Chapter #14: Autonomic Nervous System Flashcards
Branches of the Peripheral Nervous System
Somatic and Autonomic
Somatic Nervous System (SNS)
system responsible for voluntary muscle movements and somatic reflex arcs (mostly voluntary)
Autonomic Nervous System (ANS)
-Almost all effectors are visceral (automatic)
-Do we have voluntary control over our visceral organs?
-no, we do not think about heart rate or digesting
-General function: helps maintain a stable internal environment
-Ex: regulation of heart rate, blood vessel diameter, pupil size, body temperature, increases/decreases stomach secretions
3 distinct differences between ANS and SNS
- Effector organs
- Efferent pathways and ganglia
- Neurotransmitter effects
Difference between effector organs
SNS - skeletal muscle tissue
ANS - cardiac muscle, smooth muscle, & glands
Difference between effector pathways and ganglia
SNS - single neuron extends from CNS to effector
-Motor neuron cell bodies located in CNS, axons in PNS extend to skeletal muscle
ANS - consists of two-neuron chain to reach effector
-Preganglionic neuron
-Postganglionic neuron
-Ganglia
Preganglionic neuron (ANS)
cell body in CNS, axon synapses with second motor neuron
-motor neuron, never sends sensory information
Postganglionic neuron (ANS)
cell body is outside the CNS, axon extends to effector organ
-motor neuron, never sends sensory information
Ganglia (ANS)
site of synapse between the preganglionic neuron and postganglionic neuron
Difference between neurotransmitter effects
SNS - all release acetylcholine (ACl) at synapses
-Effect is always excitatory
ANS - release norepinephrine or acetylcholine
-Effect can be excitatory or inhibitory
2 divisions of the ANS
Parasympathetic and sympathetic
Parasympathetic
-“Rest and Digest”
-Function: Directs “housekeeping” activities concerning digestion & waste elimination, heart rate & blood pressure, airway diameter, pupil diameter, reproduction, etc.
-Origin of Fibers: the brain and the sacral spinal cord
Preganglionic fibers are long, postganglionic fibers are short
-Location of Ganglia: in or near the effector organ
Is energy use high or low when the parasympathetic division is active?
low because it’s resting, not much energy is needed to use
Cranial portion of Parasympathetic Division
-Function: supplies parasympathetic fibers to head, neck, thoracic & abdominal regions
-Preganglionic fibers run in oculomotor, facial, glossopharyngeal, and vagus cranial nerves (oculomotor nerve, facial nerve, glossopharyngeal nerve, and vagus nerve)
Oculomotor nerve
-innervates smooth muscle in eyes & muscle associated with lens
-What is the effect? rest & digest, pupils become smaller, control muscles associated with iris & lens
Facial nerve
-stimulates large glands of head (salivary glands, nasal glands, lacrimal glands)
-What is the effect? stimulatory, want more saliva & fluids
Glossopharyngeal nerve
-activates parotid salivary gland
-What is the effect? stimulate the carotid, producing more saliva
Vagus Nerve
-provide fibers to neck and almost every organ in thoracic & abdominal cavities
-Cardiac plexus: supplies fibers to heart
-effect: slower/resting heart rate
-Pulmonary plexus: supplies fibers to lung
-effect: maintain slow/resting respiratory rate
-Esophageal plexus: serves esophagus
-Fibers extend into abdominal cavity from esophageal plexus - innervates liver, gallbladder, stomach, small intestine, pancreas, proximal half of large intestine
-effect: stimulatory - organs become more active
Sacral Portion of Parasympathetic division
-Form pelvic splanchnic nerves
-Function: serves pelvic organs (bladder & gonads) and distal portion half of large intestine
-What is the effect on each organ? stimulatory, waste removal is at its highest, bladder and large intestine become more active, ovaries and testes become more active and produce more gonads
Sympathetic division
-“Fight or flight”: Activated when we are excited/scared/embarrassed
-Function: Mobilizes the body for action by affecting heart rate and blood pressure, airway diameter, pupil diameter, digestion & waste elimination, reproduction, etc. (generally inhibitory)
-Origin of Fibers: thoracolumbar region of spinal cord (T1-L2)
-Preganglionic fibers are short, postganglionic fibers are long
-Cell bodies of this division form lateral horns of spinal cord
-Location of Ganglia: close to the spinal cord
How is the sympathetic division more complex than the parasympathetic division?
