Autonomic Nervous Systen

Question 1

What is the structure of the autonomic nervous system?

Answer 1

• ANS contains motor neurones in the spinal cord that innervate peipheral structures
• The ANS uses two groups of motor neurones to stimulate the effector inseas of one

Question 2

What is the two-neuroen efferent pathway ?

Answer 2

• pre-ganglionic neurone in CNS
• Post-ganglionic neurone in PNS
• Both the parasympathetic and sympathetic have these

Question 3

Where are the pre-ganglionic neurones located?

Answer 3

• SYMPATHETIC
• Pre-ganglionic cell bodies are in the lateral horn of the spial grey matter from T10-L2 (tHROCOLUMBAR)
• Short synapse with postganglionic neurones near spinal cord
• Parasympathetic
• Preganglionic neurones are in grey matter of brainste, or lateral horn of the spinal cord frey matter from S2-4 (cranioscacral)
• Long synapse wuth postganglionic neurones at or near organ.

Question 4

Where are the post-ganglionic neurones located?

Answer 4

• Sympathetic :
• Cell bodies or other named ganglia are in the sympathetic chain
• Long, synapse on the target organ

Parasympathetic :

• cell bodies are in distinct ganglia near or on their final target organ
• Short, synapse on target organ

Question 5

Where do pre-ganglionic sympathetic neurones lies?

Answer 5

• In the lateral horn of the spinal grey matter (T1-L2)
• They leave the spinal cord via the ventral nerve roots and join the spinal nerve
• They synapse with post-ganglionic sympathetic neurones who have their cell bodies in one of two locations :
  1.) Sympathetic chain of ganglia
  2.) Other ganglia ( Coeliac, superior, mesenteric or inferior mesenteric
  To reach other of these locations they must firstly enter the sympathetic chain- via the rami communicantes (communicating branch)

Question 6

How do the pre-ganglionic fibres pass into the sympathetic chain?

Answer 6

• Via the white ramus commuicans (white because of myelinated fibres)
• Fibres concerened with head and thorax terminate with post-synaptic cell bodies in the sympathetic chain. These return to spinal nerve via grey ramys communicans (grey = unmyelinated_
• Pre-ganglionic fibres concerned with pelvic and abdominal viscera pass uninterrupted through chain to the plexuses- to the corresponding post- ganglionic neurones

Question 7

Where do the pre-ganglionic parasympathetic neurones lie?

Answer 7

• In the brainstem, midbrain, pons, medulla and sacral region of the spinal cord,
• Brainstem parasympathetic pre-ganglionic neurones are located in a number of nuclei

Question 8

What are some disorders of the autonomic nervous system?

Answer 8

**
Postural hypotension** (prolonged reduction in blood pressure on standing)
Symptoms: Dizziness/light headed/feeling faint
Due to: Disruption to sympathetic nerves innervating blood vessels
Causes: e.g. diabetes & syphilis — damage sympathetic fibres.
Why? Normally, sympathetic nerves cause blood vessels to contract. This increases bp & so increases perfusion
to upper body (inc brain) - relieves symptoms. Disruption to sympathetic nerves may prevent vasoconstriction, leading to postural hypotension.
**
Horner’s syndrome: **
Symptoms: Drooping of upper eyelid (ptosis), constricted pupil (miosis), loss of sweating on one side of face
(anhidrosis).
Due to: Interruption of sympathetic nerve supply to the eye
Causes: Lesions of hypothalamus, brainstem, cervical spinal cord (interrupts innervation to pre-ganglionic
fibres), lung tumour (interrupts pre-ganglionic)
Why? Interrupts sympathetic fibres innervating the muscles of the eyelid, unopposed parasympathetic drive
leads to pupil constriction, decreased sympathetic drive to sweat glands.
Why ?