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3/20/16 The Brain Stem The brain stem is the extension from thalamus towards the spinal cord. It is a pathway for ascending and descending tracts. It also is an area containing specific "primitive" ( but crucial) reflex centers as well as nuclei that form the basis of our cranial nerves. Elements of the brain stem are the Midbrain, Pons and Medulla oblongata. 1 The Brain Stem 2 1 3/20/16 The Brain Stem Midbrain or Mesenencephalon • Peduncles are tracts , bundles of axons, that send information from either cerebrum to the spinal cord (and back again) or relay information to and from the cerebellum. • on anterior side are the cerebral peduncles • on posterior side are the superior cerebellar peduncles 3 The Brain Stem Midbrain • Dorsal area of the midbrain (also called the tectum) contains nuclei within the white matter . They are collectively named the corpora quadrigemina • Superior colliculi : reflex center for movement of eyes, neck, head to visual stimuli • Inferior colliculi : reflex center for head trunk movement in response to auditory stimuli 4 2 3/20/16 The Brain Stem Midbrain • The Floor of the Midbrain (inner area) contains cerebral aqueduct and several internal gray matter nuclei with specific functions. • Red nuclei : subconscious control of upper limb and background muscle tone • Substantia nigra : regulates activity of basal nuclei • Reticular formation: helps to filter in-coming stimuli and maintains consciousness. Present along all brainstem areas. 5 The Brain Stem Pons • Anterior region contains mostly longitudinal conduction tracts for motor activities on ventral side (extension of the cerebral peduncles) • Dorsal side contain lateral tracts that connect to cerebellum : middle cerebellar peduncles • Internally are the nuclei of Apneustic and pneumotaxic center (aid in control of respiration center located in Medulla) and RAS 6 3 3/20/16 The Brain Stem Pons 7 The Brain Stem Medulla oblongata • Inferior part of brain stem and blends into the spinal cord • Ventral side contains the two large extension of the cerebral peduncles, descending from motor cortex. • They are also called the pyramids. • Pyramids cross over to opposite side right above the Spinal Cord. This is called the 'decussation of pyramids' . 8 4 3/20/16 The Brain Stem Within the Medulla are several important regions of gray matter reflex centers • Cardiovascular center : regulates force and rate of heartbeat, diameter of blood vessels (relates to origin of Vagus nerve) • A Respiratory center that adjust basic rhythm of breathing • Extensions of Reticular activating Center (RAS) • Olivary nuclei : relay motor information to the cerebellum • Other centers for swallowing & vomiting (relates to CN IX), hiccups, coughing, sneezing. 9 The Brain Stem • Dorsal side of the medulla contains the Inferior cerebellar peduncles: • It connects medulla to cerebellum and relays information from motor cortex to cerebellum via the olivary nuclei 10 5