Somatosensory system Flashcards
What are the properties of primary sensory neurones?
all excitatory - Using glutamate
Ability to generate action potentials from free nerve endings
All their cell bodies are located in the dorsal root ganglion.
What are the different classifications of primary sensory nerve fibres depending on their function?
A alpha
A beta
A delta
C
(in order of diameter largest-smallest and speed of conduction smallest - highest)
What are A alpha afferent fibres used for?
Proprioceptors of skeletal muscles
What are A beta afferent fibres used for?
Mechanoreceptors of skin
What are A delta afferent fibres used for?
Pain/temperature
What are C afferent fibres used for?
Temperature
Pain
Itch
What are receptive field properties?
Axons have distinct receptive fields where each axon innervates a specific receptive field in its dermatome.
What is a dermatome?
Area of skin innervated by nerve fibres from a single nerve
What determines the size of a receptive field?
2 point discrimination
Receptive field sizes vary depending on the precision of localisation
Why does the precision of sensory localisation vary greatly across the body?
Related to the area of the cerebral cortex devoted to each region.
What is an adequate (prefered) stimulus?
The right stimulus for a neurone that will cause a response
What are some general properties of sensory receptors?
Adequate stimulus depends on the nerve ending
Threshold for signal depends on the nerve ending
Firing rate is proportional to the stimulus strength.
How is a signla transduced form sensory receptors?
The stimulus causes transduction channel opening.
Graded receptor potential if threshold is passed causing an action potential
What are some adaptations of sensory receptors?
Phasic or tonic receptors
What is a phasic receptor?
Fast adapting receptor:
Detects how fast a stimulus can change.
Therefore is useful when attntion to a stimulus is no longer required (such as wearing clothes)
What is a tonic receptor?
Slow/non-adapting:
Stimulus is only detected whilst it is being maintained.
Important when maintaining information about a stimulus such as amount of pain.
What are the major cutanous senory receptors?
Mechanorecepotrs - Touch/pressure/vibrations
Thermoreceptors - Hot/cold (temperature)
Nociceptors - Noxious stimuluation (pain)
What are some properties of cutaneous mechanoreceptors?
A beta fibres - Detect tactile touch
nerve ending has specialised sensory apparatus (organ)
Apparatus comprises of a specialised cell - Structure determines function => function determines location.
What are the 4 main types of mechanoreceptor and where are they found in the skin?
Foundin superficial skin layers:
Merkels Receptor
Meissners Corpuscles
Found in deeper skin layers:
Ruffinies’ corpuscle
Pacinian corpuscle
What are the Meissners copruscles?
Found in papillary dermis
Rapidly adapting
Detect light touch and vibrations
What would meissners corpuscles be used for?
Adjustment of grip whilst holding objects
Putting on clothes but not wearing them.
What are merkels receptors?
High density in the epidermis of digits and around the mouth Slow adapting Detect sustained light touch Apparatus is a specialised keratocyte Perception of form and texture
What are ruffinis’ corpuscles?
Respond to lateral movement or stretching of the skin
Detect deep touch
Apparatus is a netwokr of collagen fibres
What are pacinian corpuscles?
Found in deep layers of the dermis Rapidly adapting detect deep touch and poke Fully encapsulated nerve ending Onion structure deforms on distortion.
What are hair follicle receptors?
Detect light touch activation in the dermis
Rapidly adapting
Nerve fibre wrapped around hair
Hair deflection detected.
What are cutaneous thermoreceptors?
Bare nerve endings
Slow adapting
Two types detecting either warming or cooling
Poor indicators of absolute temperature
sense of temp comes from comparison of signals
What are thermoreceptor channels?
TRP (transient receptors)
non specific cation channels.
Nerve ending sensitivity depends on the transducer expressed
What temperature do the TRPV3/4 channels open at?
Warm - channels open at 29-45 degrees
What temperature do the TRPM8 channels open at?
Cold - Channels open at 8-38 degrees
What temperature do the TRPA1 channels open at?
Cold - <17 degrees
What are cutaneous nociceptors?
Bare nerve endings
Non adapting - high threshold
Require an adequate stimulus capable of damaging tissue.
What is proprioception?
Sense of 3D dimensions of the body
Detection of the mechanical status of the musculoskeletal system
What do proprioceptors detect?
Joint position Muscle length Muscle movement Acceleration Tension/force Simple reflexes
What are the 2 proprioceptors found in muscles?
Muscle spindle
Golgi tendon organ
What does the muscle spindle detect?
Length and acceleration of muscle
Stretch sensitive
What fibres are found in the muscle spindle?
Groups of A delta afferents wrapped around a central sensory portion
What does the golgi tendon organ detect?
Muscle tension
Located at the junction of muscles and tendons
Sensitive to tension generated by contraction
What are the fibres found in the golgi tendon organ?
Innervated by the A beta afferents
What sensory fibres are found in the dorsocolumn pathway and what information does it carry?
Large A beta fibres Information: Touch Virbation 2 point discrimination proprioception.
What sensory fibres are found in the Spinothalamic pathway and what information does it carry?
Small A delta and C fibres Information: Pain Temperature Non-discriminatory touch
