Nervous system flashcards

Question 1

What two processes are needed to establish a resting potential in neurons?

Answer 1

Active transport and passive transport

Question 2

What is the difference between active transport and passive transport?

Answer 2

Active transport requires ion pumps, requires energy, and pumps ions against their concentration gradient.

Passive transport uses ion channels (if transporting ions), does not require energy, and moves ions down their concentration gradient.

Question 3

How many Na+ ions and K+ ions does a sodium/potassium ion pump move and where?

How does the pump use ATP to actively move these ions?

Answer 3

A sodium/potassium ion pump transfers 3 Na+ ions out of the cell, and 2 K+ ions into the cell.

This process requires energy, and the energy is used through the hydrolysis of ATP into ADP and a phosphate ion. The phosphate ion binds to the pump, and causes the pump to undergo a conformational change. Ions are released, then the phosphate ion is released returning the pump to its original structure.

> 3 Na+ ions binds to the pump.
ATP is hydrolysed and a phosphate ion binds to the pump.
Pump undergoes a conformational change and its affinity for Na+ is decreased, so Na+ is released outside the cell.
2K+ from outside the cell binds to the pump, and then the phosphate ion is released.
Pump returns to its original shape and 2 K+ is released inside the cell.

Question 4

What two factors determines how ion channels work?

Answer 4

Gating- What causes a channel to open or activate? What then causes it to close or deactivate?

Permeation- What ions are capable of passing through this channel? How much current can flow through this channel?

Question 5

There are 4 main factors that are capable of activating ion channels. What are they?

Answer 5

Chemicals- The binding of a ligand to a receptor connected to the ion channel. (Ligand gated ion channels).

Electrical- Voltage gated ion channels (opening and closing determined by electrical gradient of membrane).

Mechanical- Mechanoreceptors (responds to changes in pressure applied).

Thermal- Chemoreceptors (responds to changes in temperature).

Question 6

What type of ion channels are involved in action potential generation in neurons?

Answer 6

Sodium and potassium voltage gated ion channels

Question 7

Describe the amplitude and the opening times of an ion channel in general.

Answer 7

The amplitude of the channel current of ions is constant everytime the ion channel opens and closes.

Current- movement of electrical charges.

It should be noted that the duration for each closing and opening is not constant, as well as when it opens. The duration for which an ion channel opens for is very fast and quick- it is only open for milliseconds.

Question 8

The movement of ions through an ion channel is passive, unlike ion pumps, so what drives or causes ions to move through this channel?

Answer 8

An electro-chemical gradient. This is a net gradient of the chemical gradient (concentration gradient of an ion) and electrical gradient (distribution of charges across the membrane).

Question 9

One factor that determines how ion channel function is permeation. What does permeation mean?

Answer 9

Permeation determines what ion can enter the ion channel. An ion’s accessibility to the channel is determined by size (is it too big to come through the channel?) and charge (is it too charged to come through the channel?).

Question 10

What is the permeability of an ion channel determined by?

Answer 10

Selectivity filter in the ion channel’s structure.

Question 11

What are leaky channels?

Answer 11

Leaky channels are non-gated channels, so they are constantly open (they do not need a stimulus in pressure, temperature or voltage, or need ligand binding to open) and ions are constantly flowing through.

Question 12

Why are ion channels termed as ‘transmembrane proteins’?

Answer 12

The ion channels span the whole length of the membrane, so is in content with the internal and external environment.

Question 13

What membrane proteins are needed for establishing a membrane potential in neurons?

Answer 13

Ion pumps and ion channels (LEAKY ion channels!!).

Question 14

Define voltage, current and resistance.

Answer 14

Voltage- Electrical potential energy between two points (volts, V)

Current- movement of electrical charges (in biology this will be the movement of ions, like Na+). Amps (I).

Resistance- Hindrance to movement of ions (in biology plasma membrane provide resistance to flow of ions). Ohms (R).

Question 15

What are the rules about the generation and duration of action potentials and their stimulus strength?

