Chapter 6: Neuronal Signaling and the Structure of the Nervous System Flashcards
(47 cards)
1
Q
Excitable cells
A
excitable cells: rapidly change their membrane potential (this change acts as an electrical signal)
2
Q
Two types of Excitable Cells
A
- Nerve Cells (Neurons)-Neurogenic
2. Muscle Cells-Myogenic
3
Q
3 Important factos to Establish a Membrane Potential
A
- The distribution of ions across the plasma membrane (at rest)
- The permeability of the membrane to these ions (highly permeable to a certain ion)
- Charge on the ions that are moving
4
Q
Goldman Equation
A
- describe the effects the facts have on membrane potential
- if the membrane is not permeable to an ion,the ion does not contribute to the membrane potential
- if the membrane is highly permeable to anon that ion makes a large contribution to the membrane potential
- excitable cells selectively alter the permeability of their membranes to ions (By opening and closing gated ion channels in the membrane)(Changing ion permeability alters the membrane potential and generates electrical signals)
- Predicts the equilibrium potential for certain ions
- No net movement of ions
5
Q
3 parts of the Neuron Cell
A
- Cell Body
- Dendrites
- Axon
6
Q
Cell Body
A
enlarged part of cell that contains the nucleus and organelles
7
Q
Dendrites
A
cytoplasmic extensions from the cell body; receive incoming signals
8
Q
Axon
A
long cytoplasmic extension; specialized for signal transduction
9
Q
Neuronal Zones
A
- Signal Reception Zone
- Signal Integration Zone
- Signal Conduction Zone
- Signal Transmission Zone
10
Q
Signal Reception Zoen
A
dendrites and the cell body
receives incoming signals
11
Q
Signal Integration Zone
A
axon hillock
where the cell body meets the axon; if there is enough large stimulus, the stimuli is converted to an electrical signal (change in membrane potential) that is sent down the axon
12
Q
Signal Conduction Zone
A
axon
neurons wrapped in a myelin sheath transmit the electrical signal
13
Q
Signal Transmission Zone
A
collaterals
swelling at axon terminus where comes in close contact with the target cell; does not touch (electrical signal is converted to a chemical signal [neurotransmitter])
14
Q
Signals in the Dendrites
A
DENDRITES RECEIVE INCOMING SIGNALS
- convert chemical signal to electrical signal
- ion channels opening or closing
- alter membrane potential
ALL ELECTRICAL SIGNALS SENT TO DENDRITES ARE GRADED POTENTIALS
- vary in magnitude or size (based on stimulus)
- vary in amplitude or strength (based on stimulus)
- strong-ion channels will stay open longer time
NEUROTRANSMITTER
15
Q
GRADED POTENTIALS
A
- graded potentials can either hyper polarize or depolarize the cell
- depending on the type of ion channel that is opened or closed
- most important ion channels in the dendrites of a neuron are Na+, K+, Cl-, and Ca2+ channels
- Goldman Equation (Opening Na+ or Ca2+ channels will depolarize a neuron; Opening K+ or Cl- channels will hyperpolarize a neuron)
16
Q
Graded Potentials: Conduction with Decrement. Electronic Current Spread. Why.
A
- Leakage of charged ions across the membrane
- Electrical resistance in the cytoplasm
- Electrical properties
17
Q
Graded Potentials: Conduction with Decrement
A
- ability to spread through a cell
- strength of the stimulus decreases as distance from the stimulus decreases
- short distance signals
- ripples in a pond
- neuron will use action potentials cover greater distances
- action potential must reach threshold potential to fire
18
Q
Resting Membrane Potential
A
- voltage is a difference in electric potential between two points
- separation of positive and negative electric charges on opposite sides of a resistive barrier
- resting membrane potential of a cell arises from the separation of intracellular potassium ions from anions across the cel membrane of the cell
- concentration gradient of potassium ions must be set up.
- Na+/K+-ATPase (sodium-potassium pump)
- in a resting (unstimulated) cell and membrane has the potential to conduct electrical signal or action potential
- sodium potassium pump
- not an equilibrium potential; requires energy to maintain
19
Q
Sodium Potassium Pump
A
- 3 sodium ions pumped out of the cell
- 2 potassium ions pumped out of the cell
- creates a deficit of positive ions on the inside of the cell
- so inside is more negative than the outside
20
Q
Steps of Action Potentials
A
- Resting Membrane Potential
- Threshold Potential
- Depolarization
- Repolarization
- Hyperpolarization
21
Q
Resting Membrane Potential
A
- 70mV
- inside the cell membrane is more negatively charged than the outside
- defined as a relatively stable, ground value of transmembrane voltage in animal and plant cells
22
Q
Threshold Potential
A
- must be reached for action potential to “fire”
- remember these are graded potentials
- 55mV to be excitatory potentials
- inhibitory potentials (too low-subthreshold potentials)(too high supra-threshold potentials)
23
Q
Depolarization
A
- membrane potential becomes less negative
- either positively charged ions enter the cell or negatively charged ions leaving the cell
- sodium/potassium leaky channels
- very leaky to potassium, not so leaky to sodium (potassium leaks out of the cell)
24
Q
Repolarization
A
- returns to the normal resting membrane potential
- either negatively charged ions enter the cell or positively charged ions leaving the cell
- re-established by Na+/K+ ATPase pump
25
Hyperpolarization
- become more negative
- either negatively charged ions entering the cell or positively charged ions leaving
- re-estalish resting membrane potential
26
Integration of Graded Signals
SPATIAL SUMMATION
-interaction of graded potentials from different receptors will "meet" at the axon hillock
(add together to fire an action potential)
(different sites)
TEMPORAL SUMMATION
