Chapter 3, Neurophysiology Flashcards
What is Neurophysiology?
The study of the life processes within neurons that use electrical and chemical signals
What is Action Potential?
Rapid electrical signals that travel along the axon of a neuron
What is a neurotransmitter?
A chemical messenger between neurons
What is a Neuron at rest?
it is a balance of electrochemical forces
What are ions?
Electrically charged molecules
What is an Anion?
A negatively charged ion
What is a Cation?
A positively charged ion
What is the Resting membrane potential?
The difference in electrical potential across the membrane of a neuron during an inactive period (-50 to -80 mV)
What is the negative polarity of a cell interior in humans?
in humans, it is -60 mV
What is a cellular membrane?
It is a lipid bilayer, it has a Hydrophilic head that loves water. It has also a Hydrophobic tail that hates water.
What is a Concentration Gradient?
Molecules move from areas of high concentration to areas of low concentration. It is also called Diffusion
What is an Electricalchemical Gradient?
Like charges repel each other
What does Electrostatic pressure do?
It causes ions to flow to areas of opposite charges. (Positive attracts to negative)
What is the equilibrium potential?
The voltage across the membrane counteracts the movement of ions due to the concentration gradient.
What is a cell membrane of a neuron permeable to?
It is permeable to (K+) ions due to open (K+) channels but it is not permeable to (Na+) ions.
So the diffusion takes place through semipermeable membranes.
What is it called when opposite charges are attracted to each other?
It is called Electrostatic Pressure.
What do the Concentration Gradient and Electrostatic Pressure do to (K+)?
It pushes (K+) out and then electrostatic pressure pulls them in.
What type of mechanism does a neuron use to maintain resting potential?
It uses a sodium-potassium pump to maintain the resting potential.
What does the sodium-potassium pump do?
It pumps three sodium ions (Na+) out for every two (K+) ions pumped in
What do (K+) ions do when the neuron is at rest?
It moves the (K+) ions into the negative interior of the cell due to electrostatic pressure.
What happens when (K+) ions build up inside the cell?
They also diffuse out through the membrane, along the concentration gradient.
How does the (K+) reach equilibrium?
When the movement out is balanced by the movement in.
What is the mV value of resting membrane potential when it corresponds to the (K+) equilibrium?
It is about -60 mV (values range between -50 and -80 mV).
Where do most of the (K+) ions reside during resting potential?
they reside inside the cell
Where are most (Na+) and (Cl-) and Calcium (Ca^2+) residing during resting potential?
They reside in the extracellular fluid.
How do the (K+), (Na+), (Cl-), and (Ca^2+) ions exchange?
They exchange through ion channels.
Do neurons often change their electrical charge?
Yes they do with Hyperpolarization and Depolarization
What is Hyperpolarization?
It is an increase in the membrane potential, the inside of the cell becomes more negative.
What is Depolarization?
It is a reduction in membrane potential, so the inside of the cell becomes less negative.
What is Capacitance?
The ability of the membrane to store an electrical charge
What is Graded Potential (Response)?
It is a change in the neuron’s response dependent on the strength of the stimulation.
What is a Local Potential?
An electrical potential that is initiated by stimulation at a specific site, which is a graded response that spreads passively across the cell membrane, decreasing in strength with time and distance
What does weak depolarizing stimulation produce?
A graded response
What is the Depolarizing threshold?
it is -40mV and this is when the action potential (spike) occurs
What is the All-or-none property?
The fact that amplitude of the action potential is independent of the magnitude of the stimulus.
What are the phases of Action Potential?
Resting Potential - Depolarization - Threshold / Absolute refractory period - Relative refractory period - All voltage-gated channels closed
What is the first phase of the Action Potential?
Resting potential, open (K+) channels/voltage, and gated (Na+) channels are closed
What is the second phase of the Action Potential?
Depolarization, the (K+) ion channels close.
What is the first part of the third phase of Action Potential?
Threshold, (Na+) channels open, and sodium floods into the cell leading to the action potential.
What is the second part of the third phase of Action Potential?