Answer 15

Rule 1 is that in order for an action potential to be generated, the stimulus must reach the threshold value; this is the all-or-nothing principle- if the stimulus does not reach the threshold value, no action potential is generated.

Rule 2 is that nerve action potentials have a very short duration, about 1msec.

Rule 3 is that the size of a stimulus may vary, however the amplitude of each action potential is always constant- what varies is their frequency.

Question 16

What does it mean for the relative charges of inside and outside a cell if the overall charge is negative? (Neurons are negatively charged).

Answer 16

The inside of the cell is more negatively charged compared to the outside. (Inside has more negative charges and outside has more positive charges).

Question 17

Give a definition for resting potential.

Answer 17

The ion gradient at equilibrium across the membrane separates charge, which gives rise to a voltage. The voltage is known as the resting potential.

Question 18

What is the range of resting potentials normally in neurons?

Answer 18

-60 to -70mV

Question 19

The resting potential of different cells varies. What may cause the resting potential to vary between cells?

Answer 19

Chemical and electrical properties of ion flow.
Ion channels (especially leaky channels) present.
Ion pumps present.

Question 20

What are chemical forces, in terms of diffusion?

Answer 20

Chemical force is the driving force, acting to move a specific molecule or ion across the membrane, due to its concentration gradient.

Question 21

What are electrical forces, in terms of movement of an ion across the membrane?

Answer 21

Electrical forces are a driving force that moves an ion across the membrane due to the distribution of charges of all molecules across the membrane. The movement of the ion is determined by this rule: like-charges repel and opposite charges attract.

Question 22

What is an electochemical force?

Answer 22

An electrochemical force is the net driving forces of both chemical and electrical forces, causing the net movement of ions across the membrane.

Question 23

Describe the movement of K+ ions, assuming the membrane is only permeable to K+ ions. Assume the pumps have already done their job to pump 2K+ inside the cell.

Answer 23

> Inside the cell, there is a high conc of K+ and negatively charged proteins (A-).
K+ moves down the chemical gradient, so K+ starts moving out of the cell.
Accumulation of K+ outside the cell creates a more positive charge outside the cell compared to inside the cell (also remember inside the cell there is A-). An electrical gradient is established.
K+ starts to move back inside the cell, down the electrical gradient, as K+ is attracted to A- inside the cell.
As K+ continues to move down the chemical gradient out of the cell, the tendency for K+ to move back inside the cell grows due to a steeper electrical gradient.
At a point, enough K+ ions leaves the cell that the electrical force becomes strong enough to oppose further movement of K+ ions due to the chemical force, resulting in no movement of K+ ions.

Question 24

What is the equilibrium potential of potassium?

Answer 24

-94 mV

Question 25

Describe the movement of Na+ ions, assuming the membrane is only permeable to Na+ ions. Assume the pumps have already done their job to pump 3 Na+ outside the cell.

Answer 25

> Outside the cell, there is a high concentration of Na+ and Cl-.
Na+ travels down this chemical gradient into the cell, due to a chemical force.
As Na+ continues to move inside the cell, the inside becomes more increasingly positive compared to outside the cell.
The change in charge distribution causes an electrical force that pushes Na+ outside the cell, opposing the chemical force.
Eventually, the electrical force becomes large enough to oppose the chemical force, so there is no net movement of Na+.

Question 26

What is the electrochemical force at equilibrium?

Answer 26

0

Question 27

What is the equilibrium potential for Na+?

Answer 27

+60 mV

Question 28

If the equilibrium potential of K+ is -94mV and the equilibrium potential of Na+ is +60mV, how is total cell membrane -70mV?

Answer 28

The membranes permeability to different ions varies. The membranes is approximately 40 times more permeable to K+ ions at rest, than Na+ ions. This is because of more K+ ion channels being present in the membrane.

Question 29

Describe the changes in total membrane potential when establishing a resting potential, in terms of chemical and electrical diving forces, with the assumption the membrane is permeable to both Na+ and K+.

