CH 16 - Autonomic Nervous System Flashcards
Describe the somatic nervous system (SNS) operations.
Consciously controlled
Effector: skeletal muscle
Integrative center: cerebral cortex
Describe the autonomic nervous system (ANS) operations.
Unconsciously controlled
Effectors: smooth/cardiac muscle, glands, adipose
Integrative center: hypothalamus
What is the enteric nervous system (ENS)?
Where is it found?
“The brains of the gut”
Found along length of GI tract and within the walls of the GI tract/pancreas/gallbladder
What are the sensory neuron receptors of the enteric nervous system (ENS)?
Chemoreceptors- monitor chemical changes of GI tract
Mechanoreceptors- monitor stretching of walls
What do enteric motor neurons control?
Contraction of the smooth muscles of GI tract to move food along
Secretions of GI tract organs
Activity of GI tract endocrine cells
What is a short reflex?
Complex visceral reflexes that are locally coordinated and function independently of the CNS
What is a long reflex?
Reflexes that involve the brain and that are influenced by either the sympathetic or parasympathetic divisions
2 Visceral motor neurons would synapse with the ENS interneuron
Preganglionic fibers
Axons of preganglionic neurons
*Type B fibers
Postganglionic fibers
Axons of postganglionic neurons
*Type C fibers
Autonomic ganglia
Where preganglionic and postganglionic neurons synapse
*Contains postganglionic neuron cell bodies
Cholinergic neurons
Neurons that release/exocytosis acetylcholine (ACh) into the synaptic cleft
Cholinergic receptors
Receptors that ACh binds to
Either nicotinic or muscarinic
Adrenergic neurons
Neurons that release/exocytosis norepinephrine (NE) to specific target organs
Adrenergic receptors
Receptors that NE (or epinephrin) binds to
Either alpha (NE potent) or beta (epi potent)
What are the divisions of the autonomic nervous system?
Sympathetic (thoracolumbar) division
Parasympathetic (craniosacral) division
How do the sympathetic and parasympathetic divisions interact?
- Dual innervation- opposing effects (excitatory vs inhibitory)
- They work independently- they control different things
- Cooperative effects- each division controls different stages of the same process; working together
Where are the cell bodies of sympathetic preganglionic neurons located?
Within lateral grey horns between segments T1-L2 of the spinal cord
Where are the cell bodies of sympathetic postganglionic neurons located?
Within sympathetic chain ganglia (paravertebral ganglia), collateral ganglia (prevertebral ganglia), or adrenal medulla
What is found within the thoracolumbar outflow?
Axons of sympathetic preganglionic neurons
What is the rule about sympathetic preganglionic and postganglionic fibers?
Preganglionic fibers are short
Postganglionic fibers are long
What is the exception about sympathetic preganglionic and postganglionic fibers?
The adrenal medulla
Preganglionic fiber is long
What are the major effects of the sympathetic division?
Increased:
- mental alertness
- metabolic rate
- respiratory rate
- heart rate & force of contraction
- blood pressure
- muscle tone
Decreased:
- digestive/urinary functions
- salivation
Energized feeling
Energy reserves activated
Sweat glands activated
Pupils dilated
Glycogenolysis
The release of glucose from the liver
Glycogen becomes glucose
Lipolysis
The breakdown of triglyceride reserves from adipocytes
Triglycerides become fatty acids and glycerol
Proteolysis
The breakdown of proteins into amino acids
Gluconeogenesis
The combination of lipolysis and proteolysis
Which structures are only found within spinal cord segments T1-L2?
Lateral grey horns and white rami
Describe the route that all sympathetic preganglionic neurons initially follow.
What are the options from there?
The cell body of the sympathetic preganglionic neuron is located within the lateral grey horn of spinal segments T1-L2. The preganglionic fibers will exit the spinal cord through the ventral root and enter the white ramus.
The sympathetic preganglionic neuron will then synapse with a sympathetic postganglionic neuron in a sympathetic chain ganglion or a collateral ganglion, or an adrenal medulla
If a synapse occurs at a sympathetic chain ganglion, what will the postganglionic axon leave as?
Cephalic periarterial nerves (head structures) Sympathetic nerves (heart and lungs) Spinal/peripheral nerves (skin structures)
If a synapse occurs at a collateral ganglion, what will the preganglionic axon leave as?
Splanchnic nerves (abdominopelvic structures)
List the regions of the sympathetic chain ganglia and where they are located.
Cervical ganglia (C1-C8 cervical spinal nerves) *Superior, middle, and inferior cervical ganglia
Thoracic ganglia (T1-T12 thoracic spinal nerves)
Lumbar ganglia (L1-L5 lumbar spinal nerves)
Sacral ganglia (S1-S5 sacral spinal nerves)
Coccygeal ganglion (C1)
- Also called ganglion impar
- Fused
What does the ganglion impar respresent?
The fusion of the left and right sympathetic chains
Which structures are associated with spinal/peripheral nerves?
Skin of body/neck/limbs
Which structures are associated with sympathetic nerves?
Structures of the thoracic cavity (above the diaphragm)
What structures are associated with cephalic periarterial nerves?
