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chap 12 - 15 - 1 Notes for Test 3 B C hapter 12 The central...

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1 Notes for Test 3 B Chapter 12 The central nervous system consists of the brain and the spinal cord, enclosed within the protective cranial vault and vertebrae. The peripheral nervous system is composed of the cranial nerves and the spinal nerves. o Afferent pathways (ascending pathways) with carry sensory impulses towards the CNS. o Efferent pathways (descending pathways) with innervate skeletal muscle or effect organs by transmitting motor impulses away from the CNS. o Functionally can be divided into the somatic nervous system and the autonomic nervous system. Somatic Nervous system Consists of the pathways(motor and sensory) that regulate voluntary motor control (skeletal muscles) Ex: Pick my arm up Autonomic Nervous System Motor and sensory pathways regulating the body’s internal environment (viscera) through involuntary control of organ systems. o Happen and we don’t have to think about it Divided into sympathetic and parasympathetic divisions
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2 o This stimulation, sympathetic or parasympathetic, is to control smooth muscle contraction, regulate cardiac muscle, or stimulate or inhibit glandular secretion o Sympathetic It is always active at a basal level (called sympathetic tone) and becomes more active during times of stress . Its actions during the stress response comprise the fight-or-flight response o Parasympathetic The actions of the parasympathetic nervous system can be summarized as "rest and digest" (as opposed to the "fight- or-flight" effects of the sympathetic nervous system). Organs innervated by specific components of the nervous system are called effector organs . Neuron o Primary cell of the nervous system o Has three components: (1 ) Soma (cell body)and the thin process of the cell Most located inside the CNS and those found in the PNS are usually found in groups called ganglia (2) Dendrites Extensions that carry nerve impulses toward the cell body (3) Axons Long, conductive projections from the cell body that carry nerve impulses away from the cell body.
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3 A typical neuron has only one axon, which may be covered with a segmental layer of lipid material called myelin , an insulating substance. o Helps cushion or insulate. o This entire membrane is referred to as the myelin sheath. This sheath is interrupted at regular intervals by the nodes of Ranvier. Endoneurium - a layer of delicate connective tissue that encloses the myelin sheath of a nerve fiber within a fasciculus Neurilemma - outermost nucleated cytoplasmic layer of Schwann cells that surrounds the axon of the neuron Synapses o Neurons are not physically continuous with one another o Region between adjacent neurons is called a synapse o Impulses are transmitted across the synapse by chemical and electrical conduction Have to get from one neuron to another o Presynaptic neurons –impulses toward the synapse o Postsynaptic neurons –impulses away from the synapse o Neurotransmitters
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