Lecture 20 - Organisation of the CNS, PNS & ANS

Question 1

This lecture was mostly visual - visit lecture notes to gain better understanding.

Answer 1

Aite say nuttin bro.

Question 2

Describe the basic layout of the nervous system.

Answer 2

Sensory input is processed either by the CNS (brain & SC) or the PNS, before motor output is produced.

• The PNS can be further divided into the somatic NS (controls voluntary and conscious perception) and autonomic NS (controls involuntary features, e.g.: HR).
• The ANS can be further sub-divided into the sympathetic and parasympathetic branches.
• It is important to note that the ANS also encompasses the enteric NS which governs the GI tract.

Question 3

How many SC segments are there and what are the 5 different sections?

Answer 3

• 31

- Cervical, Thoracic, Lumbar, Sacrum, Coccyx

Question 4

Describe the structure of a spinal cord segment

Answer 4

• Grey matter in H shape centrally, white matter on periphery.
• Superior horn = dorsal horn - sensory afferent fibres run through here
• Inferior horn = ventral horn - motor efferent fibres run out through here
• Dorsal and ventral horns link up to form spinal nerve (mixture of sensory and motor fibres).
• Spinal canal directly in the middle (small hole)

NB: Look at lecture and be able to label a picture.

Question 5

Where is a synapse between two autonomic neurones found?

Which branch of the ANS has longer pre-ganglionic fibres?

Answer 5

• In an autonomic ganglia

- Parasympathetic

Question 6

Where are autonomic preganglionic neurone cell bodies of the sympathetic and parasympathetic branches found?

Answer 6

Sympathetic = Lateral horn in T1-L2 segments
Parasympathetic = S2-S4 cord segments and brainstem

Question 7

What are the 3 routes by which sympathetic fibres arising in the T1-L2 cord segments supply the skin?

Answer 7

1) Synapse at level of entry - to supply dermatomes at T1-L2 level
2) Ascend the chain - to supply head and neck
3) Descend the chain - to supply lower limbs

Question 8

What other route can sympathetic fibres take?

Answer 8

They can transverse the chain and synapse in a pre-aortic ganglion to supply the abdominal viscera. Sensory fibres travel along sympathetic destines for the abdomen and relay pain from viscera back to CNS.

Question 9

Where do parasympathetic preganglionic neurones typically synapse?
What is the major source of parasympathetic preganglionic input to the thoracic and abdominal viscera?

Answer 9

• To ganglia that sit close to their target organs (often in the wall of their target).
• The vagus nerve

Question 10

What are the 4 specialised parasympathetic ganglia of the head?
Where do they receive parasympathetic preganglions from and where do they distribute postganglionic fibres to?

Answer 10

1) The ciliary ganglion - from the oculomotor nerve to the eye
2) The pterygoplatine ganglion - from the facial nerve to the lacrymal gland
3) The submandibular ganglion - from facial nerve to submanidular and sublingual salivary glands
4) The otic ganglion - from the glossopharyngeal nerve to the parotid gland.