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Physiology > Basic Principles > Flashcards

Basic Principles Flashcards

1
Q

First messengers

A

Signalling molecules released into the extracellular fluid with the aim of affecting functioning of other cells

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2
Q

Neurotransmitters

A

Secreted by a neurone to affect another excitable cell across a synapse eg. acetylcholine

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3
Q

Hormones

A

Secreted by glands and enter the bloodstream to reach their target cells or organ eg. insulin, adrenaline

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4
Q

Autocrine molecules

A

Act on the cell type that has secreted it eg. monocytes/macrophages, Interleukin

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5
Q

Paracrine molecules

A

Act on neighbouring target cells in close proximity eg. NO (nitric oxide)

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6
Q

How do cells recognise first messengers?

A

Receptors (cell-surface or intracellular)
- First messenger (agonist) combines with the receptor
- Receptor is activated
- Cellular response is activated (signal transduction pathway)

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7
Q

Ion channel linked receptors

A
  • Ach binds to receptor -> ion channels open
  • Ions can enter the cell, causing depolarisation or hyper-polarisation of the membrane
  • Results in cellular effects
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8
Q

G-protein linked receptors

A
  • Link receptor to effector
  • 3 sub-units: alpha, beta, gamma
  • Associates with guanosine-based molecules
  • Active form (influencing cell function) = GTP
  • Inactive forum (bound to receptor portion) = GDP
  • FM associates with receptor portion
  • Initiates dissociation of G-protein from receptor portion
  • Splits into alpha sub-unit and beta+gamma sub-unit
  • Alpha sub-unit moves through cell locating target enzyme
  • Can either increase or decrease enzyme activity in order to influence levels of SM
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9
Q

Diffusion

A

Movement of molecules from high to low concentration.
- Small molecules
- Hydrophobic molecules
eg. fatty acids, CO2, O2

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10
Q

Osmosis

A

Diffusion of water from high to low concentration through a semi-permeable membrane.

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11
Q

Rate of diffusion

A
  • Size of concentration gradient
  • Permeability of membrane to substance
  • SA of membrane
  • Molecular weight of substance
  • Diffusion distance
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12
Q

Facilitated diffusion

A

Movement of molecules down their concentration gradient but a membrane-bound protein is necessary to facilitate their passage (carrier and channel proteins)
eg. glucose, amino acids, ions

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13
Q

Active transport

A

Transport of substances against the concentration gradient. ATP is required
- Primary : carrier protein uses energy directly from ATP hydrolysis eg. sodium-potassium pump
- Secondary : uses energy stored in the concentration gradients of ions eg. sodium-glucose transporter

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14
Q

Vesicular transport

A
  • Exocytosis : cellular materials exit the cell
  • Endocytosis : materials are brought into the cell eg. phagocytosis, pinocytosis
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15
Q

Resting membrane potential

A
  • During cell development, number of K+ = number of A-
  • There is a conc gradient for K+ , so it diffuses out of the cell
  • There is also a gradient from A-, but they are too large to leave so remain inside
  • Chemical and electrical gradient balance out (electrochemical equilibrium)
  • Less K+ inside the cell than outside and the same amount of A- inside
  • Therefore, cell is negatively charged on the inside compared to the outside
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16
Q

REm of different cell types

A
  • Nerve cells : -70mV
  • Smooth muscle cells : -40mV
  • Skeletal muscle cells : -90mV
17
Q

Nernst equation

A
  • Equilibrium is established at the point at which the attraction of the negative charges inside the cell (caused by A-) precisely counter the outward driving force of K+ conc gradient
  • Potential at which this occurs is equilibrium potential for K+ (Ek)
  • Used to calculate the equilibrium potential for any membrane permeant ion (determines contribution of particular ion to REm)
  • Ek value not the same as REm (other ions contribute to REm)
18
Q

Potential changes

A
  • Cell is negative on the inside (at rest) = polarised
  • Cell is positive on the inside = depolarised
  • Cell returns to normal state (negative inside) = repolarisation
19
Q

