Biopsychology & Learning Past Paper - 2024 PDF

8/7/24 The Neuron PSYU2236/PSYX2236 Biopsychology & Learning Lecturer: Dr Patrick Nalepka (he/him) 1 Outline 1. Non-Associa...

8/7/24 The Neuron PSYU2236/PSYX2236 Biopsychology & Learning Lecturer: Dr Patrick Nalepka (he/him) 1 Outline 1. Non-Associative Learning Revision; Updates 2. The Cells of the Nervous System 3. The Action Potential 2 1  8/7/24 Non-Associative Learning Revision Patrick Nalepka: Habituation, Desensitisation, Sensitisation, Dishabituation posted in PSYUX2236-2 0 2 4 -S2 / Week 01 - In tro t o U nit on Saturday, 27 July 2024 3:10 p m 3 3 Updates Tutorials: For PSYU2236, “S tream A” begin their tu to ria ls th is week. Stream A are classes t h a t begin in Week 31 (Week 2) Stream B are classes t h a t begin in Week 32 (Week 3) Inform ation regarding PASS, Lecture Readings, Assessments and Tutorials have been added to iLearn (don’t m in d th e m ess as things are s till under construction 4 4 2  8/7/24 Updates The PSYX2236/OUA iLearn can be accessed via the OUA channel. 5 The PSYU2236 iLearn can be accessed via th e General channel. 5 Updates additional settings can be adjusted in the top right of the window next to your photo. 6 You can set n o tifica tio n settings and show /hide th e channels you w a n t t o stay organised. 6 3  8/7/24 2. The Cells of the Nervous System 7 Neuron Network The human brain has approximately 100 billion neurons (and even more glial cells) – the two cell types of the nervous system HUGE network for communication & complex processing PSYU2236 Brain Cells. Ramsey. 8 8 4  8/7/24 Golgi stain; The Neuron Doctrine Camillo Golgi, 1873 Impregnates tissue with silver nitrate – see physical structure of neuron Santiago Ramon Cajal - identified neurons as single entities (The Neuron Doctrine) PSYU2236 Brain Cells. Ramsey. 9 9 These neurons have a nucleus and if you have previous history in cellular biology you can refer to that but what is key here is understanding the four unique structures to neurons. Neurons Many different types Most have 4 main parts: Soma (cell body) Dendrites Axon Presynaptic Terminals PSYU2236 Brain Cells. Ramsey. 10 10 Soma; the cell body Dendrites; tree like structures that receive info from other neurons Axon; helps propagate signals throughout the neuron Presynaptic terminals; the end point of where that information goes within a neuron before it's communicated to the next neuron down the chain. 5  8/7/24 Typical Neuron Axons + dendrites = Neurites Presynaptic Terminal PSYU2236 Brain Cells. Ramsey. 11 11 A key di erence between neurons and copper wire is that if there was copper wire in my foot leading up to my brain and someone stepped on my foot the pain from that injury would go up to my brain almost instantaneously. Neurons are not that good at conducting electricity so they have evolved to develop ways around that. Axons Axons carry information to the terminal (presynaptic) boutons (or buttons) Neurons keep their shape by: Microtubules (tubulin) Neurofilaments Microfilaments (actin) Axon Hillock Axon Collaterals Axon Axon Terminal Terminal Arbor Terminal Boutons (forms synapses with other cells) PSYU2236 Brain Cells. Ramsey. 12 12 Fun fact! The length of an axon can be up to one meter long! Which is why they often use squid nerves in lab experiments because they are a similar length to meter long neurons. 6  8/7/24 White vs Grey Matter: Cortex Grey Matter: Predominately cell bodies with few myelinated axons White Matter: Few cell bodies, and mostly bundles of myelinated axons. Connects grey matter areas to each other. Fig 1.6 Bear: Similar fig 3.11 Kalat PSYU2236 Brain Cells. Ramsey. 