Autonomic Nervous System
Describe the various preganglionic sympathetic pathways
A preganglionic sympathetic fiber can enter the sympathetic chain and either: 1) ascend to higher levels of the chain before synapsing 2) synapse immediately 3) descend to lower levels of the chain before synapsing with a neuron in the chain..... 4) in the case of the abdominal viscera,a the preganglionic axons do not synapse in the sympathetic chain at all. Instead they leave the sympathetic chain and travel to one of the 'displaced' or prevertebral ganglia via the splanchnic nerves and synapse there.
Describe the schematic of the sympathetic pathways to abdominal organs
Abdominal viscera- the splanchnic nerve scheme is used. This differs slightly from the 'standard' sympathetic chain ganglia scheme because the second order neurons are displaced from the chain (and are located in the 'prevertebral' sympathetic ganglia). The splanchnic nerves which connect the sympathetic chain with the prevertebral sympathetic ganglia contain PREGANGLIONIC sympathetic fibers that have not yet synapsed with a 2nd order neuron.
Describe the visceral sensory neurons
Afferents- visceral sensory neurons General visceral sensory neurons monitor: stretch, temp, chemical changes, irritation, pain Cell bodies are located in the dorsal root ganglia. Visceral pain- often perceived to be somatic in origin- 'referred pain'
What transmitter does the sympathetic nervous system use at their synapses and what transmitter does the parasympathetic neurons release at their synapse?
At the sympathetic synapse, they release noradrenaline (adrenergic). At the parasympatheticc synapse, they release acetylcholine (cholinergic)
Describe the two neuron rule
Autonomics are always a two neuron relay! The cell body of the 1st neuron is in the CNS- its axon is the preganglionic fiber. It synapses with the 2nd neuron. The cell body of the second neuron is located in an autonomic ganglion- its axon is the postganglionic fiber. The CNS (pre-ganglionic)-----> (autonomic ganglion) ---> synapses (post-ganglionic, output) to smooth muscle, cardiac muscle, and gland. The two neuron rule for the autonomic nervous system has only one exception- the innervation of the adrenal medulla.
Describe the difference between transmitters of the divisions of the ANS
Both sympathetic and the parasympathetic preganglionic neurons release the neurotransmitter acetylcholine at their endings. However, the postganglionic axons of the sympathetic nervous system are called 'adrenergic' because they use noradrenalin as the transmitter at their synapses with target tissues. The postganglionic fibers of parasympathetic neurons release acetylcholine at their target synapses and are called 'cholinergic'. Sympathetics often have relatively short preganglionic and long postganglionic fibers; parasympathetics typically have long preganglionic and very short postganglionic fibers (typically the 2nd order neuron is located right in the wall of the target organ).
Since the superior sympathetic chain's ganglia have special names, they are not part of the paravertebral sympathetic chain.
FALSE: although they have different names, they are all part of the paravertebral sympathetic chain. At the cervical level, there are no white communicating branches.
T/F: the parasympathetic nervous system has a longer post ganglionic neuron than the sympathetic nervous system.
FALSE: the sympathetic nervous system has a longer post ganglionic neuron than the parasympathetic nervous system.
T/F- vasculature through the body is not innervated
FALSE: vasculature throughout the body is innervated. Postganglianic fibers leave the sympathetic chain at all levels and 'catch a ride' or follow vasculature through the body, innervating the smooth muscle in its walls as needed. parasympathetic- don't got to vasculature, however.
Describe the white communicating ramus/ gray communicating rams relationship, as it pertains to the sympathetic fibers
From spinal nerves T1-L3, all preganglionic sympathetic fibers enter the sympathetic chain using a white communicating rams which branches from spinal nerves T1-L3. Only the T1-L3 spinal nerves have a white communicating ramus. Once in the sympathetic thin, a variety of courses are subsequently taken by the preganglionic fibers. After synapsing in the sympathetic chain, postganglionic fibers reenter the spinal nerves via a gray communicating rams. ALL spinal nerves have a gray communicating ramus (But not all have a white ramus).
Describe the superior (upper) end of the sympathetic chain in the neck region
Here, there is a series of 3 larger ganglia (collectively called the cervical ganglia): 1) The superior cervical ganglion is the upper-most extension of the sympathetic chain 2) the middle cervical ganglion is intermediate 3) the inferior cervical ganglion is at the lower cervical vertebral level. These are fused ganglia, so they are bigger.
List some disorders linked to ANS dyregulation
Hypertension- high blood pressure Others -PTSD -Panic disorder -Astma -Hypotension issues (vasovagal syncope) -Irritable bowel and other GI tissues -Erectile dysfunction
How do sympathetic postganglionic fibers target the head?
