Otis Singleton
The nervous system is an organized network of specialized cells called neurons that transmit electrochemical signals from sensory receptors to other cells in the body. These signals facilitate communication within the body and allow it to respond to changes in the internal and external environment. The nervous system uses both electrical and chemical means to send and receive messages. Neurons send electrical signals down their axons, which are converted to chemical signals at the end through the release of neurotransmitters into the synapse. These neurotransmitters can be small-molecule chemicals like dopamine and serotonin or small neuropeptides like enkephalin. The neighboring dendrite then converts the chemical signal back into an electrical signal, continuing the transmission of information throughout the nervous system.
| Characteristics | Values |
|---|---|
| Definition | The nervous system is an organised group of cells that conduct electrochemical stimuli from sensory receptors through a network to the site where a response occurs. |
| Basic Building Block | Neuron or nerve cell |
| Neuron Structure | Dendrites, axon, and synapses |
| Neuron Types | Motor neurons, sensory neurons, and amacrine cells |
| Neuron Function | Neurons send signals or impulses to other cells in the form of electrical or chemical signals. |
| Electrical Function | Electrical impulses travel through the neuron and go through the same conversion processes as they move to neighbouring neurons. |
| Chemical Function | Chemicals called neurotransmitters are released at chemical synapses. |
| Neurotransmitter Types | Acetylcholine, Norepinephrine, Dopamine, Serotonin, and Enkephalin |
| Neurotransmitter Synthesis | Small-molecule chemicals, small neuropeptides, or large, dense-core vesicles |
| Reuptake | Pre-synaptic or by glial cells; only small-molecule chemical neurotransmitters can be reabsorbed. |
| Glial Cells | Provide structural and metabolic support to the nervous system. |
| Main Parts | Central nervous system and peripheral nervous system |
| Central Nervous System | Brain and spinal cord |
| Peripheral Nervous System | Somatic nervous system and autonomic nervous system |
| Role | The nervous system helps all parts of the body to communicate with each other and react to internal and external changes. |
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What You'll Learn
Neurons transmit electrical and chemical signals
The nervous system is a complex network that enables the various parts of the body to communicate with each other. It is comprised of two main parts: the central nervous system, which includes the brain and spinal cord, and the peripheral nervous system, which is made up of nerves branching off from the spinal cord and extending to all parts of the body. The nervous system uses electrical and chemical signals to transmit messages between the brain and the rest of the body, including internal organs, thus controlling essential functions such as movement, breathing, sight, and thought.
At the core of the nervous system are neurons, which are nerve cells that act as the basic building blocks. These neurons have distinct shapes and roles depending on their location in the body. They possess finger-like projections called dendrites and a long fibre called an axon. The axon often features a specialised membrane called the myelin sheath, which feathers out and has bumps near the dendrites of neighbouring neurons.
The communication between neurons occurs at the synapses, which are the junctions between the axon of one neuron and the dendrite of another. When a neuron sends a message, it transmits an electrical signal down its axon through an action potential, a brief electrical event. At the end of the axon, the electrical signal transforms into a chemical signal through the release of neurotransmitters. These neurotransmitters, or chemical messengers, diffuse across the synaptic cleft and bind to specific receptors on the neighbouring dendrite.
The type of neurotransmitter released plays a crucial role in determining the quality and intensity of the transmitted information. The neurotransmitters can either excite or inhibit the neighbouring neuron, influencing whether it will generate its own action potential. Once the neurotransmitter binds to the postsynaptic receptor, the signal converts back into an electrical form as charged ions flow into or out of the postsynaptic neuron. This electrical signal then continues through the neuron, repeating the conversion process as it moves to other neurons.
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Neurotransmitters are released at chemical synapses
The nervous system is a complex network that facilitates communication within the body and helps it react to external stimuli. It comprises the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system, which consists of nerves branching off from the spinal cord to various body parts. This system uses electrical and chemical signals to transmit messages.
At its most basic, the nervous system is composed of nerve cells or neurons. These neurons have unique shapes and functions depending on their location and role in the body. They possess dendrites, which are finger-like projections, and an axon, a long fibre. The axon, often coated by a myelin sheath, ends near a dendrite from another neuron, and the space between this axon bump and the neighbouring dendrite is called a synapse.
Neurotransmitters are indeed released at these chemical synapses. They are the chemical messengers that carry signals across the synapse from one neuron to another. When an electrical signal travels down the axon of a neuron, it triggers the release of neurotransmitters into the synapse, which then bind to receptors on the neighbouring dendrite. This binding opens ion channels on the dendrite membrane, causing a change in its electrical charge.
The process of releasing neurotransmitters involves several steps. Firstly, an action potential, or electrical impulse, reaches the synaptic terminal. This causes calcium channels to open, allowing calcium ions to enter. Next, vesicles containing neurotransmitters fuse with the plasma membrane of the sending neuron, releasing neurotransmitter molecules into the synaptic cleft. These molecules then diffuse across the cleft and bind to receptors on the receiving neuron's plasma membrane.
The release of neurotransmitters is a critical step in neuronal communication, ensuring the smooth transmission of signals across neurons and enabling the nervous system to coordinate a wide range of functions, from movement to cognitive processes.
