Complete notes for Chapter 17 Coordination and Control. Covers plant hormones, nervous system, brain structure, endocrine glands, and animal behaviour for FSc Part 2 Biology.
All organisms show response to stimuli. It is a common characteristic of all organisms. These stimuli may be internal or external, at sub-molecular level, cellular level or organism level. There should be coordination between the activities of different parts of the body.
Organisms do not show response to every stimulus. Even the most developed animals like man are unable to detect and show response to many stimuli in our environment. For example, a large number of bacteria are present on our skin but we cannot show response because sensory cells of our body cannot detect them. On the other hand, some of our internal body cells show response by killing these bacteria by chemicals (antibodies) or by phagocytosis. We can see only visible radiation of spectrum of light, but our body cannot detect the non-visible radiation.
Plants can show response to their surroundings in many ways. In fact, a plant like any other organism, responds continuously to a variety of cues and signals both from within itself and from its environment. The responses are usually gradual and based on time-consuming chemical changes. They respond to their stimuli by:
Hormones are chemical messengers that are manufactured in one part of an organism and are transported to another part where they can cause some sort of change. In some cases the messengers are not transported very far and may even act in same general area where they are manufactured. Hormones are effective in minute amounts and they are short-lived.
Plant hormones are important in a number of ways. They are involved in growth, cell division, seed germination, flowering, tissue differentiation, dormancy and other vital activities. Hormonal control is however slow process.
After hormone is transported there is delay between its release, its arrival at target cells, and its action in body so response to stimulus that induce secretion of hormones is not immediate.
Auxins are a class of hormones that largely function in growth regulation in plants. They are very small molecules with far reaching effects. The principal naturally occurring auxin is indole acetic acid (IAA).
The synthetic auxins are economic than IAA to produce and often more active in plants.
| Synthetic Auxin | Application |
|---|---|
| NAA (Naphthalene acetic acid) / Indole propionic acid | Stimulates fruiting, helps mature fruit. Sometimes causes fruit setting in absence of pollination (parthenocarpy) |
| 2,4-D (2,4-Dichloro phenoxy acetic acid) | Selective weed killer. Kills broad leaved species (dicots). Used in cereal crops and lawns to eliminate weeds |
| IPC | Inhibits sprouting of potatoes |
| NAA | Prevents premature fruit drop (retard abscission) |
The gibberellins are class of plant hormones that promote stem elongation and function in plant reproduction. They received their name from fungus in which they were first found, Gibberella fujikuroi.
Cytokinins are a class of plant hormones that stimulate cell division and retard leaf aging. Plant researchers first learned about cytokinin by using coconut milk in cell cultures. They knew that some hormone in coconut milk was encouraging cell division in their cultures. For the first time cytokinin was isolated in 1964 and named zeatin.
In the late 1940's plant researchers, encouraged by discovery of growth promoting hormones, found new growth inhibiting substances. In mid 1960s, one of the inhibitors was chemically identified and named abscisic acid (ABA). A chief source of ABA today is cotton plant.
Plant responses to different environmental stimuli are largely restricted to specific growth patterns. Such growth responses in plants are called plant movements. Movements of plant organs are modified according to nature and intensity of external stimuli.
The stimuli of such growth movements are light, gravity, touch etc.
| Type | Stimulus | Examples |
|---|---|---|
| Phototropism | Light | Shoots and coleoptiles are positively phototropic. Roots are negatively phototropic. |
| Gravitropism (Geotropism) | Gravity | Shoots and coleoptiles are negatively gravitropic. Roots are positively gravitropic. |
| Chemotropism | Chemicals | Pollen tubes are positively chemotropic to chemicals produced at micropyle of ovule. |
| Hydrotropism | Water | Roots and pollen tubes are positively hydrotropic. Shoots are negatively hydrotropic. |
| Thigmotropism | Solid surface or touch | Tendrils are positively thigmotropic. Tentacles of sundew are positively thigmotropic. |
In living things, behaviour or activities occur at regular intervals which are called biorhythms or biological rhythms.
Biorhythms may occur showing periodicity of about 24 hours. These are called circadian (Latin circa = about, dien = day) which means about one day, so they are also called diurnal rhythms. If biorhythms are about 365 days, these rhythmic activities are called circannual.
The organisms come across environmental changes that are cyclical in nature, such as days, tides and seasons etc. Many organisms maintain internal rhythm or clock to predict the onset of periodic changes and to keep them prepared for these changes.
