Axonial transmission Flashcards
What is a neuron?
- basic cellular unit of the neuron
What components makes up a neuron?
- ) Dendrites
- ) Cell body/soma
- ) Axon
- ) Presynaptic terminal
What is axonal transmission
Transmission of information from location A to location B
What is synaptic transmission
Integration/processing of information and transmission between neurons
What is an example of axonal transmission failure
Multiple sclerosis
Key symptoms of multiple sclerosis
- eye movements: uncontrolled
- speech: stunted
- paralysis: partial/complete
- tremor
- co-ordination: lost
- weakness: tired
- sensory: numbness
Prognosis of MS
- initial symptoms: slight with remission
- difficult to diagnose
Who gets MS
- young adults 20-40
- temperate zones
- areas with high standards of sanitation
What is the neurons resting potential
It is -70 mV
Why is it this figure?
- neuronal cell membranes are semi permiable
What ions can/can’t pass
- Electrically charged K+ and Cl- can cross readily
- Na+ crosses with difficulty
- Large organic proteins (-ve charge) can’t pass)
What forces are at work here?
- ) Diffusion
2. ) Electrostatic attraction/repulsion
Ions
- ) A-: restricted to inside of cell
- ) Na+: mostly outside neuron. Membrane quite impermeable to Na+.
- ) K+: mostly inside neuron
- ) Cl-: mostly outside neuron
Sodium-potassium pump
- Active process to transport Na+ ions out of neuron and K+ in
- Three Na+ for every two K+
- Require energy supplied by ATP
What is the action potential
- Neuron fires: sudden pulse where the negative resting potential is temporarily reversed
- Transmits information: the message
Events within the action potential
Depolarization & threshold
Reversal of membrane potential
Repolarisation to resting potential
Refractory period
Describe what takes place during an action potential
- neurotransmitters initiate changes at the dendrites of neurons: membrane permeability changes
Neurotransmitters activate receptors on dendrites / soma
Receptors open ion channels
Ions cross plasma membrane, changing the membrane potential
The potential changes spread through the cell
If the potential changes felt at the axon hillock are positive (+mV), and large enough, an action potential is triggered
Depolaisation
- Excitatory neurotransmitters depolarise the cell membrane
- Increases probability of AP being elicyed
Cause an EPSP
Hyperpolarisation
- inhibitory neurotransmitters hyperpolarise the cell membrane
- decreases probability of an A.P being elicted
- causes an IPSP
What is temporal summation
tWO THINGS don’t occur at quite the same time. They summate and become bigger
What is passive conduction
- voltage changes spead away from point of origin
- whether AP is generate depends on what reaches the axon hilock
The AP
- ESPs begin to depolarise cell membrane
- Threshold: -60mV. When threshold is reaches Na+ channels open and polarity reverses to +30mV inside
- Membrane potential reverses with the inside going positive
- Voltage gated Na+ channels close so K+ channels open
- This restores resting membrane potential
What are voltage gated channels
- These are channels that are opened by detecting opposite polarity in an adjacent bit of membrane
- voltage changes control the ion channels which control the voltage changes
- the AP is self perpetuating
What speeds up axonal conduction
Myelination
Propagation of action potential with myelinated axons
- There is decremental conduction between nodes
- This is saltatory conduction
Propagation of AP without myelinated axons
- have signal loss due to lack of insulation
- slow due to time to activate each channel
- mainly short axon interneurons
Synaptic transmission: what happens when action potential reaches terminal
- triggers voltage gated Ca2+ channels to open.
- Get release of Ca2+ ions
They get released from their vesicles by fusing with the presynaptic membrane and it exocytoses
Binds to receptors on the postsynaptic membrane
What is acetylcholinesterase
Is the nsame of the enzyme that breaks down neurotransmitter acetylcholine
- The neurotransmitter get enzyme degradation to break it down
What is novichok
It is an AChE inhibitor
What are the 5 processes of synaptic transmission
- ) Manufacture: intracellular biochemical processes
- ) Storage: vesicles
- ) Release: by action potential
- ) Interact with post-synaptic receptors: diffusion across the synapse
- ) Inactivation: break down/re-uptake
Examples of fast neurotransmitters
- ) Acetylcholine
- ) Glutamate
- ) Gamma-aminobutyric acid
Examples of neuromodulators
- ) Dopamine
- ) Noradrenalin
- ) Serotonin
Examples of local anaesthetic
Procaine and lignocaine
How does local anaestetic work?
- Na+ channels blockers
- Blocks progress of action potential
ACh
- transmitter at te neuromuscular junction
What is ACh affected by
1.) Cigarettes
2.) Poison
3>) Spider toxins
4.) Nerve gas
