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CHAPTER 9 The Nervous System The Nervous System-Intro • The nervous system is responsible for coordination and integration. • Feeling, thinking, remembering, moving, having awareness • Nervous tissue consists of neurons which transmit electrochemical nerve impulses to other neurons. • Nervous tissue is composed of neurons and neuroglial cells. • Neuroglial cells provide support, insulation, and nutrients to neurons • Neurons consist of a cell body and extensions called dendrites and axons • Axons send information in the form of nerve impulses; each neuron has only one axon (usually) • Dendrites are numerous and receive the nerve impulses (electrochemical message) CNS & PNS • The organs of the nervous system can be divided into two groups: • Central Nervous System (CNS) • The brain and the spinal cord • Peripheral Nervous System (PNS) • Nerves • These two systems provide three general functionsintegrative, sensory, and motor General Functions-Sensory • Each peripheral neuron has a sensory receptor that gathers info and detects changes inside and outside the body. • Monitor light and sound intensities • Monitor temperature and oxygen level • This information is converted into a nerve impulse that travels up the peripheral nerve to the CNS (into the spinal cord and on to the brain) • Nerve impulses are converted into a sensation or a memory or a thought General Functions-Integrative • The conscious or subconscious decisions we make based on the nerve impulses gather by sensory receptors are the integrative aspect of the nervous system • The desire to yawn is a subconscious reaction to low oxygen levels detected by peripheral nerves General Functions-Motor • Motor functions (movement) are employed once sensory information is integrated. • Actually yawning (opening the mouth and inhaling) are motor functions triggered by integrative and sensory information • SENSORYINTEGRATIVEMOTOR PNS-Two Divisions • Somatic Nervous System-Controls skeletal muscles • Autonomic Nervous System-Controls effectors that are involuntary such as the heart, smooth muscle in blood vessels, and various glands Neuroglial Cells • Neurons cannot exist without neuroglial cells. • Neuroglial cells produce a fatty lipoprotein called myelin. • Special neuroglial cells called Schwann cells form a myelin sheath around axons. • Gaps between Schwann cells are called nodes of Ranvier. • There are a great many more neuroglial cells than neurons. White vs Gray • Axons with myelin sheaths are said to be myelinated. • Areas within the CNS that are myelinated are called white matter. • Axons and neural cell bodies that are not myelinated are said to be unmyelinated. • These areas are called gray matter. The Synapse • Nerve impulses travel along nerve pathways. • The junction between any two communicating neurons is called a synapse. • Neurotransmitters are biochemicals that cross the synaptic cleft. • Can you think of any? • Acetylcholine, epinephrine, norepinephrine, serotonin, dopamine • What happens if any of these neurotransmitters are out of homeostatic balance? Meninges • Meninges lie between the bony coverings of the spinal cord and brain. They are protective coverings. • There are three layers to the meninges: • Dura mater-outermost layer of the meninges • White, tough connective tissue that contains many blood vessels and nerves • Arachnoid mater-middle layer of the meninges • Thin, weblike membrane without blood vessels • Pia mater-innermost layer of the meninges • Very thin, contains many nerves and blood vessels that nourish the underlying cells of the brain and spinal cord. • Actually touches the brain and spinal cord, dipping into each crevice Spinal Cord • It is continuous with the brain. • The spinal cord actually begins at the foramen magnum at the base of the brain. • It tapers to a point and terminates near the intervertebral disc that separates the first and second lumbar vertebrae (last discs).