Module 4 How Do Neurons Use Electronic Signals to Transmit Information Flashcards
How Do Neurons Use Electrical Signals to Transmit Information
- Searching for Electrical Activity in the Nervous System
- Electrical Activity of a Membrane
- How Neurons integrate Information
- Into the Nervous System and Back Out
Behavioral Response to Stimulation
- How do out nerves detect a sensory stimulus and inform the brain about it?
- How does the brain decide what response should be made?
- How does the brain command muscles to move to produce a behavioral response?
Early Clues that Linked electricity and Neuronal Activity
-Galvani (18th Century)
~Electrical current applied to a dissected nerve caused the muscle connected to the nerve to twitch; concluded that electricity flows along the nerve
~Electrical Stimulation
*Passing an electrical current from the tip of an electrode through brain tissue, resulting in changes in the electrical activity of the tissue
Electricity and Electrical Stimulation
-Electricity
~A flow of electrons from a body that contains a higher charge (more electrons) to a body that contains a lower charge (fewer electrons)
-Negative Pole
~The source of electrons; higher charge
-Positive Pole
~Location to which electrons flow; lower charge
Early Clues That Linked Electricity and Neuronal Activity
-Electrical Stimulation Studies
-Fritsch and Hitzig (Mid-19th Century)
~Electrical stimulation and neocortex causes movement (arms and legs)
-Bartholow (1874)
~First report of human brain stimulation
-Caton (Early 19th Century)
~First to attempt to measure electrical currents of the brain using a voltmeter and electrodes on the skull
-Electroencephalogram
~Electrical brain graph that records electrical activity through the skull or from the brain and represents graded potentials of many neurons
-Von Helmholtz (19th Century)
~Flow of information in the nervous system is too slow to be flow of electricity
*Nerve conduction 30-40 meters/second
*Electricity 3X 10^8 meter/second
-It is not the charge but the wave that travels along the axon (Bernstein, 1886)
Electricity and Electrical Stimulation
-Electrical Potential
~An electrical charge measured in volts; the ability to do work through the use of stored potential electrical energy
-Volt
~A measure of a difference in electrical potential
-Voltmeter
~A device that measures the difference in electrical potential between two bodies
Tools for Measuring a Neuron’s Electrical Activity
-Giant Axon of the Squid
-Much larger in diameter that human axons
~Humans: 1 to 20 micrometers
~Squid: up to 1 millimeter (1000 micrometers)
-Easier on which to perform experiments
~Used by Hodgkin and Huxley in the 1930s and 1940s
Tools for Measuring a Neuron’s Electrical Activity
-The Oscilloscope
- A device that serves as a sensitive voltmeter
- Used to record voltage changes on an axon
Tools for Measuring a Neuron’s Electrical Activity
-Microelectrodes
-A set of electrodes small enough to place on or into an axon
-Can be used to:
~Measure a neuron’s electrical activity
~Deliver an electrical current to a single neuron (stimulation)
Use of Microelectrodes
-Measure voltage across the membrane
- Tip of one microelectrode placed on (outside) an axon
- A second microelectrode used as the reference, inserted into the axon
Use of Microelectrodes
-Patch Clamp
- Place microelectrode tip in the neuron’s membrane and apply a little back suction until the tip becomes sealed to a patch of the membrane
- Allows recording to be made from only the small patch of membrane that is sealed within the perimeter of the microelectrode tip
How the Movement of Ions Creates Electrical Charges
-Captions ~Positively Charged Ions ~Example *Sodium (NA+), potassium (K+) -Anions ~Negatively charged Ions ~Example *Chloride (Cl-), Protein molecules (A-) -Diffusion ~Movement of Ions from an area of higher concentration to an area of lower concentration through random motion -Concentration Gradient ~Differences in concentration of a substance among regions of a container that allows the substance to diffuse from an area of higher concentration to an area of lower concentration -Voltage Gradient ~Difference in charge between two regions that allows a flow of current if the two regions are connected *Opposite charges attract *Similar charges repel ~Ions will move down a voltage gradient from an area of higher charge to an area of lower charge
Equilibrium
- Efflux of chloride ions down the chloride concentration gradient is counteracted by the influx (Inward flow) of chloride ions down the chloride voltage gradient
- Equilibrium is reached when the concentration gradient of chloride ions on the right side of the beaker is balanced by the voltage gradient of chloride ions on the left
- Concentration Gradient = Voltage Gradient
Electrical Activity of a Membrane
