The Nervous System

• The nervous system is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS consists of the brain and spinal cord. It acts as the control centre for the entire body, processing information and coordinating responses.
• The PNS consists of all the nerves outside of the CNS. It is further divided into the somatic nervous system (controls voluntary movements like walking) and the autonomic nervous system (controls involuntary actions like heart rate).
• Neurons, or nerve cells, are the basic units of the nervous system. They transmit electrical signals around the body.
• There are three types of neurons: sensory neurons (carry signals from sensory receptors to the CNS), motor neurons (carry signals from the CNS to the muscles or glands), and interneurons (process signals within the CNS).
• Neurons have specialised structures to help them carry signals. These include dendrites (receive signals), axons (transmit signals), and a myelin sheath (insulates axon and speeds up transmission).
• Nerve impulses are electrical signals that travel along neurons. They are ‘all-or-nothing’ - this means they always have the same strength and speed.
• Synapses are junctions between neurons. Signals cross these gaps using chemicals called neurotransmitters.
• Reflex actions are automatic, involuntary responses to stimuli. They are faster than voluntary actions because they do not involve the conscious part of the brain.
• The term “homeostasis” refers to the body’s ability to regulate its internal environment in response to changes in the external environment. This is an important function of the nervous system. Examples of homeostasis include maintaining body temperature, heart rate, and blood glucose levels.
• Hormones are chemical messengers secreted by glands in the endocrine system. They travel in the bloodstream to target cells. Unlike nerve impulses, hormones have slower, longer-lasting effects.
• Many responses involve both the nervous system and the endocrine system. For example, the ‘fight or flight’ response to danger involves nerve impulses (for fast, immediate action) and hormones (for longer-term preparation).