sensory physiology Flashcards
- Five major divisions based on stimuli they respond to
○ Mechanoreceptors ○ Thermoreceptors ○ Photoreceptors ○ Chemoreceptors ○ Nociceptors
- Two types of receptor cells
○ A nerve cell
○ A specialised cell + afferent neurone
Stimulus intensity encoded by
AP firing rate
RA (phasic) neurones
respond poorly to steady stimuli, but very well to dynamic stimuli
SA (tonic) neurones
detect continuous stimuli, but not dynamic stimuli
C fibres
slow
no myelin
Aa fibres
super fast
thick myelin
Ab fibres
fast
A delta fibres
kinda fast
stimulus acuity
Ability to distinguish between two spatially separate stimuli
stimulus acuity depends on
§ Density of peripheral receptors
§ Size of receptive fields
§ Central convergence and lateral inhibition
Lateral inhibition restricts
spatial spread of excitation
label line principle
§ Receptor does not dictate what the brain will understand, the location of the afferent nerve does
○ Action potentials in labelled lines generate specific sensory percept
2 unencapsulated nerve endings
free nerve endings and Merkel’s disks
free nerve endings
(slowly adaptive, variable gating)
□ Pain, warm, cold A-delta or C fibres
merles’s disks
(slowly adapting, mechanoreceptor)
□ Continuous light tough (steady state info) Ab fibres
3 encapsulated nerve endings
meissner’s corpuscle, lamellar corpuscle, bulbous corpusle
miessner’s corpuscle
(rapidly adapting mechanoreceptor
□ Altered touch, spatial characteristics Ab fibres
lamellar corpuscle
(rapidly adapting mechanosensor)
□ Deep pressure, vibration, Ab fibres
bulbous corpusclee
(slowly adapting mechanosensor)
□ Heavy touch, stretch (joints) Ab fibres
Na/Ca channels
§ Excitatory
K/Cl channels
§ Inhibitory
○ Golgi tendon organs
§ Compression, stretch
§ Rapid adapt, Aa, Ab fibres
§ Joint position, reflex response to over-flexion
○ Muscle spindles
§ Compression, stretch
§ Rapid adapt of slowly adapt, Aa/Ab fibres
§ Rate of change and muscle stretch
joint capsule receptors
§ Around the joint capsule
§ Fire information at different angles
§ Stretch receptors - ruffini
§ Joint angle information
3 instruments for positional sense
joint capsule receptors
muscle spindles
Golgi tendon organs
Transient receptor potential (TRP) channels
temperature sensitive ion channels
§ Excitatory Na/Ca channels
cold receptors
TRPM8 channels
§ Firing rate increases as temp decreases
cold receptors also respond to
eucalyptus, menthol
cold receptors
§ Temperature range spanning about 10-35°C
Warm receptors
TRPV1/3, TREK1 channels
§ Firing rate increases as temp increases
TRPV3
22-40°C
TRPV1
42°C +
2 distinct affarent pathways of somatosensory
DCML and anterolateral pathway
- The dorsal column medial lemiscal pathway DCML
○ Larger fibres (30-110 m/s)
○ More spatial organisation
DCML does
§ Localised touch § Fine grade touch § Vibration § Movement against skin § Joint position § Fine pressure
- Anterolateral pathway
○ Thinner fibres (<40m/s)
○ Less spatial organisation
anterolateral pathway does
§ Pain § Heat cold § Crude touch § Crude pressure § Tickle and itch § Sexual sensation
Strong pressure/pinch/squeeze
§ High threshold stretch-gated Na/Ca channels
- Temperature pain (hot, cold)
○ Thermally gated ion channels
○ TRPV1/2/3 (HOT) and TRPM8 (cold) channels
Polymodal nociceptors
- Receptive to all other painful stimuli
○ Respond to heat, cold, pinch and chemical stimuli
○ Express multiple receptors