What makes biological clock is not clear. However rhythms exist in single cells so it is thought that clock must be intra-cellular. Cellular processes that may play role in timing processes are in one's genes. However environmental factors also affect to some extent. Thus biological clock is combination of rhythmical internal processes and timed events of environment.
Erwin Bunning of the University of Tubingen, Germany has shown that exposure of fruit fly Drosophila to constant conditions for 15 consecutive generations failed to eliminate the essentially 25 hr rhythm of this insect.
In animals coordination takes place by nervous coordination and chemical coordination.
The type of coordination which involves specialized cells called neurons is called nervous coordination. This type of coordination takes place with the help of neurons which are the functional and structural unit of nervous system.
Receptors detect changes in the internal and external environment of animal. The receptor may be cell, or neuron, organ or receptor organ.
Each principal type of sensation that we can experience (pain, touch, sight, sound) is called modalities of sensation. Although we experience these different modalities of sensation, nerve fibres transmit only similar impulses. Each nerve tract terminates at specific point in CNS and type of sensation is determined by point in nervous system to which fibre leads.
In skin, receptors are concerned with at least five different senses: touch, pressure, heat, cold and pain. Several types of tactile (touch) receptors are present in human skin. Touch receptors include Merkel's disks, Meissner's corpuscles and free nerve endings.
These lie in the papillae that extend into ridges of fingertips. The corpuscle consists of spirally and much twisted endings, each of which ends in a knob.
Pressure in skin is detected by bulbous Pacinian corpuscles which are located deeper in the skin and in some deep organs of body such as pancreas. Those located in the limbs probably form a basis for vibration sense.
Pain receptors are nearly 27 times more abundant than cold receptors. The cold receptors are not distributed evenly over entire surface of body. Touch receptors are much more numerous in finger tips than in skin of back, as might be expected in view of normal function of those two parts of body.
The stimulus received by receptor in skin which are the endings of sensory neurons is passed to motor neurons via inter or associative neurons which are present in brain and via spinal cord. Impulse is sent by motor neurons to effectors, which are muscles and glands.
Neurons are chief structural and functional unit of nervous system. They are highly specialized cells capable of conducting electro-chemical nerve impulses.
Neurons are protected, supported and insulated by surrounding neuroglia (or glia cells). Neuroglia cells make up as much as half of nervous system. Neuroglia are smaller than neurons and five to ten times as abundant. There are several types of neuroglia.
Neuron consists of cell body which contains nucleus and most of cell's cytoplasm. The cytoplasm includes various organelles such as ribosomes, an endoplasmic reticulum, Nissl's granules, microtubules, mitochondria etc. Two major types of processes extend from cell body: the dendrites and the axons.
The axons of many neurons outside the brain and spinal cord are covered by flattened and rolled Schwann cells, that contain fatty material called myelin forming myelin sheath. Nodes of Ranvier are spaces along a myelin of neuron that are gaps between individual Schwann cells.
There are three functional types of neurons:
The structures which respond when they are stimulated by impulse coming via motor neuron. The principal effectors are glands which respond by secreting and muscles which respond by contracting.
Reflex arc is the pathway of passage of impulse during a reflex action. Reflex action is type of involuntary action.
Reflex involves receptors, neurons and effectors. The direction of stimulus is from receptor to sensory neurons, then from sensory neurons to associative neurons and finally from associative neuron to effectors.
Receptor → Sensory neuron → Association neuron → Motor neuron → Effector
In the reflex arc, messages are generated in special receptors called stretch receptors that respond when it is elongated. The message is then transmitted to sensory neuron, which enters the spinal column through dorsal root of spinal nerve. The sensory neuron then excites the proper motor neuron. The motor neuron leaves the spinal cord through ventral root of spinal nerve and travels outward to effector (muscle group). In most of the reflex arcs, impulse is transmitted from sensory to motor neurons by an inter neuron.
Example: Pain withdrawal reflex - when a body part touches a damaging stimulus, the sensory neuron carries action potentials to muscles, causing them to contract and withdraw the body part from the damaging stimulus.
Nerve impulse is a wave of electrochemical changes, which travels along the length of neuron involving chemical reaction and movement of ions across the cell membrane.
