Introduction to the ANS Flashcards
what does the ANS innervate
o Interval organs
o Blood vessels
o Glands
o Pre and post ganglionic neurones
what does the SNS innervate
o Skin
o Skeletal muscle
o Joint
o Single moto neurone
what is the ANS efferent pathway
- Pre ganglionic neurones are myelinated – travels from CNS to ganglion
- Ganglion in the middle
- Post ganglionic neurone is unmyelinated and leads from ganglion to the target organ
what are the nerves of the parasympathetic system
• Cranial nerves III (oculomotor - oculomotor ), VII (facial - salivary glands), IX (glossopharyngeal – salivary gland), X (vagus – heart, lungs, stomach, liver, small intestine, colon, rectum)
what is the nerve in the parasymaptic system
craniosacral
- S2,S3,S4 sacral outflow
describe the pre ganglionic and post ganglionic fibre in the parasympathetic system
• Long preganglionic fibre and a short postganglionic
what is the sympathetic neurone
Thoracolumbar T1-L2
describe the pre ganglionic and post ganglionic fibre in the sympathetic system
• Short preganglionic fibre and long postganglionic
where do the preganglionic fibres originate from
• Preganglionic fibres originate in the lateral horn and pass out through the ventral horn
describe ganglia near organs
- Ganglia sit in the sympathetic trunk – paravertebral ganglia = T1-T4
- Prevertebral ganglia the preganglionic fibre passes through the trunk and the ganglia are nearer the organs = T5-L2
what chain does the sympathetic neurone have
2 neurone chain
are nerves paired in the sympathetic nervous system
yes • Adrenal medulla – EXCEPTION – only 1 nerve – no postganglionic fibre straight to adrenal medulla through the prevertebral ganglia
what is the enteric nervous system
• Nervous system of the GI system
what are the plexus in the enteric nervous system
- Myenteric plexus – controls motor functions of the gut, made up for circular and longitudinal muscle that controls perstalisis
- Submucosal plexus – controls secretion and blood vessel dilation/constriction in mucosal layer, controls the amount of blood going through the gut, controls muscle in the muscular mucosa
what are the plexi interconnected by
unmyelinated fibres
describe how the parasympathetic and sympathetic interaction on the enteric nervous system
- Sympathetic – postganglionic fibres project onto enteric nerves
- Parasympathetic – receives innervation from vagal preganglionic fibres so enteric nerves act as postganglionic fibres
describe the difference between the autonomic and somatic nervous system
Autonomic
- 2 neurone chain – relay station called the ganglion
- Pre synaptic comes from the CNS and goes to the ganglion, releases acetyl choline in the ganglion
- The post synaptic ganglion – excitatory as it has nictinic ACh receptors
T- Post synaptic axon goes to the organ
- Inhibitory or stimulatory – depends on the neurotransmitter and the receptor
Somatic
- No pre ganglionic and post ganglionic axon
- One single neurone
- Heavily myelinated
- Release acetylcholine on skeletal muscle
- Stimulatory
sensory nerves are
afferent
motor neurones are
efferent
motor nerves divide into
parasympathetic and sympathetic system
what is the hypothalamus
- Starting point for the parasympathetic and sympathetic action
- This is part of the brain but is not part of the conscious brain
what information do visceral afferents send to the hypothalamus
- Blood pressure
- Body temperature
- Electrolyte balance
where is the sacral outflow and where does it go
- S2-S4 via pelvic splanchnic
- Goes to the distal colon, rectum, pelvic viscera, external gentialia
what is the clinical relevance of sacral outflow
- Surgery for colorectal cancer puts pelvic splanchnic at risk of damage
- Bladder, bowl and sexual dysfunction
where do the preganglionic fibres synapse in (sympathetic nervous system)
- paravertebral ganglia
- prevertebral gingival
- adrenal gland
where is the paravertebral ganglia
- T1-4
* Will synapse in the sympathetic chain, they may go up a level or up several levels
where is the pre-vertebral ganglia
• Preganglionic fibers from T5-L2 pass through sympathetic chain to prevertebral ganglia, they pass through it there ganglia are around the organs
what is the sympathetic chain
• Sympathetic chain is paravertrbal – parallel to the sympathetic column
describe tonic versus phasic activity
- Dual innervation for most organs and always active to some extent – sympathetic and parasymtpathic are always turned on
