NEET MDS Synopsis
The Occipital Bone
Anatomy-> This bone forms much of the base and posterior aspect of the skull.
-> It has a large opening called the foramen magnum, through which the cranial cavity communicates with the vertebral canal.
-> It is also where the spinal cord becomes continuous with the medulla (oblongata) of the brain stem.
-> The occipital bone is saucer-shaped and can be divided into four parts: a squamous part (squama), a basilar part (basioccipital part), and two lateral parts (condylar parts).
-> These four parts develop separately around the foramen magnum and unite at about the age of 6 years to form one bone.
-> On the inferior surfaces of the lateral parts of the occipital bone are occipital condyles, where the skull articulates with C1 vertebra (the atlas) at the atlanto-occipital joints.
-> The internal aspect of the squamous part of the occipital bone is divided into four fossae: the superior two for the occipital poles of the cerebral hemispheres, and the inferior two, called cerebellar fossae, for the cerebellar hemispheres.
TEMPOROMANDIBULAR JOINT -ARTICULAR SURFACES COVERED BY FIBROUS TISSUE
Dental Anatomy
ARTICULAR SURFACES COVERED BY FIBROUS TISSUE
TMJ is an exception form other synovial joints. Two other joints, the acromio- and sternoclavicular joints are similar to the TMJ. Mandible & clavicle derive from intramembranous ossificiation.
Histologic
Fibrous layer: collagen type I, avascular (self-contained and replicating)
Proliferating zone that formes condylar cartilage
Condylar cartilage is fibrocartilage that does not play role in articulation nor has formal function
Capsule: dense collagenous tissue (includes the articular eminence)
Synovial membrane: lines capsule (does not cover disk except posterior region); contains folds (increase in pathologic conditions) and villi
Two layers: a cellular intima (synovial cells in fiber-free matrix) and a vascular subintima
Synovial cells: A (macrophage-like) syntesize hyaluronate
B (fibroblast-like) add protein in the fluid
Synovial fluid: plasma with mucin and proteins, cells
Liquid environment: lubrication, ?nutrition
Disk: separates the cavity into two comprartments, type I collagen
anterior and posterior portions
anetiorly it divides into two lamellae one towards the capsule, the other towards the condyle
vascular in the preiphery, avascular in the center
Ligaments: nonelastic collagenous structures. One ligament worth mentioning is the lateral or temporomandibular ligament. Also there are the spheno- and stylomandibular with debatable functional role.
Innervations
Ruffini
Posture
Dynamic and static balance
Pacini
Dynamic mechanoreception
Movement accelerator
Golgi
Static mechanoreception
Protection (ligament)
Free
Pain
Protection joint
Clinical Signs and Their Significance
Oral and Maxillofacial SurgeryClinical Signs and Their Significance
Understanding various clinical signs is crucial for diagnosing specific
conditions and injuries. Below are descriptions of several important signs,
including Battle sign, Chvostek’s sign, Guerin’s sign, and Tinel’s sign, along
with their clinical implications.
1. Battle Sign
Description: Battle sign refers to ecchymosis
(bruising) in the mastoid region, typically behind the ear.
Clinical Significance: This sign is indicative of a
posterior basilar skull fracture. The bruising occurs due to the
extravasation of blood from the fracture site, which can be a sign of
significant head trauma. It is important to evaluate for other associated
injuries, such as intracranial hemorrhage.
2. Chvostek’s Sign
Description: Chvostek’s sign is characterized by the
twitching of the facial muscles in response to tapping over the area of the
facial nerve (typically in front of the ear).
Clinical Significance: This sign is often observed in
patients who are hypocalcemic (have low calcium levels). The twitching
indicates increased neuromuscular excitability due to low calcium levels,
which can lead to tetany and other complications. It is commonly assessed in
conditions such as hypoparathyroidism.
3. Guerin’s Sign
Description: Guerin’s sign is the presence of
ecchymosis along the posterior soft palate bilaterally.
Clinical Significance: This sign is indicative of
pterygoid plate disjunction or fracture. It suggests significant trauma to
the maxillofacial region, often associated with fractures of the skull base
or facial skeleton. The presence of bruising in this area can help in
diagnosing the extent of facial injuries.
4. Tinel’s Sign
Description: Tinel’s sign is a provocative test where
light percussion over a nerve elicits a distal tingling sensation.
Clinical Significance: This sign is often interpreted
as a sign of small fiber recovery in regenerating nerve sprouts. It is
commonly used in the assessment of nerve injuries, such as carpal tunnel
syndrome or after nerve repair surgeries. A positive Tinel’s sign indicates
that the nerve is healing and that sensory function may be returning.
Parasympathetic Ganglia Of Head And Neck
Anatomy
Important parasympathetic ganglia in head and neck are :
(i) otic ganglion,
(ii) submandibular ganglion,
(iii) pterygopalatine ganglion
(iv) ciliary ganglion.
