Nerves Flashcards
(28 cards)
Axon Hillock
Critical Threshold
All the information for making action potentials is arranged
Closer the stimulus to axon hillock the less it degrades
Glia
Astrocytes - maintain external neural environment, surround blood vessels and maintain BBB
Microglia - Phagocytic hoovers mapping up infection
Oligodentrocytes - Form myelin sheaths in CNS
Graded Potential Examples
Determine when an Action Potential is Fired
Generator Potential at sensory receptors
Post-synaptic Potentials at synapses
Endplate Potentials at neuromuscular Junction
Pacemaker Potentials in pace make tissues
Graded Potential Examples
Determine when an Action Potential is Fired*
Generator Potential at sensory receptors
Post-synaptic Potentials at synapses
Endplate Potentials at neuromuscular Junction
Pacemaker Potentials in pace make tissues
Graded Potential Properties
Graded (signal stimulus intensity in their amplitude)
Electrotonic Potentials
Decremental Potentials
Non-Propagated Potentials
Local Potentials
Can summate (Temporal, Spatial) - Synaptic Integration
Hyperpolirising Postsynaptic Potentials
Cl- Fast IPSP
K+ Slow IPSP
GABA, Glycine
Depolarising Postsynaptic Potentials
Block leaky K channels
Open Na and K - non specific monovalent cation channels
Ligand-gated ion channels
Postsynaptic potentials produced by a neurotransmiter opening or closing ion channels.
Voltage-gated ion channels
Action potentials are produced by depolarisation of the membrane potential opening ion channels
Spatial Summation
a + b synaptic integration
Temporal Summation
b + b synaptic integration
Action Potentials
They have a threshold They are all or none They cannot encode stimulus intensity in their aplitude only in their frequency Self Propagate Have a refractory period Voltage Gated Travel Slowly
Aa Aβ Aγ Aδ B C
Nerve Fibres MOST SENSITIVE TO ANOXIA LEAST SENSITIVE TO ANAESTHETICS Aa Proprioception, Motoneurones Aβ Touch, Pressure Aγ Motorneurones of muscle spindles Aδ Touch, Cold, ''fast'' pain B preganglionic autonomic fibres C Heat, ''slow'' pain
Refractory Period
Period following stimulation during which a nerve or muscle is unresponsive to further stimulation
The neuromuscular junction
Action potential in motor neurone
Opens voltage-gated Ca2+ channels in presynaptic terminal
Triggers fusion of vesicles
Acetylcholine (ACh) released
Diffuses across synaptic cleft
Binds to ACh (nicotinic) receptors
Opens ligand-gated Na+/K+ channels
Evokes graded (local) potential (end plate potential)
Always depolarises adjacent membrane to threshold
Opens voltage-gated Na+ channels - evokes new AP
ACh removed by acetylcholinesterase
NMJ Explains the mechanism of action of: Tetrodotoxin Joro spider toxin Botulinum toxin Curare Anticholinesterases
Tetrodotoxin – blocks Na+ channels and so blocks the action potential
Joro spider toxin – blocks Ca2+ channels and so stops transmitter release
Botulinum toxin – disrupts the release machinery and so blocks transmitter release
Curare – blocks Ach receptors and so prevents the end plate potential
Anticholinesterases – block ACh breakdown and so increase trasnmission at the NMJ
NS
PNS Afferent CNS Interneurones PNS Efferent Autonomic Sympathetic, Parasympathetic Ns Somatic voluntary NS
Pre-ganglionic Fibre
Post-ganglionic Fibre
Small Myelinated
Unmyelinated
Somatic NS
Specialised NMJ
Ionotropic receptors
Always Excites target
Autonomic NS
Less Specialised
Metabotropic receptors
May Excite or Inhibit target
Sympathetic
ThoracoLumbar
Ganglia lie close to spinal cord
In Sympathetic Trunk (Paravertebral),
Collateral ganglia (Prevertebral)
Parasympathetic
CranioSacral
Ganglia lie close to target organ
White Ramus
Preganglionic Fibre
Grey Ramus
Postganglionic Fibre
