Psyc1200 Biological Psychology Lecture 3: Communication in the Nervous System PDF

Psyc1200 Biological Psychology Lecture 3: Communication in our nervous system Ms Sarentha Luther Credits to: Dr. Monika Sobczak-Edmans 2 OUTLINE OF TODAY’S LECTURE Aim of today’s lecture is to learn about: 1. The electr...

Psyc1200 Biological Psychology Lecture 3: Communication in our nervous system Ms Sarentha Luther Credits to: Dr. Monika Sobczak-Edmans 2 OUTLINE OF TODAY’S LECTURE Aim of today’s lecture is to learn about: 1. The electric signaling: conducting information within a neuron 2. The chemical signaling: information transmission between neurons 2 THE CELLS OF THE NERVOUS SYSTEM ▪ Two types of cells: _________ & __________ ▪ The human brain contains approximately 100 billion individual neurons. ▪ Behaviour depends upon the communication between neurons. 3  THE NEURON - RECAP Dendrites Soma DENDRITES: INPUT Axon SOMA: INTEGRATION (primarily) Terminal buttons AXON: CONDUCTION (or Axon Terminals) TERMINAL BUTTONS: OUTPUT NEURONAL COMMUNICATION Important terms: ▪ Ion - An electrically charged molecule ▪ Anion - Negatively charged ion ▪ Cation - Positively charged ion 1. The electric signaling: conducting information within a neuron NEURONAL COMMUNICATION ▪ ANIONS and CATIONS inside the neuron are within INTRACELLULAR FLUID ▪ Outside neuron (through the CELL MEMBRANE) are other ions in the EXTRACELLULAR FLUID  RESTING POTENTIAL Extracellular fluid Intracellular fluid Inside a neuron there are more ANIONS than cations - so it is NEGATIVELY charged MEMBRANE POTENTIAL The electrical charge across a cell membrane; the difference in electrical potential inside and outside the cell. 2 membrane potentials of interest here: Resting potential Action potential balance of ions at brief electrical impulse (big rest (generally about changes in cell membrane potential) -70 milivolts (mV)) that provides the basis for conduction of information along an axon Action potential  -55 ▪The level of DEPOLARISATION (inside of axon becoming more positive) must reach THRESHOLD OF EXCITATION in order for an action potential to occur  THERE ARE CERTAIN IONIC FORCES – FORCES THAT CONTROL THE IONS 1. Diffusion through semi-permeable membrane Molecules move from areas of HIGH concentration to areas of LOW concentration 2. Electrostatic Pressure Opposite charges ATTRACT one another Like charges REPEL one another Concentrations of important ions inside and outside neuron and forces acting on them K+ : Potassium ions A - : Organic Anions IMPORTANT IONS: Na+ : Sodium ions Cl - : Chloride ions SODIUM-POTASSIUM PUMP Pushes Na+ out Exchanges Na+ for K+ Pushes 3 Na+ out for each 2 K+ allowed in MAINTAINS RESTING POTENTIAL EVENTS LEADING TO ACTION POTENTIAL Concentrations of important ions inside and outside neuron and forces acting on them K+ : Potassium ions A - : Organic Anions IMPORTANT IONS: Na+ : Sodium ions Cl - : Chloride ions SODIUM CHANNELS? 2 MORE IMPORTANT TERMS … ▪ Ion Channel – A channel in the cell membrane that permits specific ions to enter or leave the cell ▪ Voltage-gated ion channel - An ion channel that opens or closes according to the value of the membrane potential AN ACTION POTENTIAL Opening of Sodium channels starts the action potential Potassium channels opening are a second step AN ACTION POTENTIAL ▪ Movement of Action Potential down the axon is in an all-or-nothing manner. ▪ Once it has been triggered it is transmitted down entire axon. ▪ At end of axon it splits to different terminals buttons but remains of the same power. SALTATORY CONDUCTION Areas without myelin are the only areas where an action potential can be triggered This then ‘jumps’ to next node in passive manner 2. The chemical signaling: information transmission between neurons  SYNAPTIC TRANSMISSION SUMMARY OF EVENTS 1. Action potential in pre-synaptic neuron 2. Depolarisation from action potential opens calcium channels in pre-synaptic neuron 3. Calcium enters pre-synaptic neuron  SYNAPTIC TRANSMISSION: SUMMARY OF EVENTS 4. Calcium triggers synaptic vesicles to fuse with pre- synaptic membrane 5. When vesicles fuse they can then release neurotransmitter into synapse 6. Neurotransmitter binds with receptors in post- synaptic membrane.  SYNAPTIC TRANSMIS 7. Neurotransmitter binding with post- synaptic receptors will open some ion channels in the post- synaptic neuron. SUMMARY OF EVENT 8. Opening of ion channels letting in cations = EPSP. Opening ion channels letting in anions = IPSP 9. Summation of EPSPs to IPSPs is excitatory enough to depolarize to threshold = neuron will fire an action potential  SYNAPTIC TRANSMISSION: TWO EXTRA EVENTS 10. Excess neurotransmitter degraded by enzymes 11. Excess neurotransmitter taken back by pre- synaptic neuron POSTSYNAPTIC RECEPTORS ▪ Specialised to fit particular neurotransmitters ▪ Like a particular key opening a particular lock ▪ A molecule of the correct size and shape to fit the receptor is a LIGAND LIGANDS? Ligands can be: ▪ Endogenous ligand – neurotransmitters and hormones occurring naturally in the body ▪ Exogenous ligand – drugs and toxins from outside the body NEUROTRANSMITTERS ▪ Can you name any neurotransmitters? NEUROTRANSMITTERS ▪ Dopamine – general arousal - movement ▪ Serotonin – related to mood ▪ Acetylcholine – learning, memory, attention ▪ Noradrenaline – mental arousal ▪ Glutamate – formation of long-term memories ▪ Endorphins/ Enkephalins – opioids modulate pain, reduce stress RECOMMENDED READING: ▪ Chapter 3&4 of Kolb and Whishaw textbook