The nervous system

Question 1

Divisions of the nervous system.

Answer 1

Central Nervous System (CNS)
- Brain and Spinal Cord

Peripheral Nervous System (PNS)
- Nerves and Ganglia
1- Somatic nervous system (sensory and motor)= responsible for voluntary control of skeletal muscles and mediates sensory information from outside the body to the brain.

2- Autonomic nervous system (sympathetic and parasympathetic)= controls involuntary bodily functions, e.g. heart rate, swallowing, etc

3-Enteric Nervous System- “second/little brain,” this system governs the function of the gastrointestinal system (digestion).

Question 2

difference between nerves and ganglia

Answer 2

Nerves are Bundles of axons- Transmit signals between the brain/spinal cord and the rest of the body.

Ganglia
Clusters of nerve cell bodies- Act as relay points for nerve signals.

Question 3

Label cells of the nervous system and a NEURON!

Question 4

what are the 5 types of glial cells of the nervous system.

Answer 4

Astrocytes
Ependymal cells
oligodendrocytes
microglia
neurons

BE ABLE TO IDENTIFY FROM IMAGES

Question 5

what are glial cells?
where are they located?
other names?

Answer 5

• type of cell that provides physical and chemical support to neurons and maintain their environment.
• Located in the CNS and PNS
• also known as the “glue”/ neuroglia /or just glia.

Question 6

Astrocytes
shape?
where are they abundant ?
role?

Answer 6

(Majority of glial cells)

They are star-shaped cells

abundant in the brain and spinal cord (CNs)

helps neuron communicate and send signals:
- neurotransmitter regulation
- synaptic function

Question 7

Ependymal cells
shape?
role?

Answer 7

cuboidal shape

production and movement
of cerebrospinal fluid (CSF) - surrounds the brain and spine= protection)

Question 8

Oligodendrocytes
role?

Answer 8

provides Myelination of axons

Question 9

Microglia
what is it?
Role?

Answer 9

A type of immune cell- the Brains version of macrophages (a white blood cell).

they remove debris, dead cells, bacteria, microbes, etc.

Question 10

Neurons
what?
role?

Answer 10

messenger cells
allow communication with the rest of the body.

Question 11

At rest there is a high concentration of …

Answer 11

At rest, there is a high concentration of potassium ions on the inside and a high concentration of sodium ions on the outside of the cell.

Question 12

Sodium concentration at rest.

Answer 12

Extracellular conc.mM = 150
Intracellular conc.mM = 15
Permeability = 1

Question 13

Potassium concentration at rest

Answer 13

Extracellular conc.mM = 5
Intracellular conc.mM = 150
Permeability = 25-30

Question 14

Chlorine

Answer 14

Extracellular conc.mM = 120
Intracellular conc.mM = 4
Permeability = 0

Question 15

A-(intracellular proteins) concentration at rest.

Answer 15

Extracellular conc.mM = 0
Intracellular conc.mM = 65
permeablity = 0

Question 16

The concentration of ions inside the cell versus outside at rest is very different - what is primarily responsible for this?

Answer 16

Sodium-potassium pump

Question 17

How is the ion concentration created (2).

Answer 17

Sodium-potassium pump
- sets up and Maintains concentration gradients
- Requires ATP

sodium-potassium Leak channels
- ALWAYS open- has pores that allow the ions to travel
- passive movement = No ATP
- Can establish an electrical (ion) gradient

Question 18

Are ions equally distributed across the membrane ?

Answer 18

No
high concentration of sodium outside
high concentration of potassium inside
set up by Na+/K+ pump

Question 19

At rest, what is the net charge inside the cell.

Answer 19

net negative charge (-70mv)

Question 20

what is membrane potential.

Answer 20

The difference in electrical potential (voltage difference) across the cell membrane.

Question 21

what is driving force in membranes?

Answer 21

BOTH concentration gradient and electrical gradient.

Question 22

what are the two types of channels.

1)- where? open or closed? what is it important for?
2)- open or closed? triggered by what? how does it work? what does it have? what is it important for?

Answer 22

Leak channels
– In neurons: sodium and potassium
– Always open
– Important for resting membrane potential

Voltage-gated channels
– closed- Triggered by a change in membrane potential
- work by changing shape at certain voltage
– Different activation states- they close at rest and open when there is a change in membrane potential OR become inactive.
– Important for action potentials

Question 23

what is action potential?concentration inside?
what does it cause?
is it fast or slow?
Distance?

Answer 23

• A brief reversal of electrical potential across the membrane, making the inside temporarily positive relative to the outside.
• This rapid change in voltage serves as an electrical signal that can be transmitted along the length of the cell- Electrical signal allows cells to communicate.

-very quick

• can be over long distances along the axon.

Question 24

why can action potentials travel long distances along the axon without losing energy?

Answer 24

due to the REgenerative nature of the action potential; as it travels, it triggers nearby segments of the membrane to depolarize, allowing the signal to move forwards without losing strength.

