Anatomy of the Autonomic Nervous System Flashcards
how are the CNS and PNS related?
they are anatomical
The CNS and PNS are a continuum, they are not sperate or distinct
you can have a neurone who’s cell body is located in the PNS but its axon extends into the CNS.
what is the difference between the afferent and efferent system?
they are directional
Efferent System – Carries impulses from the CNS to effectors in the PNS
Afferent – Carries sensory information from receptors in the PNS to the CNS
what is the difference between the somatic and autonomic NS?
they are functional
Somatic – produces voluntary actions via skeletal muscles
Autonomic – produces involuntary actions via smooth muscle, cardiac muscle and glands.
what part of the NS has meninges?
CNS - meninges (dura, arachnoid, pia)
PNS - no meninges and nerve made up of fascicles (endoneurium, perineurium, epineurium)
what is the structure of a transverse section of the spinal cord?
dorsal horn with dorsal root
in the dorsal root - somatic afferent synapses with CNS cell bodies
ventral horn with ventral root
in the ventral root - somatic efferent cell bodies and axons
at the start of the dorsal and ventral roots you have separate motor and sensory neurones
once the two roots merge, you get mixed nerves (i.e afferent & efferent, motor & sensory)
how do things transfer from the spinal cord (CNS) to the PNS?
horn –> root –> mixed spinal nerve –> dorsal/ ventral ramus
how does the transverse cross section of the spinal cord change as you move down the levels?
lateral horn- found in the thoracic and lumbar regions of the SC (found on the lateral portion of the grey matter
it contains the pre-ganglionic
sympathetic neuronal cell bodies (T1-L2)
in the PNS, nerves called pelvic
splanchnic nerves (parasympathetic) have pre-ganglionic cell bodies which are found in lateral (anterolateral) horn of sacral segments
(S2-4)
why is the lateral horn in the sacral segment sometimes referred to as anterolateral?
it isn’t as well defined in the sacral part causing so its called anterolateral
what does the autonomic NS do?
involuntary control
works continuously
Facilitates ‘fundamental’ life-functions
Maintains homeostasis by regulating CVS, respiratory, digestive, excretory and thermoregulation
Becomes active alongside organogenesis during embryo development
The ANS controls functions of the body by changing the balance of continuous outputs in two ‘opposing’ systems (SympaNS and ParaNS)
what is the autonomic NS divided into?
Divided into Sympathetic, Parasympathetic and enteric NS
how do the para and symp NS work together?
Both para and symp divisions are functionally antagonistic
both maintain homeostasis
what is the difference between ganglion and nuclei
ganglion- collection of neuronal cell bodies in the PNS
nuclei- collection of neuronal cell bodies in the CNS
how are the neurones arranged in the NS?
cell body - in the CNS (brain stem, cranial nerve nuclei, lateral horn of SC)
pre - ganglionic neurone would lead to a synapse which is in the ganglion in the PNS
that attaches to another ganglionic neurone (post- ganglionic fibre) that is connected to the target tissue/ organ
what is the difference between the pre and post ganglionic fibres?
pre - ganglionic:
myelinated
primary neurotransmitter is ACh
(cholinergic fibres)
post - ganglionic:
non- myelinated
depending on whether is symp or para the primary neurotransmitter is either ACh or noradrenaline
(adrenergic fibres)
what does visceral mean?
coming from organs and blood vessels
what do the different afferent fibres do?
- General visceral (coming from organs and BV) afferent (GVA) fibres (not sympathetic or parasympathetic)
send sensory information back to CNS via the dorsal root and horn. - Visceral/autonomic afferent fibres travel in the same way as somatic afferent fibres
- The neuronal cell bodies are located in specific sensory nerve ganglia of cranial nerves or dorsal root ganglia
is pain felt in the viscera?
- viscera are insensitive to cutting, crushing and burning
- excessive tension in smooth muscle and some pathological conditions produce visceral pain
what are dermatomes?
Afferent fibres have a segmental arrangement
they supply cutaneous innervation to a specific region of skin
Dermatome maps map out the region of skin innervated by a particular spinal nerve
There is considerable overlap between cutaneous innervation and spinal segments bc of the distribution of the nerves (can have visceral pain in multiple dermatomes)
what is visceral of referred pain?
pain in visceral organs (inside abdomen and thorax) interpreted in the region innervated by the same or different spinal segment
e.g irritation of the peritoneum (membrane in the abdomen) starts in the inferior surface of the diaphragm and the diaphragm is innervated by the phrenic nerve
can get referred pain in the neck bc the phrenic nerve originates in the neck
what do the different efferent fibres do?
