Term
| How is the motor nervous system organized? |
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Definition
AUTONOMIC NERVOUS SYSTEM
portion of nervous system that controls most visceral functions of the body - INVOLUNTARY
Controls:
- arterial pressure
- gastrointestinal motility & secretion
- urinary bladder emptying
- sweating
- body temperature
effector organs - glands, smooth muscle, cardiac muscle
SOMATIC NERVOUS SYSTEM
motor system that is under conscious control - VOLUNTARY
Controls
-skeletal musculature
effectors: skeletal muscle |
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Term
| Explain the somatic efferent pathway |
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Definition
| Somatic motor neurons: 1 long, heavily myelinated axon extending from the CNS to the effector (lacks ganglia); releases ACh |
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Term
| Explain the ANS efferent pathway |
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Definition
Pathways in the ANS are a two-neuron chain:
The preganglionic (first) neuron has a lightly myelinated axon (ALWAYS releases ACh); The ganglionic (second) unmyelinated neuron extends to an effector organ via the postganglionic axon (may release NE, Ach, neuropeptides) |
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Term
| What are the components of the central autonomic network? |
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Definition
Cerebral cortex, Hypothalamus, Brainstem & Spinal cord
A hierarchy of reflexes initiated from these different levels regulates ANS function |
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Term
| What are the divisions of the ANS? |
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Definition
ANS activated by: Centers located in spinal cord, brain stem & hypothalamus (some portions of cerebral cortex - limbic cortex)
ANS divided into 2 divisions: Sympathetic and parasympathetic (3rd division - Enteric nervous system "little brain" of GI tract)
Most visceral organs are innervated by both sympathetic and parasympathetic fibers; dual innervations results in dynamic antagonisms - both divisions counterbalance each other’s activity
The sympathetic mobilizes the body during extreme situations
The parasympathetic performs maintenance activities and conserves body energy |
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Term
| What are the functions of sympathetic nervous system? |
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Definition
Involves E activities - exercise, excitement, & emergency
Activity illustrated with a threat response =
"fight-or-flight" response
-increased arterial pressure
-increased heart rate, cardiac output
-increased ventilation-dilation on airways- deep & rapid breathing
-increased blood flow away from skin to skeletal muscles - cold, sweaty skin
-increased metabolic rate
-increased blood glucose concentration
-increased mental activity and alertness
-decreased GI motility and secretions
-dilated pupils
Modulates functions of heart, blood vessels, GI tract, bronchi & sweat glands
Major control over blood pressure: constricts blood vessels increasing BP
Promotes adjustments during exercise or "flight" blood flow to organs is reduced, flow to muscles is increased |
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Term
| What are the functions of the parasympathetic system? |
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Definition
Involves the D activities - digestion, diuresis & defecation
Keeps body energy use low; directs "housekeeping" activities
Activity illustrated with relaxation after a meal:
-decreased blood pressure
-decreased heart rate
-decreased respiratory rates
-increased GI tract activity - allow for digestion and waste removal
-warm skin
-constricted pupils
Dominates the heart and activity levels of the digestive and urinary systems (slows the heart)
HOWEVER - sympathetic division can override these effects during times of stress
Drugs that block parasympathetic responses increase heart rate and cause fecal and urinary retention |
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Term
| What's the organization of the SNS? |
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Definition
Origin of fibers - Thoracolumbar region of the spinal cord (between T1-L3)
location of ganglia - Close to the spinal cord - Paravertebral or prevertebral ganglia
Short preganglionic and long postganglionic fibers |
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Term
| What's the organization of the PNS? |
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Definition
Origin of fibers - Cranial nerves or sacral ventral roots (craniosacral - CN III, VII, IX, X or S2-S4)
location of ganglia - Near, on, or in the effector organs
Long preganglionic and short postganglionic fibers |
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Term
| How does the SNS innervate the heart, bronchial tree, stomach, small intestine, large intestine, adrenal medulla and male genitilia? |
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Definition
The nerve that innervates the heart comes from T1
The bronchial tree is innervated by T3-5
The stomach is innervated by T6-9 thru the celiac plexus
The small intestine is innervated by T10-11 through the superior mesenteric plexus
The large intestine is innervated by T10-11 through the superior mesenteric plexus and T12 - L3 through the inferior mesenteric plexus
Adrenal medulla is innervated by T8 and T12
The male genitalia is innervated by T12 - L3 through the inferior mesenteric plexus |
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Term
| How are the heart, bronchial tree, stomach, small intestine, large intestine, urinary bladder, and male genitalia innervated by the PNS? |
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Definition
