DAANCE Basic Sciences and Anatomy 3 — Questions and Answers
Question 1: Which neurotransmitter is the primary inhibitory neurotransmitter in the central nervous system?
- Glutamate
- Acetylcholine
- Gamma-aminobutyric acid (GABA) (Correct answer)
- Norepinephrine
Correct answer: Gamma-aminobutyric acid (GABA)
GABA is the primary inhibitory neurotransmitter in the CNS. Most sedatives and anxiolytics (benzodiazepines, barbiturates, propofol) act by potentiating GABA-A receptor activity.
GABA acts on ionotropic (GABA-A) and metabotropic (GABA-B) receptors. GABA-A receptor activation opens chloride channels, hyperpolarizing the neuron. Benzodiazepines increase the frequency of chloride channel opening; barbiturates increase duration. Understanding GABA provides the pharmacological basis for most sedative drugs used in dentistry.
Question 2: The blood-brain barrier (BBB) affects drug distribution because:
- Ionized drugs cross it more readily than unionized drugs
- Lipid-soluble drugs cross it more easily than water-soluble drugs (Correct answer)
- Large-molecular-weight drugs cross it faster than small ones
- Drug entry into the CNS is not affected by protein binding
Correct answer: Lipid-soluble drugs cross it more easily than water-soluble drugs
The BBB consists of tight junctions between cerebral capillary endothelial cells. Lipid-soluble, unionized, protein-unbound drugs traverse it most readily.
Lipid solubility is the dominant factor in BBB penetration. Fentanyl high lipophilicity gives it a rapid CNS onset. Morphine is less lipid-soluble, resulting in slower brain penetration. Protein binding also limits BBB crossing since only free (unbound) drug diffuses into the CNS.
Question 3: The autonomic nervous system parasympathetic response is best described as:
- Fight-or-flight, increasing heart rate and dilating bronchi
- Rest-and-digest, slowing heart rate and increasing gastrointestinal activity (Correct answer)
- Exclusively responsible for pain transmission
- Vasoconstrictive and reduces salivary secretion
Correct answer: Rest-and-digest, slowing heart rate and increasing gastrointestinal activity
Parasympathetic activation (via acetylcholine/muscarinic receptors) decreases heart rate, increases GI motility, promotes salivation, and conserves energy.
Vagal (CN X) stimulation is a key parasympathetic pathway, slowing the SA node and reducing cardiac output. During dental procedures, pain or stress can trigger vasovagal responses (bradycardia plus hypotension). Atropine (muscarinic antagonist) is the emergency reversal agent for symptomatic bradycardia.
Question 4: The inferior alveolar nerve (IAN) block targets the nerve before it enters the:
- Infraorbital foramen
- Mandibular foramen (Correct answer)
- Mental foramen
- Incisive canal
Correct answer: Mandibular foramen
The IAN block is deposited near the mandibular foramen on the medial surface of the ramus, where the nerve enters the mandibular canal.
The mandibular foramen is located on the medial ramus approximately 1 cm above the mandibular occlusal plane in adults. Accurate deposition of anesthetic here anesthetizes the IAN and lingual nerve, providing profound anesthesia to mandibular teeth, lower lip, and tongue on the injected side.
Question 5: During rapid IV administration of lidocaine, which central nervous system toxic effect appears first?
- Seizures
- Unconsciousness
- Circumoral numbness and tinnitus (early warning signs) (Correct answer)
- Respiratory arrest
Correct answer: Circumoral numbness and tinnitus (early warning signs)
Local anesthetic toxicity follows a progression: early CNS excitatory signs (tinnitus, metallic taste, circumoral numbness) precede seizures, then CNS depression and cardiovascular collapse.
LAST (Local Anesthetic Systemic Toxicity) follows a predictable sequence: initial CNS excitation (circumoral paresthesia, tinnitus, anxiety, dizziness) to generalized seizures, then CNS depression, respiratory arrest, and cardiovascular collapse. Recognition of early signs and cessation of injection are critical.
Question 6: Which anatomical landmark is used to identify the correct needle insertion point for a posterior superior alveolar (PSA) nerve block?
- Mental foramen on the lateral mandible
- Pterygopalatine fossa via the greater palatine foramen
- Mucobuccal fold above the maxillary second molar (Correct answer)
- Retromolar pad on the posterior mandible
Correct answer: Mucobuccal fold above the maxillary second molar
The PSA block needle is inserted at 45 degree angles in the mucobuccal fold distal to the maxillary second molar to anesthetize the PSA nerve.
The PSA nerve exits the maxillary tuberosity via several posterior superior alveolar foramina. The injection is made in the height of the mucobuccal fold at a 45 degree angle superiorly, posteriorly, and medially. It anesthetizes the maxillary second and third molars and the mesial-buccal root of the first molar in most patients.
DAANCE Basic Sciences and Anatomy 3
Which neurotransmitter is the primary inhibitory neurotransmitter in the central nervous system?