General somatic afferent : lecture notes

 General somatic afferent 

General somatic afferent

General somatic afferent fibers convey impulses for exteroreceptors of the skin (cutaneous sensation of pain, temperature, touch, vibration, or pressure) & from proprioreceptors localized in the muscles, joints, ligaments, or in the periosteum of bones via spinal nerves and some cranial nerves.

Nerves contain general somatic afferent fibres

1. All the spinal nerves, except occasionally the first cervical, and conduct impulses of pain, touch and temperature from the surface of the body through the dorsal roots to the spinal cord and impulses of muscle sense, tendon sense and joint sense from the deeper structures

2. Trigeminal nerve:

Ophthalmic nerve:   general somatic afferents fibre of this nerve supply  to the upper face, skull, and eye:

·         Face: Upper eyelid and associated conjunctiva. Eyebrow, forehead, scalp all the way to the lambdoid suture.

·          

·         Skull: Roof of orbit, frontal, ethmoid, and possibly sphenoid sinuses.

·         Eye: The eye itself (all the intraocular structures such as cornea) and the lacrimal gland and sac.

 

·         Maxillary nerve : general somatic afferents fibres of this nerve supply to the mid-face and skull:

·         Face: Lower eyelid and associated conjunctiva. Cheek, upper lip.

·         Skull: Orbital floor, maxillary sinus, upper teeth, nasal cavity, and palate, cheekbone.

 

 Mandibular nerve : The sensory fibres associated with the mandibular branch of CN V provide innervation to:

·         The facial skin in the lower third of the face, including the chin and lower lip

·         Inferior row of teeth and gingiva

·         The anterior two thirds of the tongue

3. Facial  nerve : The facial nerve carries axons of type GSA, general somatic afferent, to skin of the posterior ear. 

4. Glossopharyngeal nerve: the glossopharyngeal nerve transmits general sensory information from inside of the tympanic membrane, skin of the external ear, upper portion of the pharynx and general sensation from the posterior one-third of the tongue.

5. Vagus nerve GSA axons carry pain, temperature, and touch sensations from the posterior cranial fossa, posterior ear, external auditory meatus, pharynx, and posterior, and the external surface of the tympanic membrane

General somatic afferent (sensory) nuclei

General somatic afferent (sensory) nuclei related with spinal nerve

• Marginal zone (MZ, posterior marginalis) – located at the tip of the dorsal horn, and is important for relaying pain and temperature sensation to the brain.
• Substantia gelatinosa (SG) – located at the top of the dorsal horn, the SG is important for relaying pain, temperature and light touch sensation to the brain.
• Nucleus proprius (NP) – located in the ‘neck’ of the dorsal horn, the NP relays mechanical and temperature sensation to the brain.

General somatic afferent (sensory) nuclei related with trigeminal, facial, glossopharyngeal & vagus nerve

 

·         The main or principal sensory nucleus of the trigeminal nerve: This nucleus lies in the upper part of the pons, in the lateral part of the reticular formation. It lies lateral to the motor nucleus of the trigeminal. The superior sensory nucleus is mainly concerned in mediation of proprioceptive impulses, touch and pressure.

·         The spinal nucleus of the trigeminal nerve: The spinal nucleus is another sensory cranial nerve nucleus which extends from the main nucleus (superior sensory nucleus) in the pons down into the medulla, &  into the upper two segments of the spinal cord. The lower end of the spinal nucleus is continuous with the substantia gelatinosa of the spinal cord. The spinal nucleus receives general somatic sensations carried by the facial, glossopharyngeal and vagus nerves. Functions of the spinal nucleus includes mediation of pain and thermal sensibility. The spinal nucleus is divisible (cranio-caudally) into three sub-nuclei, the oralis, interpolaris, and caudalis.

·         The mesencephalic nucleus of the trigeminal nerve: This is also called the mesencephalic nucleus of the trigeminal nerve. It extends cranially from the upper end of the main sensory nucleus in the pons into the midbrain. In the midbrain, the mesencephalic nucleus lies in the central grey matter lateral to the aqueduct. Functionally, this nucleus appears to be similar to sensory ganglia of the cranial nerves, and to the spinal ganglia, rather than to afferent nuclei. The processes (dendrites) of the neurons of this nucleus are believed to carry proprioceptive impulses from muscles of mastication, and possibly also from muscles of the eyeballs, face, tongue and teeth. The mesencephalic nucleus is the centre for jaw jerk.

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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.

Goosecoid gene

 Goosecoid gene 

GSC (Goosecoid Homeobox) gene is a Protein Coding gene.

