PSYC/BIOL 2217 01 - Anatomy of the Nervous System (PDF)

PSYC/BIOL 2217 01 09-16-2024 Anatomy of the Nervous System cont. c. 3. Neural Conduction and Synaptic Transmission: How Neurons Send and Receive Signals c. 4 2 Themes explored in this Class: CNS anatomy Cellular...

PSYC/BIOL 2217 01 09-16-2024 Anatomy of the Nervous System cont. c. 3. Neural Conduction and Synaptic Transmission: How Neurons Send and Receive Signals c. 4 2 Themes explored in this Class: CNS anatomy Cellular resting membrane potential 1  Triune brain scheme: Triune Brain Theory (Paul MacLean 1960’s): 3 functional layers to vertebrate brain. Originally proposed as an evolutionary model of brain organization with consists of the reptilian complex, the paleomammalian complex (limbic system), and the neomammalian complex (neocortex). Ancestral parts conserved with newly evolved parts on top. “I wouldn’t do that if I were you!” Does the harder Cortex = Bark Neocortex: Consciousness, cognition, perception thing when the easier is Helps control impulsivity - difference between having often more satisfying! Human Cognition: the thought and carrying it out. Sets goals and tracks Grati cation postponement their progress Rational vs. emotional brains Limbic: Rudimentary sensory processing, emotional drives Damage frontal cortex: Impair uid (valence of feelings), behavioural drives. Electrically intelligence, planning, decision making stimulate it and can evoke fear, joy, anger, pleasure, pain. Become disinhibited, physically, sexually Hypothalamus →pituitary control neuroendocrinological Most hypothalamic aggressive, lack impulse control. function functions are appetitive and Behaviour dominated by limbic system it’s the hypothalamus which Reptilian: Robotic function, re exive control of body shapes our motivation to Damage limbic system; loose empathy, systems. Heart rate, breathing, arousal. achieve those appetitive compassion, love, emotional saliency, at Medulla and pons of brain stem (autonomic nervous goals. Freudian ID, basic affect system). mammalian drives Triune Brain model misleading - fell out of favour in Damage reptilian brain: dead! 1990: Falsely implies neocortex is evolutionarily more advanced. The brain did not evolve with more sophisticated layers built over simpler layers. Emotional-limbic structures also in neocortex Cann’t truly separate Functional interconnectivity, different areas wired emotions from cognition. MacLean’s model was a neuroanatomical cousin to together so they work together. They are integrally Freud’s tripartite view of the mind, with its Bottom-up & ‘top-down’ control. intertwined. warring superego, ego and id. 2 Reptiles and birds also have neocortices. fi fl fl fl  Triune brain scheme: Top-Down vs. Bottom-up? Ascending (bottom-up) connections and pathways are often much stronger drivers of behaviour than the descending (top-down) projections. Newly evolved parts of our brain (the neocortex) are really only in control when; you’re not hungry, not curious, not sexually aroused, not angry, not too terri ed, not too cold, not too warm. Then the neocortex can reign supreme, but for the rest of the time, it’s the limbic and hypothalamic brains which run the show. One example of this is when you’re rationally arguing-discussing with someone about something which you feel passionate. What happens when you run out of argument? You begin to feel yourself getting angry! You’ve switched from a frontal cortical analytical mode to a limbic-emotional state. Remove the neocortex in a mammal - decortication (and even Clinical psychologists are cortico-centric - like to think that it’s the parts of limbic system), animal still moves around, explores, eats, newly evolved neocortex that runs the show. After all, CBTs (cognitive copulates, displays sham rage. behavioural therapies) are all about cognitive approaches to rethink SHAM RAGE: The aggressive responses of decorticate animals are abnormal in two respects: They are inappropriately severe, and repurpose emotions and behaviours. But in fact, animal behaviourist and they are not directed at particular targets. and neuropsychologists scoff at this idea and have known for decades that limbic and hypothalamic structures are the real boss. fi  Brains do not contain emotional circuits - rather emotions are guesses based on millions of neuronal computations The brain is Triune! The brain is adaptive! Emotions are primitive. Emotions-Moods are created depending on state. 