NEET MDS Synopsis
Functional Divisions of the Nervous System
PhysiologyFunctional Divisions of the Nervous System:
1) The Voluntary Nervous System - (ie. somatic division) control of willful control of effectors (skeletal muscles) and conscious perception. Mediates voluntary reflexes.
2) The Autonomic Nervous System - control of autonomic effectors - smooth muscles, cardiac muscle, glands. Responsible for "visceral" reflexes
Group A Streptococcus
General Pathology
Group A Streptococcus
- scarlet fever usually begins as a Streptococcal pharyngitis/tonsillitis and then develops an erythematous rash beginning on the trunk and limbs with eventual desquamation.
- rash is due to elaboration of erythrogenic toxin by the organism
- face is usually spared, but, if involved there is a characteristic circumoral pallor and the tongue becomes bright red, thus the term "strawberry tongue".
- post-streptococcal immune complex glomerulonephritis is a possible sequela of scarlet fever.
- Dick test is a skin test that evaluates immunity against scarlet fever; no response indicates immunity (anti-toxin antibodies present); erythema indicates no immunity.
- impetigo due to Streptococcus pyogenes is characterized by honey colored, crusted lesions, while those with a predominantly bullous pattern are primarily due to Staphylococcus aureus.
- cellulitis with lymphangitis ("red streaks") is characteristic of Streptococcus pyogenes.
- hyaluronidase is a spreading factor that favors the spread of infection throughout the subcutaneous tissue unlike Staphylococcus aureus which generates coagulase to keep the pus confined.
- erysipelas refers to a raised, erythematous ("brawny edema"), hot cellulitis, usually on the face that commonly produces septicemia, if left untreated.
Cerebral palsy and Treatment
PedodonticsCerebral palsy (CP) is a neurological disorder resulting from damage to the
brain during its development before, during, or shortly after birth. This
condition is non-progressive, meaning that it does not worsen over time, but it
manifests as a range of neurological problems that can significantly impact a
child's mobility, muscle control, and posture.
Causes:
The primary cause of CP is any factor that leads to decreased oxygen supply
(hypoxia) to the developing brain. This can occur due to various reasons,
including complications during pregnancy, childbirth, or immediately after
birth.
Classification of Cerebral Palsy:
Based on Anatomical Involvement:
Monoplegia: One limb is affected.
Hemiplegia: One side of the body is affected.
Paraplegia: Both legs are affected.
Quadriplegia: All four limbs are affected.
Based on Neuromuscular Involvement:
Spasticity: Characterized by stiff and tight muscles; this
is the most common type, seen in 70% of cases. Affected individuals may
have limited head movement and a limp gait.
Athetosis: Involves involuntary, writhing movements, seen in
15% of cases. Symptoms include excessive head movement and drooling.
Ataxia: Affects balance and coordination, seen in 5% of
cases. Individuals may exhibit a staggering gait and slow tremor-like
movements.
Mixed: A combination of more than one type of cerebral
palsy, seen in about 10% of cases.
1. Spastic Cerebral Palsy (70% of cases)
Characteristics:
Limited Head Movement: Individuals have restrictions in moving their
head due to increased muscle tone.
Involvement of Cerebral Cortex: Indicates that the motor control areas
of the brain (especially those concerning voluntary movement) are affected.
Limping Gait with Circumduction of the Affected Leg: When walking, the
patient often swings the affected leg around instead of lifting it normally,
due to spasticity.
Hypertonicity of Facial Muscles: Increased muscle tension in the facial
region, contributing to a fixed or tense facial expression.
Unilateral or Bilateral Manifestations: Symptoms can occur on one side
of the body (hemiplegia) or affect both sides (diplegia or quadriplegia).
Slow Jaw Movement: Reduced speed in moving the jaw, potentially leading
to functional difficulties.
Hypertonic Orbicularis Oris Muscles: Increased muscle tone around the
mouth, affecting lip closure and movement.
Mouth Breathing (75%): The individual may breathe through their mouth
due to poor control of oral musculature.
Spastic Tongue Thrust: The tongue pushes forward excessively, which can
disrupt swallowing and speech.
Class II Division II Malocclusion (75%): Dental alignment issue often
characterized by a deep overbite and anterior teeth that are retroclined,
sometimes accompanied by a unilateral crossbite.
Speech Involvement: Difficulties with speech articulation due to muscle
coordination problems.
Constricted Mandibular Arch: The lower jaw may have a narrower
configuration, complicating dental alignment and oral function.
2. Athetoid Cerebral Palsy (15% of cases)
Characteristics:
Excessive Head Movement: Involuntary, uncontrolled movements lead to
difficulties maintaining a stable head position.
