Action Potentials and Synapses

Question 1

define electrical gradient

Answer 1

when a rest, a membrane maintains the difference in electrical charges between the inside and outside of the cell, also known as polarization

Question 2

Is the inside of the cell more positive or negative compared to the outside?

Answer 2

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

Question 3

define selectively permeable

Answer 3

the membrane provides a barrier that permits some chemicals to pass more readily than others such as oxygen, water, and carbon dixoide.

Question 4

define concentration gradient

Answer 4

difference in the distribution of ions across the neuron’s membrane. 1 action potential will not change this gradient.

Question 5

why do neurons have a resting potentail?

Answer 5

in order for the neuron to be able to respond rapidly, the resting potentials prepares the neuron for such actions.

Question 6

define action potentials

Answer 6

• 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

Question 7

define hyperpolarization

Answer 7

an increase in polarization (electrical gradient) across a membrane, adding negative charge inside

Question 8

define depolarize

Answer 8

to reduce polarization towards zero across the membrane, and create a more positive charge inside

Question 9

define the all-or-none law

Answer 9

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

Question 10

what are the 3 main steps behind an action potential?

Answer 10

1. sodium ions are mostly outside and potassium is mostly inside
2. depolarizing the membrane opens Na-K pump
3. at the peak of the action potential, the pump closes

Question 11

define voltage-gated channels

Answer 11

membrane channels whose permeability to sodium depends on the volt difference across the membrane

only open/close depending on the voltage across the membrane

Question 12

how do local anesthetic drugs work?

Answer 12

they attach to the sodium pumps on the membranes, stopping action potentials from occuring

Question 13

define propagation of the action potential

Answer 13

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.

Question 14

describe how an action potential occurs

Answer 14

• 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

Question 15

define refractory period

Answer 15

the time when the cell resists the production of further action potentials

Question 16

describe the difference between an absolute and relative refractory period

Answer 16

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.

Question 17

what is myelin composed of?

Answer 17

it is an insulating material composed of fats and protiens

Question 18

define saltatory conduction

Answer 18

the jumping of action potentials from node to node (node of ranvier) due to myelin on the axon

Question 19

what is a neuron called when it doesn’t have an axon?

Answer 19

local neurons and they can only communicate via immediate neighbors

Question 20

define graded potential

Answer 20

in local neurons, a membrane potential that varies in magnitude in proportion to the intensity of the stimulus

Question 21

define synapse

Answer 21

a specialized gap as a point of communication between two neurons anatomy of chemical events

Question 22

define relexes

Answer 22

an automatic muscular response to a stimulus. reflex arc is a circuit from the sensory neuron to the muscle.

Question 23

describe the difference between a presynaptic and postsynaptic neuron

Answer 23

presynaptic is the part that delivers transmission and postsynaptic is the part that receives it

Question 24

define EPSP and IPSP

Answer 24

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

Question 25

can neurons create actions potentials without synapses input?

Answer 25

yes and its called spontaneous firing rate, a period of production of action potentials without synaptic input

Question 26

who are Hodgkin and Huxley?

Answer 26

- 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

Question 27

what are the ion concentration in and outside the cell?

Answer 27

outside/ECF: high in Na and Cl inside/ICF: high in K

Question 28

what are the ways that ions move in the cell?

Answer 28

1. diffusion: move down the concentration gradient 2. electrostatic force: same charge repel and opposites attract - these 2 forces can repel each other and cause no movement of ions

Question 29

define multiple sclerosis

Answer 29

- 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

Question 30

how does the myelin break down in MS?

Answer 30

1. The blood-brain barrier becomes porous 2. lymphocytes (killer cells) invade the brain 3. microglia go to lymphocytes and release inflammatory substances 4. the substances go to break down myelin (oligodendrocytes)

Question 31

how do the neurons become dysfunctional in MS?

Answer 31

- 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

Question 32

how do the axons conduct in MS?

