Chapter 2: Continued

Question 1

Thanksgiving

Answer 1

Mmmm

Question 2

What are the main reasons for the negative membrane potential at rest

Answer 2

Negative charged protein anions are the main reason and make the cell -100 mv but potassium diminishes the negativity to -70mv at rest

The sodium potassium pump also contributes to the resting potential because its throwing three positive potassium ions out and bringing two in

Question 3

How many different types of electrical responses can a nephron generate?

Answer 3

Graded electrical potential - small

Action potential - large

Question 4

Is the membrane permeable? To what?

Answer 4

The membrane is selectively permeable, allowing some chemicals to pass more freely than others. The protein anions (A-) are negatively charged and are too large to pass so they stay inside the cell.

Sodium, potassium and chloride pass through specified channels

Question 5

What protein channels are open / closed when the membrane is at rest?

Answer 5

Na+ channels are closed, and K+ channels are partially closed allowing the slow passage of K+. Some K+ comes inward due to electrical attraction. But more K+ leaks out down the concentration gradient

Question 6

What does the resting potential of a neuron refer to?

Answer 6

The state of a neuron prior to the sending of a nerve impulse

Question 7

What is the electrical charge of the membrane?

Answer 7

It is slightly negative on the inside relative to outside at -70 mv

Question 8

What is an electrical gradient

Answer 8

The neuron membrane maintains an electrical gradient, which is a force acting on ions due to the difference in the electrical charge on the inside and outside of the cell.

Question 9

What is the concentration gradient?

Answer 9

The difference in number of ions present inside relative to outside of the neuron

Question 10

What is the electrical polarization?

Answer 10

At rest, the membrane maintains an electrical polarization (inside vs outside electrical charge difference), due to the 1) anions, 2) k+concentration and electrical gradients and 3) Na+/K+ pump

Question 11

What kind of transport is the sodium-potassium pump

Answer 11

The sodium-potassium pump is a protein complex that continually pumps 3 sodium ions out of the cell, while drawing two potassium ions into the cell. It helps to maintain the electrical gradient

Because na+ and k+ ions are being moved against their concentration gradient they need energy for it to occur

Question 12

What happens in a graded electrical potential?

Answer 12

The resting potential remains stable until the neuron is stimulated.

Hyperpolarization is due to an effluent of k+ ions (or an influx of CI- ions) making the inside more negative

Depolarization is due to an influx in Na+ ions

Typically occur on the dendrites and soma

Question 13

What is an action potential?

Answer 13

Any stimulation beyond a certain level, called the threshold of excitation, produces sudden massive depolarization

Na+ channels open and permit a rapid massive flow of these ions into the cell.

Occurs in axon

Question 14

What kind of channels are sodium channels?

Answer 14

Sodium channels are voltage activated channels whose permeability depends upon the voltage difference across the membrane

Requires high positive depolarization to occur

Question 15

First step of an action potential at a molecular basis

Answer 15

At rest the Na+ channels are closed

The membrane at the axon hillock depolarizes corresponding to the arrival of the graded electrical potentials.

Question 16

Second step of action potential at a molecular basis

Answer 16

When the action potential reaches the threshold, na+ channels open wide resulting in an influx of ions triggering the depolarization phase of the action potential

The inside state of the region of the neuron becomes more and more positive as na+ ions enter.

Gets more positive obv

Question 17

Action potential at a molecular basis step 4

Answer 17

With increasing depolarization the electrical gradient for k+ flips, and the k+ channels open wide, permitting k+ to exit down its concentration and electrical gradient

Then, as the depolarization reaches its maximum, the Na+ channels close

Question 18

Action potentials on a molecular basis Step 4

Answer 18

As K+ to exit the reporalization phase of the action potential occurs.

The membrane potential returns approaching threshold, and the k+ channels close

Question 19

Action potential molecular basis step 5

Answer 19

The Na-K pump restores ionic distribution and the resting membrane potential to -70mv

Question 20

When do sodium ions cross?

Answer 20

During the peak of the action potential

Question 21

When do potassium ions cross

Answer 21

Later in the opposite direction, helping to return the membrane to its original negative inside polarization

Question 22

What is the all-or-none law

Answer 22

It states that the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated the ap

Question 23

What happens in a neuron after an action potential?

Answer 23

The neuron has a refractory period during which time the neuron resists the production of another action potential

Question 24

What is the absolute refractory period?

Answer 24

It is the first part of the period in which the membrane cannot produce an action potential

Question 25

What is the relative refractory period

Answer 25

It is the second part in which it take a stronger than usual stimulus to trigger An action potential

Question 26

Where does an action potential begin?

Answer 26

In the neuron the action potential begins at the axon hillock, which is a swelling where the axon exits the soma

Question 27

What is propagation of the action potential

Answer 27

Is the phrase used to describe the transmission of the action potential down the axon

Question 28

Steps to an action potential

Answer 28

If the electrical responses added up can add to -50mv at the axon hillock then an action potential is initiated

Then it goes to the axonial endings where the neurotransmitter is being housed

Question 29

Steps to an action potential

Answer 29

If the electrical responses add up to -50mv at the axon hillock then an action potential is intiated

Then it goes to the axonal endings where the neurotransmitter is being housed

The action potential is regenerated at each node of ranvier in the mylien

This is called saltatory conduction

This effect spreads the conduction of the impulse down the axon

How does the next node know when to fire?

