Midbrain Flashcards
Where does the midbrain lie and what is it’s length?
The midbrain or mesencephalon extends from the pons to the diencephalon and is about 2.5 cm (1 in.) long.
Describe the structure of the midbrain?
The aqueduct of the midbrain (cerebral aqueduct) passes through the midbrain, connecting the third ventricle above with the fourth ventricle below. Like the medulla and the pons, the midbrain contains both nuclei and tracts.
Made up of an anterior and posterior section.
Outline the anterior part of the midbrain?
The anterior part of the midbrain contains paired bundles of axons known as the cerebral peduncles (pe-DUNK-kuls or PE ̄- dung-kuls little feet. The cerebral peduncles consist of axons of the corticospinal, corticobulbar, and corticopontine tracts, which conduct nerve impulses from motor areas in the cerebral cortex to the spinal cord, medulla, and pons, respectively.
What is the posterior part of the midbrain called?
What are the 4 rounded elevations that it consists of called?
Tectum
Superior colliculi and inferior colliculi
Explain the superior colliculi of the midbrain?
The two superior elevations, nuclei known as the superior colliculi (ko-LIK-u ̄-l ̄ı little hills; singular is colliculus), serve as reflex centers for certain visual activities. Through neural circuits from the retina of the eye to the superior colliculi to the extrinsic eye muscles, visual stimuli elicit eye movements for tracking moving images (such as a moving car) and scanning stationary images. The superior colliculi are also responsible for reflexes that govern movements of the head, eyes, and trunk in response to visual stimuli.
Explain the inferior colliculi of the midbrain?
The two inferior elevations, the inferior colliculi, are part of the auditory pathway, relaying impulses from the receptors for hearing in the inner ear to the brain. These two nuclei are also reflex centers for the startle reflex, sudden movements of the head, eyes, and trunk that occur when you are surprised by a loud noise such as a gunshot.
Other than the sup. and inf. colliculi, what other nuclei does the midbrain contain?
The midbrain contains several other nuclei, including the left and right substantia nigra (sub-STAN-she ̄-a substance; NI ̄-gra black), which are large and darkly pigmented. Neurons that release dopamine, extending from the substantia nigra to the basal nuclei, help control subconscious muscle activities. Loss of these neurons is associated with Parkinson disease.
Also present are the left and right red nuclei, which look reddish due to their rich blood supply and an iron containing pigment in their neuronal cell bodies. Axons from the cerebellum and cerebral cortex form synapses in the red nuclei, which help control muscular movements.
List the nuclei contained in the midbrain?
Superior colliculi
Inferior colliculi
Substantia nigra
Red nuclei
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Good luck
The midbrain has nuclei associated with 2 cranial nerves, which are they?
Oculomotor (III) nerves.
Trochlear (IV) nerves.
Explain the oculomotor nerves in relation to the midbrain?
Oculomotor (III) nerves. Nuclei in the midbrain provide motor impulses that control movements of the eyeball, while accessory oculomotor nuclei provide motor control to the smooth muscles that regulate constriction of the pupil and changes in shape of the lens via the oculomotor nerves.
Explain the trochlear nerves in relation to the midbrain?
Trochlear (IV) nerves. Nuclei in the midbrain provide motor impulses that control movements of the eyeball via the trochlear nerves.
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