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Physiology 31 Lecture Chapter 11 – PNS: Somatic & Autonomic Divisions I. Overview A. Two divisions of the _____ 1. ____________ (voluntary) NS consists of a. Motor nerves from the CNS control skeletal ________ b. Sensory nerves from ______ceptors of the skin, muscles, bones, and joints send information to the CNS 2. _________________ (involuntary) NS consists of a. Motor neurons from the CNS control _________, cardiac and smooth ___________ b. Sensory input from ______ceptors of the internal viscera send information to the CNS 3. The two subdivisions of the ANS are the: ______________ & Parasympathetic II. The Somatic Motor Division A. _____________ motor pathway features 1. _____ type of somatic motor neuron extends from the CNS to 2. ___________ muscle 3. Somatic motor neurons are always _____________, and cause muscle contraction B. A somatic motor pathway consists of ____ type of motor neuron 1. Somatic motor neuron cell ________ originate in the gray matter of the brain and spinal cord 2. Their _________ extend outward from cranial and spinal nerves to skeletal muscles a. Axons branch near the muscle to form a cluster of enlarged axon terminals (___________) that synapse with muscle cells b. Axon _________ allow one neuron to control many muscle cells C. The synapse between the somatic neuron and muscle cell is called the neuron____________ junction. It consists of 1. ____synaptic axon _________ that contains synaptic vesicles with _____ neurotransmitter 2. Synaptic ________ – a minute, fluid filled gap that contains a. ___________ fibers b. Acetycholinesterase (______) that degrades ACh 3. _____synaptic motor end _________ of a skeletal muscle fiber a. _________ ACh receptors are in the motor end plate membrane D. _____________ at the neuromuscular junction 1. An action potential stimulates release of _____ into the synaptic cleft 2. ACh binds to nicotinic ACh receptors in the motor end ________ 3. __________ ACh receptors, which are ligand-gated ion channels, open to allow _____ into the muscle cell 4. Na+ influx ____________ the muscle membrane, which results in muscle contraction E. ____________ is an agonist to ACh 1. Nicotine binds to nicotinic _____ receptors and opens Na+ channels, causing depolarization 2 2. Nicotine binding to ACh receptors in _______________ neurons causes vasoconstriction, and leads to high blood ___________ III. The Autonomic Nervous System A. The autonomic nervous system (_____) is the general visceral _________ division of the PNS, and contains two subdivisions 1. _____________ N.S. – involved in “fight or flight” responses; this branch prepares the body for ____________ activity 2. ______sympathetic N.S. – involved in “rest & ___________” activities; this division is in control the majority of the time B. Involuntary __________ (smooth & cardiac muscle and glands) are regulated by autonomic motor impulses via the ANS C. Autonomic ___________ are important for homeostasis 1. The _____________ NS, endocrine system, and behavior work together to maintain homeostasis 2. ___________ input from somatosensory and visceral receptors goes to control centers in the hypothalamus, pons and medulla a. These centers __________ and regulate functions such as blood pressure, temperature, and water balance 3. _________ output from the ______thalamus and brain stem creates autonomic, endocrine, and behavioral responses, such as drinking, food seeking, etc. 4. _________ reflexes can occur without input from the brain (e.g., urination, defecation, etc.) a. People with spinal cord _________ that disrupt communication between the brain and spinal cord retain some spinal _________, but lose the ability to sense or control them (e.g., incontinence) D. The sympathetic and parasympathetic branches demonstrate Cannon’s 4 properties of ______________ 1. Maintenance of the __________ environment 2. Up-down ______________ of target tissues 3. _______________ control – one branch excites some tissues, whereas the other inhibits the tissues 4. Variable tissue responses due to different types of __________ E. The autonomic motor pathway involves ___ types of motor neurons (recall that the somatic motor pathway had 1 type of motor neuron): 1. ____ganglionic (presynaptic) neurons - have their cell bodies in the gray matter of the brain or SC, and release ____ neurotransmitter; their axon terminals synapse with 2. ______ganglionic (postsynaptic) neurons that extend from an autonomic ganglia and synapse with an __________ organ 3. Autonomic _____________ are located in the head, neck, & abdomen, and on each side of the spinal cord 3 IV. Sympathetic & Parasympathetic divisions of the ANS A. Sympathetic “fight or ___________” responses include 1. __________ pupils 2. Stimulates _________ glands 3. Vaso___________ blood vessels to glands and internal organs 4. ______ bronchioles and blood vessels to heart & skeletal muscles 5. Stimulates adrenal medulla to secrete _______________ (adrenalin) & norepinephrine into the blood stream 6. Increases heart ______ and force of contraction, as well as blood ___________ 7. Stimulates break down and release of __________ from liver and lipids from fat cells to supply glucose to blood stream B. Parasympathetic “rest and ___________” responses 1. Pupils are ___________ 2. Glands are stimulated to __________ 3. Heart rate is __________ and steadied 4. Blood vessels to heart, and bronchioles are vaso_____________ 5. Smooth muscle of bladder and digestive organs are contracted, promoting __________________. C. Sympathetic and parasympathetic branches exit the spinal cord in different regions, have different ganglia, and