Coordinationa nd responses

Core body temperature

The maintenance of an internal temperature around 37 °C in humans.

Metabolic waste concentrations

Levels of substances like carbon dioxide and urea that are regulated in the blood.

Blood pH

The acidity or alkalinity of blood, kept within narrow limits for enzyme activity.

Blood glucose concentration

The amount of glucose in the blood, regulated for energy balance.

Blood water content

The amount of water in blood, maintained to prevent cell swelling or shrinking.

Blood oxygen concentration

The level of oxygen in blood, regulated for cellular respiration.

Homeostasis

The maintenance of a constant internal environment within narrow limits.

Importance of homeostasis

Maintains conditions that support enzyme activity and cellular function.

Nervous system

Communication system allowing rapid responses to stimuli via electrical impulses along neurones.

Endocrine system

Hormonal communication system controlling slower, long-term responses via blood.

Blood pH must be kept constant

True. Enzymes may denature if pH changes too much.

Core body temperature in humans is around 37 °C

True. Optimum for enzyme activity.

Enzymes may denature if core body temperature increases too much

True. High temperature changes the shape of the active site.

Blood water content consequences

Too high → water enters cells (may burst); too low → water leaves cells (cells shrink).

Stimulus

A change in the environment detected by receptors.

Receptor cells

Detect stimuli and convert them into electrical impulses.

Effector

Muscle or gland that brings about a response.

Coordination centre

Brain or spinal cord; receives info from receptors and initiates responses.

IGCSE stimulus → response → muscle contraction

Stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response (muscle contracts).

Central nervous system (CNS) organs

Brain and spinal cord.

CNS role

Receives information from senses and coordinates responses.

Sensory neurone

Carries impulses from receptors to CNS.

Motor neurone

Carries impulses from CNS to effectors.

Relay neurone

Connects sensory and motor neurones within CNS.

Myelin sheath

Insulates axons and increases speed of impulse transmission.

Synapse

Junction between two neurones with a small gap.

Neurotransmitter

Chemical that transfers impulses across synapses.

Impulse across synapse

Neurotransmitters released → diffuse across gap → bind to receptor → new impulse generated.

Neurotransmitters move across synapse

By diffusion, not active transport.

Neurotransmitters after impulse

Broken down by enzymes to prevent continuous stimulation.

Reflex

Automatic, rapid response that does not involve conscious brain processing.

Reflex examples

Pain withdrawal, blinking, pupil reflex, coughing, knee-jerk reflex.

Reflex arc pathway (hot object)

Hot object → sensory neurone → relay neurone in spinal cord → motor neurone → muscle → contraction.

Spinal cord in reflex arc

Acts as coordinator, generating motor output without conscious brain involvement.

Hormones

Chemical messengers carried by blood to target cells.

ADH (antidiuretic hormone)

From pituitary; increases water reabsorption in kidneys.

Insulin

From pancreas; lowers blood glucose by stimulating uptake into cells and glycogen formation.

Glucagon

From pancreas; raises blood glucose by stimulating glycogen breakdown in liver.

Adrenaline

From adrenal glands; increases heart rate, blood glucose, and prepares body for “fight or flight.”

Oestrogen

From ovaries; controls female secondary sexual characteristics and menstrual cycle.

Testosterone

From testes; controls male secondary sexual characteristics and sperm production.

Hormones affect all cells

False. Only target cells with specific receptors respond.

Hormonal responses are long-lived

True. Nervous system responses are short-lived.

Hormones control instant responses

False. Nervous system is faster.

Nervous vs endocrine system

Nervous: fast, short-lived, electrical impulses; Endocrine: slow, long-lived, hormones in blood.

Examples of stimuli

Light, sound, touch, pressure, pain, temperature, chemicals.