Question 25

what are ions attached to?
what does an ion needs to cross?
concentration gradient of ions?
what do ion channels facilitate?

Answer 25

Ion are attached to an area of the opposite electrical charge?

For an ion to cross, the membrane needs to be permeable.

Ions will travel form an area of high concentration to an area of low concentration, along its concentration gradient.

Ion channels facilitate the movement of ions across an impermeable lipid bilayer.

Question 26

what are the 7 stages of action potentials?

Answer 26

1) The trigger event
2) Threshold
3) Depolarisation
4) Peak
5) Repolarisation
6) Hyperpolarisation
7) Resting potential restored.

Question 27

Explain what happens in the first 2 stage of action potentials?

what needed to be done first?
what does this causes?
what does this create?
What happens once the threshold is reached?
Threshold not reached?

Answer 27

Stimulus Activation: A stimulus (chemical, mechanical, thermal, etc.) causes specific ion channels in the neuron’s membrane to open (depending on the stimulus)

Sodium Influx: stimulus causes voltage-gated Sodium ions channels to open, allowing sodium ions (Na⁺) to enter the neuron cell, leading to a local depolarization of the membrane- The membrane potential becomes more positive (inside of the cell is more positive).

Graded Potential: This depolarization creates a graded potential (Change in membrane potential) If the membrane potential reaches the threshold (around -55 mV), it triggers the action potential.

Once the threshold potential is reached, K+ channels are also activated (Slower to open).

If threshold is not reached, the depolarisation wont trigger the Na+ channels to open and it will die away (yellow line).

Question 28

what causes the influx of Na+.

what does it causes?

Answer 28

due to both the concentration gradient (more Na⁺ outside the cell than inside) and the electrical gradient (the inside of the cell is negatively charged compared to the outside)- *the electrical gradient of sodium ions will oppose the concentration gradient *

This influx of positive charge causes the membrane potential to rise quickly.

Question 29

what are the different stimuli that trigger an event.

Answer 29

Due to both the concentration gradient and the electrochemical gradient.

1) volatge= Changes in the membrane potential.

2) Chemical: The binding of neurotransmitters to receptors .

3)Mechanical: Physical deformation of the cell membrane such as stretching

4) Thermal: Temperature changes

5)Optical (light): In photoreceptor cells, exposure to light.

Question 30

what does the term “All or Nothing” mean?

Answer 30

Once the threshold is reached, an action potential occurs in an all-or-none manner. This means that if the threshold is surpassed, the action potential will fully propagate down the axon; if it is not reached, no action potential will occur.

Question 31

what is the 3rd stage of Action potentials. (4)

what does reaching threshold cause?- what is the effect of this on membrane potential?
when does this stop?
what happens to the flow of Na+ at this stage?

Answer 31

Reaching threshold causes nearby voltage-gated sodium channels to open, causing the membrane to become approximately 600 times more permeable to sodium ions (Na+).

As Na+ channels open, Na+ rush into the cell causing the membrane potential to become more positive, rapidly shifting it from a resting state -70 mV to +30 mV).

As more Na+ channels open, the depolarization becomes self-reinforcing until a peak is reached.

The sodium channels are still open and Na wants to enter the cell because there is still a huge concentration gradient (more sodium outside) but when the membrane potential becomes positive, Na+ (positive ions) are repelled and so the flow of ions/current into the cell will slow down.

Question 32

stage 4- peak

Answer 32

Once the action potential reaches its peak (+30 to +60mV), Voltage gated sodium channels quickly close and become inactivate- Therefore Na+ stops entering the cell stopping the membrane potential from getting anymore positive.

At the same time, the (slow) voltage-gated potassium channels open and potassium leaves the cell along a concentration gradient (there is still more K+ inside than outside) and an electrical gradient (inside the cell is positive compared to the outside and K+ ions are repelled by positive charges).

Question 33

stage 5 - Repolarisation

Answer 33

As potassium ions RAPIDLY leave the cell, the membrane potential starts rapidly drops back down toward its resting state- This restores the negative charge inside the cell.

Question 34

stage 6- Hyperpolarisation
1- what happens once K+ channels close?
2- what state are the Na+ channels in?

Answer 34

Once the K+ channels get down to the resting potential they start to close, but because they are slow to close (i.e. still open), they still let K+ leave the cell (overshoot), resulting in a brief hyperpolarisation- this is where a membrane potential that is more negative than resting potential.

During hyperpolarization, the Na⁺ channels are STILL in a closed but inactivated state. They are “reset” and ready to open again when the membrane potential reaches the threshold level again.

Question 35

what happens to the level of depolarisation needed after hyperpolarisation?

Answer 35

once the membrane is hyperpolarized, a greater depolarization is needed to reach this threshold.

Question 36

stage 7- Resting Potential Restored
- how is resting membrane potential restored?
- how is resting membrane potential maintained?