-Innervates smooth muscle, cardiac muscle, and glands in body cavities
-Also innervates smooth muscle and glands in superficial regions
-Sweat glands, arrector pili, smooth muscle in blood vessel walls
-controls how much blood goes to which parts of your body during fight or flight
Anatomy of sympathetic division
-Preganglionic fibers leaving the spinal cord form the sympathetic trunk
-Importance: the sympathetic trunk allows preganglionic axons to travel to spinal nerves that are higher or lower than where they originate
-Sympathetic trunk is located on both sides of the spinal cord
Pathway to sympathetic trunk
1) Preganglionic fiber exits the spinal cord
2) Fiber passes through white ramus comminucans
-Function: white ramus communicans guides the preganglionic fiber to the sympathetic trunk
3) Fiber enters the sympathetic trunk ganglion
-Function: sympathetic trunk ganglion is where the preganglionic fiber synapse with the postganglionic fiber
3 ways that the preganglionic and postganglionic fibers can form synapses
1) Preganglionic neuron and postganglionic neuron synapse at same level
2) Preganglionic neuron and postganglionic neuron synapse at higher or lower level
3) ) Preganglionic neuron and postganglionic neuron synapse at a distant collateral ganglion in abdomen and pelvis
Pathways with Synapses in Trunk Ganglia
-If synapse forms in trunk ganglia - postganglionic fibers travel through gray rami communicans to enter ventral or dorsal ramus of adjoining spinal nerve
Gray rami communicans
-carry postganglionic fibers from sympathetic trunk ganglion to periphery
-from here travel to effectors
Pathways to the Head
-Preganglionic fibers emerge from T1-T4, synapse with postganglionic fibers at superior cervical ganglion of the sympathetic trunk
-Function: serves skin and blood vessels of head, stimulate dilator muscles of eyes, inhibits nasal and salivary glands, innervates muscle to upper eyelid, sends branches to heart
Pathways to the Thorax
-Preganglionic fibers emerge from T1-T6
-Most postganglionic axons pass through cardiac, pulmonary, & esophageal plexuses to effector organ
Pathways with Synapses in Collateral Ganglia
-Preganglionic fibers from T5-L2 synapse in collateral ganglia
-Form splanchnic nerves:
–Greater splanchnic nerve, lesser splanchnic nerve, least splanchnic nerves
–Lumbar splanchnic nerves and sacral splanchnic nerves
-Function: serves abdominal viscera
Pathways to the Abdomen
-Fibers T5-L2 innervate abdomen
-Function: serve the stomach, most of intestines, liver, spleen, and kidneys
Pathways to the Pelvis
-Fibers T10-L2 innervate pelvis
-Function: serves the bladder, reproductive organs, distal half of large intestine
What is the general effect of the sympathetic division on abdominopelvic viscera?
THINK do I need this to happen if I’m fighting a bear?
yes - sympathetic
no- parasympathetic
-inhibits these organs during fight or flight, do not need to digest or reproduce
Visceral reflex arcs have 5 components:
1) Receptor in viscera
-chemical changes like pain and stretch
2) Sensory neurons
-Non-encapsulated nerve endings
-Function: send sensory information about changes in chemical composition, stretch, temperature, & irritation of viscera
3) Integration center
4) Motor neurons
-Preganglionic and postganglionic neurons
5) Visceral effector
-Smooth muscle, cardiac muscle, and glands
Acetylcholine (ACh)
-Effect is not entirely excitatory or inhibitory - depends on receptor it binds
-Released by cholinergic fibers at:
1) All ANS preganglionic axons
2) All parasympathetic postganglionic axons at synapse with effector
Acetylcholine (ACh)
-Effect is not entirely excitatory or inhibitory - depends on receptor it binds
-Released by cholinergic fibers at:
1) All ANS preganglionic axons
2) All parasympathetic postganglionic axons at synapse with effector
Cholinergic Receptors that bind ACh
1) Nicotinic receptors
2) Muscarinic Receptors
Nicotinic Receptors
-Found on: all postganglionic neurons (sympathetic & parasympathetic), hormone-producing cells of the adrenal medulla, sarcolemma of skeletal muscle cells
-Which of these is not autonomic?
-skeletal muscle tissue
-Effect: Binding of ACh here is always stimulatory
Muscarinic Receptors
-Found on: all parasympathetic effectors and some sympathetic effectors
-Effect: Binding of ACh here is stimulatory or inhibitory
-Ex: binding of ACh to muscarinic receptors of heart is inhibitory
-Ex: binding of ACh to muscarinic receptors of smooth muscle of gastrointestinal tract is stimulatory
Norepinephrine (NE)
-Effect is not entirely inhibitory or excitatory-depends on receptor it binds
-Released by adrenergic fibers at:
1) Sympathetic postganglionic axons
Adrenergic Receptors that bind NE
1) Alpha receptors
-Locations: All sympathetic target organs
2) Beta receptors
-Locations: heart, adipose tissue, kidneys, lungs, blood vessels
-Binding of NE or epinephrine can be stimulatory or inhibitory
-Ex: NE binding at beta receptors of heart increases activity
-Ex: Epinephrine binding at beta receptors of bronchioles causes dilation
How are the effects of increased sympathetic activity important for “fight or flight”?
