Functional Neuroanatomy PHS 410 by ADEDAYO Lawrence D
Functional Neuroanatomy (PHS 410) by ADEDAYO, Lawrence D. Department of Physiology Faculty of Basic Medical and Health Sciences Bowen University Iwo Second Semester 2019/20 session
Midbrain connections Lecture 7
Introduction • The Midbrain (mesencephalon) • The mesencephalon is the most superior part of the brainstem. • It is divided into an anterior and a posterior section by the Aqueduct of Sylvius which connects the third and fourth ventricles. • Motor tracts, including the fibers of the pyramidal system, pass downward on the midbrain's anterior surface. • Sensory axons, including those of the spinothalamic tract also ascend, along the front of the midbrain behind the motor tracts.
Introduction (cont’d) • On each side, the midbrain contains a red nucleus and a substantia nigra. • The red nucleus contains numerous blood vessels and receives information from the cerebrum and cerebellum and directs subconscious motor commands concerned with muscle tone and posture. • Lateral to the red nucleus is the melanin- containing substantia nigra which secretes dopamine to inhibit the excitatory neurons of the basal nuclei.
The midbrain connections
The midbrain connections (cont’d) • The corpora quadrigemina, which is located on the posterior surface of the midbrain, is composed of two superior colliculi and two inferior colliculi. • The superior colliculi are part of the visual system, relaying input from the optic tract to the lateral geniculate bodies of the thalamus (control reflex movements of the eyes, head and neck in response to visual stimuli). • The inferior colliculi are part of the auditory pathway and send information to the medial geniculate bodies of the thalamus, (control reflex movements of the head, neck and trunk in response to auditory stimuli).
Nuclei in the midbrain • Several important nuclei are located in the midbrain, including the red nuclei, the substantia nigra, and the nuclei of cranial nerves III (oculomotor nerve. ) and IV (trochlear nerve). • The red nuclei connect the midbrain to the cerebellum and to the inner ear. • It is also an important part of the extra pyramidal tract. • The cerebellum compares input from muscles and joints with motor output from the cortex and relays subsequent adjustments to the cortex through the red nucleus and thalamus. • The substantia nigra is a group of dark-colored, dopaminergic cells. • Lesions here cause Parkinson's disease. Both of these cranial nerves provide innervation for motor movements of the eyes
Dorsal Mesencephalic syndromes • Mainly neuroophthalmologic abnormalities • Commonly seen in: Hydrocephalus • Consists of : • Paralysis of conjunctiva Upward gaze (downward occlusion) • Pupillary abnormality • Convergence retraction (Nystagmus) • Pathalogic lid retraction (Collier‘s sign)
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