A reflex action is a quick, automatic and involuntary response to a stimulus, usually through a reflex arc. Walking is a voluntary activity controlled by the brain, though it involves coordinated muscle action and balance.
At a synapse, the electrical impulse at the end of one neuron causes release of chemical neurotransmitters. These chemicals cross the synaptic gap and start a new electrical impulse in the next neuron.
The cerebellum, a part of the hindbrain, maintains posture and equilibrium of the body.
The smell molecules from the agarbatti reach olfactory receptors in the nose. These receptors generate nerve impulses that travel to the brain, where the smell is interpreted.
A reflex action is mainly controlled by the spinal cord for a quick response. The brain is informed about the stimulus and response after the reflex action, and it can modulate reflexes based on experience or context.
Plant hormones are chemical substances produced in plants that coordinate growth, development and responses to stimuli. Examples include auxins, gibberellins, cytokinins and abscisic acid.
The movement of sensitive plant leaves is a rapid nastic movement caused by changes in water pressure in cells and is not directional with respect to the stimulus. Movement of a shoot towards light is phototropism; it is directional, slower and caused by unequal growth due to auxin distribution.
Auxin is a plant hormone that promotes growth, especially cell elongation in shoots.
When a tendril touches a support, auxin moves to the side away from the contact. Cells on that side elongate more, so the tendril bends towards the support and coils around it.
Place germinating seeds in moist sawdust or soil in a tray. Keep a porous pot containing water on one side so that moisture is greater near the pot. After a few days, observe the roots. They bend and grow towards the water source, demonstrating positive hydrotropism.
Chemical coordination in animals takes place through hormones secreted by endocrine glands. Hormones are released into blood and carried to target organs, where they regulate activities such as growth, metabolism, stress response and blood sugar control.
Iodised salt supplies iodine, which is needed by the thyroid gland to make thyroxine. Thyroxine regulates metabolism, and iodine deficiency can cause goitre and related disorders.
Adrenaline prepares the body for emergency action. The heart beats faster, breathing rate increases, blood flow to muscles increases, blood flow to the digestive system and skin decreases, and stored glucose is made available for energy.
Some diabetic patients do not produce enough insulin or cannot use it properly. Insulin helps cells take up glucose and lowers blood sugar level, so injections are given to control high blood glucose.
- a. Insulin
- b. Thyroxin
- c. Oestrogen
- d. Cytokinin.
Cytokinin is a plant hormone; insulin, thyroxin and oestrogen are animal hormones.
(d) Cytokinin.
- a. dendrite.
- b. synapse.
- c. axon.
- d. impulse.
The junction or gap between two neurons is a synapse.
(b) synapse.
- a. thinking.
- b. regulating the heart beat.
- c. balancing the body.
- d. all of the above.
Different parts of the brain control thinking, heart beat and balance.
(d) all of the above.
Receptors detect stimuli such as light, sound, smell, taste, touch, heat or pain and send signals to the nervous system. If receptors do not work properly, the body may fail to detect danger or changes in the environment, such as not smelling smoke, not feeling burns, or having poor vision or hearing.
A neuron has dendrites, a cell body with nucleus, a long axon and axon terminals. Dendrites receive information from receptors or other neurons. The impulse passes through the cell body and along the axon. At the axon terminal, chemicals are released across the synapse to pass the signal to another neuron, muscle or gland.
Phototropism occurs because auxin distribution becomes unequal when light comes from one side. Auxin accumulates on the shaded side of the shoot, causing those cells to elongate more. The shoot bends towards the light.
Signals between the brain and body parts below the injury will be disrupted, including sensory signals to the brain and motor signals from the brain. Reflex actions controlled by the injured part of the spinal cord may also be affected.
Chemical coordination in plants occurs through plant hormones. Auxins, gibberellins, cytokinins, abscisic acid and other hormones move from where they are produced to other tissues and regulate growth, cell division, dormancy, wilting, and responses to light, gravity and water.
An organism has many organs and tissues working at the same time. Control and coordination are needed so that responses to stimuli are quick, body functions are regulated, and different parts work together efficiently for survival.
Involuntary actions are automatic actions not under conscious control, such as heartbeat and breathing, and are often controlled by the brain. Reflex actions are sudden automatic responses to a specific stimulus, such as pulling a hand away from a hot object, usually mediated through the spinal cord.
Nervous control uses electrical impulses through neurons and is very fast, short-lived and usually specific to particular muscles or glands. Hormonal control uses chemicals carried by blood; it is slower, longer-lasting and can affect many target tissues. Both systems coordinate body activities and often work together, for example in stress responses.
Movement in a sensitive plant is caused by changes in water pressure in specialised cells and does not involve nerves or muscles. Movement in our legs is caused by contraction and relaxation of muscles under nervous control.