Central Nervous System 3

Learning & Test Objectives

  1. Identifying on brain specimens its surface and subcortical structures and general function.
  2. Brain hemispheres, lobes, gyri and sulci, ventricles, and functions related to these structures.
  3. Identifying subcortical structures on brain sections (specimens and imaging) and explainig theri function.
  4. Blood vessels observable on specimens as well their supplying zones.   
  5. External structures of cerebellum, brain stem and spinal cord as well meninges.

Description of the test

The test is held by the general rules of oral examinations (see Continuous Testing – Organisation).

The third test on the central nervous system is in oral format. In this test the student's ability to demonstrate specimen of the brain and spinal cord and models, schemes and radiological images of the central nervous system is examined. The examination is focused on the location, division, internal structure, external appearance, syntopy, blood supply and main functions of the spinal cord, brain stem, cerebellum, diencephalon and telencephalon (cerebral hemispheres, functional cortical areas, basal ganglia and the white substance). Furthermore, the students are required to explain and describe the limbic system, sensory and motor systems, ventricular system of the brain, subarachnoid cisterns, vessels of the brain and spinal cord, meninges of the brain and spinal cord and the chemical systems of the brain. The examiner may also ask questions based on clinical correlations, curiosities, radiological images and topics covered in the test CNS 1 and CNS 2. During the examination the student may be asked to draw one of the required schemes (see below). The examination has six parts, the details of which are described below. During each part the student is asked several questions.

Part 1 – cerebral hemispheres

The student is required to demonstrate a cerebral lobe chosen by the examiner. The student will describe the gyri and sulci and the functional cortical areas of the chosen lobe.

Part 2 – subcortical structures

The student is required to show and explain the functions of various subcortical structures chosen by the examiner.

Part 3 – identification of other structures

The student is required to show and describe various other structures of the central nervous system chosen by the examiner.

Part 4 – theoretical part

The student is asked questions on the following topics. For each of the following structure they should be able to give the basic definition and describe its classification and subcomponents. When considered appropriate the student should use the specimen, models and draw schemes to describe the topics.

  1. Cerebellar afferents and efferents
  2. Thalamic nuclei
  3. Hypothalamic nuclei
  4. Basal nuclei
  5. Limbic system and Papez circuit
  6. Association, commissural and projection fibres
  7. Motor systems
  8. General sensory systems
  9. Special sensory systems
  10. Ventricular system of the brain and subarachnoid cisterns
  11. Chemical systems of the brain
  12. Meninges of the brain and spinal cord
  13. Arteries of the brain and spinal cord
  14. Veins of the brain and spinal cord
     

Part 5 – clinical notes and other curiosities

The examiner can ask questions on several clinical notes and curiosities, predominantly from the list below.

Part 6 – radiological images

The student may be asked questions on radiological images of the central nervous system (see below).

 

Clinical correlations

Anterolateral thalamic syndromes usually manifest with contralateral paresis, uncoordinated movements and dysphagia.

The thermoregulatory centres are responsible for shivering and fever.

Damage of the lateral hypothalamic zone (centre of hunger) can lead to partial or complete loss of appetite.

Damage to the ventromedial nucleus can lead to compulsive eating (hyperphagia).

Tonsillar herniation occurs when the cerebral tonsils herniate through the foramen magnum, which can be caused by expansive processes in the posterior cerebral fossa. Tonsillar herniation is a life-threatening situation because it results in compression of the medulla oblongata, which compromises the cardiorespiratory centres. The most common clinical signs of this type of hernia are headache in the occipital region, diplopia, paresis or paralysis and ataxia. Consciousness rapidly deteriorates and death results from cardiorespiratory depression.

Damage to the premotor area does not result in paresis or paralysis. Instead, it results in the inability to execute complex movements. This is known as ideomotor apraxia. Such a patient is not able to imitate the use of tools (e.g. using a knife and fork or opening a door with a key).

Primary somatosensory area damage manifests as contralateral hypesthesia or anaesthesia (involvement of tactile and discriminative sensation). Pain and thermic sensation are typically spared because they are processed at the level of the limbic system.

Damage to the primary visual area leads to cortical blindness. Damage to the secondary visual area causes visual agnosia. Visual agnosia is a condition in which a patient cannot recognise the objects he/she sees.

Unilateral damage of the primary auditory area leads to a bilateral hearing impairment. Damage to the anterior part of the primary auditory area affects low frequencies and damage to the posterior region affects higher frequencies. Damage to the secondary auditory area results in the inability to interpret sounds and voices (perceptive aphasia).

Damage to Broca's area causes expressive (motor) aphasia. The patient is able to understand spoken and written language. His/her speech is non-fluent and slow but meaningful.

