Anatomy and Physiology Flashcards

The pterygomandibular space is bounded superiorly by the lateral pterygoid muscle and inferiorly by the medial pterygoid muscle. Which nerve passes through this space and is the primary target of an inferior alveolar nerve block?

Answer: Inferior alveolar nerve

The inferior alveolar nerve (IAN) travels through the pterygomandibular space before entering the mandibular foramen, making it the primary target of the inferior alveolar nerve block. The lingual nerve is also in this space but anterior and medial to the IAN. The buccal nerve exits superiorly and the mylohyoid nerve branches off just before the mandibular foramen.

During local anesthetic administration, a patient experiences a sudden bradycardia followed by vasodilation and syncope despite no intravascular injection. This vasovagal response is primarily mediated by which autonomic pathway?

Answer: Activation of cardiac C-fibers triggering the Bezold-Jarisch reflex

The Bezold-Jarisch reflex (cardiorespiratory reflex) is triggered by activation of ventricular mechanoreceptors (C-fibers) during reduced preload states such as anxiety-induced hypoventilation and orthostasis. This causes paradoxical bradycardia and vasodilation via enhanced vagal efferent activity — the hallmark of vasovagal syncope. Sympathetic activation and catecholamine release would produce the opposite (tachycardia/vasoconstriction).

The mental foramen typically presents with an accessory mental foramen in approximately 10% of patients. Which anatomical variant poses the greatest risk of incomplete anesthesia during a mental/incisive nerve block?

Answer: Bifid inferior alveolar canal with dual foramina at different horizontal positions

A bifid inferior alveolar canal (dual mandibular canals) creates two separate mental foramina at different horizontal positions. A standard single-site mental block may anesthetize only one canal's terminal branch, leaving the other canal's pulpal and soft tissue distributions partially or fully unanesthetized. This is the most clinically significant variant for block failure at the mental foramen.

Which layer of the periosteum is primarily responsible for intramembranous ossification and would be disrupted by a subperiosteal injection technique?

Answer: Cambium (inner) layer — containing osteoprogenitor cells and osteoblasts

The cambium (inner or osteogenic) layer of the periosteum contains osteoprogenitor cells, osteoblasts, and a rich vascular supply — it is the bone-forming layer responsible for intramembranous ossification and periosteal bone apposition. Subperiosteal injections elevate this layer from cortical bone, disrupting osteogenic activity and potentially causing transient postoperative pain or delayed healing.

A patient receiving sedation develops end-tidal CO₂ readings of 55 mmHg alongside SpO₂ of 94%. The MOST likely physiologic explanation for these concurrent findings is:

Answer: Hypoventilation causing CO₂ retention with a compensatory rightward oxyhemoglobin dissociation curve shift

Opioid or sedative-induced hypoventilation reduces alveolar ventilation, causing CO₂ accumulation (hypercapnia, EtCO₂ >45 mmHg). Elevated CO₂ decreases blood pH, shifting the oxyhemoglobin dissociation curve rightward (Bohr effect), reducing hemoglobin's oxygen affinity and lowering SpO₂. This combination — hypercapnia plus mild hypoxemia — is the classic presentation of sedation-induced hypoventilation rather than V/Q mismatch or diffusion hypoxia.

The greater palatine nerve, a branch of the maxillary division (V2) of the trigeminal nerve, descends through the greater palatine canal. At which anatomical landmark does this nerve emerge onto the hard palate, and what adjacent structure must be avoided during a greater palatine block to prevent entering the foramen?

Answer: Opposite the maxillary second or third molar; avoid aspirating the greater palatine artery traversing the foramen

The greater palatine foramen is located on the hard palate opposite (or slightly anterior to) the maxillary second or third molar, approximately 1 cm medial to the palatal gingival margin. The greater palatine artery accompanies the nerve through this foramen; aspiration before injection is mandatory to avoid intravascular delivery into the artery, which communicates with the sphenopalatine artery and could cause systemic local anesthetic toxicity.