Somatasensation Flashcards
What are the three functions of Primary afferent neurones
- Exteroception
- from external environment - Proprioception
- posture and movement - Inter/enteriception
- internal environment
What information about stimuli can PANs encode
Modality= type of stimuli Intensity= total stimuli energy Timing= when starts/ stops Location= where receptors are active
What property of PANs allows for detection of modality
- Respond to one form of energy more than any other
2. Respond to a narrow range of stimuli
Describe ‘adequate stimulus’
- Type of stimulus receptors respond to under normal conditions
- Type of stimulus that has lowest threshold for receptor activation
- Primary afferent fibres carry information from a single type of receptor
- Verity of specialised receptor structures = submodalites
Describe ‘labelled line code’
Perceived MODALITY depends on SPECIFICITY of receptor and fibre type activated and pathway to area of cortex
Describe the specificity principle
Whatever the stimulus the perception is the same (rub eyes but see stars)
Describe free nerve endings
- Most body tissue
- ## Pain, temp and pressureCan be modified (Merkles Discs)
- Basal layer of epidermis
- Light pressure
Define sensory threshold
Minimum intensity of a stimulus to produce response from sensory system
- Receptor threshold
- AP threshold
- Perception threshold
Define saturation
Maximum Intensity of stimuli to produce a response from sensory system
Define the ‘dynamic range’
- The rage of intensities that will produce a response from receptor/ sensory system
- The range between threshold and saturation
Describe how receptor threshold can be modified
ADAPTATION
Receptor process when response to constant stimulus declines over time
What are the two types of adaptation
Slow
- better for coding intensity of stimulus for entire duration
Fast
- better for coding changes in stimulus intensity but not duration
What defines speed of conduction
- Diameter= faster AP conduction
2. Myelination
What are the three pathways in the ascending sensory system
- Anterolateral system
- Dorsal column-medial lemniscal pathway
- Somatosensory cerebellum pathway
Describe the anterolateral system
Includes:
- Spinothalamic
- spinohypothalamic
- spinoreticular
- spinomesencephalic
- spinotectal
Relay of
- pain and temperature
- non-discriminative touch (crude non localised)
- touch
- pressure
Describe the Dorsal-column medial lemniscus pathway
Includes: - fasciculus garcilis - fasciculus cuneatus - medial lemmiscus Relays - fine touch - vibration - position sense
Describe the somatosensory pathways to the cerebellum
- anterior
- posterior
- rostral
Spinocerebelluar tracts
+ cuneocetebllar tract
Relays proprioceptive information
What tracts relay conscious perception
- Spinothalamic
- DCML
To the ventral posterior lateral nucleus of thalamus
Describe the transmission of discriminative touch
- low threshold non-noxious
- mechanoreceptors and proprioceptors
DCML pathways
Describe the transmission of pain and temperature
- high threshold noxious
- temp, itch, crude and visceral sensation
Anterolateral pathways
Describe the transmission of proprioception
- low threshold non-noxious
- muscle stretch, joint position, tendon tension
Cerebellar pathways
Describe the general organisation of sensory pathway to cortex
- Receptor
- PAN synapses on the dorsal root ganglion
- Projects to nucleus (medulla or other)
- Nucleus to Thalamus via lemniscus
- From thalamus to cerebral cortex via thalamus radiations
What are the 3 fundamental steps in informational processing
- Receptor - transduction
- Neural pathways - transmission (& modulation)
- Cerebral cortex- perception
Describe stage one of DCML pathways
- PANs detect sensation at receptor
- Enters through dorsal root
Cell bodies in DRGA
Describe the second stage of DCML
- Second order neurone in medulla
- Multiple PANs synapse
- Respond to mine than one class of PAN = convergence
- Inhibitory receptive fields (mediated though interneurones
Describe the 3rd stage of DCML pathway
- Synapse on third order neurones in thalamus
- Cell bodies in VPL nucleus of thalamus
- Radiations via posterior limb of internal capsule
- Somatotopy maintained
Where does spinoreticular tract terminate
Reticular formation -> cortex
Where does the Spinomesencephalic tract terminate
Midbrain nuclei (including PAG)
What is the primary nociceptive NT
Glutamate (excitatory)
What do the Lateral/anterior spinothalamic tracts carry
These are the direct tracts
Lateral (neospinalthalmic tract)
- pain and temperature
Anterior (paleo)
Crude touch and pressure
Describe some characteristics of the spinothalamic pathway
- Intensity: sharp dull pain
- Location- poor localisation
- Timing- ongoing, can be chronic
What does the dorsal horn contain
Afferent nuclei
What does the lateral horn contain
Afferent and efferent nuclear columns
What does the ventral horn contain
Motor nuclei (skeletal muscle innervation)
Describe lamina 1
- Low neuronal density
2. Variable size and distribution
Lamina 2
- High neuronal density
- Small fusiform neurones
- Islet cells, GABA and Stalked cells
Lamina 4
- Dendrites spread towards lamina 2 and 3
2. Transverse cells
Lamina 5 & 6
- Fusiform and triangular neurones (medial part)
2. Medium sized multipolar neurones (lateral part)
Where do pain and temp receptors (free nerve ending) synapse
The substantia gelatinosa
What are the two ways of coding stimulus intensity
Frequency coding
- increasing size of receptor potential
- increasing stimulus intensity
- stimulating receptive field
Population coding
- increase no. Of neurones responding
- recruitment of neurones with high threshold
- stimulating more of receptive field
Role of Acetylcholine
- Primary afferent terminals innervate dorsal horn laminae I, III, IV
- activate interneurones to modulator motor and nociceotive pathways
Role of monoamines (Na, 5-HT, DA)
- Dorsal horn, intermediate gray, ventral horn
- alagesia
What are the 3 types of unencaplusated receptors
- Free nerve endings
- Modified free nerve endings like Merkles discs AND
Hair follicle receptors
What are the 3 types of encapsulated receptors
- Mesisners corpuscles (tactile)
- dermal papillae of hairless skin
- light pressure and vibration - Pacini corpuscles (lamellar)
- subcutaneous tissue, joints, fingers
- deep pressure, stretch, vibration - Ruffini endings (bulbous)
- deep in dermis, joint capsules
- deep pressure, stretch
