Session 4 - The Cerebellum Flashcards
What does the cerebellum include?
Cerebellum means ‘little brain’ and it sits immediately beneath the occipital lobe. They are separated from each other by a fold of dura known as the tentorium cerebelli. The cerebellum is also located immediately posterior to the brainstem and is connected to the brainstem via three pairs of cerebellar peduncles. The fourth ventricle is trapped in the space between the posterior pons and medulla (ventrally) and the cerebellum (dorsally).
How is the cerebellum similar to the cerebrum?
Like the cerebrum, the cerebellum is divided into separate lobes by fissures. The anterior lobe is found on the superior surface of the cerebellum and is divided from the larger posterior lobe by the primary fissure. A horizontal fissure is present within the posterior lobe. The third lobe, the flocculonodular lobe, is located most ventrally and is made of the flocculus and nodule. The flocculus is located beneath the cerebellar peduncles, and the nodule is found in the midline.
Again, like the cerebrum, the cerebellum has two hemispheres, a left and right. They are divided by a midline structure called the vermis. The cerebellum also has gyri, like the cerebrum, but they are much smaller and called folia.
What is the functional area of the spino,cerebro and vestibulo-cerebellum like?
Spino-cerebellum
Vermis
Spinocerebellar tracts
Superior and Inferior
Correction and modulation of fine movements
Cerebro-cerebellum
Lateral hemispheres
Cerebral cortex
Middle
Planning and execution of coordinated movements
Vestibulo-cerebellum
Flocculonodular lobe
Vestibular system
(inner ear)
Inferior
Balance, posture, tone and stabilisation of eye movements
What else about the cerebro cerebellum?
With regard to the cerebro-cerebellum and its function, it may help with think of the cerebellum as a computer programme, able to automate certain motor functions which allows the cerebral cortex to concentrate on other tasks. In cases where the cerebellum is dysfunctional, the motor cortex of the cerebrum is able to plan and execute some of these complex coordinated movements itself, but this requires concentration.
What is the blood supply of the cerebellum?
The blood supply to the cerebellum comes from three paired arteries:
• Superior cerebellar arteries (SCA) – branch from the most superior part of the basilar artery, just before it bifurcates into the posterior cerebral arteries.
• Anterior inferior cerebellar arteries (AICA) – branch from the most inferior part of the basilar artery, just after it is formed from the vertebral arteries.
• Posterior inferior cerebellar arteries (PICA) – branch from the vertebral arteries before they merge to form the basilar artery.
All three of these paired arteries also supply part of the brainstem so a blockage to one of them may cause more than just cerebellar dysfunction.
What causes cerebellar dysfunction?
Heavy alcohol consumption or a lesion of the cerebellum such as a stroke or tumour may cause symptoms reflective of disruption to the cerebellum’s functions. The acronym VANISHED can be used to remember these symptoms:
• V – Vertigo – as the cerebellum receives and processes a large amount of input from the vestibular system such as our sense of balance and the perception of movement, vertigo may be caused if it is damaged.
• A – Ataxia – this term means poor coordination. Typically, it is obvious when observing a patient’s gait, as the patient may appear unstable, with a very wide step to try to stabilise themselves.
• N – Nystagmus – this term refers to the subtle, rapid, backwards-and-forwards eye movements that can be observed when looking closely at a patient’s eyes at the extremes of their gaze. A small amount of horizontal nystagmus may be considered normal, but vertical or rotational nystagmus is almost always abnormal. There are other causes of nystagmus, but without a functioning cerebellum able to stabilise eye movements, patients may develop this symptom.
• I – Intention tremor – tremors are features of various neurological diseases and vary in character. In contrast to a Parkinson’s disease tremor, a tremor caused by a cerebellar lesion is absent at rest and appears as the patient ‘intends’ to do something, such as put their arms outstretched, or pick something up. This is because the cerebellum is unable to correct and modulate fine movements to stabilise the arm and hand.