Saltatory conduction is just the perception its leaping from node to node

First event of an action potential is the sodium channel at the first node in the axon hillock

So sodium is in high concentration outside the cell

So positive sodium ions wont go inside because its negative and it wants to go down its concentration and electrical gradient

This leads to depolarization

Question 30

What is the myelin sheath

Answer 30

Insulting material of fats and proteins

Question 31

Nodes of ranvier

Answer 31

At each node, the action potential is regenerated by a chain of positively charged ions pushed along by the previous segment

Question 32

Saltatory conduction

Answer 32

Describes the leaping of the action potential from node to node

Provides rapid conduction of impulses

Conserves energy

Question 33

What does myelin do?

Answer 33

With no myelin the inside positive charge would decay with distance

With myelin inside positive charge is sustained above threshold permitting ap at next mode

Think of a stoned dropped in water producing a circular wave of passive spread

Question 34

Arrival of action potential at the axonal ending

Answer 34

Synaptic vesicles fuses with the presynpatic membrane and the neurotransmitters are released into the synapse and bind tot he receptors on the cell body and/or dendrites

This causes channels nearby to open dependent on the type of neurotransmitter positive / negative channel —> going to cause hyperpolarization or depolarization

Question 35

The arrival of the action potential into axonal ending causes

Answer 35

Triggers voltage gated Ca++ channels to open. The influx of Ca+ ions induces the migration of transmitter filled vesicles towards the pre synaptic membrane

Question 36

What is exocystosis

Answer 36

It refers to the excretion of the neurotransmitter from the presynaptic terminal into the synapse; the synaptic vesicles fuse with the membrane and rupture releasing their contents into he synapse

The neurotransmitters quickly diffuse across the synapse chemically binding to the matching receptor

Each activated receptor in turn triggers ion channels to open in the receiving cells membrane, allowing ions to flood across, changing the electrical potential across the post synaptic membrane.

Question 37

What did Charles Scott Sherrington discover

Answer 37

He coined the term synapse to describe the specialiazed gap that existed between neurons.

He conducted his research investigating hoe neurons communicated by studying reflexes

He used behavioral observations to infer major synaptic properties

1857-1952

Observed difference in speed conduction in a reflex arc from measured axon potentials

Speed along axon versus at synapse(slower and more variable)

Question 38

Temporal summation

Answer 38

Sherrington observed that repeated stimuli over a short period of time produced a stronger response

This led to the idea of temporal summation or that repeated stimuli when occurring close enough in time can have a cumulative effect and can produce an action potential if the EPSPs combine to exceed threshold

Question 39

Spatial summation

Answer 39

Sherrington saw that several stimuli on a similar location produced a reflex when a single stimulus did not

This led to the idea of spatial summation that synaptic input at the same time from several locations can have a cumulative effect and trigger an action potential

Question 40

What is an inhibitory post-synaptic potential

Answer 40

Occurs when synaptic input selectively opens the gates for positively charged potassium ions to leave the cell of for negatively charged chloride ions to enter the cells.

Serves as an action “brake”, that suppresses excitation

Question 41

Sherrington 3 major findings

Answer 41

1. Reflexes are slower than the conduction along an axon
2. Several weak stimuli presented at slightly different times or slightly different locations produces a stronger reflex than a single stimulus does

Question 42

John Carew Eccles

Answer 42

A student of Sherrington developed convincing evidence that signals do not spark across synapse but rather operate by releasing packages of chemicals called neurotransmitters

They travel across the synapse and allow communication between neurons

They bind to receptors on the post-synaptic membrane and induce a graded electrical potential

Question 43

Loewi

Answer 43

A pharmacologist was the first to show that the electrical impulses generated by nerve cells are transmitted to other cells via a chemical messenger

Identified the neurochemical transmitter as vagusstoff (vagal substance) because it was released from the vagus nerve where it was electrically stimulated

Later when the chemical structure was determined would be given the name acetylcholine

Question 44

What is an antagonist

Answer 44

Drugs block the effects of neurotransmitters

Question 45

Agonist

Answer 45

Drugs mimic or increase the effects of neurotransmitters

Question 46

Steps of chemical events at the synapse

Answer 46

1a. Synthesis of peptide neurotransmitters and vesicles

1b. Synthesis of smaller neurotransmitters such as acetylcholine

2. Transport of peptide neurotransmitters
3. Action potential causes calcium to enter, releasing neurotransmitter
4. Neurotransmitter binds to receptor
5. Separation from receptors
6. Reputable of neurotransmitter by transporter protein
7. Postsynaptic cell releases retrograde transmitters that slow further release from presynaptic cells
8. Negative feedback sites respond to retrograde transmitter or to presynaptic cells own transmitter

Question 47

Ssris do what

Answer 47

Act to increase the amount of serotonin that is permitted to hang around in the synapse by blocking the reuptake mechanism

Effect is to inhibit excessive or inappropriate emotions or moodiness

Also tricked the dopamine transports into retrieving serotonin into dopamine vesicles