6 basic human emotions: happiness sadness fear anger surprise disgust Brains don’t work by stimulus and response. All your neurons are Using (i) electrical stimulation, (ii) pharmacological challenges, and ring at various rates all the time. (iii) brain lesions of vertebrate brains (mostly mammalian), Panksepp carved out seven primary emotional systems called SEEKING, CARE, Emotion and cognition are often studied independently, but it is PLAY, and LUST on the positive side, whereas FEAR, SADNESS, and now believed that they are better studied as different components ANGER belong to the negative affects. of the same system Jaak Panksepp “An emotion is your brain’s creation of what your bodily sensations mean, in relation to what is going on around you in the world”. Our brains’ carry an ingrained emotional and Lisa Feldman Barrett motivational systems we share with other mammals which has been shaped by natural selection. Triune gives false impression that our brain is like a circuit board, throw 1 switch and get a certain output, another and a different output. 4 fi  Thinking about the Biology of Behaviour: Nature vs. Nurture, from Dichotomies to Interactions Figure 2.3 A schematic illustration of the way in which most biopsychologists think about the biology of behaviour. Model boils down to the single premise that all behaviour is the product of interactions among three factors: (1) the organism’s genetic endowment, which is a product of its evolution; (2) its experiences; and (3) its perception of the current situation. The primary functions of a brain is to react and to create a perceptual world in which to move and act. Because the world is not constant, the brain needs to be exible in structure and function, a capacity referred to as neuroplasticity 5 fl Doctrine of Modularity in Biopsychology -- the idea that different parts of the brain are involved in different mental functions. Modularity of mind is the notion that our brains may, at least in part, be composed of innate neural structures or mental modules which have distinct, established, and evolutionarily developed functions. Supported by human lesion/stroke studies, animal electrical stimulation experiments (Jaak Panksepp) Brain is a hodge-podge collection of elaborately interconnected networks of neurons Akin to a house that has been added to and refurbished multiple times, not by ripping out the old and replacing the wiring, plumbing and structural support with the new, but refurbished by keeping the old and adding on new stuff (Lisa Feldman Barrett) With evolution also get cortical expansion of some networks, think prefrontal cortex expansion in human primates and new motor areas for digits and toes. Problem: Brain lesion and stimulation studies are very reductionistic. Normally the brain works together, so if you show that stimulation of one area produces a particular behaviour, it’s not going to be ecologically valid (from a psychological perspective), since that particular part in the brain is never alone, it’s always interacting with other regions. Cognition, mood and emotional tones are all ‘state’ dependant. How hungry you are, how curious, how happy, are all dependent on past, present, and future (goals) states. 6 Directions in the Vertebrate Nervous System 7  Divisions of the Adult Human Brain 2-3 weeks 9 weeks 5 Divisions of brain based on embryology 8 Hindbrain & Midbrain 9  Figure 3.22 Diencephalon Thalamus: Portal to the neocortex. Bilateral egg-shaped structure in the middle of your brain. It’s known as a relay station of all incoming motor (movement) and sensory information — hearing, taste, sight and touch (but not smell) — from your body to your brain Like a relay or train station, all information must rst pass through Sensory relays and gating: Describes the your thalamus before being routed or directed to its destination in your ltering of relevant sensory cues from brain’s cerebral cortex (the outermost irrelevant or redundant stimuli. One such layer of your brain) for further lter may involve cortical control of sensory processing and interpretation. relay through the thalamus. Damage to your thalamus can result Thalamus also plays a role in sleep, in: Unconsciousness and even coma. wakefulness, consciousness, learning and Sleep disorders memory Thalamus has approximately 60 different nuclei, for example: Lateral Geniculate Nucleus: Vision Medial