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Structure of a Vertebrate Neuron Basic Tasks of the Nervous System Sensory Input: Monitor both external and internal environments. Integration: Process the information and often integrate it with stored information. Motor output: If necessary, signal effector organs to make an appropriate response. A system that controls all of the activities of the body. The nervous system is made of: The brain The spinal cord The nerves The senses The Central Nervous System is made of the brain and the spinal cord. The Central Nervous System controls everything in the body. The Outer Nervous System is made of the nerves and the sense organs. Nerves Sense organs Myelinated Neurons • Many vertebrate peripheral neurons have an insulating sheath around the axon called myelin which is formed by Schwann cells. • Myelin sheathing allows these neurons to conduct nerve impulses faster than in non-myelinated neurons. What is An Action Potential? Saltatory Conduction in Myelinated Axons Myelin sheathing has bare patches of axon called nodes of Ranvier Action potentials jump from node to node Fig. 48.11 How does a signal move from one neuron to another? • A synape divides 2 neurons • The action potential will not move across the synape • Neuro transmitters –Released by the signal cell to the receiver cell –Move by diffusion Detail of Axon Terminal Transmission Across the Synapse Source: Gray A chemical synapse Detail of the Synapse Itself Neurotransmitter molecules (e.g., Acetylcholine or Dopamine) Postsynaptic membrane Review the Synapse • What is a synapse? • A synapse is the “gap” between the axon of one nerve and the dendrite of the next one. • The average neuron has 1,000 synapses with other neurons. Neurotransmitters • There are dozens of different neurotransmitters (NT) in the neurons of the body. • NTs can be either excitatory or inhibitory • Each neuron generally synthesizes and releases a single type of neurotransmitter • The major neurotransmitters are indicated on the next slide. Major Neurotransmitters in the Body Neurotransmitter Role in the Body Acetylcholine A neurotransmitter used by the spinal cord neurons to control muscles and by many neurons in the brain to regulate memory. In most instances, acetylcholine is excitatory. Dopamine The neurotransmitter that produces feelings of pleasure when released by the brain reward system. Dopamine has multiple functions depending on where in the brain it acts. It is usually inhibitory. GABA (gamma-aminobutyric acid) The major inhibitory neurotransmitter in the brain. Glutamate The most common excitatory neurotransmitter in the brain. Glycine A neurotransmitter used mainly by neurons in the spinal cord. It probably always acts as an inhibitory neurotransmitter. Norepinephrine Norepinephrine acts as a neurotransmitter and a hormone. In the peripheral nervous system, it is part of the flight-or-flight response. In the brain, it acts as a neurotransmitter regulating normal brain processes. Norepinephrine is usually excitatory, but is inhibitory in a few brain areas. Serotonin A neurotransmitter involved in many functions including mood, appetite, and sensory perception. In the spinal cord, serotonin is inhibitory in pain pathways. NIH Publication No. 00-4871 Examples of chemical neurotransmitters found in synapse • Acetylcholine: neuromuscular junctions, glands, brain and spinal cord • Norepinepherine: affects brain regions concerned with emotions, dreaming The Brain On Drugs • http://www.thirteen.org/closetohome/scien ce/html/animations.html Higher Brain function Spatial Vision Speech, memory, hearing Motor control-Posture & equilibrium Autonomic Functions: breathing, heartbeat, respiration, etc, Put It all Together - Stimulus- temperature/pressure on skin light- sound- eyes and ears correct shape molecule taste buds /nose - Action Potential proagates along axon - Neurotransmitter released into synapse - New action potential begins in adjoining nerve or muscle cell