In order to reach sympathetic target in the heard, the preganglionic sympathetic fibers enter the sympathetic chain and ascend in the chain without synapsing immediately. When these fibers get to a higher appropriate level, they synapse with a neuron in the cervical part of the sympathetic chain and then the postganglionic sympathetic fibers leave the chain ganglia and follow vasculature into the head.
How is the adrenal medulla unique?
It is directly innervated by preganglionic sympathetic fibers. Thus, it contains chromatin cells that are modified sympathetic neurons. It is unique in that it gets direct preganglionic sympathetic innervation. The adrenal medulla functions as part of the sympathetic nervous system and releases adrenalin when it is stimulated by the pre ganglionic fibers.
Where are postganglionic sympathetic fibers located?
It is important to note that while the origin of the pre ganglion fibers is ONLY from the thoracolumbar cord, postganglionic sympathetic fibers are found in all regions of the body, including the head. Thus, sympathetic fibers must reach their final targets by several different routes.
Describe the schematic of the 'paravertebral sympathetic anatomy
Most of the second order neurons (that prove postganglionic fibers) are located in the sympathetic chain ganglia (also called the 'paravertebral' ganglia). These ganglia extend as a chain from the neck to the pelvic cavity on both sides of the vertebral column. The other pathway involves displaced or 'prevertebral' ganglia.
Describe the difference between the sympathetic targets on the left side and the on the right side of the body.
On the left side, sympathetic targets located in the 'body wall' and extremities are shown- namely sweat glands of the skin, rector pili muscles and smooth muscles in the walls of arteries and arterioles (vasculature). On the right side, targets in the heat region as well as organs within the various vanities of the body are shown- such as salivary glands, heart and gut. These are dually innervated.
Where do the sympathetic/thoracolumbar division of ANS originate from on the spine?
Preganglionic fibers from intermediolateral cell column of spinal cord. These fibers originate from the T1- L2/3 cord levels. These preganglionic fibers exit via VENTRAL roots and enter sympathetic chain.
The sacral division of the parasympathetic nervous system
Preganglionic parasymapthetic fibers arise from the S2-S4 spinal cord regions in an intermediolateral cell column and exit via ventral roots. They course to small postganglionic parasympathetic pelvic ganglia that are located in or close to the walls of the organs that they innervate and synapse. The postganglionic axons then go on to innervate important targets such as the excretory sphincters of the urethra and rectum as well as the sex organs/erectile tissue of genitalia that are responsible for erecton.
Describe the two neuron hook-up scheme
The 1st neuron is in the CNS and its axon leaves the CNS and is called the preganglionic fiber. That axon makes a synapse on the 2nd neuron in the chain which is located in a peripheral autonomic ganglion. The 2nd neuron provides the postganglionic fiber (axon) that ultimately synapses with the target tissue.
What is the one exception to the two neuron rule
The adrenal medulla
What areas are innervated by the autonomic nervous system
The autonomic nervous system is innervated by smooth muscle, cardiac muscle and glands.
What sympathetic and parasympathetic aspects innervate the heart
The cervical sympathetic ganglia (and the 1st 4 thoracic sympathetic ganglia) are used). Postganglionic sympathetic fibers leave the sympathetic thin directly and forma cascade of axons in the cardiac plexus. The cardiac autonomic nerve plexus also has parasympathetic fibers (that join in from the vagus nerve) as well as visceral afferent fibers.
Describe the autonomic nervous system
The general visceral motor division of the PNS. It has different targets than the somatic system (spinal). It innervates smooth muscle, cardiac muscle and glands. It functions independently It functions continuously It functions without conscious control Regulates visceral functions, maintains homeostasis: heart rate, blood pressure, digestion, urination. Is regulated by visceral reflexes.
Describe briefly the three regions of the splanchnic nerves
The greater splanchnic nerves-- preganglionic fibers to the celiac ganglion where they synapse (stomach, duodenum, liver, pancreas, spleen) Less splanchnic nerves carry preganglionic fibers to the superior mesenteric ganglion where they synapse. The postganglionic fibers from this ganglion serve the midgut derivatives (duodenum, jejunum, ilium, cecum, ascending and tranverse colon). The lumbar splanchnic carry preganglionic fibers to the inferior mesenteric ganglion (descending colon, sigmoid and rectum and pelvic viscera).
