Biopsychology Chpt 4 Flashcards
What is the membrane potential?
difference in electrical charge inside and outside of the cell
What causes the uneven distribution of ions?
- The membrane is selectively permeable to some ions (more permeable to K+)
- Sodium-Potasium pumps
What factors contribute to the even distribution of ions?
- Random motion > particles move down their concentration gradient
- electrostatic pressure > like repels like, opposites attract
What is equilibrium potential
the potential at which there is no movement of an ion> it will try to reach this point if allowed to move freely
What is the equilibrium potential of
Na+ (sodium)
K+ (potassium)
Na+ = 62 mV K+ = -80mV
What is the resting membrane potential of the neurons we are studying?
-70mV
Is the sodium-potassium pump directly involved in the action potential?
no, but it helps to create the uneven distribution of ions that polarizes the cell and contributes to AP
What are factors acting on Sodium ions (NA+)
- Sodium in high concentration outside cell > wants to move down gradient to inside
- Sodium also attracted to -A protein inside cell
- Membrane is not very permeable to Sodium
- Sodium Potassium pump is sending Na+ out of cell
What are the factors acting on Potassum ions?
- Potassium in high concentration inside cell > wants to move out down the concentration gradient
- K+ is being brought in by the sodium-potassium pump
- K+ is attracted to A- protein
What are PSP’s
Post Synaptic Potentials > when neurotransmitters bind at postsynaptic receptors and cause electrical changes
How does an EPSP affect the electrical charge of the cell?
Excitatory PSP’s makes the membrane potential less negative (depolarization) and more likely that the neuron will fire
How does an IPSP affect the electrical charge of the cell?
Inhibitory PSP’s makes the membrane potential more negative (hyperpolarization) and less likely that the neuron will fire
What is the mechanism that causes IPSP’s to make the membrane potential more negative?
Protein channel opens to allow Cl- into the cell making it more polarized
What is the mechanism that causes EPSP’s to make the membrane potential more positive (depolarization)?
Protein channels open to allow Na+ in
What does it mean the PSPs are graded?
They vary in size
When will a neuron fire an action potential?
When the membrane potential reaches -65Mv at the AXON INITIAL SEGMENT
How do EPSPs and IPSPs travel?
Passively from their site of origin > get smaller as they travel
What is integration in regards to the action potential
integration of several post synaptic potentials is needed for a neuron to reach -65Mv and fire an action potential.
What are the two types of integration?
Spatial summation: integration of PSPs happening at different places
Temporal summation: integration of PSPs happening at different times
At what phase in the AP are sodium channels opened? When are they closed?
Opened: The rising phase
Closed: Peak of rising phase +50mV
When are the Potassium channels opened during the AP?
When are they closed?
Opened: delay open after Na+ channels
Closed: start to close at -70 mV, results in hyperpolarization and a potential of -80mV
Why does the neuron hyperpolarize to -80mV?
Because the potassium is being pushed quickly out by sodium ions and -80mV is it’s equilibrium potential (desired state)
What brings the neuron back to resting potential?
random motion (concentration gradient) and sodium-potassium pump
What is an absolute refractory period
> When it is impossible to initate another AP
>Sodium channels are inactivated/closed and need time until they will open again
What is the relative refractory period?
> period of time when the sodium channels are open but the cell is still depolarized below resting potential
harder for an AP to be fired
What does the refractory period do?
> Prevent the backwards movement of APs and limit the rate of firing
What are 3 features of Action Potentials
> Nondecremental
Conducted more slowly than PSPs
Passive and active
What is antidromic conduction?
Orthodromic conduction?
Antidromic: toward cell body
Orthodromic: down axon towards dendrites
What is Saltadory conduction?
> fast transmission of APs in myelinated axons
>because conduction jumps from node to node
What are the nodes of ranvier?
spaces between myelin sheath
What are the two most common synaptic transmissions?
axodendritic: axons on dendrites
axosomatic: axons on cell bodies
What are two less common synaptic transmissions?
dendrodendritic: dendrite on dendrite
axoaxonic: axon on axon
What is special about dendrodendritic transmissions?
can transmit in either direction
what are axoaxonic transmissions potentially involved in?
presynaptic facilitation or inhibition
How is an AP passive AND active?
