Topics to be learn : Introduction Animals – nervous system Coordination in plants. Hormones in animals

Introduction :

• Movements: Visible movements are associated with life. Movements are thought to be a response to a change in the environment of the organism.
• Living organisms respond and react to their environment.
• The response to stimulus such as light, heat and cold varies in different organisms. It should be carefully controlled.
• Control and Coordination: Living organisms must use systems which provide control and coordination.
• Depending on the body organisation in multicellular organisms, specialised tissues are used to provide control and coordinated movements.
• In animals, such control and coordination are provided by nervous and muscular tissues.
• Plants do not have elaborate systems for control and coordination as in animals. .
• Growth and movement in plants are regulated by both external and internal factors. Plants show movements which are dependent on growth

Animals – nervous system :

Receptors  : Animals receive a variety of external information through specialized structures called receptors. They are located in our sense organs like inner ears, the nose, the tongue, etc.

Receptors are of the following types:

• Photoreceptors: They detect light.
• Phonoreceptors: They detect sound.
• Olfactoreceptors: They detect smell.
• Gustatory receptors: They detect taste.

Importance of receptors :

• Receptors are usually present in sense organs. They make us aware about changes in the environment, so that our body can respond according to the sensation our receptors convey.
• Suppose touching a hot object is not conveyed immediately and properly due to the mal-functioning of receptors of touch, it may become a dangerous situation for us.

Neuron :

• Neuron is the structural and functional unit of nervous system.
• There is a network of nerve cells or neurons in the nervous system. It is specialised for conducting information via electrical impulses from one part of the body to another.

Structure of neuron :

• A neuron has three components: (i) cell body, (ii) dendrites, and (ii) axon.

• The functional junction or neuromuscular junction between the two neurons is called Synapse.

• Dendrites conduct a nerve impulse towards cell body. It receives information from axon of other neuron through synapsis
• Axon conducts impulses away from the cell body to another neuron or tissue through Synapsis.

Synapse: The junction point between two neurons is called synapse. It is the junction between the axon of one neuron and the dendrite of next neuron in the chain. At the synapse, the axon and the dendrite do not touch each other, there is a small gap between the two. The message passes from one neuron to other neuron through synapse by a chemical called neurotransmitter

Schematics of travelling nerve impulses in the body :

• A neuron acquires information through dendrites.

• This information acquired at the end of the dendrite tip of a neuron sets off a chemical reaction that creates an electric impulse.
• This impulse travels from the dendrite to the cell body and then along the axon to its end.
• At the end of the axon, the electrical impulse sets off the release of some chemicals.
• These chemicals cross the gap or synapse and start a similar electrical impulse in a dendrite of the next neuron.

Thus, information is transmitted from one neuron to the other.

Sensory neurons and motor neurons : Sensory neurons carry sensory impulse from receptor to central nervous system whereas motor neurons carry impulse from central nervous system to effector organ.

Autonomic nervous system : Many activities of the internal organs like heart, blood vessels and glands are controlled by autonomic nervous system. Autonomic nervous system is divided into (i) sympathetic, and (ii) para-sympathetic systems.

Voluntary movements: Voluntary movements of body organs are those which are under control of our will. For example, movement of arms or legs.

Involuntary movements; Involuntary movements are those which are not in control of will. For example, beating of heart and peristalisis in intestine. These movements are controlled by the brain.

What happens in Reflex Actions? :

• Reflex action is defined as a quick, automatic involuntary and often unconscious action brought about when the receptors are stimulated by external or internal stimuli. The path along which the action is carried out is called reflex arc.
• Reflex arc : Reflex actions are controlled by CNS. Reflex arc is the structural or functional unit of reflex action.

• When we touch a hot object, receptors of heat in skin receive the sensation. This sensation of heat is acquired by dendrites of sensory neuron. This information travels as electric impulse along the sensory neuron to the relay neuron in the spinal cord, which passes information to effector i.e., muscles in arm through motor neuron.

• Most of the reflex actions are controlled by spinal cord. But there are some reflex actions which involve brain. Such reflex actions are termed as cerebral reflexes.
• Examples of cerebral reflexes are salivation at sight or smell of food, contraction of pupil of human eye in the presence of bright light and peristalsis.

Human nervous system :

Human nervous system is composed of (i) central nervous system and (ii) peripheral nervous system. They receive information from all parts of the body and integrate it.