-Resting Potential
- Electrical charge across the cell membrane in the absence of stimulation
- A store of negative energy on the intracellular side relative to the extracellular side
- The inside of the membrane at rest is -70 millivolts relative to the extracellular side
Resting Potential
-Four charged particles take part in producing the resting potential ~Sodium (Na+) and chloride (Cl-) *Higher concentration outside the cell ~Potassium (k+) and large proteins (A-) *Higher concentration inside the cell
Resting Potential
-Maintaining the Resting Potential
-Large A- molecules cannot leave cell
~Make inside negative
-Ungated channels allow K+ and Cl- to move into and out of cell more freely, but gated sodium channels keep out NA+ ions
-Na+ - K+ pumps extrude Na+ from intracellular
fluid and inject K+
Graded Potentials
-Hyperpolarization
~Increase in electrical charge across a membrane (more negative)
~Usually due to the inward flow of chloride ions or outward flow of potassium ions
-Depolarization
~Decrease in electrical charge across a membrane (more positive)
~usually due to the inward flow of sodium
The Action Potential
-Action Potential
- Large, brief reversal in polarity of an axon
- Lasts approximately 1 millisecond (ms)
The Action Potential
-Threshold Potential
- Voltage on a neural membrane at which an action potential is triggered
- Opening of Na+ and K+ voltage-sensitive channels
- Approximately -40 mV relative to extracellular surround
The Action Potential
-Voltage-Sensitive Ion Channels
- Gated protein channel that opens or closes only at specific membrane voltage
- Sodium (Na+) and potassium (K+)
- Closed at membrane’s resting potential
- Na+ channels are more sensitive than K+ channels and therefore open sooner
- Occurs when a large concentration of, first, Na+ ions, then K+ ions crosses the membrane rapidly
The Action Potential
-Depolarization due to Na+ influx
-With tetrodotoxin (to block sodium channels), a slightly different action potential due entirely to the efflux of potassium is recorded
The Action Potential
-Hyperpolarization due to K+ efflux
-With TEA surrounding the axon (blocks potassium channels), a smaller-than-normal action potential due entirely to a Na+ influx is recorded
Voltage-Sensitive ion Channels
- Closed at resting potential; ions cannot pass through
- When the membrane reaches threshold, channels open briefly, enabling ions to pass through, then close again to restrict their flow
The Action Potential
-Absolute Refractory Period
-The state of an axon in the repolarizing period during which a new action potential cannot be elicited (with some exceptions) because gate 2 of sodium channels, which is not voltage-sensitive, is closed
The Action Potential
-Relative Refractory Period
- The state of an axon in their later phase of an action potential during which increased electrical current is required to produce another action potential
- Potassium channels are still open
The Toilet Flushing Analogy
- During the flush, the toilet is absolutely refractory: another flush cannot be induced at this time
- During refilling the bowl, the toilet is relatively refractory, meaning that reflushing is possible but harder to bring about
The Nerve Impulse
-Nerve Impulse
-Propagation of an action potential on the membrane of an axon
-Refractory period create a single, discrete impulse that travels using the axon in one direction only
-Size and shape of action potential remain constant along the axon
~All-or-none law
Domino Analogy
- Voltage-sensitive channels along the axon similar to series of dominoes
- When one domino falls it knocks over its neighbor, and so on down the line
- There is no decrement in the size of the fall
Saltatory Conduction and the Myelin Sheath
-Myelin
- Produced by oligodendroglia in the CNS and Schwann cells in the PNS
- Speeds up neural impulse
Saltatory Conduction and the Myelin Sheath
-Node of Ranvier
-Part of an axon that is not covered by myelin
-Tiny gaps in the myelin sheath
-Enables Saltatory Conduction
~An axon is insulated by (A) oligodendroglia in the CNS and (B) Schwann cells in the PNS
~Each my myelin sheath segment is separated by a gap, or node of Ranvier
Saltatory Conduction and the Myelin Sheath
-Saltatory Conduction
- Saltare: (to dance in Latin)
- Propagation of an action potential at successive nodes of Ranvier
How Neurons Integrate information
- Through dendritic spines, a neuron can establish more than 50,000 connections to other neurons
- Nerve impulses traveling from other neurons bombard the receiving neuron with all manner of inputs (excitatory and inhibitory)
- The cell body, location between the dendritic tree and its axon, can receive inputs from many other neurons
- How does the neuron integrate this enormous array of inputs into the nerve impulse?
