Neuro 500 -- ANS & pathology (class 11/12) Flashcards
Autonomic Tone
-most organs receive innervation from both divisions of the ANS, which typically work in opposition to one another
-autonomic tone is the balance between sympathetic and parasympathetic activity
What regulates autonomic tone?
Hypothalamus
A few structures only receive sympathetic innervation:
-sweat glands
-arrector pili muscles
-kidneys
-spleen
-most blood vessels
-adrenal medullae
-although they don’t have opposition from the parasymp nervous system, they still exhibit a range in responses: an increase in sympathetic tone has one effect and a decrease in sympathetic tone has the opposite effect
Sympathetic responses
-pupils dilate
-heart rate, force of heart contraction and BP increases
-airways dilate (faster movement of air into and out of lungs)
-BV to skeletal muscles dilate
-BV to cardiac muscles dilate
-BV to GI tract constrict
-BV to kidneys constrict
-BV to liver dilate
-BV to adipose tissue dilate
Parasympathetic responses
Salivation
Lacrimation
Urination
Digestion
Defecation
-decreased heart rate
-decreased diameter of airways
-decreased diameter of pupils
ANS sensory input
-from interoreceptors (sensory receptors located in BVs, visceral organs, mm and nn that monitor conditions in the internal environment)
-not usually consciously perceived
somatic nervous system motor output
-Primary motor area of cerebral cortex
-voluntary
(with contributions from basal nuclei, cerebellum, brainstem and SC)
ANS motor output
-involuntary control from hypothalamus
somatic nervous system motor neuron pathway
-one neuron pathway
-somatic motor neuron goes from CNS to skeletal muscle
ANS motor neuron pathway
-two neuron pathway
-to chromaffin cells in adrenal medulla
somatic nervous system neurotransmitters
-somatic motor neurons only release ACh
-autonomic motor neurons release ACh or NE
—> hormones: NE (norepinephrine) & Epinephrine
effectors
-skeletal muscle
vs.
-smooth muscle, cardiac muscle or glands
responses
-contraction of skeletal muscle
vs.
-contraction or relaxation of smooth muscle
-increase or decreased rate & force of contraction of cardiac muscle
-increased or decreased secretion of glands
anatomy of autonomic motor pathways – main parts
1) Preganglionic neuron
2) Postganglionic neuron
3) Autonomic ganglion
1) Preganglionic neuron
-the first neuron in an autonomic motor pathway
-cell body is in CNS
-axon is a type B fiber
-usually goes to an autonomic ganglion and synapses with a postganglionic neuron
A fibers
-largest diameter
-myelinated
-brief absolute refractory period
-fast
-sensory neurons, motor neurons to skeletal mm
B fibers
-medium diameter
-myelinated
-medium absolute refractory period
-conduct nerve impulses from viscera to CNS
-all preganglionic neurons
C fibers
-smallest diameter
-unmyelinated
-longest absolute refractory period
-pain from viscera
-all postganglionic neurons
preganglionic neuron …
Thoracolumbar division/sympathetic
Craniosacral division/parasympathetic
Thoracolumbar division/sympathetic
-in the sympathetic division, preganglionic neurons have their cell bodies in the lateral horns of gray matter in T1 to L2 (sometimes L3)
—> In the sympathetic system,
the preganglionic axons
travel out from the SC
with spinal nerves T1-L2 (L3)
Craniosacral division/parasympathetic
-in the parasympathetic division, cell bodies of preganglionic neurons are in the nuclei of 4 cranial nerves (10, 9, 7, 3) and in the lateral gray matter of S2 to S4
—> In the parasympathetic, preganglionic axons travel out with 4 cranial nn
—> Parasympathetic, preganglionic axons
also travel out the spine in the sacrum
2) Postganglionic neuron
-the second neuron in an autonomic motor pathway
-in the PNS
-cell body is in an autonomic ganglion
-type C fiber
-terminates in a visceral effector
3) Autonomic Ganglia
-where the preganglionic and post ganglionic neurons synapse
Sympathetic division
-the sympathetic division has 2 different groups of ganglia:
1) Sympathetic trunk ganglia
2) Prevertebral ganglia
1) Sympathetic trunk ganglia
AKA
Vertebral chain ganglia/
Paravertebral ganglia
-aka vertebral chain ganglia
-aka paravertebral ganglia
-lie in a vertical row on either side of vertebral column
-the post ganglionic axons from here innervate organs above the diaphragm
-the sympathetic trunk ganglia in the neck have specific names:
—> superior cervical ganglia
