Chapter: 3 Movement in & out of Cells

12.1 The human nervous system

• Changes in an organism’s environment are called stimuli (singular: stimulus) and are sensed by specialized cells called receptors.
• The organism responds using effectors.
• Muscles are effectors and may respond to a stimulus by contracting.
• Glands can also be effectors. For example, if you smell good food cooking, your salivary glands may respond by secreting salvia.
• Animals need fast and efficient communication systems between their receptors and effectors.
• This is partly because most animals need to be able to respond very quickly to catch their food or to avoid predators.
• To make sure that the right effectors respond at the right time, there needs to be some kind of communication system between receptors and effectors.
• If you touch something hot, pain receptors on your fingertips send an electrical impulse to your arm muscles to make them contract, pulling your hard away from the hot surface.
• The way in which receptors detect stimuli, and then pass information on to effectors, is called coordination.

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• Most animals have two methods of sending information from receptors to effectors.
• The fastest is by means of nerves.
• The receptors and nerves make up the animal’s nervous system.
• A slower method, but still a very important one, is by means of chemicals called hormones.
• Hormones are part of the endocrine system, and this is described in topic 12.3 in this chapter.

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