Otic Ganglion
Topographically, it is connected to mandibular nerve, while functionally it is related to glossopharyngeal (IX) nerve. Its roots are:-
Sensory root:-By Auriculotemporal nerve.
Sympathetic root:-By sympathetic plexus around middle meningeal artery.
Parasympathetic (secretomotor) root: - This root is by lesser petrosal nerve. Preganglionic fibres begin in inferior salivatory nucleus, pass through glossopharyngeal nerve, then its tympanic branch, tympanic plexus, and the lesser petrosal nerve and relay in otic ganglion.
Postganglionic fibers pass through auriculotemporal nerve and supplies parotid gland.
Motor root :- It is derived from nerve to medial pterygoid which passes unrelayed through ganglion and supplied tensor veli palatini and tensor tympani (Note :- Otic ganglion has a motor root, beside three standard roots of parasympathetic ganglion of head and neck: sensory, sympathetic and parasympathetic).
Submandibular Ganglion
Functionally, submandibular ganglion is connected to facial nerve, while topographically it is connected to lingual branch ofmandibular nerve. Its roots are :-
Sensory root: - It is from lingual nerve.
Sympathetic root: - It is from sympathetic plexus around facial artery, which contains postganglionic fibers from superior cervical ganglion of sympathetic trunk.
Secretomotor (parasympathetic) root: - Preganglionic fibers arise from superior salivatory nucleus pass through facial nerve then its chorda tympani branch which joins lingual nerve and relay in submandibular ganglion.
Postganglionic fibers supply :-Directly submandibulargland.
Through lingual nerveSublingual salivary gland and glands in oral cavity.
Pterygopalatine Ganglion (Sphenopalatine Ganglion)
It is the largest parasympathetic ganglion, suspended by two roots to maxillary nerve. Functionally, it is related to facial nerve. It is called ganglion of "hay fever". Its roots are:-
Sensory root:-It is from maxillary nerve.
Sympathetic root:-It is sympathetic plexus around internal carotid artery through deep petrosal nerve.
Secretomotor (parasympathetic) root:-Preganglionic fibers arise from lacrimatory nucleus, pass through facial nerve, then to its greater petrosal branch. Greater petrosal nerve unites with deep petrosal nerve (sympathetic fibers) to form nerve to pterygoid canal (Vidian nerve). Fibers reach to pterygopalatine ganglion; only fibers of greater petrosal nerve relay in the ganglion, not of deep petrosal nerve.
Postganglionic fibers supply lacrimal gland and palatal glands, and pharyngeal glands.
Branches of the pterygopalatine ganglion are :-
For lacrimal gland: - Postganglionic fibers pass through zygomatic nerve (branch of maxillary nerve), its zygomaticotemporal division which gives communicating branch to lacrimal nerve for supplying lacrimal gland.
Nasopalatine nerve:-For nasal and palatal glands.
Nasal branches: - For mucous membrane and glands oflateral wall of nasal cavity.
Palatine branches: - One greater palatine and 2-3 lesser palatine branches for glands of soft palate and hard palate.
Orbital branches: - For orbital periosteum.
Pharyngeal branches:-For glands of pharynx.
Ciliary Ganglion
Topographically, ciliary ganglion is related to nasociliary nerve (a branch of ophthalmic division of trigeminal nerve), but functionally it is related to oculomotor nerve. Its roots are:-
Sensory root:-It is from nasociliary nerve.
Sympathetic root: - It is from plexus around ophthalmic artery.
Parasympathetic root: - It is from a branch to inferior oblique muscle. These fibers arise from Edinger – Westphalnucleus, join oculomotor nerve and then to its branch to inferior oblique to relay in ciliary ganglion.
Postganglionic fibers pass through short ciliary nerves to supply sphincter pupillae and ciliary muscles.
PERTUSSIS
General Pathology
PERTUSSIS (Whooping Cough)
An acute, highly communicable bacterial disease caused by Bordetella pertussis and characterized by a paroxysmal or spasmodic cough that usually ends in a prolonged, high-pitched, crowing inspiration (the whoop).
Transmission is by aspiration of B. pertussis
Symptoms and Signs
The incubation period averages 7 to 14 days (maximum, 3 wk). B. pertussis invades the mucosa of the nasopharynx, trachea, bronchi, and bronchioles, increasing the secretion of mucus, which is initially thin and later viscid and tenacious. The uncomplicated disease lasts about 6 to 10 wk and consists of three stages: catarrhal, paroxysmal, and convalescent.
Anti Anginal Drugs
Pharmacology
Anti-Anginal Drugs
Nitrates
- It include nitroglycerin (glyceryl trinitrate) or pentaerythritol tetranitrate, isosorbide dinitrate and isosorbide mononitrate.