Excitatory and Inhibitory Postsynaptic Potentials
-Excitatory Postsynaptic Potential (EPSP)
- Brief depolarization of a neuron membrane in response to stimulation
- Neuron is more likely to produce an action potential
Excitatory and Inhibitory Postsynaptic Potentials
-Inhibitory Postsynaptic Potential (IPSP)
- Brief hyperpolarization of an neuron membrane is response to stimulation
- Neuron is less likely to produce an action potential
Excitatory and Inhibitory Postsynaptic Potentials
-Both EPSPs and IPSPs last only a few milliseconds before they decay and the resting potential is restored
-EPSPs are associated with the opening of sodium channels
~Allows influx of Na+
-IPSPs are associated with the opening of potassium channels (K+) or with the opening of chloride channels (Cl-)
~Allows an efflux of K+
~Allows an influx of Cl-
Summation of Inputs
EPSPs and IPSPs Are Summed
-Temporal Summation
-Pulses that occur at approximately the same time on a membrane are summed
Summation of Inputs
EPSPs and IPSPs Are Summed
-Spatial Summation
-Pulses that occur at approximately the same location on a membrane are summed
Summation of Input
- A neuron sums all inputs close together in time and space
- Provides an indication of the summed influences of multiple inputs
- If the summed ionic input exceed the threshold (approx. -50 mV) at the axon hillock, an action potential will be initiated
Voltage-Sensitive Channels and the Axon Hillock
-The Axon Hillock
- Junction of cell body and axon
- Rich in voltage-sensitive channels
- Where EPSPs and IPSPs are integrated
- Where action potentials are initiated
- If the summated EPSPs and IPSPs on the dendritic tree and cell body charge the membrane threshold at the axon hillock, and action potential is generated and travels down the axon membrane in all-or-none fashion
Back Propagation
-Reverse movement of an action potential from the axon hillock into the dendritic field
-Signals the dendritic field that the neuron is sending an action potential over its axon and may play a role in plastic changes in the neuron that underlie learning
How Sensory Stimuli Produce Action Potentials
-We receive information about the world through
~Bodily sensation (touch and balance)
~Auditory sensation (hearing)
~Visual sensation (sight)
~Chemical sensations (taste and olfaction)
-Neurons related to these diverse receptors all have ion channels on their cell membranes
-These ion channels initiate the chain of events that produces a nerve impulse
How Sensory Stimuli Produce Action Potentials
-Example Touch
- Each hair on our body allows us to detect the slightest displacement
- Dendrite of a touch neuron is wrapped around the base of each hair
- Hair displacement opens stretch-sensitive channels in the dendrite’s membrane
- When channels open, they allow an influx of Na1 ions sufficient to depolarize the dendrite to its threshold level
How Nerve Impulses Produce Movement
-Spinal motor neurons send nerve impulses to synapses on muscle cells
-Axon of each motor neuron makes one or more synapses with target muscle
-End plate
~Part of the muscle membrane that is contacted by the axon terminal
How Nerve Impulses Produce Movement
-Acetylcholine
- Chemical transmitter that the axon terminal releases at the muscle end plate
- Attaches to transmitter-sensitive channels
- Channels open all owing Na+ and K+ ions across the muscle membrane to depolarize the muscle to the threshold
- Muscles then generate action potentials in order to contract
Electroencephalogram (EEG)
-When a strobe light was flashed before the eyes, the EEG displayed a series of abnormal electrical pattern characteristics of epilepsy
Electrographic Seizures
- Abnormal rhythmic neuronal discharges; may by recorded by an electroencephalogram
- Innocuous stimuli- events that would not typically cause seizures in people who do not have epilepsy
Descartes
‘s Theory
-Was incorrect but brought up three good question
~How do out nerves detect a sensory stimulus and inform the brain about it?
