27.

a) What is reflex action? Draw neat labeled diagram of reflex arc.

(b) Mention a cause and symptom of each:

(i) Osteoporosis (ii) Constipation.

(iii) Asthma (iv) Tetany

(c) Write four functions of the human skeletal system.

(a) A reflex action is an involuntary response in the body to a stimulus. Many such actions in the body, from breathing to moving away from a hot object, are done without requiring thought. A group of neurons called a neuron arc cause the reflex action to occur; the neuron arc consists of the receptor, the sensory neuron, the interneuron, the motor neuron and the effector.

(i) Osteoporosis is a disease that cause bones to become thin and brittle. The disorder is most common in women after menopause. The exact cause is unknown, but marked lack of physical activity seems to play a part in bringing the condition. The condition accelerates after prolonged treatment with steroid drugs.

Symptoms.

1. Bones may be broken compressed by only minor injuries or even normal activities.

2. Persistent backache.

3. The back may curve, resulting n loss of height.

4. Sometime, no symptoms are visible. The condition is then discovered only if an X - ray is taken for regular exercise.

(ii) Infrequent or difficult defecation, which produces discomfort, is known as constipation. It is caused by decreased motility of the intestines. Because the faeces remain in the colon for prolonged periods of time, there is excessive water absorption and the faeces become dry and hard.

Causes. Constipation may be caused by improper bowel habits, spasms of the colon, insufficient fiber in the diet, inadequate fluid intake, lack of exercise, and emotions. Symptoms. Difficult of infrequent passing of motions is the main symptom of constipation. In the case of old people or ill patients persistent failure to empty the bowl may lead to spurious diaorrhea (a watery discharge, often soiling bed clothes) produced by hard faeces blocking and irritating the rectum.

(iii) Asthma is an allergic condition marked by attacks of labored breathing with wheezing and usually coughing gasping and a sense of constriction in the chest.

(iv) Tetany : A disorder in which an abnormally low level of calcium in the blood causes muscle spasms and twitching, mainly in the hands, feet and face. In children there may be laryngeal spasm and convolutions.

(c) Four functions of human skeletal system are:

(i) The skeleton provides the supporting framework of the body and protects the internal organism the skull protects the brain column to the spinal cord.

(ii) It participates in movement and locomotion by acting as levers the magnify muscular contractions.

(iii) It is store houses of various minerals like calcium and phosphorous. Some fat is also stored in bone marrow which can be used as source of energy.

(iv) All types of blood cells are made in bone. This function takes place in bone marrow flat bones like ribs, skull, pelvis, etc.