Absolute Refractory Period, when the cell is insensitive to further stimulation (no further action potentials can occur)
What is the fourth phase of Action Potential?
Relative refractory period, (Na+) channels close, and the (K+) channels open. It requires a stronger stimulation required for the action potential. It is when Hyperpolarization occurs.
During Action Potential what does the sodium-potassium pump do?
It restores the original distribution of ions.
What is the fifth phase of the Action Potential?
All voltage-gated channels are closed, returning to resting potential.
Where do action potentials occur?
Only in the axon. it starts at the axon hillock and moves down the axon. It only moves in one direction because of the refractory period.
What are some examples of a (Na) channel blocker?
- Tetrodotoxin, a toxin carried by pufferfish and other species
- Lidocaine, a local anesthetic
What are Postsynaptic Potentials?
A local potential that is initiated by stimulation at a synapse. It varies in amplitude and spreads passively across the membrane. It decreases in strength with time and distance.
What are the two types of Postsynaptic Potentials?
- Excitatory postsynaptic potentials (EPSP)
- Inhibitory postsynaptic potential (IPSP)
What is an Excitatory Postsynaptic Potential?
A stimulation causes an action potential and a release of neurotransmitters. (Na+) channels on postsynaptic cells open, causing small local depolarization (EPSP) that moves cells closer to an action potential. This forms an excitatory synapse.
What is an Inhibitory Postsynaptic Potential?
A stimulation causes an action potential and a release of neurotransmitters, increasing the resting potential and opening the (Cl-) channels on the postsynaptic cell. This causes small local hyperpolarization (IPSP) that moves cells further away from an action potential. This forms an inhibitory synapse.
What is Summation?
it is the collective effect of both the Inhibitory Postsynaptic Potential and the Excitatory Postsynaptic Potentials.
What are the two types of Summation?
- Spatial
- Temporal
What is Spatial Summation?
Summation of all postsynaptic inputs generated at different locations on the neuron.
What is Temporal Summation?
Integration of inputs arriving at axon hillock at different times, the closer together in time that they arrive, the greater the summation and possibility of an action potential.
Action potentials last 1-2 ms, whereas EPSP’s and IPSP’s, can last up to 100 ms. It can arrive at the axon hillock at different times.
What are the Synaptic Transmission stages?
(1. ) The action potential arrives at the presynaptic terminal.
(2. ) In response, voltage-gated Ca2+ channels open and Ca2+ flows into the presynaptic terminal.
(3. ) The Ca2+ causes synaptic vesicles to fuse with the presynaptic membrane,
(4. ) releasing NTs into the synaptic cleft.
(5. ) NTs bind with receptors on the postsynaptic cell
(6. )causing EPSPs and IPSPs, which spread through the postsynaptic cell (potentially generating an action potential).
(7. ) NTs are degraded or removed from the synaptic cleft by transporters.
What causes the (Ca^2+) channels to open to allow (Ca^2+) to flow in?
Action Potential
What do the Vesicle fuse with and release?
They fuse with the presynaptic membrane and release neurotransmitters.
What is Exocytosis?
The process by which a synaptic vesicle fuses with the presynaptic terminal membrane to release neurotransmitters into the synaptic cleft.
In Exocytosis what role do the SNAREs serve?
They serve as tethers
What do v-SNAREs attach to?
Vesicles
What do t-SNAREs attach to?
The presynaptic membrane
What is Synaptotgmin?
A protein attached to the vesicle is activated by (Ca^2+) and triggers the fusion of the vesicle with the presynaptic membrane, releasing neurotransmitters.
What are Botulinum toxin and Tetanus toxin?
Both toxins cut up SNARE proteins and disable exocytosis/synaptic transmission.
What do Ligands do?
They fit receptors exactly and activate or block them.
What are the types of Ligands?
- Endogenous Ligands - which are neurotransmitters and hormones
- Exogenous Ligands - which are drugs and toxins outside the body.
At the synapses that use acetylcholine (ACh) are there ligand binding sites?
Yes, there are binding sites for (ACh) in the receptor molecules in the postsynaptic membrane.
