Sensory Systems Flashcards
5 Sensory receptors in skin
Meissner’s Corpuscle
Merkle’s Corpuscle
Free nerve ending (nociceptor)
Pacinian corpuscle
Ruffini corpuscle
Functions of Messienrs Corpuscle
Sensory for light touch
Merkles corpuscle function
touch
Nociceptors
Pain
Pacinian corpuscle
deep pressure
Ruffini corpuscle
warmth
What happens to when sensory receptor stimulated
tranduce stimulate into a depolarisation, the receptor generator potential.
Degrading, and size of generator potential determined by stimulus.
What happens to the generator potential
It evokes an action potential, for long distance transmission
Frequency encodes intesity of stimulus
Receptive field encodes location of stimulus
What determines Acuity
Density of innervation and size of receptive field.
What are the 3 types of primary afferent fibres involved in cutaneous sensation
A (beta): large myelinated (30-70 ms),
A (Delta): Small myelinated (5-30ms)
C: unmyelinated (0.5-2ms)
What do A (beta) detect
touch, pressure, vibration
what do A (delta) detect
cold, ‘fast pain’, pressure
what do C fibres detect
warmth, ‘slow’ pain
What is proprioception mediated by
Mechanoreceptors
A (alpha), A (beta) primary afferent fibres. (muscle spindles, golgi tendon organs.)
Where do primary afferent nerve fibres enter
spinal cord via dorsal root ganglia (or cranial nerve ganglia for head)
How are mechanoreceptors transmitted?
projects up through ipsilateral dorsal colums
synapse in cueate and gracile nuclei
2nd order fibres cross over midline (decussate) in brainstem. then project to reticular formation, thalamus and cortex.
How are Thermoreceptive and nociceptive fibres transmitted (A (delta), C)
Synapse in the dorsal horn.
2nd order fibres cross over midline in spinal cord.
project up through the lateral spinothalamic tract to reticular formation, thalamus –> cortex.
Where is the termination of the sensory information
Somatosensory cortex of the postecentral gyrus
Sensory Homunculus: indicates which region of the cortex has the specific nerve ending,.
What is rapidly adapting sensory receptors
Sensory receptors which stop firing after a while when they have a long and constant stimulus
example of rapidly adapting sensory fibre
Mechanoreceptors
What are slowly adapting fibres
They continue to be activated during while stimulus is present
examples of slowly adapting nerve fibres
Nociceptors and Muscle spindles
What activates Nociceptors
Low PH, Heat (via ASIC, TRPV1 etc.)
Local chemical mediators (bradykinin, histamine, prostaglandins.)
What happens if theres activity in the mechanoreceptor fibres
activates inhibitory interneurons which release opiod peptides (endorphins), which inhibit transmitter release from Nociceptor fibres (closes gate)
