General somatic efferent: summarized lecture notes

 

General somatic efferent

General somatic efferent fibers carry motor impulses to somatic skeletal muscles.

GSE neurons innervate striated muscle of embryonic somite & limb buds origin

Nerves contain GSE functional components:

·         All Spinal nerves,

·         4 pure Motor Cranial nerves

1.      III (oculomotor ),

2.      IV(trochlear nerve ),

3.      VI (abducent nerve ), and

4.      XII (hypoglossal) carry these fibers.

General Somatic Efferent Nuclei

Spinal nerves :  The ventral horns of the spinal cord (lamina IX of Rexed ) contains somatic efferent neurons (motor neurons) arranged into clusters called motor nuclei. There are two groups of nuclei, medial and lateral .

Medial motor nuclei (column) extend the entire length of the spinal cord and contain motor neurons to the axial musculature

The larger lateral motor nuclei (columns)  of cervical and lumbosacral enlargements contain neurons to the musculature of upper and lower extremities. The alpha motor neurons of lateral nuclei are larger than the medial motor nuclei .

Cranial nerves :

1.      Oculomotor nucleus

2.      Trochlear nucleus

3.      Abducent nucleus

4.      Hypoglossal nucleus

Muscles supply by General somatic efferent

Spinal nerves:

Medial motor nuclei (unlabeled) innervate axial musculature and are present at all levels of spinal cord. Lateral motor nuclei (labeled below) innervate limb musculature and are found in cervical and lumbosacral enlargement segments.

In spinal nerve this functional components passes through the ventral roots, carrying motor impulses to skeletal muscle through a neuromuscular junction. As shown below, lateral motor nuclei are somatotopically organized. Proximal muscles are ventral; distal muscles are dorsal. Cranial muscles are lateral; caudal muscles are medial.

Cranial nerves

1.      Oculomotor nucleus: extra ocular muscles except superior oblique and lateral rectus

2.      Trochlear nucleus: superior oblique

3.      Abducent nucleus: lateral rectus muscle

4.      Hypoglossal nucleus: muscles of tongue

 

 

 

 

 

Cranial nerve nuclei : summarized lecture notes

Cranial nerve nuclei

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The cranial nerve nuclei are aggregate of cells (collection of cell bodies). Attached to these cell bodies are fibers called cranial nerves (bundles of axons). These nuclei are either sensory or motor but never both. However, cranial nerves can be sensory, motor or mixed nerves (when they have both sensory and motor functions).

The cranial nerve nuclei are a series of bilateral grey matter motor and sensory nuclei located in the midbrain, pons and medulla that are the collections of afferent and efferent cell bodies for many of the cranial nerves.

Some nuclei are small and contribute to a single cranial nerve, such as some of th motor nuclei.

 Other nuclei, however, are long and span several regions of the brainstem contributing to several cranial nerves.

 Several motor and sensory nuclei form longitudinal columns in the brainstem, leading to some authors describing them as single discontinuous longitudinal nuclear columns rather than the more numerous individual separate nuclei.

Three long discontinuous efferent columns have been described: somatic, brachiomotor and parasympathetic.

Extensive interconnections exist between many of these nuclei, as well as with other brainstem nuclei and white matter tracts such as the medial lemniscus and medial longitudinal fasciculus.

1. oculomotor nucleus: somatic motor nucleus for the oculomotor nerve
2. Edinger-Westphal nucleus: general visceral motor (parasympathetic) nucleus for the oculomotor nerve,
3. trochlear nucleus: somatic motor nucleus for the trochlear nerve
4. motor nucleus of CN V: somatic motor nucleus for the trigeminal nerve
5. ​mesencephalic nucleus of CN V: somatic sensory nucleus for the trigeminal nerve
6. main sensory nucleus of CN V: somatic sensory nucleus for the trigeminal, facial, glossopharyngeal and vagus nerves
7. spinal nucleus of CN V: somatic sensory nucleus for the trigeminal nerve
8. abducent nucleus: somatic motor nucleus for the abducens nerve
9. facial nucleus: special visceral motor (branchial) nucleus for the facial nerve
10. superior salivatory nucleus: general visceral motor (parasympathetic) nucleus for the facial nerve
11. cochlear nuclei: group of two special sensory nuclei for the cochlear branch of the vestibulocochlear nerve
12. vestibular nuclei: group of four special sensory  nuclei for the superior and inferior vestibular branches of the vestibulocochlear nerve
13. inferior salivatory nucleus: general visceral motor (parasympathetic) nucleus for the glossopharyngeal nerve

14.    solitary tract nucleus: special visceral sensory nucleus for the facial, glossopharyngeal and vagus nerves

15.    ambiguus nucleus: special visceral motor (branchial) nucleus for the glossopharyngeal and vagus nerves

16.    dorsal motor nucleus: general visceral motor (parasympathetic) nucleus for the vagus nerve

17.    hypoglossal nucleus: somatic motor nucleus for the hypoglossal nerve

18.     the gracile and cuneate nuclei

the cranial nerve nuclei with motor functions can be grouped according to the following functional components to which their fibers belong:

·         General Somatic Efferents (GSE)

·         Special Visceral Efferents (SVE)

·         General Visceral Efferents (GVE)

Similarly, the cranial nerve sensory nuclei are grouped according to the information they receive, which constitutes the functional components to which their attached nerves belong. These functional components are:

·         General Somatic Afferents (GSA)

·         Special Somatic Afferents (SSA)

·         General Visceral Afferents (GVA)

·         Special Visceral Afferents (SVA)

In the brainstem, there are about 18 cranial nerve nuclei comprising of 10 motor cranial nerve nuclei and 8 sensory cranial nerve nuclei. 

 

General somatic efferent nuclei	Oculomotor, trochlear, abducens, hypoglossal
Special visceral efferent nuclei	Motor nucleus of trigeminal nerve, nucleus of facial nerve, nucleus ambiguus
General visceral efferent nuclei	Accessory oculomotor nucleus (Edinger-Westphal nucleus), salivatory nuclei, dorsal vagal nucleus
General and special visceral afferent nuclei	Nucleus of the solitary tract, commissural nucleus of the vagus, gustatory nucleus
General somatic afferent nuclei	Principal sensory nucleus of the trigeminal nerve, spinal nucleus of the trigeminal nerve, mesencephalic nucleus of the trigeminal nerve
Special somatic afferent nuclei	Cochlear and vestibular nuclei

 

Alar plate : the part of mantle layer of neural tube

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Alar plate

 Definition :

The alar plates (or alar lamina) is a neural structure in the embryonic nervous system. Sensory area in the dorsal region of the spinal cord and brain

Development:

they develops from dorsal aspect of mantle layer of neural tube

Location :  

the dorsal region of the spinal cord and brain

Functional components deal by alar plate :

 general somatic afferent (collect touch, pain, pressure, vibration temperature  sensation from body wall ) and general visceral afferent(collect  pain, pressure  sensation from viscera )  .

Structures derived from alar plate :

1. dorsal gray matter of the spinal cord,

2. the sensory nuclei of cranial nerves V, VII, VIII, IX, and X.

3. The inferior olivary nucleus, mesencephalic nucleus of V, and main sensory nucleus of V are also developed from this plate.

4.  the rhombic lip of the alar plate develops the cerebellum, which is considered to be a big exception since alar plate gives rise to sensory derivatives only.