Geniculate Nucleus: Audition Ventral Basal: vestibular & Nociceptive Thalamic reticular nucleus (TRN): Attention 10 fi fi fi Midline structures like the brainstem and thalamus necessary to regulate the level of brain arousal. Small, bilateral lesions in many of these nuclei cause a global loss of consciousness. Remember Hans Eysenck and extroversion vs. introversion, Reticular Activating Systems (ACh, NE & Serotonin) 11  Hypothalamus Hypothalamus: Collection of nuclei important for homeostatic control. Limbic areas provide excitatory as well as inhibitory control Centres for controlling appetitive behaviours like hunger, thirst, sex. Centres important for circadian rhythmicity and temperature regulation Strong connections to autonomic nervous systems (Sympathetic - ight or ght, or parasympathetic - rest & digest). Hypothalamic-Pituitary-Adrenal axis (HPA-axis) the mammalian stress response. Hormone control centre: Pituitary control of reproduction, cellular metabolism and uid balance (ADH or vasopressin) Figure 3.23 The human hypothalamus (in colour) in relation to the optic Pair bonding & childbirth - Vasopressin and Oxytocin chiasm and the pituitary gland. Appetite - Leptin, Ghrelin, 12 fl fl fi Diencephalon: Limbic System and the Basal Ganglia Limbic system – Regulates motivated behaviours – Structures Basal ganglia – Regulates movement – Structures 13  Limbic System Limbic System: Learning & memory and Papez circuit /Payps/, (James Papez, 1930’s) is regulation of motivated behaviours a neural circuit for the control of emotional The 5 ‘F’s’: expression: Hippocampus → fornix → mammillary →cingulate cortex back to Feeding, Fleeing, Fighting, Feeling, Sex! hippocampus. Called the ‘visceral brain’ by Paul Maclean. 14 Copyright © 2021, 2018, 2014 Pearson Education, Inc. All Rights Reserved Figure 3.28 Basal Ganglia Basal Ganglia: Voluntary movement, motor planning, motor learning. Implicated in OCD, Tourette’s Addictions: Nucleus accumbens (NAc) important for motivation and drive - seeking behaviours - Dopaminergic inputs provide this activation 15 Copyright © 2021, 2018, 2014 Pearson Education, Inc. All Rights Reserved  Figure 3.24 Human Cerebral Cortex The major ssures of the human cerebral cortex. 16 Copyright © 2021, 2018, 2014 Pearson Education, Inc. All Rights Reserved fi  Figure 3.25 The Lobes of the Cerebral Hemispheres Cerebral Hemispheres - Higher brain functions like perception and cognition, consciousness? Sulci/gyri increase surface area of neocortex - each hemisphere size of medium pizza 3.25 The lobes of the cerebral hemispheres. 17 Copyright © 2021, 2018, 2014 Pearson Education, Inc. All Rights Reserved Figure 3.26 Layers of Neocortex Figure 3.26 The six layers of neocortex. The thickness of the cell layers can give a clue as to the function of an area of neocortex. For example, the thickness of layer IV indicates that this is sensory neocortex. 18 Copyright © 2021, 2018, 2014 Pearson Education, Inc. All Rights Reserved  Connectome of the human brain Structural: Genome, proteome Functional: Connectome More sophisticated view of brain function - replaces triune thinking. Connectome of the human brain. The human brain is organized as a small-world network. Neurons (black dots) form functional modules (grey shaded area). Within such modules, high connectivity is established by short intramodular connections (black lines). Additionally, long intermodular connections located in the white matter (red lines in yellow shaded area) connect different modules with each other. 19 Figure 3.3 Cerebral Ventricles and Central Canal 20 Copyright © 2021, 2018, 2014 Pearson Education, Inc. All Rights Reserved  Glymphatics: Rhythmic uid ows in deep sleep allow communication and clearance of waste products Especially during deep sleep (3&4). ventricle Cerebrospinal uid (blue) ows through the brain and Cerebral spinal uid (CSF) tap rst thing in morning vs. late clears out toxins through a series of channels that evening observe lower toxins and proteins associated with expand during sleep Parkinson’s disease (α-Synuclein) and Alzheimer’s (Tau and amyloid-β) 21 fl fl fl fi fl fl  Test your Knowledge Forebrain structures include: A. the neocortex, thalamus, hypothalamus and limbic system B. the neocortex, thalamus, hypothalamus C. the neocortex, thalamus D. the neocortex 22  Ionic Basis of Action Potentials 2 Themes explored in this Class: Ionic Basis of the resting potential