Introduction to the Nervous System CNS and PNS

Introduction to the Nervous System

CNS and PNS Central Nervous System (CNS) brain and spinal cord Peripheral Nervous System (PNS) nerves extending from the brain and the spinal cord

Organization of the Nervous System

Neurons (Nerve Cells) Cell Body –metabolic center of the neuron Dendrites –relay incoming messages towards the cell body -each neuron may have hundreds of dendrites Axon –send impulse messages away from cell body -only one axon per neuron Axon Terminal –ends of axons that connect to the muscle, organ, etc -contain neurotransmitter Myelin Sheaths –most nerve fibers (axon) covered with myelin sheath (fatty material) Function: protects and insulates the fibers and increases the transmission rate of impulse Multiple scelerosis (MS) –myelin sheath gradually destroyed, resulting in nerve fiber malfunction

Neuron Terminology Nuclei: clusters of neuron cell bodies found in the CNS Ganglia: clusters of neruron cell bodies found in the PNS Tracts: nerve fibers running through the CNS Nerves: nerve fibers running through the PNS

Multipolar example: carry nerve impulses out of the brain; nerves to muscles Bipolar example: found within specialized structures; eye, nose, ear Unipolar example: nerves receive signal from body and send to spinal cord and brain

Functional differences in neurons Sensory neurons: (afferent) Receive signals from body and send to brain, most are unipolar Interneurons: link sensory neurons to motor neurons, found in spinal cord and brain Motor neurons: (efferent ) send signals from the brain to body to cause response Ex: send impulse to muscle to cause contraction

Action Potential How the neuron sends the electrical impulse