neurons and their actions get ready to sense, receive, and react

Neurons and their Neurons and their ActionsActions

Get ready to sense, Get ready to sense, receive, and react.receive, and react.

Things that make you go hmmm…Things that make you go hmmm…Average number of neurons in the Average number of neurons in the human brain= 100 billionhuman brain= 100 billion

Average number of neurons in an Average number of neurons in an octopus brain= 300 billionoctopus brain= 300 billion

Rate of neuron growth during Rate of neuron growth during development of a fetus (in the development of a fetus (in the womb)= 250,000 neurons/minutewomb)= 250,000 neurons/minute

Longest axon of a neuron= around 15 Longest axon of a neuron= around 15 feet (Giraffe primary afferent axon feet (Giraffe primary afferent axon from toe to neck)from toe to neck)

Velocity of a signal transmitted Velocity of a signal transmitted through a neuron= 1.2 to 250 through a neuron= 1.2 to 250 miles/hour miles/hour

Neuron Neuron

A nerve cell; consists of many different A nerve cell; consists of many different parts.parts.

Parts of a Neuron Parts of a Neuron

Cell Body:Cell Body: Life support center of the neuron.Life support center of the neuron.

Dendrites:Dendrites: Branching extensions at the cell body. Branching extensions at the cell body. Receive messages from other neurons.Receive messages from other neurons.

Axon: Long single extension of a neuron, covered Axon: Long single extension of a neuron, covered with myelin [MY-uh-lin] sheath to insulate and with myelin [MY-uh-lin] sheath to insulate and speed up messages through neurons.speed up messages through neurons.

Terminal Branches of axon:Terminal Branches of axon: Branched endings of Branched endings of an axon that transmit messages to other neurons.an axon that transmit messages to other neurons.

Synapse Synapse

Synapse [SIN-aps]Synapse [SIN-aps] aa junction between the junction between the axon tip of the sending neuron and the axon tip of the sending neuron and the

dendrite or cell body of the receiving neuron. dendrite or cell body of the receiving neuron. This tiny gap is called the This tiny gap is called the synaptic gapsynaptic gap or or

cleft.cleft.

Types of NeuronsTypes of Neurons

Most communicate within the central Most communicate within the central nervous system (CNS - brain & spinal nervous system (CNS - brain & spinal cord) with rare exceptions.cord) with rare exceptions.

There are three major types of neurons There are three major types of neurons upon which information travels. The upon which information travels. The information travels from the information travels from the Sensory Sensory NeuronsNeurons to the to the InterneuronsInterneurons, and then , and then finally to the finally to the Motor NeuronsMotor Neurons..

Sensory NeuronsSensory Neuronsbring information from sensory receptors to the bring information from sensory receptors to the central nervous system. Brings information central nervous system. Brings information from the eyes, ears, etc., as well as from from the eyes, ears, etc., as well as from within the body like the stomach. within the body like the stomach.

InterneuronsInterneurons

neurons in the brain neurons in the brain and spinal cord that and spinal cord that serve as an serve as an intermediary intermediary between sensory between sensory and motor neurons. and motor neurons. They carry info They carry info around the brain for around the brain for processing. processing.

Motor Neurons Motor Neurons

carry the information from the CNS to carry the information from the CNS to the appropriate muscles to carry out the appropriate muscles to carry out behaviors. behaviors.

Follow the Neuron PathFollow the Neuron PathFor example, if you hold your hand over a hot flame, For example, if you hold your hand over a hot flame, the information about "heat" travels from your hand on the information about "heat" travels from your hand on the sensory neurons, to the Interneurons where it is the sensory neurons, to the Interneurons where it is brought to the appropriate brain region to process the brought to the appropriate brain region to process the information (now you know it is "hot") and make a information (now you know it is "hot") and make a decision about a corresponding action (too hot, let's decision about a corresponding action (too hot, let's move the hand). The information then travels on the move the hand). The information then travels on the Motor Neurons from the brain to the hand so that your Motor Neurons from the brain to the hand so that your muscles move the hand from the hot flame. See how muscles move the hand from the hot flame. See how easy that is? easy that is?

Neural Impulse (A Neuron Firing)Neural Impulse (A Neuron Firing)

Defined as: Defined as: the electrical and chemical the electrical and chemical transmission of information from one neuron transmission of information from one neuron to another.to another.

It takes the same path all the time - it is a It takes the same path all the time - it is a process of conducting information from a process of conducting information from a stimulus by the dendrite of one neuron and stimulus by the dendrite of one neuron and carrying it through the axon and on to the carrying it through the axon and on to the next neuron. Let's look at all the elements next neuron. Let's look at all the elements that are involved in the neural impulse:that are involved in the neural impulse:

Change of the NeuronChange of the Neuron

inside the neuron, the ions are mostly negatively inside the neuron, the ions are mostly negatively charged. Outside the neuron, the ions are mostly charged. Outside the neuron, the ions are mostly positively charged. In this state (with mostly negative positively charged. In this state (with mostly negative charge inside and positive charge on the outside) the charge inside and positive charge on the outside) the neuron is said to be Polarized neuron is said to be Polarized

When a neuron fires (neuron impulse), that all When a neuron fires (neuron impulse), that all changes… Just watch!changes… Just watch!