The electrical potential that exists across a cell membrane is known as membrane potential. In case of neuron, the charges are positive and negative ions and charge separating barrier is plasma membrane.
The resting potential in a neuron refers to the period when no impulses are being transmitted. Resting neuron is polarized, that is the condition in which electrical charges outside the axon's plasma membrane are different from those inside. Specifically resting neuron is more negative inside than outside. Typically this potential difference is about -70 mV.
Action potential in a neuron is a travelling depolarizing wave, a short-lived change in membrane potential that produces nerve impulses.
When a neuron is stimulated the point of stimulus becomes suddenly and briefly depolarized (without positively and negatively charged areas) and depolarization moves rapidly along the length of neuron followed within about 1 millisecond by repolarization. The depolarization is created by rapid change in membrane permeability and corresponding shift in ions. This shift of ions and electrical charges produces action potential.
Soon after the passage of the impulse there is movement of small number of K+ ions inward. It restores the resting membrane potential. This neuron is ready to conduct another impulse.
In myelinated neuron, the impulse jumps from node to node (Nodes of Ranvier). This is called "saltatory impulses".
The normal speed of nerve impulse in man is 100 meters per second. The maximum speed recorded is 120 meters per second.
A synapse is a junction between one neuron and next, across which impulse passes, or between neuron and muscle cells.
In cells communicating by electrical synapses the impulse travels directly from one cell to another cell. It permits very rapid transmission of an impulse with no interruption but they are very rare.
In chemical synapse an electrochemical nerve impulse is converted into chemical signal that forms a bridge across the synapse between neurons. This bridge allows the chemical signal to pass to adjacent cells.
The action potential cannot jump from one neuron to next directly. Rather the message is transmitted across synapse in form of chemical messenger called neurotransmitters. Neurotransmitters are chemicals which are released at axon ending of neurons at synapse.
Types of Neurotransmitters:
This transmission is always one way. When synaptic neuron (one carrying the impulse) reaches the synapse, it initiates a series of events in synaptic bulbs, which are located at ends of axon terminals. Within the synaptic bulbs are thousands of synaptic vesicles filled with neurotransmitters.
Hydra has diffused nervous system. The nervous system has network of neurons, which is present between ectoderm and endoderm. There is no head in this animal so there is no centralized nervous system i.e. no brain and nerve cords etc. However a cluster of neuron cell bodies forming ganglia can be seen here and there.
These neurons are so arranged in network that it is not possible to distinguish them in connected functional types of neurons as in higher animals i.e. no sensory, associative (inter/relay) neurons or motor neurons. There are no specialized sense organs or brain in this animal.
It has been observed that when any appropriate stimulus is given, Hydra responds and whole body responds as a unit. The tentacles are more responsive and react to stimulus instantaneously.
Planaria has centralized nervous system.
Brain and spinal cord both are soft portions of the body so they are well protected. Cranium which is part of skull protects the brain and neural arches. The spinal cord is protected by vertebrae of vertebral column. The brain and spinal cord are directly enclosed by tough elastic coverings called meninges. The spaces between these membranes and cavities within brain itself are filled with pressurized shock-absorbing cerebrospinal fluid.
The central nervous system of man is divided into two portions: brain and spinal cord.
Human brain consists of three regions:
It is the largest and most dominant part of human brain. It is further divided into:
The thalamus is located at the base of forebrain. It consists of densely packed neurons which provide connection between forebrain and hindbrain.
The limbic system is located in an area between thalamus and cerebrum. Limbic system works together to produce our more basic and primitive emotions, drives and behaviour such as hunger, rage, pleasure etc. Memory is formed in some of the portion of limbic system.
The limbic system consists of:
Cerebrum is the largest part of brain and is divided into two halves called cerebral hemispheres. These halves communicate with each other by means of a band of axons called corpus callosum. Tens of billions of neurons are packed in this part.
The outer region, the cerebral cortex, forms folds called convolutions which greatly increase its surface area. This part receives sensory information, processes it, stores some in memory for future use, directs voluntary movements and is responsible for poorly understood process that we call thinking. The left cerebral hemisphere controls right side of body and right controls left side.
Cerebral Cortex: The outer layer of cerebrum is called cerebral cortex which is of gray unmyelinated cells. It receives signals from sensory organs such as eyes and ears. This area is also involved in speech and also interprets sensations of touch from all parts of body. It is also a center for sending impulses to voluntary muscles controlling movements. This is also involved in intelligence, reasoning and judgement.