• Central nervous system consists of (i) brain, and (ii) spinal cord.
• Peripheral nervous system consists of cranial nerves (which arise from brain) and spinal nerves (which arise from spinal cord).
• Peripheral nervous system helps in the communication between central nervous system and other body parts.

Human brain :

• Brain is the main coordinating centre in the body.
• It has complex mechanisms and more neural connections for thinking in man.
• It receives information carrying impulses from all the sensory organs of the body and also from the spinal cord.
• The brain responds to the information by sending its own instructions to the muscles and glands to act accordingly.
• The brain also stores information and acts as organ of thought and intelligence.

Structure :

• Human brain is lodged in a bony case, the cranium which protects it from injuries.
• It is wrapped in three sheets of connective tissue, known as meninges.
• The space between the meninges is filled with cerebrospinal fluid which helps in absorption of shocks.

There are three parts of brain: (i) Fore-brain, (ii) Mid-brain and (iii) Hind-brain.

(i) Fore-brain: It consists of two main parts—Cerebrum and Olfactory lobes.

(a) Cerebrum:

• It forms about two-third of the human brain
• A deep longitudinal fissure divides the cerebrum into two hemispheres which are held together by a horizontal sheet of fibrous tissue.
• Cerebrum contains an outer grey matter and an inner white matter.
• Grey matter shows many convolutions which are directly inked with intelligence of the organism.
• Cerebrum controls the function of perception of smell, sight, hearing, ability of speech and movements of various parts of the body.
• Various mental abilities like thinking, reasoning, memorising, consciousness and sense of responsibility are the different abilities which are controlled by cerebrum. Cerebrum also has different lobes which receive and respond to stimuli received from sense organs.

(b) Olfactory lobes: It is the part of forebrain which is associated with the smell. It is poorly developed in human beings.

The fore brain is the main thinking part of the brain. It has regions which receive sensory impulses from various receptors. (i) Optical lobe is the region for visual reception.(ii) Temporal lobe is the region for auditory reception. (iii) Parietal lobe is related with touch, smell, temperature and conscious association. (iv) Frontal lobe is a region for muscular activities.

(ii) The mid-brain: It is a small region which connects hind-brain with fore-brain

• Involuntary actions are controlled by the mid-brain and hind-brain.
• Mid-brain controls optic reflex such as changes in the size of the pupil.

(iii) The hind-brain: It consists of three centres, namely, cerebellum, pons and medulla oblongata.

• Cerebellum : It is a part of hind brain is responsible for precision of voluntary action and maintaining the posture and balance of the body.
• Activities like walking in a straight line, riding a bicycle, picking up a pencil. These are possible due to a part of the hind-brain called the cerebellum.
• Pons: It serves as a link between the cerebral cortex and the cerebellum. It regulates some aspects of respiration.
• Medulla oblongata: It is the regulating centre for swallowing, coughing, sneezing and vomiting. It also takes part in regulation of heart beat and breathing rates.

The spinal cord:

• The spinal cord is cylindrical and has the same diameter as the little finger.
• Medulla of the brain extends downwards to form spinal cord that lies protected in the backbone (or vertebral column).
• In the centre, it has a fluid filled cavity called central canal.
• The spinal cord conducts impulses to and fro from the brain.
• It also acts as reflex centre.
• Spinal cord is formed of two types of nervous tissues, the grey matter and white matter.
• The grey matter surrounds the central canal while the white matter lies outside the grey matter. The grey matter is entirely made up of nerve cells. Two upward and two downward dorsal and ventral horns can be seen in the T.S. of spinal cord.

Functions of spinal cord:

• All the stimuli and responses are passed from and to the brain through the spinal cord.
• It is the centre of reflex actions.

Autonomic nervous system :

• The specific set of nerves that mainly controls and integrates the functions of internal organs is called autonomic nervous system.
• It controls the body organs, such as heart, blood vessels glands, lungs, stomach and uterus in the body; these are not directly under control of our will.

 Autonomic nervous system consists of:

(i) sympathetic and (ii) para-sympathetic systems. They have opposite effects on the organ i.e., if one stimulates the organ, the other inhibits its action.

How does the Nervous Tissue cause Action?

• Brain collects information from the body through nerves, makes decisions based on the information and conveys decisions to muscles for action.
• When a nerve impulse reaches the muscle, the muscle fibre must move.
• Muscle cells have special proteins that change both their shape and their arrangement in the cell in response to nervous electrical impulses.
• New arrangement of these proteins gives the muscle cells a shorter form and this leads to movement of the muscles.
• After the action is over, reverse process takes place and the muscles take their original size and shape.
• All information from our environment is detected by specialised tips of some nerve cells.
• Specialised tips of nerve cells are called receptors.
• They are located in our sense organs such as inner ear, the nose, the tongue, etc.

