Lecture 20 - Organisation of the CNS, PNS & ANS Flashcards
This lecture was mostly visual - visit lecture notes to gain better understanding.
Aite say nuttin bro.
Describe the basic layout of the nervous system.
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.
How many SC segments are there and what are the 5 different sections?
- 31
- Cervical, Thoracic, Lumbar, Sacrum, Coccyx
Describe the structure of a spinal cord segment
- Grey matter in H shape centrally, white matter on periphery.
- Posterior horn = dorsal horn - sensory afferent fibres run through here
- Anterior 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).
- The cell body of sensory neurones can be seen in the dorsal root ganglion
- Spinal canal directly in the middle (small hole)
NB: Look at lecture and be able to label a picture.
The ANS is a motor system, how is it different to the somatic NS?
Where is a synapse between two autonomic neurones found?
Which branch of the ANS has longer pre-ganglionic fibres?
- It has a chain of two neurones between the CNS and targets organs (preganglionic & postganglionic)
- The synapse is found in the autonomic ganglion (hence why we have pre and postganglionic fibres).
- Parasympathetic, sympathetic has shorter preganglionic fibres but longer post-ganglionic.
Where are autonomic preganglionic neurone cell bodies of the sympathetic and parasympathetic branches found?
Sympathetic = Lateral horn in T1-L2 segments Parasympathetic = S2-S4 cord segments and brainstem
What are the 4 routes by which sympathetic fibres arising in the T1-L2 cord segments supply the skin + through/along what do the postganglionics get to their target
1) Synapse at level of entry - to supply dermatomes at T1-L2 level. Postganglionics get to their targets through T1-L2 spinal nerves.
2) Ascend the chain - to supply head and neck. Postganglionics get to their targets along walls of blood vessels.
3) Descend the chain - to supply lower limbs - postganglionics get to their targets through spinal nerves below L3 levels.
4) Transverse the chain and synapse with a pre-aortic ganglion to supply abdominal organs. Postganglionics get to their targets along blood vessels.
Where do parasympathetic preganglionic neurones typically synapse?
What is the major source of parasympathetic preganglionic input to the thoracic and abdominal viscera?
- To ganglia that sit close to their target organs (often in the wall of their target).
- The vagus nerve
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?
The head have 4 specialised parasympathetic ganglia
1) The ciliary ganglion - receives parasympathetic preganglionics from the oculomotor nerve and distributes parasympathetic postganglionics 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.
Describe the sequence of events for a motor efferent of the sympathetic nervous system leaving the ventral horn to communicating with effector tissues.
1) Preganglionic fibre leaves SC via ventral horn and into the spinal nerve.
2) Joins with the sympathetic nerve ganglion via the white ramus communicans and synapses (as preganglionic fibre is myelinated)
3) The unmyelinated post-ganglionic fibre then leaves via the white ramus communicans, loops around and leaves to supply effector tissues.
