PBL 5: Brainstem anatomy

Amelia Clifford

Brainstem• provides the main motor and sensory innervation to the face and neck via the cranial

nerves• nerve connections of the motor and sensory systems from the main part of the brain to

the rest of the body pass through the brainBrainstem contains: • corticospinal tract (in the pyramids of the medulla)

motor• posterior column-medial lemniscus pathway

fine touch, vibration sensation and proprioception• spinothalamic tract

pain, temperature, itch and crude touchRoles of the brainstem: • regulation of cardiac and respiratory function• regulation of the central nervous system, and is pivotal in• maintaining consciousness • regulation of the sleep cycle

The brainstem is divided into…

• mesencephalon (midbrain), which is the first part of the brainstem seen when an intact adult brain is examined, and is at the junction between and in both the middle and posterior cranial fossae

• metencephalon, which gives rise to the cerebellum and the pons

• myelencephalon (medulla oblongata), the caudal most part of the brainstem, which ends at the foramen magnum or the uppermost rootlets of the first cervical (cranial nerves VI to XII are attached here)

midbrain• tectum: roof that includes superior and inferior colliculi involved in vision • tegmentum and cerebral peducles: transmit axons of upper motor neurons

Midbrain internal structures• Periaqueductal gray: the area around the cerebral aqueduct, which

contains various neurons involved in the pain desensitization pathway– neurons cause activation of neurons in the nucleus raphe magnus, which then

project down into the dorsal horn of the spinal cord and prevent pain sensation transmission

• Substantia nigra: This is a concentration of neurons in the ventral portion of the midbrain that uses dopamine as its neurotransmitter and is involved in both motor function and emotion. (dysfunction > Parkinson’s)

• Reticular formation: contains lower motor neurons, is involved in the pain desensitization pathway– involved in the arousal and consciousness systems, alerness and autonomic

reflexes• Central tegmental tract: projects up to cortex and down to spinal cord

medulla oblongata

• The medulla oblongata is the lower half of the brainstem

• The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and deals with autonomic functions, such as breathing, heart rate and blood pressure.

• The medulla is often thought of as being in two parts:– an open part or superior part where the dorsal surface of

the medulla is formed by the fourth ventricle– a closed part or inferior part where the metacoel lies within

the medulla

medulla oblongata functions

• The medulla oblongata controls autonomic functions, and relays nerve signals between the brain and spinal cord. It is also responsible for controlling several major points and autonomic functions of the body:

• respiration ----- chemoreceptors• cardiac centre ----- sympathetic, parasympathetic

system• vasomotor centre ---- baroreceptors• reflex centers of vomiting, coughing, sneezing and

swallowing

ventral respiratory group

• The ventral respiratory group (VRG) is a column of neurons located in the ventrolateral region of the medulla

• Respiratory effects:– inspiratory and expiratory neurons– secondarily responsible for initiation of inspiratory activity, after

the DRG – responsible for motor control of inspiratory and expiratory

muscles during exercise– pre-Bötzinger complex is the hypothesized location of central

respiratory rhythm pattern generation circuitry (it is currently unclear how this system regulates its output)

Lateral view

Sagittal section

Blood supply - Circle of willis

Circle of willis

Circle of willis

Circle of willis

Circle of willis

Circle of willis

Circle of willis

Circle of willis