Animal Physiology MCQ - IIT JAM MCQ

A synapse is a junction between 2 cell types. This junction provides functional continuity. The synapse have 2 types:
(i) Electrical synapse : In this, plasma membranes of cells come very close to each other but are not physically connected. This closeness is in range of 2-3 nm. In such regions cells contain barrel shaped channels made of connexin protein units. 6 units of connexin make one such channel. Connexin is an integral membrane protein. The extracellular domains of these proteins from apposing cells are tightly linked but not cells themselves. This channel allows continuous flow of molecule less than 1000 Da in size. Thus, it allows free flow of ions and provides for functional integration of cells. The flow of information by current is faster in this mode. These are also known as gap junction. E.g.: Stimulation of heart muscles for contraction in mammals, stimulation of smooth muscle cells is esophagus and intestine to generate peristaltic wave.
(ii) Chemical synapse : In this, a neuron interacts with another cell. This other cell is target cell of neuron’s actions and could be another neuron, muscle cell or gland cell. When stimulated, the action potential reaches the axon terminal membrane in neuron. This membrane is also called presynaptic membrane. After this, is a gap of 20-50 nm and called synaptic left. On other side is the membrane of target cell and is called post synaptic membrane. The action potential at presynaptic membrane causes release of chemicals called neurotransmitters. It is for this reason, they are called chemical synapse. The neurotransmitters travel across synaptic left and bind to their receptors in postsynaptic membrane.

Pituitary gland is located at the base of brain just below hypothalanus. It has two parts viz. anterior pituitary and posterior pituitary. In posterior pituitary, many neurons of hypothalanus end. The endings are axonal terminals of neurons that originate in hypothalamus. They produce two peptide hormones called vasopressin and oxytocin. These move down into posterior pituitary via axonal endings and stored in secretory vesicles for release. It is the oxytocin hormone released from posterior pituitary that contracts the smooth muscle cells in uterus during parturition (child birth) in mammals. It also contracts mammary glands during lactation.

During heavy, sternous exercise anaerobic metabolism prevails in skeletal muscles to cope with increased energy demand. During this process muscle glycogen is converted into lactate in muscle cells. Cori cycle helps transport this lactate to liver and convert the lactate back to glucose. The cycle is

Brain has three parts viz. forebrain, mid brain and hind brain.
Cerebrum : It is part of forebrain and largest part of brain. It is divided into two halves called cerebral hemispheres. These halves are connected by a tract of nerve fibers called corpus callosum. It contains major areas seasory and processing.
Hypothalamus : It is part of forebrain and found below thalamus, hence its name. It produces hypothalamic hormones that control secretion of pituitary gland hormones. It also controls body temperature and urge for eating and drinking.
Cerebellum : It is found in hind brain. It is major part involved in coordinating the movements of body. Thus, statements P and S are correct for cerebrum.

Water reabsorption is promoted by vasopressin hormone from posterior pituitary.
Thyroid hormone synthesis is initiated by thyroid stimulating hormone (TSH) secreted by anterior pituitary.

Gossypol is a polyphenolic pigment isolated from cotton plant. It was used as male oral contraceptive in China. Its use has been stopped due to high toxicity. It made sperms immobile by inhibiting the motor protein dynein. Dynein is an ATPase found associated with microtubules in sperm flagella. It hydrolyzes ATP, whose energy is used for sperm motility. If dynein ATPase is inhibited, sperm is immobile and can not swim to ova for fertilization. This leads to contraceptive effects.

A neurotransmitter is an endogenous chemical that enables neurotransmission. They transmit signals across target neuron/muscle/gland cell. Chemically, they are of two types :
1. Small molecule transmitters : These are rapidly acting and cause most acute response of nervous system by diffusing across synaptic cleft. Their examples are : Acetylcholine, glutamate (glutamic acid), glycine, gamma-amino butyric acid (GABA), epinephrine, norepinephrine, dopamine, serotonin and histamine. Glycine and GABA are most common inhibitory neurotranomitters.
2. Neuropeptides : These cause more prolonged action in nervous system such as long term changes in number and size of synapses. E.g. Enkephlins, endorphins etc. Since glutamine is not found in synapses. It is not a neurotransmitter.

