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The Nervous System Part I 1 The Nervous System: Overview Nervous System controls/regulates body functions (other organ systems) using electrical signals for communication): Sensory input – monitoring stimuli (feel) Integration – interpretation of sensory input (think) Motor output – response to stimuli (do) 2 Nervous System – includes all neural tissue in the body Neural tissue – includes 2 types of cells: 1) Neurons – cells that send and receive electrical signals 2) Neuroglia (glial cells) – cells that support and protect neurons Organs of the Nervous System: 1) Brain and spinal cord 2) Sensory receptors of sense organs (eyes, ears, etc.) 3) Nerves connect nervous system with other systems 3 Anatomical Divisions of the Nervous System Central nervous system (CNS) • Brain & spinal cord • Integration and command center CNS Brain Spinal Cord Peripheral nervous system (PNS) • Includes all neural tissue outside CNS • Paired spinal and cranial nerves • Carries messages to and from the spinal cord and brain PNS 4 Peripheral Nervous System: Two Functional Divisions Sensory Division - carries sensory information from senses → to CNS Motor Division - carries motor commands from CNS → to muscles & organs Central Nervous System (brain & spinal cord) carries info from senses Sensory Division carries info to effector organs to perform a function Motor Division 5 Motor Division Two Components: Somatic nervous system - controls voluntary skeletal muscle contractions Autonomic nervous system (ANS) – controls involuntary actions (contractions of smooth & cardiac muscle, glandular secretions) Central Nervous System (brain & spinal cord) carries info from senses Sensory Division carries info to effector organs to perform a function Motor Division Autonomic (Involuntary) Somatic (Voluntary) 6 Autonomic nervous system (ANS) Two Components: Sympathetic nervous system (SNS) - stimulating effect • fight or flight Parasympathetic nervous system (PNS) - relaxing effect • rest and digest Motor Autonomic (Involuntary) Parasympathetic NS Somatic (Voluntary) Sympathetic NS 7 Central Nervous System Brain Spinal Cord Peripheral Nervous System Sensory Motor Autonomic (Involuntary) Parasympathetic NS Somatic (Voluntary) Sympathetic NS 8 Neuron Structure • Structural units of the nervous system • Plasma membrane functions in electrical signaling • Composed of: • body - contains nucleus & other organelles • axon - conducts nerve signals • dendrites - receive signals from sensory receptors or other neurons 9 Neuroglia (glial cells) Oligodendrocytes – wrap around CNS axons to form “myelin sheath” • myelin insulates axons to increase the speed of electrical signals Schwann cells – surround fibers of the PNS to form “myelin sheath” 10 Axon terminal – small swelling at tips of branched end of an axon Synapse – region of close proximity between two neurons Presynaptic membrane – membrane of first neuron Postsynaptic membrane – membrane of next neuron Synaptic cleft – small gap between presynaptic and postsynaptic neuron Neurotransmitters – molecules that transmit nerve impulse across a synapse 11