C2.2

Question 1

Resting and Action Potential

Action Potential?

Answer 1

• A sequence of events that allows electrical impulses to travel through a nueron.
• They are how nuerons send messages within a single nueron.
• Steps largely involve the change in the relative charge of the nueuron’s axons due to the movement of sodium and potassium ions.

Question 2

Resting and Action Potential

Resting Potential?

Answer 2

• When a nueron is not currently sending a messge but is ready to recieve and transfer one.
• Resting: not currently transmitting a mesage
• Potential: ready to initate when signalled (by a nuerotransmitter)
• At RP, the nueron is relatively negative, charged inside the axon at -70mV.

Question 3

Resting and Action Potential

Membrane Potential?

Answer 3

• Refers to the difference in charge between the inside of the axon (cytoplasm) and the outside of the axon (the extracellular environment).
• Measured using a volatge meter
• When an AP is initiated, the movement of Na+ ions insude cause the axon to rapidly become positive in relative charge.

Question 4

Resting and Action Potential

Polarized?

Answer 4

• When the axon is at resting potential - meaning it has negative charge inside the axon.

Question 5

Resting and Action Potential

Schwann Cell?

Answer 5

• Speciazlied living cells that wrap around the axon.
• The cytoplasm loops around, eventually pushing out the nueclus and organelles, leaving only a thick layer of myelin.
• These cells insulate the axon and ions can’t move in and out of the axon in areas covered in schwann cells.
• AP can only occur in the gaps between myelin.

Question 6

Resting and Action Potential

Nodes of Ranvier?

Answer 6

• Gaps between the myelin
• There are functional ion channels in the nodes that initiate and propogate (move along) action potentials.
• APs move straight through myelinated regions without any ion movement, then are strengthened/propogated at the ion channels in the Nodes

Question 7

Resting and Action Potential

Role of Neuron parts: Dendrites

Answer 7

• Short branched nerve fibres at the end of the nueron.
• They’re covered in different receptors for different types of nuerotransmitters.
• Branching expands the area of the synapses covered with receptors to increase reception of messages.
• Receptors on the dendrites recieve messages from the nuerotransmitters and initiate action potentials down the axon to deliver messages to the next cell along.

Question 8

Resting and Action Potential

Role of Nueron parts: Axon

Answer 8

• Elongated section of the nueron
• Contains cytoplasm and ion channels along the membrane

Question 9

Resting and Action Potential

Role of Neuron parts: Terminal Buttons

Answer 9

• End of the axon branches, thin sections (axon terminals)
• Effective for increasing how much of the synapse the neuron is covering.
• At the end of each terminal there is a terminal button that has neurotransmitters stored within the vesicles
• When AP reaches end of termianl –> triggers Release of neurotransmitters from membrane of terminal button into the synapse.

Question 10

Resting and Action Potential

Sodium & Potassium at Resting Potential

Answer 10

• At resting potential, potassium ions are inside the axon and the sodium ions are outside (both are positively charged)
• The greater amount of Na+ outside the nueron renders the inside relatively negative

Question 11

Resting and Action Potential

Events during an Action Potential

Answer 11

• Sodium channels open in response to a neurostransmitter.
• Sodium ions thus move into the axion, making the inside positively charged
• This triggers the opening of the potassium channel causing them to exit the axon, returning the charge back to negative
• Finally, the ions move back to their original position via the sodium potassium pump

Question 12

Resting and Action Potential

Role of ATP in Neural Transmission

Answer 12

• Following an AP, the sodium and potassium ions aren’t in the correct position for resting potential
• Hence, the Na/K pump pumps out 3 Na+ ions and in 2 K+ ions
• This requires a shape change, which requires ATP

Question 13

Resting and Action Potential

Myelination and Speed of Nerve Impulses

Answer 13

• If myelinated, the negative charge moves straight through the area covered in myelin, not using the ion channels.
• This increases the speed of transmission
• Transmission is also faster for axons with greater diameters by allowing ions to flow easier

Question 14

Action Potential Propagation

Depolarisation?

Answer 14

• When the reception of excitatory nuerotransmitters is sufficient to create a voltage charge, it causes the opening of sodium ion channels.
• Sodium passively diffuses into the axon, creating a highly positive charge in that area.
• This change from relatively negative at resting potential to a now very positive charge is depolarisation.

