Download General Sympathetic Responses

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
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Central Nervous System: Spinal Cord
Fig. 6-41
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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).
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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.)
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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
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Autonomic Nervous System Controls Homeostasis
Para
Symp
Neurotransmitters of the Peripheral Nervous System
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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.
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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
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Synthesis of Catecholamines
Fig. 6-35
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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
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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. •
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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
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End of Material For Test 2