Involvement of Basal Ganglia: Damage to this area affects muscle tone
and coordination, leading to issues like chorea (involuntary movements).
Bull Neck Appearance: The neck may appear thicker and less defined,
owing to abnormal muscle development or tone.
Lack of Head Balance, Drawn Back: The head may be held in a retracted
position, affecting posture and balance.
Quick Jaw Movement: Involuntary rapid movements can lead to difficulty
with oral control.
Hypotonic Orbicularis Oris Muscles: Reduced muscle tone around the mouth
can lead to drooling and lack of control of oral secretions.
Grimacing and Drooling: Facial expressions may be exaggerated or
inappropriate due to muscle tone issues, and there may be problems with
managing saliva.
Continuous Mouth Breathing: Patients may consistently breathe through
their mouths rather than their noses.
Tissue Biting: Increased risk of self-biting due to lack of muscle
control.
Tongue Protruding: The tongue may frequently stick out, complicating
speech and intake of food.
High and Narrow Palatal Vault: Changes in the oral cavity structures can
lead to functional difficulties.
Class II Division I Malocclusion (90%): Characterized by a deep bite and
anterior open bite.
Speech Involvement: Affected due to uncontrolled muscle movements.
Muscle of Deglutition Involvement: Difficulties with swallowing due to
affected muscles.
Bruxism: Involuntary grinding or clenching of teeth.
Auditory Organs May be Involved: Hearing impairments can coexist.
3. Ataxic Cerebral Palsy (5% of cases)
Characteristics:
Slow Tremor-like Head Movement: Unsteady, gradual movements of the head,
indicative of coordination issues.
Involvement of Cerebellum: The cerebellum, which regulates balance and
motor control, is impacted.
Lack of Balance Leading to Staggering Gait: Individuals may have
difficulty maintaining equilibrium, leading to a wide-based and unsteady
gait.
Hypotonic Orbicularis Oris Muscles: Reduced muscle tone leading to
difficulties with oral closure and control.
Slow Jaw Movement: The jaw may move slower, affecting chewing and
speech.
Speech Involvement: Communication may be affected due to poor
coordination of the speech muscles.
Visual Organ May be Involved (Nystagmus): Involuntary eye movements may
occur, affecting visual stability.
Varied Type of Malocclusion: Dental alignment issues can vary widely in
this population.
4. Mixed:
Mixed cerebral palsy involves a combination of the above types, where the
individual may exhibit spasticity, athetosis, and ataxia to varying degrees.
Dental Considerations for Mixed CP:
- Dental care for patients with mixed CP is highly individualized and depends on
the specific combination and severity of symptoms.
- The dentist must consider the unique challenges that arise from the
combination of muscle tone issues, coordination problems, and potential for
involvement of facial muscles.
- A multidisciplinary approach, including occupational therapy and speech
therapy, may be necessary to address oral function and hygiene.
- The use of sedation or general anesthesia might be considered for extensive
dental treatments due to the difficulty in managing the patient's movements and
ensuring safety during procedures.
Associated Symptoms:
Children with CP may exhibit persistent reflexes such as the asymmetric tonic
neck reflex, which can influence their dental treatment. Other symptoms may
include mental retardation, seizure disorders, speech difficulties, and joint
contractures.
Dental Problems:
Children with cerebral palsy often experience specific dental challenges:
They may have a higher incidence of dental caries (tooth decay) due to
difficulty in maintaining oral hygiene and dietary preferences.
There is a greater likelihood of periodontal disease, often exacerbated
by medications like phenytoin, which can lead to gum overgrowth and dental
issues.
Dental Treatment Considerations:
When managing dental care for children with cerebral palsy, dentists need to
consider:
Patient Stability: The child’s head should be stabilized, and their back
should be elevated to minimize swallowing difficulties.
Physical Restraints: These can help manage uncontrolled movements during
treatment.
Use of Mouth Props and Finger Splints: These tools can assist in
controlling involuntary jaw movements.
Gentle Handling: Avoid abrupt movements to prevent triggering the
startle reflex.
Local Anesthesia (LA): Administered with caution, ensuring stabilization
to prevent sudden movements.
Premedication: Medications may be given to alleviate muscle
hypertonicity, manage anxiety, and reduce involuntary movements.
General Anesthesia (GA): Reserved for cases that are too challenging to
manage with other methods.
Surgical Considerations for the Submandibular and Parotid Glands
Oral and Maxillofacial SurgerySurgical Considerations for the Submandibular and Parotid Glands
When performing surgery on the submandibular and parotid glands, it is
crucial to be aware of the anatomical structures and nerves at risk to minimize
complications. Below is an overview of the key nerves and anatomical landmarks
relevant to these surgical procedures.
