Psyc 301 Brain Dysfunction & Recovery Structural Neuroanatomy PDF, Jan 2025

Psyc 301 Structural Brain Dysfunction & Recovery Neuroanatomy Jill Dosso, PhD Jan 2025 Speaking...

Psyc 301 Structural Brain Dysfunction & Recovery Neuroanatomy Jill Dosso, PhD Jan 2025 Speaking to you from the traditional, ancestral, and unceded territory of the xwməθkwəy̓əm (Musqueam) People.  Part 3 Cells & neurotransmitters Topics 70 Cells of the nervous system Resting membrane potential Action potential Neurotransmitters Learning Objectives 71 1. Name the two broad categories of cells within the nervous system 2. Identify three mechanisms of molecular transport across the cell membrane 3. Define the resting membrane potential and describe how it is maintained 4. Describe the key events of the action potential and neural conduction 5. Identify the major components of a synapse 6. Describe the general role of neurotransmitters 7. Use key drug-related terminology: agonist, antagonist, reuptake inhibitor 8. Name three types of glial cells and describe some of the functional roles for each 1. Neurons are electrically conductive 72 Neuron morphology is diverse and specialized 73 Parekh & Ascoli, 2013 Neuron  74 Processes = axons and dendrites (Like siblings = brothers and sisters) Unipolar = one process leaves cell body Interneuron Bipolar = two processes leave cell body Multipolar = 3+ processes extend from cell body Interneuron = no axon or short axon Unipolar Bipolar Multipolar  75 The inside of the neuron is chemically different from the outside (the extracellular fluid) Molecules and ions cross into/out of neurons via 1. Passive diffusion (for fat- soluble molecules) 2. Facilitated diffusion through channels 3. Active transport, requires energy, through pumps Resting membrane potential 76 A healthy neuron has a resting membrane potential (voltage) been -60 mV and -80mV As ions of sodium (Na+) and potassium (K+) move into or out of the cell, they change the potential (voltage) at the membrane  Resting membrane potential 77 The resting membrane potential is maintained by sodium- potassium pumps 3 Na+ out: 2 K+ in Uses 2/3rds of brain’s total energy (ATP) At rest: More Na+ outside the cell More K+ inside the cell Each have dedicated channels (doors that only they fit through) that are closed at rest but open at predictable voltages Neither can cross the membrane when channels are closed  Action potential 80 If the charge across the membrane exceeds -55 mV, the neuron fires an action potential: the charge across the membrane changes in a specific pattern When voltage-gated Na+ channels open, Na+ “falls down” its concentration gradient and enters the cell > cell becomes more + When K+ channels open, K+ “falls down” its concentration gradient and leaves the cell As voltage-gated channels close, sodium-potassium pumps catch up and restore the cells resting potential Conduction down the axon 83 Action potential 84 The AP travels down the axon and does not decay All or none principle Action potential 85 Unmyelinated axons have Na+ channels (Nav) all along their surface Myelinated axons have Nav only at the nodes of Ranvier Action potentials travel more quickly down myelinated axons (faster conduction speed)  86 Why does charge across the membrane change to begin with? Could be caused directly by a stimulus in a sensory cell E.g., light activates rods in the eye, stretch activates muscle sensory cells  87 Why does charge across the membrane change to begin with? Or, can be caused by inputs from other neurons At the end of each axon is a terminal button Button has vesicles filled with molecules called neurotransmitters – molecules that allow neurons to communicate with one another When an action potential reaches the terminal button, NTs are released into the synapse  88 The synapse Synapse: small, active gap between two neurons Sending = presynaptic neuron Receiving = postsynaptic neuron  89 The synapse Postsynaptic neurons have a variety of receptors that fit, like a lock and key, with specific neurotransmitters When NTs bind to a corresponding receptor, they trigger changes that push the charge of the postsynaptic cell up (towards depolarizing) or down (towards hyperpolarizing) Neurotransmitters are molecules that allow 90 neurons to communicate  Neurotransmitters can be 91 Excitatory: make the receiving neuron more likely to fire an action potential Inhibitory: make the receiving neuron less likely to fire an action potential Modulatory: trigger other changes In this class we will discuss neurotransmitters like dopamine, serotonin, and GABA  92 When drugs act upon NT receptors, they can act as agonists (turning on the receptor and activating its effects) antagonists (blocking the receptor from being turned on) or have other effects such as blocking reuptake or transport Example 93 Example 94 Opioid antagonist Neurotransmitter cleanup 97 1. Diffuse away 2. Broken down by enzymes 3. Reuptake By presynaptic neuron By glia Reuptake inhibitors 98 Serotonin (5-HT) & norepinephrine (=noradrenaline) are Serotonin system neurotransmitters These drugs are generally used to treat depression, anxiety, and pain Selective serotonin reuptake inhibitors (SSRIs) include citalopram (Celexa), escitalopram (Cipralex), fluoxetine (Prozac), fluvoxamine (Luvox), sertraline (Zoloft) Selective norepinephrine reuptake inhibitors (SNRIs) include desvenlafaxine (Pristiq), duloxetine (Cymbalta), levomilnacipran (Fetzima), venlafaxine (Effexor) [you do NOT need to know these drugs] (brainstem)  99 Reuptake inhibitors No SSRI SSRI Pre-synaptic Pre-synaptic cell By blocking cell reabsorption of serotonin into the pre-synaptic cell, the drug lengthens the time serotonin is available in the synapse to act on the post-synaptic cell Post-synaptic Post-synaptic cell cell 2. Glia do everything else 100 Glia = “glue,” “sticky” 10x more numerous than neurons  101 Oligodendroglia wrap around the axons of neurons in CNS, forming many myelin sheaths per cell  102 Schwann cells wrap around the axons of neurons in PNS, forming one myelin sheath per cell  103 Microglia respond to injury & disease, engulfing debris and triggering immune response Only in CNS  104 Astroglia are the largest glial cells Support endothelial cells of the BBB Provide nutrients to neurons Maintain ion balance in CNS Repair after injury Communicate with neurons and glia Control and maintain synapses Only in CNS Blood-brain barrier 105 Protects brain Active transport for large molecules  106 Glia in brain dysfunction Glia likely play an underestimated role in many neurological conditions given their immune and “clean-up” roles Future drugs may target them Research is ongoing for topics including: depression stroke spinal cord injury multiple sclerosis autism schizophrenia Questions? 107 Cells of the nervous system Neurotransmitters References 108 Barth, P. 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