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SL12100 Health and Disease Y1 > Lecture 20 - Nerve cells and excitability - the resting membrane potential > Flashcards

Lecture 20 - Nerve cells and excitability - the resting membrane potential Flashcards

1
Q

What are neurons

A

cells. The basic unit of the nervous system.

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2
Q

Where are most neurons found?

A

The CNS- the central nervous system.

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3
Q

What makes the CNS?

A

brain and spinal cord

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4
Q

What makes up the PNS?

A

the nerves which connect the brain and the spinal cord with the body’s muscles, glands, sense organs and other tissues

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5
Q

Neurons are postmitotic cells. What does this mean? Why does this explain why brain diseases are so debilitating?

A
  • they are fully differentiated and cannot divide
  • no cell division to produce new cells for healing, hence why brain diseases are so debilitating.
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6
Q

Draw the general structure of a nerve cell

A
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7
Q

What is found in the cell body/soma? Why organelle is not and why?

A
  • Neurons contain a cell body/soma containing the nucleus and other organelles.
  • Neurons lack centrioles because they are postmitotic so do not divide- centrioles are used for cell division (spindle fibre formation)
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8
Q

What are attached to the cell body/soma?

A

dendrites.

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9
Q

What is the role of dendrites- what is their role in excitability?

A

part of the receptive zone of the neurone- changes in the environment changes in environment causes them to send weak electrochemical signals toward the cell body and along axon. This is excitability

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10
Q

What is the role of the axon?

A

it transports action potentials away from the cell body by conduction, causing the release of neurotransmitters from the synaptic terminals/ axon terminals. Neurotransmitters diffuse across extracellular gaps to the cell opposite the terminal.

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11
Q

Axons can be long. How do action potential travel more quickly along the axon?

A

cover the axon with a myelin sheath- this speeds up the conduction of electrical signals along the axon and conserves energy. The myelin sheath acts as an insulator

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12
Q

Myelin is produced by …..

A

Schwann cells

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13
Q

What are nodes of Ranvier?

A

the gaps between adjacent myelin sections, where the axon’s plasma membrane is exposed to extracellular fluid.

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14
Q

An axon covered with myelin sheath is given the name…

A

nerve fibre.

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15
Q

How do neurons communicate with each other?

A
  • through the dendrites and axon.
    -Incoming signals are received at the dendrites
    -Outgoing signals travel along the axon to the synaptic terminals
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16
Q

There are four structural classes of neurons. Draw and name them.

A
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17
Q

Name the three classes of neurons on the basis of function.

A

afferent neurone, efferent neuron and interneuron.

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18
Q

Role of afferent neuron =

A

convey information from the tissues and organs of the body towards the CNS

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19
Q

Role of efferent neuron =

A

convey information away from the CNS to effector cells, like muscles, gland, etc.

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20
Q

Role of the interneuron =

A

connect afferent and efferent neurons within the CNS

21
Q

What is an excitable cell?

A

a cell which may be electrically excited, which results in the generation of action potentials.

22
Q

Give examples of excitable cells

A

neurons, muscle cells and endocrine cells- insulin releasing pancreatic b cells.

23
Q

Give example of a non-excitable cell

A

red blood cell

24
Q

ALL cells have a resting…

A

membrane potential

25
Q

What is the RMP? In excitable cells, what can happen to the RMP?

A
  • -an electrical charge across the plasma membrane- the interior of the cell is negatively charged, and the exterior is more positively charged.
  • In an excitable cell, the resting membrane potential can change- an action potential is produced – in response to a stimulation
26
Q

What is the RMP range for an excitable cell?

A

-50mV —> -85mV.

27
Q

What is the RMP range of a non excitable cell?

A

-5mV —> -10mV

28
Q

The reason for the resting potential is because what property of a cell?

A

the selective permeable membrane of the cell which separates the inner environment of the cell from the outer cell

29
Q

Membranes are made from…

A

phospholipids

30
Q

What can easily cross the membrane and what cannot

A
  • small, uncharged molecules diffuse easily across, down the concentration gradient
  • charged ions/very large uncharged molecules do not- they need a transporter protein to get across the membrane.
31
Q

Describe the chemical and electrical gradient

A

chemical- based upon concentration, goes from high to low
electrical - gradient based upon charge. Ions will move following their charge.