Describe the cranial division of the parasympathetic nervous system
The parasympathetic positions of cranial nerves III, VII, and IX remain in the head region. These preganglionic axons which arise from neuronal cell groups in the brain stem synapse with specific ganglia located in the head. The postganglionic parasympathetic fibers then pass a short distance to innervate their targets (glands, smooth muscle). Parasympathetic postganglionic neurons in the head are found in the: ciliary ganglia (III), ptergopalatine and submandibular ganglia (VII) and the otic ganglia (IX). The vagus nerve (X) provides the main parasympathetic preganglionic feed to much of the rest of the body. It does not project to a parasympathetic ganglion in the head; instead, the postganglionic parasympathetic neurons are located in the walls of its target organs. Among the important targets of the vagus: heart, bronchi, stomach and intestines.
Give a brief overview of the parasympathetic division of the ANS
The pre ganglion fibers from the cranial division run via: III VII IX X (parasympathetic captain. The preganglionic fibers from the spinal division are from the S2-4 spinal cord. The parasympathetic division of the ANS is considerably simpler than the sympathetic division. The parasympathetic component is sometimes referred to as the 'craniosacral' part of the ANS because it takes origin from both neurons in the brain stem and neurons in the sacral part of the spinal cord.
Describe the schematic pathway of the sympathetic nervous system between T1 and L3
The simples scheme occurs at the T1-L3 level for sympathetics that will innervate structures in the 'body wall' and extremities: the preganglionic axon that enters the sympathetic chain via a white communicating ramus synapses with neuron in the sympathetic chain. The postganglionic axon leaves the sympathetic chain via a gray communicating ramus and re-enters the spinal nerve. Those postganglionic sympathetic fibers then travel with the spinal nerve and leave the nerve at various places hat contain targets.
What are splanchnic nerves?
These are displaced preganglianic fibers.
Describe what the celiac, superior meseneric and inferior mesenteric ganglia all have in common
They are displaced away from the main sympathetic chain to a position anterior to the aorta ('prevertebral' or 'preaortic' position). These ganglia are functionally the same as those in the sympathetic chain but they are in an unusual location. Splanchnic nerves! these are the preganglionic fibers. These are unpaired, not segmentally arranged. They occur only in abdomen and pelvis. They lie anterior to the vertebral column (pre aortic--> all about gut). Main ganglia-Celiac, superior mesenteric and inferior mesenteric.
Describe what occurs in Autonomic Dysreflexia- Hyperreflexia
This affects quadriplegics and paraplegics. This is caused by the over-activity of the autonomic nervous system causing an abrupt onset of excessively high blood pressure. Persons at risk for this problem generally have spinal cord injury levels above T5. This is due to sudden strong stimulation of the visceral afferents below the level of injury (bladder hyperextension due to catheter block) without higher CNS toning or dampening down of the reflex. This can cause massive sympathetic discharge throughout the body.
Describe what happens in Autonomic Dysfunction in Raynaud's Disease
This disorder of the ANS is characterized by abnormal constriction of blood vessels in extremities and it is provoked by exposure to cold or by emotional stress. In people with Raynauds disease, small arteries to the fingers or toes can go into vasospasm. This constricts the vessels dramatically and temporarily limits blood supply. The affected body part can turn white or blue and fee cold or numb until the attack subsides. With severe Raynaud's, prolonged or repeated episodes have been know to cause sores or tissue death (gangrene).
How is afferent information (sensory input) from visceral regions conveyed?
This is conveyed by spinal ganglion (DRG) neurons. The peripheral branch axons of spinal ganglion neurons reach viscera by following autonomics or vasculature. The visceral afferents are not considered part of the autonomic nervous system (which is purely efferent), but they travel along with the autonomics to reach body cavities.
Describe reference pain
This is pain from viscera that is typically referred to the body wall and perceived as pain in one or more dermatomes. Thus, the reference of pain to the body wall is the result of 'confusion' at higher CNS levels that consciously perceive pain. This results because visceral afferents enter the spinal cord at the same segmental level as somatic afferents form the same spinal ganglion. There are sex differences.
Is there ever dual innervation for the sympathetic and parasympathetic nervous system?
YES. so, this means that they have opposing actions.
Sympathetic pathways to pelvic organs
the preganglionic fibers synapse in a displaced ganglia (reaching there via a splanchnic nerve) and the postganglionic fibers follow a plexus of fibers to reach genital tissue and excretory targets (smooth muscle).
Describe the two divisions of the ANS
the sympathetic (it prepares for energy expending, stressful or emergency situations (fight or flight). The parasympathetic- active under ordinary, restful conditions (Rest and Digest). The parasympathetic division is simpler and less extensive than the sympathetic division.
Describe autonomic dysfunction in Achalasia Cardia
there's a defect in the autonomic innervation of the esophagus. Hyperactive lower esophogeal sphincter which fails to relax on swallowing.