- Liberation of NO
- Cause venodilation, decrease VR and ventricular filling pressure and wall tension; therefore decrease O2 consumption
- Problem with Tolerance – fix with intermittent administration (patch 12hrs on 12hrs off)
- Often offered sublingually or transdermally
Beta-Blockers
- It include either cardioselectives such as acebutolol or metoprolol, or non-cardioselectives such as oxprenolol or sotalol.
- Reduce myocardial O2 demand by decreasing HR and contractility; blocking B1
- Contraindicated in variant angina, good for chronic prophylaxis of stable angina
Calcium Channel Blockers
-It include Class I agents (e.g., verapamil), Class II agents (e.g., amlodipine, nifedipine), or the Class III agent diltiazem.
- All existing CCBs block L-Type channels
- 1st Generation; 3 Classes: - Phenylalkalamines (ex: Verapamil) , - Benzothiazepinones (ex: Diltiazem) , - Dihydropyridines (ex: nifedipime)
- Less depressant activity on heart than the other
- Associated with reflex-tachycardia from baroreceptors
- Problem in pts with angina
Nifedipine is more a potent vasodilator and more effective in angina. It is in the class of dihydropyridines and does not affect refrectory period on SA node conduction.
Lysosomal (lipid) storage diseases
General Pathology
Lysosomal (lipid) storage diseases
- Genetic transmission: autosomal recessive.
- This group of diseases is characterized by a deficiency of a particular lysosomal enzyme. This results in an accumulation of the metabolite, which would have otherwise been degraded by the presence of normal levels of this specific enzyme.
Diseases include:
Gaucher’s disease
(1) Deficient enzyme: glucocerebrosidase.
(2) Metabolite that accumulates: glucocerebroside.
(3) Important cells affected: macrophages.
Tay-Sachs disease
(1) Deficient enzyme: hexosaminidase A.
(2) Metabolite that accumulates: GM2 ganglioside.
(3) Important cells affected: neurons.
(4) Symptoms include motor and mental deterioration, blindness, and dementia.
(5) Common in the Ashkenazi Jews.
Niemann-Pick disease
(1) Deficient enzyme: sphingomyelinase.
(2) Metabolite that accumulates: sphingomyelin.
(3) Important cells affected: neurons.
Thyroid goitres
General Pathology
Thyroid goitres
A goitre is any enlargement of part or whole of the thyroid gland. There are two types:
1. Toxic goitre, i.e. goitre associated with thyrotoxicosis.
2. Non-toxic goitre, i.e. goitre associated with normal or reduced levels of thyroid hormones.
Toxic goitre
Graves disease
This is the most common cause of toxic goitre
Toxic multinodular goitre
This results from the development of hyperthyroidism in a multinodular goitre
Non-toxic goitres
Diffuse non-toxic goitre (simple goitre)
This diffuse enlargement of the thyroid gland is classified into:
Endemic goitre—due to iodine deficiency. Endemic goiter occurs in geographic areas (typically mountainous)) where the soil, water, and food supply contain little iodine. The term endemic is used when goiters are present in more than 10% of the population in a given region. With increasing availability of dietary iodine supplementation, the frequency and severity of endemic goiter have declined significantly. Sporadic goiter is less common than endemic goiter. The condition is more common in females than in males, with a peak incidence in puberty or young adult life, when there is an
increased physiologic demand for T4.
Sporadic goitre—caused by goitrogenic agents (substances that induce goitre formation) or familial in origin. Examples of goitrogenic agents include certain cabbage species, because of their thiourea content, and specific drugs or chemicals, such as iodide, paraminosalicylic acid and drugs used in the treatment of thyrotoxicosis. Familial cases show inherited autosomal recessive traits, which interfere with hormone synthesis via various enzyme pathways (these are dyshormonogenic goitres).
Hereditary enzymatic defects interfering with thyroid hormone synthesis (dyshormonogenetic goiter).
Physiological goitre—enlargement of the thyroid gland in females during puberty or pregnancy; the reason is unclear.
Multinodular goitre
This is the most common cause of thyroid enlargement and is seen particularly in the elderly (nearly all simple goitres eventually become multinodular). The exact aetiology is uncertain but it may represent an uneven responsiveness of various parts of the thyroid to fluctuating TSH levels over a period of many years.
Morphological features are:
• Irregular hyperplastic enlargement of the entire thyroid gland due to the development of wellcircumscribed nodules of varying size.
• Larger nodules filled with brown, gelatinous colloid; consequently, it is often termed multinodular colloid goitres.
Clinical features
- A large neck mass, goiters may also cause airway obstruction, dysphagia, and compression of large vessels in the neck and upper thorax.
- A hyperfunctioning ("toxic") nodule may develop within a long-standing goiter, resulting in hyperthyroidism. This condition is not accompanied by the infiltrative ophthalmopathy and dermopathy.
- Less commonly, there may be hypothyroidism.