The heart, bronchial tree, stomach, small intestine, and large intestine are all innervated by the vagus nerve
The large intestine is also innervated by the pelvic splanchnic nerves originating from S2-4
The urinary bladder and male genitalia are innervated by the pelvic splanchnic nerves from S2-4 |
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Term
| Explain the somatic nervous system pathway |
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Definition
Consists of a single motoneuron (cell body in CNS, axons synapse on skeletal muscle);
Neurotransmitter is Ach (stimulatory effects);
Receptors on effector organ are nicotinic (ACh) |
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Term
| Explain the autonomic nervous system pathway |
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Definition
consists of 2 neurons: preganglionic and postganglionic neuron
Cell body of preganglionic neuron in CNS (brain stem or spinal cord)
Axons of preganglionic neurons synapse on cell bodies of postganglionic neurons in ganglia outside CNS or near effector organ
Axons of postganglionic neurons travel to periphery and synapse on effector organs (heart, bronchioles, vascular smooth muscle, GI tract, & bladder)
Neurotransmitter linking ALL preganglionic neurons to postganglionic neurons: ACh
Neurotransmitter linking postganglionic neurons to effector organs: Ach (PNS) or NE (SNS) (effects are inhibitory/stimulatory)
Receptors on effector muscles are alpha & beta (NE) or muscarinic (ACh) |
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Term
| What are the exceptions to the rule that the SNS uses NE as the transmitter at the target cell? |
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Definition
Sweat glands and vascular smooth muscle of skeletal muscle have muscaranic receptors for ACh
Renal vascular smooth muscle uses dopamine as its NT
Adrenal medulla mostly releases EPI (80%) but uses NE (20%) as well |
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Term
| What are the types of receptors in the ANS? |
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Definition
SNS
Postganglion: Nicotinic
Effector Organ:
a1, a2, b1, b2 & Muscarinic
PNS
Postganglion: Nicotinic
Effector Organ: Muscarinic
NOTE - The physiological event elicited by a neurotransmitter depends on the RECEPTOR being occupied....NOT by the transmitter |
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Term
| What are the characteristics of nicotinic and muscarinic receptors? |
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Definition
Nicotinic and Muscarinic: both receptor types bind Ach (named after nicotine & muscarine that bind to them and mimic ACh effects)
Nicotinic receptors:
Effect of ACh binding is always stimulatory
Found on
(a) Motor end plates of skeletal muscle
(b) ALL postganglionic neurons of both SNS & PNS
(c) Chromaffin cells of the adrenal medulla
Muscarinic receptors:
Effect of ACh binding can be either inhibitory or excitatory
Found on
(a) ALL effector organs of PNS (heart, GI tract, bronchioles, bladder, male genitalia)
(b) Certain effector organs of SNS (sweat glands, vascular smooth muscle of skeletal muscle) |
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Term
| What are the characteristics of adrenergic receptors? |
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Definition
Found in target tissues of SNS
Activated by catecholamines NE (from postganglionic
neurons) & E (from adrenal medulla)
Divided into 2 types: alpha and beta
Each type is subdivided into alpha1, alpha2, beta1, beta2
Each type has a different mechanism of action = different
physiologic effects
NE is better alpha receptor agonist than beta receptor agonist
E is better beta receptor agonist than alpha receptor agonist (esp. beta 2) |
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Term
| What is the target tissue, function, and mechanism of action of alpha1 receptors? |
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Definition
target tissue - vascular smooth muscle, skin and sphlanchnic vessels, GI tract, sphincters, bladder, radial muscle in iris
function - constriction, smooth muscle contraction
mechanism - use IP3 and DAG as 2nd messengers to increase ICF [Ca2+] |
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Term
| What is the target tissue, function, and mechanism of action of alpha2 receptors? |
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Definition
location - GI tract and wall, presynaptic membrane of postganglionic adenergic neurons
function - relaxation, decreases NE release
mechanism of action - inhibits adenyl cyclase to reduce cAMP levels |
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Term
| What is the target tissue, function, and mechanism of action of beta1 receptors? |
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Definition
KASH
location - kidney, adipose tissue, salivary glands, heart
function - increases contraction/contractility/heart rate, lipolysis, gluconeogenesis, and renin secretion
mechanism - stimulation of adenyl cyclase --> increased cAMP levels |
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Term
| What is the target tissue, function, and mechanism of action of beta2 receptors? |
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Definition
location - vascular smooth muscle of skeletal muscle, GI tract and wall, bladder and bladder wall, bronchioles
function - dilation, smooth muscle relaxation
mechanism - stimulation of adenyl cyclase -> increased cAMP levels |
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Term
| What is the target tissue and mechanism of action of nicotinic receptors? |
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Definition
location - skeletal muscle, motor end plate, postganglionic neurons on SNS and PNS, adrenal medulla
mechanism - opening of Na+ and K+ channels -> depolarization |
