L11 Synapses and imbalances

Page 1: Ion Channel Status During Action Potential

• Process Overview: This page outlines the status of Na+ (sodium) and K+ (potassium) ion channels during different phases of an action potential.

  • A: Resting Potential - Both Na+ and K+ channels are closed.

  • B: Depolarisation - Na+ channels are open; K+ channels are closed.

  • C: Repolarisation - Na+ channels are closed; K+ channels are open.

  • D: Undershoot - Na+ channels remain closed; K+ channels are open.

  • E: Threshold Level.

  • X: Action Potential - Na+ channels are open; K+ channels are closed.

    

Page 3: Membrane Potential Overview

• Membrane Potential Table: This table illustrates the membrane potential at various stages of action in an axon, measured in mV.

  • A: -70 mV

  • B: -50 mV

  • C: -20 mV

  • D: +40 mV

  • E: +60 mV

  • F: Changes reflecting the state of Na+ and K+ channels are recorded.

    • Na+ channels are open or closed in stages A-F as defined previously.

    • K+ channels exhibit similar open/close states contingent on the phase of action potential.

      

Page 4: Action Potential Frequency Calculation

• Ionic Influence: The specific ions affecting electrical potential shifts are Na+ and K+.

• Frequency Calculation: A mathematical problem indicating the number of action potentials occurring in one second based on a graph's frequency.

  

Page 5: The Action Potential Wave Analogy

1. During the resting potential, the axon's internal charge is at -70 mV.

2. Upon stimulation, the first segment of the axon begins to depolarise, akin to the first row in a Mexican wave standing up.

3. This change propagates along the axon, bringing about further depolarisation in adjacent sections.

4. Propagation continues with sections of the axon returning to their resting state as the wave advances, demonstrated by sequential lines standing and sitting during the wave.

Page 6: ECG Measurements

• An electrocardiogram (ECG) detects the heart's depolarization wave, manifesting small electrical signals on the skin surface, captured by several electrodes.

Page 8: ECG Wave Components

• P Wave: Represents atrial depolarisation.

• QRS Complex: Indicates ventricular depolarisation.

• T Wave: Corresponds to ventricular repolarisation.

  

Page 9: Heart Rate Calculation

• Time Measurement: Each small box on the ECG represents 0.04 seconds. Calculating the intervals between R waves reveals the person's heart rate.

  

Page 10: Membrane Changes During Action Potential

• Membrane Permeability: At point 1 on the graph, the sodium channels open when the membrane potential reaches -70 mV. This results in an increased permeability of the membrane to Na+, leading to a rapid influx of sodium due to the established concentration gradient.

Page 11: Answer to exam question

• Sodium channels open at a potential of -70 mV, causing an influx of Na+ into the axon, altering its electrical states.

  

Page 13: Structure of a Synapse

• Components: Include presynaptic neurone with vesicles of neurotransmitters, synaptic cleft, and postsynaptic neurone.

• Directional Transmission: The synapse structure ensures impulses travel only in one direction, as neurotransmitters are released by the presynaptic neurone and bind only to receptors on the postsynaptic neurone.

Page 14: Synaptic Transmission Sequence

1. Arrival of action potential at presynaptic terminal.

2. Voltage-gated calcium channels open, allowing Ca2+ to diffuse in.

3. Calcium binding prompts vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft via exocytosis.

4. Neurotransmitters adhere to receptors on the postsynaptic membrane, facilitating neural communication.

   

Page 15: Postsynaptic Effects

• Following neurotransmitter binding, sodium channels on the postsynaptic membrane open, causing depolarisation and potentially initiating a new action potential.

• The neurotransmitter is then broken down by enzymes and reabsorbed to terminate the signal effectively.

  

Page 17: Drugs and Neurotransmitter Interaction

• Agonist Drugs: Such as nicotine, enhance neurotransmitter function, increasing action potentials.

• Antagonist Drugs: Such as atropine, inhibit neurotransmitter functioning, thereby reducing action potentials.

Page 18: Neurotransmitter Functions

• Acetylcholine: Found in muscle synapses, facilitates contraction.

• Serotonin: Affects mood and feelings, predominantly in brain synapses.

• Dopamine: Links to motor control, speech, and emotional regulation.