• S – Slurred speech – coordination of fine movements is one of the functions of the cerebellum and this extends to the coordination of muscles involved in articulation of speech so cerebellar dysfunction may cause patients to have slurred speech.
• H – Hypotonia – maintenance of tone and posture are functions of the vestibulocerebellum and therefore, cerebellar dysfunction will cause lack of tone.
• E – Exaggerated past-pointing – this is observed when asking a patient to touch their own nose, then reach out to touch the tip of your finger as you hold it in front of them. Rapid correctional movements are coordinated by the cerebellum to ensure their finger touches the target. Patients with cerebellar dysfunction are unable to correct their movements, so often ‘overshoot’ your fingertip when reaching for it and ‘point past’ it.
• D – Dysdiadochokinesia – often abbreviated to DDK, this symptom is demonstrated by asking a patient to rapidly alternate between touching the palmar and dorsal parts of their fingers onto the opposite palm. Patients with cerebellar dysfunction will struggle to coordinate this movement smoothly and will have difficulty rapidly pronating and supinating their forearms or will miss the palm entirely.
What are some midline structures of the Brain?
Corpus callosum – the primary connection between the left and right hemispheres of the cerebrum. The corpus callosum is categorised as a group of commissural fibres (fibres that cross the commissure into the opposite cerebrum).
• Thalamus – a very important, central structure that acts as a relay for numerous functions of the brain including motor, sensory, visual, auditory, cognitive and emotional pathways.
• Hypothalamus – as its name would suggest, the hypothalamus sits immediately below the thalamus, and is key to homeostasis. It exerts control over numerous hormonal endocrine functions of the body and the autonomic nervous system.
• Pituitary gland – located at the end of a stalk known as the infundibulum, the pituitary gland secretes numerous important hormones, often under direction from the hypothalamus. The pituitary gland sits in the pituitary fossa (sella turcica) of the sphenoid bone, and the optic chiasm is immediately superior to it.
• Pineal gland – considered to be part of the diencephalon but located immediately posterior to the colliculi of the midbrain, the pineal gland secretes melatonin. This hormone controls our sleep-wake cycle.
• Calcarine sulcus – within this sulcus of the occipital lobe is the primary visual cortex.
What is the limbic system like?
Limbic system – the limbic system is a group of deep brain structures that play a significant role in numerous important functions including learning, memory, and emotional control. There are several parts to the limbic system including:
o Fornix – similar in shape to the corpus callosum, but much smaller.
o Mammillary bodies – small, round nuclei located at the anterior tip of the fornix.
o Hippocampus – located immediately inferior to the inferior horn of each lateral ventricle, the hippocampi are part of the temporal lobes and are integral in converting short-term to long-term memory. It’s named is derived from its shape, which resembles a seahorse.
o Parahippocampal gyri – as their name suggests, these gyri of the temporal cortices are located next to the hippocampi.
o Cingulate gyrus and cingulate sulcus – this is a large gyrus and associated sulcus that is superior to it which are located immediately superior to the corpus callosum on both sides of the cerebrum. Fibres that travel from the cingulate gyrus to other parts of the limbic system, namely the parahippocampal gyrus, are called the cingulum. The cingulum is an example of a group of association fibres (fibres that connect different parts of the same hemisphere).
o Other parts of the limbic system include sections of the olfactory and insular cortex, thalamus, hypothalamus, and nucleus accumbens and amygdala (discussed in the next section).
What is amnesia?
Amnesia
As the limbic system, and particularly the hippocampus, is responsible for formation of memory and conversion of short-term memory into long-term memory, a head injury or a disease which affects this area of the brain can cause amnesia. Amnesia can be classified into retrograde amnesia (meaning patients cannot recall events that took place prior to the onset of amnesia) or anterograde amnesia (meaning patients cannot create new memories after the onset but are able to recall long-term memories of things prior to the onset).
