The Nervous System (Luke)

The Nervous System is Made of How Many Neurons?
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Axons conduct impulses _______ the cell bodyAxons conduct impulses away from the cell body towards the axon terminals.What are chemical messengers?Neurotransmitters - used to communicate with other cells, neurons or target cells. (i.e. seratonin and dopamine)What do myelin sheaths do?Myelin Sheaths help insulate the axons.What are myelin sheaths made of?Myelin Sheaths are made of layers and layers of plasma membrane wrapped around the axon.What are the spaces between myelin sheaths called?The spaces between the myelin sheaths are called nodes of ranvier. The nodes of ranvier will be where you see electrical signals.What are the three types of neurons?Afferent Neurons, Efferent Neurons, and InterneuronsAfferent NeuronsAfferent neurons send information to the central nervous system (CNS).Efferent NeuronsEfferent neurons send information from the central nervous system (CNS).InterneuronsInterneurons connect neurons with the CNS. (links between the two types of neurons)The SynapseWhere two neurons meet, or where a neuron and a target cell meets. The JUNCTION between the two cells.What is the neuron that's sending the signal called?The presynaptic neuron.Presynaptic NeuronHas electrical event and release the neurotransmitters and tell the other cell what to do.Postsynaptic NeuronCells that receive the signals.Locations of synapsesDendrites AND Cell body. 1 neuron get get lots of synapses. A neuron can send many signals or receive many signals.Action PotentialThe change in membrane potential. Quick reversal in membrane voltage.At rest, what is the charge of the membrane potential?-70 mV. Neurons have a NEGATIVE resting membrane potential.What is the peak value of the action potential?+30 mV. Peak of action potential. When that value is reached, it allows you to INITIATE the electrical events and allows you to SPREAD the signal all the way down to the axon terminals where you release chemical messengers.Where does the Action Potential take place?Axon. No A/P in dendrites or cell bodies. Starts at base of cell body, base of axon. The baseWhat are graded potentials?Not action potentials, just smaller changes in voltage. Travels through the cell body towards the axon hillock (base of cell body).Axon HillockHas voltage gated sodium channels that are responsible for summing up your inputs. The neuron can receive a bunch of inputs. Determines whether it's enough to fire an action potential or not enough to fire an action potential.Which voltage gated channel is responsible for summing up your inputs?Sodium Gated Channels are responsible for summing up your inputs.At rest, is the inside more negative or positive than the outside? (membrane potential)It's more negative on the inside. Note: The action potential lets in positive ions to reverse that membrane potentials. This makes the inside more positive than the outside. At rest, the membrane potential is -70. At the peak of the action potential, the membrane potential is +30.Electric CurrentMovement of ions (charge responsible for electric current)What are the major ions in neurons? (hint: there are 4 major ions)Sodium, Potassium, Calcium, ChlorideWhat contributes to the -70 resting potential of the membrane potential?Ion channels that are leak channels. Leak channels allow ions to move passively through them. With these leak channels, you have them go with the gradient. Sodium and potassium gradient. 3 Na outside, 2 K inside of cell. This sets up the gradient for the A/P.Sodium wants to move _________ of the the cell. Potassium wants to move _________ of the cell.Sodium wants to move inside of the cell. Potassium wants to move outside of the cell.You have more of Potassium or Sodium leak channels?More Potassium leak channels. More permeable to potassium. Since we have more potassium leaving the cell and not a lot sodium entering the cell, this sets up the -70 value at resting membrane potential.What are the two forces that act on the ions?Concentration gradient and electric gradient.Electrochemical gradientIn addition to chemical gradient, you also observe the electric charge. With potassium ion, it wants to diffuse out of the cell with the concentration gradient. Initially, the concentration gradient is stronger than electric gradient. So, you have movement of K outside of cell. But this leaves negative charges on the inside of the cells. So, as more K leaves the cell, the electric gradient gets stronger and stronger - reducing the outward flow of the K. So you'll reach a point where electric gradient and chemical gradient balance each other, AKA equilibrium potential. Two forces are balanced, no more net diffusion. That's what Nernst equation is for - it tells you the equilibrium potential... two forces are balanced. Different values for the forces. -90 mV. -90 mV is the equilibrium of K, after this value, they pull K back into the cell because it's too negative inside, it pushes Na out.Nernst EquationTells you the equilibrium potential where the two forces are balanced.Depolarizationwhen membrane potential is LESS NEGATIVE than resting potential. (or more positive than resting potential) Anything less negative or more positive than -70 mV value is depolarization.Hyperpolarizationwhen membrane potential is MORE NEGATIVE than resting potential. (or less positive than resting potential) Anything more negative or less positive than -70 mV value is hyperpolarization.Repolarizationwhen membrane potential has been depolarized (or hyperpolarized) returns to its resting value. HEADS BACK to -70.2 channels that are involved in Action PotentialsVoltage