Ischemia and CSF Compression of the Cerebellum
Because of the design of the human skull, spine and circulatory system of the brain, the cerebellum, also known as the hindbrain, is predisposed to: compression from Chiari malformations, compression from an increase in CSF volume in the fourth ventricle or cisterns, called normal pressure hydrocephalus (NPH), and ischemia due to the compression of the vertebral-basilar arteries resulting in decreased blood flow.
In brief the internal organization of the cerebellum is of a superficial cortex overlying a dense core of white matter. The cortex is highly convoluted forming sulci and fissures giving it its cauliflower appearance. It is located in the the lower compartment of the brain called the posterior fossa. The posterior fossa is separated from the rest of the brain by a covering called the tentorium cerebelli. In the brain scan above, the tentorium cerebelli is in the dark shadow above the cerebellum beneath the occipital lobe of the brain.
The cerebellum is most noted for its function in muscle coordination, gait (walking and running) and balance and its anticipatory involvement with movement. But it also plays less well-known roles in cognition, attention, language and possibly even emotions. The reason why it plays a role in these lesser known functions is because of its role in muscle coordination.
Good cognition requires concentrated effort on the part of the mind, which requires subjugation and control of the body. It also requires attention to the senses of smell, sight, sound, taste and touch and the ability to discriminate and focus on what is most important.
Sometimes attention requires the muscles to be still and calm while under no load. Other times it requires keeping the muscles calm and steady while under a strain such as a hunter holding his gaze to aim, at the same time holding a loaded spear or bow poised and ready to release at prey. Another example would be a yoga practioner holding a special pose for stretching while standing on one leg or simply sitting and gazing at a candle.
Emotions can trigger muscle responses in the face and body as well. Anger can make a child or an adult lash out and strike. Learned responses hold back the tendency of the muscles to react and strike out. Thus the hindbrain plays a much more complicated role in our daily lives than we fully realize.
The Cerebellum and the Fourth Ventricle
Cerebrospinal fluid (CSF) flows through the ventricles where it is produced and into the subarachnoid space which surrounds the brain and cord. Among other things, the role of CSF is to cushion and protect the brain and cord, as well as supply support for the brain so that it can float above the bones of base of the skull and foramen magnum.
The fourth ventricle is the lowest of the ventricles and is located on the midpoint of the front surface of the cerebellum at the nodular portion of the flocculonodular lobe. This nodular portion penetrates into the fourth ventricle. In the brain scan above, the fourth ventricle is the black shadow in front of the cerebellum above the arrow pointing to the herniation.
The fourth ventricle drains through four openings. The top one, called the foramen of Magendie is located in the midline. Lower down there are openings on the left and right sides called the foramen of Lushka. On the bottom, the fourth ventricle opens into the central canal of the spinal cord. In fact, some anatomists consider the fourth ventricle in humans to be a dilation of the central canal of the cord.
An increase in CSF volume in the fourth ventricle can compress the flocculonodular lobe, which is the oldest lobe of the hindbrain. Its function is related head and eye movement, as well as postural muscles and balance. Compression of the flocculonodular lobe by excess CSF volume in the fourth ventricle may explain the problems with walking (gait), balance and stooped posture seen in Alzheimer's and Parkinson's disease.
Blood Supply To The Hindbrain
The blood supply to the hindbrain comes from the vertebral-basilar arteries. The vertebral-basilar arteries feed the cerebellar arteries. The picture below shows the SCA (superior), AICA (anterior inferior) and PICA (posterior inferior) cerebellar arteries. Compression of the vertebral-basilar arteries can occur in the cervical spine, especially the upper cervical spine and base of the skull. It can also occur as the vertebral arteries pass through the foramen magnum and along the base of the skull called the clivus. Compression of the vertebral-basilar arteries can decrease blood flow to the hindbrain and similarly cause problems with gait (walking), balance, coordination and posture. Brain blood supply, drainage and CSF are discussed in depth in Upright Doctor's book.
The brainstem and vertebral-basilar arteries are protected by cerebrospinal fluid (CSF) in the cisterns from compression caused by contact with the clivus of the base of the skull. A decrease in CSF volume can cause compression of the vertebral-basilar arteries. Conversely, an increase in CSF volume can also affect the vertebral-basilar arteries, especially the smaller branches, such as the pontine branches. Among other things, the pontine branches supply the accoustic (vestibulochoclear) or eighth cranial nerve which can cause ringing in the ears and dizziness. The trigeminal nerve also gets its blood supply from the pontine branches. Compression of the vertebral-basilar arteries can cause tinnitis, dizziness and trigeminal neuralgia.
Lastly, abnormal curvatures and misalignments of the spine, especially the upper cervical spine can cause Chiari type malformations. They can also compress the vertebral-basilar arteries and decrease blood flow to the hindbrain. In either case, they can affect blood and CSF pathways and thus flow.
The cerebellum is frequently involved in neurodegenerative diseases, as well as migraine headaches and transient ischemic attacks called mini strokes. The design of the human skull, spine and circulatory system of the brain and cord predisposes humans to cerebellar problems.
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