The Nervous System – A Level Biology WJEC Revision

The nervous system regulates the body’s responses to its environment and controls all body functions.
It is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
The CNS comprises the brain and spinal cord, while the PNS includes all nerves outside the CNS.
It operates via a network of nerve cells known as neurons, each consisting of a cell body, axon, and dendrites.

Neurons are specialised cells that carry electrical signals, or impulses, around the body.
They communicate via small gaps called synapses, where electrical signals are converted into chemical signals called neurotransmitters.
An action potential triggers the release of neurotransmitters into the synapse, initiating the signal’s continuation.
Neurotransmitters attach to receptors on the next neuron, causing a new action potential.

The brain controls higher functions like emotions, creativity, memory, and learning.
It processes sensory information from sense organs to make decisions about how the body should respond.
The spinal cord is a major pathway for impulses passing up to the brain or down from the brain to the rest of the body.
It also controls some automatic responses known as reflex actions.

The PNS connects the CNS to every other part of the body.
It contains two main types of neuron: motor neurons and sensory neurons.
Motor neurons carry signals from the CNS to muscles or glands, leading to a response.
Sensory neurons carry signals from sensory receptors to the CNS for processing.

The PNS is further divided into the autonomic and somatic systems.
The autonomic system controls involuntary actions like heart rate and digestion.
It’s divided into the sympathetic and parasympathetic systems, which often have opposite effects on organs.
The somatic system controls voluntary actions involving skeletal muscles.

A variety of disorders can affect the nervous system, including Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis.
These disorders can result in symptoms ranging from muscle weakness and movement problems to changes in mood, memory, and behaviour.
Alzheimer’s disease is characterised by the formation of plaques and tangles in the brain, leading to cell death.
Parkinson’s disease is caused by a deficiency of the neurotransmitter dopamine, causing symptoms such as tremors and rigidity.
In multiple sclerosis, the immune system attacks the protective covering of nerve fibers, resulting in communication problems between the brain and the rest of the body.