Science exam 2025 - body

Five main human senses

Sight, hearing, smell, taste, and touch.

Central Nervous System (CNS)

The brain and spinal cord.

Function of the Central Nervous System

It receives messages from the body, processes them, and sends out instructions.

Order of the stimulus-response pathway

Stimulus → Receptor → Sensory neuron → Brain/Spinal cord → Motor neuron → Effector → Response.

Stimulus

→ A change in the environment that is detected.
Example: A hot stove.

Receptor

→ Detects the stimulus and sends a message.
Example: Temperature sensors in your skin.

Sensory neuron

→ Carries the message from the receptor to the brain or spinal cord.
Example: Nerve from your hand to spinal cord.

Brain/spine

• → Processes the information and decides what to do.
  Example: Spinal cord decides to pull hand away.

Motor neuron

• → Sends the response message to a muscle or gland.
  Example: Sends signal to arm muscles.

Effector

→ The muscle or gland that carries out the response.
Example: Arm muscles contract.

Response

→ The action taken.
Example: You pull your hand away from the hot stove.

Role of the spinal cord in reflexes

It coordinates the response before the message reaches the brain.

Hormones

Chemical messengers produced by glands that travel in the blood.

Homeostasis

The maintenance of a stable internal environment in the body.

Negative feedback

A process that reverses a change to keep conditions stable (e.g., sweating to cool down).

Positive feedback

A process that increases a change (e.g., during childbirth contractions).