Coordination and Response

Coordination in living organisms

The process by which different parts of an organism communicate and work together to respond to changes in the environment.

Stimulus

A change in the environment that an organism can detect.

Response

How an organism reacts to a stimulus.

Main types of human receptors

Eyes: detect light; Ears: detect sound; Nose: detect chemicals (smell); Tongue: detect chemicals (taste); Skin: detect touch, pressure, temperature, and pain.

Function of the nervous system

To detect stimuli, process information, and coordinate rapid responses.

Neurons

Specialized nerve cells that carry electrical impulses.

Types of neurons

Sensory neurons: carry impulses from receptors to CNS; Relay neurons: connect sensory to motor neurons; Motor neurons: carry impulses from CNS to effectors.

Reflex action

A fast, automatic response to a stimulus that does not involve conscious thought.

Examples of reflex actions

Blinking, pulling hand away from hot object.

Difference between nervous and hormonal responses

Nervous: fast, short-lived, electrical impulses; Hormonal: slower, long-lasting, chemical signals in blood.

Examples of endocrine glands and hormones

Pituitary: growth hormone; Thyroid: thyroxine; Pancreas: insulin; Adrenal: adrenaline.

What is homeostasis?

The maintenance of a constant internal environment inside the body.

Why is homeostasis important?

It keeps conditions like temperature and pH stable so enzymes can work efficiently and cells function properly.

What are some internal conditions controlled by homeostasis?

Body temperature, blood glucose level, and water balance.

What are the main control systems in the body?

The nervous system (fast responses) and the endocrine system (slower, hormonal control).

What are the three main components of a control system?

1. Receptor - detects changes (stimuli) 2. Coordination centre - brain, spinal cord, or gland processes information 3. Effector - muscle or gland that carries out the response

What is negative feedback?

A process that reverses changes away from normal levels to maintain stability.

Give two examples of negative feedback in the human body.

Regulation of body temperature, Regulation of blood glucose concentration.

What detects changes in body temperature?

The thermoregulatory centre in the hypothalamus of the brain.

What happens if body temperature rises too high?

Vasodilation (blood vessels widen → more heat lost), Sweat glands produce sweat (evaporates → cools skin), Hair lies flat to reduce insulation.

What happens if body temperature drops too low?

Vasoconstriction (blood vessels narrow → less heat lost), Shivering (muscles contract to release heat), Hairs stand up to trap air for insulation.

What hormone controls blood glucose levels?

Insulin, produced by the pancreas.

How does insulin work?

Causes glucose to move from the blood into cells and converts excess glucose to glycogen in the liver.

What hormone raises blood glucose when it is too low?

Glucagon, which converts glycogen back to glucose in the liver.

What hormone controls water balance in the body?

ADH (antidiuretic hormone), released by the pituitary gland.

How does ADH regulate water balance?

Increases the permeability of the kidney collecting ducts, so more water is reabsorbed into the blood.

What happens when the body is dehydrated?

More ADH is released → kidneys reabsorb more water → small volume of concentrated urine.

What happens when the body has too much water?

Less ADH is released → kidneys reabsorb less water → large volume of dilute urine.

Which organs are mainly involved in homeostasis?

Brain (hypothalamus), pancreas, kidneys, liver, skin.