Passive when it moves along myelin sheath, active when it moves between nodes of ranvier
What is it called when the site of neurotransmitter release and reception are close?
directed synapse
What is it called when the site of neurotransmitter release and reception are far away?
nondirected synapse
Where are small neurotransmitter molecules synthesized and packaged?
small: synthesized in terminal button, packaged in vesicles
Where are large neurotransmitter molecules synthesized and packaged?
Large: synthesized in the cell body and packaged in vesicles to be transported to the axon terminal
How does exocytosis occur?
AP causes voltage-activated CA2+ channels to open which causes vesicles to fuse with the terminal membrane and release contents
What is a ligand?
A molecule that binds to a receptor (neurotransmitters)
What are ionotropic receptors?
associated with ligand-activated ion channels (ligand triggers channel to open to allow ion to pass)
What are metabotropic receptors?
> They do NOT have a channel that opens
By binding with receptor they activiate G-protein which then
G protein activates secondary messenger
may or may not open an ion channel somewhere else on the membrane
What is a signalling cascade
When a metabotropic receptor causes a g-protein to activate a chain of messenger molecules (not a direct opening of an ion channel by G-protein)
What is the function of autoreceptors?
> regulate concentration of NT in the synapse
bind to neuron’s own NT
on presynaptic membrane
What are two mechanisms for terminating NT action in the synapse?
- Reuptake by autoreceptors
2. Enzymatic degradation
What are gap junctions?
Electrical synapses that allow electrical signals and small molecules to pass directly between cells
Why are gap junctions necessary?
When simultaneous firing of neurons is necessary
ex. embryonic development, heart muscle
What two types of neurons often use gap junctions?
- astrocytes > star-like glial cells of CNS
2. Oligodendrocytes > myelin sheath creating CNS glial cells
Where can gap junctions occur?
Between neurons, glia, and neurons and glia
What is a tripartite synapse?
a synapse that includes a presynaptic terminal + post synaptic terminal + astrocyte
What does the astrocyte do in a tripartite synapse?
releases NT glutamate and ATP to modulate activity of pre and post synaptic terminal
What are three characteristics of small molecule NT?
- directed synapses
- ionotropic and metabotropic receptors
- fast and brief signals
What are three characteristics of large molecule NT?
- non-directed synapse
- metabotropic receptors
- slow and lasting signals
What are three classes of small molecule NT?
- Amino Acids
- Monamines (dopamine, seratonin)
- Acetylcholine
What is the one large molecule NT class?
Neuropeptides
What is a prevalent excitatory amino acid NT and where is it found?
Glutamate > fast acting directed synapses in the CNS
What is a prevalent inhibitory amino acid NT and where is it found?
GABA > synthesized from glutamate in the CNS
What are two more common amino acid NT?
Aspartate and glycine
What are two classes of Monoamines?
Catecholamines > synthesized from Tyrosine 1. dopamine 2. norepinephrine 3. epinephrine Indolmines > synthesized from tryptophan 1. seratonin
Where is acetylcholine important?
at neuromuscular junctions
What are two types of unconventional NT?
- Endocannabinoids
2. soluble gases (Nitric Oxide, Carbon Monoxide)
What do endocannabinoids and soluble gases do?
They inhibit synaptic transmission through backwards messaging
What are 5 categories of neuropeptides?
Pituitary peptides hypothalamic peptides Brain-gut peptides Opioid peptides Misc. Peptides
What are two examples of agonist drugs?
- Cocaine > catecholamine agonist > blocks reuptake preventing NT from being turned off
- Benzodiazepines > GABA agonists > increases frequency of GABA channel openings
What are two examples of antagonist drugs?
- Atropine > Ach antagonist > women used to put in eyes to make the pupils larger > disrupts memory
- Curare > Ach antagonist > causes paralysis
What are two families of endogenous Opioids and what do they do
- enkephalins
- endorphins
produce anelgesia
What kind of molecules are enodogenous opioids and what kinn of receptors do they bind to?
large molecules > neuropeptides > bind to metabotropic receptors
What kind of symptoms do antischizophrenic drugs produce?
parkinsonian > because drugs disrupts the dopaminergic pathway from substantia nigra to the hypothalamus
What kind of agonists produce schizophrenic sympotms?
dopamine agonists