gated Sodium Channel and Voltage gated Potassium Channel. LEAK CHANNELS HAVE NOTHING TO DO WITH ACTION POTENTIALS. Only focus on the voltage gated channels.Do Leak Channels have anything to do with Action Potentials?NO. Leak Channels have nothing to do with action potentials. Leak channels are ALWAYS open.Voltage Gated Sodium ChannelA protein channel that's specific to sodium. Has three main states.What are the Three main states of Voltage Gated Sodium Channel?In Voltage Gated Sodium Channel, the three main states are: 1) Closed at resting potential 2) Open 3) InactivatedWhat happens when Na comes into the cell?More depolarization which opens more voltage gated Na channels. (POSITIVE Feedback Mechanism)At what voltage does ALL Na voltage gated channels open?At -50 mV. At -50 mV, ALL Na channels are opened. The threshold is reached at -50 mV. To ENSURE action potential, you have to hit threshold of -50 mV. If you DON'T hit -50, NOTHING happens.What does Axon Hillock determine?Axon hillock sums up all inputs. If it hits -50, it fires an A/P. If not, it'll go back to rest and wait for another summation of inputs that hit -50.Na channels have TWO gates, what are they?Activation Gate and Inactivation GateRefractory PeriodVoltage-Gated Na channels have a refractory period during which they cannot open.Voltage Gated Sodium Channel - Activation GateActivation Gate is CLOSED at REST (prevents Na from coming in). Activation Gate is OPENED at DEPOLARIZATION.Voltage Gated Sodium Channel - Inactivation GateInactivation Gate OPENS at REST. STARTS CLOSING at DEPOLARIZATION.At rest, the Activation Gate is ____________.ClosedAt Depolarization, the Activation Gate is __________.OpenAt rest, the Inactivation Gate is __________.OpenAt Depolarization, the Inactivation Gate __________.Starts closingVoltage Gated Channels - When do they Open and Close?1) AT REST: Na and K channels are CLOSED. Na Inactive is open. 2) AT DEPOLARIZATION: Na is OPEN K is CLOSED Na Inactive is OPEN 3) AT THRESHOLD/PEAK: ALL Na is OPEN Na Inactive CLOSES K OPENS 4) AT REPOLARIZATION: K OPENS, keeps on flowing. 5) AT HYPERPOLARIZATION: K is SLOWLY CLOSING 6) AT REPOLARIZATION: K FINISHES CLOSINGSteps of Action Potential : At RestAt rest, both VG-Na and VG-K are closed. Na Inactivation Gate is Open.Steps of Action Potential : At DepolarizationWhen depolarization occurs, some VG Na are triggered to open causing more VG Na to open. VG K are still closed.Steps of Action Potential : At thresholdIf threshold reached, almost ALL VG-Na open and there is a massive influx of Na into the cell. This is the spike of the action potential.Steps of Action Potential : At peakAt peak, the VG Na inactivation gate blocks the flow of sodium ions. Essentially, the VG Na Inactivation gate CLOSES. The VG K opens and starts repolarizing the membrane.Steps of Action Potential : At RepolarizationAt Repolarization, the VG K is open, K is flowing.Steps of Action Potential : At HyperpolarizationAt Hyperpolarization: the VG K channels are slowly closing. (they're slow, that's why it hyperpolarizes)Steps of Action Potential : At Repolarization (after Hyperpolarization)K finishes closing the channels, until both channels are closed towards resting potential membrane.What happens when inactivation gate closes?When inactivation gate closes, you can't restimulate them...including strong stimulus. Closed for a short period of time.What happens to the action potential down the axon?Once it reaches threshold, the action potential it can regenerate itself down the axon until it hits the axon terminals.How do neurons generate and transmit electrical signals? (What are the TWO unique characteristics of an action potential?)1) ALL-OR-NOTHING. An action potential is an all-or-none event - positive feedback to voltage gated Na channels ensures the maximum action potential. 2) SELF-REGENERATING. An action potential is self-regenerating because it spreads to adjacent membrane regions.What is the triggering event of an Action Potential?Graded potentials added up to thresholdWhat are Glial Cells?A supportive cell in the central nervous system. Unlike neurons, glial cells do not conduct electrical impulses. The glial cells surround neurons and provide support for and insulation between them. Glial cells are the most abundant cell types in the central nervous system. Types of glial cells include oligodendrocytes, astrocytes, ependymal cells, Schwann cells, microglia, and satellite cells.How does myelin speed up the action potential?When positive current reaches the next node, the membrane is depolarized, another action potential is generated. Action potentials appear to jump from node to node, a form of propagation called saltatory conduction. Myelination by glial cells increases the conduction velocity of axons. The nodes of Ranvier are regularly spaced gaps where the axon is not covered by myelin. Action potentials are generated at the nodes and the positive current flows down the inside of the axon. Charges travel inside axons until they reach each node.What is Saltatory Conduction?A form of propagation were action potentials appear to jump from node to node.How does Myelination by glial cells help?Myelination by glial cells increases the conduction velocity of axons. Myelination allows the action potentials to skip patches of membrane. (speeds up, don't need to get to threshold as often)What is Myelin?Myelin is a dielectric (electrically insulating) material that forms a layer, the myelin sheath, usually around only the axon of a neuron.Where are the action potentials generated along the axons?Action potentials are generated at the NODES and the positive current flows down the INSIDE of the axon.