Damage to Wernicke's area causes perceptive (sensory) aphasia. Despite a preserved ability to hear, the patient is unable to understand spoken and written language. The patient is usually able to produce fluent speech, which is typically unintelligible.

The arcuate fascicle interconnects Broca's area with Wernicke's area. Damage of the arcuate fascicle causes conduction aphasia. Comprehension and spontaneous speech are preserved, but conversation and the ability to repeat words and sentences is disturbed.

Damage to the insular lobe can lead to impairment of breathing (regularity, frequency or depth), impairment of heart rate, and inhibition or acceleration of peristalsis.

Damage to the parietal association cortex usually manifests as an inability to recognize objects held in the hand with closed eyes (astereognosis).

Damage of the right parietal association cortex can result in neglect syndrome. A patient with neglect syndrome typically ignores the left half of his or her body, eats from only the right half of a plate and draws only the right half of an object.

Massive damage of the temporal association areas typically results in the inability of the patient to recognise his/her own face and recognise and name colours.

Damage to the prefrontal cortex results in the loss of emotion and changes in mood and behaviour. Affected patients demonstrate inappropriate behaviour, increased irritability and aggression.

The hypotonic-hyperkinetic syndrome is characterised by the occurrence of involuntary movements and a decreased in muscle tone.

The hypertonic-hypokinetic syndrome is characterised by a decrease in motor activity and an increase muscle tone.

Parkinson disease is caused by lack of dopamine in the substantia nigra and disequilibrium in the basal nuclei caused by excess of acetylcholine. It manifests as muscle rigidity, hypokinesis, tremor, hypomimia (mask face), monotone speech, and other clinical signs (e.g. early loss of the sense of smell – anosmia or impairment of the sense of taste).

Tabes dorsalis is a term used for demyelination of the posterior funiculus. It can be caused by syphilis or a deficiency of vitamin B1.

Brain plasticity refers to the ability of the brain react and adapt to changes. When part of the brain is damaged, other parts can take over the lost functions. Physiotherapy can be used to support the process of brain plasticity.

Lumbar puncture is a procedure performed to collect a sample of CSF from the subarachnoid space of the vertebral canal. The most frequently used spot for the puncture is between the spinous processes of the third and fourth lumbar vertebra as the risk of damaging the spinal cord is minimal at this position. The needle penetrates into the extension of the subarachnoid space (lumbar cistern) where only the cauda equina passes.

Hydrocephalus is a pathological state caused by an accumulation of CSF. It can result from an increased production of CSF, reduced absorption of CSF, or occlusion in the ventricular system.

Clinical differences in the manifestation of hydrocephalus:
In infants, hydrocephalus that develops prior to suture closure often results enlargement of the head.
In adults, the ventricles enlarge to accommodate the increased volume of CSF, in doing so they compress the brain from within and damage brain tissue, which leads to brain atrophy. The typical symptoms are decreased mental function (damage to the white matter fibres and metabolic changes of cortical neurons), disorientation and urinary incontinence.

Alzheimer disease is characterised by decreased concentration of acetylcholine in the cerebral cortex, which is caused by neuronal degeneration of the basal nucleus and by atrophy of the posterior part of the cingulate gyrus and temporoparietal cortex. There are also noticeable changes which can be visualized by imaging techniques (MRI, PET, SPECT).


Other anatomical curiosities

The primary motor area forms only 60 % of the pyramidal tracts. The rest of the fibres of the pyramidal tracts come from premotor, association and somatosensory areas.

Functions of the right hemisphere: spatial recognition, recognition of faces, recognition of emotional content of speech, creativity and artistic ability.

Functions of the left hemisphere: language (in almost 100 % of right-handed people and 70 % of left-handed people) and logical thinking.

The circumventricular organs are specialised structures in the brain characterised by their extensive vasculature and lack of a normal blood-brain barrier. They participate significantly in neuroendocrine interactions.

Daily production of cerebrospinal fluid is approximately 500 ml. The amount of CSF in the ventricular system is 150 ml on average. Only one fourth of the volume is contained in the cerebral spaces (ventricles and central canal). The majority of the CSF volume fills the subarachnoid space and cisterns (extracerebral location).

Buoyant forces exert upward on the brain immersed in CSF (the brain is buoyed up more than 30 times). This is why the immersed brain, which weights 1500 g, exerts equal force on the skull base as weighing 50 g. CSF washes the whole brain and mechanically protects the brain from injury.

 

Radiological images

radiological images

Created: 17. 4. 2017 / Modified: / Responsible person: MUDr. Azzat Al-Redouan