Structure & Function of Nervous System - Structures of the Nervous System (GCSE Biology)
Structures of the Nervous System
Neurones
Neurones, Nerves and Nerve Impulses
- Neurones carry electrical signals. The nervous system sends information in the form of electrical signals, called nerve impulses. These nerve impulses pass along cells called neurones (or nerve cells).
- Nerves are made up of neurones. Nerves are made up of bundles of neurones (nerve cells). Students often get mixed up between nerves, neurones and nerve cells. Neurones and nerve cells are the same thing. Nerves are made up of lots of neurones / nerve cells.
Properties of Neurones
Neurones have some similar properties:
- Axons – each neurone has a long axon, which carry information across the body.
- Myelin sheath – the axons are coated in myelin sheaths, which are insulating layers of fat. These prevent short circuits – i.e. the electrical current cannot pass on to other neurones from different circuits.
- Cell body – the nerve cell body is found at the end of the axon. It has the nucleus and lots of dendrons and dendrites extending from it.
- Dendrons – The cell body has short dendrons extending from it. The dendrons have even shorter dendrites at the end. These parts of the cell receive information from other neurones.
- Synapses – between each neurone is a gap known as a synapse. Electrical impulses reach the synapse then trigger the release of molecules called neurotransmitters.
Sensory Receptors
- Sensory receptors detect a stimulus. Receptors are a group of cells that can detect a change in environment which is known as a stimulus. They can be of different types for example, skin receptors can detect changes in temperature and pressure whereas eye receptors can detect light. Once the change is detected, the information is converted to an electrical signal and is sent through a sensory neurone (more below).
Types of Neurones and their Structures
Neurones carry information from receptors to the control centres (in the CNS), and ultimately to the effectors. There are three types of neurone, which together form a circuit.:
- Sensory neurones – these are the first neurone in the circuit. Sensory neurones send impulses from the receptor to the CNS. They have a long dendron, a cell body placed centrally and a short axon.
- Relay neurones – the information from sensory neurones is passed to relay neurones, which carry the impulse through the CNS. The relay neurone forms a link (a relay) between the sensory and motor neurones. They have lots of short dendrites, a cell body and a long axon.
- Motor neurones – motor neurones are the final neurone in the circuit. Motor neurones receive impulses from the relay neurones, and then carry the impulses from the CNS to the effectors. The effectors could be glands or muscles, and they bring about a response (e.g. glands release hormones, muscles contract). They have lots of short dendrites and a long axon. They can be myelinated or unmyelinated.
This circuit is important in homeostasis and also in the reflex arc, which is a circuit that helps us carry out reflex actions subconsciously. We will learn about this in more detail later.
The nervous system is a complex network of cells, tissues, and organs that are responsible for transmitting and processing signals in the body. It coordinates and controls our thoughts, movements, and sensations.
The main structures of the nervous system include the brain, spinal cord, and nerves. The brain is the central control center for the nervous system, the spinal cord is a long, delicate tube of nerve tissue that runs from the brain down the center of the back, and nerves are long, thin fibers that carry signals between the brain and other parts of the body.
The brain is responsible for controlling and coordinating all the functions of the body. It receives and processes sensory information, generates thoughts and emotions, and commands the muscles to move.
The spinal cord is responsible for transmitting signals between the brain and the rest of the body. When a nerve signal reaches the spinal cord, it is processed and sent to the appropriate part of the body. The spinal cord also helps to control reflex actions, which are automatic responses to stimuli that do not require conscious thought.
Nerves are long, thin fibers that carry signals between the brain and other parts of the body. They are made up of nerve cells called neurons, which are specialized cells that are capable of transmitting electrical signals.
A nerve impulse is an electrical signal that is transmitted along a neuron. It carries information from one part of the body to another, and is responsible for transmitting signals such as sensations of touch, pain, and temperature, as well as messages to muscles to move.
The central nervous system (CNS) consists of the brain and the spinal cord, while the peripheral nervous system (PNS) consists of all the nerves that lie outside the CNS. The CNS is responsible for processing and coordinating information, while the PNS is responsible for transmitting signals between the CNS and the rest of the body.
A synapse is a small gap that separates the axon terminal of one neuron from the dendrites of another neuron. When a nerve impulse reaches the axon terminal of a neuron, chemicals called neurotransmitters are released into the synapse. These neurotransmitters then cross the synapse and bind to receptors on the dendrites of the next neuron, transmitting the impulse from one neuron to the next.
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