Major Nerves at Risk During Submandibular Gland Surgery
Hypoglossal Nerve (CN XII):
This nerve is responsible for motor innervation to the muscles of
the tongue. It lies deep to the submandibular gland and is at risk
during surgical manipulation in this area.
Marginal Mandibular Nerve:
A branch of the facial nerve (CN VII), the marginal mandibular nerve
innervates the muscles of the lower lip and chin. It runs just deep to
the superficial layer of the deep cervical fascia, below the platysma
muscle, making it vulnerable during submandibular gland surgery.
Lingual Nerve:
The lingual nerve provides sensory innervation to the anterior
two-thirds of the tongue and carries parasympathetic fibers to the
submandibular gland via the submandibular ganglion. It is located in
close proximity to the submandibular gland and is at risk during
dissection.
Anatomical Considerations for Parotid Gland Surgery
Parotid Fascia:
The parotid gland is encased in a capsule of parotid fascia, which
provides a protective layer during surgical procedures.
Facial Nerve (CN VII):
The facial nerve is a critical structure to identify during parotid
gland surgery to prevent injury. Key landmarks for locating the facial
nerve include:
Tympanomastoid Suture Line: This is a reliable
landmark for identifying the main trunk of the facial nerve, which
lies just deep and medial to this suture.
Tragal Pointer: The nerve is located about 1 cm
deep and inferior to the tragal pointer, although this landmark is
less reliable.
Posterior Belly of the Digastric Muscle: This
muscle provides a reference for the approximate depth of the facial
nerve.
Peripheral Buccal Branches: While following
these branches can help identify the nerve, this should not be the
standard approach due to the risk of injury.
Submandibular Gland Anatomy
Location:
The submandibular gland is situated in the submandibular triangle of
the neck, which is bordered by the mandible and the digastric muscles.
Mylohyoid Muscle:
The gland wraps around the mylohyoid muscle, which is typically
retracted anteriorly during surgery to provide better exposure of the
gland.
CN XII:
The hypoglossal nerve lies deep to the submandibular gland, making
it important to identify and protect during surgical procedures.
Water Acid Bases & Buffers
Biochemistry
Keq, Kw and pH
As H2O is the medium of biological systems one must consider the role of this molecule in the dissociation of ions from biological molecules. Water is essentially a neutral molecule but will ionize to a small degree. This can be described by a simple equilibrium equation:
H2O <-------> H+ + OH-
This equilibrium can be calculated as for any reaction:
Keq = [H+][OH-]/[H2O]
Since the concentration of H2O is very high (55.5M) relative to that of the [H+] and [OH-], consideration of it is generally removed from the equation by multiplying both sides by 55.5 yielding a new term, Kw:
Kw = [H+][OH-]
This term is referred to as the ion product. In pure water, to which no acids or bases have been added:
Kw = 1 x 10-14 M2
As Kw is constant, if one considers the case of pure water to which no acids or bases have been added:
[H+] = [OH-] = 1 x 10-7 M
This term can be reduced to reflect the hydrogen ion concentration of any solution. This is termed the pH, where:
pH = -log[H+]
MICROBIAL VIRULENCE FACTORS
General Microbiology
MICROBIAL VIRULENCE FACTORS
Microbial virulence factors are gene products required for a microbial pathogen to establish itself in the host. These gene products are located on the bacterial chromosome, or on mobile genetic elements, such as plasmids or transposons.
Primary pathogens express virulence factors that allow them to cause disease in the normal host.
Opportunistic pathogens are environmental organisms or normal flora that lack the means to overcome normal host defense mechanisms. They cause disease only when the normal host defenses are breached or deficient.
Virulence factors can be divided into several categories.
Skin - Propionibacterium acnes, Staphlococcus epidermis , diptheroids; transient colonization by Staphlococcus
aureus
Oral cavity - Viridans Streptococci, Branhamella species, Prevotella melaninogenicus, Actinomyces species, Peptostreptococcus species, other anaerobes
Nasopharynx Oral organisms; transient colonization by S. pneumoniae, Haemophilus species, N. meningitidis
Stomach Rapidly becomes sterile
Small intestine Scant
Colon - Bacteroides species, Clostridium species, Fusobacterium species, E. coli, Proteus species, Pseudomonas aeruginosa, Enterococcus species, other bacteria and yeasts
Vagina - Childbearing years:Lactobacillus species, yeasts, Streptococcus species
Prepuberty / Postmenopause: colonic and skin flora
A. Enzyme production can be of several types depending on the needs of the organism, its requirements for survival, and the local environment.
