- Control is the power of regulation by which something can be started, slowed down, expedited or stopped. Working together of various systems in a body to adjust the vital activities of life is called coordination.
- Integration is the process which makes two or more organs work as a functional unit in harmony.
- The coordination and integration in animals are brought about by the nervous and endocrine system. In plants, it is brought about by certain chemicals known as phytohormones or plant hormones
- Movement is an attempt by living organisms to bring about a change of position either due to growth or changes in their environment to their advantage.
- Some movements like germination in seed, flowering etc., are caused due to growth.
Movements like the running of a cat, children playing on swings, buffaloes chewing cud are growth independent movements.
Animals - Nervous System
- When we touch a hot object, we detect the change in the environment and respond by immediately withdrawing our hand. This also helps us to protect ourselves.
- The stimulus is an agent, factor, chemical or change in external or internal environment which brings about the reaction in the organism.
- All information from the environment is detected by the specialised tips of some nerve cells present in tissues and organs. These are called receptors. They are located in our sense organs like nose, tongue, skin, eye and inner ear.
- Sensory receptors are of different types. Photoreceptors, phonoreceptors, olfactoreceptors, gustatoreceptors, thermoreceptors and so on. They detect light, sound, smell, taste, heat and cold respectively.
- The above mentioned receptors initiate electrical impulses to be picked up by sensory nerves. This impulse travels in a neuron from the dendrite to the cell body, and then along the axon to its end. Axon ending of one neuron is placed close to dendrites of the next neuron. This junction is called a synapse or gap. As soon as the impulse reaches the end of the neuron it sets off the release of some chemicals (Neurotransmitters).
- These chemicals cross the gap or synapse and start a similar electrical impulse in the dendrite of the next neuron. Finally, the impulse reaches a muscle or a gland.
- Effectors are muscles, glands, tissues or cells which act in response to a stimulus received by the nervous system.
- Nervous system comprises of sense organs, nerves and neurons that form a network throughout the body for conducting information via electrical impulses. Nerve cell or neuron is the structural and functional unit of the nervous system.
Try yourself:In a synapse, chemical signal is transmitted from
In a synapse, the electrical signal is 'translated' into the neurotransmitter by the presynaptic neuron the chemical diffuses (swims) across the synaptic cleft until it reaches the other neuron. The signal thus travels from the axonal end of one neuron to the dendritic end of the next neuron.
Thus, the correct answer is option D.
The Human Brain
- Human nervous system consists of three divisions: central nervous system (CNS), peripheral nervous system (PNS) and autonomic nervous system (ANS).
- Brain and spinal cord constitute the central nervous system (CNS). The nerves arising from the brain (cranial nerves) and nerves arising from the spinal cord (spinal nerves) constitute the peripheral nervous system.
- The human brain is protected by a bony skull, also called the cranium. Internal to the skull it is covered from outside by three membranes called meninges. In between the meninges, there is a fluid called cerebrospinal fluid. Beneath the membranes brain is subdivided into three major parts namely the forebrain, midbrain and hindbrain.
- Fore-brain is the main thinking part of the brain. It has different regions or areas such as:
(i) Sensory area - It receives sensory impulses from various receptors.
(ii) Auditory area - It is concerned with hearing.
(iii) Olfactory area - It is concerned with the smell.
(iv) Gustatory area - It is concerned with taste.
(v) Optic area - It is concerned with sight.
(vi) Association area - This area interprets various sensory information and makes a decision on how to respond.
(vii) Motor area - Decisions made by association area are passed on to this area which controls the movement of voluntary muscles.
- Midbrain comprises of four lobes. The actions of involuntary muscles are controlled by the mid-brain and hind-brain.
Try yourself:The brain is responsible for -----------------.
The cerebellum is the convoluted subdivision of the brain stem and is associated with the coordination of muscular movement, muscle tone and balance. Medulla oblongata controls consciousness and arousal (the reticular formation) and its cardiovascular reflex centre controls the heartbeat. The cerebrum is the largest and uppermost division of the brain. It is the centre for higher thought processes required for learning, memory, language and speech. The correct answer is D.