Autonomic Nervous System Flashcards
What is the structural difference between the somatic and autonomic nervous system?
The somatic nervous system has one ganglion: dorsal root ganglion
The autonomic nervous system has two ganglions: dorsal root ganglion and the autonomic ganglion
Why does the autonomic nervous system need an extra ganglion?
To spread the signal more widely
What are the two divisions of the autonomic nervous system?
Sympathetic
Parasympathetic
What is the sympathetic nervous system responsible for?
Fight-or-flight
What is the parasympathetic nervous system responsible for?
Rest and digest
What neurotransmitter do sympathetic pathways use?
Acetylcholine neurotransmitter on the nicotinic receptor of the autonomic ganglionic
Norepinephrine neurotransmitter on the adrenergic receptor of target tissue
What neurotransmitters do parasympathetic pathways use?
Acetylcholine neurotransmitter on the nicotinic receptor of the autonomic ganglionic
Acetylcholine neurotransmitter on the muscarinic receptor of target tissue
What is the outflow for the sympathetic nervous system?
Thoracolumbar division (T1 to L2,3)
Where is the lateral horn of the spinal cord found?
In spinal cord only between T1 and L2/3 aka thoracolumbar outflow
What is the outflow of the parasympathetic nervous system?
Caniosacral outflow
Neurons begin at the cranial nerves (CN3, CN7, CN9, CN10) and the sacral spinal cord (S2–S4).
What does the lateral horn contain?
Cell bodies of sympathetic neurons
What are the two types of sympathetic ganglia?
Paravertebral ganglia
Prevertebral ganglia
What are paravertebral ganglia?
The site where preganglionic fibers synapse with postganglionic neurons
Where do paravertebral ganglia lie?
Anterior to the aorta and vertebral column
Occur on either side of the vertebral column from C-S5
What do paravertebral ganglia form?
Two sympathetic trunks
Where are prevertebral ganglia found?
Abdominal cavity around the origin of the major branches of the abdominal aorta.
How do preganglionic fibres enter the sympathetic trunk?
After passing briefly through the anterior rami, preganglionic fibers enter the sympathetic trunk via white rami communicantes.
What do postganglionic fibres do?
Approximately one preganglionic fiber synapses with at least thirty postganglionic fibers.
What happens to post ganglionic fibres after synapsing?
Leave the ganglia through gray rami communicantes and travel through the anterior and posterior rami of the spinal nerves.
Where do preganglionic nerve fibres synapse?
Paravertebral sympathetic chain ganglia or the prevertebral ganglia
What is the sympathetic chain/trunk a mechanism for?
A mass distribution mechanism for sympathetic supply to all parts of the body
What (white or grey) ramus communication is myelinated?
White ramus communication = myelinated
Grey ramus communication = unmyelinated
What fibres do spinal nerves contain?
Post ganglionic sympathetic fibres as well as somatic fibres
What do white ramus communication do?
The white ramus communicans carries preganglionic sympathetic fibers to the sympathetic chain.
What do gray ramus communication do?
The gray ramus contains postganglionic sympathetic fibers rejoining the spinal nerve, going to the efector.
What is the role of white matter?
Found in the deeper tissues of the brain, containing axons.
Many axons are myelinated, giving the white matter its color.
White matter helps conduct nerve signals and protect the axons.
What is the role of grey matter?
Grey matter makes up the outer most layer of the brain.
Mainly composed of neuronal cell bodies and unmyelinated axons.
gets its grey tone from a high concentration of neuronal cell bodies
Summarise the journey the sympathetic fibres go on
- Sympathetic fibres originate in the lateral horn cells between spinal levels T1-L2/3.
- They travel in the ventral root of the spinal nerve to the mixed spinal nerve (MSN).
- They leave the MSN via a white ramus communication as preganglionic fibres to enter the sympathetic ganglion of the same vertebral level.
- After synapsing in the sympathetic chain ganglion, they re-enter the spinal nerve via they grey ramus communication as post ganglionic fibres and are distributed via both dorsal and ventral rami of the spinal nerve.
- The rami then go to supply skin and body wall structures such as arrector pili muscles, blood vessels and glands at that vertebral level (dermatome) with sympathetic input.
If sympathetic fibres originate between T1-L2/3, how do parts of the body above and below T1-L2/3 receive sympathetic innervation?
Preganglionic fibres can travel up or down the sympathetic chain from between vertebral levels T1-L2/3 without synapsing there to then only synapse at the sympathetic ganglion levels higher or lower than T1-LW2/3 and enter the spinal nerve occurring at that level therefore all parts of the body receive sympathetic supply.
What are the three options available in the sympathetic chain to the sympathetic fibres emerging from lateral horn cells?
- Synapse in the chain at the same level
- They can run up or down the chain and synapse at a different level
- They can pass straight through the chain and synapse elsewhere eg in an autonomic nerve ganglion or plexus in the thorax or abdomen.
What feature of the sympathetic chain allows mass activation?
Ability of the sympathetic preganglionic fibres to travel up or down the sympathetic chain
What are splanchnic nerves?
Sympathetic preganglionic fibres which travel to supply organs
What do splanchnic nerves to thoracic organs do?
T1-T4
Synapse in the sympathetic chain and then run as postganglionic fibres to that organ.
What do splanchnic nerves to abdominal organs do?
T5-L2/3
Do not synapse in the sympathetic chain (just run through it) but pass as preganglionic fibres that synapse instead in prevertebral ganglia outwith the sympathetic chain and then run on from there as postganglionic fibres to supply the organ
What do all postganglionic fibres of non-splanchnic nerves do?
Leave the sympathetic chain via grey ramus communication to jin the spinal nerve as the same vertebral level as the sympathetic ganglion in which they have synapsed
What are the three main ganglia within the sympathetic chain?
Superior
Middle
Inferior
What supplies the head and neck synapse?
Sympathetic fibres from T1-L2/3 supplying the head and neck synapse with the main ganglia from where postganglionic branches continue to the head and neck
How can sympathetic fibres be stretched or damaged?
Along their course to the head and neck.
What happens if sympathetic fibres are unilaterally distributed?
Produces a main symptom of Horner’s syndrome:
Partial ptosis - drooping of the eyelid
Miosis - dropping of the eyelid
Anhydrosis - decreased sweating
Does the ANS consist of sensory fibres?
Yes
Discuss sympathetic fibres
Short preganglionic
Long postganglionic
Discuss parasympathetic fibres
Long preganglionic
Short postganglionic