1. Hyaluronidase breaks down hyaluronic acid to aid in the digestion of tissue.
2. Protease digests proteins to enhance the spread of infections.
3. Coagulase allows coagulation of fibrinogen to clot plasma.
4. Collagenase breaks down collagen (connective tissues).
B. Toxins
1. Exotoxins are heat-labile proteins with specific enzymatic activities produced by many Gram-positive and Gram-negative organisms. Exotoxins are released extracellularly and are often the sole cause of disease.
a. Some toxins have several domains with discrete biological functions that confer maximal toxicity. An example is A-B exotoxin, where the B subunit binds to host tissue cell glycoproteins and the A subunit enzymatically attacks a susceptible target.
b. Many toxins are ADP-ribosylating toxins
2. Endotoxin is the heat-stable lipopolysaccharide moiety found in the outer membrane of Gram-negative organisms. when released by cell lysls, the lipid A portion of lipopolysaccharide can induce septic shock characterized by fever, acidosis, hypotension, complement consumption, and disseminated intravascular coagulation (DIC).
C. Surface components
may protect the organism from immune responses such as phagocytosis or aid in tissue invasion. For example, the polysaccharide capsules of H. influenzae type b and the acidic polysaccharide capsule of Streptococcus pneumoniae interfere with phagocytosis. Other surface proteins, such as adhesins or filamentous appendages (fimbriae, pili), are involved in adherence of invading microorganisms to cells of the host.
Cell, or Plasma, membrane
PhysiologyCell, or Plasma, membrane
Structure - 2 primary building blocks include
protein (about 60% of the membrane) and lipid, or
fat (about 40% of the membrane).
The primary lipid is called phospholipids, and molecules of phospholipid form a 'phospholipid bilayer' (two layers of phospholipid molecules). This bilayer forms because the two 'ends' of phospholipid molecules have very different characteristics: one end is polar (or hydrophilic) and one (the hydrocarbon tails below) is non-polar (or hydrophobic):
Functions include:
supporting and retaining the cytoplasm
being a selective barrier .
transport
communication (via receptors)
Lateral Pharyngeal Space
Oral and Maxillofacial SurgeryLateral Pharyngeal Space
The lateral pharyngeal space is an important anatomical area in the neck that
plays a significant role in various clinical conditions, particularly
infections. Here’s a detailed overview of its anatomy, divisions, clinical
significance, and potential complications.
Anatomy
Shape and Location: The lateral pharyngeal space is a
potential cone-shaped space or cleft.
Base: The base of the cone is located at the base
of the skull.
Apex: The apex extends down to the greater horn of
the hyoid bone.
Divisions: The space is divided into two compartments
by the styloid process:
Anterior Compartment: Located in front of the
styloid process.
Posterior Compartment: Located behind the styloid
process.
Boundaries
Medial Boundary: The lateral wall of the pharynx.
Lateral Boundary: The medial surface of the mandible
and the muscles of the neck.
Superior Boundary: The base of the skull.
Inferior Boundary: The greater horn of the hyoid bone.
Contents
The lateral pharyngeal space contains various important structures,
including:
Muscles: The stylopharyngeus and the superior
pharyngeal constrictor muscles.
Nerves: The glossopharyngeal nerve (CN IX) and the
vagus nerve (CN X) may be present in this space.
Vessels: The internal carotid artery and the internal
jugular vein are closely associated with this space, particularly within the
carotid sheath.
Clinical Significance
Infection Risk: Infection in the lateral pharyngeal
space can be extremely serious due to its proximity to vital structures,
particularly the carotid sheath, which contains the internal carotid artery,
internal jugular vein, and cranial nerves.
Potential Complications:
Spread of Infection: Infections can spread from the
lateral pharyngeal space to other areas, including the mediastinum,
leading to life-threatening conditions such as mediastinitis.
Airway Compromise: Swelling or abscess formation in
this space can lead to airway obstruction, necessitating urgent medical
intervention.
Vascular Complications: The close relationship with
the carotid sheath means that infections can potentially involve the
carotid artery or jugular vein, leading to complications such as
thrombosis or carotid artery rupture.
Diagnosis and Management
Diagnosis:
Clinical examination may reveal signs of infection, such as fever,
neck swelling, and difficulty swallowing.
Imaging studies, such as CT scans, are often used to assess the
extent of infection and involvement of surrounding structures.
Management:
Antibiotics: Broad-spectrum intravenous antibiotics
are typically initiated to manage the infection.
Surgical Intervention: In cases of abscess
formation or significant swelling, surgical drainage may be necessary to
relieve pressure and remove infected material.