Anatomy of the Eye: Lens and Accommodation

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Questions and Answers

Which of the following structures is NOT surrounded by the carotid sheath?

Internal jugular vein

Common carotid artery

Vagus nerve

Subclavian artery (correct)

Which ligament connects the styloid process to the angle of the mandible?

Pterygomandibular ligament

Sphenomandibular ligament

Stylomandibular ligament (correct)

Stylohyoid ligament

What is the purpose of the axillary sheath?

To connect the styloid process to the hyoid bone

To facilitate the passage of the brachial plexus and subclavian artery into the axilla (correct)

To surround the common carotid artery

To support the cervical lymph nodes

Which of the following muscles attaches to the pterygomandibular ligament?

Superior constrictor Signup and view all the answers

Which layers of the deep fascia contribute to the formation of the carotid sheath?

Prevertebral, pretracheal, and investing layers Signup and view all the answers

What is the function of the stylohyoid ligament?

To connect the styloid process to the hyoid bone Signup and view all the answers

What is the main function of the suspensory ligament in the accommodation of the eye?

To keep the elastic lens flattened Signup and view all the answers

What is the effect of the ciliary muscle contraction on the suspensory ligament?

It relaxes the suspensory ligament Signup and view all the answers

What is the purpose of the constriction of the pupil during accommodation?

To reduce spherical aberration Signup and view all the answers

What is the effect of aging on the lens's ability to accommodate?

It becomes denser and less elastic Signup and view all the answers

What is the result of the convergence of the eyes during accommodation?

A single object is seen as one Signup and view all the answers

What is the primary function of the ciliary processes?

To attach the suspensory ligament to the lens Signup and view all the answers

What is the main function of the medial rectus muscles during accommodation?

To converge the eyes Signup and view all the answers

What type of objects can cause severe damage to the eye despite the protection of the bony orbit?

Small objects, such as golf balls Signup and view all the answers

Which nerve supplies the skin of the forehead, upper eyelid, conjunctiva, and the side of the nose?

Ophthalmic nerve Signup and view all the answers

What is the region supplied by the mandibular nerve in the face?

Region developed from the mandibular process of the first pharyngeal arch Signup and view all the answers

Which nerve supplies the skin over the angle of the mandible and the parotid gland?

Great auricular nerve Signup and view all the answers

What is the function of the sensory nerves of the face in addition to supplying the skin?

Supplying proprioceptive fibers to the underlying muscles of facial expression Signup and view all the answers

Which branch of the ophthalmic nerve supplies the skin and conjunctiva of the lateral part of the upper eyelid?

Lacrimal nerve Signup and view all the answers

Which branch of the ophthalmic nerve supplies the skin of the forehead?

Supraorbital nerve Signup and view all the answers

Which nerve division has the least overlap with the other two divisions in the face?

All of the above Signup and view all the answers

What is the origin of the region supplied by the maxillary nerve?

Maxillary process of the first pharyngeal arch Signup and view all the answers

Which muscle has a posterior belly that attaches to the mastoid process of the temporal bone?

Digastric Signup and view all the answers

What is the origin of the sternothyroid muscle?

Manubrium sterni and clavicle Signup and view all the answers

Which muscle is responsible for elevating the hyoid bone?

Stylohyoid Signup and view all the answers

What is the function of the omohyoid muscle?

Depresses the hyoid bone Signup and view all the answers

Which nerve supplies the anterior belly of the digastric muscle?

Nerve to mylohyoid Signup and view all the answers

Which muscle has an intermediate tendon that is held to the hyoid bone by a fascial sling?

Digastric Signup and view all the answers

What is the function of the scalenus anterior muscle?

Lateral flexes and rotates the cervical part of the vertebral column Signup and view all the answers

What is the primary function of the parathyroid hormone in bones?

Stimulating osteoclastic activity to mobilize bone calcium Signup and view all the answers

Which structure is a network of nerve fibres that supplies innervation to some of the structures in the neck and trunk?

Cervical plexus Signup and view all the answers

Which muscle has a origin from the transverse processes of the upper six cervical vertebrae?

Scalenus medius Signup and view all the answers

Where are the inferior parathyroid glands usually located?

Close to the inferior poles of the thyroid gland Signup and view all the answers

What is the insertion of the sternothyroid muscle?

Body of hyoid bone Signup and view all the answers

What is the primary source of arterial supply to the parathyroid glands?

Superior and inferior thyroid arteries Signup and view all the answers

What is the effect of parathyroid hormone on phosphate reabsorption in the kidney?

It strongly diminishes phosphate reabsorption Signup and view all the answers

What is the primary factor controlling the secretion of parathyroid hormone?

Calcium levels in the blood Signup and view all the answers

Which of the following lymph nodes drain the parathyroid glands?