Midbrain connects the hindbrain and forebrain. It is very reduced in humans and processes information from ears and eyes. Midbrain contains reticular formation which is very important in screening the input information before they reach higher brain centers.
Hindbrain consists of medulla, pons and cerebellum.
The medulla oblongata is directly connected to spinal cord and has centers of nuclei that help regulate such functions as breathing rate, blood pressure and heart rate. All communication between brain and spinal column must pass through medulla.
Pons which is just above the medulla contains ascending and descending nerve tracts that run between brain and spinal cord. It appears to influence transitions between sleep and wakefulness and rate or pattern of breathing.
Cerebellum is a large bulbous structure with general appearance of two halves of an enlarged walnut. It guides smooth and accurate motions and initiates body position. The cerebellum is also involved in learning and memory storage for behaviour. It is best developed in birds, which engage in complex activity of flight.
The spinal cord is a cylinder of nervous tissue that extends from medulla oblongata of brain. It is sheltered in vertebral column. It is made up of very large number of neurons, the cell fibers and bodies of which are arranged in a definite pattern.
In cross section the spinal cord shows two areas:
Peripheral nervous system includes all the neural structures that lie outside the central nervous system. It comprises sensory neurons and motor neurons, which may form ganglia and nerves. Ganglia are the concentrations of cell bodies of neurons. The nerves are the bundles of axons or dendrites, bounded by connective tissues.
Peripheral nervous system is further divided into two functionally different systems:
It includes sensory pathway and motor pathways. The control of voluntary movements which are under conscious control of body involving skeletal muscles.
The autonomic nervous system is essentially a motor system. This means that it carries impulses from brain and spinal cord to organs it serves. The general function of autonomic nervous system is to promote homeostasis.
This system is generally active during emergency or threatening conditions. It is often referred to as the "fight or flight" system. This system accelerates the heart beat and dilates bronchi and inhibits digestive tract.
A few cranial nerves including the vagus nerve together with fibers from the bottom portion of spinal cord form the parasympathetic nervous system. This system is active when the body is calm and at rest and controls such responses as contraction of pupils, promoting digestion of food, and retards heartbeat.
This is a nervous disorder in which involuntary tremors and diminishing of motor power and rigidity occurs. Onset of this disease is in 50's and 60's.
Cause: It causes cell death in brain area which produces dopamine. The disease is slowly progressive and patient may result by head trauma.
Drugs: Drugs available are (i) L-dopa (ii) naturally occurring protein called glial cell line derived neuro-trophic factor (GDNF).
It is one of the convulsive disorders of nervous system which are characterized by abrupt transient symptoms of motor, sensory, psychic or autonomic nature frequently associated with changes in consciousness. These changes are believed to be secondary to sudden transient alterations in brain function associated with excessive rapid electric discharges in gray matter.
The onset of epilepsy is usually before age 30. Later age onset suggests organic disease. In some patients, emotional disturbances play a significant trigger role.
Treatment: Electroencephalography is most important test in study of epilepsy. Anticonvulsant drugs are used. Alcohol aggravates the situation.
Alzheimer's disease was first described by Alois Alzheimer in 1907.
Symptoms: The brain functioning is highly affected. The memory is lost in this disease.
Causes: The causes of this disease are genetic so it runs in families. High levels of aluminium is also a reason.
Nicotine affects post-synaptic membrane in CNS and PNS. It minimizes the action of acetylcholine on nicotine receptors so it is stimulant of nerve impulse. The effects of this drug are increased heart beat, blood pressure and digestive tract mobility. Nicotine may induce vomiting and diarrhea and even may cause water retention by kidneys.
Chemical coordination takes place with the help of endocrine system which comprises endocrine glands in various parts of body which secrete hormones. The endocrine glands are ductless glands.
Hormones are organic compounds of varying complexity. They are effective in minute quantities. They are poured directly into blood which cause changes only in target cells that respond to hormone.
Functions: They do not initiate new biochemical reactions but produce their effects by regulating enzymatic and other chemical reactions. Hormones may also control some long-term changes such as rate of growth, rate of metabolic activity and sexual maturity.
Chemical Composition:
It is a part of forebrain. It is here that many of sensory stimuli of nervous system are converted into hormonal responses. It is believed that oxytocin and antidiuretic hormone (ADH) are produced in hypothalamus and travel down the nerves to the posterior lobe of pituitary to be stored. They are released from their storage after receiving nerve impulses from hypothalamus.
