Anatomy of the ANS

Question 1

How would you define the ANS

Answer 1

Maintains homeostasis of internal environment
Involuntary control of the viscera and glands
Influences respiration, digestion, excretion, thermoregulation & cardiovascular activity
3 divisions: sympathetic, parasympathetic & enteric

Question 2

Ultimately, what is the function of the SNS

Answer 2

Fight or flight

o Is involved in mass responses and mobilises energy in the fight and flight response.

Question 3

Ultimately, what is the PSNS

Answer 3

Rest and digest

o Is involved in LOCAL responses and conservation of energy at rest

Question 4

How many neurones between the CNS and viscera in autonomic supply

Answer 4

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

Question 5

Which CNS structure provides high level regulation of autonomic activity?

Answer 5

Part of the limbic system (emotional centre)

Responds to changes from internal and external environments

Question 6

Describe the role of the hypothalamus

Answer 6

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).

Question 7

Describe the role of the NTS too

Answer 7

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.

Question 8

Describe the neural output from the hypothalamus

Answer 8

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

Question 9

Describe thoracolumbar outflow

Answer 9

Preganglionic fibres of the sympathetic system emerge from thoracic (T1-12) and upper lumbar (L1-2/3) spinal cord segments as spinal nerves

Question 10

Describe craniosacral outflow

Answer 10

Preganglionic fibres of the parasympathetic system emerge as cranial nerves and sacral spinal nerves (S2-S4)

Question 11

Which cranial nerves are associated with the parasympathetic nervous system?

Answer 11

III Oculomotor (ciliary)
VIII Facial (pterygopalatine, submandibular)
IX Glossopharyngeal (otic)
X Vagus

Question 12

Which structures does the sympathetic nervous system innervate?

Answer 12

Eye
Glands and mucous membranes within the head and neck
Thoracic, abdominal and pelvic viscera (internal organs)
Blood vessels, sweat glands and erector pili

Question 13

Describe the synapses of the SNS

Answer 13

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

Question 14

What is the exception to this synapse in the SNS

Answer 14

Adrenal gland, ACH nicotinic, except releases A/NA to bloodstream

Question 15

Describe the synapses of the PNS

Answer 15

ACh nicotinic to effector

ACh muscarinic within effector (ganglia inside the effector)

Question 16

Describe the locations of the exceptions of the synapses in the SNS

Answer 16

Splanchnic nerves: coeliac, superior mesenteric, inferior mesenteric ganglia (prevertebral)
NO synapse for adrenal (suprarenal) gland innervation

Question 17

What does the SNS consist of

Answer 17

The SNS consists of:
o TWO sympathetic trunks
o Nerve plexuses.
o Subsidiary plexuses.

Question 18

Where do the neurones of the PSNS synapse

Answer 18

Found close to or even in the organ/ viscera they innervate

Ganglia (head and neck): ciliary, pterygopalatine, submandibular, otic

Question 19

Why does the anatomy of the symp. & parasymp. NS differ?

Answer 19

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

Question 20

Describe the lateral horn of the spinal cord

Answer 20

Cell bodies of preganglionic neurons
T1 - L2/3 (sympathetic)
S2 – S4 (parasympathetic)
Axons pass through ventral root to spinal nerve

Question 21

Describe the rami communicantes

Answer 21

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

Question 22

Describe the ciliary ganglion

Answer 22

Parasympathetic – ganglion lies close to target organ!
Cranial nerve III Oculomotor
Constricts pupils and contracts ciliary eye muscles (accommodation)

Question 23

In the SNS, what can the nerve in the ganglion do

Answer 23

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

Question 24

Where are the ganglia of the SNS distributed to

Answer 24

§ 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.

Question 25

Describe the vagus nerve

Answer 25

§ Enters the neck and thorax via the carotid sheath.

§ Branches to the lungs, heart, oesophagus, stomach and intestines – internal viscera

Question 26

Describe the glossopharyngeal nerve

Answer 26

§ Associated ganglion is the Otic ganglion.
o Postganglionic fibres to the parotid gland.
o This is another salivary gland.

Question 27

Describe the fascial nerve

Answer 27

§ 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.

Question 28

Describe the oculomotor nerve

Answer 28

§ The associated ganglion is the ciliary ganglion.

o Postganglionic fibres to the sphincter pupillae and the ciliary muscles in the eye.