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Nervous System Copyright © 2010 Pearson Education, Inc. 2 types of cells 1. Neurons (nerves) – receive & transmit biochemical & electrical signals 2. Glial cells – provide support for neurons CNS Anatomy of the Brain Brain – 3 main parts • Cerebrum – largest part – controls conscious functions (reasoning, sight, speech, touch, hearing, etc) • Cerebellum - coordinates body movement (linked to motor neurons) • Brain stem (midbrain, pons, medulla) – connects brain & spinal cord – Controls unconscious functions (heart rate, breathing, blood pressure, vomiting, etc) Sensory and Motor Areas of the Cerebral Cortex homunculus Brain Dysfunctions • Traumatic Brain Injuries – Concussion – brain impact – Contusion – tissue destruction – Cerebral edema - swelling • Cerebrovascular Accidents – Ischemic stroke – blood clot – Hemorrhagic stroke – brain bleed • CNS Degenerative Diseases – Alzheimer’s Disease – shortage of ACh/brain atrophy, results in dementia – Parkinson’s Disease - dopamine-releasing neurons in midbrain, results in persistent tremors, overstimulation – Huntington’s Disease – cerebral cortex, inhibition of motor reflexes Spinal Cord • Long, thin bundle of nervous tissue (~ 18 in long) • Passes message from brain to body and body to brain • Surrounded by vertebrae Spinal Cord Structure Cord – Outside: white matter (myelin sheaths) – Inside: gray matter (cell bodies w/no myelin sheaths) Meninges - dura mater - arachnoid mater - pia mater PNS Figure 11.23 A simple reflex arc. Stimulus 1 Receptor Interneuron 2 Sensory neuron 3 Integration center 4 Motor neuron 5 Effector Spinal cord (CNS) Response Copyright © 2010 Pearson Education, Inc. Structure of a motor neuron Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleolus Axon (impulse generating and conducting region) Nucleus Nissl bodies Axon hillock (b) Copyright © 2010 Pearson Education, Inc. Impulse direction Node of Ranvier Schwann cell Neurilemma (one interTerminal node) branches Axon terminals (secretory region) Figure 11.4a Structure of a motor neuron. Neuron cell body (a) Copyright © 2010 Pearson Education, Inc. Dendritic spine Figure 11.16 Synapses. Axodendritic synapses Dendrites Axosomatic synapses Cell body Axoaxonic synapses (a) Axon Axon Axosomatic synapses (b) Copyright © 2010 Pearson Education, Inc. Cell body (soma) of postsynaptic neuron Nerve Transmission Neurotransmission(NIH): https://www.youtube.com/embed/XfeaMbT KdV8?modestbranding=1 3-D neurotransmission: http://www.youtube.com/watch?v=90cj4N X87Yk Chemical Synapse Ion movement Graded potential Binding of neurotransmitter opens ion channels, resulting in graded potentials. Copyright © 2010 Pearson Education, Inc. Figure 11.15a Action potential propagation in unmyelinated and myelinated axons. Stimulus Size of voltage (a) In a bare plasma membrane (without voltage-gated channels), as on a dendrite, voltage decays because current leaks across the membrane. Copyright © 2010 Pearson Education, Inc. Figure 11.15b Action potential propagation in unmyelinated and myelinated axons. Stimulus Voltage-gated ion channel (b) In an unmyelinated axon, voltage-gated Na+ and K+ channels regenerate the action potential at each point along the axon, so voltage does not decay. Conduction is slow because movements of ions and of the gates of channel proteins take time and must occur before voltage regeneration occurs. Copyright © 2010 Pearson Education, Inc. Figure 11.15c Action potential propagation in unmyelinated and myelinated axons. Myelin sheath Stimulus Node of Ranvier 1 mm Myelin sheath (c) In a myelinated axon, myelin keeps current in axons (voltage doesn’t decay much). APs are generated only in the nodes of Ranvier and appear to jump rapidly from node to node. Copyright © 2010 Pearson Education, Inc. How do drugs affect neurotransmission? https://www.youtube.com/watch?v=7VUlKP4 LDyQ