3 Nervous System = Communication Function:Receives StimuliInterprets informationCauses a response-Controls and coordinates bodily functions-Responds to stimuli (inside or outside the body)
4 What is the basic functional unit of the nervous system? Neuron!What does the neuron do?Carries messages throughout the bodyHow does it carry the messages?By conducting electrical signalsWhat are these signals called?Nerve impulses!
10 Additional Parts of a Neuron Neuron AnatomyAdditional Parts of a NeuronDendriteCell bodyAxon terminalMyelin sheathNodes ofRanvierAxonNucleusStructure of a Typical Neuron
11 Neuron anatomy What do you remember? dendrites 3 1 2 4 5 6 7 Myelin sheathnucleusDirectionof impulseCell bodyaxonNodes of RanvierAxon terminals
12 Three Types of Neurons II. Motor Neurons: Carry impulses to muscles and glandsCause a response to some stimuliIII. Interneurons:Connect sensory and motor neuronsAllow for quick response (reflex action)
14 Neurons What is grey matter? What is white matter? Collective cell bodies and dendrites of all neuronsWhat is white matter?Myelinated nerve fibersAxons of all neuronsCan be approximately one meter in lengthWhite matterGray matter
15 What is a Nerve? Bundle of axons held together by connective tissue. What color is a nerve?White!Why?Because axons are white matter and they compose nerves
16 How are nerves held together? Connective tissueWhat is this connectivetissue called?Neuroglial cells (nerve glue)Approximately half of the volume of the brain is composed of neuroglial cellsMost brain tumors develop in mesoglial cells – NOT neurons
17 What do neuroglial cells do? Support the axonsInsulate the electrical impulsesLike electrical tape insulates electric wires this prevents “leaking” of electric signals
18 An example of a neuroglial cell Schwann cellThis wraps around the axon in multiple layersIt is composed of a fatty material called…MyelinRegular breaks in the myelin sheath are called…Node of Ranvier
19 Impulse speed Some neurons are fast, good conductors of impulses Other neurons are slow, poor conductors of impulsesWhat distinguishes these two types?Diameter of the axonMyelinationFastest axons have a large diameter and are myelinated. How much faster?Up to 100 times faster! (Reflexes are this type)
20 The Nerve ImpulseHow are messages (impulses) carried by the nervous system?As electrical and chemical signals.How does the impulse develop?Charged particles (ions) move across the cell membraneA neuron is ready to transmit an impulse when it is in the resting state.Resting membrane potential is -70 mV
21 Resting Membrane Potential The inside of the cell has a negative charge as compared to the outside of the cell membrane.How does this charge difference develop?There are more Na+ (sodium) ions outside and fewer K+ (potassium) ions inside.
22 The Nerve Impulse How does the impulse begin? The neuron is stimulated by another neuron or by stimuli from the environment.
23 The Nerve ImpulseIf the stimulus is strong enough, it reaches threshold level.This stimulates an impulse.If the stimulus is not strong enough, no impulse occurs (all-or-none principal)
24 The Nerve Impulse What happens if threshold is reached? An action potential (nerve impulse) beginsWhat is an action potential?Rapid reversal of membrane potential in response to a stimulusHow does this happen?Sodium channels open allowing Na+ to flood into the cell.The membrane potential rises to +30 mV (rising phase) as inside of cell becomes more positive
25 The Nerve Impulse Please, please, tell us what happens next… When the membrane potential reaches +30 mV, the sodium channels close.Potassium channels open and K+ flows out of the cell.This causes the membrane potential to become more negative again (falling phase).
30 The Nerve ImpulseWhat happens when the action potential passes down the axon?The resting potential is restored via the sodium/potassium pump.Now the membrane is ready to transmit another impulse.extracellular fluidcytoplasmNa+ATPADPK+
31 The Nerve ImpulseAn action potential only moves in one direction down the axon.From axon hillock, thru axon fiber to the axon terminal.The action potential is regenerated at each Node of Ranvier down the length of the axon.
32 The Nerve ImpulseWhat happens when the impulse reaches the axon terminal?It must pass thru the synapse.What is a synapse?It is the gap between two neurons, or between a neuron and organ (effector).Why is there a gap?So the neurons don’t short each other out!!
33 The Synapse How do neurons pass the impulse across the synapse? Using chemicals called neurotransmittersWhat do neurotransmitters do?Stimulate the dendrites of other neurons or membranes of other cells.If a dendrite is stimulated, it sends its message to the cell body and the message is passed onIf a muscle or gland is stimulated, a reaction occurs in that organ.
37 Neuron Smear:Identification: Note distinctive shape of neuron, with long processes (dendrites and/or axons, 5) extending out from main cell body.Features to Know:The large, irregularly shaped cell body (3) contains a darker nucleus (2), which contains an even darker-staining nucleolus (1).There are also numerous supporting glial cells, though only their small dark nuclei (4) are easily seen.