NEET MDS Synopsis
Neurophysiology
Pharmacology
Neurophysiology
Nerve fibers exhibit wide range of sensitivity to nerve blockade-in order of increasing resistance to block are the sensations of pain, cold, warmth, touch, pressure, proprioception and motor function
Nerve Fibers:
Types
Size
Speed
Occurrence
A (α)
20 µm
80 - 120
Myelinated (Primarily for muscular activity).
β
8 - 15 µm
Myelinated (Touch and pressure)
γ
4 - 8 µm
Myelinated (Muscle spindle tone)
δ
3 - 4 µm
10-15
Myelinated (Pain and temperature sensation)
B
4 µm
10-15
Myelinated (Preganglionic autonomic)
C
1-2 µm
1 - 2
Unmyelinated (Pain and temperature sensation)
Myelinated = faster conducting
Unmyelinated = slower conducting
- Small non-myelinated fibers (C- pain fibers) and smaller myelinated pre-ganglionic B fibers are more readily blocked than are larger myelinated fibers responsible for muscle activity and touch [A-alpha and A-beta].
- Clinically, a person would notice complete lack of sensation to a pinprick, while at the same time still be able to move their fingers.
Types of Fixed Orthodontic Appliances
OrthodonticsTypes of Fixed Orthodontic Appliances
Braces:
Traditional Metal Braces: Composed of metal
brackets bonded to the teeth, connected by archwires. They are the most
common type of fixed appliance.
Ceramic Braces: Similar to metal braces but made of
tooth-colored or clear materials, making them less visible.
Lingual Braces: Brackets are placed on the inner
surface of the teeth, making them invisible from the outside.
Self-Ligating Braces:
These braces use a specialized clip mechanism to hold the archwire
in place, eliminating the need for elastic or metal ligatures. They can
reduce friction and may allow for faster tooth movement.
Space Maintainers:
Fixed appliances used to hold space for permanent teeth when primary
teeth are lost prematurely. They are typically bonded to adjacent teeth.
Temporary Anchorage Devices (TADs):
Small screws or plates that are temporarily placed in the bone to
provide additional anchorage for tooth movement. They help in achieving
specific movements without unwanted tooth movement.
Palatal Expanders:
Fixed appliances used to widen the upper jaw (maxilla) by applying
pressure to the molars. They are often used in growing patients to
correct crossbites or narrow arches.
Components of Fixed Orthodontic Appliances
Brackets: Small metal or ceramic attachments bonded to
the teeth. They hold the archwire in place and guide tooth movement.
Archwires: Thin metal wires that connect the brackets
and apply pressure to the teeth. They come in various materials and sizes,
and their shape can be adjusted to achieve desired movements.
Ligatures: Small elastic or metal ties that hold the
archwire to the brackets. In self-ligating braces, ligatures are not needed.
Bands: Metal rings that are cemented to the molars to
provide anchorage for the appliance. They may have attachments for brackets
or other components.
Hooks and Accessories: Additional components that can
be attached to brackets or bands to facilitate the use of elastics or other
auxiliary devices.
Indications for Use
Correction of Malocclusions: Fixed appliances are
commonly used to treat various types of malocclusions, including crowding,
spacing, overbites, underbites, and crossbites.
Tooth Movement: They are effective for moving teeth
into desired positions, including tipping, bodily movement, and rotation.
Retention: Fixed retainers may be used after active
treatment to maintain the position of teeth.
Jaw Relationship Modification: Fixed appliances can
help in correcting skeletal discrepancies and improving the relationship
between the upper and lower jaws.
Advantages of Fixed Orthodontic Appliances
Continuous Force Application: Fixed appliances provide
a constant force on the teeth, allowing for more predictable and efficient
tooth movement.
Effective for Complex Cases: They are suitable for
treating a wide range of orthodontic issues, including severe malocclusions
that may not be effectively treated with removable appliances.
Patient Compliance: Since they are fixed, there is no
reliance on patient compliance for wearing the appliance, which can lead to
more consistent treatment outcomes.
Variety of Options: Patients can choose from various
types of braces (metal, ceramic, lingual) based on their aesthetic
preferences.
Disadvantages of Fixed Orthodontic Appliances
Oral Hygiene Challenges: Fixed appliances can make it
more difficult to maintain oral hygiene, increasing the risk of plaque
accumulation, cavities, and gum disease.
Discomfort: Patients may experience discomfort or
soreness after adjustments, especially in the initial stages of treatment.
Dietary Restrictions: Certain foods (hard, sticky, or
chewy) may need to be avoided to prevent damage to the appliances.
Duration of Treatment: Treatment with fixed appliances
can take several months to years, depending on the complexity of the case.
Paralleling Technique
PedodonticsParalleling Technique in Dental Radiography
Overview of the Paralleling Technique
The paralleling technique is a method used in dental radiography to obtain
accurate and high-quality images of teeth. This technique ensures that the film
and the long axis of the tooth are parallel, which is essential for minimizing
distortion and maximizing image clarity.
