Nervous System Structure & Function

Nervous System Master control & communication system for the body Works with other systems to maintain homeostasis

Nervous System 3 Main functions – Sensory input - Monitors changes (stimuli) inside and out – Integration - Processes and interprets input – Motor output - Effects a response to stimuli

Structural Classification 2 subdivisions – Central nervous system (CNS) Brain Spinal cord – Peripheral nervous system (PNS) Nerves outside of CNS

Functional Classification (PNS only) Sensory (afferent) division – Sends impulses TO the CNS – Somatic-skin, muscles, joints – Visceral-organs Motor (efferent) division – Carries impulses FROM the CNS – 2 divisions Somatic-voluntary Autonomic-involuntary

Nervous Tissue 2 Types: – Supporting cells Neuroglial cells “glial” – Neurons Nerve cells Two major functions – Irritability – conductivity

CNS Neuroglial Cells Astrocytes – Star shaped – Mops up leaked chemicals Ependymal – Line central cavities Microglial – Spider like, debris disposal Oligodendrocytes – Form myelin sheaths – insulates

PNS Neuroglial Cells Schwann Cells – Myelin sheath – Insulates – External sheath “neurilemma” – Nodes of Ranvier Gaps in between Schwann cells Satellite Cells – Cushion and protect

Neurons Structure Cell body- Metabolic center – Special Rough ER Nissel substance & neurofibrils maintain shape Processes – Microscopic to 4 foot long – Dendrites-carry impulses TO the cell body – Axons-carry impulses FROM the cell body Myelin sheaths

Special Terminology Clusters of cell bodies – Nuclei-CNS – Ganglia-PNS Bundles of nerve fibers – Tracts-CNS – Nerves-PNS White matter - Myelinated regions Gray matter – Unmyelinated regions

Neuron Classification Afferent – Cell bodies outside CNS – Carry impulses from sensory receptors Efferent – Cell bodies inside CNS – Carry impulses to organs, muscles, or glands Interneurons – Connect the motor and sensory neurons

Neuron Structural Classification Multipolar – Many processes – All motor and sensory neurons Bipolar – Two processes Axon & dendrite – Rare, found in special sense organs Unipolar – Single processes – Axon process with dendrite branches at end

Nervous System Physiology Resting state – Plasma membrane is polarized More positive ions outside than inside

Nervous System Physiology Action Potential – Activated by neurotransmitters – Changes polarity (permeability of membrane) Allows positive ions to enter “Depolarization” More positive inside than outside

Nervous System Physiology Repolarization – Positive ions exit membrane – Must occur before next impulse

Reflexes Programmed, rapid, predictable, involuntary Somatic reflexes – Skeletal muscle reflexes Autonomic reflexes – Smooth muscle reflexes

Reflex Arc 5 elements – Sensory receptor – Sensory neurons – Integration center – Motor neurons – Effector organ