13 13 Classification of Neuron Type Neurons are classified by The number of Neurites (from cell body) Their dendrites - how many and if they have spines or not Their axon length: Golgi type I – long “internuncial” Golgi type II – small “interneurons” The neurotransmitter used by the neuron Neuronal connections - primary sensory neurons or motor neurons PSYU2236 Brain Cells. Ramsey. 14 14 7  8/7/24 A neurite is either an axon or a dendrite.If you have 1 axon and 1 dendrite you have two neurites. If you have 1 dendrite it's 1 neurite but you can also nd out what's a neurite based on how many are connected to the soma. Classification by Neurites (Axons and Dendrites) Cells can be unipolar, bipolar or multipolar - defined by the number of neurites connected to the soma Check out: figure 1.8 Kalat multipolar unipolar bipolar PSYU2236 Brain Cells. Ramsey. 15 15 Bipolar neurons are pretty common Unipolar dendrites are not found in vertebrates Classification by Dendrites Neurons are classified by the shape and kind of dendrites Stellate (starshaped) vs pyramidal (triangular) Has spines (spinous) or doesn’t have spines (aspinous) Dendritic spines are involved in learning and memory Dendritic trees constantly change (grow or receed) - aids in neuroadaptation Dendrites are sources of information for the neuron – the more dendrites the more info the neuron receives PSYU2236 Brain Cells. Ramsey. 16 16 8  8/7/24 There's usually a gap in between this synaptic connection Afferent vs Efferent Neurons Afferent Connects with Another neuron (to the connection) Axon Synaptic connection Soma Dendrites Efferent (from the connection) PSYU2236 Brain Cells. Ramsey. 17 17 Neuron Summary v The cortex is composed of white (myelinated axons) and grey matter (neuron cell bodies) v There are 4 main parts to a neuron: soma (cell body), dendrites, axons, presynaptic terminal v Neurites are projections from the cell body of a neuron (e..g, axons and dendrites) v Neurons are classified by the number of neurites, type of dendrites, axon length, neurotransmitter & synaptic connections v Afferent neurons go TO the synapse, efferent neurons project FROM the synapse PSYU2236 Brain Cells. Ramsey. 18 18 9  8/7/24 There are about 3 to 4 times as many Glial cells as there are neurons Glial Cells Glial cells are the supporting cells of neurons v Astrocytes - most numerous, fill the space between neurons v Regulates the chemical environment of the extracellular space v Supplies nutrients, ions, oxygen from blood supply v Synchronise neurons (wraps around many) v Can be regulated by neurotransmitters! v Oligodendrocytes (central) - wrap cells in myelin (fatty insulation) v Myelin sheath is interrupted by nodes of Ranvier (helps with propogation of electrical signal along the axon) v This glial cell shares myelin with several axons v Schwann cells (periphery) - similar to oligodendrocyte, but does not share myelin - each cell myelinates only a single axon v Radial glia - guide neuron migration and axon growth (embryonic) v Microglia – remove cellular debris due to injury or cell turnover; get rid of toxins PSYU2236 Brain Cells. Ramsey. 19 19 Astrocytes; the extracellular space is the chemical environment outside/surrounding the neurons. Oligodendrocytes; found in the CNS as opposed to Schwann cells which are found in the PNS (Peripheral Nervous System). Myelination; helps facilitate communication of electrical signals within a neuron Glial Cells II Peripheral nervous system (PNS) only Central nervous system (CNS) only Fig 1.9 Kalat PSYU2236 Brain Cells. Ramsey. 20 20 10  8/7/24 Glial Cell Summary v There are several types of glial cells - astrocytes (radial), oligodendrocytes, microglia, Schwann cells (peripheral) v Glial cells support neurons chemically and physically v Glial cells of the central nervous system connect with several neurons, helps to physically stabilise neurons and synchronise their activity. PSYU2236 Brain Cells. Ramsey. 