Identify and describe Why We Need a Nervous System, Structure of a Neuron and Synapses: Connecting Nerve Cells in the context of structure and function.
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GCSE Biology Revision
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GCSE Biology revision
Structure and function
The human nervous system
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Explain the relationships between Why We Need a Nervous System, Structure of a Neuron and Synapses: Connecting Nerve Cells and how they contribute to structure and function.
Apply and analyse knowledge of Why We Need a Nervous System, Structure of a Neuron and Synapses: Connecting Nerve Cells to interpret unfamiliar information about structure and function.
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Key knowledge
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Why We Need a Nervous System
- Large multicellular organisms like humans need a way for different body parts to communicate so they can coordinate behaviour and respond to their surroundings.
- The body uses two organ systems for communication: the nervous system and the endocrine system.
Structure of a Neuron
- A neuron (nerve cell) is a specialised cell adapted to carry electrical impulses from one point to another.
- Neurons are long and thin with many branching connections at each end, allowing them to pass messages to other nerve cells.
- Neurons function similarly to a biological wire, carrying a small electrical current through the body.
Synapses: Connecting Nerve Cells
- A synapse is the junction (gap) between two nerve cells where communication takes place.
- When an electrical impulse reaches the end of a neuron, it triggers the release of chemicals that diffuse across the synapse.
- These chemicals bind to the next neuron and trigger a new electrical impulse, allowing the signal to continue along the nervous system.
The Central Nervous System (CNS)
- The central nervous system (CNS) is made up of the brain and the spinal cord, and is where processing and decision-making take place.
- The CNS receives sensory information, decides what action is needed, and sends instructions to the rest of the body.
Sensory and Motor Neurons
- Sensory neurons carry information from receptors all over the body (such as temperature or carbon dioxide levels) to the CNS.
- Once the CNS has processed the information, it sends impulses back out via motor neurons to effectors.
- Effectors are muscles or glands that respond by contracting or releasing hormones.
Reflex Arcs
- A reflex arc is the nerve pathway that underlies unconscious reflexes, such as pulling your hand away from a hot object.
- Reflexes are rapid and automatic, allowing the body to respond quickly to potentially harmful stimuli without conscious thought.
- In a reflex arc, a stimulus is detected by receptor cells, which stimulate a sensory neuron to carry an impulse to the spinal cord.
- Inside the spinal cord, a relay neuron transfers the impulse to a motor neuron, which carries it to an effector such as a muscle.
The Full Pathway of a Reflex Arc
- The sequence of a reflex arc is: stimulus receptor sensory neuron relay neuron (in spinal cord) motor neuron effector response.
- At each junction between neurons, a synapse converts the electrical signal into a chemical signal so it can pass between nerve cells.
- This entire process occurs without the brain needing to make a conscious decision, making the response extremely fast.