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Term
| What is the target tissue and mechanism of action of muscarinic receptors? |
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Definition
location - all effector organs in PNS, sweat glands (SNS), vascular smooth muscle of skeletal muscle (SNS)
mechanism - uses IP3 as a 2nd messenger to increase ICF [Ca2+] |
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Term
| What is the importance of G proteins in the nervous system? |
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Definition
Autonomic receptors are coupled to HETEROTRIMERIC GTP-binding proteins (G proteins)
G PROTEINS:
Serpentine cell membrane proteins: span the cell membrane 7 times winding like a "snake"
3 subunits: a, b, g
- 16 a; 6 b; 12 g - provides various members of 5 g protein families
Stimulatory (Gs) or inhibitory (Gi)
- a subunit binds to either GDP (inactive) /GTP (active) - stimulatory/inhibitory activity in a subunit)
Couple receptors to enzymes (adenylyl cyclase/ PLC) generating 2nd messengers (cAMP/ IP3) which amplifies message and executes final physiological action |
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Term
| How is the heart controlled autonomically? |
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Definition
The SA node (heart rate), AV nodal conduction, and contractility are increased by sympathetic action at beta1 receptors
They are all decreased by parasympathetic action at muscarinic receptors (for contractility only atria is affected) |
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Term
| How is vascular smooth muscle controlled autonomically? |
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Definition
FOR VASCULAR SMOOTH MUSCLE
Splanchnic muscle in the skin and skeletal muscle are constricted by sympathetic action at alpha1 receptors
Skeletal muscle is dilated by sympathetic action at beta2 receptors
Endothelium is caused to release EDRF by parasympathetic action at muscarinic receptors |
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Term
| How are bronchioles controlled autonomically? |
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Definition
Dilated by sympathetic action at beta2 receptors
Constricted by parasympathetic action at muscarinic receptors |
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Term
| How is the GI tract controlled autonomically? |
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Definition
Smooth muscle walls are relaxed by sympathetic action at alpha2 and beta2 receptors
They are constricted by parasympathetic action at muscarinic receptors
Smooth muscle in the sphincters are contracted by sympathetic action at alpha1 receptors
Saliva secretion is increased by sympathetic action at beta1 receptors and parasympathetic action at muscarinic receptors
Gastric acid and pancreatic acid secretion is increased by parasympathetic action at muscarinic receptors |
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Term
| How is the bladder controlled autonomically? |
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Definition
The bladder wall and detrusor muscle are relaxed by sympathetic action at beta2 receptors and contracted by parasympathetic action at muscarinic receptors
The sphincter is contracted by sympathetic action at alpha1 receptors and relaxed by parasympathetic action at muscarinic receptors |
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Term
| How is the male genitalia controlled autonomically? |
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Definition
Point and Shoot (Skeet)
Erection is caused by parasympathetic action at muscarinic receptors
Ejaculation is caused by sympathetic action at alpha receptors |
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Term
| How is the eye controlled autonomically? |
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Definition
The radial muscle of the iris leads to pupil dilation (mydriasis) caused by sympathetic action at alpha1 receptors
The circular sphincter muscle in the iris leads to pupil constriction (miosis) by parasympathetic action at muscarinic receptors
The ciliary muscle leads to dilation (far vision) by sympathetic action at beta receptors
The ciliary muscle contracts for near vision due to parasympathetic action at muscarinic receptors |
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Term
| How is the skin controlled autonomically? |
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Definition
Thermoregulatory action of sweat glands is increased by sympathetic action at muscarinic receptors (exception)
Stress action of sweat glands is increased by sympathetic action at alpha receptors
Contraction of the pilomotor muscle (goose bumps) is increased by sympathetic action at alpha receptors |
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Term
| How are the lacrimal glands controlled autonomically? |
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Definition
| Secretion is caused by parasympathetic action at muscarinic receptors |
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Term
| How is the liver controlled autonomically? |
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Definition
| Gluconeogenesis and glycogenolysis are increased by sympathetic action at alpha and beta2 receptors |
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Term
| How is the adipose tissue controlled autonomically? |
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Definition
| Lipolysis is increased by sympathetic action at beta1 receptors |
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Term
| How is the kidney controlled autonomically? |
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Definition
| Renin secretion is increased by sympathetic action at beta1 receptors |
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