Neurons and Synapses 6.5 Flashcards
1
Q
What do neurons do?
A
- Carry messages at high speed in the form of electrical impulses.
- Many are very elongated and carry impulses long distances in a very short time.
2
Q
What are the 2 main devisions of the nervous system?
A
- Peripheral nervous system (PNS) = peripheral nerves
- Central nervous system (CNS) = brain and spinal cord
3
Q
What is saltadory conduction?
A
- myelinated fibres have a myelin sheath eith small gaps called nodes of Ranvier
- this allows the nerve impulse to jump from node to node
- speeds up the transmission
4
Q
What is the structure of a motor neuron?
A
- dendrites (short branched nerve fibres)
- cell body
- nucleus
- axon
- nodes of Ranvier (myelin sheath) (shwann cells)
- exon terminals
5
Q
What is a synapse?
A
- a junction between two neurons or a junction between neruons and receptor or effector cells.
- the plasma membranes of the neurons are separated by a narrow fluid-filled gap called the synaptic cleft.
- messages passed across the synapse in the form of chemicals called neurotransmitters
- pre-synaptic——–>post-synaptic
6
Q
How does a synapse function?
A
- Nerve impulse reaches the end of the pre-synaptic neuron.
- Vesicles of neurotransmitters move to the membrane and release their contents.
- Neurotransmitter diffuses across the synaptic cleft and binds to receptors.
- Sodium ions enter the post-synaptic neuron and cause depolarization.
- Nerve impulse setting off along the post-synaptic neuron.
- Neurotransmitter is broken down in the cleft and reabsorbed into the vesicles.
7
Q
What is a cholinergic synapse?
A
- Synapses that use acetylcholine as their neurotransmitter.
8
Q
What are neonicotinoid pesticides and why are they dangerous?
A
- Neonicotinoids bind to acetylcholine receptors in the postsynaptic membranes of cholinergic synapses in insects.
- Cholinesterase does not break down the pesticides, they remain bound to the receptors preventing acetylcholine from binding.
- This blocks synaptic transmission, killing the insect.
- Honey bee are killed along with other insects that are the intended target of neonicotinoids.
9
Q
What are membrane potentials?
A
- Neurons have a difference in charge across their membranes due to the distribution of positively charged ions (Na+ & K+)
- Electrical signals are created by changing membrane polarity.
- Resting Potential (Polarity of a neuron when it is at rest) -70mV
- Action Potential (Polarity of a firing neuron) +30mV
10
Q
What is myelination?
A
- Nerve impulses are Action Potentials propagated via axons.
- Action Potentials are only propagated if a certain threshold potential is reached (~-55mV)
- The axon is covered by a myelin sheath.
- Enables saltatory conduction (speeds up transmission)
- The Action Potential jumps between gaps in the myelin sheath (nodes of Ranvier) for faster transmission.
11
Q
What is the Resting Potential?
A
- Maintained by a Na+/K+ pump
- It exchanges sodium ions (3 out) and potassium ions (2 in) so that the membrane potential becomes slightly negative.
12
Q
What is the Action Potential?
A
- Changes the resting membrane potential
- The opening of sodium channels causes a sodium influx
- This creates a positive membrane potential (depolarization)
- Opening potassium channels causes a potassium efflux
- This restores a negative membrane potential (repolarisation)
13
Q
How is a nerve impulse propagated along an axon?
A
- A nerve impulse is an action potential that travels along the bacon of a neuron from one end to the other.
- An action potential in one part of the axon triggers an action potential in the next part.
- This is called propagation of the nerve impulse.
- This is due to diffusion of sodium ions between a region with an action potential and the next region that is still at a resting potential.
- The diffusion of spdoum ions along the axon, both inside and outside the membrane, is called local currents.
- This changes the voltage across the membrane from -70mV to the threshold potential -50mV.
- Causing an action potential because voltage-gated sodium channels open.
14
Q
How does a nerve message pass from one neuron to the next?
A
- Nerve impulse reaches the end of the presynaptic neuron
- Depolarization causes calcium channels in the membrane to open
- Calcium diffuses into the presynaptic neuron
- Vesicles containing the neurotransmitter move and fuse with the presynaptic membrane
- The neurotransmitter is released into the synaptic cleft by exocytosis
- The neurotransmitter diffuses across the synapse and attaches to receptors on the postsynaptic neuron
- Receptors cause ion channels to open and sodium diffuses into the postsynaptic neuron
- The postsynaptic neuron is depolarized which causes a new action potential
- The neurotransmitter on the psotsynaptic membrane is broken down and reabsorbed into the presynaptic neuron
