Nervous system 2 - Nov. 20th Flashcards
Mastery
Two types of propagation
Contiguous conduction
Saltatory conduction
what does myelin do
composed of? CNS? PNS?
Action Potentials
Two types of propagation
Contiguous conduction
* Conduction in unmyelinated fibres
* Action potential spreads along every portion
of the membrane
Saltatory conduction
* Rapid conduction in myelinated fibres
* Impulse jumps over sections of the fibre
covered with insulating myelin
at the nodes of ranviergates are there
Fatty insulator
Primarily composed of lipids
* Formed by oligodendrocytes in CNS
* Formed by Schwann cells in PNS
Leaves exposed nodes
Multiple Sclerosis
Nerve Conduction
Depends on
Loss of myelin
Decreased speed of impulses
Loss of coordination in muscles and nerves
Neuron diameter
Myelination
Temperature
Eg. Frog nerves vs human
A-delta fibres vs C fibres
Regeneration of Nerve fibres
what does regen depend on
in PNS and CNS
Regeneration of Nerve fibres
Regeneration of nerve fibres depends on its
location
Schwann cells in PNS guide the regeneration of cut axons
fibres in CNS myelinated by oligodendrocytes do not have regenerative ability
Oligodendrocytes inhibit regeneration of cut
central axons
synapses
two types
synapse anatomy
Synapses
Junction between two neurons
Primary means by which one neuron directly interacts
with another neuron
Signal at synapse either excites or inhibits the postsynaptic neuron
Two types of synapses
Excitatory synapses (Na+ or ion gates)
Inhibitory synapses (K+ gates or Cl- gates)
AP arrives at terminal end
Voltage-gated Ca2+ open
Ca2+ moves into knob
Triggers release of neurotransmitter (NT)
NT migrates across synapse
Binds to receptor site
Opens ion gates
Triggers graded potentia
NT release
NT release
Calcium binds to synaptotagmin
Stimulates
SNARE proteins
* Ensnare vesicles
– causes NT release
2 types of post synaptic receptors
synaptic delay
direction of current flow
Activates
Ionotropic receptors – actual ion channels
Metabotropic receptors – 2nd messenger
activation of channel
Synaptic delay-
.2 to .5 msec
positive excitatory moves to axon hillock
inhibitory moves current other way
what does the size of a postsynaptic potential depend on
Depends on:
- Calcium levels (fatigue)
- NT levels
- Desensitization / hypersensitization(small impulse leads to a large release of NT)
- Pre-synaptic inhibition or facilitation(many impulses coming in
Spatial summation
Temporal Summation
EPSP and IPSP interaction
Summation of many EPSP’s occur at different locations on the dendrites at the same time
Temporal Summation
Summation of many EPSP’s occurring at the same location over a very short period of time
some have 200,000 terminals, many EPSPs and IPSPs
Pre- synaptic Facilitation / Inhibition
Neurotransmitters.
how do they vary? the same NT? Removed? some common NTs
Eg. Opiates
Neuron A releases neurotransmitter that can either increase or decrease release from neuron B
***NEUROTRANSMITTERS
Vary from synapse to synapse
Same neurotransmitter is always released at a
particular synapse
Quickly removed from the synaptic cleft
Some common neurotransmitters
HANDGG
Histamine
Acetylcholine
Norepinephrine / Epinephrine
Dopamine / Serotonin
Glutamate
Gamma-aminobutyric acid (GABA)
Neuropeptides
what do they consist of? site of synthesis? site of release?how long is the response? Site of action? Effect?
common types of neuropeptides
- Large molecules consisting of from 2 to 40 amino acids
- Endoplasmic reticulum and Golgi complex in cell body, travel to synaptic knob by axonal transport
- Axon terminal, may be cosecreted with
neurotransmitter - slow and prolonged
- Nonsynaptic sites on either presynaptic or
postsynaptic cell at much lower concentrations than classical neurotransmitters - Usually enhance or suppress synaptic
effectiveness by long-term changes in
neurotransmitter synthesis or postsynaptic
receptor sites (act as neuromodulators)
Neuropeptides
HACSED
- Hypothalamic releasing and inhibiting hormones
- Angiotensin II
- Cholecystokinin
- Substance P (pain)
- Enkephalins /Endorphins(turn off p)
- Dynorphins