21 21 Break Break Time 22 11  8/7/24 3. The Action Potential 23 Resting Membrane Potential COMMUNICATION IN THE BRAIN Phospholipid bilayer Inside (intracellular) Cytoplasm/intracellular fluid Plasma membrane around the neuron Allows uncharged molecules through NOT ions/charged molecules Outside These need to pass through (extracellular) channels or receptors Extracellular Figure 1.12, Kalat, 12th Ed. fluid 24 24 Because of this impermeable membrane there are key channels (like to prevent ooding in a basement) is maintaining a chemical balance between potassium (K+) and sodium (NA+). So the sodium potassium pump kicks sodium out and brings potassium in. Potassium can leave whenever they want, but there has to be this balance between these two opposing forces. On average there's more (K+) in the neuron than (NA+) on the outside. 12  8/7/24 Resting Membrane Potential COMMUNICATION IN THE BRAIN Inside (intracellular) An electrochemical gradient Cytoplasm/intracellular ― intracellular ion concentration ≠ fluid extracellular ion concentration. ― Since these are different - it has the POTENTIAL to change Extracellular vs intracellular fluid ion concentration at rest Ions important for neurophysiology Outside Cations: Na+, K+, Ca2+ (extracellular) Anion: Cl- Extracellular Figure 1.12, Kalat, 12th Ed. fluid 25 25 How is membrane potential created? COMMUNICATION IN THE BRAIN Difference in electric charge across membrane gives it potential Proteins (P-) and Chloride ions (Cl-) = overall resting potential of the inside cell negative. Usual resting membrane potential = -70 mV This difference in charge means some ions will move across if their channels are open High [Na +]/Low [K+] Na+ Na+ K+ Na+ K+ Na+ positive Extracellular fluid (ECF) K+ Cl- K+ Na+ P- K+ Na+ negative High [K+]/Low [Na+] P- K+ K+ K+ Cl- K+ Cl- Intracellular fluid (ICF) K+ Na+ Na+ Na+ Na+ K+ Na+ positive 26 26 13  8/7/24 Regulation of Na+ and K+ COMMUNICATION IN THE BRAIN Electrical Gradient: causes K + to flow in Concentration Gradient: causes K + to flow out At rest, K + channels are open, and potassium flows in and out. K+ High [Na +]/Low [K+] Na+ K+ Na+ K+ Na+ Na+ Extracellular fluid (ECF) K+ Cl- K+ Na+ P- K+ Na+ K+ High [K+]/Low [Na+] P- K+ K+ K+ Cl- K+ Cl- K+ K+ Intracellular fluid (ICF) K+ Na+ Na+ Na+ Na+ K+ Na+ Na+ Na+ 27 27 Resting Membrane Potential: Summary COMMUNICATION IN THE BRAIN Electrical gradient: the difference in electrical charge between two adjacent areas. If an area is negative, positive ions will flow to it. ― Positive K+ ions will flow from the outside of the cell (more positive charge) to the inside (more negative). Concentration gradient: the difference in concentration of a particular ion between two adjacent areas. If an area has many K+ ions, the K+ ions will flow to an area with less K+ ions. ― The inside of the cell has more K+ ions than the outside. K+ ions will then cross from the inside to the outside of the cell. 28 28 14  8/7/24 Restoring the chemical potential COMMUNICATION IN THE BRAIN Why is there more K+ inside the cell at rest? Sodium Potassium (Na +/K +) Pump Brings in 2 K + and removes 3 Na + ions Restores chemical potential (greater [K +] inside) Restores electrical potential (greater - charge inside) Requires energy (ATP) K+ Na+ K+ Na+ K+ Na+ Na+ K+ Cl- K+ K+ Na+ P- K+ Na+ P- K+ K+ K+ Cl- K+ Cl- K+ K+ ATP ADP K+ Na+ Na+ Na+ Na+ K+ Na+ Na+ Na+ Na+ 29 29 Voltage-gated ion channels COMMUNICATION IN THE BRAIN Na + ion channels are voltage gated: only open with certain membrane potentials (e.g. -50 to +30mV) Voltage gated K + channels: only open when the cell becomes positive K+ Na+ K+ Na+ K+ Na+ Na+ K+ K+ Cl- K+ Na+ P- K+ Na+ P- K+ Cl- K+ K+ Cl- K+ K+ K+ ATP ADP K+ Na+ Na+ Na+ Na+ K+ Na+ Na+ Na+ Na+ 30 30 15  8/7/24 Regulating membrane potential: summary COMMUNICATION IN THE BRAIN K+ channels: open when the neuron is at rest, K+ ions flow into the cell driven by electrical gradient and out of the cell driven by chemical gradient Na+/K+ pumps: actively (i.e. with energy) pump Na+ out of and K+ into the cell on a 3:2 ratio Na+ channels: only open at limited voltages. When open Na+ will flow into the cell along the chemical and electrical gradient Voltage-gated K+ channels: would allow K+ ions into and out of the cell, except only open when the cell potential is positive (i.e. not at rest) 31 31 The typical resting state of a neuron is -70. If it's receiving a change in voltage in the axon compared to the outside world if that voltage changes from -70 up to a critical threshold (-55mV) these sodium potassium channels are activated and that is part of triggering an action potential. Once this threshold is reached the neuron depolarises (meaning the neuron is now positive) which will raise it from -80 to -65 triggering the action potential. The neuron will repolarise after the action potential. Action potentials begin at the axon hillock COMMUNICATION IN THE BRAIN Dendrites Presynaptic Terminals Neuron 1 Axon hillock Axon Neuron 2 Depolarisation -65mV Neuron 3 -80mV Other neurons causes small changes in charge via communication at dendrites These changes accumulate at the axon hillock When charge comes within range, Na + ion channels will open è Massive influx of positively charged Na + ions 32 32 16  8/7/24 Sodium wants to be inside the neuron due to its charge and the chemical environment surrounding it. Neuron at Rest (-70mV) COMMUNICATION IN THE BRAIN K+ K+ Na+ K+ K+ Na+ K+ K+ Na+ + + + + + + - - - - - - K+ K+ K+ - -70mV - - -70mV - - -70mV - + + + + + + Na+ We are here K + channels open and at equilibrium Voltage gated K + channels closed Na + channels closed Na +/K + pump setting up potential 33 33 Positive charge reaches threshold (-50mV) COMMUNICATION IN THE BRAIN K+ K+ Na+ K+ K+ Na+ - - - - + + + + + + - - K+ K+ K+ + -50mV + + -70mV + - -70mV - - - - - + + Na+ We are here Voltage-gated Na + and K+ channels open closest to hillock. K+ channel is slower to open. Massive influx of Na + ions è depolarisation K+ ions leave (electrical gradient) 34 34 17  8/7/24 Refractory periods COMMUNICATION IN THE BRAIN K+ K+ K+ K+ Na+ - - - - - - + + + + - - + +30mV + - -50mV - - K+ -70mV - - - + + + + K+ We are here Na+ Voltage gated Na+ channels close in first part of axon (positive membrane potential) Massive efflux of K+ ions è hyperpolarisation. First part of the axon is in its refractory period Next part of the neuron becomes depolarised…… Voltage gated K+ channels close, and the Na +/K + pumps restores resting potential 35 35 Propagation of action potentials COMMUNICATION IN THE BRAIN Dendrites Neuron 1 Axon hillock Presynaptic Terminals Neuron 2 ++ + -+ -+ -+ -+ -+ + - + - +- +- -+ -+ + - + - + - +- +- +- +- +- +- +- + - + - +- +- -+ -+ -+ -+ + - +- +- +- +- -+ -+ + - + - + - + - + - +- -+ -+ + - -+ -+ -+ -+ -+ -+ -+ + - + - + - +- +- +- + - +- +- +- +- -+ -+ + - + - + - + - + - +- -+ -+ + - -+ -+ -+ -+ -+ -+ -+ + - + - + - +- +- +- -+ -+ -+ -+ -+ + - + - +- +- -+ -+ + - + - + - +- +- +- +- +- +- + - + - + - +- +- -+ -+ -+ -+ 36 36 18  8/7/24 If you have sustained information or triggers for the action potential, you'll most likely get lots of small-medium sized peaks rather than the huge depolarisation demonstrated below. The thicker the axons are (the more myelinated) the faster the axon res (less electrical resistance) Rapid Reversal of Membrane Potential COMMUNICATION IN THE BRAIN Influx: into the neuron Efflux: out of the neuron Polarise: make negative Voltage-gated Na+ closes Voltage-gated Na+ Hyperpolarisation: and K+ channels Absolute refractory period undershoot due to continued Relative refractory period open (K+ are slower K+ efflux before voltage-gated 37 to open) K+ channel closes 37 It's called undershooting because it goes below baseline When it's in the refractory period the cell can't receive anymore information (that's called the absolute refractory period) In the relative refractory period the axon can receive information but it's a lot harder. You'd need to receive a stronger voltage change than the original voltage change to get it to re again. Refractory periods COMMUNICATION IN THE BRAIN Absolute Refractory Period: 1ms after action potential. The neuron cannot fire again during this period. Relative refractory period: 2-4 ms after action potential. The neuron is hyperpolarized and is more difficult to produce an action potential due to the greater depolarization event needed. 38 38 19  8/7/24 Action Potential Demo Neuron Demo 39 39 Summary: Membrane potential COMMUNICATION IN THE BRAIN The resting membrane potential (RMP) is produced by the electrochemical gradient between the intracellular and extracellular fluid bordering the phospholipid bilayer membrane of the neuron Cells can have different RMP’s, commonly neurons have an RMP of -70mV At rest, the inside of the neuron is negative due to many proteins and chloride ions which have a negative charge, and proteins cannot leave the neuron At rest, inside the neuron there is a high concentration of K+ ions and a low concentration of Na+. Outside of the cell is the opposite K+ ions channels are open (not the voltage-gated ones) which allows K+ to enter the cell (electrical gradient) or to leave the cell (concentration gradient) Voltage-gated Na+ ion channels and K+ ion channels are not open The membrane potential is regulated by the Na+/K+ pump. Adenosine triphosphate (ATP; energy) is required to pump 3Na+ ions out and 2K+ ions in 40 40 20  8/7/24 Summary: Action Potential COMMUNICATION IN THE BRAIN An action potential only occurs if enough positive charge reaches the axon hillock to go above the threshold potential of the neuron The threshold potential (threshold of excitability) is commonly around -50mV in neurons Once this threshold is reached, Na+ channels open and heaps of Na+ comes into the cell - depolarisation (more positive). Voltage-gated K+ channels also open, but slower. At the peak of the action potential (+30mV) Na+ channels close and voltage-gated K+ channels become fully open: K+ leaves the cell - repolarisation (more negative). At this stage the neuron is in the absolute refractory period - it cannot fire. Hyperpolarisation - undershoot to more negative than RMP - the neuron is in the relative refractory period RMP is restored by Na+/K+ pump and open K+ channels 41 41 Neuronal insulation: Myelin COMMUNICATION IN THE BRAIN Waiting for all of the channels to open and close takes time. There is also the potential for current to ‘leak’ with many channels in the membrane The neuron is insulated with myelin (oligodendrocytes: glial cells) Myelin wraps the axon - with small gaps in between - the Nodes of Ranvier. ― The Nodes of Ranvier are where channels and pumps are concentrated along the axon ― Myelination insulates the axon so charge speeds along between nodes - energy efficient Dendrites Presynaptic Terminals Oligodendrocyte Node of Ranvier Myelin Sheath (Degraded myelin sheaths – Multiple Sclerosis) 42 42 21  8/7/24 Saltatory Conduction COMMUNICATION IN THE BRAIN Unmyelinated notes are 1000 x smaller than myelinated sections Action Potential Refractory periods mean the action potential can only proceed in one direction 43 43 Propagation of Action Potential: Summary COMMUNICATION IN THE BRAIN Movement of charge along the axon is propagated by myelin sheaths and nodes of Ranvier The myelin (fatty) sheaths come from glial cells: oligodendrocytes Oligodendrocytes make contact with several different neurons (unlike peripheral nervous system [PNS] where Schwann cells only wrap around one nerve) Propagation of action potentials only occurs in one direction due to refractory periods (action potential can only go forward not back where it has just been) The process of propagation of the action potential along myelinated neurons is called saltatory conduction (“jumping”). 