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Chapter 3

psych 1000 - Chapter 3 - Biological Foundations of Behaviour.pdf

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Psychology 1000

Chapter 3 - Biological Foundations .of Behaviour October-18-12 3:37 PM NEURAL BASES OF BEHAVIOUR Neurons → Basic building blocks of nervous sys → Receive, process, send msgs → Linked together in circuits → 3 main parts... 1. Soma ○ Cell body Has biochemical structures to keep neuron alive ○ ○ Contain in DNA in nucleus ○ Combines and processes messages 2. Dendrites ○ Receiving units ○ Collect messages from neighbour neurons ○ Sends message to cell body 3. Axon ○ Conducts electrical impulses from cell body to muscles, glands, other neurons ○ Branches out at ends: axon terminals ○ Connects with dendritic branches ○ Neuron in spinal cord can have axon that extend over 1m (e.g. to fingers) ○ Neurons in brain can have axons less than 1mm Glial Cells → Support neurons in their function → Hold them in place → Manufacture nutrient-rich chemicals → Form myelin sheath (for some axons) → Absorbs toxins that can damage neurons → Send out long fibres that guide newly divided neurons to their targeted place in prenatal brain development → Protect brain from toxins… Blood-brain barrier ○ Prevents many substances rom entering ○ Walls of blood vessels in brain have smaller gaps, covered by special glial cell Myelin Sheath ○ Myelinated axons have node of Ranvier (where myelin very thin or absent) ○ In myelinated axons, electrical current skips from node to node ○ gives high conduction speeds Damage to myelin sheath seen in MS. Disrupts timing of nerve impulses, leadingto jerky uncoordinated movements, and eventuallyparalysis **May also help with modulating the communication among neurons ElectricalActivity of Neurons Neuronsdo 2 importantthings → Generate electricity (nerve impulses) → Release chemicals (so they can communicate) NERVE ACTIVATION 1. At rest 2. Stimulated 3. Restored → Neurons surrounded by fluids, and have a membrane → Membrane allows certain substances to pass through the ion channel, by opening → Process whereby a nerve impulse is created involved exchange of ions Fluid outsideneuron → More positive Part 1 Page 1 → More positive → Na+ and Cl- Inside neuron → More negative → Large negatively charged protein molecules, and K+ → Uneven distribution of positive and negative ions → Therefore interior negative compared to outside → Internal difference is 70 millivolts --> Resting potential → State of polarization ACTION POTENTIAL → Sudden reversal in neuron's membrane voltage → If axon stimulated (mild electrical stimulus), int voltage differential shift-70mVm to +40mV → Shift from negative to positive voltage --> depolarization How does this happen? Restingstate → Na+ and K+ channels closed → Na+ concentration 10x more outside of neuron Stimulated → Na+ channels open → Na+ attracted by negative protein ions in neuron, so they flood into axon → Interior now positive compared to outside (by +40mV) --> state of depolarization Restore → Reflex action to restore resting potential → Cell closes Na+ channels → K+ flows out of neuron though K+ channels to restore proper charge → (eventually Na+ flows out, K+ recovered) **when action potential occurs at any point on membrane, effects spread of adjacent Na+ channels, so action potential moves down axon to terminals Absolute refractoryperiod → When K+ flows out → Membrane no excitable, can't generate another action potential at this time → This puts limit on rate (300/s for humans) All-or-None Law → Action potentials occur at uniform and mx intensity, or not at all → Na+ needs to change negative potential in axon from -70mV to -50mV --> action potential threshold → Changes in neg resting potential that don’t reach this --> graded potentials → Graded potentials can cause action potentials if added up Synaptic Transmission Synapse → Functional connection b/w neuron and target → Not physical → Small gap b/w axon terminal, and dendrite of other neuron --> synaptic cleft NEUROTRANSMITTERS → Chemical substances that carry messages across synapse to excite or inhibit other neuron → Process of chemical communication… 1. Synthesis Chemicals formed in neuron 2. Stored In synaptic vesicles (in axon terminal) 3. Released Into space b/w presynaptic and postsynaptic neurons 4. Bind At receptor sites 5. Deactivation
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