2Neuron Functions What are the functions of the nervous system? Receive sensory input, interpret & make a decision, and effect a responseIndividual neurons have two major functional properties: irritability and conductivity.Irritability = ability to respond to a stimulus and convert it to a nerve impulseConductivity = ability to transmit the impulse to other neurons, muscles, or glands.How do irritability and conductivity relate to the functions of the nervous system?
3IrritabilityIrritability = ability to respond to a stimulus and convert it to a nerve impulseWhat type of stimulus?Receptor neurons respond to specific stimuli (e.g. touch, temperature, pressure, tension, sight, hearing, chemical)All other neurons (interneurons, motor neurons) respond to neurotransmitters released by other neuronsWhat is a nerve impulse?A quick switch in voltage potential (charge difference) across the membrane that travels all the way along the axon of the neuronOccurs due to flow of ions across the membraneAll – or - nothingNow to understand the process of a nerve impulse / action potential in much more detail …
4Resting PotentialNeurons at rest have an electrochemical gradient across the cell membrane, known as the resting potential. The resting potential is approximately -70mV.Extracellular fluidCell membranecytoplasm
5Resting potential The resting potential is maintained by: Sodium-potassium pump(3 Na+ pumped out for every 2 K+ pumped in)Greater membrane permeability of K+(K+ can diffuse back out to some degree)Organic anions (- ions) within cellThis ‘rest state’ takes energyto createExtracellular fluidNa+Cell membraneK+Organic anioncytoplasm
6Action PotentialAn action potential involves the rapid depolarization and repolarization of the membrane.
7Action potentialWhen a stimulus is applied to a nerve, some Na+ gates open, allowing Na+ to diffuse in.Extracellular fluidNa+Na gateCell membraneK+K gateNa / K pumpOrganic anioncytoplasm
8Action potentialOnce a threshold is reached, all Na+ gates open, causing depolarization of the membrane.When the membrane is depolarized, the inside of the membrane is more positively charged than the outside.Extracellular fluidNa+Na gateCell membraneK+K gateNa / K pumpOrganic anioncytoplasm
9Action potentialMembrane repolarization occurs when Na+ gates close and K+ gates open, allowing net diffusion of K+ outside.Repolarization returns the membrane to resting potential (more negatively charged inside)Extracellular fluidNa+Na gateCell membraneK+K gateNa / K pumpOrganic anioncytoplasm
10Action potentialThe K+ gates close and the resting potential is maintained by the Na+ / K+ pumpWatch me!Extracellular fluidNa+Na gateCell membraneK+K gateNa / K pumpOrganic anioncytoplasm
11Action Potential – Turn & Talk Scholar with more siblings …At rest, what ions are most abundant outside the cell, and which are most abundant inside the cell?Which side of the membrane is more negative at rest?Scholar with less siblings …Describe how the movement of ions causesDepolarizationRepolarization
12Action Potential – Turn & Talk Scholar with more siblings …At rest, what ions are most abundant outside the cell, and which are most abundant inside the cell?Which side of the membrane is more negative at rest? At rest, Na+ ions are mostly outside the membrane, while K+ and anions are mostly inside. The inside of the cell membrane is more negatively charged.Scholar with less siblings …Describe how the movement of ions causesDepolarization – Na+ ions rush into the cellRepolarization – K+ ions rush out of the cell
13Nerve Impulse Propagation The nerve impulse moves along the axon. The change in voltage of one area triggers the depolarization of the next area. Repolarization follows immediately.
14Nerve ImpulsesIn myelinated neurons the impulse “jumps” from node to node, rather than traveling the whole length of the axon – makes the impulse transmission much more efficient.Watch me!..and me!Saltatory conduction is 10-60X faster than smooth conduction
15Irritability vs. Conductivity Generation and propagation of nerve impulse along one neuron= irritability Conductivity is the ability of one neuron to signal another. This occurs in an entirely different fashion at the synapse, or gap, between neurons.
16Synapses The fluid-filled space between neurons is called a synapse Chemicalscalledneurotransmitterscarry the nerveimpulse acrossthe synapse.
17Synapses The nerve impulse reaches the axon terminal. Ca+ gates open, allowing Ca+ into the axon.The Ca+ causesvesicles containingneurotransmittersto empty into thesynapse
18SynapsesThe neurotransmitters diffuse across the synaptic cleft and binds with receptors of the next neuron.Na+ channels openin the dendrites ofthe post-synapticneuronPost-synapticneuron depolarizes7. Remainingneurotransmitter isbroken down.
19SynapsesPre-synaptic neuron Action potential calcium ions release neurotransmitter release Post-synaptic neuron Neutrotransmitter uptake sodium gates open action potential Note: information travels as electrical signal within neurons and as chemical signal between themWatch me!
20Reflex ArcsWatch me!Reflexes are rapid, predictable, involuntary responses to stimuli.May be somatic or autonomicContain 5 elements
21ClosureWhat were our objectives today, and what did we learn about them?What was our learner profile trait and how did we use it?How does what we did today relate to our unit question?HOMEWORK: Quiz on Thursday / Friday!
22Exit Ticket Count off by three. Identify the steps that take place during an action potential. Make a diagram of the cell membrane demonstrating the changes that occur during each step.Draw a diagram of the voltage changes that occur during an action potential. Label the diagram with the changes that occur within the cell during each step.Identify the steps that take place during synaptic transmission. Make a diagram of the events that within the pre- and post-synaptic neurons during each step.