Central and peripheral nervous system

The Central Nervous System (CNS) is made up of the brain and spinal cord.
The CNS is the main processing centre where responses to stimuli are co-ordinated. It receives information, interprets it and initiates responses.
The brain is responsible for complex processes such as thought, emotion and regulation of homeostatic processes.
It is divided into various parts each with its own roles, including the cerebrum, cerebellum, and brain stem.
The cerebrum controls voluntary actions, speech, intelligence, memory, and emotions. It’s divided into two hemispheres.
The cerebellum is involved in balance, coordination of movement and control of posture.
The brain stem controls involuntary processes like heart rate, breathing, and blood pressure.
The spinal cord is a two-way highway for impulses. Ascending tracts take sensory information up to the brain, and descending tracts take motor information to the body from the brain.
It is also responsible for simple reflex actions.

The Peripheral Nervous System (PNS) includes all the nerves outside the central nervous system.
Its primary role is to connect the CNS to the rest of the body, enabling information to be sent back and forth.
It is divided into the somatic nervous system and the autonomic nervous system.
The somatic nervous system controls voluntary actions through skeletal muscle, and carries sensory information to the CNS.
The autonomic nervous system regulates functions that are usually not under conscious control, including heart rate, digestion, and breathing.
The autonomic system is itself divided into the sympathetic and parasympathetic systems.
The sympathetic system prepares the body for ‘fight or flight’ situations by speeding up heart rate, expanding airways, and inhibiting digestion.
The parasympathetic system promotes ‘rest and digest’ responses, like slowing heart rate and stimulating digestion.

Neurons, or nerve cells, carry the electrical impulses that allow communication within the nervous system.
The organization of neurons into the CNS and PNS enables efficient information processing and response, whilst the structure of different types of neurones aids specific functions.
The connection between neurons is a synapse, and signal transmission across a synapse is carried out by neurotransmitters.