Answer 36

Voltage-gated potassium (K⁺) channels finally close, reducing the outflow of K⁺ ions. This returns the membrane potential back toward its resting level.

The resting membrane potential is primarily maintained by two mechanisms:

K⁺ Leak Channels: allows a small, constant flow of K⁺ ions out of the neuron.

Na⁺/K⁺ Pump: actively transports Na⁺ ions out of the cell and K⁺ ions back in.

Question 37

what is the Final outcome.

Answer 37

Membrane potential back to resting state (-70mV).

Voltage-Gated Na⁺ Channels: These channels are closed and reset, they are ready to open again when the membrane potential reaches the threshold during the next action potential.

voltage-Gated K+ channels: closed, slow open when threshold is reached. and fully open in repolarisation of next action potential.

Question 38

What are the two Refractory Periods.

Answer 38

Absolute and Relative

Question 39

Absolute Refractory period.
1) When does it occur?
2) What happens during this period?
3) Can an action potential be generated? why?

Answer 39

1) during the repolarisation stage.

2) Sodium Channels Inactivated:
After the peak of the action potential,(Na⁺) channels close and become inactivated. This means they cannot open again until the membrane potential returns to a more negative value.

3)No Action Potentials Can Be Generated: During this period, regardless of the strength of any incoming stimulus, the neuron cannot generate another action potential. Because, the inactivation of Na⁺ channels prevents depolarization from occurring, meaning that the neuron is unresponsive to new signals.

Question 40

Relative Period
1) when does it occur?
2) Can an action potential be generated?

Answer 40

1) Hyperpolarisation stage

2) An action potential CAN be generated during the relative refractory period, but it requires a stronger-than-normal stimulus.
Two reasons why:
- hyperpolarization caused by delayed voltage-gated potassium channels.
- while some Na+ channels are resetting and can potentially open, majority of them remain inactivated.

Question 41

What is Axonal Propagation- Contiguous Conduction.

Answer 41

Axonal Propagation is the process by which an action potential travels along the axon of a neuron.

Question 42

Through axonal propagation, how does a single action potential spread across a neuron to another neuron (signalling).

Answer 42

Depolarizing Current Spread:
The depolarizing current flows to areas of opposite charge - Because of this, the influx of Na+ flows towards the more negative portions of the cell further down the axon. This depolarises that portion of the membrane, allowing the voltage-gated Na+ channels in this area to open, flooding the area with positive sodium ions.

THIS CONTINUES ALONG THE LENGTH OF THE AXON.

Question 43

Direction of the propagation of the action potential.
WHY?

Answer 43

ONE DIRECTION
Due to refractory period and inactivation of Na+ it cannot move backwards.

Question 44

How does axon Diameter affect conduction speed.

Answer 44

Larger diameter = more space for ions to move = REDUCED INTERNAL RESISTANCE to flow of ions= depolarising current can spread more quickly.
Vice versa !

Question 45

How does myelination affect conduction speed?

Are all neurons myelinated?

what does myelin do?
what do nodes of ranvier do?

Answer 45

Increases conduction speed

No

Myelin is an insulating layer that wraps around the axon that reduces the leakage of ions across the membrane, allowing the electrical signal to travel more efficiently.

Nodes of Ranvier (small gaps)- the axonal membrane is exposed, allowing for the influx of sodium ions during depolarization. This results in “saltatory conduction.”

Question 46

why are sensory neurons faster than nocieptive neurons.

Answer 46

this question refers to conduction speed. so answer should include axon diameter, myelination.

Question 47

what are the two glial cells involved in Myelination.
where is found?
what many neurons can they myelinate?

Answer 47

Oligodendrocytes
- CNS
- Oligodendrocyte can myelinate several neurons at once.

Schwann cells.
- PNS
- Each Schwann cell myelinates only one segment of a single axon. This means that multiple Schwann cells are needed to myelinate a single neuron.

Question 48

Explain Saltatory conduction.

Answer 48

The myelin prevents Na+ and K+ exchange, except at the nodes of Ranvier, where there is a high density of voltage-gated sodium channels.

In myelinated axons, action potentials do not propagate continuously along the axon. Instead, they jump between Nodes of Ranvier- the distance between the nodes is short enough to allow the electrical current to flow from one node to the next.

Question 49

which type of conduction is faster?

Answer 49

Action potential are faster in Saltatory Conduction (myelinated axons) is faster than contiguous conduction (unmyelinated axon).

Question 50

summary questions !
1) what is the nervous system made up of ?
2) how do neurons communicate?
3) what is an action potential?
4) what are action potentials generated by?
5) what do refractory periods do?

Answer 50

1) neurons and glia
2) via action potentials- electrical signals which travel along the axon from the dendrites to the axon terminals
3) a brief reversal in membrane potential
4) generated by voltage-gated Na+ and K+ channels
5) limit the number of APs and ensure unidirectional flow of current.