~How does the brain decide what response to make?
~How does the brain command muscles to move?
Electrical Stimulation
- Passage of an electrical current from the uninsulated tip of an electrode through tissue, resulting in changes in the electrical activity of the tissue
- Passing an electrical current from the uninsulated tip of an electrode onto a nerve to produce behavior- a muscular contraction
Voltmeter
- Device that measures that strenght of electrical voltage by recording the difference in electrical potential between two points
- A device that measure the flow and the strenght of electrical voltage by recording the difference in electrical potential between two bodies
Electroencephalogram (EEG)
- Graph of electrical activity from the brain, which is mainly composed of graded potentials from many neurons
- Standard tool used for, monitoring sleep stages and detecting the excessive neural synchrony that characterizes electrographic seizures
Hermann von Helmholttz (19th century scientists)
- Stimulated a nerve leading to a muscle and measured the time the muscle took to contract
- The nerve conducted information at only 30 to 40 meters per second, whereas electricity flows among a wire about a million times faster
The Wave Effect
- When a stone is dropped in water, the contact produces a wave that travels away form the site of impact
- The water itself moves up and down and does not travel away from the impact site
- Only the change in pressure moves, shifting the height of the water surface and producing the wave effect
Oscilloscope
- Specialized device that serves as a sensitive voltmeter, registering changes in voltage over time
- A voltmeter with a scree sensitive enough to display the minuscule electrical signals emanating from a nerve or neuron over time
- Units used when recording the electrical charge from a nerve of neuron are millivolts (one-thousandth of a volt) and milliseconds (one-thousandth of a second)
Microelectrode
-A microscopic insulated wire or a saltwater-filled glass tube whose uninsulated tip is used to stimulate or record from neurons
-Can deliver electrical current to a single neuron as well as record from it
-Etch the tip of a piece of thin wire to a fine point about 1 mm in size and insulate the rest of the wire with a synthetic polymer, like plastic
-The tip is placed on or in the neuron
-Can also be made of thin glass tube tapered to a very fine tip
~The tip of hollow glass microelectrode can be as small as 1 mm
~When the glass tube is filled with salty water, a conducting medium through which electrical current can travel, it acts as an electrode
*A wire in the salt solution connects the electrode to either a stimulating device or a recording device
-The tip of one electrode can be placed on the surface of the axon, and the tip of a second electrode can be inserted into the axon
-The glass microelectrode is to place its tip on the neuron’s membrane and apply a little suction until the tip is sealed to a patch of the membrane
Nerve Impulse
-Is a charge in the concentration of specific ions across the cell membrane
Cations
-A positively charged ions
Anions
-A negatively charged ions, including protein molecules
Diffusion
- Movement of ions from an area of higher concentration to an area of lower concentration through random motion
- Requiring no additional energy results from the random motion of molecules as they move and bounce off one another to gradually disperse in a solution
Concentration Gradient
-Difference in the relative abundance of a substance among regios of a container; allows the substance to diffuse from an area of higher concentration to an area of lower concentration
-Ions are initially highly concentrated where they enter at the top of a beaker of water compared to the bottom of the beaker
~As time passes, concentration gradients flow down due to diffusion
*Movement down (for sodium and chloride ions)
Voltage Gradient
- Difference in charge between two regions that allow a flow of current of the two regions are connected
- Ions move down a voltage gradient from an area of higher charge to an area of lower charge
- Just as they move down a concentration gradient from an area of higher concentration to an area of lower concentration
- *Movement down (for the positive and negative charges)
Resting Potential
-Electrical charge across the insulating cell membrane in the absence of stimulation; a store of potential energy produced by a greater negative charge on the intracellular side relative to the extracellular side
~70 mV id the approximate difference; the charge is on the outside of the membrane is actually positive, by convention it is given a charge of zero
~The inside of the membrane rest is -70 mV relative to the extracellular side
-Is a store of energy that can be used later
-Most of the body’s cells have a resting potential, but it is not identical on every axon
~Vary from -40 to -90 mV, depending on the neuronal type and animal species
Four Charge Particles Take Part in Producing the resting Potential
-Sodium (Na+)
-Potassium (K+)
-Chloride (Cl-)
-Large Negatively Charged Proteins (A-)
~These charged particles are distributed unequally across the axon’s membrane, with more protein anions and potassium ions in the intracellular fluid and more sodium and chloride ions in the extracellular fluid
