c2.2 neural signalling Flashcards
What type of signal is a nerve impulse?
Electrical
Cell body function
Contains nucleus and cytoplasm, associated with the production of proteins and neurotransmitters.
Dendrite func
Carry electrical impulses towards cell body from other neurons in brain/spinal cord.
Axon
Carry electrical impulses away from cell body to transmit nerve impulses along longer distances (tips of the finger to spinal cord).
Define nerve impulse
The facilitated diffusion of positively charged ions across the nerve cell membrane.
Resting potential
+ ve ion concentration is greater outside the membrane than inside (-70mV).
Outline how action potential starts:
1) Na+ channels open
2) Na+ ions diffuse into the membrane across a concentration gradient.
3) Charge imbalance is reversed, membrane potential reaches +40mV
4) K+ channels open and they diffuse out.
5) MP falls back to -70
6) Na-K pumps re-establish Na+ and K+ conc gradients.
Outline 3 ways that resting potential is maintained:
- Na-K pumps pump 3 Na+ outside per 2 K+ inside, so charge outside is higher.
- Differential permeability causes K+ to diffuse into the cell more.
- Organic anions contribute to overall -ve charge.
Synapse
A 20-40um junction between a neuron and a post-synaptic membrane.
Give 3 examples of a synapse
- Between 2 neurons in the brain/SC.
- Between a neuron and a sensory receptor cell
- Between a neuron and an effector cell (muscle fibre/gland cell).
Outline the how NTs are released from pre-synaptic membrane:
1) Nerve impulse in transmitting neuron reaches the pre-s membrane.
2) The synaptic knob is depolarized, voltage gated Ca2+ channels open.
3) Influx of Ca2+ ions causes vesicles with NTs to move to Pre-S membrane, releasing them by exocytosis.
3) NTs that are not received are loaded into vesicles and pumped back from synaptic gap into pre-S membrane.
What is the diameter of a human axon, and hence what is its speed
1 um, 1ms
What are 2 factors that effect the speed of nerve impulses?
- The diameter of the axon: wider axon»less resistance»higher speed.
- Myelination: myelin is deposited by schwann cells that wrap around the axon and insulate it, nerve impulses increase as they jump from one node to another (up to 100ms).
Outline excitatory post-synaptic potential:
1) NTs bind to a receptor on post-s membrane.
2) Na+ channels open Na+ ions diffuse down concentration gradient, potential rises to threshold potential.
3) Action potential is propagated away from synapse.
4) NT is broken down by enzymes or reabsorbed by pre-s membrane.
At which synapses can AcH be found?
- Neuron-Neuron Synapses
- At neuromuscular junction synapses
How AcH trigger a response?
1) Binds to receptors that act as Na+ ion channels.
2) Na+ channels open and Na+ ions diffuse into membrane.
3) Potential reaches action potential and a nerve impulse is propagated.
How is a nerve impulse propagated along an axon?
- (inside): Na+ ions move from the depolarized (high c) area to the polarized (low c)
- Outside: Na+ ions move from the polarized (high c), to the depolarized (low c).
State a device used to measure membrane potential:
Oscilloscope
How does an oscilloscope measure membrane potential:
A microelectrode is placed on either side of the membrane and measures the charge difference that way.
Exogenous chemicals
Chemicals that enter the body by an external source and either promotes or blocks synaptic transmission.
Neonicotinoid
Synthetic compounds similar to nicotine that are used in pesticides (imidacloprid for ex).
What do nicotinoids do:
- Bind to receptors in cholinergic synapses, prevent AcH from binding and blocks synaptic transmission.
- Acetylcholinesterase does not recognize them so doesn’t break them down, so permanent binding, causing paralysis and death.
What does cocaine do:
- Acts at synapses were dopamine is a NT.
- binds to DPN re-uptake transporters, prevents DPN from being uptaken back to PRE-synaptic membrane.
- DPN builds up and causes continous post-synaptic transmission.
- causes feelings of euphoria with actions related to the release of dopamine.
Ex of excitatory NT
AcH
Ex of inhibitory NT
GABA
EPSP vs ISPSP
- Depolarizes potential
- Makes membrane potential more negative.
How does GABA inhibit a response?
1) Binds to receptor
2) Cl- channels open
3) Cl- ions diffuse into neuron and hyperpolarize the neuron.
How does a post-synaptic membrane with mutiple pres regulate response?
- no response is triggered in the case of the single release an excitatory NT.
- response is triggered if several adjacent pres release an excitatory NT.
- response is triggered if 1 pre-s repeatedly releases a neurotransmitter.
How does a post-synaptic membrane with mutiple pres regulate response in the case conflicting messages, bigger picture this:
- a response is triggered only if one type of NT outnumber the other.
- helps in integrating signals from different sources, helps with decision-making in CNS.
How does the body start a sensation of pain:
- Pain on skin/other receptors detect external stimuli.
- channels of ions associated with the receptors open and the ions diffuse inside.
- Threshold potential is reached and nerve impulse passes to the spinal column from the sensory neuron.
- Interneurons in the SC carry the response to the cerebral cortex.
- then to pre-frontal cortex for evaluation.
Conscious
A state of complex awareness of many things simultaneously.
What to scientists agree on in terms of consciousness:
emerges from the interaction of individual neurons in the brain and spinal cord
Consciousness is an…
emergent property