Answer 29

> As membrane is more permeable to K+, K+ ions flows out of the membrane faster down a concentration gradient, due to a chemical force.
With K+ leaving the cell, the inside becomes more negative and outside becomes more positive. This establishes an electrical gradient and allows Na+ to move in via an electrical force.
Increasing chemical gradient of K+ creates an electrical gradient for K+, so electrical force driving K+ inside the cell opposes chemical force driving K+ outside cell. The increasing chemical gradient of K+ also favours the inflow of Na+.
K+ outflow slows down and Na+ inflow speeds up. Membrane potential eventually stabilises.
Na+ / K+ pump counteracts any excess leakage flows to maintain gradient.

Question 30

Describe the changes in total membrane potential when establishing a resting potential, in terms of chemical and electrical diving forces, with the assumption the membrane is permeable to both Na+ and K+.

Answer 30

> As membrane is more permeable to K+, K+ ions flows out of the membrane faster down a concentration gradient, due to a chemical force.
With K+ leaving the cell, the inside becomes more negative and outside becomes more positive. This establishes an electrical gradient and allows Na+ to move in via an electrical force.
Increasing chemical gradient of K+ creates an electrical gradient for K+, so electrical force driving K+ inside the cell opposes chemical force driving K+ outside cell. The increasing chemical gradient of K+ also favours the inflow of Na+.
K+ outflow slows down and Na+ inflow speeds up. Membrane potential eventually stabilises.
Na+ / K+ pump counteracts any excess leakage flows to maintain gradient.

Question 31

When establishing membrane potential, what is the direction of chemical forces and electrical forces of a K+ ions?

Answer 31

Chemical force driving K+ outside the cell. Electrical force driving K+ inside cell.

Question 32

When establishing membrane potential, what is the direction of chemical and electrical driving forces of a Na+ ion?

Answer 32

Both chemical and electrical forces drive Na+ inside cell. Initially there is already a chemical force driving Na+ inside cell due to Na+ own concentration gradient. Then with the additional outflow of K+ ions and the establishment of an electrical gradient, it creates an electrical gradient that drives Na+ inside the cell.

Question 33

If the direction of chemical and electrical forces of Na+ is going inside the cell, why is the total membrane potential not more positive than -70mV?

Answer 33

The membrane is 40 times more permeable to K+ ions than Na+ ions due to more leaky ion channels present in the membrane. Therefore any movement of Na+ ions are comparatively insignificant compared to movement on K+. K+ is also primarily moving out the membrane which gives a negative membrane potential.

Question 34

What is the equilibrium potential of an ion?

Answer 34

The equilibrium potential is the measured potential difference across the membrane for this ion, when the chemical and electrical driving forces of this ion is balanced so that the ion comes to rest. (And there is no net electrochemical force of this ion).

Question 35

What can the Nernst equation help us calculation?

Answer 35

It can calculate the equilibrium potential of an ion, based on knowing the ion concentration inside and outside the cell.

Question 36

What can the Nernst equation be abbreviated to for monovalent ions at 37 degrees Celsius?;

Answer 36

E ion = 61 × log 10 ([ ion oustide] / [ ion inside])

Question 37

What is membrane potential?

Answer 37

The potential difference across the membrane due to the distribution of charges. Also refers to inside the cell compared to outside the membrane.

Question 38

What is membrane potential?

Answer 38

The potential difference across the membrane due to the distribution of charges. Also refers to inside the cell compared to outside the membrane.

Question 39

What are the three main stages when an action potential in generated?

Answer 39

Depolarization, repolarization and hyperpolarization

Question 40

What are the difference between graded and action potentials?

Answer 40

One key difference between graded and action potentials is that for each graded potential, their amplitude changes depending on the size of the stimulus (so it is proportional). On the other hand, even if the size of the stimulus changes, action potentials will always have the same amplitude (frequency of action potentials may change).