Local potentials

A
  • Produced when neurone is stimulated
  • Na+ channels open and Na+ flow into the cell (depolarisation)
  • Vary in size depending on how many channels open
  • Decline as they get further from point of stimulation
  • Do not depolarise the entire length of the neurone
20
Q

Threshold potential

A
  • The soma contains an area of membrane called the trigger zone; has a very high density of Na+ channels
  • If local potentials are strong enough to reach this zone, they can trigger an AP
  • Membrane potential at which this occurs is called the threshold potential
21
Q

Action potential

A
  • Rapid and uniform electrical signal conducted down (along) a cell membrane
  • Stimulus causes Na+ channels to open, causing an influx of Na+
  • Depolarisation occurs; inside of the cell becomes more positive
  • Repolarisation begins; Na+ channels close and K+ channels remain open. This prevents any more Na+ from entering, but still allows K+ to leave. Inside of cell becomes more negative and REm is reestablished. Cell is polarised. K+ channels close
22
Q

Hyperpolarisation

A

Charge inside cell falls below REm at the end of repolarisation; K+ channels take longer to close than Na+ channels, letting slightly more K+ out than Na+ entered. Inward diffusion of Na+ through leakage channels bring Em back to normal

23
Q

Refractory period

A
  • Absolute refractory period : Na+ channels are shut and inactivated; impossible to open; impossible to stimulate the membrane to depolarise again
  • Relative refractory period : lasts until after hyperpolarisation; Na+ channels may be open, but as K+ channels are also open it requires a greater stimulus; difficult to stimulate the membrane to depolarise again
24
Q

Propagation of AP in a myelinated neurone

A
  • Not every part of the axon has to depolarise
  • Gaps in myelin; Nodes of Ranvier
  • Signal jumps from node to node
  • Faster AP propagation; saltatory conduction
25
Q

Synaptic transmission

A
  • Depolarisation of the pre-synaptic bulb opens voltage-dependent Ca2+ channels
  • Ca2+ ions enter the cells
  • Influx of Ca2+ causes exocytosis of the vesicles containing the neurotransmitter
  • Ach is released from the pre-synaptic membrane
  • Ach diffuses across the synaptic cleft and reaches receptors in the post-synaptic membrane
  • Ach interacts with ligand-gated ion channels permeable to Na+
  • Ion channels open and Na+ flows into the post-synaptic cell
  • Depolarisation of the post-synaptic cell occurs
26
Q

Ionotropic receptors

A
  • Ligand-gated
  • Cause a rapid opening of ion channels resulting in depolarisation or hyperpolarisation of the post-synaptic cell membrane
  • Mediate fast ionic synaptic responses (milliseconds)
27
Q

Metabotropic receptors

A
  • G-protein coupled
  • Initiate a wide variety of cellular responses
  • Mediate slow biochemically-mediated synaptic responses (seconds-mins)
28
Q

Different effects of the same neurotransmitter

A

Ach in skeletal and cardiac muscle:

  • Nicotinic (ionotropic) : neuromuscular junction of skeletal muscle muscle; activates muscle fibres by causing rapid depolarisation; stimulation
  • Muscarinic (metabotropic) : neuromuscular junction of cardiac muscle; activates G-protein sequence, ultimately resulting in K+ expulsion and membrane hyperpolarisation; inhibition
29
Q

Excitatory and inhibitory post-synaptic potentials

A
  • EPSP : brings the membrane potential closer to the threshold for an AP. If threshold is exceeded, AP is generated
  • IPSP : causes hyperpolarisation and brings membrane potential away from threshold for AP, making it more difficult to generate
30
Q

Summation

A
  • A single post-synaptic cell may interact with multiple other cells, therefore EPSPs can ‘add up’ (summation)
  • Temporal summation : EPSPs arrive rapidly in succession, subsequent EPSP adds to amplitude of preceding EPSP and so on, therefore post-synaptic membrane is brought closer to threshold; AP more likely
  • Spatial summation : post-synaptic cell is stimulated by multiple pre-synaptic end bulbs at once, so post-synaptic membrane is closer to threshold; AP more likely

Physiology (7 decks)

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