Action Potentials and Synapses Flashcards
Chapter 1.3 and 2.1
define electrical gradient
when a rest, a membrane maintains the difference in electrical charges between the inside and outside of the cell, also known as polarization
Is the inside of the cell more positive or negative compared to the outside?
Inside of the membrane is slightly more negative, due to negatively charged proteins and more positive ions outside. this difference in voltage is known as the resting potential of -70mV
define selectively permeable
the membrane provides a barrier that permits some chemicals to pass more readily than others such as oxygen, water, and carbon dixoide.
define concentration gradient
difference in the distribution of ions across the neuron’s membrane. 1 action potential will not change this gradient.
why do neurons have a resting potentail?
in order for the neuron to be able to respond rapidly, the resting potentials prepares the neuron for such actions.
define action potentials
- an electrical signal that starts at the axon Hillick
- travels down the axon and remain the same size, doesn’t loose strength
- will continue unattenuated down all the branches of the axon to the presynaptic
define hyperpolarization
an increase in polarization (electrical gradient) across a membrane, adding negative charge inside
define depolarize
to reduce polarization towards zero across the membrane, and create a more positive charge inside
define the all-or-none law
the principle that the amplitude and velocity of an action potential are independent of the stimulus that initiated it, provided that the stimulus reaches the threshold
only applies to parts that have action potentials
what are the 3 main steps behind an action potential?
- sodium ions are mostly outside and potassium is mostly inside
- depolarizing the membrane opens Na-K pump
- at the peak of the action potential, the pump closes
define voltage-gated channels
membrane channels whose permeability to sodium depends on the volt difference across the membrane
only open/close depending on the voltage across the membrane
how do local anesthetic drugs work?
they attach to the sodium pumps on the membranes, stopping action potentials from occuring
define propagation of the action potential
describing the transmission of an action potential down an axon. the action potential gives birth to a new AP at each point along the axon.
describe how an action potential occurs
- resting potentail, K channel is slightly open
1. when threshold is reach, Na-K pumps open (3 an out, 2 k in, need ATP, constantly running)
2. sodium rushed in, k pump does little to nothing
3. positive charges flow down axon, opening voltage-gated sodium channels
4. peak of action potential, sodium channel closes
5. potassium ions flow out of axon, returning it towards original depolarization (repolarization)
6. then voltage-gated potassium channel closes
7. Na-K pumps open (3 an out, 2 k in, need ATP, constantly running) to get back to normal
define refractory period
the time when the cell resists the production of further action potentials
describe the difference between an absolute and relative refractory period
absolute is when the membrane is unable to produce an action potential and refractory is the time after the absolute when a stronger stimulus is required to initiate an action potential.
what is myelin composed of?
it is an insulating material composed of fats and protiens
define saltatory conduction
the jumping of action potentials from node to node (node of ranvier) due to myelin on the axon
what is a neuron called when it doesn’t have an axon?
local neurons and they can only communicate via immediate neighbors
define graded potential
in local neurons, a membrane potential that varies in magnitude in proportion to the intensity of the stimulus
define synapse
a specialized gap as a point of communication between two neurons anatomy of chemical events
define relexes
an automatic muscular response to a stimulus. reflex arc is a circuit from the sensory neuron to the muscle.
describe the difference between a presynaptic and postsynaptic neuron
presynaptic is the part that delivers transmission and postsynaptic is the part that receives it
define EPSP and IPSP
excitatory postsynaptic potential: graded depolarizing from sodium entering the neuron
inhibitory postsynaptic potential: graded hyperpolarization from the flow of negatively charged chloride entering the cell
can neurons create actions potentials without synapses input?
yes and its called spontaneous firing rate, a period of production of action potentials without synaptic input
who are Hodgkin and Huxley?
- they experimented with an axon of a squid and used a microelectrode to measure the voltage difference across the membrane
- created the used diagram of the electrical charges of an action potentail
what are the ion concentration in and outside the cell?
outside/ECF: high in Na and Cl
inside/ICF: high in K
what are the ways that ions move in the cell?
- diffusion: move down the concentration gradient
- electrostatic force: same charge repel and opposites attract
- these 2 forces can repel each other and cause no movement of ions
define multiple sclerosis
- when the myelin in the PNS starts to break down
- muscle weakness, sensory problems and cognitive deficit
- stage 1 (symptoms fad ina nd out, can see lesion on scan), stage 2 (symptoms are persistent)
- high in Europe
how does the myelin break down in MS?
- The blood-brain barrier becomes porous
- lymphocytes (killer cells) invade the brain
- microglia go to lymphocytes and release inflammatory substances
- the substances go to break down myelin (oligodendrocytes)
how do the neurons become dysfunctional in MS?
- damage to myelin exposes segment of axon without ion channel and action potential is disrupted
- axon withers downstream of demyelinated section, no interactions with other neruons will cause it to die (apoptosis)
- axonal avoid is formed at bottom of axon, no longer functional
how do the axons conduct in MS?
- t-cells (lymphocytes) and microglia release nitric acid
- nitric acid damages mitochondria
- lack of ATP impair Na-K pump = more Na inside cell
- high levels of Na inside will depolarize the axon
- depolarization causes increase of Ca
- Ca damages the mitochondrial further and triggers inflammation
what are the 3 outcomes that can occur when an axon starts to degenerate?
- remyelination of the axon by oligodendrocytes
- new ion channels are inserted to allow the action potential to continue
- a healthy neuron takes over the function of the damaged one
how does the gut play a role in MS?
