Organization of the Nervous System Objectives I will be able to: List the general functions of the nervous system. Explain the structural and functional classifications of the nervous system. Define central nervous system and peripheral nervous system, and list the major parts of each. https://www.youtube.com/watch?v=qPix_X-9t7E

Functions of the Nervous System Sensory input – gathering information to monitor changes occurring inside and outside the body (changes = stimuli) Integration – to process and interpret sensory input and decide if action is needed Motor output – A response to integrated stimuli The response activates muscles or glands Together, these functions work like a feedback loop.

Structural Classification of the Nervous System The nervous system is composed of two separate systems: Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Nerves outside the brain and spinal cord

Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system

Functional Classification of the Peripheral Nervous System Motor (efferent) division has two subdivisions: Somatic nervous system = voluntary Autonomic nervous system = involuntary Has two parts: sympathetic parasympathetic

Organization of the Nervous System

 How do the three functions of the nervous system work like a feedback loop? Which system carries information to the CNS? Which systems carries information away from the CNS? Stimulus is received, evaluated, and responded to Sensory motor

Nervous Tissue: Support Cells (Neuroglia or Glia) Nervous tissue is made up of two types of cells, supporting cells and neurons. neuroglia: non-neuron tissue of the CNS that performs supportive and other functions for neurons There are four types of neuroglia, astrocytes, microglia, ependymal cells, and oligodendrocytes.

Nervous Tissue: Support Cells (Neuroglia or Glia) Astrocytes Abundant, star-shaped cells Brace neurons Form barrier between capillaries and neurons Control the chemical environment of the brain (CNS)

Nervous Tissue: Support Cells Microglia (CNS) Spider-like phagocytes Dispose of debris Ependymal cells (CNS) Line cavities of the brain and spinal cord Circulate cerebrospinal fluid

Nervous Tissue: Support Cells Oligodendrocytes(CNS) Produce myelin sheath around nerve fibers in the central nervous system

 Which support cell controls the chemical environment of the brain? Which support cell disposes debris? Which support cell creates the myelin sheath in brain cells? astrocytes microglia oligodendrocytes

Nervous Tissue: Support Cells glia: non-neuron tissue of the PNS that performs supportive and other functions for neurons There are two types of glia in the PNS, Schwann cells and satellite cells.

Support Cells of the PNS Satellite cells Protect neuron cell bodies Schwann cells Form myelin sheath in the peripheral nervous system

Neuroglia vs. Neurons Neuroglia and glia can divide (mitosis). Neurons cannot divide. Most brain tumors are “gliomas.” Most brain tumors involve the neuroglia cells, not the neurons. Consider the role of cell division in cancer!

Nervous Tissue: Neurons Neurons: cells of the nervous system specialized to transmit messages through-out the body Different types of neurons have different structures but do share some features. Common features of all neurons: Cell body – nucleus and metabolic center of the cell Processes – fibers that extend from the cell body (dendrites and axons)

 How are glia different from neuroglia? What are the two types of glial cells? Neuroglia = CNS, glia = PNS Schwann cells and satellite cells

Neuron Anatomy The cell body is the metabolic center of a neuron. Cell body contains a nucleus and the usual organelles in the surrounding cytoplasm. The nucleus contains a large nucleolus.

Neuron Anatomy Processes outside the cell body: Dendrites – conduct impulses toward the cell body (more than 1) Axons – conduct impulses away from the cell body (only 1!)

Neuron Anatomy Nissl bodies: consisting of granular ER and ribosomes that occurs in nerve cell bodies and dendrites and synthesize proteins. neurofibrils: any of the long, thin microscopic fibrils that run through the body of a neuron and extend into the axon and dendrites Neurofibrils are important in maintaining cell shape. Neuroglia = CNS, glia = PNS Schwann cells and satellite cells

Axons and Nerve Impulses Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters Axonal terminals are separated from the next neuron by a gap synaptic cleft: the fluid-filled space at a synapse between axons and dendrites of a neuron synapse: the region of communication between neurons

Nerve Fiber Coverings Schwann cells – produce myelin sheaths in jelly-roll like fashion. Nodes of Ranvier – gaps in myelin sheath between each Schwann cell along the axon.

Nerve Fiber Coverings myelin: a white, fatty, lipid substance covering the axon of a neuron Myelin Sheaths protect and insulate the axon fibers and increases the transmission rate of nerve impulses. Axon fibers may be myelinated (having myelin sheaths) or unmyelinated (no myelin sheaths).

Neuron Cell Body Location Most cell bodies are found in the central nervous system ganglion: a group of nerve cell bodies located in the PNS tract: a bundle of nerve fibers running through the CNS Nerve fiber bundles running through the PNS are just called nerves. gray matter: cell bodies and unmyelinated fibers white matter: dense collections (tracts) of myelinated fibers in the CNS nuclei: clusters of cell bodies within the white matter of the central nervous system

 What is the difference between gray matter and white matter? Why would some of the CNS axons be unmyelinated? Gray matter is unmyelinated, white matter is myelinated Communication between brain cells is easier without the myelin sheaths

Application In Multiple Scleroses the myelin sheath is destroyed. The myelin sheath hardens to a tissue called the scleroses. This is considered an autoimmune disease. Why does MS appear to affect the muscles?

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