Somatic efferent fibres consist of a single neurone which synapses with skeletal muscle.
General visceral efferent (GVE) fibres/autonomic efferent fibres consist of two neurone pathway.
- Pre-ganglionic fibres synapse within a ganglia
- Post-ganglionic fibres synapse with cardiac or smooth muscle cells or with a gland cells
what are myotomes?
essentially the same as dermatome maps HOWEVER, rather than being segmented by cutaneous innervation its the muscle that it supplies
some muscles tend to span different dermatomes which is why you have myotomes
Efferent fibres from spinal nerves, supply innervation to skeletal muscles within a specific compartment
Most skeletal muscles are innervated by nerves derived from several spinal cord levels
what is the sympathetic NS?
Fight or flight response
involved in constriction of cutaneous arteries at the surface of skin (inc blood supply to heart, muscle and brain)
inc BP and contract sphincters in the GI tract
Pre-ganglionic cell bodies located in lateral
horn between T1-L2 spinal levels (known as Thoracolumbar outflow)
Ganglion is found in the sympathetic chain or near the target organ
Short pre-ganglionic neurone and long post-ganglionic neurone
what is an exception to the structure of the sympathetic NS?
instead of having pre and post ganglion with synapse in the middle…
direct innervation from sympathetic preganglionic neurons to adrenal medulla (chromaffin cells) for production of adrenaline.
neurotransmitter- ACh
what is another exception to the structure of the sympathetic NS?
Theres a synapse within the ganglion but rather than using noradrenaline at the post- synaptic neurotransmitter ACh is used instead
post- ganglionic neurone known as ‘sudomotor’ neurons (innervating sweat glands and arrector pili muscle of skin)
how does the sympathetic NS work?
1) Pre-ganglionic neurones depart the lateral
horn (T1 –L2)
2) Fibres pass through the ventral root (myelinated)
3) Enters the sympathetic chain via the white
ramus communicantes (the reason its white is bc the neurones are myelinated)
4) Synapse at sympathetic ganglion
5) Post-ganglionic neurons depart via the
grey ramus communicans (grey bc its unmyelinated)
6) From here, it can take 1 of 3 routes:
- the dorsal ramus will supply the back
- the ventral ramus will supply the anterior body
and limbs
- the meningeal ramus supplies the dura
(depending on which rami it leaves via, it will innervate that region e.g ventral ramus supplies the back)
what are the routes in the sympathetic chain?
3 options:
- can either synapse with the ganglion at the same level
- or synapse with ganglia above or below
- or it can synapse with a ganglion that isn’t in the sympathetic trunk
Divergence- one pre-ganglionic neurone projects to several post- ganglionic neurones
Convergence- one post-ganglionic neurones receives input from several pre-ganglionic neurones (at diff spinal lvls)
- connection of the descending/ascending nerves occurs via the inter-ganglionic nerves connecting the ganglia
- Allows widespread effects on target organs
where are the sympathetic ganglia found?
within the sympathetic chain (para- vertebral chain) - found within the thoracic cavity lateral to vertebral column
pre- aortic ganglia (pre- in front, aortic - aorta, ganglia - swell of neurones) - found on the aorta aka pre- vertebral ganglia
identify the different structures in the cadevaric image
medialateral view of the thoracic cavity
vertebral column and aorta
sympathetic chain down the middle
swellings of tissue - ganglia
connecting tissue from ganglia to neuromuscular bundle in intercostal place is the rami communicantes
what is cervical ganglia?
