Exiteable cells 2

Question 1

What neurones do we have in the brain?
What is their function?

Answer 1

• Most sensory neurons are pseudounipolar, which means they only have one axon which is split into two branches
• Motor neurons and interneurons are multipolar, each with one axon and several dendrites

Question 2

Compare the function of Neuronal cells and Glial cells.

Answer 2

1. Neurons – (signaling cells) electrically excitable cell that communicates with other cells via specialized connections called synapses
2. glial cells – (support cells) non-neuronal cells in the CNS (microglia, astrocytes, and oligodendrocyte) and the PNS (Schwann cells) that do not produce action potentials
   > control CNS environment within which neurons function

Question 3

Function of Astrocytes?
What is the PNS glia?

Answer 3

Question 4

Function of oligodendrocytes?
What is the PNS glia?

Answer 4

Question 5

Function of Microglia?

Answer 5

Question 6

Function of Ependymal cells?

Answer 6

Question 7

How do ion channels work?

Answer 7

• Select either cations or anions to permeate
• Non-gated or gated (voltage-gated ion channels & ligand-gated)
  > So that ions flow only when needed, the pathway through an ion channel can be opened and closed by conformational changes that displace an obstruction called a gate

Question 8

How do Ion pumps work?

Answer 8

• Expending energy to slowly move ions thermodynamically uphill
• Primary active transport - hydrolyze ATP to produce energy in order to transport ions across the membrane
• Secondary active transporters - use electrochemical gradient created across the membrane by pumping ions in or out of the cell
  E.G. Na+/K+ ATPase

Question 9

What is the membrane potential?

Answer 9

• Distribution of charge across the cell membrane
  > expressed by its value inside the cell relative to the extracellular environment

Question 10

What is the electrostatic gradient?

Answer 10

1. Movement of the cation from inside to outside cell leaves behind a negative anion, & thus the inside of the cell becomes more negative, while the outside of the cell becomes more positive
2. The negative charges inside the cell start to exert a force to keep the positively charged K+ ions inside the cell, a force that opposes the movement of the ions down the concentration gradient.
   > When this negative electrostatic charge is opposite the force of the concentration gradient, there is no movement of the ions

Question 11

How is a resting membrane potential brought about?

Answer 11

1. Na+-K+ pump actively transports 3Na+ out of and 2K+ into the cell keeping the concentration gradient of Na+ high in the ECF and the concentration gradient of K+ high in the ICF.
2. K+ drives the membrane potential to K+’s equilibrium potential (-90mv), whereas Na+ drives the membrane potential to Na+’s equilibrium potential (+60mv)
3. However, K+ exerts the dominant effect on the resting membrane potential because the membrane is more permeable to K+.
4. The resting membrane is slightly permeable to Na+ and the relatively small net diffusion of Na+ inward neutralizes some of the potential that would be created by K+ alone.
5. Bringing the resting membrane to -70mV

Question 12

How is RMP achieved?

• At rest, the concentration of Na+ ions outside of the cell is higher or lower than the concentration inside of the cell?
• At rest, the concentration of K+ ions outside of the cell is higher or lower than the concentration inside of the cell?

Answer 12

• uneven distribution of ions between the inside and the outside of the cell, and by
  the different permeability of the membrane to different types of ions
• Extracellular concentrations of Na+ & Cl− > intracellular concentrations
• Extracellular concentration of K+ < intracellular concentration

Question 13

What is equilibrium potential? How can it be expressed?

Answer 13

• Electrical potential difference across the cell membrane that exactly balances the concentration gradient for an ion is known as the equilibrium potential
  (Potential level across a membrane that will exactly prevent net diffusion of an ion)
• can be expressed by the Nernst equation

Question 14

Describe Action potentials.
- What they are
-Underlying mechanism
- means of…
- type of phenomenon

Answer 14

• Electrical impulses, or changes in membrane potential, that travel along the surface of a neurone.
• Change in membrane permeability for different ions, first Na+ & then K+ in the recovery phase.
• APs are the means of communication between neurons.
• APs are an all-or-nothing phenomenon

Question 15

What are the two types of refractory periods?

The action potential moves along the axon in one direction because of the…

Answer 15

• Absolute refractory period - no stimulus can cause second action potential
• Relative refractory period - stronger stimulus needed (strength needed reduces as membrane reduces)

> Refractory period as an AP cannot be generated in this time as it requires a greater influx of Na+ to reach threshold again until MP returns back to resting potential

Question 16

Describe saltatory conduction.

Answer 16

• Myelin provides high resistance to ion flow across the membrane.
• Node of Ranvier = less resistance
• Nodes of Ranvier - concentration of voltage-gated sodium and potassium channels.
• APs continues down the length of a myelinated axon, jumping from one node to the next

Question 17

How are post-synaptic potentials different to action potentials?