secrete different neuron____________ 1. Sympathetic (______________) division a. Preganglionic neurons are _______, exiting the spinal cord lateral horns from T1 to L2 and synapse with postganglionic neurons in the b. Sympathetic chain ___________, which are located on both sides of the vertebral column and along the descending aorta 1) Some preganglionic neurons synapse with ____________ postganglionic neurons, leading to ______ ____________ of several organ systems at once c. Postganglionic neurons are _______, extending out to target organs, and are _____________, most secrete norepinephrine neurotransmitter 2. Parasympathetic (_____________) division a. Preganglionic neurons are _________; they exit from the midbrain, brain stem (including cranial nerves III, VII, IX, & ___) and sacrum, and synapse with b. Postganglionic neurons in terminal __________ near or on target organs; these neurons are short; most are _____________ – they release ACh neurotransmitter c. Each preganglionic neuron synapses with only about _____ postganglionic neurons; thus parasympathetic effects are more ___________; no mass activation of organs occurs D. The ANS uses a variety of neuron____________ and modulators 1. All autonomic preganglionic neurons secrete _____ onto cholinergic ____________ receptors of postganglionic neurons 2. Most postganglionic __________ neurons release norepinephrine onto _______________ receptors on effectors 4 3. Most postganglionic ______sympathetic neurons secrete _____ onto cholinergic ____________ receptors on effectors 4. A few autonomic neurons are not adrenergic or cholinergic; they secrete other neuron_______________, such as substance P, somatostatin, adenosine, nitric oxide, and ATP E. Autonomic pathways control glands, smooth and cardiac _______ 1. The synapse between a postganglionic neuron and its target cell is called the _______________ junction a. Autonomic neuron axon terminals form bead-like strands called ________________, which lie across the target tissue b. Neurotransmitter released from the varicosities diffuses to ____________ on the target tissue to produce a response c. The response ceases as the neurotransmitter diffuses _______ from the synapse or is broken down by __________ 2. The release of neurotransmitters may be ___________ by several sources a. Sympathetic varicosities have receptors for ____________ and paracrines, such as histamine; these modulators may _________ or facilitate neurotransmitter release b. Some preganglionic neurons secrete neuron___________ with ACh; the peptides _______ synaptic potentials and modify postganglion neuron activity F. The adrenal medulla secretes _____________ 1. The adrenal medulla is actually a modified sympathetic ________ 2. It secretes epinephrine (_____________) into the bloodstream in response to sympathetic stimulation G. Most sympathetic pathways secrete norepinephrine (____) onto adrenergic receptors 1. NE can have different effects in different tissues due to alpha and beta ______________ receptors a. __________ (α) adrenergic receptors are the most common sympathetic receptor; they respond _________ to NE and weakly to epinephrine; α receptors are found in many _________ b. ____ (β) adrenergic receptors have two main subtypes β1 and β2 1) ___ receptors respond ___________ to NE and epinephrine; ___________ muscle and kidneys have β1 receptors 2) ____ receptors are not associated with sympathetic neurons, and respond more strongly to _____________; allows dilation in blood vessels and in bronchioles 2. All adrenergic receptors are linked to ___ proteins, but the different subtypes use different second ____________ H. Parasympathetic pathways secrete _____ onto muscarinic receptors 1. ____________ cholinergic receptors are also G protein-linked 2. Some muscarinic receptors activate 2nd ____________ systems, whereas others affect gated K+ channels I. Autonomic agonists and antagonists are important tools in research and ___________ 1. _____________ are molecules that bind to a receptor and ______ the effect of the receptor’s normal ligand. Examples: a. Nicotine binds to nicotinic receptors and mimics _____ b. Muscarine (a mushroom chemical) binds to ___________ receptors and mimics ACh 5 2. _______________ are molecules that bind to a receptor and _______ the receptor’s normal neurotransmitter action. Examples: a. ____________, a poison, binds to ___________ receptors and blocks _____; paralysis results because the nerve impulse cannot be transmitted to postganglionic neurons or muscle tissue b. _________ (bella donna) is a poison that binds to ___________ receptors and blocks parasympathetic responses 3. Many __________ used to treat depression act either on a. Membrane ___________ for neurotransmitters (e.g., selective serotonin reuptake inhibitors allow serotonin to remain in synapses longer) or b. ________________ of the neurotransmitters (e.g., monoamine oxidaze inhibitors ) 4. Discovery of α and β ______________ receptors led to the development of drugs that block only one of the receptor types a. ______ blockers prevent high blood pressure by blocking β1 receptors on the heart and kidneys J. Primary ____________ of the ANS are relatively uncommon 1. Damage to the _______thalamus can cause abnormalities in water balance or temperature regulation 2. _______________ dysfunction may result from diseases such as cancer and diabetes mellitus a. Diabetic autonomic ____________ is a gradual desensitization of neurons due to high blood __________ levels b. It results in _________________, gastrointestinal, urinary, and reproductive problems, which can cause c. Blindness, limb ______________, heart attacks, etc.