Control and Coordination · Class 10 Science: 66 flashcards

The structural and functional unit of the nervous system — a specialised cell that receives, conducts and transmits information as electrical impulses at high speed.

Dendrites — receive information; cell body — contains the nucleus, maintains the cell; axon — the long fibre conducting the impulse away; nerve endings — transmit the message onward at synapses.

As an electrical impulse, moving from dendrite through the cell body and along the axon to the nerve endings.

The tiny gap between one neuron's nerve endings and the next neuron's dendrites (or a muscle/gland). The electrical impulse triggers release of chemicals that diffuse across the gap and start a fresh electrical impulse on the other side.

The chemical-releasing machinery exists only at the axon endings, and the receptors for those chemicals only on the receiving cell — so transmission cannot reverse.

Photoreceptors (eyes) for light; phonoreceptors (ears) for sound; olfactory receptors (nose) for smell; gustatory receptors (tongue) for taste.

A rapid, automatic response to a stimulus that occurs without conscious thought — e.g., instantly withdrawing the hand from a flame, blinking at a sudden object, sneezing at dust.

The nerve pathway of a reflex: receptor → sensory neuron → spinal cord (where the connection/decision is made) → motor neuron → effector (muscle or gland).

The brain's processing takes time; emergencies need instant answers. The spinal cord's direct sensory-to-motor connection responds in milliseconds — the brain merely receives the report afterwards.

After. The reflex arc through the spinal cord moves the hand first; the sensory information travels on to the brain slightly later, which is when pain is perceived.

Fore-brain (mainly the cerebrum), mid-brain, and hind-brain (cerebellum, medulla and pons).

(1) Thinking, reasoning and memory; (2) control of all voluntary actions; (3) housing the centres for sight, hearing and smell; (4) registering sensations such as hunger; its association areas interpret inputs and decide responses.

It ensures precision of voluntary actions and maintains posture and balance. Examples: riding a bicycle without falling; walking in a straight line; picking up a pencil in one smooth motion.

The medulla (in the hind-brain) — the centre for these involuntary actions.

The mid-brain — one of its involuntary control functions.

It is enclosed in the bony skull (cranium) and floats in a fluid-filled cushion — the fluid absorbs shocks and jolts before they reach the delicate tissue.

It runs through the canal of the vertebral column — the chain of ring-like backbones enclosing it in bone along its whole length.

When the nerve's chemical signal arrives, special contractile proteins inside the muscle cell change their shape and arrangement, shortening the cell. Many cells shortening together contract the muscle and move the body part.

Voluntary: consciously willed, controlled by the fore-brain (writing, kicking a ball deliberately). Involuntary: not under conscious control, run by mid-brain/medulla (heartbeat, blood pressure, salivation, vomiting).

(1) Impulses reach only cells connected to nervous tissue — not every cell of the body; (2) neurons cannot generate impulses continuously — they need time to reset. Slow, steady, body-wide regulation therefore uses chemical hormones instead.

The muscle or gland that carries out the response ordered by the nervous system — the last station of a reflex arc.

The cerebrum can still issue the voluntary command, but the cerebellum's precision-and-balance processing is lost — so movements become jerky, overshooting and unbalanced.

(1) Growth-independent (nastic) movements — immediate, turgor-driven, like the touch-me-not's fold; (2) growth-dependent directional movements — tropisms, like a shoot bending toward light.

Touch is sensed and relayed cell-to-cell by electrical-chemical signals; hinge cells at the leaflet bases then LOSE water, their turgor pressure collapses, and the limp cells let the leaflets fold. No growth is involved — it is a hydraulic movement.

By changing the amount of water inside them — swelling (turgid) or shrinking (flaccid). The resulting pressure change alters cell shape, moving the plant part.

A tropism is a slow, directional growth movement in response to a stimulus. Positive = growth TOWARD the stimulus; negative = growth AWAY from it.

Shoots are positively phototropic — they grow/bend toward light. Roots are negatively phototropic — they grow away from light.

Roots are positively geotropic — growing downward with gravity; shoots are negatively geotropic — growing upward against it.

Directional growth toward water — roots bend and grow toward moist soil regions, e.g., roots invading a leaking water pipe.

Growth directed by a chemical stimulus. Classic case: the pollen tube growing down through the style toward the ovule, guided by chemicals, to achieve fertilisation.

Growth response to touch. When a tendril contacts a support, the touching side grows slower than the far side; the unequal growth bends the tendril around the support in a coil.

At the shoot tip. It diffuses down and stimulates cells to ELONGATE — it is the hormone behind the shoot's bending toward light.

When light falls on one side, auxin shifts toward the SHADY side of the shoot. The higher auxin there makes those cells elongate more than the cells on the lit side — the unequal growth curves the shoot toward the light.

It promotes growth of the stem — contributing to taller plants and stem elongation.

