Essential idea: Neurons transmit the message, synapses modulate the message. 6.5 Neurons and synapses By Chris Paine https ://bioknowledgy.weebly.com/ The image shows a tiny segment of a human brain the lines show neurons and the dots show synapses. The image is intended to illustrate both the how complex even a small mammal's brain is and additionally how important the synapses between neurons are; it is the synapses that drive communication and conscious thought. With the exception of the memory centre the number of cells in the human brain does not increase after birth, what increase is the number of connections and hence synapses between neurons. http://med.stanford.edu/mcp/_jcr_content/hero/hero_banner/images/ima geSlide8.img.620. high.jpg
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6.5 Neurons and synapses - Pritzker College Prep Freshman … · 2018-03-20 · Synapses are junctions between neurons and between neurons and receptor or effector cells. Only chemical
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Essential idea: Neurons transmit the message, synapses modulate the message.
6.5 Neurons and synapses
By Chris Paine
https://bioknowledgy.weebly.com/
The image shows a tiny segment of a human brain the lines show neurons and the dots show synapses. The image is intended to illustrate both the how complex even a small mammal's brain is and additionally how important the synapses between neurons are; it is the synapses that drive communication and conscious thought. With the exception of the memory centre the number of cells in the human brain does not increase after birth, what increase is the number of connections and hence synapses between neurons.
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
The sodium-potassium pump (Na+/K+ pump)maintains the electrochemical gradient of the resting potential. Some K+ leaks out of the neuron (making the membrane potential negative, -70mv).
1 In response to a stimulus (e.g. change in membrane potential) in an adjacent section of the neuron some voltage gated Na+ channels open and sodium enters the neuron by diffusion. If a sufficient change in membrane potential is achieved (threshold potential) all the voltage gated Na+ channels open. The entry of Na+ causes the membrane potential to become positive (depolarisation)
Action potential is the reversal (depolarization) and restoration (repolarization) of the membrane potential as an impulse travels along it.
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
The depolarisation of the membrane potential causes the voltage gated Na+ channels to close and the voltage gated K+ channels open. K+ diffuses out of the neuron rapidly and the membrane potential becomes negative again (repolarisation)
4 Before the neuron is ready to propagate another impulse the distribution of Na+ (out) and K+ (in) needs to be reset by the Na+/K+ pump, returning the neuron to resting potential. This enforced rest (refractory period) ensures impulses can only travel in a single direction.
*The jump along the axon is actually just the very rapid conduction inside the myelinatedportion of the axon.
As myelin acts as an insulator myelinatedaxons only allow action potentials to occur at the unmyelinated nodes of Ranvier.
This forces the the action potential to jump* from node to node (saltatory conduction).
The result of this is that the impulse travels much more quickly (up to 200 m/s) along myelinated axons compared to unmyelinated axons (2 m/s).
Saltatory conduction from node to node also reduces degradation of the impulse and hence allows the impulse to travel longer distances than impulses in unmyelinated axons.
The myelin sheath also reduces energy expenditure over the axon as the quantity of sodium and potassium ions that need to be pumped to restore resting potential is less than that of a un-myelintated axon
6.5.U7 Synapses are junctions between neurons and between neurons and receptor or effector cells.
To function the nervous system needs to receive input/stimuli and then to coordinate a response to it.
For this to happen impulses need to travel from sensory receptor cells via a series of nerve cells to effectors, which are commonly muscles and glands.
There are junctions between each cell called synapses across which impulses cannot travel.
A special group of molecules called neurotransmitters move across the synapse to effect an impulse in the adjacent cell.
Acetylcholine is a neurotransmitter used in many synapses through the nervous system
One use is at the neuromuscular junction, i.e. it is the molecule that motor neurons release to activate muscles. Interfering with the action of acetylcholine can cause a range of effect from paralysis to convulsions.