Physiology Of The Nervous System Flashcards
Types of nervous system cell and function
Neurone - action potential generation and transmission
Astrocytes - support neurones and form bbb
Oligodendrocytes - insulate CNS neurones
Microglial cells - immune CNS response
Ependymal cells - line ventricles and spinal cord
Schwann cells - insulate PNS
Term for myelinated conduction down an axon?
Saltatory
Types of nerve fibre with example in order of decreasing size (with rough size)
Aalpha - proprioception and somatic motor - 12-20mm
Abeta - touch, pressure - 2-12mm
Agamma - muscle spindle 3-6mm
Adelta- pain, touch, temperature 2-5Mm
B - preganglionic ANS <3mm
C dorsal root - pain, temp, mechanoreceptors, reflex 0.4-1.2mm
C sympathetic - postganglionic ANS 0.3-1.3mm
Conduction speed of A type fibres
A alpha 70-120m/s
A beta 30-70m/s
A gamma 15-30m/s
A delta 12-30m/s
Speed of conduction in b and c type fibres
B 3-15m/s
C 0.5-2m/s (approx)
How is the neurone resting membrane potential set up?
NaKATPase 3:2 ratio
Both na and K diffuse back down their concentration gradient but membrane more permeable to K
Membrane impermiable to anions
Overall results in interior being more negative at -70mV
Term for the gaps in the myelin sheath
Nodes of Ranvier
What is the definition of ion conductance in relation to APs
The reciprocal of elctrical resistance of the membrane to a specific ion.
Key phases of a neuronal action potential
Slow rise to threshold
Spike potential - triggered by marked increase in Na permeability
After depolarisation
After hyperpolarisation
What limits the action potential depolarisation process
Na channels open only very transiently
Inside of cell becomes increasingly electropositive thus gradient that drives na influx disappears
K conductance also increases causing repolarisation
What is the after hyperpolarisation of an action potential
Slight but prolonged overshoot on repolarisation
Caused by slow return of k conductance to normal
What are the refractory periods of a neurone
Absolute refractory period - totally unresponsive to any stimuli regardless of strength - from time threshold is reached until repolarisation 1/3rd complete
Relative refractory period - period where stronger than normal stimuli may lead to excitation - from 1/3rd of repolarisation until start of after hyperpolarisation
What forms a synapse? Number per synapse?
Terminal buttons of a neurone (1-1000s) with cell body or axon of another neurone
What is the role of a synapse
UNIDIRECTIONAL impulse conduciton
What is an electrical synapse?
The synapse consists of the membranes meeting to form gap junctions allowing continued diffusion of ions
Width of a typical synaptic cleft
20nm
What are the three key organelles found in the synaptic button
Vesicles
ER
Mitochondira
Mechanism of synapse neurotransmitter release
Determining factor for amount released
Action potential reaches synaptic button.
Opening of voltage gated calcium channels - influx of calcium.
Proteins in vesicles bind to the calcium and spread apart allowing fusion with terminal membrane
Contents of vesicles released into cleft
Amount determined by calcium concentration
Why are post synaptic potentials transient
Reuptake of neuro transmitter
Enzymatic deactivation of neurotransmitter
Auto receptors on presynaptic membrane inhibit continued neurotransmitter release
What categories of effects can be mediated by neurotransmission
Excitatory (EPSP) eg opening of na channels causing depolarisation
Inhibitory (IPSP) eg opening of Cl or K channels causing hyperpolarisation
What are the main CNS neurotransmitters?
ACh
NA
A
Dopamine
Serotonin
Location and function of ACh neurotransmitter in CNS
Cerebral cortex, thalamus, limbic - memory, perception, cognition, attention
Location and function of NA neurotransmitter in CNS
Locus coeruleus, cerebellum, hypothalamus - decending pain, inhibition of purkinje cells, regulation of anterior pituitary secretion
Location and function of adrenaline neurotransmitter in CNS
Medulla - uncertain