Chapter 15 - Autonomic Nervous System Flashcards
The autonomic/visceral motor system consists of motor neurons that…
- Innervate smooth and cardiac muscle, and glands
- Make adjustments to ensure optimal support for body activities
- Operate via subconscious control
Also called involuntary nervous system or general visceral motor system
Somatic vs Autonomic Nervous System…
Both have _______ but differ in what 3 things?
- Both have motor fibers
Differ in…
1.) Effectors - Somatic innervates skeletal muscles
- Autonomic innervates smooth muscle, cardiac muscle, and glands
2.) Efferent pathways and ganglia - Somatic has one nerve reaching towards the effector
- Autonomic has two nerves that are used to reach the effector
3.) Target organ responses to neurotransmitters - In somatic, Ach is the main neurotransmitter
- Autonomic uses Ach and also uses norepinephrine (NE)
What are the different parts of the somatic nervous system pathway?
- Somatic sensory neuron –> detects stimuli and transmits nerve signals from skin, special senses, and proprioreceptors in joints and muscles
- Passes posterior root ganglion and out the anterior root
- Somatic motor neuron –> transmits nerve signals to skeletal muscle
Describe the somatic nervous system in terms of its efferent pathway and ganglia
- A single lower motor neuron extends from CNS to skeletal muscle fibers
- Cell body in CNS: thick, myelinated fiber extends in spinal or cranial nerve to skeletal muscle
Describe the autonomic nervous system in terms of its efferent pathway and ganglia
- Pregandlionic neuron in CNS has a thin, lightly myelinated pregangionic axon extending to the autonomic gangion in PNS –> releases ACh from synaptic knob to excite second motor neuron
- Postgangionic (ganglionic) neuron in autonomic ganglion outside CNS has nonmyelinated postganglionic axon that extends to effector organ with the cell body and synapse within autonomic ganglion –> releases ACh or norephinephrine (NE)
2 neuron pathway has advantage of increased communcation and control b/c ___________ and __________
Neuronal convergence: Occurs because axons from numerous preganglion neurons synapse with and influence a single ganglion neuron
Neuronal divergence: Occurs because axons from one preganglionic cell synapse with and influence numerous ganglionic neurons
A __________ is a collection of cell bodies in PNS
Ganglion
The effect of somatic nervous system is __________ and either ______ or ________ for ANS
- Somatic nervous system –> always stimulatory
- ANS –> either stimulatory or inhibitory, depending on receptors
Dual innervation
When organs are served by both parasympathetic and sympathetic divisions (ex: saliva glands)
Examples of antagonistic effects with dual innervation
- Heart rate (Parasympathetic decreases heart rate, sympathetic increases heart rate)
- Muscles in GI tract (parasympathetic increases GI tract motility, sympathetic stimulation decreases motility)
- Pupil diameter of the iris (parasympathetic stimulation and sphincter pupillae causes pupil constriction, sympathetic stimulation and radial muscular layer causes pupil dialation)
What are examples of organs controlled by sympathetic system only?
- Adrenal medulla
- Sweat glands
- Arrector pili muscles
- Most blood vessels
- Kidneys
What are examples of organs controlled by parasympathetic system only?
- Lacrimal glands (tear production)
- Ciliary muscles of the eye (lens accommodation for near vision)
Where are alpha 1 (α1) receptors located and what typically happens?
- Arteries (blood vessels)
- Arrector pili
- Bladder
- Uterers
- Pupil
Constricts blood vessels and visceral organ sphincters; dilates pupils of the eye
Where are the alpha 2 (α2) receptors located and what typically happens?
- pAncreas
- gAstrointestinal tract sphincters
- CNS
inhibits NE release from adrenergic terminals; inhibits insulin secretion
Where are the beta 1 (β1) receptors and what typically happens?
- Heart (1 heart, beta 1!)
- Kidneys
Increases heart rate and force of contraction; stimulates kidneys to release renin
Where are the beta 2 (β2) receptors and what typically happens?
- Lungs (2 lungs, beta 2!)
- Blood vessels
- Uterus
- GI tract
Effects mostly inhibitory
Where are the beta 3 (β3) receptors and what typically happens?
- Adipose (beta thrEE is greasEE)
- Bladder
Stimulates lipolysis by fat cells
Describe the parasympathetic (craniosacral) division in terms of the fibers
Long preganglionic fibers from brain stem and sacrum
- Extend from CNS almost to target organs
- Synapse with postganglionic neurons in terminal ganglia close to/within target organs
Short postganglionic fibers
- Synapse with effectors
Describe the sympathetic (thoracolumbar) division in terms of the fibers
Short preganglionic axons
- In spinal cord segments T1-L2
- Form lateral horms of spinal cord
-Preganglionic fibers pass through white rami communicantes and enter sympathetic trunk (chain or paravertebral) ganglia
Long postganglionic axons
- Ganglia are close to spinal cord (lateral or anterior to it)
Describe the parasympathetic division (crandiosacral division)
- Preganglionic neurons originate in brainstem nuclei and S2-S4 segments of spinal cord
- Conserves energy and replenishes nutrient stores
- Regulates either 1 or only a few effectors at the same time without having to turn on or off all other organs
- Autonomic ganglion is close to (terminal ganglia) or within effector organ wall (intramural ganglia)
What cranial nerves are part of the parasympathetic division?