Ionic basis of action potentials 23 24  Cells Store Potential Energy Transformer Dam Sluice Gate Storage reservoir Turbine Downstream outlet Potential energy in a cell can be in the form of: (1) concentration gradients (2) electrical gradients both together called - Electrochemical gradients 25  Ionic distribution established & maintained by Na+/K+ATPase pump. your tears & blood taste salty K+ is a potassium ion, a potassium atom which has lost an electron, it carries a net +1 electrical charge Cl- is chloride ion, a chloride atom which has an extra electron, it carries a net -1 electrical charge A- refers to all other organic anions (negatively charged proteins, nucleic acids, metabolites etc) 26  Ionic distribution established & maintained by Na+/K+ATPase pump. K+ is a potassium ion, a potassium atom which has lost an electron, it carries a net +1 electrical charge Cl- is chloride ion, a chloride atom which has an extra electron, it carries a net -1 electrical charge A- refers to all other organic anions (negatively charged proteins, nucleic acids, metabolites etc) 27  Ionic distribution established & maintained by Na+/K+ATPase pump. Our kidneys work to maintain these ion distributions. Ringer’s solution @ 300 mM, isotonic I.V. for uid replacement K+ is a potassium ion, a potassium atom which has lost an electron, it carries a net +1 electrical charge Cl- is chloride ion, a chloride atom which has an extra electron, it carries a net -1 electrical charge A- refers to all other organic anions (negatively charged proteins, nucleic acids, metabolites etc) 28 fl Establishment of a resting membrane potential begins with K+ leaking out of cell via the Potassium leak channel Cations and Anions are attracted to each other The inside and outside of the cells is isoelectric (every cation has an anion). 29 Establishment of a resting membrane potential begins with K+ leaking out of cell via the Potassium leak channel Cations and Anions are attracted to each other The inside and outside of the cells is isoelectric (every cation has an anion). Membranes of cells with resting potentials have channels that are selectively permeable to K+, allowing K+ to ow down its concentration gradient - called a potassium leak channel. What is the anion (A+) going to want to do? Its going to want to follow the K+ ion out of the cell but it can’t. 30 fl Establishment of a resting membrane potential begins with K+ leaking out of cell via the Potassium leak channel Due to the electrical gradient established by the K+ leaving, cations move to inside of membrane surface. Intracellular membrane compartment gets more negative. 31 Establishment of a resting membrane potential begins with K+ leaking out of cell via the Potassium leak channel Now, in addition to a concentration gradient, there is an electrical gradient. Bath tub Concentration gradient wants K+ to leave the cell, BUT, electrical gradient attracts K+ back into cell. with plunger When the concentration gradient is equal and opposite to the electrical gradient of K+ is out water in = said to be at equilibrium. water out 32 Establishment of a resting membrane potential begins with K+ leaking out of cell via the Potassium leak channel When and at what voltage is the concentration gradient = to the electrical gradient? When the membrane voltage is ≈ -90 mV, K+ is at equilibrium. Known as the K+ equilibrium potential of the cell. 33  What would happen to our cell if you injected a little positive charge? Inside of cell now -60 mV. K+ would no longer be at equilibrium, the new electrical gradient would push K+ ions down their electrical gradient ( owing out of the cell) until enough K+ ions left and a -90 mV potential is re-established. So, a cellular resting potential is stable. 34 fl  Important points - summary #1 Channels in cell membrane allow potassium (K+) to move freely across the cell membrane (K+ leak channels). K+ wants to leave the cell driven by its concentration gradient 145 mM (inside) → 5 mM (outside). This creates a charge separation across the membrane, with anions on the inside surface and cations on the outside. An electrical gradient is created. When the concentration gradient for K+ is equal and opposite to the electrical gradient for K+, the out ow of K+ equals the in ow and K+ is at equilibrium. The electrical potential at which this EK+), and is around -90 mV. occurs is called the potassium equilibrium potential ( 35 fl fl