—> middle cervical ganglia
—> inferior cervical ganglia
2) Prevertebral ganglia
AKA collateral ganglia
-aka collateral ganglia
-they lie anterior to the vertebral column
-their post ganglionic axons innervate organs below the diaphragm
-5 major prevertebral ganglia:
Celiac ganglion
Superior mesenteric ganglion
Inferior mesenteric ganglion
Aorticorenal ganglion
Renal ganglion
Parasympathetic division
-the parasympathetic division has only one group of ganglia
1) Terminal ganglia
1) Terminal ganglia
-most of these are located close to or within the wall of a visceral organ
-in the head they have specific names:
-in the head terminal ganglia have specific names:
Ciliary ganglion
Otic ganglion
Pterygopalatine ganglion
Submandibular ganglion
4 ways sympathetic preganglionic neurons connect with post postganglionic neurons:
- In the first ganglion it reaches
- The axon may ascend or descend to a higher or lower ganglion and synapse there
- The axon may go through the sympathetic trunk (paravertebral) ganglion to synapse in a prevertebral ganglion
- The axon may pass through the sympathetic trunk (paravertebral) ganglion and prevertebral ganglion to synapse with chromaffin cells of the adrenal medulla
SNS & divergence
A single sympathetic preganglionic fiber has many axon collaterals and may synapse with 20+ postganglionic neurons.
This is an example of divergence and helps to explain why many sympathetic responses affect almost the entire body simultaneously.
does parasympathetic nervous system have divergence?
Not really
Parasympathetic preganglionic neurons pass to terminal ganglia near or within a visceral effector.
They usually only synapse with 4 or 5 postsynaptic neurons, all of which supply a single effector.
So parasympathetic responses are localized to a single effector.
Autonomic Plexuses
-tangled networks of axons of sympathetic and parasympathetic neurons
-in thorax, abdomen and pelvis
-also contain sympathetic ganglia and axons of autonomic sensory neurons
autonomic plexus list
Cardiac plexus (in thorax)
Pulmonary plexus (in thorax)
Celiac (solar) plexus:
—> largest autonomic plexus
—> surrounds celiac trunk
—> contains 2 large celiac ganglia,
2 aorticorenal ganglia, autonomic axons
—> supplies stomach, spleen, pancreas, liver, gallbladder, kidneys, adrenal medullae, testes, ovaries
more autonomic plexuses
Superior mesenteric plexus
—> supplies small + large intestines
Inferior mesenteric plexus
—> supplies large intestine
Hypogastric plexus
—> supplies pelvic viscera
Renal plexus
—> supplies renal arteries and ureters
4 ways sympathetic postganglionic neurons connect with visceral effectors:
1) spinal nerves
2) cephalic periarterial nerves
3) sympathetic nerves
4) splanchnic nerves
- Spinal nerves
-postganglionic neurons enter a short pathway called the ‘grey ramus’ and then merge with the anterior ramus of the spinal nerve
-grey rami communicantes contain sympathetic post ganglionic axons
-these axons provide sympathetic innervation to visceral effectors in skin of neck, trunk, limbs (sweat glands, smooth muscle in blood vessels and arrector pili muscles)
- Cephalic periarterial nerves
-axons coming off the superior cervical ganglion leave the trunk by forming cephalic periarterial nerves
-these are nerves that extend to the head by wrapping around and following the course of various arteries that pass from the neck to the head
-these neurons provide sympathetic innervation to visceral effectors in the skin of the face (sweat glands, blood vessels, arrector pili muscles) and visceral effectors of the head (smooth muscle of the eye, lacrimal glands, pineal gland, nasal mucosa and salivary glands)
- Sympathetic nerves
-axons leave the sympathetic trunk by forming sympathetic nerves that extend to visceral effectors in the thoracic cavity
-axons coming off the superior, middle, inferior ganglia and T1-T4 ganglia form sympathetic nerves that enter the cardiac plexus to supply the heart
-axons coming off T2-T4 ganglia form sympathetic nerves that enter the pulmonary plexus to supply smooth muscle of the bronchi and bronchioles of the lungs
- Splanchnic nerves
-these are preganglionic neurons that don’t synapse in the sympathetic trunk ganglia – once they leave the trunk they form splanchnic nerves which go to prevertebral ganglia
Greater splanchnic nerve
Lesser splanchnic nerve
Least (lowest) splanchnic nerve
Lumbar splanchnic nerve
to adrenal medulla