Another key difference is that there is no threshold potential that needs to be reached for graded potentials to be generated- for every stimulus, a graded potential is generated. On the other hand, the threshold potential of the membrane needs to be -55 mV for action potentials to be generated.

The duration of graded potentials is short and variable, whereas the duration of action potentials is short and fixed (normally 1-2 milliseconds).

In graded potentials, there is no refractory period, but in action potentials there is a refractory period.

Last key difference is that graded potentials uses ligand gated ion channels (as well as mechanoreceptors and chemoreceptors) to be generated, and action potentials uses voltage gated ion channels to be generated.

Question 41

What is a graded potential?

Answer 41

Graded potentials are caused as a response to a stimulus and graded potentials travels from dendrites or cell body to the axon hillock.

Question 42

What is an action potential?

Answer 42

Action potentials are caused by the accumulation of graded potentials, and travels from the axon hillock to the end of the neuron.

Question 43

Graded potentials can be hyperpolarizing or depolarizing. What does it mean if the graded potential is hyperpolarizing, and what is it caused by?

Answer 43

If a graded potential is hyperpolarizing, it causes a more negative membrane potential from the dendrites to the axon hillock, via the influx of negative ions (or efflux of positive ions).

Hyperpolarizing is caused by inhibitory neurotransmitters, like GABA and glycine. These neurotransmitters can bind to chloride ion channels in the post synaptic neuron, causing an influx of Cl- into the neuron, decreasing membrane potential (equally it can bind to K+ ion channels and cause the efflux of K+).

The bigger the stimulus, the bigger the hyperpolarizing potential.

Question 44

Graded potentials can be hyperpolarizing or depolarizing. What does it mean if the graded potential is depolarizing, and what is it caused by?

Answer 44

If a graded potential is depolarizing, it causes a more positive membrane potential (from the dendrites to axon hillock) by the influx of positive ions, or efflux of negative ions.

Depolarizing graded potentials is caused by the release of excitatory neurotransmitters, like acetylcholine and glutamate. These neurotransmitters binds to the Na+ or Ca2+ ions channels in the post synaptic neuron, which causes an influx of the Na+ or Ca2+ into the neuron.

The bigger the stimulus, the bigger the depolarizing graded potential.

Question 45

What type of graded potential invokes an action potential?

Answer 45

Depolarizing graded potentials invokes action potentials.

If we think about it, the resting potential is -70mV and the threshold to invoke action potentials is -55mV. Hence, it would make sense that we would need depolarizing graded potentials, to make the membrane potential more positive to reach this value.

Question 46

What is the axon hillock?

Answer 46

The axon hillock is region of the neuron that connects the cell body to the axon.

This is where action potentials are generated because this is the point where voltage gated ion channels start to be present in the neuron.

Question 47

What is decremental conduction?

Answer 47

Decremental conduction only applies to graded potentials only, and is basically when they weaken as they move away from their site of origin.

On the other hand, action potentials can travel the length of the axon with the same amount o strength.

Question 48

In what part of the body do graded potentials occur?

Answer 48

At the tips or surface of the body, where there are receptors present. When pressure is exerted on this receptor, or an increase in temperature, or ion binds to the channels on the receptor, a graded potential is stimulated.

Like in a Pacinian corpuscle, a graded potential is caused by a change in pressure exterted.

Question 49

In order to reach the threshold value for the generation of an action potential, graded potentials may need to be added and summed together. It can be done in two ways: temporal summation or spatial summation. How do these two techniques differ?

Answer 49

Temporal summation refers when the same stimulus generates graded potentials frequently and rapidly, one after another. With a higher frequency of graded potentials, the threshold membrane potential can be reached to generates action potentials.

On the other hand, spatial summation is when different neurons join to one post synaptic neuron and they each have a different stimulus. The graded potential for each stimulus in each neuron is generated simultaneously into the post-synaptic neuron to reach a threshold value to generated an action potential.

Question 50

How do inhibitory neurotransmitters affect action potentials?