Answer 32

- 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

Question 33

what are the 3 outcomes that can occur when an axon starts to degenerate?

Answer 33

1. remyelination of the axon by oligodendrocytes 2. new ion channels are inserted to allow the action potential to continue 3. a healthy neuron takes over the function of the damaged one

Question 34

how does the gut play a role in MS?

Answer 34

- 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

Question 35

how can the Epstein-Barr virus cause MS?

Answer 35

- 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

Question 36

what is the other explanation for how an axon moves and transports signals?

Answer 36

- 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

Question 37

define adhesion molecules

Answer 37

molecules that are on both pre and postsynaptic sides that hold the two together to go and create the synaptic celft

Question 38

what are the different kinds of neurotransmitters?

Answer 38

- amines: catecholamine (dopamine, epinephrine), indoleamine ( serotonin, melatonin), acetylcholine - amino acids: GABA (inhibitory), glutamate (excitatory) - peptides: oxytocin, insulin - gases: nitric oxide, carbon monoxide - other: ATP

Question 39

define SNARE proteins

Answer 39

docking and priming in the active zone to release NT into synaptic cleft

Question 40

what are the 3 kinds of vesicle pools?

Answer 40

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

Question 41

what are the steps in how a synapse releases its neurotransmitters/

Answer 41

1. action potential is created, Na and K pumps work to depolarize 2.Ca pumps open 3. Ca triggered exocytosis (vesicle fuses with the membrane of the synapse to release the contents) SNARE-mediated fusion to create fusion pore 4. NT gets released 5. ligand gated channels on postsynaptic side to try to depolarize 6. NT reuptake on presynaptic by transporter protein 7. NT attach to autoreceptor to communicate and give feedback 8. some neurons will be completely deactivated 9 NT can do retrograde transmission (when the signal travels back to original source)

Question 42

what are EPSP and IPSP?

Answer 42

Excitatory postsynaptic potentials: bringing the neuron closer to trigger an action potential, graded depolarization inhibitory... : graded hyperpolarization, bring the neuron away from threshold

Question 43

what is the difference between temporal and spatial summation?

Answer 43

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

Question 44

What are the kinds of receptors that can be on the postsynaptic neuron?

Answer 44

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

Question 45

what are 2 types of effects a NT can have?

Answer 45

convergence: mutliple NT can open up on channel divergence: one specific NT for each channel

Question 46

define spontaneous firing rate

Answer 46

a periodic production of action potentials even without synaptic input

Question 47

define autoreceptor

Answer 47

receptors on a presyn neuron that provide negative feedback by responding to the transmitter released by that neuron

Question 48

define hormone

Answer 48

chemical that is secreted by cells in one part of the body an conveyed by the blood to influence other cells

Question 49

define the pituitary gland and its two parts

Answer 49

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

Question 50

define tripartite synapse

Answer 50

- axon terminal, astrocyte, dendritic spine

Question 51

what are the different kinds of synaptic connections you can have?

Answer 51

presynaptic-postsynaptic axon-(dendritic,somatic,axonic)***most common dendro-(dendritic,somatic,axonic) somato-(dendritic,somatic,axonic)

Question 52

what is the war of soups and sparks?

Answer 52

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

Question 53

define electrotonic synapse

Answer 53

- 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

Question 54

define connexon

Answer 54

lies on the surface on the cell's membrane and create a central pore where molecules can move through

Question 55

how do mixed synapses work?

Answer 55

- 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)

Question 56

define neuropeptide

Answer 56

- 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

Question 57

define co-transmission

Answer 57

a single neuron can release multiple kinds of neurotransmitters

Question 58

define amyotrophic lateral sclerosis (ALS)

Answer 58

- 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

Question 59

what are the possible causes of ALS?

Answer 59

genetic: gene mutations (SOD1), proteins misfold/impaired function, impairment of axonal transport environment: smokers, who consume cycad seeds, toxic chemicals in water

Question 60

define creutzfeldt-jakob disease

Answer 60

- 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