Chapter 14 Autonomic Nervous System (ANS) Flashcards
What type of motor neurons make up the ANS?
visceral motor neurons
What is the primary function of the ANS?
to make adjustments to maintain homeostasis
What regulates and coordinates the ANS?
the higher brain centers
Compare and contrast the somatic and autonomic motor system.
somatic
effector: SKELETAL muscle
control: voluntary
motor pathways: one neuron with cell body inside CNS, no ganglia outside CNS, thick myelinated, fast transmission
neurotransmitters: ACH - always excitatory
AUTONOMIC
effector: smooth muscle or cardiac muscle
control: involuntary
motor pathway: 2 neuron chain. cell body of first neuron inside CNS, cell body of neuron 2 outside CNS in ganglion. Fibers vary in size, myelination, and speed
neurotransmitters: ACh or NE - affect changes based on receptor
What are the two divisions of the ANS?
Parasympathetic and sympathetic
What is another name for the parasympathetic division of the ANS?
Craniosacral division
named after its origin (craniosacral)
What does the parasympathetic division do?
controls body under NORMAL conditions by promoting maintenance activities and conserving E
ex after a meal: BP, HR, resp. are low, gastrointestinal activity is high, pupils are constricted, lenses are accommodated for close vision
What is another name for the sympathetic division of the ANS?
Thoracolumbar division
named after its origin (thoracolumbar)
What does the sympathetic division (thoracolumbar division) do?
- mobilizes the body during activity
- controls body under ABNORMAL conditions
- promotes fight or flight
ex during exercise: blood flow is shunted to skeletal muscles and heart bronchioles dilate, liver releases glucose
How are most organs innervated by the ANS?
most organs are innervated by both divisions (parasympathetic and sympathetic)
only a few organs are innervated by one and fine control is enabled because the brain can control both the inhibitory and excitatory stimuli
explain the autonomic motor pathway
CNS preganglionic neuron I lightly myelinated axon v Synapse (ganglion) I post ganglionic neuron, unmyelinated axon v effector
describe the nerve pathway of the parasympathetic division.
Long preganglionic
Short postganglionic
ganglion is located in or close to effector
no rami communicantes
Describe the nerve pathway of the sympathetic division
Short preganglionic
Long postganglionic
chain ganglia near vertebral column
rami communicantes
Describe the neurotransmitters for the parasympathetic and sympathetic divisions.
Parasympathetic: all secrete ACh (are cholinergic)
Sympathetic:
all preganglionic are cholinergic (ACh)
most postganglionic are adrenic (secrete NE)
what cranial nerves carry PS fibers
III, VII, IX, and X
Where are the preganglionic cell bodies located for nerves III, VII, and IX? Where are their ganglia located?
preganglionic: Brain stem nuclei
postganglionic: close to the parts supplied
Where are the preganglionic cell bodies and the ganglia located for cranial nerve X (vagus nerve)?
preganglionic: in the medulla
ganglia: in the wall of organs supplied
where is the ganglion located for cranial nerve III (oculomotor)? What does it innervate and what does it control?
ganglion located in the eye orbit
innervates the eye muscles and controls accommodation (focus) of the eye
Where is the ganglion located for cranial nerve VII, what does it innervate and what is its effect?
ganglion located behind jaw
innervates nasal, lacrimal, and salivary glands
effect: mucous secretion, tears, and salivation
Where is the ganglion located for cranial nerve IX (glossopharyngeal) what does it innervate and what is its effect?
ganglion located just below the skull
innervates parotid salivary glands
effect: secretion of saliva
Where do the preganglionic axons of cranial nerve X (vagus nerve) run to and what do these do?
they run into plexus in thorax and abdomen
Cardiac plexus -> heart -> cardiac muscle
slows and steadies HR, constricts coronary vessels
Pulmonary plexus -> lungs -> smooth muscle
constricts bronchioles
Aortic plexus:
- > gall bladder = contraction to release bile
- > stomach = increase motility and secretion (normal)
- > pancreas = secretion
- > small intestine = inc motility and secretion
Describe the sacral component of the parasympathetic division.