44 44 22  8/7/24 Synaptic transmission is about the neurons communicating to each other. Post Synaptic Potentials COMMUNICATION IN THE BRAIN Dendrites Presynaptic Terminals Neuron 1 Axon hillock Axon Neuron 2 Depolarisation Hyperpolarisation -65mV -80mV Neuron 3 -80mV -95mV 1. Excitatory Post Synaptic Potential (EPSP) 2. Inhibitory Post Synaptic Potential (IPSP) 3. Action Potential 45 45 Post Synaptic Potentials COMMUNICATION IN THE BRAIN Excitatory Post Synaptic Potential (EPSP) Communication with dendrites from other neurons can bring positive ions into the cell Positive ions produce a small depolarisation - an Excitatory Post Synaptic Potential Small EPSPs are not enough to produce an action potential Inhibitory Post Synaptic Potential (IPSP) Communication with dendrites from other neurons can bring negative ions into the cell Negative ions produce a small hyperpolarisation - an Inhibitory Post Synaptic Potential IPSPs will not produce an action potential (pushes potential down) 46 46 23  8/7/24 Postsynaptic neurons receive multiple inputs COMMUNICATION IN THE BRAIN IPSP and EPSP can cancel each other out A small depolarisation (EPSP) will cancel the effect of a small hyperpolarisation (IPSP) Sufficient EPSP will produce an action potential Once positive charge at axon hillock reaches threshold, Na+ channels are opened, positive ions flood the intracellular space and an action potential is generated. Sufficient IPSP will inhibit action potentials Large IPSPs are due to many negative ions entering the cell. The integration of charge at the axon hillock can’t reach the excitation threshold. An action potential cannot occur. NEURAL INTEGRATION 47 47 Neural Integration: Temporal and Spatial COMMUNICATION IN THE BRAIN Figure 2.4, Kalat 48 48 24  8/7/24 Neural integration and neuronal activation COMMUNICATION IN THE BRAIN Figure 2.3, Kalat From same presynaptic neuron From different presynaptic neurons 49 49 Neural Integration: Summary COMMUNICATION IN THE BRAIN Dendrites (mostly) receive information from different transmitters at the same time ― polarity of these dendrites may differ ― Excitatory Post Synaptic Potentials (EPSPs) increase the likelihood of generating an action potential by elevating the mV at the axon hillock ― Inhibitory Post Synaptic Potentials (IPSPs) reduce the likelihood of generating an action potential by lowering the mV at the axon hillock All of these ‘polarities’ produced by chemical transmission are integrated at the axon hillock Neural integration is the sum of the EPSP and IPSPs where increases in mV above the excitability threshold will result in an action potential Depolarisation of the neuron will occur - action potential 50 50 25  8/7/24 Next Time The le ctu re to p ic next w eek is “The Synapse” Reading: The Kalat chapter t it le d “Synapses” Tutorials s ta r t th is w eek fo r s tu d e n ts enrolled in Stream A classes. In - person: Arrive t o your class on tim e ! (12SW Room 317) Online: Visit your class’s te a m channel on tim e! OUA: Tutorial 1 w ill be posted later today - I’ll m ake an iLearn announcem ent. Make use o f our PSYUX2236-2 0 2 4 -S2 Team fo r u n it discussions, ask questions, or help answer questions f r o m your peers! Have a good day! 51 26