-preganglionic axons go to chromaffin cells in adrenal medullae of adrenal glands
-adrenal medullae are modified sympathetic ganglia
-chromaffin cells release hormones into blood: —> epinephrine —> norepinephrine
Horner’s syndrome
Sympathetic innervation is lost when trauma or disease affect the sympathetic outflow through the superior cervical ganglion
-ptosis
-miosis
-anhydrosis
-enopthalmos
-on the affected side
Structure of the Parasympathetic Division (cranial)
(Recall: in the head terminal ganglia (of parasympathetic division) have specific names)
Cranial parasympathetic outflow
Cell bodies in nuclei in brain stem
Preganglionic axons that extend from the brain stem along 4 cranial nerves
4 pairs of ganglia:
1. ciliary ganglia – their post ganglionic neurons supply smooth muscle of the eye
2. pterygopalatine ganglia – their post ganglionic neurons supply nasal mucosa, palate, pharynx and lacrimal glands 3. submandibular ganglia – their post ganglionic neurons supply submandibular and sublingual salivary glands 4. otic ganglia – supply parotid salivary glands
*preganglionic axons that leave the brain as part of the vagus nerve carry about ____% of the total craniosacral outflow
*preganglionic axons that leave the brain as part of the vagus nerve carry about 80% of the total craniosacral outflow
Structure of the Parasympathetic Division (sacral)
Sacral parasympathetic outflow
Cell bodies in lateral gray matter of S2-S4
Preganglionic axons that extend from the anterior roots of S2-S4 spinal nerves
Preganglionic axons travel with spinal nerves and then branch off to form pelvic splanchnic nerves
Then they synapse with parasympathetic postganglionic neurons in terminal ganglia
Post ganglionic neurons innervate smooth muscle and glands in the walls of the colon, ureters, urinary bladder and reproductive organs
ANS NEUROTRANSMITTERS & RECEPTORS
receptors are integral membrane proteins in plasma membrane of post-synaptic cell
Cholinergic neurons:
- release ACh
(- ACh is stored in synaptic vesicles and released by exocytosis)
Cholinergic neurons:
—> all preganglionic neurons
—> all parasympathetic postganglionic neurons
—> sympathetic postganglionic neurons that innervate sweat glands
2 types of cholinergic receptors:
nicotinic receptors
muscarinic receptors
- Nicotinic receptors
- sympathetic & parasympathetic post ganglionic neurons
- chromaffin cells
- motor end plate at NMJ
- Muscarinic receptors
- all effectors innervated by parasympathetic post ganglionic neurons
- sweat glands
Adrenergic neurons
-release norepinephrine (NE) aka noradrenalin
-most sympathetic post ganglionic neurons
-NE is stored in synaptic vesicles and released by exocytosis
-adrenergic receptors bind to both NE and epinephrine
-NE can be released as a neurotransmitter by sympathetic postganglionic neurons or as a hormone by chromaffin cells
-epinephrine is released as a hormone by chromaffin cells
2 main types of adrenergic receptors
- alpha α
- beta β
alpha vs beta adrenergic receptors classification
- are further classified into subtypes: alpha 1, alpha 2, beta1, beta2, beta3
- alpha1 + beta1 receptors generally produces excitation
- alpha2 + beta2 causes inhibition
- beta3 receptors are only on cells of brown adipose tissue, where their activation causes thermogenesis (heat production)
adrenergic vs cholinergic neurons effect length
Effects triggered by adrenergic neurons are usually longer lasting than those triggered by cholinergic neurons
NE taken up
NE is either taken up by the axon that released it or inactivated by enzymes
enzymes e.g.:
-COMT (catechol-O-methyltransferase)
-MAO (monoamine oxidase)
Receptor agonists & antagonists
..
receptor agonist
- is a substance that binds to and activates a receptor
- so it mimics the effect of a natural neurotransmitter or hormone
receptor antagonist
- is a substance that binds to and blocks a receptor
- so it prevents a natural neurotransmitter or hormone from exerting its effect
Effects of sympathetic stimulation are longer lasting and more widespread that in the parasympathetic system because:
1) Sympathetic postganglionic axons diverge more so many tissues are activated simultaneously
2) Acetylcholinesterase quickly inactivates ACh but NE lingers in the synaptic cleft
3) NE and E secreted into the blood from the adrenal medullae intensify and prolong the responses caused by the neurotransmitter norepinephrine