It promotes CELL DIVISION; hence it is present in higher concentration where rapid division occurs — in fruits and seeds.

Abscisic acid (ABA) — it slows/inhibits growth, promotes dormancy of seeds and buds, and its effects include wilting of leaves. Often called the stress hormone.

It is a GAS. It promotes fruit ripening — released by a ripening fruit, it spreads through air and ripens neighbouring fruits too, which commerce exploits in ripening rooms.

They are synthesised at one location and diffuse (or travel in the sap) to the parts where they act — slow chemical transport suited to a stationary organism.

Touch-me-not: instant (seconds), caused by turgor/water loss, no growth, quickly reversible. Tendril: slow (hours-days), caused by differential GROWTH, directional around the support, permanent. Both respond to touch by opposite machinery.

Plants lack nervous tissue and muscles; their coordination relies on chemical hormones moving by diffusion and on growth or turgor changes — inherently slower processes than electrical impulses and muscular contraction.

In the touch-me-not, touching ONE leaflet folds leaflets further away too — the stimulus information clearly travels from cell to cell across the plant, by electrical-chemical signalling between ordinary cells.

Thigmotropism. The tendril's side touching the trellis grows more slowly than the outer side, so continued unequal growth wraps the tendril around the support.

Abscisic acid — it maintains seed dormancy, holding germination back until conditions improve.

The overripe fruit releases ethylene gas, which diffuses to neighbouring fruits and accelerates their ripening (and thus over-ripening) in a chain reaction.

Chemical messengers secreted by endocrine (ductless) glands directly into the blood, which carries them throughout the body to act on target cells — providing slow, sustained, body-wide coordination.

Because they have no ducts — their secretions (hormones) pass directly into the surrounding blood, unlike exocrine glands (salivary, sweat) that deliver through tubes.

The adrenal glands (one atop each kidney) — secreted in large amounts during fear, stress or excitement, preparing the body for 'fight or flight'.

(1) Heart beats faster, supplying more oxygen to muscles; (2) breathing rate rises through faster diaphragm/rib-muscle action; (3) blood is diverted from the digestive system and skin (their small arteries contract) to skeletal muscles; (4) the body is readied for fighting or fleeing.

The nervous system perceives the danger and sends impulses ordering the adrenal glands to secrete adrenaline; the hormone then produces the body-wide response. The fast system triggers the broad one.

Thyroxine, from the thyroid gland in the neck, regulates the metabolism of carbohydrates, proteins and fats — controlling the body's fuel-processing rate for balanced growth.

The thyroid needs iodine to synthesise thyroxine. Without dietary iodine, thyroxine falls and the thyroid swells — goitre. Iodised salt supplies the daily trace.

The condition caused by iodine deficiency in which the thyroid gland enlarges — appearing as a characteristic swollen neck.

Growth hormone, secreted by the pituitary gland — governing growth and development of the body.

Deficiency leads to dwarfism (stunted growth); excess leads to gigantism (excessive height/growth).

Insulin, produced by the pancreas — it helps regulate blood sugar levels by promoting sugar uptake from blood.

A condition in which blood sugar remains high because insulin is deficient (or ineffective); excess sugar may appear in urine, with many harmful effects. Patients are treated with insulin injections to supply the missing hormone.

Testosterone from the testes in males; oestrogen from the ovaries in females — both drive the changes of adolescence including secondary sexual characteristics.

A self-regulating arrangement in which the hormone's effect controls its own secretion: the changing level of the regulated quantity (e.g., blood sugar) is detected and dials the hormone's release up or down, keeping amounts precise and timely.

When blood sugar rises (after a meal), pancreatic cells detect it and secrete more insulin, which lowers the sugar; as the level falls back to normal, the secretion of insulin is reduced. The regulated quantity itself governs the regulator.

(1) Signal: electrical impulses vs chemicals in blood; (2) speed: milliseconds vs seconds-to-days; (3) reach and duration: only cells wired to nerves, briefly — vs every cell of the body, in a sustained way.

Hormonal action takes seconds or longer to build and is body-wide rather than targeted — far too slow and diffuse for the millisecond, single-muscle response a burn demands. That is the nervous reflex's territory.

Growth needs a steady instruction reaching every cell for years. Nerve impulses reach only wired cells and cannot fire continuously — sustained, universal signalling is exactly what blood-borne hormones provide.

By receptors — specific molecules on/in the cell that bind only the matching hormone. All cells receive the blood broadcast; only receptor-bearing target cells respond.

The pituitary — besides growth hormone, it releases hormones that direct several OTHER endocrine glands, effectively conducting much of the hormonal orchestra.

Adrenaline contracts the small arteries of the digestive system, diverting its blood to skeletal muscles — the odd hollow feeling is your gut's circulation being downgraded during the emergency.

Deficiency (or ineffectiveness) of insulin, produced by the pancreas — the picture of diabetes.