S2-S4 have cell bodies in sacral spinal cord
pelvic nerves connect to hypogastric plexus
- > rectum = inc activity and defecation
- > urinary bladder = constriction of wall, relaxation of urethral sphincter, voiding
- > reproductive organs = causes erection of penis and clitoris
What does the sympathetic division supply?
visceral organs and all superficial visceral structures (sweat glands, hair muscles, smooth muscles of vessels)
Where are the preganglionic cell bodies of the sympathetic division located?
in the lateral horns of spinal cord segments T1-L2
how many paravertebral ganglia are there in the sympathetic system?
23 on each side of the spinal cord
Explain how the signal passes from the preganglionic neuron.
preganglionic axons -> through the ventral root -> through rami communicantes -> into sympathetic chain ganglion
once it enters the sympathetic chain ganglion, it does one of the following:
- synapse with a post ganglionic neuron at same level
- ascend the chain and synapse above or descend and synapse below
- exit from chain ganglia without synapsing via splenic nerves to collateral ganglia
Explain what a collateral ganglion is.
it is a ganglion that is located anterior to the spinal cord. It is not paired and occurs only in the abdominal and pelvis
from what vertebrae do the sympathetic pathways to the head emerge from?
T1-T4
describe the pathway of the sympathetic division to the brain.
exit from T1-T4 -> up chain -> synapse with superior cervical ganglion -> postganglionic axons
To:
eye = dilate pupils
nasal, lacrimal and salivary glands = inhibits secretion
skin and blood vessels of head = constriction
Describe the sympathetic pathway to the thorax
Preganglionic fibers emerge between T1-T6 -> synapse in middle and inferior ganglia -> post ganglionic fibers -> enter cervical nerves -> cardiac plexus
To:
heart = inc rate and force
thyroid gland = secretion of thyroxine
skin = constricts vessels
For some:
preganglionic fibers synapse with the nearest chain ganglion -> postganglionic fibers run directly to organ
ex heart, aorta, lungs, esophagus
What are the two types of cholinergic receptors in the ANS?
Nicotinic
Muscarinic
Where are Nicotinic receptors found?
in all ANS ganglionic cells
hormone producing cells of adrenal medulla
motor end plates of skeletal muscles
What is the effect of ACh on Nicotinic receptors?
ACh is always excitatory for Nicotinic receptors
Where are Muscarinic receptors found?
on all effectors of parasympathetic postganglion neurons
What is the effect of ACh on Muscarinic receptors?
varying effects
inhibitory in heart muscle
excitatory in smooth muscle of digestive tract (contraction)
What are the two types of nerve fibers in the ANS?
cholinergic and andrenergic fibers
What do cholinerergic fibers do and where are they found?
release ACh
includes all ANS preganglionic neurons and all parasympathetic post ganglionic neurons
What do adrenergic fibers do? Where are they found?
release NE (norepinephrine)
includes most sympathetic postganglionic neurons
EXCEPTIONS: sweat glands and some blood vessels in skeletal muscles secrete ACh instead
What are the two types of adrenergic receptors and what is the effect of NE or E on them?
Alpha receptors: usually stimulated by NE or E
Beta receptors: usually inhibited by NE or E
EXCEPTION: NE binding to beta receptors of heart stimulates heart.
What does the effect of NE or E on adrenergic receptors depend on?
which subclass of receptor predominates on the target organ
What is the effect of Atropine? When is it used?
it is an anticholinergic:
BLOCKS muscarinic receptors
inhibits salivation and constriction of pupils during surgery
What is the effect of Neostigmine? When is it used?
Inhibits AChesterase
used to treat MYASTHENIA GRAVIS (an autoimmune disease that results in weakening of skeletal muscles)
What is the effect of over the counter drugs for colds, allergies, and nasal congestion?
