Neuro Physiology

Question 1

Neuromuscular junction

Answer 1

The point where myelinated alpha motor neurones connect with skeletal muscle
- terminal bouton of nerve axon
- synaptic cleft
- post-synaptic membrane (muscle)

Question 2

Neurotransmission

Answer 2

Terminal bouton
- ACh synthesised and stored in vesicles. 1% active ready to go, 80% in reserve, 19% stationary
- AP reaches, VGCa channels open, calcium triggers vesicles in active zone to release contents into synaptic cleft (via SNARE proteins)
In synaptic cleft
- ACh diffuses across to motor end plate
At motor end plate
- nACh receptor - non specific ion channel
- 2 Ach bind to alpha subunts
- Na+ in K+ out
- depolarisation of membrane
- Ach moves away and broken down by cholinesterase

Question 3

Resting membrane potential

Answer 3

-70mV (inside negative)
Maintained by Na/K ATPase
Ion channels allow passage across membrane - ligand gated or voltage gated
Nernst equation
- describes balance between concentration gradient and electrical gradient
- equilibirium - two forces balanced
- RMP is the sum of Nernst equations of all ions

Question 4

Action potential

Answer 4

propagated disturbance of resting membrane potential
passes in one direction
Na in
- 70mv RMP. - 55mv threshold - AP unstoppable to +35mV
- repolarisation - K out - hyper polarisation leads to refractory period

Question 5

Types of axons

Answer 5

Aa - motor neurones 70-120m/s
AB - touch, pressure 30-70m/s
Ay - muscle spindles 15-30m/s
Ad - pain, cold, touch 12-30m/s
B - preganglionic autonomic 3-15m/s
C - pain, temp, postganglionic sympathetic 0.5-3m/s

Question 6

Cerebral blood flow

Answer 6

750ml.min
High O2 consumption
determinants - MAP, PaCO2, PaO2
- MAP - CBF auto regulated 50-150mmHg
- PaO2 CBF stable, increased below 8kPa
- PaCO2 - sigmoid curve with linear increase between 2.5kpa and 10kpa

Question 7

Cerebral auto regulation theories

Answer 7

1. Myogenic - stretch of blood vessels leads to vasoconstriction
2. Flow-metabolism coupling - extravascular concentration of metabolic mediators. inc metabolic activity - increased mediations - increased vasodilation to remove mediators. I.e. Increased neural activity –> increased energy demand –> increased CBF
   3, Metabolic - CO2 - 1kpa reduction in CO2 25% reduction in CBF. O2 - <8kpa increased CBF

Autoregulation impaired by disease

Question 8

Munro-Kelly doctrine

Answer 8

Skull is a fixed rigid enclosure within which is brain, blood and CSF
An increase in the volume of one e.g. brain can initially be compensated by reduced the others e.g. blood and CSF up to a point.
Eventually compensation overwhelmed and ICP increases
Intracranial elastane - change in pressure for given change in volume.

CPP = (MAP - CVP) - ICP

Question 9

blood Brain barrier transfer

Answer 9

simple diffusion - small lipid soluble molecules e.g. CO2
facilitated diffusion - glucose
endocytosis
tight junctions opened by mediators e.g. glutamate