32
Q

Describe ion channels and their role.

A
  • Ion channels allow the passage of ions in and out of cell by diffusion
  • They are membrane proteins that form water filled passages through the membranes. They connect the cytosol in the cell to the cell exterior
  • The movement of ions through the channels is fast, goes down the concentration gradient, is passive- no ATP is required
  • ion channels are selective- for example, ion channels will only transport sodium or only transport potassium ions
33
Q

What are the two types of ion channels?

A
  • Non-gated = ion channels which are always open. AKA ‘leak’ channels. For example, K+ leak channels are always open so allow K+ ions to travel out of the cell freely, depending on the concentration gradient of K+
  • Gated = built in mechanism that only permits ions to flow when specific conditions are met. When the appropriate stimulus is supplied, the get opens and ions can pass through, from high to low concentration.
34
Q

What are ion pumps?

A
  • active transporters
  • they are proteins which move ions across the membrane against the concentration gradient.
  • energy in the form of ATP is required to do this.
35
Q

How many Na+ ions are pumped out of the cell by NA+/K+ pumps and how many K+ ions are moved in?

A
  • three Na+ ions pumped out
  • three K+ ions pumped in
36
Q

Describe the concentration gradient of Na+ and K+ ions across the cell

A

There is a higher concentration of Na+ outside of the cell and lower K+. There is a lower concentration of Na+ inside of the cell and higher K+.

37
Q

How do ion pumps create an electrical gradient in terms of Na+ and K+ ions?

A

The electrical gradient is created because with every pump, three positive charged ions are removed from the cell and only replaced by two positive charges. So, there is a net -1 difference in the electrical charge in the cell with each cycle.

38
Q

Describe the steps taken by the pumps to move Na+ and K+ ions across the membrane

A
  1. 3 Na+ ions inside of the cell bind to transporter proteins in the membrane
  2. ATP converts to ADP. The phosphate phosphorylates the transporter, changing it’s configuration and causing Na+ to be released out of the cell
  3. 2 K+ bind to the transporter from outside of the cell
  4. Transporter is dephosphorylated- a phosphate is removed. This induces a conformational change and K+ are released into the cell.
39
Q

Every cell has…

A

a RMP

40
Q

What is the RMP of a neuron?

A
  • 70mV
41
Q

What is ‘potential’?

A

the separation of charge across the lipid membrane- in the case of nerve cells, we have negative charge within the membrane and more positive charge outside of the membrane

42
Q

What does the membrane potential measure?

A

A measure of the electrical force created by the difference in ionic concentration across the cell membrane

43
Q

The membrane potential requires an uneven distribution of charges between the outside and the inside of a cell. What is this created by?

A

Na+/K+ pumps

44
Q

Give the values for the difference in concentration between the outside and inside of membrane for Na+ and K+ ions

A
  • There is a high concentration of potassium ion inside the cell – 140mM, but small concentration outside of the cell – between 4 and 5 mM
  • There is high levels of sodium ion concentration outside of the cell – around 145 mM, but a small concentration inside of the cell, around 10-15 mM.
45
Q

What is the most important component in maintaining the RMP? - its not the ion pumps but instead the…

A

K+ leak channels/ ungated K+ channels

46
Q

Describe the role of the K+ leak channels in maintaining the RMP

A

There are no Na+ leak channels. Therefore, when pumped out of the cell by the sodium/potassium ion pumps, Na+ ions cannot return back into the cell.
The membrane is more permeable to K+ than Na+. When pumped into the cell, the concentration of K+ rises and the membrane potential becomes more negative. The increased concentration gradient causes K+ ions to diffuse out of cell to an area of low concentration.
- Once the inward rate of K+ from pumps balances the rate of K+ flow out of the cell via the ungated channels, a resting membrane potential stabilises at -70MmV.

47
Q

The Nernst equation is used to find the equilibrium electrical potential for an Eion. Give the equation.

A
48
Q

Vm- the resting potential can be calculated using the Goldman equation. Give the equation

A

SL12100 Health and Disease Y1 (18 decks)

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