Coordination in plants :

Movement Due to Growth :

Tropic movement :

The directional response of plants towards or away from the stimulus such as light, water, gravity, etc., is known as tropism.

• Tropic movements in plants occur due to growth. Plants respond to stimuli slowly by growing in a particular direction, either towards stimulus or away from stimulus. Example: Bending of shoot towards light
• Because of growth it appears as if plant is moving. The growth related tropic movements are regulated by a plant hormone called auxin.

Nastic movements :

• This movement is neither towards nor away from the stimulus.
• Example: Bending and drooping of ‘touch-me-not’ leaves on touching.

Photoperiodism :  The phenomenon of regulation of flowering and germination of seeds photoperiodic stimulus is called photoperiodism.

Geotropism :

The upward growth of shoot and downward growth of roots in response to the pull of earth or gravity is known as geotropism.

Experiment: Take a small healthy potted plant make hole at the bottom of the pot.

Place the potted plant at a safe space III horizontal position as shown in Fig. Water the plant time to time.

After some days, you will find the shoot is growing upwards, that is, away from the force of gravity (negative geotropism) and, the roots coming out of the bottom of the pot are growing downwards, that is, towards the force of gravity (positive geotropism).

Chemotropism : The movement of a plant in response to a chemical stimulus is called chemotropism

• Example : Growth of pollen tubes towards ovules being stimulated by sugary substance (Lactic Acid) secreted by the stigma, the style and the, ovary.

Hydrotropism: Growth movements in response to the stimulus of moisture (water) are termed as hydrotropic movements (hydrotropism).

Experiment:

• Take two troughs A and B and fill them with soil. In the trough B place a small claypot. Now plant a small seedling in both troughs.
• Water the soil of trough A uniformly but in trough B put water in clay pot only.
• After a few days dig out the seedlings from both the troughs.
• The seedling in trough A which gets uniform water has straight roots while roots of seedling which is in trough B grows and bends towards the clay pot containing water.

Immediate Response to Stimulus :

• At the base of each touch-me-not leaf a flat structure called pulvinus is present.
• Cells of pulvinus have abundant water and thus they are turgid.
• In this condition pulvinus keeps the leaves upright.
• When a person touches a leaf an electrical impulse is generated in the ordinary cells of leaf.
• This impulse is transmitted to pulvinus cells and as a response half of these cells losing water become flaccid.
• As a result of this, pulvinus loses firmness and the leaves fold and droop down.
• After some time of folding of leaves water from the intercellular spaces reaches to pulvinus cells and they again become turgid. This will lead to opening of leaves.

Hormones :

Hormones are chemical substances which are transported from the site of synthesis to the place of action or in other words we can say that they are chemical substances that are synthesized at one region of the body of organism and are transported to the site of action. They are needed in very small amount.

Plant Hormone:

These are special chemical compounds which are synthesised at places away from where they act and simply diffuse to the area of action. Different plant hormones control and coordinate growth, development and responses to the environment.

Auxin :

• Auxin is the plant growth hormone which is synthesized at the shoot tip

• Auxin promotes the growth of a tendril around a support.
• Auxins promote cell elongation, root formation and development of parthenocarpic fruits (development of fruits without seeds).
• It also leads to apical dominance and phototropism.

Gibberellins:

• They induce cell division, cell elongation, induce flowering, lead to development of parthenocarpic fruits.
• In some plants they also induce elongation of stem.

Cytokinins:

• They initiate cell division, cell elongation and delay aging.
• They enhance chloroplast development in leaves.

Abscisic Acid (ABA):

• Abscisic acid retards growth, promotes leaf and fruit fall and causes dormancy of seeds and bulbs. It also causes aging of leaves.

Hormones in animals

Electrical impulses are an excellent means of quick transfer of information in animals but there are limitations to the use of electrical impulses.

• Electrical impulses reach only to those cells that are connected by nervous tissue.
• Once an electrical impulse is generated in a cell and transmitted, the cell will take some time to reset its mechanisms before it can generate and transmit a new impulse i.e., cells cannot continually create and transmit electrical impulse.

Chemical communication :

Because nervous system alone cannot handle so many wide-ranging changes where many tissues are needed to meet a situation or environmental change in multicellular organisms. Therefore other means of communication are used by most multicellular organisms which is a chemical communication by hormones.

