Spicy foods imitate the membrane of your mouth, which triggers goblet cells to produce a protective layer of a thick substance called mucus. What membrane must be lining the mouth?

The marked structure is the frontalis muscle, which is the anterior portion of the occipitofrontalis muscle located in the forehead region. It is a thin, broad muscle of facial expression that lies within the superficial musculoaponeurotic system of the scalp. The frontalis has no bony attachments to the skull; instead, it is anchored to the galea aponeurotica posteriorly. Its primary function is elevation of the eyebrows and wrinkling of the forehead, especially during expressions of surprise or attention.

A. Orbicularis oculi: The orbicularis oculi is a circular muscle surrounding the orbit of the eye. It is responsible for closing the eyelids during blinking and squinting, protecting the eye from debris and excessive light. It has orbital and palpebral portions that control forceful and gentle eyelid closure. Unlike the frontalis, it is located around the eye rather than the forehead region.

B. Masseter: The masseter is a powerful muscle of mastication located on the lateral aspect of the mandible. It elevates the mandible during chewing and is one of the strongest muscles in the body relative to its size. It originates from the zygomatic arch and inserts on the ramus of the mandible. Compared to the frontalis, it is located in the lower face and is involved in jaw movement, not facial expression of the forehead.

C. Temporalis: The temporalis is a broad, fan-shaped muscle located on the lateral side of the skull in the temporal fossa. It assists in elevating and retracting the mandible during chewing. It inserts onto the coronoid process of the mandible and is a key muscle of mastication. Unlike the frontalis, it is deeper, lateral, and involved in jaw movement rather than forehead expression.

D. Frontalis: The frontalis is the frontal belly of the occipitofrontalis muscle, located in the forehead region. It elevates the eyebrows and wrinkles the skin of the forehead, contributing to facial expressions such as surprise and curiosity. It is innervated by the facial nerve (CN VII) and has no direct bony attachment, instead connecting via the epicranial aponeurosis. Since the marked area is in the anterior forehead region, it corresponds to the frontalis muscle.

The spinal cord is a major component of the central nervous system that extends from the medulla oblongata down through the vertebral canal. In adults, the spinal cord typically ends at the level of L1–L2 vertebrae, forming a tapering structure known as the conus medullaris. Below this point, spinal nerve roots continue to descend within the vertebral canal before exiting at their respective intervertebral foramina. This collection of descending nerve roots is known as the cauda equina, named for its resemblance to a horse’s tail.

A. Cord of connective tissue that anchors spinal cord to the coccyx: This describes the filum terminale, not the cauda equina. The filum terminale is a fibrous extension of pia mater that anchors the spinal cord to the coccyx, providing longitudinal stability. It does not contain functional nerve roots. This structure is connective tissue rather than a bundle of nerves.

B. The inferior tip of the spinal cord: the inferior end of the spinal cord is called the conus medullaris. It represents the tapering terminal portion of the spinal cord itself, typically ending at L1–L2 in adults. The cauda equina lies inferior to this structure and consists of nerve roots extending beyond it. This option confuses two distinct anatomical structures.

C. Outermost protective layer covering the brain and spinal cord: This describes the dura mater, which is one of the three meninges. The dura mater is the tough outer protective membrane surrounding the central nervous system. It has no role in forming nerve root bundles. Therefore, it is unrelated to the cauda equina.

D. Bundle of nervous tissue that extends beyond tip of spinal cord: the cauda equina consists of a collection of lumbar, sacral, and coccygeal nerve roots that descend below the conus medullaris. These nerve roots travel within the lumbar cistern of the subarachnoid space before exiting the spinal canal. This arrangement allows lower limb and pelvic organ innervation. Its appearance resembles a horse’s tail, which is the origin of its name.