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The Nervous System Chapters 10 &11
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BASIC IDEAS: ANATOMY PHYSIOLOGY STRUCTURE OF A NEURON
TYPES OF NEUROGLIAL CELLS BRAIN STRUCTURE CEREBRUM CEREBELLUM BRAIN STEM PHYSIOLOGY CONDUCTION OF NERVE IMPULSE REFLEXES SPECIFIC FUNCTIONS OF THE BRAIN
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General Overview: Function: Maintain Homeostasis
Sensory Information Perception and Integration Motor responses Structure: Neurons and Neuroglial Cells Neurons classified by function (sensory, inter- and motor neurons) OR by structure (unipolar, bipolar, and multipolar) Nerves – collections of neurons Systems: Central Nervous System (brain and spinal cord) & Peripheral Nervous System (motor and sensory nerves) Autonomic – involuntary Nervous System Sympathetic – danger Parasympathetic - Peaceful
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Structure of a Neuron Cell Body – cell processes
Endoplasmic reticulum and golgi bodies (neurotransmitter production) Nissl Bodies – groups of ribosomes Cytoskeleton shape Dendrites – receptive surfaces Axon – conducts nerve impulse (action potential) Axon hillock Axon terminals & Synapse Schwann Cells Myelin Nodes of Ranvier
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Neuroglial Cells Def. – accessory cells of the nervous system Types
Schwann cells – form myelin sheath around axons of PNS Astrocytes - star shaped; structural support, nourishment, communication, clean-up Oligodendrocytes – form myelin in CNS Microglia – phagocytosis Ependyma – porous barrier between fluid of brain/spinal cord neurons and cerbrospinal fluid Regeneration of Nerve fibers Injury to cell body, usually kills nerve cell Injury to axon, axon can usually regenerate itself Nerve growth factors and Glial cells help direct growth CNS less likely to regenerate than PNS
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Nerve Impulse Key idea: nerves communicate with each other and effectors (muscles and glands) by sending an “action potential” down the axon, which cause a release of neurotransmitters into the synapse Action Potential – nerve impulse Series of changes in the neuron membrane which cause charged ions to flow in and out of the neuron
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Establishing a Resting Potential
Potential difference (voltage) – difference in electrical charges between two places Unequal distribution of positive and negative ions inside and outside of the neuron creates a small voltage Resting Potential – normal voltage when neuron is not sending a signal -70mV Sodium-potassium pump moves Na+ ions out and K+ ions in Potassium diffuses out of the cell faster than sodium diffuses in more positive charges outside the cell Negative ions are trapped inside the cell
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Conduction of a Nerve Impulse
Creating an Action Potential Dendrites or cell body react to stimuli Different stimuli for different types of neurons Temperature, light, pressure, chemical mechanical Stimuli causes changes in the cell membrane Gates open allowing movements of ions Depolarization – change from -70 to +30 mV Sodium ions rush in This change in voltage causes the next part of the neuron to do the same Works like dominos Repolarization – return to resting potential repolarization causes K+ channels to open and potassium rushes out
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Actions at the Synapse Synapse – the space between the axon terminal of one neuron and 1) the dendrites of the next neuron OR 2) an effector Effectors are muscles or glands Events: Action potential reaches synaptic knob Ca++ to rush in Exocytosis of neurotransmitter Vesicles reenter and refill Examples of Neurotransmitters Acetylcholine, dopamine, epinephrine, norepinephrin, serotonin
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Conduction of a Nerve Impulse
Speed of nerve impulses Refractory period – time in which a neuron cannot be stimulated again About 1 impulse per millisecond Saltatory Conduction – nerve impulses on myelinated neurons Faster than unmyelinated Action potentials jump between Nodes of Ranvier Greater the diameter of nerve fiber, the faster the nerve impulse
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Odds and Ends Control of neurotransmitters: inhibitory and excitatory post-synaptic potentials Impulse Processing Neuronal pools Facilitation Convergence vs. Divergence Nerve fiber classification General vs. Special Somatic vs. visceral Afferent vs. Efferent
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Reflexes Def: a subconscious action that automatically respond to stimuli Receptor Sensory neuron interneuron motor neuron effector Breath rate, heart rate, and blood pressure are controlled by reflexes Examples Knee-Jerk – helps to keep posture by contracting the quadriceps if tendon becomes stretched Simple one sensory neuron and one motor neuron Other common reflexes: ankle-jerk, biceps-jerk, triceps-jerk, plantar Babinski reflex – toes spread apart; normal in babies (under 1) Withdrawal Reflex – contraction of biceps when finger touches something hot/sharp Reduces tissue damage Biceps contract; triceps relax Crossed extensor reflex – opposite side does opposite action
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Structure of the Nervous System
Phineas Gauge – 1st brain study CNS – Brain + Spinal Cord Meninges – coverings Dura Mater Arachnoid Mater Pia Mater Cerebrospinal Fluid Real Life Applications: Subdural Hematoma, Epidural, Meningitis, Hydroencephaly (hydrocephalus) Spinal Cord White and Gray Matter Ascending and Descending Nerve Tracts
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The Brain Parts: Cerebrum Cerebellum Brain Stem
Perception and higher level thinking Hemispheres Lobes Convulutions Cerebellum Arbor Vitae coordination Brain Stem Medulla oblongata, pons and midbrain Vital functions
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