Answer 50

The release of inhibitory neurotransmitters causes hyperpolarization and hence affects whether or not the threshold value -55mV is reached. If the time of when the threshold value is reached is dependent on inhibitory neurons, then the time of when action potentials are generated is also dependent on the inhibitory neurotransmitters.

Question 51

What is the difference depolarization and rapid depolarization?

Answer 51

Depolarization occurs when the membrane becomes more positive due to depolarizing graded potentials. These graded potentials increase the membrane potential to +55mV and works at a relatively slower pace to action potentials.

On the other hand, when voltage gated ion channels are activated, they work at such a fast pace during depolarization, hence the name rapid depolarization.

Question 52

Describe the stages in the generation of an action potential.

Answer 52

1. Graded potentials increase membrane potential from -70mV to -55mV, so threshold value is reached.
2. Voltage gated sodium ion channels open, and there is an influx of Na+ into the cell. Here, Na+ is moving down its concentration and electrical gradient. When the neuron becomes more positive, more Na+ voltage gated channels open, causing a further increase in membrane potentials towards Na+ equilibrium potential.
3. Upon reaching a membrane potential of about +40 mV, Na+ voltage gated ion channels start to close and K+ voltage gated channels starts to open. K+ ions moves out the neuron. Membrane potentials starts to head back to -70 mV (close to equilibrium potential of K+).
4. K+ voltage gated ion channels are still open causing repolarization to excessed -70mV (so more negative, even close to K+ equilibrium potential)- this is hyperpolarization.
5. Na+/K+ pumps used to return membrane to its resting potential of -70 mV.

Question 53

Why does hyperpolarization occur?

Answer 53

K+ voltage gated ion channels stay open longer during repolarization, than when Na+ voltage gated ion channels were open during depolarization.

Wit K+ voltage gated ion channels being opened for a longer time period, more K+ left the neuron (than Na+ went in the neuron during depolarization), leading to a more membrane potential.

Question 54

Na+ voltage gated ion channels open with depolarization, and should close with depolarization. Except, Na+ voltage gated ion channels closes when the membrane is starting to repolarize. How is this possible?

Answer 54

A Na+ voltage gated ion channel has two gates- an activation gate and an inactivation gate. The activation gate is closed at rest and opens quickly during depolarization. The inactivation gate is open at rest and closes with depolarization slowly.

Question 55

During an action potential, which ion has more permeability, Na+ or K+?

Answer 55

Na+ has a higher permeability thang K+ during activation potentials.

Question 56

During spatial summation of nerve transmission, what effect does the release of an excitatory neurotransmitter and inhibitory neurotransmitter (from two presynaptic neurons) have on the graded potential in the post-synaptic neuron (assuming these neurotransmitters are caused by same amplitude stimulus)?

Answer 56

There is no response in terms of graded potentials, because the hyperpolarization and depolarization graded potentials cancel each other out.

Question 57

TTX is a toxin found in pufferfish and can be fatal if consumed. TTX is capable of blocking voltage gated sodium channels- what effect does this have on the action potentials?

Answer 57

Graded potentials can still occur to increase membrane potential from -70mV to -55mV. This is because graded potentials are reliant on chemoreceptors, thermoreceptors, and ligand gated receptors to being about a potential.

So when threshold value of -55mV is reached, no further depolarization occurs because there will be no voltage gated Na+ to being about this depolarization.

Question 58

Tetraethylammonium is a compound that can block K+ voltage gated ion channels. What effect does this have on action potentials?

Answer 58

Blocking K+ voltage gated ion channels causes there to be a reduction or absence in the efflux of K+ out of a neuron during repolarization.
As there is a reduced efflux of K+, the time needed to get the membrane potential back to -70mV will take longer, making the repolarization phase elongated, hence elongating the action potential.

Question 59

Stimuli can be categorized into three sections: subthreshold, threshold and suprathreshold. How do each of these stimuli differ?

