B13: Coordination and Response – Study Notes
Hello future scientists! This chapter, Coordination and Response, is all about how living organisms—especially humans—detect changes around them and inside them, and how they react.
Think of your body as a high-tech machine: it needs constant communication to run smoothly. We'll explore the two main communication systems: the super-fast electrical system (nerves) and the slower, chemical system (hormones). Let's dive in!
1. The Nervous System (The Fast Messenger)
The nervous system is like your body's internet network, allowing for extremely quick communication using electrical signals.
What is Coordination?
Coordination and Regulation is the nervous system's job. It ensures all your body functions (like breathing, running, or thinking) work together correctly.
1.1 Neurones and Electrical Impulses (Core)
The messages carried by the nervous system are called electrical impulses, and they travel along specialised cells called neurones.
Types of Neurones
- Sensory Neurone: Carries impulses from the receptor (sense organ) to the CNS.
- Relay Neurone: Found entirely within the Central Nervous System (CNS). It links sensory and motor neurones.
- Motor Neurone: Carries impulses from the CNS to the effector (muscle or gland).
Memory Aid: S-R-M (Sensory, Relay, Motor) helps you remember the order of information flow.
1.2 Structure of the Mammalian Nervous System (Core)
The nervous system is split into two main sections:
- Central Nervous System (CNS): This is the control centre. It consists of the brain and the spinal cord. It processes information and coordinates responses.
- Peripheral Nervous System (PNS): This consists of all the nerves found outside the brain and spinal cord. The PNS carries signals to and from the CNS.
1.3 Sense Organs and Stimuli (Core)
Before you can respond, you must detect the change! Sense organs are groups of receptor cells that respond to specific changes in the environment, called stimuli.
Examples of stimuli detected by receptors in sense organs:
- Light: Detected by the eye (receptors in the retina).
- Sound: Detected by the ear.
- Touch, Temperature, Pressure: Detected by receptors in the skin.
- Chemicals: Detected by the nose (smell) and tongue (taste).
1.4 Reflex Actions: The Quick Response (Core)
A reflex action is a rapid, automatic, and involuntary response to a stimulus. Reflexes are essential because they coordinate stimuli with immediate responses from effectors (muscles or glands), often protecting the body from harm. Think about pulling your hand away from a hot stove!
The Simple Reflex Arc (A Step-by-Step Path)
A reflex arc is the pathway taken by the nerve impulse during a reflex action:
- Receptor: Detects the stimulus (e.g., heat/pain in the skin).
- Sensory Neurone: Carries the impulse to the CNS (spinal cord).
- Relay Neurone: Links the sensory and motor neurones within the spinal cord.
- Motor Neurone: Carries the impulse away from the CNS.
- Effector: The muscle or gland that carries out the response (e.g., a muscle contracts to pull the hand away).
Quick Review: Nervous System
- Speed: Very fast (electrical impulses).
- Components: CNS (Brain & Spinal Cord) and PNS (Nerves).
- Key action: Reflexes are automatic and rapid responses, following the Receptor -> Sensory -> Relay -> Motor -> Effector path.
2. The Endocrine System (The Chemical Messenger)
While the nervous system uses fast electrical signals, the endocrine system uses slow, chemical signals called hormones.
2.1 What is a Hormone? (Core)
A hormone is a chemical substance produced by a specialised organ called an endocrine gland.
The hormone is carried by the blood and travels throughout the body, but it only affects specific cells or organs called target organs, altering their activity.
Analogy: If the nervous system is a phone call (fast, direct), the endocrine system is the postal service (slower, but the chemical message eventually reaches the correct address—the target organ).
2.2 Key Endocrine Glands and Hormones (Core & Supplement)
You need to know the glands and the hormones they secrete:
- Adrenal Glands: Secretes adrenaline.
- Pancreas: Secretes insulin and glucagon (Supplement).
- Testes: Secretes testosterone (male sex hormone).
- Ovaries: Secretes oestrogen (female sex hormone).
