Chapter 14: The Autonomic Nervous System Flashcards
What division of the nervous system are the somatic and autonomic nervous systems part of
motor (efferent) divison
How do the SNS and ANS differ
- effectors
- number of neurons between CNS and effectors
- actions of their neurotransmitters at the effectors
Efferent Pathways & Ganglia: SNS vs ANS
SNS: cell body is in CNS and a single thick myelinated group axon extends in spinal or cranial nerves directly to skeletal muscle
ANS: pathway uses a two-neuron chain
Neurotransmitter effects on effectors: SNS vs ANS
SNS: all somatic motor nerves release acetylcholine; effect is always excitatory
ANS: preganglionic fibers release ACh; postganglionic gibers release NE at most sympathetic fibers, ACh at most parasympathetic fibers- effect: either excitatory or inhibitory depending on type of receptors
2 subdivisions withing autonomic nervous system
- Parasympathetic division:
- Sympathetic division
Main effects PNS has on the body when activated
- keeps body energy use as low as possible even while carrying out maintenance activities
- directs digestion, diuresis, defecation
- rest and digest system
When PNS activated what happens to specific organs
- ex. person relaxing after meal
- blood pressure, heart rate, respiratory rates low
- gastrointestinal tract activity high
- pupils constricted, lenses accommodate for close vision
Main effects SNS has on the body when activated
- mobilizes body during activity
- fight or flight
- exercise, excitement, emergency, embarrassment activates sympathetic system
When SNS activated what happens to specific organs
- ex. person during vigorous activity
- increased heart rate; dry mouth; cold, sweaty skin, dilated pupils
- shunts blood to skeletal muscles and heart
- dilates bronchioles
- causes liver to release glucose
Parasympathetic division: length of preganglionic and postganglionic fibers
- long preganglionic
- short postganglionic
Sympathetic division: length of preganglionic and postganglionic fibers
- short preganglionic
- long postganglionic
Other name for parasympathetic division
craniosacral division
Other name for sympathetic division
thoracolumbar division
Where do nerve fibers in PNS originate from within the CNS
craniosacral part: brain stem nuclei of cranial nerves III, VII, IX and X
* spinal cord segments S2-4
Where do nerve fibers in SNS originate from within CNS
- thoracolumbar part: lateral horns of gray matter of spinal cord segments T1-L2
Where do nerve fibers in PNS synapse once they are outside of CNS and in peripheral nervous system
- terminal ganglia near or withing target organ where preganglionic axons synapse with postganglionic neurons
Where do nerve fibers in SNS synapse once they are outside of CNS an in peripheral nervous system
- postganglionic fiber in a sympathetic chain ganglia (paravertebral ganglia) or collateral ganglia
Which division (sympathetic or parasympathetic) is more complex
sympathetic divisions: innervates more organs- some structures are innervated only by sympathetic: sweat glands (eccrine and apocrine, arrector pili muscle of hair follicle, smooth muscles of all blood vessels
Parasympathetic fibers: site of origin
craniosacral: originate in brain and sacral spinal cord
Sympathetic fibers: site of origin
thoracolumbar: originate in thoracic and lumbar regions of spinal cord
Location of parasympathetic ganglia
located in or near visceral effectors
Location of sympathetic ganglia
lie close to spinal cord
Most dominant cranial nerve associated with parasympathetic division of ANS
- Vagus nerves (X): account for ~90% of all preganglionic parasympathetic fibers in body
- serve all thoracic and abdominal viscera
- branch into nerve plexuses
Division that has localized effects and what contributes to these effects
- parasympathetic division: elicits short-lived and highly localized control over effectors
- ACh quickly destroyed by acetylcholinesterase
Division that has widespread diffuse effects and what contributes to these effects
- Sympathetic division: longer lasting with body wide effects
- NE is activated more slowly than ACh
- NE and epinephrine hormones from adrenal medulla have prolonged effects that last even after sympathetic signals stop
Innervation of the adrenal medulla (adrenal gland) – how is this unique in comparison to the rest of the autonomic nervous system
Sympathetic preganglionic fibers directly innervate the adrenal medulla, stimulating it to release epinephrine (adrenaline) and norepinephrine into the bloodstream. This bypasses the postganglionic neuron.
Motor neuron in SNS
a single lower motor neuron axon extends from spinal cord to skeletal muscles
Motor neurons in ANS
two-neuron chain (preganglionic and postganglionic
Preganglionic fibers: what neurotransmitter do they release / where are they found
- found in both sympathetic and parasympathetic divisions
- release ACh
Postganglionic fibers: where are they found / what neurotransmitter do they release
- sympathetic: release norepinephrine (most) or ACh (sweat glands)
- parasympathetic: release ACh
What neurotransmitter is associated with cholinergic fibers
Acetylcholine
Subtypes of cholinergic fibers
- Nicotinic receptors
- Muscarinic receptors
(named after drugs that bind to them and mimic ACh effects)
Where would you find cholinergic receptors; nicotinic receptors
Nicotinic receptors: all postganglionic neurons (sympathetic and parasympathetic); hormone producing cells of adrenal medulla; saroclemma of skeletal muscle cells at neuromuscular junction
Where would you find cholinergic receptors; muscarinic receptors
Muscarinic receptors: all effector cells stimulated by postganglionic cholinergic fibers; parasympathetic target organs
Which neurotransmitter is associated with adrenergic fibers and receptors
norepinephrine and epinphrine released by adrenal medulla
Subtypes of adrenergic receptors
- Alpha receptors: divided into subclasses: a1, a2
- beta receptors: divided into subclasses: b1,b2,b3
Where would you find adrenergic receptors
found on postganglionic sympathetic target organs
Beta-blocker medications- what do they do and what conditions are they used to treat
Function: block beta-adrenergic receptors, reducing heart rate and blood pressure
Uses: treat hypertension, angina, arrythmias, and heart failure
Sympathetic tone (vasomotor tone)
- blood vessels in continuous state of partial contraction
- maintains blood pressure (even at rest) by regulating vasoconstriction
- allows shunting of blood to body areas that need it while limiting blood flow to other areas that are not as important
Parasympathetic tone
- baseline, constant level of parasympathetic stimulation that slows the heart and sets normal activity level for digestion and urination
- maintains resting heart rate and digestive activities
