Functional Neuroanatomy

Question 1

What are the 2 main types of processing?

Answer 1

• hierarchical
• distributive

Question 2

Describe the hierarchy of signalling in the CNS

Answer 2

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 in the brain

Question 3

What happens in distributive processing?

Answer 3

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

Question 4

What is the difference between hierarchical and distributive processing?

Answer 4

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

Question 5

What do the 2 components of the NS include?

Answer 5

• CNS - brain and spinal cord
• PNS - nerves

Question 6

What are the 2 nerve classifications?

Answer 6

• afferent - towards the CNS
• efferent - away from CNS

Question 7

What are the lowest point of the hierarchy in the CNS?

Answer 7

afferents

Question 8

What are the 3 types of afferent fibres and what is there myelination?

Answer 8

• Aβ; large with high degree of myelination
• Aδ; myelinated but less than Aβ
  -C; unmyelinated, much thinner

Question 9

What is conduction velocity?

Answer 9

the speed by which the signal is conducted from the periphery to the CNS

Question 10

What afferent fibre type have the highest conduction velocity?

Answer 10

Aβ fibres

Question 11

What afferent fibre type has the highest frequency in the mammalian body?

Answer 11

C fibres

Question 12

What are mechanoreceptors?

Answer 12

receptors that contribute to sensations that arise from mechanical stimuli in the non-painful range e.g. mild pressure

Question 13

What type of receptor is each of the afferent fibre types?

Answer 13

• Aβ - mechanoreceptor only
• Aδ - mechanoreceptor and nociceptor
• C - mostly nociceptor

Question 14

What is meant by slowly adapting?

Answer 14

the receptors fire very robustly when stimulus is applied; activity may decrease but never silence for the duration of the stimulus

Question 15

What is meant by rapidly adapting?

Answer 15

the receptors respond when initial stimulus is applied (first AP) then silence until the stimulus is removed (second AP)

Question 16

Give an example of a mechanoreceptor

Answer 16

Pacinian corpuscle

Question 17

What do nerve endings of mechanoreceptors generally have?

Answer 17

a specialised coating

Question 18

What are the nerve endings of nociceptors generally?

Answer 18

free nerve endings embedded in the skin without any specialised coating

Question 19

What does loss of Aβ fibres lead to?

Answer 19

loss of response to non-painful stimulus

Question 20

What does loss of Aδ/C fibres lead to?

Answer 20

insensitivity to both superficial and deep painful stimuli

Question 21

What do individuals with CIPA have loss of?

Answer 21

NGF-dependent C/ Aδ fibres due to LOF mutations in the NTRK1 gene

Question 22

What are the 2 main subtypes of C fibres?

Answer 22

peptidergic and non-peptidergic

Question 23

What do peptidergic fibres contain?

Answer 23

TRP (transient receptor potential proteins)

Question 24

What do 90% of non-peptidergic fibres contain?

Answer 24

Mrgprd (mas-related GPCR D) and bind isolectin B4

Question 25

Why can peptidergic and non-peptidergic fibres be destroyed separately?

Answer 25

the terminal of the 2 fibre types is separated in the spinal cord

Question 26

What can destroy TRP+ fibres?

Answer 26

capsaicin

Question 27

What stimuli are Mrgprd and TRP+ fibres responsible for respectively?

Answer 27

• Mrgprd - mechanical
• TRP+ - thermal

Question 28

What are Pacinian corpuscles?

Answer 28

myelinated nerve endings covered in connective tissue embedded in the skin

Question 29

What is the trigger zone?

Answer 29

where APs are generated which then travel along the fibre all the way to the spinal cord

Question 30

What are the 3 steps of signal generation and relay to the CNS?

Answer 30

1. receptors transduce external stimuli to an electrical change
2. electrical change is depolarising in nature and leads to an AP
3. AP is relayed to CNS and processed leading to sensation

Question 31

What is the cellular basis of depolarisation?

Answer 31

an external stimulus typically evokes an inward current carried by cations that depolarise the membrane e.g. noxious heat acts via TRPs or TRPs on free nerve endings

Question 32

What is the best technique to investigate the cellular basis of depolarisation?

Answer 32

patch clamp technology

Question 33

What can electrical changes be?

Answer 33

voltage changes, depolarisation or hyperpolarisation

Question 34

When are TRP channels activated?

Answer 34

at temperatures above 45º to sense temperature and pain

Question 35

What does opening of TRP channels do?

Answer 35

depolarise nociceptors

Question 36

When is there complete loss of sensation via TRP channels?

Answer 36

when all types are absent

Question 37

What is the highest part of the hierarchy in the CNS?

Answer 37

the cortex

Question 38

What are the 3 somatosensory areas of the cortex with increasing complexity?

Answer 38

• primary somatosensory cortex
• somatosensory and posterior parietal complex
• association complex