Notes on Hypoglossal Nerve

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HYPOGLOSSAL NERVE

Function:

Motor.

1. General somatic efferent: Motory to intrinsic tongue muscles except palatoglossus. (This is supplied by the vagus).

Nucleus:

Sited between dorsal nucleus of the vagus and median plane of the 4th ventricle - i.e. hypoglossal triangle in the floor of the 4th ventricle.

Exits:

By two bundles from the groove between the olive and pyramid (10 - 15 rootlets), pass through the hypoglossal canal.

Branches:

1. Communicating from:

a. Inferior ganglion of the vagus.

b. Superior cervical ganglion of the sympathetic.

c. From 1st and 2nd cervical nerves (loop).

2. Meningeal (C1 fibres) - diploë of the occipital bone, and posterior cranial fossa dura.

3. Thyro-hyoid and genio-hyoid: C1 hitch-hiking fibres.

4. Motory (muscular): Styloglossus, hyoglossus, genioglossus and intrinsic muscles of the tongue. Genio hyoid via C1.

5. Superior root (C1 fibres) of ansa cervicalis (descendens hypoglossi): Descending down over carotid sheath, forms the ansa cervicalis with a branch from C2 + 3 (inferior root of ansa or descending cervical nerve). From the loop the following muscular branches are given off to:

a. Sterno-hyoid.

b. Sterno-thyroid.

c. Omo-hyoid (both bellies).

Summary:

The loop or ansa cervicalis is formed by two contributing roots.

a. Superior root of ansa cervicalis (descendens hypoglossi): C1 fibres.

b. Inferior root of ansa cervicalis (descendens cervicalis): C2 + C3 fibres.

Lesion of Hypoglossal Nerve:

Lesion of left or right hypoglossal nerve causes ipsilateral deviation of the tongue to the affected side - "licking your wounds."

Further Topics on Cranial Nerves:

1. Introduction to Cranial Nerves
2. Notes on Olfactory Nerve CN 1
3. Notes on Optic Nerve CN 2
4. Notes on Oculomotor Nerve CN 3
5. Notes on Trochlear Nerve CN 4
6. Notes on Trigeminal Nerve CN 5
7. Notes on Abducens Nerve CN 6
8. Notes on Facial Nerve CN 7
9. Notes on Vestibulocochlear Nerve CN 8
10. Notes on Glossopharyngeal Nerve CN 9
11. Notes on Vagus Nerve CN 10
12. Notes on Accessory Nerve CN 11
13. Notes on Hypoglossal Nerve CN 12
14. Summary of Cranial Nerve Nuclei
15. Summary of Cranial Nerve Functions

Additional Reading:

Basic Neurology

1. Peripheral Nervous System
2. Central Nervous System
3. The Ventricular System
4. The Spinal Cord
5. The Brain Stem
6. The Cerebellum
7. Visual Pathways
8. Diencephalon
9. Basal Ganglia
10. Cerebral Cortex
11. Sleep Disorders
12. Autonomic Nervous System
13. Cranial Nerves and Parasympathetic Ganglia
14. Cells of the Nervous System
15. Cerebrospinal fluid
16. Additional short notes on Cerebrum
17. Functions and Diseases of Cerebrum
18. Subcortical Grey Matter
19. Notes on The Spinal Cord
20. Regulation of Heart Rate by Autonomic Nervous System
21. Action Potentials, Axon Conduction, and Neuromuscular Junction
22. Types of Seizures
23. What is a Cough Reflex?
24. Notes on Congenital Prosopagnosia
25. Findings in Parkinson's Disease
26. Types of Heat Strokes
27. Types of Strokes
28. What is Benign Intracranial Hypertension?
29. What is Cauda Equina Syndrome?
30. Cranial Nerve Locations in Brain Stem

Neurology Videos

1. Video of Neurology Examination in a Clinical Setting

Medical Images

Useful Medical Images & Diagrams (link opens in a new window)

Related Topics

1. Nervous System Disorders
2. Histology of Nervous Tissue
3. Cranial Nerve Reflexes
4. Motor System Examination

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