It is a tiny lobed structure about size of kidney bean. It is about 0.5 gm in the adult and is connected to brain through a short stalk called infundibulum.
It has three lobes: anterior, median and posterior. The anterior lobe is referred to as "master gland" because in addition to producing primary hormones it produces the trophic hormones which control the secretion of hormones in many of other endocrine glands.
Somatotrophin releasing factor (SRF) is secreted from hypothalamus throughout life. It is essential for normal growth. Although bones and muscles are their major targets, if it is too much secreted then it can produce pituitary giants (gigantism) which leads to abnormal development. People severely affected by this condition may grow to be 7 to 9 feet tall. If there is under secretion, dwarfism results.
Also known as thyrotrophin. The release of TSH from hypothalamus is controlled by levels of thyroxine in blood. In presence of low levels of thyroxine, there is increasing production of TSH. It acts on thyroid gland. It is secreted throughout life but particularly reaches high levels during periods of rapid growth and development. It acts directly on cells of the thyroid gland increasing both their numbers and their secretory activity.
First stimulated by hypothalamus and is then regulated by negative feedback control system. The target of ACTH is cortex of adrenal gland. Excess and deficiency results in disturbance of normal adrenal function.
These are follicle stimulating hormone (FSH), luteinizing hormone (LH) and prolactin.
FSH: In females it stimulates follicle development and secretion of estrogens from the ovaries. In males stimulates development of germinal epithelium of testis and sperm production.
LH: Works with FSH to stimulate estrogen secretion and rupture of mature follicles to release egg or ovum. It also causes the lutenisation of the follicle and acts synergistically with prolactin to maintain corpus luteum. In males it stimulates interstitial cells of testes to secrete testosterone.
Prolactin: Promotes milk production in mammals. Toward the end of pregnancy the blood level of prolactin increases dramatically as mother prepares to nurse her offspring.
Melanophore Stimulating Hormone (MSH): Its secretion is controlled by hypothalamus. External light governs its secretion. During pregnancy its secretion increases. It stimulates melanocytes in skin to produce brown pigment melanin which darkens the skin. Excess MSH is secreted in Addison's disease in which skin becomes dark.
Antidiuretic Hormone (ADH) or Vasopressin: Antidiuretic is an agent that decreases urine volume by bringing about an increase in the recovery of water by urine collecting ducts of kidney. It is secreted when there is decrease in blood pressure, blood volume and osmotic pressure of blood detected by osmoreceptors in hypothalamus. A lack of this hormone produces diabetes insipidus in which large quantities of urine is excreted and patient feels great thirst.
Oxytocin: Its release depends upon the decrease in progesterone level in blood and neural stimuli during parturition and suckling. Primary action is on smooth muscle, particularly uterus during childbirth and causes milk ejection from mammary gland.
The thyroid gland is shaped somewhat like a bow tie and is located in front of the larynx. It secretes three hormones:
T4 and T3 have same targets and action, but whereas T4 is more abundant, T3 is much more powerful.
Functions:
This is the third hormone and works in concert with hormone from parathyroid glands in regulating calcium ion level in blood. Calcitonin inhibits bone breakdown and accelerates the uptake of calcium ions by bone, thereby lowering blood level of calcium.
Parathyroid glands are pea-sized bodies embedded in the posterior part of lateral lobes of thyroid. These produce hormone called parathormone. This is a polypeptide that helps raise the calcium levels of the blood acting as an antagonist of calcitonin.
Effects of Parathormone: Increases calcium ion concentration in blood, decreases calcium excretion by kidneys, speeds calcium uptake by intestine and increases calcium release from bones into blood stream.
Abnormalities: Low levels of parathyroid hormone cause muscle convulsions and eventually death. In high level of parathyroid hormone, severe decalcification of bone (osteoporosis) occurs in which the fibrous cysts are formed in skeleton.
The pancreas is a ducted exocrine gland since its major secretions (digestive enzymes and sodium bicarbonate) are released into small intestine.
Scattered through the pancreas are groups of true endocrine cells. These clumps of cells are islets of Langerhans. Each clump consists of alpha, beta and delta cells. This hormone is under the control of STH and ACTH secreted by pituitary.