Can (ACh) be excitatory and inhibitory?
Yes, it can, it can be excitatory by opening channels for (Na+) and (K+), it can also be inhibitory which would open the channels for (Cl-).
What is Cholinergic?
it refers to cells that use Acetylcholine as their synaptic transmitter.
What are some of the chemicals that fit cholinergic receptors and block and mimic the action of (ACh)?
- Antagonists, block (ACh) receptors
- Agonists, mimic (ACh), stimulating the nerve.
What are some Antagonists that block (ACh) receptors?
- Curare (plant-derived)
- Bungarotoxin (from the venom of snakes in the cobra family)
What are some Agonists that mimic (ACh) and stimulate the receptor?
- Muscarine
- Nicotine
Which agonist is produced by most (ACh) receptors in the brain?
Muscarine, which is also found on organs innervated by the parasympathetic division of the autonomic system.
What did the understanding of the nicotine (ACh) receptor structure lead to?
It led to the understanding of other neurotransmitter receptor structures
What does up-regulation mean?
increase
What does down-regulation mean?
decrease
What can the number of receptors in cells vary from?
- Daily adulthood
- During development
- With drug use
The interactions between neurotransmitters and receptors control the opening of ion channels in what two ways?
- Ionotropic Receptors
- Metabotropic Receptors
What are Ionotropic Receptors?
They are both neurotransmitter receptors and ion channels. When a neurotransmitter binds to an ionotropic receptor, the ion channel opens.
(this can also be called a ligand-gated ion channel)
What are Metabotropic Receptors?
It is not an ion channel and when neurotransmitters bind to the receptor, a G-protein is activated. This activated G-protein can then open a nearby ion channel.
(Called a G-protein coupled receptors)
Can a single neurotransmitter have multiple receptor subtypes?
Yes it can
What does the receptor determine for the effect of a neurotransmitter?
It decides if it is an excitatory or inhibitory effect on the postsynaptic neuron.
What can a receptor activation result in?
- The opening of a (Na+) channel, which will then result in an influx of (NA+) and the generation of (EPSP)
- It can also result in the opening of a (Cl-) channel, which will result in an influx of (Cl-) and the generation of an (IPSP)
What is Degradation?
The chemical breakdown of a neurotransmitter into inactive metabolites.
What is a re-uptake?
The process by which released synaptic transmitter molecules are taken up and reused by the presynaptic neuron, this stopping synaptic activity.
What are the types of synaptic connections?
- Axo-dendritic (axon - dendrite)
- Axo-somatic (axon - Soma)
- Axo-axonic (Axon - Axon = Soma)
- Dendro-dendritic (Dendrite - dendrite)
What are neural circuits?
neurons that are organized into circuits.
A neural chain is a simple series of neurons.
What is the simplest neural circuit?
A neural chain. (Knee Reflex)
What is convergence?
When multiple neurons converge onto fewer neurons
What is divergence?
When a signal from a single neuron spreads to many neurons.
What is common in a neural circuit?
- Convergence
- Divergence
What is an Electroencephalogram (EEG)?
It is a recording of the electrical activity of millions of neurons. It is usually used on awake individuals to permit activity across the brain asynchronously.
What can recording electrical activity in the brain provide?
Diagnostic data, for example, seizures involve synchronized electrical activity in the brain and this can be seen on an (EEG).
What is the brain wave pattern referred to as during a seizure?
Epileptiform activity
What are some categories of seizures?
- Tonic-clonic seizures
- Simple partial seizure
- Complex partial seizures
- Kindling
What is a tonic-clonic seizure?
It has abnormal activity throughout the brain, movements are characterized as tonic and clinic contractions. The seizure is followed by confusion and sleep.
What is Simple partial seizure
Brain waves show patterns of seizure activity for 5-15 seconds, sometimes several times a day. No unusual muscle activity, except for stopping and staring. The events during the seizure are not remembered.
What is a complex partial seizure?
Does not involve the entire brain, usually preceded by an Aura which is an unusual sensation that may precede a seizure.
What is Kindling?
A medically induced seizure