Answer 59

The stimuli differ in terms of the highest potential it can reach:

A subthreshold stimulus means the stimulus cannot reach threshold value of -55mV and hence does not elicit any action potentials.

A threshold stimulus is a stimulus that elicits action potentials by reaching the minimum potential.

A suprathreshold stimulus is a stimulus that has by far surpassed the potential needed to elicit action potentials. This is where the all-or-nothing principles into play; even if we have a stronger stimulus, the magnitude of the stimulus will still be the same.

Question 60

What is a refractory period?

Answer 60

A short period of decreased excitability following an action potential in which the neuron cannot respond to a give stimulus.

Question 61

There are two types of refractory periods: what are they and how do they differ?

Answer 61

The two types of refractory periods are absolute refractory period and relative refractory period.

An absolute refractory period follow right after an action potential, and in this period of time, an action potential is impossible to generate.

The relative refractory period follows after the absolute refractory period, and an action potential is possible if there is a strong enough stimulus.

Question 62

Why are refractory periods important to the functioning of neurons?

Answer 62

> Refractory period ensures action potentials are uni-directional, and does not fire back in the other direction.
Refractory period prevents over-firing of action potentials, which could lead to seizures or nerve damage (cramps in muscles are caused by continuous contraction of muscle, caused by action potential of nerves leading to muscle).
The coding of information in the nervous system is based on the frequency of action potentials, which is especially important when the brain is interpreting nerve impulses. Neurons encode information based on the rate of firing- this is called frequency coding. If refractory periods did not exist, it would be difficult for neurons to differentiate between differ size stimuli (as they are expressed via the frequency of action potentials).
Refractory period allows for the restoration of ion gradients.

Question 63

Why do no action potential occur in the absolute refractory period, even if a stimulus is applied?

Answer 63

Inactivation of sodium voltages gated ion channels.

> During depolarization of an action potential, Na+ voltage gated ion channels are open, to allow Na+ to rush in.
After these channels are finished with depolarization, they close very quickly; they enter an inactive state (and this ensures the action potential is one-way).
In the refractory period, the Na+ voltage gated channels still exist in an inactive state, so cannot aid in depolarization even if a new stimulus is applied.

Question 64

Why are action potentials capable of occurring in the relative refractory period? Why does the relative refractory period encode for the strength of a stimulus?

Answer 64

Action potentials are capable of occurring in the relative refractory period because the Na+ voltage gated channels have entered an active state.

A stronger stimulus is needed to elicit a second action potential because of the hyperpolarization that occurs after the first action potential, which causes membrane potential to become more negative than -70mV. Therefore, the membrane has to work even harder (than if it was just one stimulus) to move from a membrane potential of less than -70mV to -55mV in a shorter amount of time, in order to elicit a second action potential. Normally if it was one stimulus, the absolute and relative refractory period would serve as enough time to return the membrane potential back to resting potential using Na+/K+ pump.

This is why we day that strength of stimulus is encoded by the relative refractory period- whether or not a stimulus can occur in this period to give a higher frequency of stimulus is determined by the strength of the stimulus.

Question 65

How does stimulus strength needed to elicit second action potential change with time after start of relative refractory period?

Answer 65

As time after start of relative refractory period changes, the stimulus strength needed to invoke a second action potential decreases.

Question 66

Does the duration of a stimulus affect the number of action potentials generated?

Answer 66

A long duration stimulus can produce more than one action potential.

Question 67

Talk about the movement of an action potential along a non-myelinated neuron.

Answer 67

Firstly, lets talk about the membrane being polarized at rest, in the sense that the inside is more negative than the outside.

An action potential initiates at the axon hillock, and it results in that region becoming depolarized. Once depolarized, these positive ions diffuses to the next region along the neuron, causing depolarization in the second section.
The site where the ions were just at (first region of depolarization) has now entered a refractory state. (You will see soon that this region where a refractory period is currently occurring soon becomes a region of repolarization).

When the ions now diffuse on to the third section, it causes depolarization. The second section where depolarization has just occurred now becomes a refractory period region. The area that was initially a refractory period now becomes an area of repolarization (the neuron is entering a resting state).