What causes EPSP/IPSP?

Answer 17

• Not all-or-nothing phenomena of a constant magnitude but rather graded changes, dependent upon the magnitude of ion flow across the membrane
  (DEPENDS OF TYPE OF CHANNEL COUPLED TO RECEPTOR + CONC OF IONS)
• GABA usually causes hyperpolarization of the postsynaptic neuron to generate
  an inhibitory postsynaptic potential (IPSP).
• Glutamate causes depolarization of the postsynaptic neuron to generate
  an excitatory postsynaptic potential (EPSP).

Question 18

Describe how EPSP work?

Answer 18

• Neurotransmitter binding to receptor causes opening of chemically gated Na+ channels
• Net movement of positive ions into cell (Na+) → membrane potential becomes more positive (towards threshold)
• Depolarisation
• EPSP increases the probability that the postsynaptic
  neuron will produce an action potential

Question 19

Describe how IPSP works?

Answer 19

• Neurotransmitter binding to receptor causes opening of chemically gated K+ and Cl- channels
• K+ flows out of cell, Cl- flows into cell (down concentration gradients)
  → membrane potential more negative (away from threshold)
• Hyperpolarisation
• IPSP reduce the probability that the postsynaptic
  cell will fire an action potential

Question 20

What does pre-synaptic inhibition involve and what does post-synaptic inhibition involve?

Answer 20

Pre synaptic: decreases release of neurotransmitter

Post-synaptic: Decreased post-synaptic A.P
- all targets inhibited equally
- inhibitory neurone modulates excitatory neurone signal below threshold

Question 21

Compare spatial and temporal summation.

Answer 21

• The sum of excitatory or inhibitory post synaptic potentials

1. Spatial summation occurs when subthreshold impulses from two or more synapses trigger an AP because of synergistic interactions.
2. Temporal summation occurs when a series of subthreshold EPSPs in one excitatory fiber produce an AP in the postsynaptic cell.
   * This occurs because the EPSPs are superimposed on each other temporally before the local region of membrane has completely returned to its resting state.

Question 22

What are the 2 types of inhibition?

Answer 22

1. feed-forward inhibition
   * excitatory neurons excite inhibitory cells, which then inhibit a group of postsynaptic excitatory neurons
2. feedback inhibition
   * excitatory neurons to drive the inhibitory cells, which in turn inhibit the same population of excitatory cells can limit excitation in a pathway

Question 23

Explain the type of inhibition involved in patella reflex.

Answer 23

Question 24

What is Fatigue of Synaptic Transmission?
What does it explain?

Answer 24

• Excitatory synapses are repetitively stimulated at a rapid rate > firing rate becomes progressively less in succeeding ms = protective mechanism against excess neuronal activity
• EXPLAINS: excitability of the brain during an epileptic seizure is finally subdued so that the seizure ceases.

Question 25

Most neurons are highly responsive to changes in pH of the surrounding interstitial fluids. Why? What are the effects of Acidosis and Alkalosis on synaptic transmission?

Answer 25

* Presynaptic calcium concentration, mediated via voltage-gated calcium channels, is pH dependent, as the opening and the conductivity of presynaptic voltage-gated calcium channels strongly depend on both extracellular and intracellular pH - Acidosis greatly depresses neuronal activity > can cause comatose state - Alkalosis greatly increases neuronal excitability > can cause epileptic seizures

Question 26

What are memories made from?

Answer 26

- Dendritic spine > Small membranous protrusion from a neurone’s dendrite that typically receives input from a single axon at the synapse - Function: 1. Storage site for synaptic strength and help transmit electric signals to the neurone’s cell body. 2. Spines provide an anatomical substrate for memory storage and synaptic transmission → more synapses → more memory coding/decoding 3. The formation, density and morphology of dendritic spines are regulated by synaptic activity - NB to memory formation

Question 27

Why are dendritic spines described as plastic? What happens in many neurological disorders?

Answer 27

- Change in shape and volume due to learning, memory and other cognitive functions. > Activity-dependent spine morphogenesis is impaired in many neurological disorders

Question 28

Why do we need post learning sleep?

Answer 28

- neurons replay activity pattern from prior wakefulness—instructing neuronal circuits to adjust synaptic strength & form new synaptic connections—serving as basic memory storage units and relay centres. >Exerting distinct influences on memory traces.

Question 29

How does BDNF, AMPA and NMDA relate with spine growth.

Answer 29

BDNF: determines spine levels AMPA: Low levels of AMPA receptor activity is necessary to maintain spine survival NMDA : synaptic activity involving NMDA receptors encourages spine growth