Principles of the Paralleling Technique
Parallel Alignment:
The fundamental principle of the paralleling technique is to
maintain parallelism between the film (or sensor) and the long axis of
the tooth in all dimensions. This alignment is crucial for accurate
imaging.
Film Placement:
To achieve parallelism, the film packet is positioned farther away
from the object, particularly in the maxillary region. This distance can
lead to image magnification, which is an undesirable effect.
Use of a Longer Cone:
To counteract the magnification caused by increased film distance, a
longer cone (position-indicating device or PID) is employed. The longer
cone helps:
Reduce Magnification: By increasing the
distance from the source of radiation to the film, the image size is
minimized.
Enhance Image Sharpness: A longer cone
decreases the penumbra (the blurred edge of the image), resulting in
sharper images.
True Parallelism:
Striving for true parallelism enhances image accuracy, allowing for
better diagnostic quality.
Film Holder and Beam-Aligning Devices
Film Holder:
A film holder is necessary when using the paralleling technique, as
it helps maintain the correct position of the film relative to the
tooth.
Some film holders are equipped with beam-aligning devices that
assist in ensuring parallelism and reducing partial exposure of the
film, thereby eliminating unwanted cone cuts.
Considerations for Pediatric Patients
Size Adjustment:
For smaller children, the film holder may need to be reduced in size
to accommodate both the film and the child’s mouth comfortably.
Operator Error Reduction:
Proper use of film holders and beam-aligning devices can help
minimize operator error and reduce the patient's exposure to radiation.
Challenges with Film Placement:
Due to the shallowness of a child's palate and floor of the mouth,
film placement can be somewhat compromised. However, with careful
technique, satisfactory films can still be obtained.
Morphine
Pharmacology
Morphine
Morphine is effective orally, but is much less effective than when given parenterally due to first-pass metabolism in the liver. Metabolism involves glucuronide formation, the product of which is excreted in the urine.
1. Central Nervous System Effects
• Morphine has mixed depressant and stimulatory actions on the CNS.
• Analgesia:
• Dysphoria – Euphoria
- morphine directly stimulates the chemoreceptor trigger zone, but later depresses the vomiting center in the brain stem. This center is outside the blood/brain barrier.
- opiates appear to relieve anxiety
• Morphine causes the release of histamine and abolishes hunger.
- causes the body to feel warm and the face and nose to itch.
• Pupils are constricted.- due to stimulation of the nuclei of the third cranial nerves.
- tolerance does not develop to this effect.
• Cough reflex is inhibited. - this is not a stereospecific effect.
- dextromethorphan will suppress cough but will not produce analgesia.
• Respiration is depressed
- due to a direct effect on the brain stem respiratory center.
- death from narcotic overdose is nearly always due to respiratory arrest.
- the mechanism of respiratory depression involves:
• a reduction in the responsiveness of the brain stem respiratory centers to an increase in pCO2.
• depression of brain stem centers that regulate respiratory rhythm.
- hypoxic stimulation of respiration is less affected and O2 administration can produce apnea.
2. Cardiovascular Effects
• Postural orthostatic hypotension.- due primarily to peripheral vasodilation, which may be due in part to histamine release.
• Cerebral circulation is also indirectly influenced by increased pCO2, which leads to cerebral vasodilation and increased cerebrospinal fluid pressure.
• In congestive heart failure, morphine decreases the left ventricular workload and myocardial oxygen demand.
3. Endocrine Effects
• Increases prolactin secretion
• Increases vasopressin (ADH) secretion
• Decreases pituitary gonadotropin (LH & FSH) secretion.
• Decreases stress induced ACTH secretion.
4. Gastrointestinal Tract Effects
• Constipation (tolerance does not develop to this effect).
• Several of these agents can be used in the treatment of diarrhea.
There is an increase in smooth muscle tone and a decrease in propulsive contractions.
Adverse Reactions
Generally direct extensions of their pharmacological actions.
1. respiratory depression, apnea
2. nausea and vomiting
3. dizziness, orthostatic hypotension, edema
4. mental clouding, drowsiness
5. constipation, ileus
6. biliary spasm (colic)
7. dry mouth
8. urine retention, urinary hesitancy
9. hypersensitivity reactions (contact dermatitis, urticaria)
Precautions
1. respiratory depression, particularly in the newborn
3. orthostatic hypotension
4. histamine release (asthma, shock)
5. drug interactions (other CNS depressants)
6. tolerance:
- analgesia, euphoria, nausea and vomiting, respiratory depression
7. physical dependence (psychological & physiological)
IONIZATION OF WATER, WEAK ACIDS AND WEAK BASES
Biochemistry
IONIZATION OF WATER, WEAK ACIDS AND WEAK BASES
The ionization of water can be described by an equilibrium constant. When weak acids or weak bases are dissolved in water, they can contribute H+ by ionizing (if acids) or consume H+ by being protonated (if bases). These processes are also governed by equilibrium constants
Water molecules have a slight tendency to undergo reversible ionization to yield a hydrogen ion and a hydroxide ion :
H2O = H+ + OH−
The position of equilibrium of any chemical reaction is given by its equilibrium constant. For the general reaction,
A+B = C + D
Heart sounds
Physiology
Heart sounds
Heart sounds are a result of beating heart and resultant blood flow . that could be detected by a stethoscope during auscultation . Auscultation is a part of physical examination that doctors have to practice them perfectly.
