Medical Physiology Year Two – Paper Two

** --- **UNIT CODE**: MBMP 2300**UNIT TITLE**: Medical Physiology**DATE**: Thursday, 13th July 2023**TIME**: 8:00 AM – 10:00 AM**DURATION**: 2 Hours --- ### **INSTRUCTIONS** - This paper consists of **two sections: A and B**. - **Attempt all questions in Section A** and **any two (2)** questions from Section B. - The use of **mobile phones** or any form of **exam irregularity** is strictly **prohibited**. --- ## **SECTION A – SHORT ANSWER QUESTIONS (60 Marks)** # PHYSIOLOGY EXAM ANSWERS - SECTION A ## Short Answer Questions (60 Marks) ### 1. Three types of nerve fibers with examples (5 marks) **A Fibers (Myelinated, Large Diameter)** - **Aα fibers**: Motor neurons to skeletal muscle, proprioceptive fibers from muscle spindles (12-20 μm diameter, 70-120 m/s conduction velocity) - **Aβ fibers**: Touch, pressure, vibration sensory fibers (5-12 μm diameter, 30-70 m/s conduction velocity) - **Aγ fibers**: Motor neurons to muscle spindle intrafusal fibers (3-6 μm diameter, 15-30 m/s conduction velocity) - **Aδ fibers**: Sharp pain, cold temperature, some touch sensory fibers (2-5 μm diameter, 12-30 m/s conduction velocity) **B Fibers (Lightly Myelinated, Medium Diameter)** - Preganglionic autonomic fibers (both sympathetic and parasympathetic) - 1-3 μm diameter, 3-15 m/s conduction velocity **C Fibers (Unmyelinated, Small Diameter)** - Postganglionic sympathetic fibers - Dull, aching pain sensory fibers - Warm temperature sensory fibers - Some visceral sensory fibers - 0.4-1.2 μm diameter, 0.5-2 m/s conduction velocity --- ### 2. Emmetropia and four types of refractive errors (5 marks) **Emmetropia** is the normal refractive state of the eye where parallel light rays from distant objects (>6 meters) focus exactly on the retina without accommodation. The eye has perfect optical power matching its axial length. **Four Types of Refractive Errors:** **A. Myopia (Nearsightedness)** - Light rays focus in front of the retina - Caused by: Excessive axial length of eyeball or excessive refractive power - Symptoms: Distant objects appear blurred, near objects clear - Correction: Concave (diverging) lenses **B. Hyperopia (Farsightedness)** - Light rays focus behind the retina - Caused by: Insufficient axial length of eyeball or insufficient refractive power - Symptoms: Near objects appear blurred (accommodation strain), distant objects may be clear - Correction: Convex (converging) lenses **C. Astigmatism** - Irregular curvature of cornea or lens causing different refractive powers in different meridians - Light rays do not focus at a single point - Symptoms: Blurred vision at all distances, eye strain, headaches - Correction: Cylindrical lenses to correct the meridian with abnormal curvature **D. Presbyopia** - Age-related loss of lens elasticity and accommodation ability - Begins around age 40-45 years - Symptoms: Difficulty focusing on near objects, need to hold reading material farther away - Correction: Convex lenses for near vision, bifocals, or progressive lenses --- ### 3. Physiological events during REM sleep (5 marks) **Neurological Events:** - Rapid eye movements (horizontal, vertical, and oblique) - Vivid, complex dreaming with emotional content - Increased brain activity similar to waking state - Activation of visual, motor, and limbic areas - Suppression of norepinephrine, serotonin, and histamine release **Motor System Changes:** - Muscle atonia (paralysis of voluntary muscles except diaphragm and extraocular muscles) - Inhibition of spinal motor neurons via glycine and GABA - Occasional muscle twitches despite atonia - Preserved respiratory muscle function **Autonomic Changes:** - Fluctuations in heart rate and blood pressure - Irregular breathing patterns - Loss of thermoregulation (poikilothermic state) - Increased oxygen consumption and metabolic rate - Penile erections in males/clitoral engorgement in females **Hormonal Changes:** - Decreased growth hormone release - Reduced cortisol secretion - Suppressed antidiuretic hormone (ADH) release --- ### 4. Decussation and its significance in the pyramidal motor system (5 marks) **Definition of Decussation:** Decussation refers to the crossing over of nerve fibers from one side of the nervous system to the other, forming an X-shaped intersection. **Pyramidal System Decussation:** - Occurs at the pyramidal decussation (decussation of pyramids) in the medulla oblongata - 85-90% of pyramidal tract fibers cross to the opposite side - Forms the lateral corticospinal tract - 10-15% remain uncrossed, forming the anterior corticospinal tract **Significance:** **A. Contralateral Motor Control** - Left cerebral hemisphere controls right side of body and vice versa - Explains why unilateral brain lesions cause motor deficits on the opposite side **B. Clinical Implications** - Stroke in left motor cortex causes right-sided hemiplegia - Upper motor neuron lesions above decussation cause contralateral symptom