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Stressor Hypothalamus CRH Sympathetic nervous system Posterior Pituitary Vasopressin (Antidiuretic Hormone ADH) ACTH 1. Conserve H2O to expand the plasma volume and thereby increase low blood pressure 2. Decrease blood flow to “non essential” tissue by promoting constriction of feeder arterioles Anterior pituitary Adrenal medulla Adrenal cortex Epinephrine Cortisol Arteriole Smooth Muscle Prepare body for “fight or flight” HR Hrt contraction force Bronchodilation (-) GI function (+) alertness, Mobilize energy stores and metabolic building blocks for use as needed Vasoconstriction Blood flow through kidneys Renin Angiotensin General Sympathetic Responses Aldosterone Fig. 17-22, p. 524 Structure of the Nervous System Afferent neurons Interneurons Efferent neurons Functional Classes of Neurons Characteristics of the Functional Classes of Neurons Central Nervous System: Brain Fig. 6-38 6 Central Nervous System: Spinal Cord Fig. 6-41 7 Peripheral Nervous System • Neurons in the peripheral nervous system transmit signals between the central nervous system and receptors and effectors in all other parts of the body. • The peripheral nervous system has 43 pairs of nerves: 12 pairs of cranial nerves and 31 pairs that connect with the spinal cord as the spinal nerves. • The 31 pairs of spinal nerves are designated by the vertebral levels from which they exit: cervical (8), thoracic (12), lumbar (5), sacral (5), and coccygeal (1). 8 Peripheral Nervous System • The eight pairs of cervical nerves control the muscles and glands and receive sensory input from the neck, shoulders, arms, and hands. • The 12 pairs of thoracic nerves are associated with the chest and upper abdomen. • The five pairs of lumbar nerves are associated with the lower abdomen, hips, and legs. • The five pairs of sacral nerves are associated with the genitals and lower digestive tract. (A single pair of coccygeal nerves associated with the tailbone brings the total to 31 pairs.) 9 Peripheral Nervous System • These peripheral nerves can contain nerve fibers that are the axons of efferent neurons, afferent neurons, or both. • All the spinal nerves contain both afferent and efferent fibers, whereas some of the cranial nerves contain only afferent fibers or only efferent fibers. • Efferent neurons carry signals out from the central nervous system to muscles or glands. The efferent division of the peripheral nervous system is more complicated than the afferent, being subdivided into a somatic nervous system and an autonomic nervous system. 10 Spinal Nerves 11 Autonomic Nervous System Controls Homeostasis Para Symp Neurotransmitters of the Peripheral Nervous System 13 Acetylcholine • Acetylcholine (ACh) is found in PNS and CNS. Neurons that use ACh as the primary neurotransmitter are known as cholinergic neurons. • ACh acts at muscarinic (G protein coupled) or nicotinic (ion channels) receptors. Nicotininic receptors are found at the neuromuscular junctions of skeletal muscles. • ACh is produced in the presynaptic axon by the enzyme choline acetyl transferase (CAT) as follows: • Acetyl CoA + choline acetylcholine + CoA • Degradation of ACh occurs in synaptic cleft and is done by the enzyme acetylcholinesterase (AChE) as follows: • Acetylcholine acetate + choline • The great majority of acetylcholine receptors in the autonomic ganglia are nicotinic receptors. • In contrast, the acetylcholine receptors on smooth muscle, cardiac muscle, and gland cells are muscarinic receptors. 15 Cholinergic System Issues • Some chemical weapons, such as the nerve gas Sarin, inhibit acetylcholinesterase, causing a buildup of ACh in the synaptic cleft. • Overstimulation of postsynaptic ACh receptors causes uncontrolled muscle contractions, ultimately leading to receptor desensitization and paralysis. • Nicotinic receptors in the brain are important in cognitive functions and behavior. The presence of nicotinic receptors on presynaptic terminals in reward pathways of the brain explains why tobacco products are among the most highly addictive substances known. 16 Alzheimer’s Disease • Neurons associated with the ACh system degenerate in people with Alzheimer’s disease. Alzheimer’s disease affects 10 to 15 percent of people over age 65, and 50 percent of people over age 85. • Because of the degeneration of cholinergic neurons, this disease is associated with a decreased amount of ACh in certain areas of the brain and even the loss of the postsynaptic neurons that would have responded to it. • These defects and those in other neurotransmitter systems that are affected in this disease are related to the declining language and perceptual abilities, confusion, and memory loss that characterize Alzheimer’s victims. 17 Biogenic Amines • Biogenic amine neurotransmitters are made from amino acids as follows: • Catecholamines • Made from tyrosine: • Dopamine • Norepinephrine • Epinephrine • Norepinephrine is released • As a hormone from the adrenal medulla • As a neurotransmitter from efferent neuron synaptic terminals • Epinephrine is released • As a hormone from adrenal medulla • As a neurotransmitter from interneurons 18 Synthesis of Catecholamines Fig. 6-35 19 Norepinephrine and Epinephrine bind with Adrenergic Receptors • Adrenergic comes from historical use as Noradrenaline (NA) and adrenaline for NE and Epi, respectively. • Adrenergic receptors are G protein coupled that are generally linked to second messenger signal transduction pathways. • Alpha adrenergic receptors Alpha2 (α 2) Subtypes: Alpha1 (α1) • Beta adrenergic receptors Subtypes Beta1 (β1) Beta2 (β2) Beta3 (β3) ‒ These receptors differ in their AFFINITY for EPI & NOREPI 20 Structure of the Nervous System Afferent neurons Interneurons Efferent neurons Autonomic Nervous System • Sympathetic division is also called the thoracolumbar division, has short pre‐ ganglionic and long post‐ganglionic synapses. The major neurotransmitters are ACh at the pre‐ganglionic synapse and usually NE and Epi at the post‐ganglionic synapse. This is the “Flight or Fight” response system. • Parasympathetic is called the craniosacral division, it has long pre‐ganglionic and short post‐ganglionic synapses. The major neurotransmitter is ACh at both pre‐ and post‐ganglionic synapses. This is the “Rest and Digest” system. DUAL INNERVATION BY BOTH BRANCHES IS COMMON – The heart and many glands and smooth muscles are innervated by both sympathetic and parasympathetic fibers; that is, they receive dual innervation. – Whatever effect one division has on the effector cells, the other division usually (but not always) has the opposite effect. – Moreover, the two divisions are usually activated reciprocally; that is, as the activity of one division increases, the activity of the other decreases. • 22 Autonomic Nervous System: Sympathetic Adrenal Medulla • One set of postganglionic neurons in the sympathetic division never develops axons. Instead, they form the adrenal medulla. • Upon activation by preganglionic sympathetic axons, cells of the adrenal medulla release a mixture of about 80 percent epinephrine and 20 percent norepinephrine into the blood (plus small amounts of other substances, including dopamine, ATP, and neuropeptides). 23 Autonomic Nervous System: Sympathetic Adrenal Medulla • • These catecholamines, properly called hormones rather than neurotransmitters in this circumstance, are transported via the blood to effector cells having receptors sensitive to them. Their effects are similar, but may be different, dependent on affinity of tissue receptors for Epinephrine as opposed to Norepinephrine 25 End of Material For Test 2