The Cells of the Nervous System and Neurotransmitters at the Synapses
Neurons are specialised cells that form the communication network of the nervous system. Each neuron consists of:
- Dendrites: Receive signals from other neurons
- Cell body: Contains the nucleus and processes information
- Axon: Conducts electrical impulses away from the cell body
The myelin sheath is a fatty insulating layer that surrounds axons, significantly increasing the speed of nerve impulse transmission. This myelin is produced by glial cells, which provide structural and functional support to neurons.
The process of myelination developingmyelinsheaths continues from birth through adolescence, explaining why:
- Nervous system control gradually improves with age
- Young children have slower responses to stimuli
- Coordination becomes more refined during development
Key Concept: Neurological Disorders
Several diseases affect the myelin sheath, including multiple sclerosis MS, polio, and Tay Sachs disease. When myelin is damaged, nerve impulses travel more slowly or may be blocked entirely, resulting in symptoms like loss of coordination, muscle weakness, and sensory disturbances.
Neurotransmitters are chemical messengers that:
- Are stored in vesicles within neurons
- Cross the synaptic cleft between neurons
- Bind to specific receptors on the receiving neuron
- Must be quickly removed after signalling through enzyme breakdown or reabsorption
The effects of neurotransmitters depend on the receptors they activate, producing either:
- Excitatory responses: Increasing the likelihood of generating an action potential
- Inhibitory responses: Decreasing the likelihood of generating an action potential
Weak stimuli typically fail to release sufficient neurotransmitters to reach the threshold needed for signal transmission, effectively filtering out low-level or unimportant stimuli.