Endocrine glands :

These glands do not have ducts and pour their secretions directly into the blood.

They secrete chemical messengers called hormones.

Their secretions (hormones) help in control and coordination of the body.

Various endocrine glands :

(i) Pituitary gland  :

It controls the working of majority of endocrine glands by secreting stimulating hormones. For example, pituitary secretes

• TSH hormone which controls the secretion of thyroxine by the thyroid.
• Follicle stimulating hormone (FSH) which stimulates the ovary to produce estrogen.
• Adrenocorticotrophic hormone (ACTH)  stimulates adrenal cortex to make glucocorticoids, etc.

Due to these reasons pituitary is called master gland.

The pituitary gland has two components i.e., adenohypophysis (Anterior Part) and neurohypophysis (Posterior Part).

Anterior Part: Hormones secreted:

• ACTH (Adrenocorticotropic hormone), which controls Adrenal gland secretions.
• PRL (Prolactin) stimulates the breasts to produce milk.
• GH (Growth Hormone) deals with every cell in the body. It is helpful for growth and repair.

Posterior Part: Hormones secreted:

• Oxytocin: Affects uterine contractions in pregnancy and birth and also helps to facilitate the release of breast milk.
• ADH (Anti-diuretic hormone) controls the blood and mineral levels in the body by affecting water retention by the kidneys.

(ii) Thyroid: Hormones secreted by Thyroid are Thyroxin, Tri-iodothyroxin and Calcitonin.

• Thyroxine T₄ and Tri-iodothyroxin (T₃) regulate metabolism and body
• Calcitonin : It reduces blood calcium level by deposition in bone.

(iii) Pancreas: Hormones secreted: insulin and glucagon

• Glucagon (alfa-cells): Helps absorb glucose into liver to form glycogen. Increases blood sugar.
• Insulin (beta-cells). Regulates sugar metabolism. Helps absorb glucose from blood to tissues and also release from liver. Too little of insulin leads to high sugar level in the blood and weakness—a condition called diabetes.

(iv) Adrenal (medulla) : Chemical signals reach all cells of the body and provide the wide ranging changes needed. This is done in many animals, including human beings, using a hormone called adrenaline that is secreted from the adrenal glands.

• Adrenaline (epinephrine) is released in case of anger and fear.

• Adrenaline makes the heart beat faster, resulting in supply of more oxvgen.
• It causes reduction in supply of blood to the digestive system and skin. This diverts tile blood to our skeletal muscle.
• The breathing rate also increases.
• All these changes enable the body to protect itself from dangerous situation.

(v) Ovary : Hormones secreted: Estrogen and Progesterone

• Estrogen is a female hormone and is secreted by the ovary. It causes development of secondary female sexual characters such as development of breasts.
• Progesterone  : Maintenance of pregnancy

(vi) Testis : Testosterone is a male hormone and is secreted by the testis. It causes development of secondary male features such as the growth of moustache and beard.

(vii) Hypothalamus gland :

• Function : Regulation of the secretion of hormones from pituitary gland.
• Hypothalamus plays an important role in the release of many hormones. For example, when the level of growth hormone is low, the hypothalamus releases growth hormone releasing factor which stimulates the pituitary gland to release growth hormone.

(viii) Pineal gland : Hormones secreted- Serotonin : Constriction of blood vessels at the site of injury.

(ix) Adrenal (cortex) : Hormones secreted-Cortisone : Produced by the outside parts (cortex) of this gland. Aids conversion of proteins to sugar.

Importance of Insulin :

• Insulin hormone regulates blood sugar levels. If this is not secreted in proper amounts, the sugar level in the blood rises. This causes many harmful effects.
• Deficiency of insulin secreted by pancreas also reduces uptake of glucose (sugar) by the body tissues. This causes harmful effects on the vital organs of the body.
• To treat harmful effects of increased level of blood sugar, the diabetic patients are provided insulin by injections of insulin.

Importance of iodised salt :

• Iodine is necessary for the thyroid gland to make thyroxine hormone. Thyroxine regulates carbohydrate, protein and fat metabolism in the body to provide balanced and proper growth. Deficiency of iodine in our diet may lead to goitre, i.e., swollen neck and other metabolic disorders.
• Iodine is needed in very small quantity to synthesise thyroxine. Iodised common salt contains proper content of iodine. To avoid deficiency of iodine, iodised salt is recommended.