Deep cervical and paratracheal lymph nodes Signup and view all the answers

Study Notes

Structure of the Lens

The lens fibers make up the bulk of the lens
The elastic lens capsule is under tension, causing the lens to constantly try to assume a globular shape
The equatorial region of the lens is attached to the ciliary processes of the ciliary body by the suspensory ligament

Accommodation of the Eye

To accommodate the eye for close objects, the ciliary muscle contracts and pulls the ciliary body forward and inward, relaxing the suspensory ligament
This allows the elastic lens to assume a more globular shape
With advancing age, the lens becomes denser and less elastic, leading to decreased ability to accommodate (presbyopia)

Constriction of the Pupil During Accommodation

The sphincter pupillae muscle contracts to reduce the size of the pupil, ensuring that light rays pass through the central part of the lens and minimizing spherical aberration

Convergence of the Eyes During Accommodation

In humans, the retinae of both eyes focus on a single object, resulting in single binocular vision
When an object moves from a distance toward an individual, the eyes converge to focus on the single object
Convergence of the eyes results from the coordinated contraction of the medial rectus muscles

Clinical Notes

Eye trauma can occur due to the lack of protection from small objects, such as golf balls
The bony orbit provides some protection from large objects, but not from small objects

Sensory Nerves of the Face

The skin of the face is supplied by branches of the three divisions of the trigeminal nerve
The ophthalmic nerve supplies the region developed from the frontonasal process
The maxillary nerve serves the region developed from the maxillary process of the first pharyngeal arch
The mandibular nerve serves the region developed from the mandibular process of the first pharyngeal arch

Ophthalmic Nerve

The ophthalmic nerve supplies the skin of the forehead, upper eyelid, conjunctiva, and side of the nose
Five branches of the nerve pass to the skin:
- Lacrimal nerve supplies the skin and conjunctiva of the lateral part of the upper eyelid
- Supraorbital nerve supplies the skin and conjunctiva of the central part of the upper eyelid and the skin of the forehead
- Supratrochlear nerve supplies the skin and conjunctiva of the medial part of the upper eyelid and the skin over the lower part of the forehead
- Infratrochlear nerve supplies the skin and conjunctiva of the lower part of the upper eyelid

Carotid and Axillary Sheaths

The carotid sheath is a local condensation of the prevertebral, pretracheal, and investing layers of the deep fascia that surrounds the common and internal carotid arteries, internal jugular vein, vagus nerve, and deep cervical lymph nodes
The axillary sheath is a sheath of fascia that surrounds the subclavian artery and the brachial plexus as they emerge from the interval between the scalenus anterior and scalenus medius muscles

Cervical Ligaments

Stylohyoid ligament: connects the styloid process to the lesser cornu of the hyoid bone
Stylomandibular ligament: connects the styloid process to the angle of the mandible
Sphenomandibular ligament: connects the spine of the sphenoid bone to the lingula of the mandible
Pterygomandibular ligament: connects the hamular process of the medial pterygoid plate to the posterior end of the mylohyoid line of the mandible

Muscles of the Neck

Digastric muscle: depresses the mandible or elevates the hyoid bone
Stylohyoid muscle: elevates the hyoid bone
Sternohyoid muscle: depresses the hyoid bone
Sternothyroid muscle: depresses the larynx
Thyrohyoid muscle: depresses the hyoid bone or elevates the larynx
Omohyoid muscle: depresses the hyoid bone
Scalenus anterior muscle: elevates the first rib and laterally flexes and rotates the cervical part of the vertebral column
Scalenus medius muscle: elevates the first rib and laterally flexes and rotates the cervical part of the vertebral column
Scalenus posterior muscle: elevates the second rib and laterally flexes and rotates the cervical part of the vertebral column

Cervical Plexus

The cervical plexus is a network of nerve fibers that supplies innervation to some of the structures in the neck and trunk

Parathyroid Glands

The two superior parathyroid glands are more constant in position and lie at the level of the middle of the posterior border of the thyroid gland
The two inferior parathyroid glands usually lie close to the inferior poles of the thyroid gland
Functions of the parathyroid glands:
- Produce parathyroid hormone, which stimulates osteoclastic activity in bones, mobilizing bone calcium and increasing calcium levels in the blood
- Stimulate the absorption of dietary calcium from the small intestine and the reabsorption of calcium in the proximal convoluted tubules of the kidney
- Strongly diminish the reabsorption of phosphate in the proximal convoluted tubules of the kidney
Control of parathyroid hormone secretion is regulated by calcium levels in the blood
Blood supply to the parathyroid glands is from the superior and inferior thyroid arteries
Venous drainage is into the superior, middle, and inferior thyroid veins
Lymph drainage is into the deep cervical and paratracheal lymph nodes
Nerve supply is from the superior or middle cervical sympathetic ganglia

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Description

This quiz covers the structure and function of the lens in the human eye, including its shape, attachments, and role in accommodation.