The nervous system

Question 1

What is Human brain divided into?

Answer 1

• Brainstem
• Cerebellum
• Forebrain

Question 2

What is the brainstem divided into?

Answer 2

Brainstem consists of:
Medulla
Pons
Midbrain

Question 3

Role of brainstem.

Answer 3

• Essential for life (controls respiration, heart rate, digestion, coordinates sensory input from spinal cord)
• Reflexes and stereotyped movement (coughing, swallowing, motor control etc.)
• Cranial nerves – 10/12 pairs originate from brainstem. (helping you see, taste, smell, hear, and feel sensations. They also help you make facial expressions, blink your eyes, and move your tongue).

Question 4

Label the brain.

Question 5

cerebellum

Answer 5

Coordinates complex voluntary
movement, balance, posture etc.

Question 6

Forebrain

Answer 6

The forebrain is the largest and most complex part of the brain, f functions, including cognitive processes, sensory perception, and voluntary motor activities.

Question 7

what are the key structures of the forebrain.

Answer 7

Diencephalon
i. Hypothalamus – homeostasis, endocrine, emotion
ii. Thalamus – motor control, sensory relay

Cerebrum
iii. Basal nuclei – motor control, reward, cognition,
memory
iv. Cerebral cortex – sensory perception, voluntary motor
control, learning and memory, language, emotion,
consciousness, personality

Question 8

Divisions of the nervous system.

Answer 8

Central Nervous System (CNS)
- Brain and Spinal Cord

Peripheral Nervous System (PNS)
Nerves and Ganglia (Nerves are bundles of axons that transmit information to and from the CNS, while ganglia are clusters of neuronal cell bodies located outside the CNS that relay signals.)

• Somatic (sensory and motor)= This part of the PNS is responsible for voluntary control of skeletal muscles and mediates sensory information from the external environment.
• Autonomic (sympathetic and parasympathetic)=he autonomic system controls involuntary bodily functions.
• Enteric=Enteric Nervous System: Sometimes referred to as the “second brain,” this system governs the function of the gastrointestinal system. It operates independently but can also communicate with the CNS, playing a significant role in controlling digestion and gut motility.

Question 9

Label cells of the nervous system.

Question 10

what are the 5 cells of the nervous system.

Answer 10

Astrocytes
Ependymal cells
oligodendrocytes
microglia
neurons
BE ABLE TO IDENTIFY FROM IMAGES

Question 11

what are glial cells

Answer 11

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

Question 12

Astrocytes
what are they ?
Role ?
shape?

Answer 12

Type of glial cell in the central nervous system (CNS)

They are star-shaped cells that are abundant in the brain and spinal cord

ROLE: de Ceglia et al. 2023

Question 13

Ependymal cells

Answer 13

type of glial cell.

cuboidal shape

production and movement
of cerebrospinal fluid (CSF)

Question 14

Oligodendrocytes

Answer 14

most common glial cell

Myelination of axons

Question 15

At rest there is a high concentration of …

Answer 15

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 16

Sodium concentration at rest.

Answer 16

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

Question 17

Potassium concentration at rest

Answer 17

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

Question 18

Chlorine

Answer 18

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

Question 19

A-(intracellular proteins) concentration at rest.

Answer 19

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

Question 20

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

Answer 20

Sodium-potassium pump

Question 21

what are the two ion concentrations

Answer 21

Sodium-potassium pump
- Maintains concentration gradient
- Requires ATP

Leak channels
- Always open (passive movement)
- Can establish an electrical gradient

Question 22

Are ions equally distributed across the membrane ?

Answer 22

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

Question 23

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

Answer 23

net negative charge (-70mv)

Question 24

what is membrane potential.

Answer 24

The difference in electrical potential across the cell membrane.

Question 25

what is driving force in membranes?

Answer 25

BOTH concentration gradient and electrical gradient.

Question 26

what are the two types of channels.

Answer 26

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

Voltage-gated channels
– Triggered by a change in membrane potential
– Different activation states
– Important for action potentials

Question 27

what is action potential?

Answer 27

• 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 axons without losing energy- due to the regenerative nature of the action potential; as it travels, it triggers adjacent segments of the membrane to depolarize, effectively propagating the signal.

Question 28

what are the 7 stages of action potentials?

Answer 28

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

Question 29

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

Answer 29

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

Sodium Influx: stimulus causes volted-gated Sodium ions channels to open, allowing sodium ions (Na⁺) to flow into the cell (Sodium ions are typically at a higher concentration outside the cell compared to the inside), 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 30

what causes the influx of sodium ions.

Answer 30

Influx of Sodium Ions: As Na⁺ channels open, sodium ions rush into the neuron 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). This influx of positive charge causes the membrane potential to rise quickly.

Question 31

what are the different stimuli that trigger an event.

Answer 31

Due to both the concentration gradient and the electrochemical gradient.

1) volatge= Changes in the membrane potential due to the influx or efflux of ions can serve as a trigger.

2) Chemical: The binding of neurotransmitters to receptors on the cell membrane can cause ion channels to open, allowing specific ions (like sodium) to flow into the cell.

3)Mechanical: Physical deformation of the cell membrane (such as stretching) can activate ion channels. This is common in sensory neurons that respond to touch or pressure.

