Neurons

Reading Quiz Draw and Label a ‘typical’ neuron

Reading Quiz Define and explain the purpose of the myelin sheath What is the charge of a neuron? What is the Post-synaptic potential that increases the likelihood of a neuron firing?

https://www.youtube.com/watch?v=H2W8XKK-3Rk&feature=youtu.be

Neurons are super cool Individual nerve cells that receive, integrate, and transmit information The basic elements of communication in the nervous system, but only the majority communicate with other neurons. However, there are some exceptions Approx. 100 billion neurons make up the brain Millions of neurons are involved in producing a single thought

A “typical” Neuron*

Now let’s

Soma Cell body that contains the nucleus and much of the machinery common to most cells (the rest of it deals with handling information)

dendrite Parts of the neurons that are specialized to receive information Look like tree branches

Axon Long fiber that transmits signals away from the soma to other neurons or to muscles or glands Quite long (sometimes several feet) Branch off to communicate with many different cells

Myelin sheath White, fatty substance insulating material that encases some axons Speeds up the transmission of signals that move along axons *signals may not be transmitted efficiently if the sheath has been deteriorated (multiple sclerosis- loss of muscle control)

Terminal buttons Small knobs that secrete chemicals called neurotransmitters Messengers that may activate neighboring neurons The point at which neurons connect are called synapses

synapse Synapses are junctions where information is transmitted from one neuron to another

Glia Cells found throughout the nervous system that provide various types of support for neurons Outnumber neurons 10-1, 50% of the brains volume Nourish neurons Remove waste products Insulation The heroes of the nervous system

The neural impulse-what happens when a neuron gets stimulated https://www.youtube.com/watch?v=-SHBnExxub8

Neuron at rest Inside and outside the neuron are fluids containing electrically charged atoms and molecules called “ions” Positively charged potassium and sodium and negatively charged chloride ions flow back and forth across the cell membrane, but do NOT cross at the same rate HIGHER CONCENTRATION of negatively charged ions inside the cell------ resulting voltage/potential energy RESTING POTENTIAL- stable, negative charge when the cell is inactive (-70 million volts)

Action potential The neuron is relatively chill and doesn’t do anything while the charge is constant However, if the neuron gets stimulated, channels in the cell membrane will open allowing positively charged sodium ions to rush in At that moment, the charge becomes less negative/even positive, creating an action potential ACTION POTENTIAL- a very brief shift in a neuron’s electrical charge that travels along an axon Voltage change will race down the axon (like a spark in a line of gunpowder)

Refractory Periods After all this excitement, the channels in the cell membranes will close up again (and this may take some time) ABSOLUTE REFRACTORY PERIOD- minimal length of time after an action potential during which another action potential cannot begin RELATIVE REFRACTORY PERIOD- the neuron can fire, but its threshold for firing is elevated, so more intense stimulation is required to initiate an action potential Imagine running a sprint. After you finish running, you will need a period of time (ARP) to calm down before you will run again. After you completely recover, you can run again, but you will need some more intense motivation (RRP), because you don’t really feel like sprinting again.

All-or-none law The neural impulse is like a gun, either it fires or it doesn’t fire Action potentials are all the same size as well Neurons convey information about the strength of a stimulus by varying the rate at which they fire action potentials Stronger stimulus- more rapid volley of neural impulses than a weaker stimulus

Synaptic cleft & Neurotransmitters Neurons don’t actually touch Synaptic Cleft-microscopic gap between the terminal button of one neuron and the cell membrane of another neuron This gap must be jumped in order for neurons to communicate Presynaptic neuron- sends signal Postsynaptic neuron- receives signal How does this happen? The arrival of an action potential at an axon’s terminal triggers the release of NEUROTRANSMITTERS- chemicals that transmit information from one neuron to another Collected together in little sacks called SYNAPTIC VESICLES Vesicles fuse together with the membrane and spill contents into the synaptic gap They may bind to certain areas at various receptor sites

Postsynaptic potentials Postsynaptic potential- voltage change at a receptor site on a postsynaptic cell membrane (caused by a neurotransmitter and receptor molecule combining) DO NOT FOLLOW THE ALL-OR-NONE LAW Vary in size and increase or decrease the probability of a neural impulse in the receiving cell

Excitatory and inhibitory PSP Excitatory (+)- increases the likelihood that the postsynaptic neuron will fire Inhibitory(-)- decreases the likelihood that the postsynaptic neuron will fire This stage lasts a short period of time, and neurotransmitters drift away from the receptor sites or are converted into inactive forms

Reuptake Reuptake- the process through which neurotransmitters are sponged up from the synaptic cleft by the presynaptic membrane. Neurons receive thousands of signals, so it must integrate the signals as they arrive to decide whether or not it will fire Firing is impacted heavily by IPSP and EPSP

The cat is back Watch the cat again, however this time, watch it and imagine that the toilet flushing is like a neuron firing https://www.youtube.com/watch?v=H2W8XKK-3Rk&feature=youtu.be