(a) Describe the formation, course, tributaries and termination of coronary sinus. 10 marks (b) Describe the role of cerebellum…

(a) Coronary sinus

The coronary sinus is the main venous channel of the heart, about 3 cm long. It forms at the junction of the great cardiac vein and the oblique vein of the left atrium (vein of Marshall), at the left end of the posterior atrioventricular (coronary) groove. It runs from left to right in this groove, between the left atrium and the left ventricle, and ends by opening into the right atrium between the opening of the inferior vena cava and the right atrioventricular orifice, guarded by the valve of the coronary sinus (Thebesian valve).

Tributaries: the great cardiac vein (from the anterior interventricular groove, joining at the left end, with a valve at the junction); the oblique vein of the left atrium; the posterior vein of the left ventricle; the middle cardiac vein (from the posterior interventricular groove), which enters near the termination; and the small cardiac vein, which runs in the right part of the groove. Anterior cardiac veins drain directly into the right atrium.

(b) Role of the cerebellum in posture and equilibrium

The cerebellum coordinates posture and balance by comparing intended with actual movement and correcting errors, without initiating movement. The vestibulocerebellum (flocculonodular lobe) receives vestibular input through the inferior cerebellar peduncle and, via the fastigial nucleus and vestibular nuclei, controls the vestibulospinal pathways, eye movements and the muscle tone needed for equilibrium. The spinocerebellum (vermis and paravermis) receives proprioceptive input from the spinocerebellar tracts and projects through the fastigial nucleus to the reticular and vestibular nuclei, and through the interposed nuclei to the red nucleus, adjusting axial and proximal tone and posture during stance and gait. Purkinje cells are inhibitory and refine the output of the deep nuclei. Lesions cause truncal ataxia, a wide-based gait, nystagmus and difficulty standing with feet together.

(c) Jaundice

(i) Jaundice is yellow discolouration of the skin, sclerae and mucous membranes caused by raised serum bilirubin, usually above 2.5 mg/dL (normal total bilirubin is about 0.3–1.2 mg/dL). It is classified as pre-hepatic (haemolytic), hepatic (hepatocellular, including viral hepatitis) and post-hepatic (obstructive or cholestatic).

(ii) Tests and interpretation: serum bilirubin, total and direct; in pre-hepatic jaundice the unconjugated fraction is raised, urine bilirubin is absent and urobilinogen is raised. In hepatic jaundice both fractions rise, ALT and AST are markedly raised and urine bilirubin is present. In obstructive jaundice the conjugated fraction is raised, alkaline phosphatase and GGT are disproportionately raised, urine bilirubin is present, urobilinogen is absent and stools are pale. Further tests are HAV and HEV IgM, HBsAg and anti-HCV, which matter in a girl with fever, together with albumin, prothrombin time, a blood count with smear and reticulocytes, and ultrasound for obstruction.

(d) Typical intercostal space

A typical space (the 3rd to 6th) lies between adjacent ribs, with costal cartilage in front and the vertebral column behind. From outside in, the layers are skin, fasciae, the external intercostal muscle (fibres downward and forward), the internal intercostal muscle (downward and backward), the innermost intercostal layer, the endothoracic fascia and the parietal pleura. The neurovascular bundle runs between the internal and innermost layers, under the costal groove of the upper rib, in the order vein, artery, nerve from above downward. The posterior intercostal artery comes from the thoracic aorta and the anterior one from the internal thoracic artery; the veins drain to the azygos system and the internal thoracic vein. The intercostal nerve (ventral ramus) gives collateral, lateral cutaneous and anterior cutaneous branches. Procedures are done over the upper border of the lower rib to avoid the bundle.

(e) REM versus non-REM sleep

Non-REM sleep (N1–N3) makes up about 75–80% of sleep. The EEG shows theta waves, then spindles and K-complexes, then slow delta waves. Muscle tone is reduced but present, eye movements are slow or absent, heart rate, blood pressure and breathing are slow and regular, dreams are few and thought-like, and the person is easily roused except in deep sleep. Sleepwalking and night terrors arise here. It aids physical restoration and memory consolidation.

REM sleep (about 20–25%) shows a low-voltage, fast, wake-like EEG (paradoxical sleep), rapid eye movements, and loss of skeletal muscle tone except in the diaphragm and extra-ocular muscles. Heart rate, blood pressure and breathing are irregular, penile or clitoral erection occurs, dreams are vivid, and the arousal threshold is higher. It lengthens in later cycles and supports emotional regulation and memory. Loss of atonia causes REM sleep behaviour disorder.