-interaction of graded potentials that occur at slightly different times at the axon hillock
(add together to fire an action potential)
(different times)
27
Axon Hillock
- acts as a decision point for the neuron
- fire an action potential only if the combination of graded potentials causes the axon hillock to depolarize beyond threshold
- summation of graded potentials allows integrated inputs from many different stimuli
28
Action Potential Rules: Travel Long Distances
1. "All-or-none"
2. Self Propagating
3. Electric Current Spreads
4. Unidirectional Flow
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"All-or-none"
does or does not occur
- once an action potential has been initiated by the Na+ channels
- always proceeds to its conclusion; never stop halfway or fail to reach peak depolarization
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Self-Propagating
- individual action potentials do not actually travel along the axon
- action potential in one part of the axon triggers other action potentials in adjacent areas of the axonal membrane
- every action potential is identical without degradation of the signal
- domino effect
31
Electric Current Spreads
- between ion channels of axon Na+ ions entering
- voltage-gated channels
- depolarize the membrane immediately surrounding the channel
- spread through the dendrites and cell body
- wave of depolarization along the axon which triggers action potentials further downstream
32
Unidirectional Flow
Absolute Refractory Period: Axon is incapable of generating a new action potential; no matter how strong. (coincides with depolarization and depolarization)
Relative Refractory Period: A new action potential can be generated but only by a very large stimulus
(coincides with hyper polarization)
33
Voltage-Gated Channels
1. Action Potentials is due to the opening and closing of voltage-gated ion channels
2. As the membrane potential reaches threshold at the axon hillock, sodium channels begin to open-beginning of depolarization
3. Sodium influx further depolarizes the region causing more sodium channels to open; increase permeability which increases sodium in cell
4. Equilibrium potential is +60mV reached
5. Sodium channels close-ends depolarization
6. Threshold depolarization of the membrane at the axon hillock causes a change in membrane potential, which causes potassium channels to open; same time that the sodium channels close
7. Potassium are slow channels
8. Potassium channels will slowly close as equilibrium potential of potassium is reached -90mV
9. As potassium ions try to get to their equilibrium-hyperpolarization "overshoot"
34
Supporting Cells in CNS
1. Astrocytes
2. Microglia
3. Ependymal Cells
4. Oligodendrocytes
5. Satellite Cells
6. Schwann Cells
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Astrocytes
most abundant; controls ionic environment around neurons
36
Microglia
smallest and least abundant; macrophages of CNS engulfing microbes, injured or dead neurons
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Ependymal Cells
form epithelium lining central cavity of spinal cord and brain; circulate cerebrospinal fluid with cilia
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Oligodendrocytes
produce myelin sheaths that insulate neurons
| same as Schwann Cells in perp. nervous system
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Satellite Cells
surround neuron cell bodies to support and protect
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Schwann Cells
neurolemmocytes
surround axons in PNS and form myelin sheaths
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Myelin Sheaths
MYELIN: lipoprotein that surrounds thicker axons
STRUCTURE: layers consist of concentric laters of plasma membrane of supporting cell
FUNCTION: insulating later that prevents leakage of electrical current from axon to increase speed of impulse conduction along axon; energy efficient
NODES OF RANVIER: gaps in myelin sheath.
Nerve impulses do not travel along myelin-covered regions but jump from node to nodes-saltatory conduction
42
Synaptic Signal Strength: Presynaptic Factors
NEUROTRANSMITTER AVAILABILITY
- availability of precursor molecules.
- activity of rate limiting enzyme
AXON TERMINAL MEMBRANE POTENTIAL
AXON TERMINAL AXON CONCENTRATION
DRUGS AND DISEASES
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Synaptic Signal Strength: Neurotransmitter Release
-Axon terminal membrane potential
-Axon terminal calcium concentration
-Drugs and diseases
-Removal of unbound transmitter
-reuptake
-diffusion away from cleft
-enzymatic transformation into inactive
substances
44
Synaptic Signal Strength: Postsynaptic Factors
ELECTRICAL POTENTIAL STATUS
-excitable (excitatory post synaptic potential or EPSP)-depolarizing event on postsynaptic cell membrane
-inhibitory (inhibitory post synaptic potential or IPSP)-hyperpolarizing event on post synaptic cell membrane
EFFECTS OF OTHER NEUROTRANSMITTERS
UP OR DOWN REGULATION OF RECEPTORS
DESENSITIZATION OF RECEPTORS
DRUGS AND DISEASES
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Neurotransmitter Characteristics
1. Synthesized in Neurons
2. Released by the presynaptic cell following depolarization
3. Binds to a postsynaptic receptor and cause an effect
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Acetylcholine (ACh)
- Major neurotransmitter in PNS at neuromuscular junction and brain
- Cholinergic Neurons
ACh RECEPTORS
- Nicotinic Receptors-Na+ driving force
- Muscarine Receptors-G Proteins
47
Catecholamines
FORMED FROM THE AMINO ACID TYROSINE
- dopamine
- norepinephrine
- epinephrine
RECEPTORS ARE METABOTROPIC AND USE SECOND MESSENGERS
MAJOR CLASSES OF RECEPTORS
- alpha-adrenergic receptors-PLC; Ca2+
- beta-adrenergic receptors-cAMP; K+ channels
PLC to initiate a change in Calcium
cAMP to initiate a change in Potassium