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Electrical signals pass directly through electrical synapses
The nervous system is a complex network that enables the body's various parts to communicate with each other and react to changes. It comprises the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system, which consists of nerves branching off from the spinal cord and extending to all body parts. This system utilises both electrical and chemical means to transmit signals.
Electrical signals play a crucial role in the nervous system, especially at the synapses, which are the gaps between neurons. There are two types of synapses: chemical and electrical. Electrical synapses, also known as gap junctions, are characterised by a direct electrical connection between neurons. These junctions are formed by proteins called connexins, which create a low-resistance pathway for the passage of ions and small molecules.
At the end of a neuron's axon, an electrical signal is converted into a chemical signal through the release of neurotransmitters into the synapse. These neurotransmitters carry the signal to the neighbouring dendrite, where it is converted back into an electrical signal. This bidirectional flow of electrical signals through electrical synapses is significantly faster than chemical transmission, making it essential for quick responses in processes such as escape mechanisms.
The structure of electrical synapses facilitates the rapid transmission of signals. In these synapses, the pre- and postsynaptic neurons come extremely close together, with a distance of approximately 3.8 nm, compared to the 20-40 nm separation in chemical synapses. This proximity allows for the direct flow of ions, carrying a positive charge and depolarising the postsynaptic cell. The bidirectional nature of electrical synapses enables impulse transmission in both directions, contributing to the synchronisation of network activity in the brain.
Electrical synapses are prevalent throughout the central nervous system, including the neocortex, hippocampus, thalamic reticular nucleus, and spinal cord. They are also found in invertebrates and vertebrates, although chemical synapses are more common in the latter. Electrical synapses play a vital role in synchronising the firing of connected neurons and creating dynamic network-level behaviour in the brain.
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The nervous system controls movement, breathing, sight, and thought
The nervous system is a network of nerve cells that communicate with each other and the outside world, controlling and regulating many of the body's functions. It uses electrical and chemical means to send and receive messages.
Movement
The nervous system controls movement through the somatic nervous system, a part of the peripheral nervous system. It relays information from the eyes, ears, skin and muscles to the central nervous system (CNS) and obeys commands from the CNS to make muscles contract or relax, allowing movement. The brain sends outgoing messages along motor pathways, which carry instructions from the brain to the muscles to move.
Breathing
Breathing is controlled by the autonomic nervous system, which is part of the peripheral nervous system. It works with the body's muscles to regulate breathing. The diaphragm, intercostal, abdominal, and muscles of the face, mouth, and pharynx all play a role in the breathing process. The autonomic nervous system also controls the rate of breathing by increasing or decreasing the heart rate and opening airways to allow for easier breathing.
Sight
The nervous system controls sight by regulating the amount of light that enters the eyes. The autonomic nervous system adjusts the pupil size to allow the correct amount of light in, enabling effective vision.
Thought
The nervous system influences thought through the brain, which is the powerhouse of the body. The brain has countless billions of neural cross-connections, giving rise to consciousness and personality. It is constantly communicating with the body, sending instructions and receiving input from the senses.
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Neurotransmitters are synthesised in different ways
The nervous system uses both electrical and chemical means to send and receive messages. When a neuron sends a message to another neuron, it sends an electrical signal down the length of its axon. At the end of the axon, the electrical signal changes to a chemical signal, which is then released with chemical messengers called neurotransmitters into the synapse—the space between the end of an axon and the dendrite of another neuron.
Neurotransmitters are signalling molecules secreted by a neuron to affect another cell across a synapse. They are synthesised in different ways depending on the type of neurotransmitter. For example, epinephrine, a neurotransmitter and hormone, is synthesised from tyrosine. It is released from the adrenal glands and plays a role in the fight-or-flight response. It does so by increasing heart rate, blood pressure, energy mobilisation, and heightening attention and focus.
Neuropeptides, on the other hand, are synthesised in the cell bodies of peptide-secreting neurons. These polypeptides, called pre-propeptides, are then processed in the rough endoplasmic reticulum, where the signal sequence of amino acids is removed. The remaining polypeptide, now called a propeptide, traverses the Golgi apparatus and is packaged into vesicles in the trans-Golgi network. The final stages of peptide neurotransmitter processing occur after packaging into vesicles and involve proteolytic cleavage, modification of the ends of the peptide, glycosylation, phosphorylation, and disulfide bond formation.
Small-molecule neurotransmitters, in contrast, undergo their final synthetic steps inside the synaptic vesicles. The synthesis of peptide neurotransmitters differs fundamentally from that of small-molecule neurotransmitters. The former is similar to the synthesis of proteins secreted from non-neuronal cells, such as pancreatic enzymes. However, a key difference lies in the distance between the site of a peptide's synthesis and its secretion. The long distance between these sites necessitates the use of fast axonal transport to carry the peptide-filled vesicles along the axon to the synaptic terminal.
Neurotransmitters play a crucial role in the nervous system, and their synthesis, packaging, release, and degradation are carefully regulated by neurons to achieve the desired levels of transmitter molecules.
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Frequently asked questions
The nervous system uses both electrical and chemical means to send and receive messages.
The nervous system uses chemical synapses, which involve the release of a chemical neurotransmitter between neurons. Neurotransmitters can be small-molecule chemicals, such as dopamine and serotonin, or small neuropeptides, such as enkephalin.
The nervous system uses electrical synapses, where electrical current or signals pass directly from one neuron to another through gap junctions.
