Homeostasis and the Nervous System

Homeostasis is the maintenance of a stable internal environment to ensure optimal cellular function. This GCSE Biology notes section covers automatic control systems and the nervous system.

Definition: Homeostasis is keeping a stable internal environment so cells have the right conditions to function and for enzyme action, maintained in both internal and external conditions.

Automatic Control Systems (ACS) regulate body temperature, blood glucose, and water content through both hormonal and nervous mechanisms. The ACS consists of three components:

1. Receptors that detect stimuli
2. Coordination centers that receive information and organize responses
3. Effectors that produce responses to counteract changes and restore optimal levels

Highlight: Negative feedback is used to automatically bring body systems back to normal when levels are too high or low.

The nervous system is composed of:

• Central nervous system (CNS): spinal cord and brain • Sensory neurons: carry impulses from receptors to CNS • Relay neurons: allow communication between sensory and motor neurons • Motor neurons: carry impulses from CNS to effectors • Effectors: muscles and glands that respond to nervous impulses

Vocabulary: A synapse is the connection between two neurons where nerve signals are transferred via chemical diffusion.

Reflexes are automatic responses to stimuli that bypass conscious brain processing to prevent injury or harm. The reflex arc shows the passage of information from receptor to effector in a reflex action.

The Endocrine System

The endocrine system uses hormones to regulate various bodily functions. This section of the AQA GCSE Biology pdf covers key endocrine glands and their functions.

Definition: Hormones are chemical molecules released directly into the bloodstream and transported to target organs, controlling processes that need constant adjustment.

Key endocrine glands include:

1. Pituitary gland ("master gland"): produces hormones regulating body conditions and directs other glands
2. Thyroid: produces thyroxine, regulating metabolism, heart rate, and temperature
3. Adrenal gland: produces adrenaline for "fight or flight" response
4. Pancreas: produces insulin to regulate blood glucose levels
5. Ovaries (females): produce estrogen for menstrual cycle
6. Testes: produce testosterone for puberty and sperm production

Example: While nerves act quickly and precisely, hormones have slower, longer-lasting, and more general effects throughout the body.