what is phasic
- Only needed at certain times so one becomes active to take control – sexual activity, urination, pancreatic secretion
what projects directly into the cells of the adrenal medulla
• Sympathetic pre-ganglionic fibres project directly to cells of the adrenal medulla
what does the sympathetic pre ganglionic fibres do in the adrenal medulla
- Stimulates medullary cells to secrete adrenaline and noradrenaline into blood
- Adrenal acts as a modified post-ganglionic organ
- Contributes to mass action
how many verbal ganglia go into the enteric nervous system
3 vertebral ganglia
describe the prevertebral ganglia in the enteric nervous system
- L1-L2 sympathetic preganglionic fibres pass through sympathetic chain and travel in lumbar splanchnic nerves and synapse on postganglionic neurons in inferior mesenteric ganglion
- Innervate transverse and distal colon rectum bladder and genital
describe the sympathetic system innervating the enteric system
- Sympathetic postganglionic neurons that innervate abdominal viscera are located in prevertebral ganglia
- T5-T9 = Great splanchnic nerve
- T10-T12 = Lesser splanchnic nerve
- Greater and lesser splanchnic nerves synapse on postganglionic neurons in celiac ganglion
- Postganglionic fibres innervate smooth muscle and glands in the stomach, small intestines, liver, spleen, pancreas and kidney
- Some pass through celiac ganglia and synapse on postganglionic neurons in superior mesenteric ganglia
where is the greater splanchnic nerve
• T5-T9
where is the lesser splanchnic nerve
• T10-T12
describe where the preganglionic and postganglionic fibres go (synthetic system)
- Some synapse on postganglionic neurons in paravertebral (sympathetic chain) ganglia
- Some postganglionic axons leave via visceral branches
- Some exit to re-enter the corresponding spinal nerve
- Some pass through paravertebral ganglia and synapse on postganglionic neurons in the prevertebral ganglia
- Some pass through the paravertebral and prevertebral ganglia and synapse in the adrenal medulla
in the sympathetic system where do the axons of the preganglionic neurones leave the spinal cord
- Axons of preganglionic neurons leave spinal cord via ventral (anterior) root between T1 and L2
- Travel via corresponding spinal nerves to sympathetic chain via the white rami (myelinated)
how many sympathetic chains are there
2
where are the sympathetic chains located
one each side of the verebral column
how many ganglia are in the sympathetic chains
• Each is made up of 25 pairs of ganglia joined by nerve trunks
• Preganglionic fibres synapse on ….
many sympathetic postganglionic axons in the sympathetic chain
what is divergence
• Divergence = pre-ganglionic fibres branch out to postganglionic fibres at different levels of the chain
what is convergence
• Convergence = a postganglionic neuron can receive information from many pre-ganglioinic fibres
No cranial nerves….
have sympathetic neurones
what is a typical ANS efferent pathway
- ANS two neurone relay
- Pre ganglionic
- post ganglionic
what are visceral afferents
Visceral afferents are small myelinated and unmyelinated fibres that like somatic afferents have cell bodies in the DRG or ganglia of cranial nerves
what does the response of the visceral nerve depend on
Response of the visceral effect depends on the neurotransmitter and receptors present on the visceral effector cells – can either stimulation/excitation or suppression/inhibition
what do visceral affernts create
Create referred pain
Carry stretch, ischemia, chemical composition of the blood or tension
where is the visceral sensory information relayed to
Hypothalamus = homeostasis
Nuclei of the medulla
Local preganglionic neuron
what are the two outputs of the visceral sensory information
Autonomic system from lateral hypothalamus projecting to lateral medulla that drive the autonomic system
Endocrine signals via pituitary
is the visceral an autonomic or somatic reflex
autonomic reflex
- they initiate autonomic reflexes at the local, ganglion, spinal and supraspinal levels
what are the two plexus from the vagus nerve
celiac plexus
hypogastric plexus
- this forms the enteric nervous system
where does the celiac plexus go
Liver and gallbladder
Stomach
where does the hypogastric plexus go
Spleen
Kidneys
Small intestine
Colon (proximal)
what does the enteric nervous system contain
Primary afferents Secretormotor neurons (+/-) interneurons
