The Nervous System Poudre High School By: Ben Kirk

Functions  Regulation of all body function  Sensory: Information reception  Response: Response transmission  Integrate: Integrate and interpret all body changes/stimuli

Organization  Central Nervous System (CNS): Brain and Spinal Cord  Control center for the entire nervous system  Receives, processes, integrates and produces responses to all stimuli  Higher Functioning (the brain primarily): intelligence, memory, thought, emotion and learning

The Central Nervous System

Organization  Peripheral Nervous System (PNS): All neural tissue outside the CNS  Delivery of sensory information from sensory glands/organs to the CNS  Transmission of motor information from the CNS to effectors glands/organs

Organization  Peripheral Nervous System  Somatic Nervous System: Voluntary  Controls voluntary muscle contractions (skeletal muscle)  Autonomic Nervous System: Involuntary  Involuntary movements, processes and reflexes  Visceral organs, cardiac muscle, smooth muscle and glands (heart rate, vessel diameter, digestion, etc…)

Organization  Autonomic Nervous System  Sympathetic Nervous System: Expenditure of energy  Fight or Flight  Increased Heart Rate  Parasympathetic Nervous System: Restoration and conservation of energy  Rest and Digest  Slows Heart Rate

Histology  Neuroglia: Glial Cells  6 Types of glia cells  Primary Function is to protect and support neurons  Smaller and more numerous (5-10X) than neurons  Common source of tumors (Gliomas)  40-45% of all brain tumors

Histology  Neurons: Conduct impulses from one part of the body to another  Cell Body (Soma):  Large, pronounced nucleus  No myotic apparatus in cytoplasm  Neuron reproduction/regeneration is compromised  Dendrites:  Highly branched processes extending from cell body  Each neuron in the CNS has 10, ,000 dendrite branches.  Each branch has 100,000-1million sensory inputs!!!

Histology  Neurons:  Axon: Single thin extension that sends electrical impulses to other neurons or tissues  1mm-1meter in length  Axon Terminal contains neurotransmitters that are released to trigger subsequent impulses  Axon Hillock: Where all electrical impulses are summated to trigger an impulse, or not.

The Neuron

Histology  Neuron:  Myelin (myelin sheath): Multiple layered, lipid and protein sheath covering neuron axons (not all axons are myelinated)  Electrically insulates axon and increases conduction speed (Ex. Leaky garden hose)  Multiple Sclerosis: Autoimmune disease that breaks down the myelin sheath in the CNS.  Tremors: Unregulated electrical impulses

Histology  Neurons:  Myelin:  Myelin Production  Schwann cells (PNS): Myelinate a single segment of a single axon.  Have limited ability to regenerate PNS neural tissue  Oligodendrocyte (CNS): A single oligodendrocyte can myelinate multiple segments of multiple axons  CNS neuron regeneration is very complex and relatively nonexistent.  Myelination = White  Unmyelinated = Gray

Classification of Neurons  Structural: Based on the # of processes extending from the cell body  Multipolar: many dendrites and one axon  Most cells of the CNS  Bipolar: One dendrite and one axon  Retina of eye, inner ear and nose  Unipolar: Has one continuous branch with both an axon and a dendrite (cell body off to side)  Dorsal root ganglia (sensory cell bodies of spinal nerves)

Classification of Neurons  Functional: Based on the direction of impulse propagation  Sensory (Afferent): Transmit impulses from receptors in skin, muscles, sensory organs, joints, and viscera to the CNS  Motor (Efferent): Transmit impulses from the CNS to peripheral effectors (muscles and glands)  Interneuron (Association): Carry impulses from sensory neurons to motor neurons within the CNS  Make up the majority of human neurons

Grouping of Neural Tissue  Nerve Fiber: Any process projecting from a cell body  Axon or dendrite  Nerve: A group of many fibers within the PNS  Not a neuron  Usually contain both sensory and motor nerve fibers  sciatic nerve, ulnar nerve  Ganglia: Group of cell bodies and synapses within the PNS.

Grouping of Neural Tissue  Tract: Bundle of fibers within the CNS  May run long distances up or down the spinal column or connecting parts of the brain  Ascending tracts carry information upward (sensory)  Descending tracts carry information downward (motor)  White Matter: Group of myelinated axons from many neurons  Look white due to myelination

Grouping of Neural Tissue  Gray Matter: Unmyelinated axons, dendrites, or cell bodies within the CNS  Found covering the outer surfaces and in the deeper regions (nuclei) of the brain  Compose the “horns” of the spinal cord