October 3 - Brain Stem & Cerebellum.docx

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Anatomy and Cell Biology
Anatomy and Cell Biology 3319

October 3, 2013 Brain Stem and Cerebellum Pp. 383-390, 431-432 - The brain stem o Medulla oblongata  Continuous with spinal cord  Part of the 4 ventricle lies here  Pyramids: large fiber tracts that descend through the brain stem and spinal cord carrying voluntary motor output from the cerebrum to the spinal cord  Formed by pyramidal tracts  2 longitudinal ridges  Decussation of the pyramids: where pyramidal fibers cross over to the opposite side of the brain  Each cerebral hemisphere control the voluntary movements of the opposite side of the body  Olive: contains and inferior olivary nucleus (large wavy fold of gray matter)  Lies lateral to pyramid  Inferior cerebellar peduncles: fiber tracts that connect the medulla to the cerebellum  Cranial nerve VIII (8): vestibulocochlear nerve attaches at the junction of the medulla and the pons and is the sensory nerve of hearing and equilibrium  Cranial nerve IX (9): glossopharyngeal nerve innervates part of the tongue and pharynx  Nucleus ambiguus – motor nucleus  Solitary nucleus – sensory nucleus  Cranial nerve X: vagus nerve innervates many visceral organs in the thorax and abdomen  Dorsal motor nucleus of vagus, solitary nucleus, and nucleus abiguus  Cranial nerve XI: accessory nerve innervates some muscles of the neck  Cranial nerve XII: hypoglossal nerve innervates tongue muscles  Reticular formation nuclei: loose cluster of brain nuclei that runs through the core of brain stem  The midline raphe nuclei  Medial nuclear group  Lateral nuclear group  The most important nuclei in the medulla’s reticular formation involved with visceral activities are: o Cardiac center adjusts the force and rate of the heart beat o Vasomotor center regulates blood pressure by stimulating or inhibiting the contraction of smooth muscle in the walls of blood vessels  constriction of arteries causes blood pressure to rise o The medullary respiratory center controls the basic rhythm and rate of breathing o Additional centers regulate hiccupping, swallowing, coughing and sneezing o Pons  Bulge wedged between the midbrain and medulla  Separated from cerebellum by 4 ventricle  Pons form ventral bridge between brain stem and cerebellum  Several cranial nerves attach to the pons  Cranial nerve V (trigeminal): innervates the skin of the face and the chewing muscles  Cranial nerve VI (abducens): innervates an eye-moving muscle  Cranial nerve VII (facial): supplies the muscles of facial expression, among other functions  Pontine nuclei: relay brain nuclei in a path that connects a portion of the cerebral cortex with the cerebellum  Interspersed among the fibers of the pyramidal motor tracts  Involved with coordination of voluntary movements  Send axons to the cerebellum in the thick middle cerebellar peduncles o Midbrain  Lies between diencephalon and pons  Cerebral aqueduct: divides the midbrain into tectum (“roof”) dorsally and paired cerebral peduncles ventrally  Cerebral peduncle appear to hold up the cerebrum  Peduncles contain pyramidal motor tracts descending from the cerebrum toward the spinal cord  Superior cerebellar peduncles: connect the midbrain to the cerebellum  Periaqueductal gray matter: involved in “fight-or-flight response” and the automatic pathway that directly invokes the physiological reactions associated with fear  Ex, elicits a terror-induced increase in heart rate and skyrocketing blood pressure, wild fleeing or defensive freezing, suppression of pain when the person is injured  Also mediates the response to visceral pain (ex, nausea), during which it decreases heart rate and blood pressure, produces a cold sweat, and discourages movement - Functions of brain stem: o Acts as a passageway for all the fiber tracts running between the cerebrum and the spinal cord o Heavily involved with the innervation of the face and head, as 10 of the 12 pairs of cranial nerves attach to it o Produces the rigidly programmed, automatic behaviors necessary for survival Region Structure Function MEDULLA OBLONGATA Gray Matter Cranial nerve nuclei: VIII-XIII Receive sensory impulses and initiate motor activity to structures innervated by these nerves Nucleus cuneatus Relay general somatic sensory info and to the cerebral cortex Nucleus gracilis Inferior olivary nuclei Relay sensory info to cerebellum Visceral motor nuclei Control visceral motor activities; includes the cardiac center, vasomotor center, and medullary respiratory center; part of reticular formation Reticular formation nuclei Stimulate cerebral alertness; regulate skeletal and visceral muscle activity; part of reticular activating system White Matter Pyramidal motor tracts Conducts nerve impulses between higher brain centers and spinal cord; decussation of tracts in medulla Inferior cerebellar peduncles Carry info on equilibrium from vestibular nuclei and proprioception from the spinal cord to cerebellum PONS Gray matter Cranial nerve nuclei: V, VI, VII Receive sensory impulses (V & VII) and initiate motor activity to structures of the head Reticular formation nuclei Stimulate cerebral alertness; regulate skeletal and visceral
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