Question 15

Action Potential Propagation

Repolarisation?

Answer 15

• Following depolarization, voltage gated postassium ion channels open, enabling potassium to diffuse out.
• This enables the inside of the neuron to be negative once again.
• The K+ ions close more slowly than Na+, allowing the axon to end up more negative (hyperolarisation) then it was at rest time.
• This return to negative charge caused by potassium movement is repolarization.

Question 16

Action Potential Propagation

Threshold Potential?

Answer 16

• A minimum/necessary change in the charge of the axon for an action potential to begin.

Question 17

Action Potential Propagation

Propagation?

Answer 17

• APs start of the first set of ion channels at the end of the axon (closest to dendtrites)
• The electrical impulse travels down the whole length of the axon.
• The volatge change that opened the first set of ion channels causes the next set of sodium channels to open
• This movement of the negative charge down the axon in propagation.

Question 18

Action Potential Propagation

Oscilloscope Traces?

Answer 18

• An electronic test graphically displaying the voltage differences between two areas and any change that occurs in the voltage difference.
• Visualizes the voltage changes that occur in an axon during an action potential

Question 19

Action Potential Propagation

Saltatory Conduction

Saltatory: “To jump”

Answer 19

• When an action potential jumps from one node of Ranvier to another.
• The channels covered in myelin aren’t active so the next set of channels to open in the actoin potential propagation are next in the node of ranvier.

Question 20

Action Potential Propagation

Depolarisation as an All-Or-Nothing event.

Answer 20

• Action potentials aren’t ever too big or too small, they are all the exact same.
• If the threshold is not reached, then no action potential is initiated.
• If threshold (-50mV) is reached, the sodium channels open and depolarization occurs
• Always causes the voltage change from -70mV at rest to +30mV.

Question 21

Action Potential Propagation

Voltage changes on an Oscilloscope

Answer 21

• Curve begins at resting potential, sitting at -70mV.
• When depolarization occurs, a rapid upwards increase in charge occurs to +30mV due to Na+ ions moving in.
• Quickly following, the charge drops to an even lower charge (hyperpolarization due to slower close of K+ channels) during repolarization
• Curve then returns to -70mV when Na/K pump returns ions to resting potential.

Question 22

Action Potential Propagation

Myelin Sheath and ATP expenditure

Answer 22

• Every set of Na/K pumps that propagate an action potential require ATP to return the ions to rest
• Without myelin, there’s many more ion channels and more Na/K pumps that require ATP
• With myelin, fewer pumps are needed

Question 23

Action Potential Propagation

Synapse?

Answer 23

• The junction between two neurons/ where a neuron contacts a muscle cell (neuromuscular junction)
• Technically, the gap between two cells in the synpatic cleft, as the synapse includes the terminal buttons of the presynaptic neuron and the dendric ends of the postynaptic neuron and the cleft of space between them.

Question 24

Action Potential Propagation

Synaptic Cleft

Answer 24

• Very small gasp between two neurons.
• Neurotransmitters are released into this space where they diffuse to reach the receptors on the dentries of the neighbouring neurons

Question 25

# Action Potential Propagation Excitatory Postsynaptic Potential?

Answer 25

* The term for the **depolarization of a postsynaptic membrane** leading to the **intitiation of an action potential** * Due to the binding of **excitatory neurotransmitters** which open Na+ ion channels causing a positive change in the axon.

Question 26

# Action Potential Propagation Difference between Pre and Post- Synpatic Neuron?

Answer 26

* **Pre-synaptic**: neuron releases neurotransmitters into the synapse **after an action potential moves through it.** (facing away from synapse) * **Post-synaptic**: has its **dendrites facing the synapse** for neurotransmitters to bind to the **receptors on the dendrites**

Question 27

# Action Potential Propagation Locations of Neurons in the Nervous System | (focusing on the synapses between two neurons within the CNS and PNS)

Answer 27

* Neurons in central and peripheral nervous systems * Synapses thus exist between: 1. The sensory receptor and initial sensory neuron. 2. Between neurons in the central and peripheral nervous system. 3. In the specific neuromuscular junctions at motor units.