Maintaining the Resting Potential
- Because the membrane is relatively impermeable to large molecules, the negatively charged proteins (A-) remain inside the cell
- Ungated potassium and chloride channels allow potassium (K+) and chloride (Cl-) ions to pass more freely, but gates on sodium channels keep out positively charges of sodium ions (Na+)
- Na+ - K+ extrude Na+ from the intercellular fluid and inject K+
Difference of Potassium Ions extracellular versus intracellular
-If the number of potassium ions that could accumulate on the intracellular side of the membrane were unrestricted, the positively charged potassium ions inside would exactly match the negative charges on the intracellular protein anions
-There would be no charge across the membrane at all
~The number of potassium ions that accumulate inside the cell is limited because when the intracellular K+ concentration becomes higher than the extracellular concentration, further potassium ion influx is opposed by its concentration gradient
Sodium-Potassium Pump
- A protein molecule embedded in the cell membrane
- A membrane’s many thousands of pumps continually exchange three intracellular sodium ions for two potassium ions
- The potassium ions are free to leave the cell through the open potassium channels, but close sodium channels slow the reentry of the sodium ions
- Sodium ions are kept out to the extent that about 10 times as many sodium ions reside on the outside of the axon membrane as on the inside
Graded Potential
-Small voltage fluctuation across the cell membrane
-Stimulating a membrane electrically through a microelectrode mimics the way the membrane’s voltage changes to produce a graded potential in the living cell
~If the voltage applied to the inside of the membrane is negative, the membrane potential increases in negative charge by a few millivolts
*It may change from the resting potential of -70mV to a slightly greater potential of -73mV
Hyperpolarization
-Increase in electrical charge across a membrane, usually due to the inward flow of chloride or sodium ions or the outward flow of potassium ions
-If a positive voltage is applied inside the membrane, its potential decreases by a few millivolts
~It may change from a resting potential -70mV to a slightly lower potential of -65mV
Depolarization
- Decrease in electrical charge across the membrane, usually due to the inward flow of sodium ions
- Graded potentials usually last only a few milliseconds
Potassium Channels
-For the membrane to become hyperpolarized, its extracellular side must become more positive, which can be accomplished with an outward movement, or efflux, of potassium ions
-Some resistance to the outward flow of potassium ions remains
~Reducing this resistance enables hyperpolarization
Chloride Channels
- The membrane can also become hyperpolarized if an influx of chloride ions occur
- Though cloride ions can pass through the membrane, more ions remain on the outside than the inside, so a decrease resistance to Cl- flow can result in brief increases of Cl- inside the cell
Sodium Channels
-Depolarization can be produced if normally cloassed sodium channel gates open to allow an influx of sodium ions
Tetraethylammonium (TEA)
-Chemical that blocks potassium channels also blocks hyperpolarization
Tetrdotoxin (TTX)
-Chemical which blocks sodium channels also blocks depolarization
~Found in puffer fish
*Leathal to humans for consumption (puffer fish) if prepared wrong
Action Potential
-Large, breif reversasl in the polarity of an axon membrane
-A breif, but very large reversal in an axon membrane’s polarity that last about 1 ms
-The voltage across the membrane suddenly reverses, making the intracellular side positive relative to the extracellular side, then abruptly reverses again to restore the resting potential
~Since the action potential is brief, many action potentials can occur within a second
-Occur when a large concentration of first Na+ and then K+ crosses the membrane rapidly
-The depolarization phase of the action potential is due to Na+ influx, and the hyperpolarization phase is due to K+ efflux
~Sodium rushes in and the potassium rushes out
Threshold Potential
-Voltage on a neural membrane at which an action potential is triggered by the opening of sodium and potassium voltage-activated channels; about -50mV relative to extracellular surround
~Called THRESHOLD LIMIT
-The relative voltage of the membrane drops to zero and continues to depolarize until the charge on the inside of the membrane is as great as 30+ mV-a totalvoltage change of 100mV
-The membrane potential reverses again, becoming slightly hyperpolarized-a reversal of a little more that 100 mV
-After the second reversal, the membrane slowly returns to its resting potential at -70 mV
Voltage-Activated Channels
- Gated protein channel that opens or closes only at specific membrane voltages
- Are closed when an axon’s membrane is at its resting potential: ions cannot pass through them
- When the membrane reached threshold voltage, the configuration of the voltage-activated channels alture: they open briefly, enabling ions to pass through, then close again to restrict ion flow
Voltage-Activated Channels Sequence of Actions
-Both sodium and potassium voltage-activited channels are attuned to the threshold voltage of about -50 mV.