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The GSC gene defines neural-crest cell-fate specification and contributes to dorsal - ventral patterning

The homeobox gene goosecoid is one of the first genes expressed in the organizer region of vertebrates and specifies future dorsal regions along the anterior/posterior axis of the embryo. this gene is expressed in embryos of all ages and localization on one side of the embryoblast In embryos collected at day 13 of pregnancy gsc expression was localised anterior to the primitive streak.

In embryos collected at day 13 of pregnancy gsc expression was localised anterior to the primitive streak.

Ectopic expression of gsc mRNA in ventral blastomeres as well as overexpression of gsc in dorsal blastomeres leads to cell movement toward the anterior of the embryo. Diseases associated with GSC include Short Stature, Auditory Canal Atresia, Mandibular Hypoplasia, And Skeletal Abnormalities and Maturity-Onset Diabetes Of The Young, Due to its role as a transcription factor in cell migration during embryonic development, GSC has been looked into as a potential role-player in cancer development and metastasis, since embryonic development and cancer development share similar characteristics. 

Major categories of EMP stimuli and markers involved in EMP. The dynamics of the epithelial – mesenchymal spectrum can be induced by five major stimulii (hypoxia, immuno-modulators, mechanical stress, altered ECM, and chemotherapeutics), which involve changes in various functional and morphological states and enlisted markers across the spectrum of epithelial–mesenchymal plasticity. ECM, extracellular matrix.

Interesting facts about Alzheimer's disease

 Interesting facts about Alzheimer's disease

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1.Education can lower your risk

rusted Sourcethe more education you have, the lower your risk of getting AD. You have lower odds of getting AD if you keep your brain active in old age by doing activities such as:

• taking classes
• learning languages
• playing musical instruments

Doing group activities or interacting with others also may lower your risk.

2.Your heart and your head are closely related

Heart disease can raise your risk of getting AD. Other conditions that cause heart disease are also linked to a higher risk of getting AD, including:

• high blood pressure
• high cholesterol
• diabetes
• poor diet
• non-active lifestyle

Heart disease may also be a cause of vascular dementia, which results from narrowed blood vessels in the brain. This leads to a decrease in oxygen to brain tissues.

3.Women have a higher risk

Nearly twice as many women have AD as men. AD also worsens more quickly in women than it does in men.

Brain shrinkage tends to be more severe in women with AD than in men with the disease. Researchers suggest that brain changes in women with AD may be due to other causes.

4. Linked with a loss of sense of smell

A person with AD may lose their sense of smell, suggest that changes in the sense of smell may be an early sign of AD.

It’s important to note that changes in your ability to smell may also be due to other causes such as:

• Parkinson’s disease
• brain injury
• sinus infection                                                                                                       5.AD first described

  AD is named after German doctor Alois Alzheimer. He described the symptoms of a patient known as “Auguste D.” in 1906. The symptoms included:

  • memory loss
  • abnormal behavior
  • shrinkage of the patient’s brain

  
  Psychiatrist Emil Kraepelin, Dr. Alzheimer’s colleague, coined the name “Alzheimer’s disease” in a 1910 medical book.

• 6.Proteins identified in AD

  The main markers of Alzheimer’s disease in the brain are high amounts of two proteins: beta-amyloid and tau.

  Beta-amyloid was discovered in 1984. Two years later, tangles of tau were discovered in people with AD.

  Both proteins may cause brain cell damage. Researchers don’t know yet if high levels of beta-amyloid and tau cause AD or if they’re symptoms.

Landmarks of skull porion

 

Porion

The porion is the point on the human skull located at the upper margin of each ear canal (external auditory meatus, external acoustic meatus). It lies on the superior margin of the tragus. It is a cephalometric landmark with significance in biological anthropology and in clinical applications such as oral and maxillofacial surgery.

The porion is one of the three anatomical points used to determine the Frankfurt plane. The Frankfurt plane (also called the auriculo-orbital plane) was established at the World Congress on Anthropology in Frankfurt, Germany in 1884, and decreed as the anatomical position of the human skull for comparative craniometric measurements. It was decided that a plane passing through the inferior margin of the left orbit (the point called the left orbitale) and the upper margin of each ear canal or external auditory meatus, a point called the porion, was most nearly parallel to the surface of the earth at the position the head is normally carried in the living subject.

In normal subjects, both orbitales and both porions lie in a single plane. However, due to pathology, this is not always the case. The formal definition specifies only the three points listed above, sufficient to describe a plane in three-dimensional space.

The Mastoid Index (a craniometric measurement) is the distance from the porion to the asterion.

The determination of the Frankfort plane differs between skeletal and soft tissues, soft tissue using the tragus as the landmark in place of the porion