Anatomy of the ANS Flashcards
How would you define the ANS
Maintains homeostasis of internal environment
Involuntary control of the viscera and glands
Influences respiration, digestion, excretion, thermoregulation & cardiovascular activity
3 divisions: sympathetic, parasympathetic & enteric
Ultimately, what is the function of the SNS
Fight or flight
o Is involved in mass responses and mobilises energy in the fight and flight response.
Ultimately, what is the PSNS
Rest and digest
o Is involved in LOCAL responses and conservation of energy at rest
How many neurones between the CNS and viscera in autonomic supply
There are a sequence of 2 neurons between the CNS and the innervated structure- pre-ganglionic neuron and postganglionic fibre
HOWEVER, there is an exception…
Preganglionic fibres from SNS continue to the adrenal medulla- responsible for glandular secretion of catecholamines (which are functionally similar to the postganglionic SNS neurones
Which CNS structure provides high level regulation of autonomic activity?
Part of the limbic system (emotional centre)
Responds to changes from internal and external environments
Describe the role of the hypothalamus
Control of the two arms of the ANS Is achieved by the hypothalamus which takes input from (image in above box):
o Homeostatic changes – i.e. body temperature changes.
o Higher brain centres – i.e. memories that remind you how to react to a certain scenario (such as a frightening experience).
Describe the role of the NTS too
Nucleus tractus solitarus (located in the medulla)- plays a role in autonomic control and communicates with the hypothalamus
the nucleus of the solitary tract integrates sensory information from the internal organs and helps to coordinate output to the autonomic brainstem nuclei.
Describe the neural output from the hypothalamus
Neural output runs from the periventricular zone to the brain-stem and spinal cord nuclei that contain preganglionic neurons of the sympathetic and parasympathetic divisions
Describe thoracolumbar outflow
Preganglionic fibres of the sympathetic system emerge from thoracic (T1-12) and upper lumbar (L1-2/3) spinal cord segments as spinal nerves
Describe craniosacral outflow
Preganglionic fibres of the parasympathetic system emerge as cranial nerves and sacral spinal nerves (S2-S4)
Which cranial nerves are associated with the parasympathetic nervous system?
III Oculomotor (ciliary) VIII Facial (pterygopalatine, submandibular) IX Glossopharyngeal (otic) X Vagus
Which structures does the sympathetic nervous system innervate?
Eye
Glands and mucous membranes within the head and neck
Thoracic, abdominal and pelvic viscera (internal organs)
Blood vessels, sweat glands and erector pili
Describe the synapses of the SNS
Presympathetic neurone within the CNS
Pre-ganglionic neurone synapses in the vertebral ganglia in an ACh nicotinic
Postganglionic neurone synapses onto the effector organ using NA/ACh
What is the exception to this synapse in the SNS
Adrenal gland, ACH nicotinic, except releases A/NA to bloodstream
Describe the synapses of the PNS
ACh nicotinic to effector
ACh muscarinic within effector (ganglia inside the effector)
Describe the locations of the exceptions of the synapses in the SNS
Splanchnic nerves: coeliac, superior mesenteric, inferior mesenteric ganglia (prevertebral)
NO synapse for adrenal (suprarenal) gland innervation
What does the SNS consist of
The SNS consists of:
o TWO sympathetic trunks
o Nerve plexuses.
o Subsidiary plexuses.
Where do the neurones of the PSNS synapse
Found close to or even in the organ/ viscera they innervate
Ganglia (head and neck): ciliary, pterygopalatine, submandibular, otic
Why does the anatomy of the symp. & parasymp. NS differ?
Sympathetic: mass response, mobilises body energy for increased activity- each preganglionic neuron can influence many different neurons in different ganglia by collaterals, coordinating the activation of ganglia at different spinal cord levels.
Parasympathetic: discrete/ localised, conserves body energy- no widespread systematic effects from Ach released by pre-synaptic neurone
Describe the lateral horn of the spinal cord
Cell bodies of preganglionic neurons
T1 - L2/3 (sympathetic)
S2 – S4 (parasympathetic)
Axons pass through ventral root to spinal nerve
Describe the rami communicantes
Connect spinal nerves to sympathetic chain
White ramus communicans– preganglionic axon of sympathetic neuron
Grey ramus communicans– sympathetic postganglionic axons to blood vessels, sweat glands and erector pili muscles
Describe the ciliary ganglion
Parasympathetic – ganglion lies close to target organ!
Cranial nerve III Oculomotor
Constricts pupils and contracts ciliary eye muscles (accommodation)
In the SNS, what can the nerve in the ganglion do
o Synapses with the ganglion to send a nerve out on that spinal cord level via grey rami.
o Go up or down in the ganglia to synapse elsewhere.
o Go straight through ganglia and synapse to a subsidiary ganglion
Where are the ganglia of the SNS distributed to
§ The sympathetic trunk is located between the base of the skull to the coccyx – the ganglia are distributed as so: o 3 – cervical region (however the fibres do not emerge at the cervical region, they just have ganglia). o 11/12 – thoracic region. o 4/5 – lumbar region. o 4/5 – pelvis. § The fact that the ganglia are all connected allows a mass response to occur such as general vasoconstriction. § The plexuses in the SNS consist of: o Cervical: § Plexus around pharynx. § Cardiac plexus. § Thyroid plexus. § Pulmonary plexus. o Thoracic: § Plexus around thoracic aorta. § Splanchnic nerves. § There are three cervical ganglia that do not reside directly adjacent to the spinal cord in the cervical region.
Describe the vagus nerve
§ Enters the neck and thorax via the carotid sheath.
§ Branches to the lungs, heart, oesophagus, stomach and intestines – internal viscera
Describe the glossopharyngeal nerve
§ Associated ganglion is the Otic ganglion.
o Postganglionic fibres to the parotid gland.
o This is another salivary gland.
Describe the fascial nerve
§ TWO associated ganglions:
o Submandibular Ganglion:
§ Postganglionic fibres to the submandibular and sublingual salivary glands.
o Pterygopalatine Ganglion:
§ Postganglionic fibres to the paranasal sinuses and lacrimal glands.
§ Involved in crying.
Describe the oculomotor nerve
§ The associated ganglion is the ciliary ganglion.
o Postganglionic fibres to the sphincter pupillae and the ciliary muscles in the eye.
