40 Questions
Which arteries supply intracranial structures with blood?
Paired internal carotid and paired vertebral arteries
Where do the vertebral arteries enter the cranium?
Foramen magnum
What is the function of the Circle of Willis?
Distribute blood flow to the brain
What determines blood flow into each artery at the branch point in the Circle of Willis?
Relative resistance and vascular caliber
Which artery supplies the midbrain?
Posterior Cerebral Artery (PCA)
Which vascular territory is associated with difficulty in speech and swallowing?
Vertebral Artery (VA)
Which artery supplies the pons?
Basilar Artery (BA)
Which vessel gives rise to the unpaired anterior spinal artery?
Vertebral Artery (VA)
What is the 2nd most common cause of subarachnoid hemorrhage?
Ruptured Aneurysm
Which artery supplies the cerebellum?
Basilar Artery (BA)
What does a stroke in the anterior spinal artery territory affect?
Ventral and lateral columns of white matter
Where does an extradural hematoma occur?
Between periosteum and bone
What does a stroke in the posterior spinal artery territory affect?
Dorsal white columns and dorsal grey horns
What forms radicular arteries supplying the spinal nerve roots?
Vertebral Arteries
Where does a subdural hematoma occur?
Between dura and arachnoid
What causes a cerebral embolism within the skull?
Clot
Which bones form the roof of the orbit?
Frontal bone and lesser wing of sphenoid bone
What structures are located in the orbit's medial wall?
Ethmoid bone and lacrimal bone
Which structure covers the sclera and is covered by the cornea?
Palpebral conjunctiva
What is responsible for the secretion of sebaceous and apocrine glands in the eye region?
Eyelashes
What is the function of the aqueous humor in the eye?
To regulate intraocular pressure
Which structure allows the drainage of aqueous humor from the eye?
Trabecular meshwork
In which type of glaucoma does peripheral vision loss occur initially?
Open-angle glaucoma
Which cell layer in the retina absorbs excess light?
Pigmented layer
Why are cones concentrated at the fovea and rods in the periphery of the retina?
Cones have higher sensitivity to light than rods
What is the ratio of photoreceptors to ganglion cells in the periphery of the retina?
1000:1
Which part of the retina has the smallest pixel size?
Fovea
What is the main function of the optic disc?
To serve as the 'blind spot'
Which layer of the eye is responsible for adjusting the thickness of the lens to further refract light?
Ciliary body
Which muscles within the iris control the size of the pupil?
Constrictor and dilator pupillae muscles
Which nerve is responsible for innervating the superior oblique muscle?
Trochlear (IV) nerve
Which nerve palsy can result in a 'down and out' eye, droopy eyelid, and large pupil?
Oculomotor (III) nerve palsy
Which layer of the eye includes the structures responsible for controlling pupillary size and accommodation reflex?
Vascular layer
Which muscles are responsible for positioning the eye in the orbit and balancing out unwanted movements?
Extraocular eye muscles
Which movement of the eye involves specific muscles responsible for elevation and depression?
Duction
Which nerve is responsible for innervating the lateral rectus muscle?
Abducens (VI) nerve
Which structure secretes aqueous humor in the eye?
Ciliary processes
Which reflex allows for adjustments in the shape and convexity of the lens to fine-tune the focus of objects on the retina?
Accommodation reflex
Which muscles contract with parasympathetic and sympathetic inputs to control pupillary size?
Constrictor and dilator pupillae muscles
Which structure extends anterior to the lens with a central aperture, the pupil?
Iris
Study Notes
Anatomy and Functions of the Eye
- The eye is composed of three layers: fibrous, vascular, and neural tunic (sclera, choroid, and retina).
- The fibrous layer consists of the opaque sclera and the transparent cornea, which covers the anterior 1/6 of the eyeball and bends light to focus it on the fovea.
- The extraocular eye muscles, including the superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique, position the eye in the orbit and balance out unwanted movements.
- Movements of the eye are balanced through elevation and depression, with specific muscles responsible for each movement.
- Clinical testing of extraocular muscles includes abduction and adduction to align the angle of gaze with the pull of specific eye muscles.
- The innervation of the eye muscles involves the oculomotor (III), trochlear (IV), and abducens (VI) nerves, with specific muscles being controlled by different nerves.
- Nerve palsies, such as oculomotor nerve palsy and abducens nerve palsy, can result in specific clinical presentations, including "down and out" eye, droopy eyelid, and large pupil.
- The pigmented (vascular) layer of the eye includes the choroid, ciliary body, iris, and structures responsible for controlling pupillary size and accommodation reflex.
- The iris, a contractile diaphragm, extends anterior to the lens with a central aperture, the pupil, the size of which is controlled by constrictor and dilator pupillae muscles within the iris.
- The ciliary processes secrete aqueous humor and provide attachment for suspensory ligaments of the lens, while the ciliary muscle, within the ciliary body, adjusts the thickness of the lens to further refract light.
- Control of pupillary size involves the constrictor and dilator pupillae muscles, which contract with parasympathetic and sympathetic inputs, respectively.
- The accommodation reflex allows for adjustments in the shape and convexity of the lens to fine-tune the focus of objects on the retina, with the ciliary muscle playing a key role in this process.
Test your knowledge of the blood supply of the central nervous system with this quiz. Identify the sources of blood supply to intracranial structures and understand the role of the internal carotid arteries.
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