Question 68

What two parameters determine velocity of action potential?

Answer 68

Acon diameter (larger diameter, faster flow).
Acon resistance (higher resistance, faster flow). Myelinated neurons comes under this section because they have fast nerve impulses due to resistance (or ions being unable to conduct) to the myeline sheath.

Question 69

State an approximate value for the faster conduction velocities and state a value for the slower conduction velocities.

Answer 69

Faster conduction velocities: 100m/s
Slower conduction velocities: 0.5m/s

Question 70

Why is it difficult for mammals to adapt to having a bigger neuron diameter to increase the speed of neuron transmission?

Answer 70

Speed of conduction is proportion to axon diameter: in order to double the speed of conduction, we need to quadruple axon diameter. This is not feasible because with too many neurons in the mammal, there will not be enough space.

Instead, we use the other factor to increase nerve transmission speed- this is done by introducing myelinated neurons.

Question 71

How do myelinated neurons increase nerve transmission?

Answer 71

Myelinated neurons are covered in a myelin sheath (myelin sheath is composed of multiple layers of plasma membrane).
The myelin sheath insulates the nerve fibre and it causes nerve impulses (ions) to jump to places on the neuron where the myelin sheath is not present (gaps along the neuron where the myelin sheath is not present is called the Nodes of Ranvier).
The action of the nerve jumping to the nodes of Ranvier for a faster impulse transmission is called saltatory conduction.

Question 72

What property allows the nerve fibre to be insulated and non-conductible to ions?

Answer 72

The myelin sheath is composed of plasma membranes, which is made of lipids. Lipids are non-polar, hence does not have a charge, so ions which do have a charge cannot interact with this myelin sheath.

Hence, there are no voltage gated ion channels present where the myelin sheath is; instead, they are present at the Nodes of Ranvier.

Question 73

What cells along the neuron produce the myelin sheath?

Answer 73

Schwann cells.

Question 74

What dysfunction in nerves leads to epilepsy?

Answer 74

Refractory periods.
In epileptic neurons, the refractory period becomes excessively shortened or dysfunctional, so it causes neurons to generate action potentials too frequently or abnormally. The hyperexcitability of neurons leads to spontaneous generation of action potentials.

This can be brought about by dysfunction in the mechanisms which produce refractory periods, or, the disruption in balance between inhibitory and excitatory neurotransmitters. Inhibitory neurotransmitters causes hyperpolarization which stops action potentials being generated too frequently (stops membrane potential reaching threshold of -55mV). If there are less inhibitory neurotransmitters, there is more chance of action potentials being generated more frequently.

These dysfunctions in the nerves leads to recurrent, unprovoked seizures.

Question 75

What dysfunction in nerves leads to the disease Congenital Insensitivity to Pain (CIP)?

Answer 75

First of all, like the name says, CIP is where individuals are unable to feel physical pain and this is a rare genetic disorder.

CIP is brought about by defects or absence of voltage gated sodium ion channels in sensory neurons. If there are no voltage gated Na+ channels, action potentials cannot be generated in sensory neurons (particularly those that function for pain sensation), hence leading to no action potentials being carried to the brain to be registered.

As we are talking about voltage gated Na+ channels in sensory receptors, as well as not feeling pain, people with CIP may fail to feel other sensations like temperature. Although there is a reduction in sensation that comes with CIP, interestingly individuals do not have a reduced sense of touch.

Question 76

What dysfunction in the nerves causes the disease multiple sclerosis?

Answer 76

Multiple sclerosis is a neurological and autoimmune disease that causes symptoms like numbness, weakness, fatigue, dizziness, and lack of co-ordination.

Multiple sclerosis is caused by a lack in production or defect of myelin sheath in nerves, which leads to slow or disrupted nerve conduction.
The defect or lack of myelin sheath is caused by an autoimmune disease that attacks the myelin sheath in the CNS.