Functional Neuroanatomy Flashcards
What are the 2 main types of processing?
- hierarchical
- distributive
Describe the hierarchy of signalling in the CNS
external pressure is translated to a signal by receptors under the skin which then flows to neurons in the spinal cord and then to the thalamus
What happens in distributive processing?
the signal can be split into 2 parts which are processed separately and are eventually put together by the CNS to form a complete picture
What is the difference between hierarchical and distributive processing?
if hierarchical processing is interrupted at any point, the whole process is disrupted but interrupting a process at point A in distributive processing will not affect point B
What do the 2 components of the NS include?
- CNS - brain and spinal cord
- PNS - nerves
What are the 2 nerve classifications?
- afferent - towards the CNS
- efferent - away from CNS
What are the lowest point of the hierarchy in the CNS?
afferents
What are the 3 types of afferent fibres and what is there myelination?
- Aβ; large with high degree of myelination
- Aδ; myelinated but less than Aβ
- C; unmyelinated, much thinner
What is conduction velocity?
the speed by which the signal is conducted from the periphery to the CNS
What afferent fibre type have the highest conduction velocity?
Aβ fibres
What afferent fibre type has the highest frequency in the mammalian body?
C fibres
What are mechanoreceptors?
receptors that contribute to sensations that arise from mechanical stimuli in the non-painful range e.g. mild pressure
What type of receptor is each of the afferent fibre types?
- Aβ - mechanoreceptor only
- Aδ - mechanoreceptor and nociceptor
- C - mostly nociceptor
What is meant by slowly adapting?
the receptors fire very robustly when stimulus is applied; activity may decrease but never silence for the duration of the stimulus
What is meant by rapidly adapting?
the receptors respond when initial stimulus is applied (first AP) then silence until the stimulus is removed (second AP)
Give an example of a mechanoreceptor
Pacinian corpuscle
What do nerve endings of mechanoreceptors generally have?
a specialised coating
What are the nerve endings of nociceptors generally?
free nerve endings embedded in the skin without any specialised coating
What does loss of Aβ fibres lead to?
loss of response to non-painful stimulus
What does loss of Aδ/C fibres lead to?
insensitivity to both superficial and deep painful stimuli
What do individuals with CIPA have loss of?
NGF-dependent C/ Aδ fibres due to LOF mutations in the NTRK1 gene
What are the 2 main subtypes of C fibres?
peptidergic and non-peptidergic
What do peptidergic fibres contain?
TRP (transient receptor potential proteins)
What do 90% of non-peptidergic fibres contain?
Mrgprd (mas-related GPCR D) and bind isolectin B4
Why can peptidergic and non-peptidergic fibres be destroyed separately?
the terminal of the 2 fibre types is separated in the spinal cord
What can destroy TRP+ fibres?
capsaicin
What stimuli are Mrgprd and TRP+ fibres responsible for respectively?
- Mrgprd - mechanical
- TRP+ - thermal
What are Pacinian corpuscles?
myelinated nerve endings covered in connective tissue embedded in the skin
What is the trigger zone?
the site where APs are generated which then travel along the fibre all the way to the spinal cord
What are the 3 steps of signal generation and relay to the CNS?
- receptors transduce external stimuli to an electrical change
- electrical change is depolarising in nature and leads to an AP
- AP is relayed to CNS and processed leading to sensation
What is the cellular basis of depolarisation?
an external stimulus typically evokes an inward current carried by cations that depolarise the membrane
What is the best technique to investigate the cellular basis of depolarisation?
patch clamp technology
What can electrical changes be?
voltage changes, depolarisation or hyperpolarisation
When are TRP channels activated?
at temperatures above 45º to sense temperature and pain
What does opening of TRP channels do?
depolarise nociceptors
When is there complete loss of sensation via TRP channels?
when all types are absent
What is the highest part of the hierarchy in the CNS?
the cortex
What are the 3 somatosensory areas of the cortex with increasing complexity?
- primary somatosensory cortex
- somatosensory and posterior parietal complex
- association complex