In amniote animals, pineal and parietal bodies regulate photoperiodism. Melatonin secreted pineal gland has an anti-gonadotrophic effect. Its secretion is in a circadian rhythm.

Note: Amniote is any land vertebrate which possesses an amnion, chorion and allantois. It includes reptiles, birds and mammals.  

Ovary in humans is a paired organ in females. It is located one on each side of uterus in pelvic cavity. It is supported by ligaments in following manner:
Ovarian ligament : It connects ovary with uterus.
Suspensory ligament : It connects ovary to body wall.
Broad ligament : It connects uterus sides with wall and floor of pelvis. In this process, it also covers ovary. So, all three ligaments are attached to ovary.

Pepsinogen is secreted by the gastric chief cells and is activated to pepsin by the low pH of the stomach,  created by secretion of HCl by the gastric parietal cells. Lipases are inactivated by low pH.

Hormones that act near their site of production and secretion are called as paracrine hormones. They are different from endocrine hormones as Latter are transported through out body by circulatory system as they are produced at a single site. The paracrine hormones are produced at many sites in body and act in their vicinity than being transported to their site of action. E.g. Prostaglandins and thromobxanes.
Correct option is (a)
Note : Prednisolone and prednisone are steriod drugs used for many different treatments. Hormones in options (b) and (d) are endocrine hormones and transported to their site of action by circulatory system.

Supporting cells in CNS : There are 4 types :
• Oligodendrocytes that form myelin sheath around axons of the CNS, producing white matter.
• Microglia that wander through the CNS and phagocytose foreign and degenerated material.
• Astrocytes that cover capil laries of the CNS and induce the blood brain barrier. Thus, these help regulate the external milieu of neurons in CNS.
• Ependymal cells that line the ventricles of the brain and the central canal of the spinal cord. Recent research has shown that ependymal cells can function as neural stem cells, i.e. they can divide to become new nervous and neuroglial cells. All these cells are together called as neuroglial cells.

Electrical synapse : In this, adjacent cells are connected by direct open fluid channels called gap junctions. These are made up of connexin protein. These gap junctions are areas of low electrical resistance so that impulses can be regenerated from one cell to the next. The impulse is conducted bidirectionally in this synapse. These synapses are used to transmit action potential among cardiac muscle fibers and smooth muscle fibers. However, these are scarce in CNS.

Fovea centralis : At the posterior pole of eye there is a yellowish pigmented spot, macula lutea. In this region rod cells are completely absent and cone cells are densely packed. There are no cells or blood vessels lying over the photoreceptors. It is the point of greatest vision or visual activity. It is called fovea centralis. This region of greatest visual sharpness is highly developed in humans.

Thick filament : It is made from myosin protein and extends from one end of A-band to other. Myosin is oligomeric and its monomers are called meromyosin. Each meromyosin has 2 parts. Heavy meromyosin (HMM) making its globular head with a short arm. Its head can bind and hydrolyze ATP, thus, is said to have ATPase activity. Light meromyosin (LMM) making the tail region.

We have the ability to increase the strength of inspiration and expiration with the help of additional accessory muscles of respiration. This is seen during labored breathing. Additional ‘accessory muscles of respiration’ are typically only used under conditions of high metabolic demand (e.g. exercise) or respiratory dysfunction (e.g. an asthma attack). The accessory inspiratory muscles are the sternocleidomastoid, the scalene muscles, the pectoralis major and minor etc.

Menses occurs 14 days after ovulation, regardless of the cycle length. Therefore in a 35 days menstrual cycle, ovulation occurs on day 21.