Alpha cells produce glucagon and it is released in blood stream when glucose levels fall below a certain level and increases the glucose level. It does this mainly by promoting breakdown of glycogen to glucose in liver and muscles. It also increases the rate of breakdown of fats.
Abnormalities: Glucagon abnormalities seem rare as endocrine disorders. Tumors on cells which damage alpha cells will cause excess glucagon secretion and consequent high blood glucose levels.
The beta cells secrete insulin.
Functions:
Abnormalities: Failure to produce insulin leads to a condition called diabetes mellitus. The symptoms are high level of blood sugar, sugar in urine, a disturbance of body's osmotic equilibrium. Toxic metabolites from fat also accumulate and are only lost from kidney with valuable metal cations. The body becomes dehydrated. If excess insulin is produced, the utilization of sugar is too great and its level falls in the blood which upsets nerve and muscle functioning.
"Ad" means on and "renal" means kidney, thus adrenal gland is present at the top of kidney. The outer layer of this gland is called cortex and inner is called medulla.
Adrenal cortex is active all the time but especially in shock or stress condition. It secretes aldosterone, cortisol and androgenic hormones.
Abnormalities:
The adrenal medulla produces hormones adrenaline (epinephrine) and noradrenaline (norepinephrine). Both adrenaline and noradrenaline are secreted in stress situations. They can cause specific changes in the body.
Adrenaline dilates blood vessels in certain parts of body such as skeletal muscles and increases heart output. Noradrenaline constricts blood vessels so effect of two hormones are synergistic in raising blood pressure. Adrenaline and noradrenaline promote the release of glucose from liver glycogen, in a way reinforcing the effects of sympathetic system.
The male gonad is called testis and female gonad is called ovary.
The ovary produces two hormones: estrogens and progesterone.
Oestrogens are secreted by ripening follicles whose development has been stimulated by FSH from pituitary.
Functions:
Abnormalities: Deficiency of sex hormones leads the young to failure to mature sexually and sterility in adults.
It is produced by ruptured follicle in response to LH from pituitary.
Functions:
The testis consists of many coiled seminiferous tubules where the spermatozoa develop and between the tubules region of interstitial cells the hormones testosterone and dehydroxy testosterone are produced.
Testosterone initiates the development of sex organs in foetus. At puberty it brings about development of male secondary characters. The castrated male fails to develop secondary sexual characteristics and his body tends more towards the form of immature females.
Some of the parts of gut function as endocrine tissue.
It is a type of interaction in which controlling mechanism is itself controlled by the products of reactions it is controlling.
Hormone secretion is regulated by feedback mechanism. For proper functioning two opposing systems are required:
In this way concentration of secretions is itself controlled because certain information is passed to the source, in other words, is "fed back" so that the output of secretion is adjusted accordingly depending on the body needs.
The interaction between pituitary and other endocrine gland is considered best example of feedback control. Feedback of thyroid gland function is as follows:
The levels of both hormones are thus kept within tight limits because of the influence they exert on each other. This is called negative feedback.
| Nervous Coordination | Chemical Coordination |
|---|---|
| Neurons (sensory, associative and motor) are the basic units of structure and function. Neuroglial cells provide nutrition and protection to neurons. | Hormone producing cells and neurosecretory cells release hormones and are units of structure and function. |
| Chemicals produced by neuron endings act where they are produced, i.e. very close to the cells they influence, commonly less than a micrometer away. | Hormones (or neurohormones) are poured into and transported by blood. These hormones affect the target cells, which are far away from where the hormones are produced. |
| Neurons release neurotransmitter onto one or a small group of specific cells. | The blood-borne hormones bathe millions of cells indiscriminately and only a few respond to these hormones. |
| Show immediate effect or show response to a stimulus instantly. | May have immediate effects (e.g. insulin), but mostly hormones have prolonged or delayed effects (e.g. growth hormones). |
| Control is affected through the electrical signals that travel within the cell itself. | Control involves only chemical stimulation and the target cells are far away from them. |
| Shows faster or rapid effect. Speed of impulse in most cases is 100 m/s; maximum speed recorded in human beings is 120 m/s. | It is not very rapid, but shows slow but prolonged effects. |
| The neurotransmitters are short-lived, broken down shortly after their release. Effects tend to be of much shorter duration. | Hormones remain active for much longer duration within the blood and thus have much longer duration for their actions. |
Behaviour is defined as a change in response to stimulus. In other words, animal behaviour is the sum of everything that animals do, i.e. flying, walking, sitting, sleeping, eating, mating, rearing young ones, etc.