Structures of the head
List the splanchnic nerves.
Greater splanchnic nerve
Lesser splanchnic nerve
Lumbar splanchnic nerve
Sacral splanchnic nerve
List the collateral (prevertebral) ganglia.
Celiac ganglia (x2)
Superior mesenteric ganglion
Inferior mesenteric ganglion
Hypogastric ganglion
What is a chromaffin cell?
What are its functions?
Specialized sympathetic postganglionic neuron without axons or dendrites
Secretes hormones (NE and epi) into blood when stimulated by a sympathetic preganglionic neuron
*Secretes 75-80% epi, 15-20% NE
What do stimulated sympathetic preganglionic neurons release? Where?
What are they called? What are their effects?
Acetylcholine into synaptic cleft
These are called cholinergic neurons, and they always have an excitatory effect on their postganglionic neurons
What do stimulated sympathetic postganglionic neurons release? Where?
What are they called? What are their effects?
Norepinephrine to specific target organs
These are called adrenergic neurons, and they can be excitatry or inhibitory depending on their effectors
What is the exception in which a stimulated sympathetic postganglionic neuron releases ACh instead of NE?
Sweat glands of the skin
If the effector is a sweat gland, the sympathetic postganglionic neuron is a cholinergic neuron. It releases ACh into the synaptic cleft that binds to muscarinic receptors.
Where do parasympathetic preganglionic fibers originate?
Where do they leave through?
If originating in the brain stem, they leave through the oculomotor, facial, glossopharyngeal, and vagus cranial nerves
If originating in sacral segments of the spinal cord, they leave through lateral grey matter of sacral spinal segments S2-S4
Cranial parasympathetic output
Preganglionic axons that extend from the brainstem in oculomotor, facial, glossopharyngeal, and vagus cranial nerves to structures in the head, organs in the thoracic cavity, and organs in the abdominopelvic cavity
Sacral parasympathetic output
Preganglionic axons that extend from S2-S4 to abdominopelvic organs via pelvic splanchnic nerves
What is the rule about parasympathetic preganglionic and postganglionic fibers?
Preganglionic fibers are long
Postganglionic fibers are short
What are terminal ganglia?
List them.
Ganglia/site of synapse close to effectors
Ciliary, pterygopalatine, submandibular, and otic ganglia
What are intramural ganglia?
Ganglia/site of synapse embedded within the wall of the effectors (abdominopelvic organs)
What are the major effects of the parasympathetic division?
Increased:
- digestive/urinary functions
- salivation
- energy storage
Decreased:
- mental alertness
- metabolic rate
- respiratory rate
- heart rate
- blood pressure
- muscle tone
Lethargic feeling
Pupil constriction
What is found within the cranial parasympathetic outflow?
Axons of parasympathetic preganglionic neurons
List the nerve-terminal ganglia pairings for cranial parasympathetic outflow.
Oculomotor nerve - ciliary ganglion Facial nerve - pterygopalatine ganglion Facial nerve - submandibular ganglion Glossopharyngeal nerve - otic ganglion Vagus nerve - Intramural ganglion
List the nerve-terminal ganglia pairings for sacral parasympathetic outflow.
Pelvic splanchnic nerve - intramural ganglion
What do stimulated parasympathetic preganglionic neurons release? Where?
What are they called? What are their effects?
Acetylcholine into synaptic cleft
These are called cholinergic neurons, and they always have an excitatory effect on their postganglionic neurons
What do stimulated parasympathetic postganglionic neurons release? Where?
Acetylcholine to specific target organs (neuromuscular and neuroglandular junctions)
Where are nicotinic receptors found?
What does ACh exposure do?
On all sympathetic and parasympathetic postganglionic cells; excitatory response
At motor end plate of neuromuscular junctions of the somatic nervous system; skeletal muscle contractions
Where are muscarinic receptors found?
What does ACh exposure do?
At all parasympathetic visceral effectors
At sympathetic neuroglandular junctions; can be excitatory or inhibitory
What are autonomic plexuses?
What are they formed by?
Nerve networks in the thoracic and abdominopelvic cavities
Formed by
- sympathetic postganglionic fibers
- parasympathetic preganglionic fibers
- visceral sensory fibers
List the autonomic plexuses.
Cardiac plexus Pulmonary plexus Esophageal plexus Celiac plexus Superior mesenteric plexus Inferior mesenteric plexus Hypogastric plexus
Autonomic tone
The resting state of organs, regulated by the hypothalamus and maintained by visceral motor neurons
*Can involve sympathetic division, parasympathetic division, or both
Vasomotor tone
An example of sympathetic tone
Sympathetic fibers innervate blood vessels to keep them in a continual state of partial contraction
- Increased vasomotor tone = vasoconstriction
- Decreased vasomotor tone = vasodilation
Vagal tone
An example of parasympathetic tone involving the heart
During exercise/stress, heart rate increases by stimulating sympathetic division and inhibiting parasympathetic division (dual innervation)
- Increased vagal tone = decreased heart rate
- Decreased vagal tone = increased heart rate
