Proprioception + pain

Definition + stimuli of hair receptors

Definition	Stimuli
Afferent neuron endings spiral around base of hair follicles	Mechanical displacement of hair

Features + function of hair receptor

Features	Function
Fast adapting ( phasic )	Detect moving objects + signals direction + speed of obj

Definition + stimuli of meissner corpuscle 

Definition	Stimuli
Encapsulated receptor in dermal papillae in glabrous skin  → stack of epithelial cells w/ afferent fibre endings in bwt	Flutter + movement  → epithelial cells slide past each other → distortion of membranes of axon terminals → receptor potential

Features + function of meissner corpuscle 

Features	Function
Rapidly adapting	Rubbing against skin + movement across surface

Definition of proprioception + what is detected 

Definition ( subtypes) : 

1. Static position sense: conscious perception of orientation of different parts of body w/ respect to one another 

2. Dynamic proprioception: rate of movement sense 

What is detected: 

1. Degrees of angulation of all joints in all planes + rates of change 

Receptors involved in proprioception

1. Skin tactile receptors 

2. Deep receptors near the joints

• Muscle spindles: feedback abt muscle length/ tension/ position 

• Golgi tendon organs: muscle  tension during active contraction of muscles 

Receptors involved in pain

1. Free nerve ending 

• Features: slow adapting / many different functions despite morphologically similar → expression of different membrane receptors that respond to different stimulus 

Difference in pain sensation based on activated nerve fibre

	Speed of signals	Pain sensation
Multimodal C fibres	Slow	Dull
A delta fibres	Fast	Sharp

Characteristics of pain

Type	Receptors	Nerve fibres	Sensation	Localisation	Sequence
Fast	Mechanical + thermal nociceptors	Myelinated A-delta fibres	Sharp + prickling	Easily	First
Pain	Polymodal nociceptors	Unmyelinated C fibres	Dull + aching	Poorly	Second + lasts longer

Interplay bwt nociception + inflammation

→ damage to skin → sensory nerve sends pain signals + inflammatory mediators released → threshold of how sensory nerve is activated → inflammation hurts more

Process of pain signalling : ascending pain pathway

1. Noxious stimulus stimulates nociceptor 

2. Substance P + glutamate released → interneuron activated →  reticular formation → limbic system ( emotional input )/ thalamus ( perception of pain ) → somatosensory cortex ( localisation of pain ) 

Effect of glutamate: 

1. W/ AMPA receptors → generation of action in dorsal horn cells → pain message to higher centers spinal cord  

2. W/ NMDA receptors → release of Ca2+ → second messenger systems  activated → hypersensitivity of dorsal horn → exaggerated sensitivity of injured area

Process of pain signalling: endogenous analgesic pathway

Periaqueductal grey matter sends inhibitory ntm down the pathway → reticular formation → synapse with part before interneuron Release of endogenous opioids ( endorphins/ enkephalins/ dynorphin ) → bind w/ opioid receptors → excitability of nerve terminal → pain signalling reduced

Response to pain signals

Withdrawal reflex → synapse  w/ pain nerves → protective response to avoid further tissue damage 

Local analgesics: 

→ lipophilic → diffuse into membranes + interact w/ voltage gated sodium channels → shut down ability to activate voltage gated sodium channels → block sensory nerve action potential generation