent fibers
-sensory afferents send signal to motor neuron
-The alpha motor neurons stimulate the muscle to contract, causing it to shorten, which counteracts the initial stretch
stretch reflex circuit - resistance
- the interneuron inhibits the alpha motorneurons and instead activated the antagonistic
negative feedback regulation of muscle tension by
golgi tendon organs
Golgi tendon organs
-main job of golgi tendon is to prevent damage to the muscle
-help maintain steady muscle tone (Muscle tone refers to the slight tension or firmness present in a resting muscle)
-relaxes muscle when heavy load is too much to prevent muscle damage
muscle spindles vs golgi tendon organs
Muscle spindles provide information about changes in muscle length, enabling the central nervous system to regulate muscle length and prevent overstretching. On the other hand, Golgi tendon organs detect changes in muscle tension, helping to prevent excessive muscle contraction and potential damage to the muscle-tendon uni
dorsal spinocerebellar pathway
-afferents from lower body go up and go to Clarkes nucleus then to dorsal spinocerebellar tract to cerebellum
-afferents from upper body go thought the ventral posterior nucleus of the thalamus
pain receptors
nociceptors
pain is transmitted
through different ways than mechanoreception
Nociceptors
-on free nerve endings that detect painful (noxious) stimuli
3 types of nociceptors
1) thermal - response to >45 degrees celsius-5 degrees celcius
2) mechanical - intense pressure
3) polymodal - respond to thermal, pressure and chemical stimuli
the first and second pain is carried by
> first pain is carried by the thinly myelinated A fiber -> for thermal/mechanical
second pain is carried with the unmyelinated C fiber -> for polymodal
TrpV1 Receptor
Sensitive to both heat and pain
-receptor detects capsaicin
-TRPV1 allows the influx of cations, particularly calcium and sodium ions
-the afferents that mediate heat get depolarized when agonists are added