-dilated pupils = more light = see better
-no reproduction or digestion necessary
-need large amounts of air
-heart will pump blood to the rest of your body faster
How are the effects of increased parasympathetic activity important for “rest and digest”?
-heart rate will be low
-do not need large amounts of air
-rest and digest
-do not need as much light
-produce more gametes
How is an organ’s activity determined?
whichever division is sending more impulses will have larger effect
Effects of the Sympathetic & Parasympathetic Divisions
-Most organs have dual innervation
-Sympathetic and parasympathetic divisions innervate organs-both send impulses to organ simultaneously
-Antagonistic Interactions of the Divisions
-Divisions have opposite effects
-Increased sympathetic activity = increased heart rate & blood pressure, dilated airways, decreased digestion & elimination, dilated pupils, decreased reproductive function
-Ex: Increased parasympathetic activity = resting heart rate, decreased airway diameter, increased digestion & elimination of waste, constricted pupils, increased reproductive function
Vasomotor (Sympathetic) Tone
-continuous partial constriction of blood vessels
-Sympathetic fibers supply blood vessels & control blood vessel diameter
-If blood pressure is low-vasomotor fibers fire more rapidly
-Effect: muscle contracts-blood vessels constrict
-If blood pressure is high-vasomotor fibers fire less rapidly
-Effect: muscle relaxes-blood vessels dilate
If muscles contract and blood vessels constrict, what effect does this have on blood pressure?
causes diameter of blood vessels to decrease
If muscles relax and blood vessels dilate, what effect does this have on blood pressure?
causes diameter of blood vessels to increase, blood has more room
Why is partial constriction (ex muscle tone) important in muscle tissue?
-continuous muscles even at rest = tone
-by having the muscle partially constricted, it allows it to respond to stimuli
Parasympathetic Tone
-Present mostly in cardiac muscle tissue, smooth muscle tissue of digestive and urinary organs
-Effect: slows heart rate, maintains normal activity of digestive & urinary organs
-Sympathetic division can override parasympathetic tone
Unique Roles of the Sympathetic Division
1) Thermoregulatory response to heat
-Effects:
A) Blood vessels dilate in response to heat, constrict in response to cold
B) Sweat glands activated in response to heat
2) Renin release from kidneys
-Effects: increases blood pressure
3) Metabolic changes
-Effects:
A) Increases metabolic rate of cells
B) Raises blood glucose levels
C) Mobilizes fats used fuel use
Effect of Increases metabolic rate of cells
produce and use more ATP
Effects of Raises blood glucose levels
glucose available for ATP production
Effects of mobilizes fats used fuel use
stimulate adipose tissue to be broken down
Parasympathetic division exerts highly localized, short-lived control
(1) One preganglionic neuron synapses with one (or a few) postganglionic neurons
(2) All parasympathetic fibers release ACh-quickly broken down by acetylcholinesterase
Sympathetic division exerts diffuse, long-lasting control
(1) Preganglionic neurons synapse with multiple postganglionic neurons
(2) NE and epinephrine prolong effects of sympathetic division activation
Hypothalamic Control of the ANS
-Anterior hypothalamic areas oversee parasympathetic division
-Posterior hypothalamic areas oversee sympathetic division
-Effects: coordinates heart activity, blood pressure, body temperature, water balance, endocrine activity
-Reminder: limbic system relays output through hypothalamus
-Emotional reactions to fear, danger, and stress activate sympathetic division
Hypertension (high blood pressure)
-Caused by: overactive sympathetic vasoconstrictor response
-Effect: heart must work harder to circulate blood through narrow blood vessels
-Future problems: heart disease, enlarged arteries, kidney failure
-Treatment: Adrenergic-receptor blocking drugs
Raynaud’s Disease
-Caused by: exaggerated vasoconstriction response due to cold or emotional stress
-Effect: skin of fingers and toes becomes pale
-Skin can eventually become cyanotic, painful
-Severity can be minimal or more extreme
Autonomic Dysreflexia
-Affects individuals who are quadriplegic or have spinal injuries above T6
-Caused by: uncontrolled activation of autonomic neurons
-usually triggered by some type of pain stimulus to skin or overfilled visceral organ
-Effect: arterial blood pressure skyrockets
-can rupture blood vessels in brain causing a stroke
-Symptoms: headache, flushed face, sweating above injury, cold/clammy skin below injury
