WEEK 2: Responses of the brain to traumas Flashcards
What is the most common cause of head injuries?
Trauma is the most common cause of head injury
Traumatic head injury
Outline the causes of head injuries.
Road traffic accidents
Interpersonal violence
Community assault
Falls
Sports injuries
Drowning
Thermal
State the two types of brain injuries (temporal).
PRIMARY: Occurs at the time of impact (damage is done)
SECONDARY: Factors compromising adequate oxygenation (↑ICP, Brain edema, Space occupying lesions, hypoxia). Prevent these to improve the patient’s outcome.
What is the main challenge faced by Survivors of TBI?
Survivors of TBI are often left with neuropsychologic impairments that result in disabilities affecting work and social activity.
Discuss the basic anatomy of the cranium: Meninges
The meninges are three layers of membrane that envelop and protect the brain and spinal cord. The cranial meninges specifically refer to the section that covers the brain. The three layers, from superficial to deep, are the dura mater, arachnoid mater, and pia mater.
- Dura Mater:
*The dura mater is the outermost layer of the meninges and is located directly underneath the bones of the skull.
*It is thick, tough, and inextensible.
The dura mater consists of two layered sheets of connective tissue:
-The periosteal layer lines the inner surface of the bones of the cranium.
-The meningeal layer is located deep to the periosteal layer and is continuous with the dura mater of the spinal cord.
The dural venous sinuses are located between the two layers of the dura mater. They are responsible for the venous drainage of the cranium and empty into the internal jugular veins.
The dura mater receives its own vascular supply primarily from the middle meningeal artery and vein.
- Arachnoid Mater:
-The arachnoid mater is the middle layer of the meninges and lies directly below the dura mater.
-It is a delicate web of tissue.
-The space under the arachnoid, known as the subarachnoid space, is filled with cerebrospinal fluid (CSF) and contains blood vessels.
Pia Mater:
-The pia mater is the innermost layer of the meninges.
-It is a thin, delicate membrane that lies closely over the brain and spinal cord.
-The pia mater is tightly bound to the surface of the brain and spinal cord and cannot be dissected away without damaging the surface
Trace the flow of CSF in the subarachnoid space. Start from where it is produced to where in reaches the venous system of the body.
- CSF Production: CSF is produced primarily by the choroid plexus, which is located within the ventricles of the brain. The choroid plexus consists of specialized cells that filter blood plasma and secrete CSF into the ventricles.
- Ventricular System: CSF flows from the lateral ventricles to the third ventricle through narrow passageways called the interventricular foramina of Monro. From the third ventricle, it passes through the cerebral aqueduct of Sylvius to reach the fourth ventricle.
- Subarachnoid Space: From the fourth ventricle, CSF flows into the subarachnoid space, which surrounds the brain and spinal cord.
It does so through three small openings called foramina: two lateral foramina of Luschka and one medial foramen of Magendie.
- Arachnoid Granulations: CSF is reabsorbed into the venous system through structures called arachnoid granulations.
These granulations act as an avenue for CSF reabsorption into the blood circulation through a pressure-dependent gradient. They are outpouchings of the arachnoid mater into the dural venous sinuses.
- Venous Drainage: The arachnoid granulations allow CSF to enter the venous drainage system.
CSF is absorbed into the superior sagittal venous sinus, intracranial venous sinuses, and around the roots of spinal nerves.
The pressure gradient between the subarachnoid space and the venous sinus facilitates the drainage of CSF into the venous outflow system.
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What is the normal CSF volume in adults?
How many times if CSF replaced in a day?
150ml
8 times
State the functions of the CSF.
- Cushioning and Protection: CSF acts as a cushion, protecting the brain and spinal cord from mechanical forces. It helps to absorb shocks and reduce the effective weight of the brain, thereby minimizing the impact of sudden movements or trauma.
- Immunological Protection: CSF provides basic immunological protection to the central nervous system (CNS).
It acts as a medium for the distribution of immune cells and antibodies, helping to defend against infections and inflammatory processes within the CNS.
- Waste Removal: CSF plays a role in removing metabolic waste products from the brain.
It helps to clear away byproducts of cellular metabolism, such as excess neurotransmitters and other waste substances, maintaining a healthy environment for proper brain function.
- Transport of Substances: CSF serves as a transport medium for various substances within the CNS.
It helps to distribute neuromodulators and neurotransmitters throughout the brain, facilitating communication between different regions.
- Homeostasis: CSF helps maintain the chemical stability and homeostasis of the interstitial fluid in the brain.
It regulates the balance of ions, nutrients, and other essential substances necessary for optimal neuronal function.
Trace the flow of CSF from the superior sagittal sinus through the venous system.
Study the atlas and write it here.
State the Physiological Concepts: The Monro–Kellie Doctrine.
State the 3 main contents that make up the Monroe Kellie Doctrine.
The total volume of the intracranial contents is constant, because the cranium is a rigid container incapable of expanding. When the normal intracranial volume is exceeded, ICP rises.
Brain tissue
CSF
Intracranial circulation
State the normal ICP for patients in the resting state.
The normal ICP for patients in the resting state is approximately 10 mm Hg.
Normal ranges from 7mmHg-15mmHg in adults.
Discuss the impact of elevated ICP.
Intracranial pressure (ICP) results in decreased Cerebral blood flow (CBF) as a compensatory mechanism of the brain as the skull cannot expand.
↑↑↑(ICP) results in ↓↓ CBF hence Brain hypoxia.
Pressures >22 mm Hg, if sustained are associated with poor outcomes.
Venous blood and CSF can be compressed out of the container resulting in pressure buffering.
Once the limit of displacement of CSF and blood has been reached, ICP rapidly increases.
Describe the graph of ICP vs volume of mass.
- At a constant mass, the ICP is initially stable at around 10 mmHg.
- As the volume of mass increases, there is a rapid exponential rise in ICP.
- This rapid increase in ICP indicates that the brain has reached a decompensation state.
- When the brain reaches a decompensation state, brain herniation can occur, which is a serious condition with potentially severe consequences.
Epidural hematomas are relatively uncommon.
How many % of patients with brain injuries have epidural hematomas?
Which regions of the brain are they usually located in?
Describe the mechanism of these injuries?
*Occurring in about 0.5% of patients with brain injuries
Location: Temporal or temporo-parietal regions
Often result from a tear of the middle meningeal artery due to fracture.
They are classically arterial in origin;
Describe the classic presentation of epidural hematoma.
Classic presentation: lucid interval between the time of injury and neurological deterioration.
Typically become biconvex or lenticular in shape as they push the adherent dura away from the inner table of the skull.