4) Thermal: Temperature changes can affect the properties of ion channels, potentially leading to depolarization when certain channels open in response to heat or cold.

5)Optical (light): In photoreceptor cells, exposure to light can trigger a biochemical cascade that ultimately leads to the opening of ion channels, resulting in depolarization.

Question 32

what does the term “All or Nothing” mean?

Answer 32

All-or-None Principle: 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 33

what is the 3rd stage of Action potentials.

Answer 33

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

As Na+ channels open, sodium ions rush into the cell. The influx of Na+ ions causes the membrane potential to become more positive, rapidly shifting it from a resting state (around -70 mV) towards a more positive value (up to about +30 mV).

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

Note that at this point, even though the sodium channels are still open, the electrical gradient of sodium ions will oppose the concentration gradient (sodium 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 into the cell (current) will slow down.

Question 34

stage 4- peak

Answer 34

Once the action potential reaches its peak (+30 to +60mV), Voltage gated sodium channels quickly close and inactivate- sodium 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 35

stage 5 - Repolarisation

Answer 35

As potassium ions RAPIDLY leave the cell, the membrane potential starts rapidly drops back down toward its resting state/resting potential (approximately -70 mV in neurons)-This stage is characterized by the restoration of negative charge inside the cell.

Question 36

stage 6- Hyperpolarisation

Answer 36

Once the potassium channels get down to the resting potential they start to close, but
because the voltage gated potassium channels are slow to close (i.e. still open) than sodium channels, they still let potassium ions to leave the cell along its concentration gradient for a little longer (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 in a closed but inactivated state. They are “reset” and ready to open again when the membrane potential returns to the threshold level. However, because the membrane is hyperpolarized, a greater depolarization is needed to reach this threshold.

Question 37

stage 7- Resting Potential Restored

Answer 37

After hyperpolarization, the voltage-gated potassium (K⁺) channels gradually close. This closure reduces the outflow of K⁺ ions, which helps to bring the membrane potential back toward its resting level.

he resting membrane potential is primarily maintained by two mechanisms:

K⁺ Leak Channels: These channels allow a small, constant flow of K⁺ ions out of the neuron, which helps keep the inside of the cell more negative relative to the outside. As the K⁺ channels close, the influence of the leak channels continues to maintain a negative membrane potential.

Na⁺/K⁺ Pump: The sodium-potassium pump actively transports Na⁺ ions out of the cell and K⁺ ions back in. This pump works to restore the ion concentration gradients that were altered during the action potential, effectively re-establishing the resting conditions.

Question 38

what is the Final outcome.

Answer 38

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

Question 39

What are the two Refractory Periods.

Answer 39

Absolute and Relative

Question 40

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

Answer 40

1) during the repolarisation stage.

2) Sodium Channels Inactivated:
After the peak of the action potential, voltage-gated sodium (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. The inactivation of Na⁺ channels prevents depolarization from occurring, meaning that the neuron is effectively unresponsive to new signals.

Question 41

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

Answer 41

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. Therefore, a stronger stimulus is needed to ensure that enough channels open to achieve the necessary depolarization to reach the threshold.

Question 42

What is Axonal Propagation- Contiguous Conduction.

Answer 42

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

Question 43

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

Answer 43

Depolarizing Current Spread:
When an action potential is initiated, the depolarizing current flows to areas of opposite charge along the axon- the influx of positive sodium ions flows towards the more negative portions of the cell further down the axon. This, in turn, depolarises that portion of the membrane, allowing the voltage-gated sodium ions in this area to open, flooding the area with positive sodium ions.

THIS CONTINUES ALONG THE LENGTH OF THE AXON.

Question 44

Direction of the propagation of the action potential.

Answer 44

ONE DIRECTION
Due to refractory period, it cannot move backwards. After an area of the axon has been depolarized, the voltage-gated Na⁺ channels in that region become inactivated. This inactivation means that those channels cannot open again immediately, preventing the action potential from reversing direction.

Question 45

How does axon Diameter affect conduction speed.

Answer 45

LARGER DIAMETER REDUCED RESISTANCE!
Axons with a larger diameter offer less internal resistance to the flow of ions. This means that when an action potential is initiated, the depolarizing current can spread more quickly along the axon because there is more space for the charged ions to move.
VICE VERSA

Question 46

How does myelination affect conduction speed?

Answer 46

Increases conduction speed

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

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

Question 47

why are sensory neurons faster than nocieptive neurons.

Answer 47

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

Question 48

what are the two glial cells involved in Myelination.
where is found?
what is its function?

Answer 48

Oligodendrocytes
- CNS
- Oligodendrocyte can myelinate (wrap around) several neurons at once, providing insulation and facilitating faster conduction of action potentials.

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, with each cell covering a specific patch of the axon.

Question 49

Explain Saltatory conduction.

Answer 49

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

when an action potential reaches a node, the local depolarization triggers the opening of these channels, allowing Na⁺ ions to flood in and generate another action potential.

In myelinated axons, action potentials do not propagate continuously along the entire 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 50

which type of conduction is faster?

Answer 50

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

Question 51

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 51

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.