Sympathetic ganglia (on either side of the neck):
- Superior cervical ganglia (found on C2/C3 level)- supplies C1- C4
LARGEST supply vasoconstrictor and sudomotor nerves to the face and neck - inc dilation of pupil & inhibits salivation
- Middle cervical ganglia (found at C6 level) - supplies C5 - C6 (can also supply C4 - C7 depending on the person) innervate thyroid gland, trachea, oesophagus, heart
SMALLEST ganglia - sometimes not even present
- Inferior cervical ganglia ( found at C7/T1 level) supplies C7, C8, T1 (sometimes C4- C6)
fusion of the cervical and thoracic ganglia so referred to as stellate ganglia (looks like star)
innervate upper limb, subclavian artery, deep cardiac plexus
the nerves synapsing in these ganglia don’t come from the cervical part of the SC
they come form T1 - T3/T5 and ascend upwards
no white rami communicantes however the grey would merge with the spinal nerves at that level
what is abdominal ganglia?
receive innervation via thoracic splanchnic nerves (i.e the ones that pass medially and don’t synapse within the sympathetic chain - 3rd route)
- 3 splanchnic nerves:
Greater –> found T5 - T9 and synapses with the coeliac ganglion (found on abdominal aorta and conveys pain and other sensations from proximal abdominal viscera)
Lesser –> found T9 - T10 and synapses with the coeliac ganglion
Least –> found T11 - T12 and synapses with the coeliac ganglion
- Superior mesenteric ganglion found where superior mesenteric artery originates from
- Inferior mesenteric ganglia receives innervation from the lumbar splanchnic nerves
- ANS fibres follow along with the blood vessels
what is the parasympathetic NS?
rest and digest
leads to decrease in HR
inc in glandular secretion and peristalsis
Provides autonomic innervation to the: head and neck, thorax, abdomen, pelvis and blood vessels
Pre-ganglionic cell bodies located in cranial nerve nuclei (CNIII, VII, IX, X) and lateral horn of sacral segments from S2-S4 (Craniosacral outflow)
Ganglion is found near the target organ or within the walls of tissue (intramural)
Long pre-ganglionic fibres and short post-
ganglionic fibres
neurotransmitter for both pre and post is ACh
what do the different pre ganglionic bodies in the parasympathetic NS supply?
what are the names of the parasympathetic ganglions?
Parasympathetic pre-ganglionic fibres synapse on post ganglionic fibres at:
- Named ganglia in the head.
- Intramural- within the wall of their
target organ.
what are the 4 parasympathetic ganglia in the head that you need to know about?
Four parasympathetic ganglia (on either side of head):
- Ciliary
- Pterygopalatine
- Submandibular
- Otic
identify the parasympathetic ganglia labelled 1
1= Ciliary
in oculomotor nerve
innervates the sphincter of the pupil and ciliary muscle
involved in accommodation reflex
identify the parasympathetic ganglia labelled 1
1= Pterygopalatine
receives innervation from facial nerve
innervates lacrimal and nasal glands
identify the parasympathetic ganglia labelled 1
1=Submandibular
innervates submandibular and sublingual glandsibular –> increases secretion of saliva
identify the parasympathetic ganglia labelled 1
1=Otic
in the glossopharyngeal nerve
innervates the parotid gland –> increases secretion of saliva
what do each of the parasympathetic cranial nerves do?
CN III Oculomotor nerve →ciliary
ganglion →pupil
* CN VII Facial nerve →pterygopalatine
ganglion →lacrimal gland
* CN VII Facial nerve →submandibular
ganglion →submandibular and
sublingual glands
* CNIX Glossopharyngeal nerve →otic
ganglion →parotid gland
what is the enteric NS?
intrinsic supply to gut
controls peristaltic activity, glandular secretion and water and ion transfer
integrated with para and symp NS BUT also works independently
capable of sustaining reflex activity w/o input from CNS
2 main plexuses that you need to be aware of:
- Myenteric plexus –> Peristalsis
- Submucosal plexus –> Glandular secretion
give a summary of the functions of the autonomic NS?
The ANS is tonically activated and maintains homeostasis.
Sympathetic outflow is thoracolumbar (T1-L2),
Parasympathetic outflow is craniosacral (CNIII, VII, IX, X and S2-S4).
Major autonomic ganglia are found in the:
Sympathetic chain including the cervical and the pre-aortic ganglia (sympathetic)
The ciliary, otic, pterygopalatine, submandibular (parasympathetic).
Intramural (within the walls of target organ) ganglia (parasympathetic).
Post-ganglionic sympathetic nerves from pre-aortic ganglia innervate the gut (sympathetic).
The CNX innervates the foregut and midgut, the pelvic splanchnic nerves innervate the hindgut. (parasympathetic)
ENS regulates peristalsis and glandular secretion
ANS nerve fibres follow blood vessels
