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Download Chapter 3 Notes (part 1) 1. Basic Elements of the Nervous System (a
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Chapter 3 Notes (part 1) 1. Basic Elements of the Nervous System (a) The Neuron i. Functional Cells of the Nervous System A. exchange of information via electrochemical transmission B. electrical signals travel from axon hillock to axon terminal C. secretion of chemical neurotransmitters either excites or inhibits other neurons ii. Key Parts A. Cell Body/Soma includes the nucleus, organelles, and other structures in the cytoplasm (interior of the cell) B. Cell Membrane/Cytoplasmic Membrane selectively-permeable membrane which separates the cytoplasm from the extracellular matrix contains ion channels and protein pumps which manage the flow of ions (charged particles) into and out of the cell C. Axon The part of the cell which carries the electrical signal (action potential); in some cases, the axon is wrapped in fatty glial cells collectively called myelin begins at axon hillock and ends at axon terminal, where there are vesicles containing neurotransmitters D. Dendrites location of the receptor sites; neurons may have hundreds or even thousands of dendrites, but relatively few axons E. Synapse the gap between the pre-synaptic neuron and the post-synaptic neuron where the axon terminal nearly meets the receptor sites, separated by a gap called the synaptic cleft iii. Types of Neurons A. Motor (efferent) neurons Carry motor signals from the brain to the body B. Sensory (afferent) neurons Carry sensory information from sensory receptors in the body to the brain C. Inter-neurons Carry information within the neural network; for example, the corpus callosum (b) Glial Cells i. Supportive cells of the nervous system ii. augment the function of neurons as myelin (speeding up transmission) iii. areas of greater glial cell density appear as “white” matter (c) Action Potentials (electrical) i. Caused by changes in the relative voltage difference between the cytoplasm and the extracellular matrix ii. Polarization A. In the resting state (the Resting Potential) the cytoplasm is negatively charged due to high levels of NEGATIVELY charged Chloride ions (Cl-) and relatively low levels of positively charged sodium (Na+) and potassium (K+). The relative charge is 70mv. B. DIFFUSION of Na+ from the more densely populated extracellular matrix is balanced by protein pumps removing positively charged ions from the cytoplasm. If nothing else happens, the cell will maintain its negative charge C. BINDING of excitatory neurotransmitters to the receptor sites will cause some Na+ channels to open, beginning the process of depolarization iii. Depolarization A. Increasing bindings raise the relative charge from -70mv to -55mv B. at -55mv (the stimulus threshold) Na+ channels all open, causing a rapid increase in the positivity of the cytoplasm. C. The charge rises to +35 or +40mv, at which point this “extra” charge propagates down the axon toward the axon terminal (this is the action potential) D. The “all or nothing” principle states that neurons are either active or inactive. EITHER the charge reaches the stimulus threshold, causing an action potential, or it fails to reach that level, in which case the cell repolarizes without firing. iv. Repolarization A. When the “wave” of the action potential passes a point on the axon, the Na+ channels close, and K+ ions are pumped out of the cell, causing the cell to repolarize B. For a brief “refractory” period, the cell is unable to fire. (d) Synaptic Transmission (chemical) i. neurotransmitters A. chemical compounds which are either excitatory (opening Na+ channels) or inhibitory (closing Na+ channels) B. released from terminal vesicles when stimulated by an action potential ii. other important parts of the synapse A. receptor sites chemically matched to specific neurotransmitters B. autoreceptors receptor sites on the pre-synaptic neuron which track how much neurotransmitter is in the synapse and initiate reuptake C. transporters responsible for “corralling” neurotransmitters from one location to the next iii. Factors that influence Neurotransmitter Action A. Agonists substances that increase the effectiveness of neurotransmitters B. Antagonists substances which decrease the effectiveness of neurotransmitters C. Reuptake re-absorption of neurotransmitters initiated by autoreceptors D. Enzyme Deactivation metabolic deactivation of neurotransmitters by substances such as monoamine oxidase or acetylcholinesterase. 2. The Structure of the Nervous System (a) Nervous System Organization i. Central Nervous System A. The “executive” responsible for decision making Brain Spinal Cord ii. Peripheral Nervous System A. All nerves radiating out from the brain or spinal cord B. Somatic Nervous System – voluntary, conscious Sensory nerves Motor nerves C. Autonomic Nervous System sympathetic division responsible for activation of the body as part of “fight or flight” response parasympathetic division responsible for non-fight/flight functions such as peristalsis and release of digestive enzymes (b) Brain Anatomy and Localization of Function i. Neuroplasticity and Neurogenesis A. neurogenesis – the growth of new neurons and neural connections primarily occurs in utero, but some continues until the late 20s or early 30s “maturation” refers to the cessation of neurogenesis (for the most part) B. Neuroplasticity – the brain’s ability to adjust, recover, and heal after an injury tied with neurogenesis; the “younger” that part of the brain is, the more easily it can restore function ii. Hindbrain A. matures first, therefore it has the least plasticity B. responsible for critical organ functions and involuntary motor functions C. Medulla responsible for autonomic responses, peristalsis, respiration, regulation of consciousness ascending reticular activating system/reticular formation – consciousness area postrema – vomit reflex D. Cerebellum muscle memory, implicit learning, balance and coordination E. Pons contra-lateral organization iii. Midbrain A. Tectum sensory orienting reflexes B. Tegmentum motor impulse generation iv. Forebrain A. Cortex divided into two hemispheres, joined together by corpus callossum each hemisphere divided into four lobes occipital – contains primary visual cortex and visual association areas temporal – contains primary auditory cortex; left side responsible for naming objects and verbal auditory processing parietal – somatosensory corext; sensory processing frontal – primary motor cortex, pre-frontal cortex (decision making, inhibition, behavioral and emotional regulation) last portion of the brain to mature B. Sub-Cortices Limbic System hippocampus (memory) amygdala (emotional impulses) basal ganglia (motor impulses) Thalamus – sensory relay center Hypothalamus – “thermostat” responsible for regulating hormone release by glands Pituitary gland – releases HGH and other hormones Pineal gland – releases Serotonin and Melatonin as part of sleep/wake cycling