~If the cell membrane changes to reach this voltage, both types of channels open to allow ion flow across the membrane
-The voltage-activated sodium channels respond more quickly than the potassium channels
~As a result, the voltage change due to Na+ influx takes place slightly before the voltage change due to K+ efflux can begin
-Sodium channels have two gates
~Once the membrane depolarizes to about +30 mV, one of the gates closes
~The Na+ influx begins quickly and ends quickly
-The potassium channels open more slowly than the sodium channels, and they remain open longer
~The efflux of K+ reverses the depolarization produced by Na+ influx and even hyperpolarizes the membrane
Absolutely Refractory
- The state of an axon in the repolarization period, during which a new action potential cannot be elicited (with some exceptions) because gate 2 of sodium channel, which are not voltage activated, are closed
- Stimulation of the axon membrane during the depolorizing phase of the action potential will not produce another action potential
- Nor is the axon able to produce another action potential when it is repolarizing
Relatively Refraction
-The state of an axon in the later phase of an action potential, during which higher-intensity electrical current is required to produce another action potential; a phase during which potassium channels are still open
-The axon membrane is stimulated during hyperpolarization, another action potential can be induced, the second stimulation must be more intense than the first one
-Result from the way gaes of the voltage-activated sodium and potassium channels open and close
~A sodium channel has two gates, and a potassium channel has one gate
Nerve Impulse
-Propagation of an action potential on the membrane of an axon
Propagate (to give birth)
-Each successive action potential gives birth to another down the length of the axon
Nodes of Ranvier
- The part of an axon that is not covered by myelin
- Sufficiently close to one another that an action potential at one node can open voltage-activated gates at an adjacent node
Saltatory Conduction (from the Latian ver saltare, meaning “to leap”)
- Fast propagation of an action potential at successive nodes of Ranvier
- A relatively slow action potential jumps quickly from node to node
Multiple Sclerosis (MS)
-Nervous system disorder resulting from the loss of myelin around axons in the CNS
-The myelin formed by oligodendroglia is damaged, which disrupts the functioning of neurons whose axons it encases
-Result from a loss of myelin produced by oligodendroglia cells in the CNS, by disrupting the affected neurons’ ability to propagate action potential via saltatory conduction; the loss of myelin occurs in patches and scarring frequently results in the affected area
-Visible with MRI
-Associated with the loss of myelin is impairment of neuron function, which causes the characteristics MS symptoms sensory loss and difficulty in moving
-Common signs
~Fatigue
~Pain
~Depression
-Complications
~Bladder dysfunction
~Constipation
~Sexual dysfunction
-Twice as common in women than men
~Affects a person’s emotional, social, and vocation functions
Autoimmune Diseases
- Illness resulting from an abnormal immune response by the body against substances and tissues normally present in the body
- Conditions in which the immune system makes antibodies to a person’s own body
Excitatory Postsynaptic Potentials (EPSP)
- Brief depolarization of a neuron membrane in response to stimulation, making the neurons more likely to produce an action potential
- Reduce (depolarize) the charge on the membrane toward the threshold level and increase the likelihood that an action potential will result
- Associated with the opening of sodium channels, which allows an influx of sodium ions
Inhibitory Postsynaptic Potential (IPSP)
- Brief hyperpolarization of a neuron membrane in response to stimulation, making the neuron less likely to produce an action potential
- Increase the charge on the membrane away from the threshold level and decrease the likelihood that an action potential will result
- Associated with the opening of potassium channels, which allows an efflux of potassium ions
Initial Segment
-Area near where the axon meets the cell body that is rich in voltage-gated channels, which generate the action potential
Temporal Summation
