Brain Stem

Definition
        It is the stalk of the brain below the cerebral hemispheres.
        the nerve connections of the motor and sensory systems from the main part of the brain to the rest of the body pass through the brainstem..
        Controls various autonomic functions such as
       respiration
       heart rhythms
       sound localization

The parts
        The midbrain
        The pons varolii
        Medulla oblongata
        Reticular formation


Midbrain
        Situated around the cerebral aqueduct between the cerebrum and pons varolii
        Consists of nerve cells and nerve fibres connecting the cerebrum with lower parts of the brain and with the spinal cord

Pons varolii
        Situated in front of the cerebellum
        Below the midbrain
        Above the medulla oblongata
        Consists of the
       1. Fibres connecting the two hemispheres of the cerebellum
       2. Fibres connecting the higher centres of the brain and the spinal cord
       3. Nuclei of the V, VI, VII, VIII Cranial nerves
       4. Nuclei which act as relay stations

Medulla Oblongata
        Extends from the pons varolii above
        Continues with the spinal cord below
        Situated within the cranium above the foramen magnum
        Central fissures anteriorly and posteriorly
        Outer white matter
        Inner grey matter passing from brain to the spinal cord.
           Contains the nuclei of IX, X, XI, XII Cranial nerves

       Medulla contains vital centres
        Cardiac centre
        Respiratory centre
        Vasomotor centre
        Reflex centres of vomiting, coughing, sneezing and swallowing

        Decussation of the pyramids motor fibres from motor area in the pyramidal tracts cross

Reticular formation
        A collection of neurones in the centre of the brain stem
        Surrounded by neural pathways from brain to spinal cord
        Has links to other parts of the brain
        Receives information transmitted in ascending and descending tracts









Functions of reticular formation
        Coordination
        Selective awareness
        Coordination of skeletal muscle activity (associated with voluntary motor movement and he maintenance of balance)
        Coordination of activity controlled by the autonomic nervous system, (e.g. cardiovascular, respiratory and gastrointestinal activity)
        Sselective blocking or passing sensory information to the cerebreal cortex, (e.g. the slight sound made bya sick child moving in bed may arouse his mother but the noise of regularly passing trains may be suppressed)

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
                                                                                                                                                                                                                                                                                                                                                                                                                                           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