Body SystemsBody Systems

Nervous SystemNervous System

Nervous System FunctionsNervous System Functions

Sensory input – sense organs, receptors, Sensory input – sense organs, receptors, – afferent neuronsafferent neurons

Integration – Central Nervous System(CNS)Integration – Central Nervous System(CNS)– interneuronsinterneurons

Motor output – glands, musclesMotor output – glands, muscles– efferent neuronsefferent neurons

The NeuronThe Neuron

Consists ofConsists of– Cell bodyCell body

– DendriteDendrite

– AxonAxon

Label your diagramLabel your diagram

The Nerve ImpulseThe Nerve Impulse Begins at dendrites, passes through to the cell Begins at dendrites, passes through to the cell

body and then through the axon, terminating at body and then through the axon, terminating at the terminal branches before the synapse.the terminal branches before the synapse.

The Nerve ImpulseThe Nerve Impulse Occurs as a result of both electrical and Occurs as a result of both electrical and

chemical changes across the membrane of chemical changes across the membrane of the neuron. the neuron.

Electrochemical nature of Electrochemical nature of membranemembrane

Due to the presence of ions, a positive electrical charge is present outside the membrane. (excess of sodium ions)

A negative charge is present inside the membrane. (mostly potassium ions)

Since both sodium (outside) and potassium (inside) are both positive ions, how can one side of the membrane be + and the other -?

Although diffusion Although diffusion of ions will occur, of ions will occur, the membrane the membrane activelyactively pumps pumps NaNa++/K/K++..

What do you call What do you call the membrane the membrane structures through structures through which the ions will which the ions will be pumped be pumped through?through?

Resting potential- unstimulated (-70 millivolts)

Action potential – channels open, Na+ ions rush in, depolarization occurs.

What is the threshold potential?

Like a domino effect, once stimulated the nerve impulse is an all or nothing response.

Repolarization – In response to the inflow of Na+, K+ rushes out of the cell, followed by closing of the Na+ channel gates.

Interpret the graph at stage 4 with respect to the events that are occurring.

Hyperpolarization – More K+ outflows than is necessary, thus undershooting threshold, more than repolarizing the membrane.

Refractory period – Although repolarized, the neuron has a period when it is unable to fire.

What has to occur to re-establish the original conditions so that a neuron can fire again?

After the membraneAfter the membrane

Once the impulse reaches the end of Once the impulse reaches the end of the axon a different set of events has the axon a different set of events has to occur to allow the impulse to to occur to allow the impulse to continue to another neuron.continue to another neuron.

This requires the crossing of the This requires the crossing of the synapse.synapse.

Most transmissions across a synapse are of a chemical nature.

Synapse SummarySynapse Summary

The gated channels for CaThe gated channels for Ca2+2+ respond to respond to the action potential by opening up.the action potential by opening up.

In turn, the CaIn turn, the Ca2+2+ enters the cell and enters the cell and triggers the release of neurotransmitters.triggers the release of neurotransmitters.

The neurotransmitter crosses the synapse The neurotransmitter crosses the synapse and binds with protein receptors on the and binds with protein receptors on the next neuron membrane.next neuron membrane.

Neurotransmitters degrade or are recycled Neurotransmitters degrade or are recycled shortly after so as not to cause continuous shortly after so as not to cause continuous stimulation.stimulation.

NeurotransmittersNeurotransmitters

Acetylcholine – stimulates muscles to Acetylcholine – stimulates muscles to contract at neuromuscular junctions. contract at neuromuscular junctions. At other junctions, acts as an inhibitor.At other junctions, acts as an inhibitor.

Epinephrine, norepinephrine, Epinephrine, norepinephrine, dopamine, serotonin (I) – all are amino dopamine, serotonin (I) – all are amino acid derivatives. Work between acid derivatives. Work between neurons. First three may be excitatory neurons. First three may be excitatory or inhibitory.or inhibitory.

GABA – inhibitory, within the brain.GABA – inhibitory, within the brain.

Saltatory ConductionSaltatory Conduction

Neurons with a myelin sheath Neurons with a myelin sheath (Schwann cells) allow a much faster (Schwann cells) allow a much faster conduction of impulses because the conduction of impulses because the impulse “jumps” between the gaps impulse “jumps” between the gaps (nodes of Ranvier) of the cells rather (nodes of Ranvier) of the cells rather than traveling along the whole length than traveling along the whole length of the axon.of the axon.

The Bigger PictureThe Bigger Picture

Billions upon billions of neurons and Billions upon billions of neurons and other cells make up your nervous other cells make up your nervous system. Appearance can be somewhat system. Appearance can be somewhat modified based on location and modified based on location and function.function.

CNS – brain, spinal cordCNS – brain, spinal cord Peripheral – all other nervesPeripheral – all other nerves

– Somatic – sensory, motorSomatic – sensory, motor– Autonomic – sympathetic, parasympatheticAutonomic – sympathetic, parasympathetic

You are always on your mind!You are always on your mind!

This diagram illustrates the relative amount of brain mass devoted to some important parts of the body. Why do you think some areas require much more than others?