-Addition of one graded potential to another that occurs close in time
Spatial Summation
- Additional of one graded potential to another that occur close in space
- Occurs when two separate inputs are very close to one another both on the cell membrane and in time
Giant Depolarizing Potentials
- Some cells in the devloping hippocampus can produce additional action potentials
- When the cell would ordinarily be refractory
- Aids in developing the brain’s neural circuitry
Back Propagation
-Reverse movement of an action potential into the soma and dendritic field of a neuron; postulated to play a role in plastic changes that underlie learning
-Which signals to the dendritic field that the neuron is sending an action potential over its axon, may play a role in plastic changes in the neuron that underlie learning
-Example
~May make the dendritic fieldrefactory to incoming inputs, set the dendritic field to an electrically natural base line, or reinforce signals coming in to certain dendrites
Optogenetics
- Transgenic technique that combines genetics and light to excite or inhibit targeted cells in living tissue
- Researchers have successfully introduced light-sensitive channels into a variety of species including worms, fruit flies, and mice
- Combines genetic and light to control targeted cell in living tissue
Chlamydomonas Reinhardtii
-Channelrhodopsin-2 (ChR2)
-Light-activivated ion channels in the green alga
-Light-activated channels absorbs blue light and in doing so, opens briefly to allow the passage of Na+ and K+
~Resulting depolarization excites the cell to generate action potentials
Halorhodopsin (NpHR)
- A light-driven ion pump, specific for chloride ions and found in phylogenetically ancient bacteria (archaea) known as halobacteria
- When illuminated with green-yellow light, NpHR pumps chloride anions into the cell, hypolarizing it and thereby inhibiting its activiey
Stretch-activated Channels
-Ion channel on a tactile sensory neuron that activates in response to stretching of the membrane, initiating a nerve impulse
-When open these channels allow an influx of sodium ions sufficient to depolarize the dendrite to threshold
~The voltage-activated sodiumand potassium channels initiate a nerve impulse that conveys touch information to your brain
Transduction (transforming)
-The energy of a sensory stimulus into nervous system activity
Amyotrophic (muscle weakness) Lateral Sclerosis (Hardening of the lateral spinal cord)
-In the US known as Lou Gehrig disease
-Begins with general weakness
~At first in int he throat or upper chest and in the arms and legs
-Gradually, walking becomes difficult and falling is common
-Does not usually affect and sensory systems, cognitive functions, bowel or bladder control or even sexual funaction
End Plate
- On a muscle, the receptor-ion complex that is activated by the release of the neurotransmitter acetylcholine from the terminal of motor neuron
- Where the axon terminal releases the chemical transmitter Acetylcholine
Transmitter-Activated Channels
-Receptor complex that has both a receptor site for a chemical and a pore through which ions can flow
-When these channels open in response, they allow a flow of Na+ and K+ across the muscle membrane sufficient to depolarize the muscle to the threshold for its action potential.
~At this threshold, adjacent voltage-activated channels open
-They in turn produce an action potential on the muscle fiber, as they do in neurons
-A single endplate channel is larger than two sodium and two potassium channels on a neuron combined
-They allow both Na+ influx and K+ efflux through the same pore
-Generating a sufficient depolarization on the endplate to activate neighboring voltage-activated channels on the muscle membrane requires the release of an appropriate amount of acetylcholine
Myasthenia Gravis
- Muscular contraction in conditions such as the autoimmune disease
- Affects individuals, the thymus, an immune system gland that normally produces antibodies that bind to foreign material like viruses, makes antibodies that bind with acetylcholine receptors on muscles, causing weakness and fatigue
- Usually well controlled with treatment, including drugs that suppress the immune system or inhibit acetylchline breakdown, extending the time the transmitter can act, or by removal of the thymus gland
