7. CONTROL AND COORDINATION

Transcription

1 7. CONTROL AND COORDINATION Multicellular animals, except sponges, have specialized cells called neurons, for responding to stimuli. A neuron or nerve cell is the structural and functional unit of the nervous system. Nervous system, which includes the brain, spinal cord and nerves, receivers. Coordination in Animals Hydra, a Cnidarians, possesses photoreceptors for light, photoreceptors for sound and olfactory receptors for smell. The receptors pass information to the brain by a type of nerve cells called sensory neurons. Organisms respond to different environmental factors called stimuli. This response is due to control and coordination in animals which is provided by never and muscular tissues. Nerves system is responsible for conducting. There are group of specialized cells called receptors. Photo receptor for light (eyes) Phonoreceptors for sound (ears) Gustatory receptor for taste (tongue) Olfactory receptors for smell (Nose) Thigmoreceptors for touch (skin) Human Nervous system Neuron (i) Cell body - The cell body is like a typical cell containing nucleus and granular cytoplasm (ii) Dendrites- Dendrites are short and branched processes. (iii) Axon-Axon is a single, elongated fiber. Both axon and dendrites arise from cell body. The functional junction between neurons is called synapse. The information passing through neurons are in the form of chemical and electrical signals called nerve impulse. In myelinated nerve cell the plasma Nucleus Cell body Never cell or Neuron Dendrite membrane of an axon is covered by a protective sheath of lipid and protein called myelin sheath, formed by the Schwann cells. It is broken into constrictions called the nodes of Ranvier. The axon endings are branched and are called synaptic terminals. The plasma membrane of an axon without myelin sheath is called non myelinated nerve sheath. Axon Never ending Page 1

2 Central nervous system (CNS) Brain Fore brain Mid brain Hindbrain Spinal cord regulate reflection and regular Carebrain thinking Olfactory lobes smell and auditory reception Cerebellum regulate movement and posture Medulla oblongata regulate swallowing, coughing, sneezing and vomiting Pons regulate, respiration, activities Peripheral Nervous System (PNS) Spinal nerves 31 pair to regulate the response of different activities Cranial Nerves 12 pairs Sympathetic Nervous System (SNS) Autonomic Nervous System (ANS) Parasympathetic Nervous System (PNS) Central Nervous system consists of (1) Brain and (2) Spinal cord. Brain is the highest coordinating center in the body. It is protected by the cranium, a bony box in the skull. Brain is covered by three membranes, called meninges. The space between membranes is filled by cerebrospinal fluid that protects the brain from mechanical shocks. The brain is broadly divided into three regions (i) Fore brain (ii) Mid brain (iii) Hind brain. Forebrain has two parts Cerebrum and olfactory lobes. It consists of two cerebral hemispheres. Medulla Oblongata Ceredrum Cerebellum Meninges Midbrai n Pons Human Brain with Spinal Cord Spinal Cord Hind Brain Occipital lobe is the region for visual reception, temporal lobe for auditory reception, parietal lobe for touch, small, temperature and conscious association and frontal lobe for muscular activities. Pairs of cranial nerves arise from the brain. The hindbrain consists of three centers, cerebellum, pons and medulla oblongata. Medulla oblongata for swallowing, coughing, sneezing and vomiting. The pons takes part in regulation of respiration. Coordination and adjustment of movement and posture are under the control of cerebellum. Spinal cord is a cylindrical structure. It begins in continuation with the medulla oblongata and extends downwards, enclosed within vertebral column. It is also surrounded by meninges, total of thirty one pairs of spinal nerves arise from the spinal cord. It also regulate normal function of the body many activities of the internal organs like heart blood vessels and glands are controlled by another specific set of nerves that form the autonomic nervous system. It mainly controls and integrates the function of internal organs like heart, blood vessels, glands, smooth muscles and uterus in the body. Autonomic nervous system is subdivided into Page 2

