Revision_Essay 2 Sept2025

Front

Internal structure of the spinal cord with the functions.

Back

The spinal cord’s cross-section shows two main areas: gray matter and white matter.

 

1. Gray Matter (3 marks):

-      Located in the centre, shaped like a butterfly or “H.”

-      Contains neuron cell bodies.

-      Dorsal horn: Receives sensory input.

-      Ventral horn: Sends motor output to skeletal muscles.

-      Lateral horn: Contains autonomic neurons (thoracic region).

-      Function: Integration and reflex processing.

 

2. White Matter (3 marks):

-      Surrounds the grey matter; made up of myelinated axons.

-      Divided into anterior, lateral, and posterior columns (funiculi).

-      Contains ascending tracts (sensory) and descending tracts (motor).

-      Function: Transmission of nerve impulses between the brain and body.

Front

The physiology of the spinal cord cells

Back

The spinal cord contains two main types of cells — neurons and neuroglial (supporting) cells.

 

1. Neurons (2 marks):

-      Neurons are the functional units of the spinal cord.

-      Sensory neurons transmit information from the body to the spinal cord.

-      Motor neurons carry impulses from the spinal cord to muscles and glands.

-      Interneurons connect sensory and motor neurons to form reflex pathways.

2. Neuroglial cells (2 marks):

-      These cells support and protect neurons.

-      Types include astrocytes (provide nutrients and maintain ion balance), oligodendrocytes (form myelin sheaths), and microglia (remove waste and protect against infection).

-      Together, they help maintain homeostasis and efficient nerve signal transmission.

Front

The relationship between cerebral perfusion pressure (CPP), mean arterial pressure (MAP), and intracranial pressure (ICP).

Back

1. Formula for CPP (1 mark)

-      CPP = MAP – ICP

 

2. Normal CPP values (0.5 mark)

-      60–80 mmHg

 

3. Effect of raised ICP on CPP (1.5 marks)

-      ↑ICP → ↓CPP → risk of cerebral ischemia

 

4. Clinical importance (3 marks)

-      Maintaining adequate CPP ensures oxygen delivery to the brain

-      Monitoring essential in traumatic brain injury, stroke

-      Guides treatment: fluids, vasopressors, ICP-lowering interventions

Front

How cerebral blood flow is regulated in the brain

Back

Cerebral blood flow (CBF) is carefully controlled to meet the brain’s oxygen and nutrient needs. The main mechanisms include:

1. Autoregulation: Cerebral arteries adjust their diameter to keep blood flow stable despite changes in blood pressure.

2. Chemical control: High carbon dioxide (CO₂) levels in blood cause blood vessels to widen (vasodilation), increasing blood flow. Low CO₂ causes narrowing (vasoconstriction). Oxygen levels also influence CBF if they drop significantly.

3. Metabolic regulation: Active brain regions release chemicals that increase local blood flow to supply more oxygen and nutrients.

Proper regulation of CBF ensures normal brain function and prevents damage from too little or too much blood flow.

 

Front

The basic principles of pharmacokinetics and how they influence drug action

Back

Pharmacokinetics is the study of how the body handles a drug after administration. It includes four main processes:

(each answer with explanation 1.5 marks)

 

1. Absorption: How the drug enters the bloodstream from its site of administration.

2. Distribution: How the drug spreads throughout body tissues and fluids.

3. Metabolism (biotransformation): How the body chemically modifies the drug, usually in the liver, to prepare it for elimination.

4. Excretion: How the drug and its metabolites are removed from the body, mainly through the kidneys.

 

These principles determine the onset, intensity, and duration of a drug’s action, and help guide appropriate dosing to achieve therapeutic effects while minimizing side effects.

Front

Role of the liver in drug metabolism

Back

The liver is the main organ responsible for drug metabolism. It chemically changes drugs to make them easier for the body to eliminate. This process often involves two phases:

(each answer with explanation 2 marks)

 

1.    Phase I (Modification): The liver adds or exposes functional groups on the drug through reactions like oxidation, reduction, or hydrolysis.

2.    Phase II (Conjugation): The liver attaches molecules (e.g., glucuronide or sulfate) to the drug, making it more water-soluble for excretion.

 

Liver metabolism helps reduce drug toxicity, regulate drug activity, and prepare drugs for elimination through urine or bile.

Front

Common neurological diseases or disorders which plasma exchange is indicated

Back

Plasma exchange is used in:

1.    Autoimmune diseases

a.    Guillain-Barré syndrome

b.    myasthenia gravis)

2.    Neurological disorders

a.    multiple sclerosis relapses

b.    Neuromyelitis optica

Front

Common complications of plasma exchange

Back

Plasma exchange (plasmapheresis) is generally safe, but some complications can occur:

 

1. Hypotension: A drop in blood pressure may happen due to fluid shifts during the procedure.

2. Allergic reactions: Patients may react to donor plasma or replacement fluids.

3. Bleeding or clotting issues: Removal of plasma can reduce clotting factors, increasing bleeding risk.

4. Infection risk: Catheter insertion can introduce infection.

5. Electrolyte imbalance: Calcium or potassium levels may change due to plasma removal.

6. Vascular access problems: Difficulty with veins or catheter-related complications.

 

Most complications are preventable or manageable with careful monitoring. Awareness of these risks ensures patient safety and effective treatment.