Stimulate alpha adrenergic receptors
What are beta blockers used for?
to dilate lung bronchioles for asthma and slow heart action
What are the five types of interactions between parasympathatetic and sympathetic divisions?
Dual innervation Antagonistic interactions Sympathetic tone Parasympathetic tone Cooperation
Describe the dual innervation interaction between the parasympathetic and parasympathetic divisions.
It is the most common way that an organ is innervated
- both innervate and both divisions are partially active most of the time
Can switch dominance:
- under stress, sympathetic dominates
- under normal, parasympathetic dominates
Describe the antagonistic interactions between the sympathetic and parasympathetic divisions.
OPPOSITE effects allow for PRECISE control
- allows for fine tuning
examples:
heart and lungs: S stimulates, PS inhibits
Digestion: S inhibits, PS stimulates
Describe what the sympathetic tone interaction is.
It refers to degree of contraction (tone) of smooth muscles in blood vessels controlled by sympathetic alone
results in vasomotor tone:
- under stress, sympathetic increases stimulation constricting further
- under normal, sympathetic decreases stimulation
Describe what the parasympathetic tone interaction is.
tone under normal times in the heart and smooth muscle of digestive system and urinary tracts
maintained by parasympathetic division:
dec heart activity, stimulates digestion and urination
can be overridden by sympathetic under stress
Describe the cooperation interaction between the parasympathetic and sympathetic divisions.
both divisions work together to carry out a function.
Ex sex organs
PS: erection of penis or clitoris (vasodilation)
S: ejaculation or reflex contraction of vagina
What are the organs/glands that only innervated by sympathetic fibers?
Adrenal medulla Arrector pili muscles Sweat glands Kidneys Most blood vessels
What are the aspects that are controlled by the sympathetic division?
temperature blood pressure via renin increases metabolic rate raises blood glucose lipolysis for ATP production
increases responsiveness of skeletal muscle
How does the sympathetic division increase mental alertness?
by stimulating the RA (reticular activation) system
Which division of the ANS is localized and short lived. Why?
Parasympathetic
fibers do not synapse widely and ACh is quickly destroyed
Which division of the ANS is wide and long lasting? Why?
Sympathetic
- fibers synapse with many ganglia
- NE acts more slowly via 2nd messenger system and is destroyed more slowly
- Adrenal medulla hormones released into the blood act more slowly, but last longer
What part of the brain is the main integrative center for the ANS?
the hypothalamus
Subconscious input by this system influences hypothalamic control of the ANS.
the limbic system
Explain the method that can be used to learn voluntary control of the ANS
Biofeedback training: use of electrical devices to monitor autonomic body functioning to allow for training and voluntary control
What do homeostatic imbalances of the ANS usually involve?
- problems with control of smooth muscle
- primarily with the vascular system
Describe what hypertension is.
high blood pressure.
can be caused by chronic stress which creates overactive sympathetic vasoconstriction
can lead to heart disease
TREAT: with adrenergic receptor blockers (ex beta blockers)
Describe what orthostatic hypotension is.
Low blood pressure upon changing positions as a result of dec sensitivity of pressure receptors to change
- common in aging: receptor sensitivity deteriorates
- results in slower response by sympathetic vasoconstrictor centers
dizzy when standing
What is Raynaud’s disease?
also known as “white finger disease”
- cold temp, vibration, stress resulting in constriction of vessels to fingers and toes
- in severe cases causes ischemia and possibly gangrene
TREAT: must cut sympathetic preganglionic fibers to the area to prevent vasoconstriction.
What is autonomic dysreflexia (mass reflex reaction)?
damage to spinal cord resulting in uncontrolled somativ and autonomic reflexes
can be life threatening
What are some effects of aging on the ANS?
orthostatic hypotension
constipation
dry eyes
frequent eye infections