3 (i) Sympathetic (ii) Parasympathetic system The organs receive nerves from both sympathetic and parasympathetic nerve fibres. They have opposite effects on the organs if one is stimulatory the other is inhibitory. Organ Sympathetic system Parasympathetic system Heart Increase contraction and Decrease contraction and rhythm rhythm Blood vessels Constriction Dilation Bronchi Dilation Constriction Eye Dilation of pupil Constriction of pupil Gastric secretion Inhibition Stimulation Urinary bladder Relaxation Contraction Reflex action An unconscious (without will) and involuntary response of effectors (muscles and glands) to a stimulus is said to be reflex action. For example-we withdraw our hands or legs on pricking a pin, or touching a very hot or cold substance. The path followed during reflex action is called reflex arc, a message from receptors is relayed by sensory nerves to the spinal cord, which sends information for response via motor nerves to effectors.. The simplest type of reflex action is knee-jerk reflex. Receptors Sensory Nervous Coordination in plants Phototropism Responds by bending towards the light Geotropism downward movement in response to gravitational force. Ex Roots of plants Chemo tropism is known as movement due to chemical stimulus, as seen during the pollen tube growth., Nastic movements movement is neither towards, nor away from the stimulus. Phytohormones are involved in regulation of several function in the plants, such as growth of root, stem and leaf, flowering, phototropism, geotropism, nastic movement, breaking of dormancy, ripening of fruits and stomatal movement Photoperiodism. Flowering and seed germination in plants are regulated by the duration of light The phytohormones and phytochromes together are involved in the control and coordination between environment and plant responses. Auxins Effects of Auxins Cell Elongation: Apical dominance: For certain period, the growth of the lateral buds remains suppresses. This phenomenon is called apical dominance or bud inhibition. Parthenocarpy: When ovary is converted into fruit without the act of fertilization, the phenomenon is called parthenocarpy. Prevention from abscission Root initiation Respiration Metabolism Gibberellins The gibberellins are plant growth hormones which enhance the longitudinal growth of stem when applied to intact plants. However, they do not enhance the growth of isolated plant parts. The presence of meristematic cell is essential for the elongation and growth caused by gibberellins. Physiological Effect Spinal cord Motor Nervous Effectors Page 3

4 Stem elongation Genetic dwarfism Bolting and flowering Increase in flower and fruit size Seed germination Leaf expansion Breaking of dormancy Parthenocarpy Flowering Sex expression : The gibberellins promote maleness in flowers. Cytokinins (Kinetins) The cytokinins are plant growth substances which act primarily on cell division and have little or effect on extension growth. Effect of Cytokinins on Plants Cell division Breaking dormancy of seeds Induction of parthenocarpy Resistance of high temperature Sex expression Growth Inhibitors Abscisic Acid (ABA) Physiological effect Ageing and abscission Germination and senescence Facing stress Checking transpiration Ethylene Ethylene is the smallest Phytohormone It is the only gaseous plant growth hormone. High concentration of auxins induces ethylene formation. Physiological effect Promotes ripening of fruits Growth inhibition Flowering Abscission Pineal gland Parathyroid glands Hypothalamus Pituitary gland Thyroid gland Thymus gland Adrenal glands Pancreas Endocrine or ductless glands Glands, which later lose their connection with the parent epithelia. Their secretions are called hormones. They diffuse directly into the blood through tissue fluid and circulate throughout the body to be utilizing by specific target tissues or cells. So they have rich blood supply. The gland in man are Testes Endocrine glands in males and females Ovaries Page 4

5 thyroid, parathyroid, Adrenal, Pituitary, thymus, pineal. Pancreas is endocrine as well as exocrine gland other Hormones:- The term hormone was introduced by Bayliss and Starling. Hormones are chemical substances secreted in trace amounts by specialized tissues, called endocrine glands. The endocrine glands do not have ducts to pass their hormones so they are also called ductless glands. The characteristics of a hormone are: (i) They are specific chemical messengers. (ii) They are secreted by endocrine glands (iii) They are poured directly into the blood and carried by blood circulation (iv) They act on specific tissue/organ called target organ. (v) Hormones are involved in the regulation of several functions, like growth, metabolic activities and reproduction. The nervous system and hormonal system in our body together perform the function of control and coordination. Endocrine glands, their hormones and functions Endocrine Hormones Functions Hypothalamus Releasing hormones Regulation of the secretion of (Master gland) hormones from pituitary Pituitary (hypophysis) Master gland Growth hormone Trophic hormone gland. Development of bones and muscles. Regulation of the secretion of hormones from endocrine gland, like adrenal, thyroid, testes and ovary Prolactin Regulation of function of mammary gland. Vasopressin Regulation of water and electrolyte balance. Oxytocin Stimulates contractions of smooth muscles, help in child birth and lactation Thyroid Thyroxin Regulation of metabolism of carbohydrate, fat, and protein. Parathyroid Parathyroid hormone Regulation of blood calcium and phosphate. Adrenal Adrenalin and Corticoids Regulation of blood pressure, heart rate, carbohydrate metabolism and mineral balance. Page 5

6 Pancreas Insulin Glucagons Lowering of blood glucose Increase of blood glucose Testes Testosterone Regulation of male accessory sex organs and secondary sexual characters like moustache, beard, and voice Ovary Estrogen and Progesterone Regulation of female accessory sex organs and secondary sexual characters like mammary gland, hair pattern and voice. Maintenance of pregnancy. Page 6