Workbook questions 2 - The CNS Flashcards
What is the carotid sheath? Which structures lie inside it?
The carotid sheath is an extension of the fascia of the neck muscles. The common and internal carotid arteries, the internal jugular vein and the vagus nerve are contained within it.
Which arteries supply the spinal cord?
The spinal cord is supplied by three arteries, the anterior spinal artery and paired posterior spinal arteries.
These arteries are derived from vertebral, intercostal and lumbar arteries depending upon vertebral levels. Thus, In the neck the spinal arteries supplying the spinal cord are branches of the vertebral arteries, in the thorax - the posterior intercostal arteries, and in the lower back & pelvis - the lumbar arteries.
What are the consequences of a blockage of a cerebral artery by an embolus?
The tissue would become ischaemic as the blood supply would become insufficient to meet its metabolic needs. Nervous tissue is highly susceptible to oxygen lack, lack of glucose K+ accumulation and other consequences of ischaemia and would rapidly die, becoming infarcted.
Define (i) vascular and (ii) haemorrhagic stroke
A vascular stroke arises when a large artery is suddenly occluded by an embolism or by a
thrombosis
An hemorrhagic stroke follows the rupture of an artery or an aneurysm
What type of blood (arterial, venous, mixed) characterises an (1) Epidural (Extradural) haemorrhage?
(1) Arterial blood: The epidural space is a potential space between the cranial bones and the dura mater. It becomes a real space if blood from torn meningeal arteries accumulates in the space. A subdural hemorrhage may follow a sharp blow to the head which gives a depressed fracture of the skull
What type of blood (arterial, venous, mixed) characterises a (2) Subdural haemorrhage?
(2) Venous blood: Although the dura and the arachnoid mater are closely apposed to each other, blood, from a torn cerebral vein may force them apart to give a subdural haematoma.
This form of haematoma is generally caused by a blow to the head that causes the brain to move within the skull
What type of blood (arterial, venous, mixed) characterises a (3) Subarachnoid haemorrhage?
(3) Arterial blood: The subarachnoid space lies between the arachnoid and pia mater. It is filled with CSF. Following rupture of an aneurysm of one of the cerebral arteries it may fill with blood.
Which imaging procedure would be most useful in diagnosing an aneurysm in a cerebral artery?
Angiography - a radio-opaque dye is rapidly injected into a local artery and its flow imaged by cineradiography (rapid sequence of plates)
What is the composition of cerebrospinal fluid?
The cerebrospinal fluid (CSF) is derived from the blood by an action of the choroid. Its composition differs in many respects from the blood plasma and is controlled by the “blood-brain barrier” formed by tight
junctions between the capillary endothelial cells and by neurological processes.
In comparison to blood plasma CSF has lower concentrations of glucose, Ca++, protein and K+ but higher concentrations of Na+, Mg++ and Cl- .
The concentrations of B & T lymphocytes, monocytes and neutrophils are normally low.
The composition may be significantly altered in some disease states e.g. bacterial meningitis causes the CSF glucose to plummet.
How and where is CSF produced?
Normally 450 - 500 ml of CSF is produced each day about 70% of this is derived from the choroid plexuses through secretion and filtration of the blood. The choriod plexuses are located in the walls of the ventricles particularly the third and fourth ventricles.
The remaining 30% of the CSF represents water-soluble metabolites of nerve cell activity.
Where is CSF reabsorbed?
The CSF circulates through the ventricles - from the lateral & third ventricle through the foramen of Munro into the third before passing through the cerebral aqueduct into the fourth ventricle. Once in the
fourth ventricle the CSF empties into the subarachnoid space through the foramina of Magendie. The flow is driven by pressure and by cilia on the choroid epithelia and some of it passes down the spinal cord.
When the CSF pressure exceeds the venous pressure CSF moves from the subarachnoid space by way of one-way valves of the arachnoid villi into the superior sagittal sinus. The villi are visible by the naked eye
and constitute what are called arachnoid granualtions
Concerning hydrocephalus, what is
a) A communicating hydrocephalus?
b) A non-communicating hydrocephalus?
The daily secretion of CSF (450 -500 ml) exceeds the capacity of the ventricles (about 120 ml) any imbalance between secretion and reabsorption or, more usually, any interference with its flow may cause
the fluid to build up giving hydrocephalus.
A non-communicating hydrocephalus is also known as an Internal hydrocephalus and arises if the blockage to the circulation of the CSF is within the ventricles. This causes the ventricles not to communicate CSF between them, hence the term “non-communicating”.
A communicating hydrocephalus arises when blockage to CSF flow is due to factors external to the ventricular system. Thus, a
communicating hydrocephalus is also known as an external hydrocephalus. The most common cause of an external hydrocephalus is when there is scarring of meninges in the region where arachnoid granulations are found along the superior sagittal sinus. Such scarring causes irreversible closure of the one-way valves
of the arachnoid granulations.
