Action potentials and Propagation

Question 1

What is the electrochemical gradient?

Answer 1

The electrochemical gradient has two parts, the chemical gradient which is depending on concentration and the electrical gradient which is dependent on charge.
Sodium follows its concentration and the electrical gradient.
Potassium goes along its concentration gradient but not the electrical gradient.

Question 2

Nervous System overview

Answer 2

CNS ( brain and spinal cord) vs PNS (Nerves that branch into other parts of the body) then divided into Sensory neurons and Efferent neurons that are divided in somatic motor neurons which deals with skeletal muscles and autonomic neurons which can be sympathetic and parasympathetic however both control cardiac, smooth muscles and do daily tasks of the body.

Question 3

Central Nervous system (CNS)

Answer 3

Made up of the brain and spinal cord that analyze information and direct body response. Have neurons and Glial cells.

Question 4

Peripheral nervous system (PNS)

Answer 4

Manage sensory and motor skills then report things back to CNS like rapid change in polarity and charge. Made up of neurons

Question 5

Parts of a Neuron

Answer 5

Dendrites- Receive and process information like inhibitory vs excitatory signals.
Nucleus
Axon Hillock- the start of action potential and where the trigger zone is
Axon- guides the action potential down to the terminal
Myelin Sheath-insulation wraps around axon with Schwan cells that help keep the signal strong
Node of Ranvier- unmyelinated region where the ions enter through
Pre-Synapse at the terminal- the signal will travel to the post-synaptic neuron

Question 6

What are glial cells?

Answer 6

They are like glues that replicate the functions of other organ systems because the CNS is hidden behind a wall.
Schwan cells are a type of glial cells
They let helpful things in and harmful things out.

Question 7

Schwann cells

Answer 7

Provide cells that provide insulation and more effective connectivity

Question 8

Node of Ranvier

Answer 8

Section of unmyelinated axon membrane where action potential occurs. Where sodium comes into cell or potassium leave out of.

Question 9

How does the nervous system use axonal transport to deliver messages

Answer 9

Neurotransmitters are built and transported to synapses in vesicles down the axon.

Question 10

EM Resting membrane potential

Answer 10

When sodium and potassium and ATPase are balanced and in equilibrium.
Resting potential is -70mv which can be checked by voltage and is determined by K concentration due to its high content in cell.

Question 11

How do graded potential leads to action potential?

Answer 11

Graded potential are small changes in membrane potential according to stimuli size or pressure. It’s like water dropping, the father away, the less signal felt. Additive signals at the dendrites leads to action potential if the threshold is above -55 at it reaches the axon hillock trigger zone.

Question 12

Subthreshold vs suprathreshold graded potential

Answer 12

Sub is when the threshold isn’t met as the stimulus travels through the cell body and reaches the trigger zone leading to no action potential.
Supa is when the threshold is met because the signal is strong enough as it reaches the trigger zone and an action potential occurs

Question 13

How do action potential occur?

Answer 13

Action potentials occur with a depolarizing stimulus of sodium influx which causes membrane to rise above the threshold (+30)
Action potential created a domino effect of sodium channel opening one by one.

Question 14

Describe the action potential graph and it’s 8 steps

Answer 14

1- resting membrane potential at -70
2-A depolarizing stimulus hit the dendrites
3-Membrane depolarizes to threshold and voltage gated sodium channel open.
4-Sodium permeability into the cell rises as it enter and depolarize.
5-Sodium channels will close (+30) and potassium channels will slowly open.
6-Potassium leaves out the cell
7-As potassium keeps leaving then the cell becomes hyperpolarized (bellow -70)
8-Potassium channel closes
9- Sodium- Potassium pumps restore membrane resting potential by pumping sodium out and letting potassium in.

Question 15

Explain the two refractory periods and their excitabilities

Answer 15

Absolute refractory period- No response to stimuli will occur because the ions channels are open and the cells excitability are at zero.
Relative refractory period- As the cell get closer to resting potential, the cell excitability will increase and another action potential can occur if the stimuli is very strong.

Question 16

Describe the sodium ion channel

Answer 16

The sodium channel has an activation gate the door and an inactivation gate the little ball. During resting potential, the activation gate blocks flow. During depolarizing stimuli, the activation gate open then sodium will enter the cell. After the inactivation gate will close the channel and stop sodium flow. After repolarization, the channel will go to its normal configuration.

Question 17

Explain the sodium inrush and the positive feedback loop

Answer 17

When depolarization happens then the sodium channels open, sodium enter the cell which created more depolarization and more sodium entering the cell until it’s stopped when the inactivation gate closes. A positive feedback loop occurs.

Question 18

Signal conduction along axon

Answer 18

Action potentials jump via saltation from one node of Ranvier to another and the depolarization signal travels through the myelin sheath.
Demyelinating diseases reduce or block conduction due the current leaks that weaken action potential and lead to its failure

Question 19

Why is there no backflow?

Answer 19

No backflow occurs due to the absolute refractory period( ions channel are open and no response to stimuli) but also the charges being attracted to the one after them.

Question 20

KeM the CaT

Answer 20

Potassium K + controls the resting potential
Calcium Ca 2+ controls the threshold

Question 21

How does change in Kalemia affect resting potential.

Answer 21

-During normokalemia, when a signal is subthreshold graded potential then no action potential will occur and when a signal is suprathreshold then action potential will occur.
-When a cell is hypokalemic( low k+) then the membrane resting potential is lower due to the cell becoming hyperpolarized which makes it harder for for threshold to be met. A signal that is normally suprathreshold won’t cause action potential.
-When a cell is hyperkalemic (High k+) then the membrane resting potential will be closer to the threshold so a stimuli that would have been subthreshold now results in an action potential.

Question 22

How does change in calcemia affect resting potential?

Answer 22

Hypocalcemia( low Ca++) lowers the threshold and make cells more excitable due to less calcium blocking sodium from entering the cell which increases depolarization.
Hypercalcemia( High Ca++) block sodium movement into the cell which causes reduced depolarization and action potentials.