Chapter 3 #2 Flashcards
What is the cause of action potential?
The sudden movement of sodium ions into the cell
Voltage gated Na+ channel
A Na+ selective channel that opens or closes in response to changes in the voltage of the local membrane potential.
Refractory
Temporarily unresponsive or inactivated
Absolute refractory phase
A brief period of complete insensitivity to a second stimulus righty after action potential has been produced
Relative refractory phase
Period of reduced sensitivity during which only strong stimulation produces an action potential, immediately follows the absolute refractory phase
What determines a neurons maximal rate of firing?
The overall duration of refractory phase
What are the 3 properties of the voltage gated Na+ channel that make it responsible for the characteristics of the action potential?
- Monitoring the axons polarity
- At threshold the channel changes shape to open and closes again a millisecond later
- Remembers it was just open and refuses to open again for a short time
How does the action potential travel along the axon?
Begins at the axon hillock. The action potential is spike of depolarizing electrical activity that in turn depolarizes the adjacent axon segment covered in voltage gated Na+ channels which creates a new action potential and this continues down the axon.
Why is the action potential propagated primarily in only one direction?
Because the cell body and dendrites are covered in far fewer voltage gated Na+ channels so they can’t produce action potential and the refractory period
Conduction velocity
The speed at which an action potential is propagated along the length of an axon
What variables affects the conduction velocity?
Axon diameter. Larger axons can propagate action potential faster. As well as amount of myelin
How fast can neural conduction be done?
Over 300 miles per hour. Not the speed of light.
Saltatory conduction
The form of conduction that is characteristic of myelinated axons, in which the action potential jumps from one node of Ranvier to the next.
What advantage do vertebrates have over invertebrates?
Myelinated axons that have much faster neural conduction
Effects of multiple sclerosis
Interference with action potential conduction by destruction if myelin
Post synaptic potentials
Brief changes in membrane potential of the post synaptic cell in response to neurotransmitters
What’s the difference between an excitatory and an inhibitory synapse?
Excitatory brings the post synaptic membrane closer to firing an action potential while an inhibitory lowers the potential away from threshold
Excitatory postsynaptic potential (EPSP)
A depolarizing potential in the postsynaptic neuron that is cause by excitatory presynaptic potentials. EPSP’s increase the probability that the postsynaptic neuron will fire an action potential
Synaptic delay
The brief delay between the arrival of an action potential at the axon terminal and the creation of a post synaptic potential. About a half a millisecond.
What is accounted for during the synaptic delay?
Neurotransmitter is released, diffuse across the synaptic cleft, and affect the postsynaptic cell.
Inhibitory postsynaptic potential (IPSP)
A hyper polarizing potential in the postsynaptic neuron that is caused by inhibitory connections. IPSP’s decrease the probability that the postsynaptic neuron will fire an action potential.
Chloride ions (Cl-)
A chlorine atom that carries a negative charge because it has gained one electron
What do IPSP’s usually result from?
Opening of channels that permit chloride ions to rush into the cell making the membrane potential more negative.
What determines whether a synapse excites or inhibits the presynaptic cell?
Which neurotransmitter is being released, some inhibit some excite. So whether a neuron fires an action potential is decided by the balance between excitatory and inhibitory signals that it receives.
Where is the trigger zone for action potentials?
Axon hillock
EPSP’s - IPSP’s = ?
The net affect. Calculated to decide whether membrane has reached threshold for firing an action potential.
Spatial summation
The summation of postsynaptic potentials that reach the axon hillock from different locations across the cell body. If this summation reaches threshold, an action potential is triggered.
Does distance from the triggering zone matter?
Yes. Postsynaptic potentials spread passively and dissipate over the cell membrane.
Temporal summation
Summation of postsynaptic potentials that reach the axon hillock at different times. The closer in time the potentials occur, the more complete the summation is.
How do dendrites effect membrane potential and summation?
Expand receptive surface of neuron increase input. The further out on a dendrite the potential occurs, the less affect it will have at the hillock
What is the function if the axon hillock?
Moment to moment to integration of all the neurons inputs and encodes into action potentials
Synaptic vesicles
Small structures that contains molecules of neurotransmitter.
What happens when an action potential reaches a presynaptic terminal?
Hundreds if synaptic vesicles to fuse with presynaptic membrane and six barge their molecules into the synaptic cleft
Calcium ion (Ca2+)
A calcium atom that carries a double positive charge because it has lost 2 electrons
What is the key event in this first part of synaptic transmission?
An influx if calcium ions into the axon terminal through a voltage gated channel in response to the arrival of an action potential.
What regulates the rate if neurotransmitter creation?
Enzymes manufactured in the neuronal cell body and transported actively down the axon to the terminals
Ligand
“Key” to receptor proteins. Must be correct shape to fit and activate or block it.
Acetylcholine (ACh)
A neurotransmitter that is produced and released by parasympathetic postganglionic neurons, by motoneurons, and by neurons throughout the brain.
Neurotransmitter receptor
A protein that captures and reacts to molecules of a neurotransmitter or hormone.
What are the chemicals that block ACh receptors?
Curare and bungarotixin
Curare
A neurotoxin that causes paralysis by blocking ACh receptors in muscle. (S. American hunt)
Bungarotoxin
A neurotoxin, isolated from the venom of the banded krait (snake), that selectively block ACh.
Agonist
A molecule, usually a drug (nicotine), that binds a receptor molecule and initiates a response like that of another molecule, usually a neurotransmitter.
Antagonist
A molecule, usually a drug (curare), that interferes with or prevents the action of the neurotransmitter.
Cholinergic
Refers to cells that use acetylcholine as their synaptic transmitter
How many subtypes of Cholinergic receptors does ACh act on?
4
What are the 2 processes that bring transmitter effects to a prompt halt?
Degradation and reuptake
Degradation
Chemical breakdown of a neurotransmitter into inactive metabolites by special enzymes
Acetylcholinesterase (AChaE)
Enzyme that inactivates ACh by breaking into parts that are recycled to make more ACh in the axon terminal.
Reuptake
Process by which released synaptic transmitter molecules are taken up and reused by the presynaptic neuron, thus stopping synaptic activity
Transporter
Specialized receptor in the presynaptic membrane that recognizes transmitter molecules and returns them to the presynaptic neuron for reuse
Axo-dendritic synapse
A presynaptic axon terminal synapses onto a dendrite of the post synaptic neuron, either via a dendritic spine or directly onto the dendrite itself
Axo-somatic synapse
A presynaptic axon terminal synapses onto the cell body of the post synaptic neuron
Axo-axonic synapse
A presynaptic axon terminal synapses onto the axon terminal of another neuron. Allows the presynaptic neuron to strongly facilitate or inhibit activity of the postsynaptic axon.
Dendro-dendritic synapse
A synapse at which a synaptic connection forms between the dendrites of 2 neurons. Allows coordination of their activities.