- CN III (3 - Oculomotor)
- CN VII (7- facial)
- CN IX (9 - glossopharyngeal)
- CN X (10 - vagus)
Describe the sympathetic (thoracolumbar division)
- preganglionic neurons originate in lateral horns of T1-L2 segments of spinal cord
- Mass activation –> important in response to stress and necessary to coordinate rapid changes in activity with numerous effects simultaneously
- Autonomic ganglion is close to vertebral column (sympathetic trunk ganglia and prevertebral ganglia)
What are the two types of ganglia in the parasympathetic system?
- Terminal ganglia: Located close to effector
- Intramural ganglia: Located within the wall of the effector
What are the different sympathetic pathways and when are they used?
1.) Spinal nerve pathway (integumentary structures in neck, torso, limbs)
2.) Postganglionic sympathetic nerve pathway (to head, neck viscera, thoracic viscera)
3.) Splanchnic nerve pathway (to abdominal and pelvic viscera)
4.) Adrenal medulla pathway
Which organs are controlled by the parasympathetic division?
- Eye
- Salivary gland
- Heart
- Lungs
- Stomach
- Pancreas
- Liver and gallbladder
- Bladder
- Genitals
Which organs are controlled by the sympathetic division?
- Eye
- Skin
- Salivary glands
- Lungs
- heart
- Stomach
- Pancreas
- Liver and gallbladder
- Adrenal gland
- Bladder
- Genitals
Visceral reflexes (autonomic reflexes) have the same components as somatic reflex arcs, but _____________
Visceral reflex arc has two neurons in motor pathway
Why does referred pain happen?
- Visceral pain afferents travel along the same pathways as somatic pain fibers
- Occurs when sensory nerve signals from certain viscera are perceived as originating not from the organ, but from somatic sensory receptors within the skin and skeletal muscles
Cholinergic neurons
- Cells that release ACh
- All ANS preganglionic axons
- All parasympathetic postganglionic axons at effector synapse
- Smpathetic ganglionic neurons innervating sweat glands and blood vessels in skeletal muscle
Adrenergic neurons
- Cells that release norepinephrine
- Most sympathetic postganglinoic
- Target cells have adrenergic receptors
- α (1-2) and β (1-3) receptors
- Cells with α receptors are typically stimulated by NE
- Cells with β receptors may be stimulated or inhibited by NE
What are the types of cholinergic receptors?
1.) Nicotinic
2.) Muscarinic
Nicotinic Receptors
- Found on sarcolemma of skeletal muscle cells at neuromuscular junction
- All postganglionic neurons (sympathetic and parasympathetic)
- Hormone-producing cells of adrenal medulla
- Effect of ACh at nicotinic receptors is ALWAYS STIMULATORY
- Opens ion channels, depolarizing postynaptic cell
Muscarinic receptors
- Found on all cells stimulated by postganglionic cholinergic fibers
- Effect of ACh at muscarinic receptors can either be inhibitory or exciatory
- All parasympathetic target organs (ex: GI tract, heart)
- Excitation in most cases, inhibition of cardiac muscle
- Limited sympathetic targets (ex: sweat glands) –> activation
_________ is the main integrative center of ANS activity
Hypothalamus
Subconscious cerebral input via __________
Limbic system
Brain stem
- Regulates pupic size, heart, blood pressure, airflow, salivation, etc.
Spinal cord
- Reflexes for urination, defecation, erection, and ejaculation
Immediately lateral to the vertebral column and anterior to the paired spinal nerves are the left and right __________
Sympathetic trunks
A sympathetic trunk looks like a pearl necklace. What are the parts?
String of the necklace –> bundles of axons
Pearls –> sympathetic trunk ganglia (paravertebral/sympathetic chain ganglia) –> houses cell bodies of sympathetic ganglionic neurons
_____ is typically associated with each spinal nerve
One sympathetic trunk ganglion
The superior cervical ganglion
- Contains cell bodies of sympathetic ganglionic neurons whose axons are distributed primarily to structures within the head and neck and to some throracic viscera
- Postganglionic axons innervate the sweat glands and smooth muscle in blood vessels of the head and neck, dialator pupillae muscle of the eye, and superior tarsal muscle of the eye (helps elevate the eye)
Middle and inferior cervical ganglia
Has cell bodies of ganglionic neurons whose axons extend to both neck structures and thoracic viscera
Connecting the spinal nerves to each sympathetic trunk are rami communicantes. What are white rami communicantes?
- Made of preganglionic sympathetic axons from the T1-L2 nerves of sympathetic trunk
- Preganglionic axons are myelinated –> rami has white appearance
- Similar to enterance ramps onto a highway
Connecting the spinal nerves to each sympathetic trunk are rami communicantes. What are gray rami communicantes?
- Composed of postganglionic sympathetic axons that extend from the sympathetic trunk to the spinal nerve
- Unmylinated postganglionic axons –> look grayish
- Connect to all spinal nerves (cervical, sacral, and coccygeal spinal nerves)
- Allows neurons of sympathetic division (thoracolumbar) to be dispersed to all parts of the body
- Like exit ramps
In the sympathetic trunk ganglia, how many ganglia are there in each part of the vertebrae?
- 3 cervical ganglia (superior, middle, and inferior)
- 11 thoracic ganglia
- 4 lumbar ganglia
- 4 sacral ganglia