Behaviour is divided into two main types:
It is a collection of responses that are predetermined by the inheritance of specific nerve or cytoplasmic pathways in multicellular or unicellular organisms. As a result of the built-in pathways, a given stimulus would produce invariably the same response. All plant behaviour is innate.
Importance: These behaviour patterns have been developed and refined over many generations and their primary adaptive significance lies in their survival value to the species. Another importance is the economy it places on nerve pathways since it does not demand higher centers of nervous system.
Kinesis: This is behaviour of organism which is performed without attention to its position in space. The organism changes the speed of random movements which help them in surviving in environment, e.g. this type of behaviour allows pill bugs to reach moist area which is necessary for their life.
Taxes: When an organism moves toward or away from a source of stimulation, the action is called taxis. The stimuli may be light, chemicals etc.
Reflexes: Among the simplest forms of behaviour are reflexes, simple reactions to external stimulation. A stimulus such as light intensity or touch can trigger an automatic, involuntary response. A classic example is human knee-jerk reflex. These include biological rhythms, territorial behaviour, courtship, mating, aggression etc.
Darwin was first who gave the definition of instinct behaviour. According to him it is complex reflexes made up of units compatible with mechanisms of inheritance and thus a product of natural selection, that had evolved together with other aspects of life.
Sign Stimulus: The early ethologists thought that animals sometimes respond instinctively to specific though often complex stimuli. Such stimulus is called sign stimulus. For example, male three-spined stickleback has red belly in breeding season. This is sign stimulus which makes it aggressive to other territorial males.
Thorpe defined learning as "that process which manifests itself by adaptive changes in individual behaviour as a result of experiences".
It is another form of learning which can be seen in ducks, birds, geese etc. After hatching, these young birds soon have the tendency to follow those objects which are moving in front of them and show a brief sensitive period during which the shape or form of objects can be imprinted. Due to this behaviour the young birds will follow those imprinted objects. Usually the first moving object in front of the young is his mother and therefore will adapt and learn from her appearance and follow her. However, if the parent is absent, the young bird may imprint on other species of birds, human beings or any other moving object. In later life such birds will attempt to court and mate with imprinted objects instead of adults of their own species.
Habituation is the simplest form of learning and involves modification of behaviour through a diminution of response to repeated stimuli. A loss of receptivity to repetitions stimuli can be useful in preventing a drain of energy and attention for trivial purposes.
Examples:
Involves the pairing of an irrelevant stimulus with a natural primary stimulus that elicits an automatic response.
Example: Pavlov conditioned the dogs to secrete saliva on ringing of the bell, which is not normal stimulus for secretion of saliva. In his experiments, he would ring the bell just before giving food to the dogs, so the dogs became conditioned to secondary stimulus or conditioned stimulus (ringing of bell) and started secreting saliva in response to it as if it were the natural stimulus.
Also called trial and error learning. It is a more complex type of learning than habituation. This type of learning has been demonstrated and studied by Thorndike and B.F. Skinner. Under natural conditions, the achievement of a particular goal is the reward that directs random activities into a habitual action by a trial and error repetitions, step by step.
Example: Experiments on rats were performed to run a maze to either get or find food, or to depress a lever and come out of the cage. In this case first experiment is accidental and then it is rewarded, animal acts with latter experience.
Thorpe defined latent learning as the association of indifferent stimuli or situations without patent reward.
Example: Suppose we put a rat in a maze as it wanders about and accidentally gets food. If we put the rat in the same maze again, it may directly reach the food. That means when the rat was wandering, it did learn something without even the incentive of any reward.
Keller performed many experiments on chimpanzees and showed that they have higher form of learning called insight learning. Insight learning is an extreme case of behavioural modification involving the application of insight or reasoning to a novel situation. If an animal can direct its behaviour to solve a problem for which it has no previous experience then reasoning is involved. This is the highest form of learning.
Example: A chimpanzee is placed in a cage in which a choice piece of fruit hangs from the ceiling. The chimp cannot reach the fruit, but the keeper has placed some boxes of different sizes in the cage. After a short period of head scratching, the chimp moves the largest box and piles other smaller boxes over it, and climbs up to reach the fruit.