Basic Anatomy of the Somatic Nervous System Flashcards
What is the axon hillock?
The initial initiation segment of an axon where membrane potentials are summated.
What is the effector organ of the somatic nervous system?
Skeletal muscle.
Is muscle tone controlled by the somatic or autonomic nervous system?
Somatic.
What is the zone that forms the boundary between the CNS and PNS?
The Redlich-Orbersteiner zone.
What is another term for the Redlich-Orbersteiner zone?
The root entry zone.
What change can be seen in the Redlich-Orbersteiner zone?
Change in type of myelin produced on both sides; oligodendrocytes produce myelin in the CNS whereas Schwann cells produce myelin in the PNS.
Why is the Redlich-Orbersteiner zone the site for most nerve-based neurological syndromes?
The Redlich-Orbersteiner zone is often the place of neuro-vascular compression.
Name some examples of nerve-based neurological syndromes that may occur in the Redlich-Orbersteiner zone.
1 - Trigeminal neuralgia
2 - Vestibular schwanomas
3 - Acoustic neuromas
4 - Facial nerve compression
5 - Vago-glossopharyngeal compression
6 - Cerebello-pontine angle nerve compressions
What is the difference in tumours in the CNS as opposed to the PNS?
In the CNS, malignant tumours exist (as an exclusive feature of glia), whereas in the PNS, all tumours are benign.
What is the morphology of a somatic efferent neurone (motoneurone)?
Multipolar
What is the morphology of most afferent neurones?
Pseudounipolar
Where are the somata of somatic motoneurones located?
- In the ventral horn of the spinal cord
* In cranial nerve motor nuclei of the brain
What gives somatic motoneurones Aα classification?
They innervate extrafusal muscle.
List the subtypes of motor neurones.
How do they differ in terms of myelination?
•Heavily myelinated: –Aα –Aβ •Lightly myelinated: –Aδ
What is a motoneurone?
An efferent that innervates skeletal muscles to:
- Displace the limbs
- Set muscle tone
What is the range of thickness of myelin in axons?
0.5-2.5 um
Name 4 demyelinating diseases.
Demyelinating diseases:
1 - Multiple Sclerosis
2 - Guillain Barre
3 - Diabetes
4 - Polyneuropathies
Other than increasing the velocity of axonal conduction of nerve impulses, what other function is served by the myelin sheath?
If a nerve axon is cut and it dies away, the myelin sheath left behind maintains the tunnel where the old axon ran. This creates a path taken by remyelinating axons
What are the 3 characteristic neuroglia of the PNS? What are their functions?
- Schwann cells:
• 1 axon myelinated per Schwann cell.
• Insulates peripheral nerve axons. - Satellite cells:
•Physical support of neurones in the PNS. - Microglia:
•Immune and inflammatory functions.
What are the membranous envelopes of nerves in the PNS from superficial to deep?
- Epineruium:
•Enseaths the entire nerve.
•Interfasicular bands attach adjacent nerve fascicles. - Perineurium:
•Enseaths a single fascicle (a collection of axons). - Endoneurium:
•Enseaths a single axon.
What are the three classes of muscle?
Skeletal, cardiac and smooth.
Which of the three classes of muscle are striated?
Skeletal and cardiac.
To which area of the muscle is the neuromuscular junction confined to?
The nerve entry point. Also known as the neruovascular hilum.
What are the important features of the nerve entry point?
- It is the geographical centre of all muscles.
- It is the site of entry of a motoneurone into the substance of a muscle.
- It is the site of entry of arterial supply to a muscle.
- It is the site of exit of venous drainage of a muscle.
What are the 4 characteristic neuroglia of the CNS? What are their functions?
- Astrocytes:
•Axon guidance
•Synaptic support
•Control of BBB - Microglial cells:
•Immune and inflammatory function - Ependymal cells:
•Give rise to epithelial tissue that produce CSF. - Oligodendrocytes:
•Many axons myelinated per oligodendrocyte
•Insulates central nerve axons.
