Warm Up List the events in the nervous system that occur if you accidentally get a paper cut. How does your body respond?

Objective Checklist List the general functions of the nervous system. Explain the classifications of the nervous system. Define central and peripheral nervous systems. Classify neurons according to their structure and function.

Introduction to the Nervous System Provides for sensation, higher mental functioning, and emotion; activates muscles and glands

Nervous System Functions Sensory input – To monitor changes (stimuli) occurring inside and outside the body Integration – To process and interpret sensory input and decide if action is needed Motor output – Respond to integrated stimuli by activating muscles or glands

Structural Classification of the Nervous System Central nervous system (CNS) – Brain – Spinal cord Peripheral nervous system (PNS) – Nerves outside the central nervous system – Cranial and spinal nerves

Functional Classification of the PNS 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; two subdivisions Somatic nervous system = voluntary skeletal muscle Autonomic nervous system = involuntary smooth/cardiac muscle

Functional Classification (PNS only)

Neurons Neurons = nerve cells – Cells specialized to transmit messages – Major regions of neurons Cell body – nucleus and metabolic center of the cell Processes – fibers that extend from the cell body

Neurons Outside the cell body – Dendrites – conduct impulses toward the cell body – Axons – conduct impulses away from the cell body – Axon terminals – contain neurotransmitters to signal to other nerve cells – Myelin sheaths – protects nerve fibers and helps conduct nerve impulses – Synapse – gap between axon terminal and dendrites of the next neuron

Neurons Dendrites Cell body Axon Terminals Myelin sheath Axon Nucleus Dendrites Cell body Axon Terminals Myelin sheath Axon Nucleus

Terminology Cell bodies in the CNS are in clusters called nuclei. In the PNS, these collections are known as ganglia. Bundles of nerve fibers (nerve processes in the CNS are called tracts. In the PNS, they are known as nerves!

Functional Classification of Neurons Sensory (afferent) neurons – Carry impulses from the sensory receptors Cutaneous sense organs of the skin Proprioceptors of the muscles and tendons Special sense organs Motor (efferent) neurons – Carry impulses from the central nervous system Interneurons (association neurons) – Found in the central nervous system – Connect sensory and motor neurons

Functional Classification of Neurons

Structural Classification of Neurons Mainly interneurons and motor neurons Rare; some sensory neurons Mainly sensory neurons

CNS Neuroglia Line brain/spinal cavities; cilia circulate cerebrospinal fluid Insulate nerve fibers with myelin sheath; Schwann cells do a similar job in the PNS Account for ½ of neural tissue; anchor neurons to nutrient supply (capillaries) Phagocytes that dispose of dead brain cells and bacteria

Myelin Sheath Fatty cells that protect/insulate nerve axons and increase the transmission rate of nerve impulses Schwann cells in PNS; Oligodendrocytes in CNS Breaks in the sheath are known as Nodes of Ranvier

Disease Associated with the Myelin Sheath Multiple Sclerosis – Causes destruction of the myelin sheath – Electrical current is short- circuited. – Causes visual and speech disturbances, inability to control muscles, and progressive disablement – An autoimmne disease caused by WBC attack of the myelin sheath

Objective Checklist List the general functions of the nervous system. Explain the classifications of the nervous system. Define central and peripheral nervous systems. Classify neurons according to their structure and function.

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