NEURONS

Draw and Label a ‘typical’ neuron

READING QUIZ

Define and explain the purpose of the myelin sheathWhat is the charge of a neuron?What is the Post-synaptic potential that increases the

likelihood of a neuron fi ring?

READING QUIZ

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

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 brainMillions of neurons are involved in producing a single

thought

NEURONS ARE SUPER COOL

A “TYPICAL” NEURON*

NOW LET’S

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

SOMA

Parts of the neurons that are specialized to receive information

Look like tree branches

DENDRITE

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 diff erent cells

AXON

White, fatty substance insulating material that encases some axons

Speeds up the transmission of signals that move along axons

*signals may not be transmitted effi ciently if the sheath has been deteriorated (multiple sclerosis- loss of muscle control)

MYELIN SHEATH

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

TERMINAL BUTTONS

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

SYNAPSE

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

GLIA

https://www.youtube.com/watch?v=-SHBnExxub8

THE NEURAL IMPULSE-WHAT HAPPENS WHEN A NEURON GETS

STIMULATED

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)

NEURON AT REST

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)

ACTION POTENTIAL

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 fi re, but its threshold for fi ring is elevated, so more intense stimulation is required to initiate an action potential

Imagine running a sprint. After you fi nish 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.

REFRACTORY PERIODS

The neural impulse is like a gun, either it fi res or it doesn’t fi re 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 fi re action potentials Stronger stimulus- more rapid volley of neural impulses

than a weaker stimulus

ALL-OR-NONE LAW

Neurons don’t actually touchSynaptic 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

communicatePresynaptic neuron- sends signalPostsynaptic neuron- receives signalHow 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

SYNAPTIC CLEFT & NEUROTRANSMITTERS

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 LAWVary in size and increase or decrease the probability

of a neural impulse in the receiving cell

POSTSYNAPTIC POTENTIALS

Excitatory (+)- increases the likelihood that the postsynaptic neuron will fi re

Inhibitory(-)- decreases the likelihood that the postsynaptic neuron will fi re

This stage lasts a short period of time, and neurotransmitters drift away from the receptor sites or are converted into inactive forms

EXCITATORY AND INHIBITORY PSP

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 fi re

Firing is impacted heavily by IPSP and EPSP

REUPTAKE

Watch the cat again, however this time, watch it and imagine that the toilet flushing is like a neuron fi ring

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

THE CAT IS BACK