Before discussion the origin and nature of the heart sounds we have to distinguish between the heart sounds and hurt murmurs. Heart murmurs are pathological noises that results from abnormal blood flow in the heart or blood vessels.
Physiologically , blood flow has a laminar pattern , which means that blood flows in form of layers , where the central layer is the most rapid . Laminar blood flow could be turned into turbulent one .
Turbulent blood flow is a result of stenotic ( narrowed ) valves or blood vessels , insufficient valves , roughened vessels` wall or endocardium , and many diseases . The turbulent blood flow causes noisy murmurs inside or outside the heart.
Heart sounds ( especially first and second sounds ) are mainly a result of closure of the valves of the heart . While the third sound is a result of vibration of ventricular wall and the leaflets of the opened AV valves after rapid inflow of blood from the atria to ventricles .
Third heart sound is physiologic in children but pathological in adults.
The four heart sound is a result of the atrial systole and vibration of the AV valves , due to blood rush during atrial systole . It is inaudible neither in adults nor in children . It is just detectable by the phonocardiogram .
Characteristic of heart sounds :
1. First heart sound (S1 , lub ) : a soft and low pitch sound, caused by closure of AV valves.Usually has two components ( M1( mitral ) and T1 ( tricuspid ). Normally M1 preceads T1.
2. Second heart sound ( S2 , dub) : sharp and high pitch sound . caused by closure of semilunar valves. It also has two components A2 ( aortic) and P2 ( pulmonary) . A2 preceads P2.
3. Third heart sound (S3) : low pitched sound.
4. Fourth heart sound ( S4) very low pitched sound.
As we notice : the first three sounds are related to ventricular activity , while the fourth heart sound is related to atrial activity.
Closure of valves is not the direct cause for heart sounds , but sharp blocking of blood of backward returning of blood by the closing valve is the direct cause.
Lymphangitis
General Pathology
Lymphangitis
is the acute inflammation due to bacterial infections spread into the lymphatics most common are group A β-hemolytic streptococci.
lymphatics are dilated and filled with an exudate of neutrophils and monocytes.
red, painful subcutaneous streaks (the inflamed lymphatics), with painful enlargement of the draining lymph nodes (acute lymphadenitis).
subsequent passage into the venous circulation can result in bacteremia or sepsis.
The Thyroid
Physiology
The thyroid gland is a double-lobed structure located in the neck. Embedded in its rear surface are the four parathyroid glands.
The Thyroid Gland
The thyroid gland synthesizes and secretes:
thyroxine (T4) and
calcitonin
T4 and T3
Thyroxine (T4 ) is a derivative of the amino acid tyrosine with four atoms of iodine. In the liver, one atom of iodine is removed from T4 converting it into triiodothyronine (T3). T3 is the active hormone. It has many effects on the body. Among the most prominent of these are:
an increase in metabolic rate
an increase in the rate and strength of the heart beat.
The thyroid cells responsible for the synthesis of T4 take up circulating iodine from the blood. This action, as well as the synthesis of the hormones, is stimulated by the binding of TSH to transmembrane receptors at the cell surface.
Diseases of the thyroid
1. hypothyroid diseases; caused by inadequate production of T3
cretinism: hypothyroidism in infancy and childhood leads to stunted growth and intelligence. Can be corrected by giving thyroxine if started early enough.
myxedema: hypothyroidism in adults leads to lowered metabolic rate and vigor. Corrected by giving thyroxine.
goiter: enlargement of the thyroid gland. Can be caused by:
inadequate iodine in the diet with resulting low levels of T4 and T3;
an autoimmune attack against components of the thyroid gland (called Hashimoto's thyroiditis).
2. hyperthyroid diseases; caused by excessive secretion of thyroid hormones
Graves´ disease. Autoantibodies against the TSH receptor bind to the receptor mimicking the effect of TSH binding. Result: excessive production of thyroid hormones. Graves´ disease is an example of an autoimmune disease.
Osteoporosis. High levels of thyroid hormones suppress the production of TSH through the negative-feedback mechanism mentioned above. The resulting low level of TSH causes an increase in the numbers of bone-reabsorbing osteoclasts resulting in osteoporosis.
Calcitonin
Calcitonin is a polypeptide of 32 amino acids. The thyroid cells in which it is synthesized have receptors that bind calcium ions (Ca2+) circulating in the blood. These cells monitor the level of circulating Ca2+. A rise in its level stimulates the cells to release calcitonin.
bone cells respond by removing Ca2+ from the blood and storing it in the bone
kidney cells respond by increasing the excretion of Ca2+
Both types of cells have surface receptors for calcitonin.
Because it promotes the transfer of Ca2+ to bones, calcitonin has been examined as a possible treatment for osteoporosis