IonsIons

  Definition:Definition: [n]   [n]  aa particleparticle thatthat isis electricallyelectrically chargedcharged ( (positivepositive oror negativenegative); ); anan atomatom oror moleculemolecule oror groupgroup thatthat has lost has lost or gained one or more electrons or gained one or more electrons We have positively (+) and negatively (-) We have positively (+) and negatively (-) charged particles called ions. charged particles called ions. Neural Impulse =Neural Impulse =Sodium (Na+) Sodium (Na+) Potassium (K-) Potassium (K-)

Selectively Permeable MembraneSelectively Permeable Membrane

The outer membrane of the neuron is not The outer membrane of the neuron is not impermeable, but instead selectively impermeable, but instead selectively allows some ions to pass back and forth. allows some ions to pass back and forth. The way it selects is easy - it has pores The way it selects is easy - it has pores that are only so big. So, only very small that are only so big. So, only very small ions can fit through. Any large ions simply ions can fit through. Any large ions simply can't pass through the small pores. can't pass through the small pores.

Lights, Stimulus, ActionLights, Stimulus, ActionThe following slides The following slides go through the stages go through the stages of a neuron firing, or a of a neuron firing, or a neural impulse, with neural impulse, with other neurons or other neurons or muscle fibers.muscle fibers.

You will want to write You will want to write down these steps as down these steps as a chain of events that a chain of events that goes in a circular goes in a circular motion.motion.

Resting PotentialResting Potential

while the neuron is Polarized, it is in a while the neuron is Polarized, it is in a stable, negatively charged, inactive state stable, negatively charged, inactive state The charge is approx. -70 millivolts, and it The charge is approx. -70 millivolts, and it means that the neuron is ready to fire means that the neuron is ready to fire (receive and send information). (receive and send information).

StimulusStimulus

eventually, some eventually, some stimulation occurs stimulation occurs (ex. hand to close to a (ex. hand to close to a flame), and the flame), and the information is brought information is brought into the body by a into the body by a sensory receptor and sensory receptor and brought to the brought to the dendrites of a neuron. dendrites of a neuron.

Threshold Threshold a dividing line that determines if a dividing line that determines if a stimulus is strong enough to a stimulus is strong enough to warrant action. If the threshold is warrant action. If the threshold is reached, an action potential will reached, an action potential will occur. occur. For example, how hot does a For example, how hot does a stove have to be for a person to stove have to be for a person to pull away. When you have pull away. When you have reached that level of reached that level of uncomfortable temperature, uncomfortable temperature, then you have reached the then you have reached the threshold.threshold.

All or None LawAll or None Law

all-or-none lawall-or-none law - a - a neural impulse will either neural impulse will either occur or not. There is no occur or not. There is no in between. Once the in between. Once the threshold is reached, threshold is reached, there is no going back, there is no going back, the neural impulse will the neural impulse will begin and will go through begin and will go through the complete cycle. the complete cycle.

Action PotentialAction PotentialOnce the stimulus reaches Once the stimulus reaches a certain threshold the a certain threshold the neural membrane opens at neural membrane opens at one area and allows the one area and allows the positively charged ions to positively charged ions to rush in and the negative rush in and the negative ions to rush out. The ions to rush out. The charge inside the neuron charge inside the neuron then rises to approx. +40 then rises to approx. +40 mv. This only occurs for a mv. This only occurs for a brief moment, but it is brief moment, but it is enough to create a domino enough to create a domino effect. effect.

Absolute Refractory Absolute Refractory PeriodPeriod

after the action potential occurs, there is a brief after the action potential occurs, there is a brief period during which the neuron is unable to have period during which the neuron is unable to have another action potential. Then the charge inside another action potential. Then the charge inside the neuron drops to about -90 mv (refractory the neuron drops to about -90 mv (refractory period) before restoring itself to normal. period) before restoring itself to normal.

Analogy: the absolute refractory period is like a Analogy: the absolute refractory period is like a gun. After you shoot it, you must reload it before gun. After you shoot it, you must reload it before you can shoot again. The charge dropping in you can shoot again. The charge dropping in the neuron is its way of reloading.the neuron is its way of reloading.

Repolarization Repolarization

the neuron tries to quickly restore the neuron tries to quickly restore it's charge by pumping out the it's charge by pumping out the positively charged ions and bringing positively charged ions and bringing back the negative ones. back the negative ones.

occurs fast enough to allow up to occurs fast enough to allow up to 1,000 action potentials per second. 1,000 action potentials per second.

The Firing of a NeuronThe Firing of a Neuron

Stimulus

Threshold(Neuron Fires =Action Potential,

Neuron becomes positively charged)

Absolute Refractory PeriodAbsolute Refractory Period(Neuron in unable to fire.)(Neuron in unable to fire.)

Repolarization(Neuron becomes

Negatively charged again.)

Resting (Beginning & End)

Speed of an Action PotentialSpeed of an Action Potential

Neural impulses can travel from 10120 Neural impulses can travel from 10120 meters/sec, or 2-270 miles/hour. meters/sec, or 2-270 miles/hour.

The speed of light is 186,000 (1.86 X 105) miles The speed of light is 186,000 (1.86 X 105) miles per second. per second.

The speed of sound, at sea-level, is 968 ft/sec.The speed of sound, at sea-level, is 968 ft/sec.

The speed of a garden snail is 0.03 mph.The speed of a garden snail is 0.03 mph.

What should you learn from this? Neurons are What should you learn from this? Neurons are slower than the energy neurons use, and faster slower than the energy neurons use, and faster than anything that uses neurons to move. than anything that uses neurons to move.

Neuron Activity (10 minutes)Neuron Activity (10 minutes)

You have 8 minutes to organize yourselves as a You have 8 minutes to organize yourselves as a neuron. neuron.

You must all have a role as a part of the neuron You must all have a role as a part of the neuron (more than one person can make one part of a (more than one person can make one part of a neuron).neuron).

After 8 minutes of preparation you must show After 8 minutes of preparation you must show me through your movements a neuron firing.me through your movements a neuron firing.

Before you fire you must identify which part of Before you fire you must identify which part of the neuron you represent. the neuron you represent.