- inbalance of pro-inflammatory (dysbiosis)
- weaking on intestinal wall
- microbial translation, into bloodstream
- lymphocytes enter via leaky blood-brain barrier
- inflammatory substance break down myelin
how can the Epstein-Barr virus cause MS?
- EBv affect your tonsils
- infect B-cells (killer immune cells) and they enter the blood stream
- B-cells enter the brain and release inflammatory mediators that activate T-cells
- microglia are activated and go break down myelin with inflammatory substances
what is the other explanation for how an axon moves and transports signals?
- axon will move in size to create a mechanical wave
- heat is partially gained and lost
- impulses cannot occur when cytoskeleton is disrupted
- water will enter and leave the axon
- impulses can occur even without Na
define adhesion molecules
molecules that are on both pre and postsynaptic sides that hold the two together to go and create the synaptic celft
what are the different kinds of neurotransmitters?
- amines: catecholamine (dopamine, epinephrine), indoleamine ( serotonin, melatonin), acetylcholine
- amino acids: GABA (inhibitory), glutamate (excitatory)
- peptides: oxytocin, insulin
- gases: nitric oxide, carbon monoxide
- other: ATP
define SNARE proteins
docking and priming in the active zone to release NT into synaptic cleft
what are the 3 kinds of vesicle pools?
reserve pool: 80-90%, just in case you run out and need more
recycling pool: 5-20%, next to go to the active zone
readily releasable pool: less than 1%, in the active zone to be released
what are the steps in how a synapse releases its neurotransmitters/
- action potential is created, Na and K pumps work to depolarize
2.Ca pumps open - Ca triggered exocytosis (vesicle fuses with the membrane of the synapse to release the contents) SNARE-mediated fusion to create fusion pore
- NT gets released
- ligand gated channels on postsynaptic side to try to depolarize
- NT reuptake on presynaptic by transporter protein
- NT attach to autoreceptor to communicate and give feedback
- some neurons will be completely deactivated
9 NT can do retrograde transmission (when the signal travels back to original source)
what are EPSP and IPSP?
Excitatory postsynaptic potentials: bringing the neuron closer to trigger an action potential, graded depolarization
inhibitory… : graded hyperpolarization, bring the neuron away from threshold
what is the difference between temporal and spatial summation?
temporal: rapidly repeated stimulation adding up over time to trigger AP
spatial: simultaneous stimulation from different axons that connect to each other being summed up to trigger AP
What are the kinds of receptors that can be on the postsynaptic neuron?
ionotropic: when the binding site is on the channel itself, synaptic effect that depends on the rapid opening of some kind of gate in the membrane (10ms)
metabotropic: the binding site has its own protein and that causes to open up the channel, separate from it, sequence of metabolic reactions that produce slow and longlasting effect a synapse(10s)
- all lead to open up either Na, K, Ca or Cl channels
what are 2 types of effects a NT can have?
convergence: mutliple NT can open up on channel
divergence: one specific NT for each channel
define spontaneous firing rate
a periodic production of action potentials even without synaptic input
define autoreceptor
receptors on a presyn neuron that provide negative feedback by responding to the transmitter released by that neuron
define hormone
chemical that is secreted by cells in one part of the body an conveyed by the blood to influence other cells
define the pituitary gland and its two parts
an endocrine gland attached to the base of the hypothalamus. The anterior is composed of glandular tissue and the posterior releases hormones synthesized by the hypothalamus
define tripartite synapse
- axon terminal, astrocyte, dendritic spine
what are the different kinds of synaptic connections you can have?
presynaptic-postsynaptic
axon-(dendritic,somatic,axonic)***most common
dendro-(dendritic,somatic,axonic)
somato-(dendritic,somatic,axonic)
what is the war of soups and sparks?
Sparks:
-John Eccles believed that there is electrical transmission across the synaptic cleft
Soups:
- Dale and Loewi believed that chemical substances were excreted from the presyn cell and influenced the postsyn cell
define electrotonic synapse
- membranes of cells sit adjacent to each other
- gap junctions line up with each other and ions are able to pass through the gap junctions
define connexon
lies on the surface on the cell’s membrane and create a central pore where molecules can move through
how do mixed synapses work?
- chemical part allows for more change to occur, its activity influences activity of the electrical synpase through secondary messangers (bigger gap)
- electrical part does not have very much control, becomes active from the chemical signals (tightly bounded)
define neuropeptide
- synthesized in teh cell body and are released from dendrites
- much bigger in size and send singles all around the body (ex. influence gene transcription)
- ex. oxytocin and insulin
define co-transmission
a single neuron can release multiple kinds of neurotransmitters
define amyotrophic lateral sclerosis (ALS)
- neurodegenerate disease (dying motor neurons that project into the brainsteam and spinal cord)
- symptoms: cogntivie impairmetn, frontotemperal dementia, dysphagia (trouble swallowing), dysarthia (trouble moving muscles for speech), respiratory problems, muscle cramps
what are the possible causes of ALS?
genetic: gene mutations (SOD1), proteins misfold/impaired function, impairment of axonal transport
environment: smokers, who consume cycad seeds, toxic chemicals in water
define creutzfeldt-jakob disease
- cognitive and behavioural decline due to prior protein dysfunction
- creates holes in the brain tissue
- Scrapie prion protein cause issue by taking the normal proteins (just by contact) and changing the function