Question 28

# Action Potential Propagation Role of Calcium in the Synapse

Answer 28

* In **terminal buttons** there are voltage gated **Ca2+ ion channels** that are normally closed, keeping calcium outside the neuron. * When the **positive charge** of the **action potential** reaches the axon terminal the **depolarization** of that area causing the Ca2+ channels to open and calcium to enter the terminal buttons. * Calcium **triggers the movement of vesicles** to the cell **membrane**, leading to the exocytosis of **neurotransmitters into the synapse**.

Question 29

# Action Potential Propagation Neurotransmitters initiate Action Potentials

Answer 29

* Most neurotransmitters bind directly to **volatge gated ion channel receptors** * This binding causes the ion channel to **open allowing Na+ ions** to enter (or in the case of inhibitory neurotransmitters, Cl-) * For **excitatory neurotransmitters** the influx of Na+ causes the voltage change to reach the threshold, opening the **first sodium channels** of the axon, causing the **depolarization** and the **initiation of an action potential**

Question 30

# Action Potential Propagation Acetycholinesterase in the Synapse | "ase" - enzyme

Answer 30

* An **enzyme in the synapse** that breaks down acetylcholine and recycles the choline into the **presynaptic neuron**. * Important so as to continue continue to trigger action potentials without stimuli.

Question 31

# Excitatory and Inhibitory Neurotransmitters Exogenous Chemicals?

Answer 31

* Enter the body from **the environment**, but can interact with cell signalling pathways. * Chemicals are often naturally found it food/the environment/ or can be synthetically produced.

Question 32

# Excitatory and Inhibitory Neurotransmitters Neonicotinoids?

Answer 32

* A chemical created, structurally similar to nicotine. * Doesn't create an action potential but **binds irreversibly** (becomes enzymes can't break them) to the **receptors**, meaning that **acetycholine can't bind**, causing muscle paralysis and death. * Used in **insecticides**.

Question 33

# Excitatory and Inhibitory Neurotransmitters Hyperpolarization?

Answer 33

* **Inhibitory neurotransmitters** have the opposite effect of excitatory ones. * They makes action potentials **less likely to occur** * The neurontransmitter does bind and open an **ion channel**, but this is a **chlorine channel**, sending **negative Cl- ions** into the axon, making it more negative.

Question 34

# Excitatory and Inhibitory Neurotransmitters Consciousness?

Answer 34

* Our awareness and ability to knowlingly think and consider and be aware of experiences. * Out ability to plan complex actions, it is the result of complex interactions that are holistically creating an emergent property

Question 35

# Excitatory and Inhibitory Neurotransmitters Ion Movement and Pain Perception

Answer 35

* Free nerve endings in **nocioreceptors** that have ion channels at the ends. * When exposed to heat/acid/etc., the ion channels **open and sodium moves in** initiation an action poential that delivers the message of pain to the **spinal cord and then brain**. * Relates to **threshold**, as the pain stimuli must be sufficient to cause **depolarization of the nocioreceptor**

Question 36

# Excitatory and Inhibitory Neurotransmitters Cocaine and Dopamine Transmission

Answer 36

* Cocaine interacts with dopamine in the **synapse** * Dopamine is a neurotransmitter associated with pleasure (released in response to positive actions, our brains wants us to repeat it) * **Cocaine binds to the reuptake protein** transporters in the **terminal buttons** * This **prevents dopamine** from going back into the presynaptic neuron. * Instead it **remains in the synapse**, bidning **over and over to receptors**, generating repeated pleasure signals that create a feeling of **euphoria**

Question 37

# Excitatory and Inhibitory Neurotransmitters Excitatory vs Inhibatory Neurotransmitters

Answer 37

* **Both agonists**, meaning they bind to **receptors on dendrites**, and both lead to **ion channels opening**. * **Excitatory** neurotransmitters let positive **Na+** in which **depolarizes** the axon leading to an **action potential** to travel through to another neuron. * **Inhibatory** neurotransmitters let negative **Cl-** in which makes the axon **more negative**, **not causing an action potential** but instead making it more difficult.

Question 38

# Excitatory and Inhibitory Neurotransmitters Capsaicin in Peppers and Sensory Perception

Answer 38

* Capsaicin seeds have a chemical that triggers **nocioceptor receptors** causing a pain sensation.

Question 39

# Excitatory and Inhibitory Neurotransmitters Reductionism vs Emergence

Answer 39

* **Reductionism**: trying to understand the **specific** functioning of individual parts, often not the whole. * **Emergence**: looks at interactions and holistic functioning.