Cellular neuroscience and physiology

Question 1

What are some examples of excitable cells?

Answer 1

Neurons, cardiac myocytes, skeletal muscle.

Question 2

What does potential difference across plasma membranes have key roles in?

Answer 2

Medical physiology and pathophysiology.

Question 3

What does passive movement across membranes include?

Answer 3

Permeability of membrane, driving force (electrochemical gradient).

Question 4

What does active transport across membranes include?

Answer 4

Against conc and/or electrical gradient, requires expenditure of metabolic energy by cell.

Question 5

What do we need to consider to understand how PD arises across membranes?

Answer 5

Passive movement and active transport.

Question 6

What is the name of a membrane that a substance can permeate?

Answer 6

Freely permeable.

Question 7

What is the name of a membrane that a substance cannot permeate?

Answer 7

Impermeable.

Question 8

What can membranes be in terms of permeability?

Answer 8

Impermeable to an ion, slightly permeable (large driving force required), readily permeable (small driving force).

Question 9

What are cell membranes permeabilities like at rest?

Answer 9

Fairly readily permeable to K+ and Cl-, poorly permeable to Na+, impermeable to various large organic anions.

Question 10

What is the model that is used to describe the overall structure of membranes?

Answer 10

The fluid mosaic model.

Question 11

What are the typical concentrations of Na+, K+ and Cl- inside the cell (ICF)?

Answer 11

15mM, 150mM, 5mM.

Question 12

What are the typical concentrations of Na+, K+ and Cl- outside the cell (ECF)?

Answer 12

145mM, 5mM, 100mM.

Question 13

What happens when there’s a low vs high concentration gradient?

Answer 13

Substance moves down concentration gradient.

Question 14

What happens when there’s a potential electrical difference/gradient?

Answer 14

Ion moves down electrical gradient.

Question 15

What happens if both a concentration and electrical gradient exist at the same time?

Answer 15

Need to convert concentration gradient into equivalent electrical gradient using the Nernst equation.

Question 16

What is the Nernst equation? (do not need to know off by heart).

Answer 16

Ex = -RT/zxF x ln([X]i/[X]o

Question 17

What do the components of the Nernst equation stand for?

Answer 17

x = ion, Ex = eqm potential for x, R = gas constant, T = temp, z = valence of ion, F = faradays constant, [X]o = conc outside cell, [X]i = conc inside cell.

Question 18

What would Ex normally be at body temp (37 degrees)?

Answer 18

61 log [X]o/[X]i millivolts.

Question 19

What is the significance of the Nernst equation?

Answer 19

Tells us the magnitude of electrical gradient that would exactly balance a given conc gradient of a given ion, gives us eqm potential for that ion.

Question 20

What two fundamental properties of cells give rise to the existence of a resting membrane potential?

Answer 20

Unequal distribution of ions across membrane (maintained by Na+/K+ pump), selective permeability of the cell membrane (Pk&raquo_space; PNa).

Question 21

What equation is used to calculate resting membrane potential (Vm)?

Answer 21

Goldman-Hodgkin-Katz (GHK) equation.
Vm = 61 log Pk[Ko] + etc…/ Pk[Ki] + etc…

Question 22

What does the P stand for in the GHK equation?

Answer 22

Membrane permeability to each particular ion based on the number of ion channels open, closed etc…

Question 23

What do changes in membrane potential determine?

Answer 23

If an action potential will occur or not (all or nothing).

Question 24

What can excitatory neurotransmitters cause?

Answer 24

Small changes in membrane potentials.

Question 25

What can excitatory post synaptic potentials (EPSPs) do?

Answer 25

Can sum and cause an AP to occur.

Question 26

What do inhibitory neurotransmitters cause?

Answer 26

Inhibitory postsynaptic potentials (IPSPs), which can prevent action potentials firing.

Question 27

What are action potentials required for?

Answer 27

Correct functioning of the brain, heart, skeletal muscles.

Question 28

What is a threshold?

Answer 28

Degree of depolarisation that triggers action potential, determined by the ion channels in a membrane, varies between different neurons and different parts of the same neuron.

Question 29

What kind of fibres have lower thresholds generally speaking?

Answer 29

Thicker fibres because their diameter provides less resistance to the flow of ions.

Question 30

What are the different kinds if channels?

Answer 30

Ligand-gated, G-protein-coupled receptors, voltage gated sodium, voltage gated potassium.

Question 31

What is the positive feedback cycle triggered by an event?

Answer 31

Depolarisation (decreased membrane potential), opening of some voltage gated Na+ channels, influx of Na+, further decreases membrane potential.

Question 32

What are voltage gated potassium channels like compared to voltage gated sodium channels?

Answer 32

Comparatively slower to open and close.

Question 33

What are axons like in skeletal muscles?

Answer 33

Thick, myelinated axons - rapid conduction.

Question 34

What junctions are in skeletal muscles?

Answer 34

Neuromuscular junctions.

Question 35

What is excitation contraction coupling?

Answer 35

Propagation of AP down into T-tubules.

Question 36

What are the first three steps of excitation contraction coupling?

Answer 36

Propagation of AP into T-tubules, activation of dihydropyridine receptors, release of calcium form SR.

Question 37

What are the last four steps of excitation contraction coupling?

Answer 37

Binding of Ca2+ to troponin, cross bridge formation, cross bridge cycling, Ca2+ removed from troponin restoring tropomyosin and Ca2+ taken back up by SR.

Question 38

How does AP propagation to T-tubule happen?

Answer 38

ACh neurotransmitter, AChR at motor end plate, propagation of AP bidirectionally within muscle fibre.

Question 39

How is calcium released from the SR?

Answer 39

Activation of dihydropyridine receptors.

Question 40

What is the cross-bridge cycling?

Answer 40

Actin and myosin dissociate when ATP is bound by myosin, ATP breakdown to ADP and Pi causes a change in angle of head region of myosin molecule, enables it to move relative to thin filament, cycle repeated.

Question 41

What is rigor mortis caused by?

Answer 41

Depletion of ATP.

Question 42

How does depletion of ATP cause rigor mortis?

Answer 42

ATP causes actin-myosin bridges to separate during relaxation of muscle, without ATP to separate the cross-bridging skeletal muscles are locked in place.

Question 43

What happens to myosin heads as part of the decomposition process?

Answer 43

Eventually degraded by cellular enzymes allowing release of cross-bridges and muscle to relax.

Question 44

When is peak rigor mortis and when does decomposition of myofilaments take place?

Answer 44

~13hrs after death, ~48-60hrs after peak of rigor mortis.

Question 45

How were length tension curve experiments carried out initially?

Answer 45

On isolated frog muscle fibre, clamp both ends and stretch muscle fibre.

Question 46

What are molecular cross bridges important for?

Answer 46

Skeletal muscle tension.

Question 47

What is a myogram?

Answer 47

Measures twitch tension development in muscle.

Question 48

What are the different phases of a myogram?

Answer 48

Latent or latency period, contraction phase, relaxation phase.

Question 49

What are skeletal muscles classified as being fast or slow twitch based on?

Answer 49

Speeds of sarcomere shortening.

Question 50

What are morphological differences between fast and slow twitch muscles?

Answer 50

Fast = white (lower myoglobin & capillary content), slow = red (high myoglobin & capillary content).

Question 51

What is time course of contraction dependent on?

Answer 51

Muscle fibre type.

Question 52

What is tetanus?

Answer 52

The prolonged contraction of a muscle caused by rapidly repeated stimuli.

Question 53

What does TFF stand for?

Answer 53

The frequency of APs that are needed to not see summation and produce smooth graded contraction as seen in normal muscle contraction.