2.3 Adrenaline: The 'Fight or Flight' Hormone (Core)
Adrenaline is secreted rapidly by the adrenal glands in dangerous, stressful, or exciting 'fight or flight' situations. It prepares the body for immediate action.
The effects of adrenaline include (you must know these!):
- Increased Heart Rate: Pumps blood faster.
- Increased Breathing Rate: Increases oxygen supply.
- Increased Pupil Diameter: Allows more light into the eyes, improving vision.
Quick Review: Hormones
- Nature: Chemical substances.
- Transport: Carried by the blood.
- Action: Slower but often longer-lasting than nerve impulses.
- Adrenaline effects: Faster heart, faster breathing, wider pupils.
3. Homeostasis (Keeping the Internal Environment Constant)
Don't worry if this seems tricky at first—homeostasis is just your body working hard to keep everything inside balanced!
3.1 Defining Homeostasis (Supplement)
Homeostasis is the maintenance of a constant internal environment. Your body needs constant conditions (like temperature and blood sugar) to ensure enzymes work optimally.
3.2 Homeostatic Control by Negative Feedback (Supplement)
Most coordination in the body uses negative feedback. This mechanism ensures that if a level (like temperature) moves away from a target value (the set point), changes are triggered to bring it back to the set point.
Analogy: A thermostat is a perfect example of negative feedback. If the temperature goes above the set point, the thermostat switches the heater OFF. If the temperature drops below the set point, the thermostat switches the heater ON. It always works to reverse the change.
3.3 Control of Blood Glucose Concentration (Supplement)
The pancreas controls the concentration of glucose in the blood, often in coordination with the liver.
When Blood Glucose is too High (e.g., after eating):
- The pancreas detects the high glucose level.
- It secretes the hormone insulin into the blood.
- Insulin travels to the liver and muscles, causing them to take up glucose and convert it into the storage molecule glycogen.
- Blood glucose concentration drops back to the set point. (Negative feedback!)
When Blood Glucose is too Low (e.g., after exercise):
- The pancreas detects the low glucose level.
- It secretes the hormone glucagon into the blood (Supplement).
- Glucagon travels to the liver, causing it to break down stored glycogen back into glucose.
- Blood glucose concentration rises back to the set point.
Did you know? Diabetes occurs when the body either doesn't produce enough insulin or stops responding to it, meaning blood glucose control fails.
3.4 Maintenance of Constant Body Temperature (Supplement)
Mammals (like humans) are warm-blooded, meaning they maintain a constant internal body temperature, even when the outside temperature changes. The brain plays a crucial role as the control centre for temperature regulation.
The Role of the Skin (Supplement)
You should be able to identify these parts of the skin related to temperature control:
- Hairs and Hair erector muscles.
- Sweat glands (for cooling).
- Blood vessels (arterioles supplying skin surface capillaries).
Responses to Overheating (Temperature too High)
- Sweating: Sweat is released onto the skin surface. As it evaporates, it takes thermal energy (heat) from the body, causing cooling.
- Vasodilation: Arterioles supplying the skin surface capillaries widen. This increases blood flow near the surface, allowing more thermal energy to be lost to the surroundings. The skin looks red/flushed.
- Insulation: Hair erector muscles relax, laying hairs flat, trapping less air and reducing insulation.
Responses to Cooling (Temperature too Low)
- Shivering: Rapid, involuntary muscle contraction releases thermal energy as a by-product of increased respiration.
- Vasoconstriction: Arterioles supplying the skin surface capillaries narrow. This reduces blood flow near the surface, limiting heat loss. The skin looks pale.
- Insulation: Hair erector muscles contract (making goosebumps). This raises hairs, trapping a layer of insulating air near the skin (though less effective in humans than in furry animals).
Key Takeaway: Coordination uses two systems—quick electrical (nervous) and slower chemical (endocrine). Homeostasis uses these systems, often employing negative feedback, to keep essential internal conditions like temperature and glucose concentration stable.