The Brain Stem

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

The nerve cells serve as relay stations for the ascending and descending fibres
Contains nuclei of III & IV Cranial nerves

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)