Anatomy of the Cranium (Head) & Face

Overview of the Lab and Structures Covered

  • Discussion about lab experiences with cadavers focusing on unknown structures in the anterior and posterior neck.

  • Mention of the facial and cranial muscles and the intracranial region.

Objectives of the Session

  • Total Objectives: Approximately 10-11 goals for today's session.

    • Description of main objectives including:

    • Listing locations, innervation, and actions of facial expression muscles.

Facial Expression Muscles (Mimetic Muscles)

  • Definition: Mimetic muscles (facial muscles) are involved in facial expressions.

  • Quantity: More than 20 muscles categorized as right/left or midline muscles.

  • Major Muscles Discussed:

    • Frontalis Muscle:

    • Old Name: Frontalis muscle.

    • Current Name: Frontal belly of the occipitofrontalis.

    • Epicranial Aponeurosis:

    • Definition: A flat, wide part of a tendon, similar to an intermediate tendon found in digastric muscles.

  • Obicularis Oculi Muscle:

    • Parts: Composed of two parts but generally referred to as one muscle.

  • Obicularis Oris Muscle:

    • Function: Acts like a sphincter muscle around the mouth.

  • Additional Notable Muscles:

    • Zygomatic Minor and Zygomatic Major Muscles:

    • Risorius Muscle:

    • Variation not always present, related to smiling.

    • Depressor Angularis Oris Muscle:

    • Depressor Labii Inferioris Muscle:

    • Mentalis Muscle:

    • Nasalis Muscle:

    • Considered as one muscle despite having two parts.

    • Levator Labii Superioris Muscle:

    • Corrugator Muscle (located between eyes):

Innervation of Facial Muscles

  • Cranial Nerve Involvement:

    • Facial Nerve (CN VII): Innervates all mimetic muscles (motor function).

    • Trigeminal Nerve (CN V): Innervates the skin on the face (sensory function).

  • Differences in Innervation:

    • Facial muscles (motor - CN VII) vs. skin of face (sensory - CN V).

Platysma Muscle

  • Classification:

    • Considered a superficial muscle rather than mimetic muscle but still innervated by CN VII.

  • Muscle Action:

    • Related to movement and functions of facial expression and neck region.

Additional Facial Muscles and Concepts

  • Muscle Around the Ear:

    • No specific names given but mentioned that some people can move their ears due to ear muscles innervated by CN VII.

  • Mastoid Foramen:

    • Facial nerve exits the skull through the stylo-mastoid foramen, making a curve to innervate facial muscles.

Detailed Course of the Facial Nerve

  • Branches of the Facial Nerve:

    • Five major branches: Temporal, Zygomatic, Buccal, Mandibular, and Cervical branches.

    • Posterior Auricular Nerve:

    • Innervates muscles around the ears.

    • Digastric and Stylohyoid Branches:

    • Innervate the posterior belly of the digastric muscle and stylohyoid muscle, part of the suprahyoid muscle complex.

Buccinator Muscle

  • Definition:

    • A deep mimetic muscle important for various facial functions, often associated with the action of a trumpeter.

  • Innervation:

    • Innervated by the facial nerve (CN VII).

  • Modiolus:

    • Junction point for fibers of many facial muscles around the corners of the mouth.

Parotid Gland and Duct

  • Parotid Duct Course:

    • Originates from the parotid gland, goes anteriorly, runs along the masseter muscle, and pierces the buccinator muscle to enter the oral cavity near the upper second molar.

Clinical Concepts

  • Facial Nerve Paralysis:

    • Conditions leading to facial nerve paralysis: typically leads to unilateral facial paralysis if peripheral, whereas central lesions may present differently.

  • Fry's Syndrome:

    • Resulting from incorrect nerve regeneration after surgery, causing sweating in the temporal region when chewing.

Sensory Innervation of the Face

  • Cranial Nerve V (Trigeminal Nerve):

    • Divided into three branches: V1 (ophthalmic), V2 (maxillary), and V3 (mandibular).

  • V1, V2, V3 have specific zones of sensory distribution over the face.

Innervation Details of Facial Structures

  • Parasympathetic Innervation:

    • Lesser petrosal nerve (from CN IX) providing parasympathetic innervation to the parotid gland in conjunction with the auriculotemporal nerve.

Dural Venous Sinuses and Related Structures

  • Dural Venous Sinuses:

    • Explanation of what they are, their location between the dural layers, and their role in draining venous blood.

  • Cranial Meninges:

    • Discussion on layers and significance of dura mater (for blood supply).

Distinction Between Epidural and Subdural Hematomas

  • Subdural Hematoma:

    • Can spread widely across the same side due to less attachment to dura at midline.

  • Epidural Hematoma:

    • Limited spread due to strong adhesion to the dura at the sutures of the skull, does not cross suture lines.

Summary of Cranial Base Structures

  • Discussion of cranial nerves passing through various foramina and their functions, emphasizing their roles in sensory and motor innervation of the face and structures in proximity to the skull base.

Infections and Their Spread in Cranial Cavity

  • Potential Pathways for Infections:

    • Superior ophthalmic vein and emissary veins are critical in spreading infections from facial regions to the cranial cavity, potentially leading to serious conditions like cavernous sinus thrombosis.