Your nervous system is basically your body's electrical network, constantly...
Biology280 views·Updated 12 Jul 2026·2 pagesWJEC A Level Biology: Nervous System Overview
Caitlin Ellis@caitlinellis0312
1
of 2
The Nervous System Structure and Function
Think of your nervous system as your body's personal internet - it detects changes (called stimuli), processes the information, and sends out responses faster than you can blink. The whole system is split into two main parts that work together seamlessly.
The Central Nervous System (CNS) includes your brain and spinal cord - basically your body's command centre. Meanwhile, the Peripheral Nervous System consists of all the nerves branching out from your CNS, including the somatic nerves (which you control consciously) and the autonomic nerves (which handle unconscious stuff like your heartbeat).
Neurones are the specialised cells that carry these electrical messages around your body. You've got three types: sensory neurones (carry signals from receptors to your CNS), relay neurones (connect things up in your CNS), and motor neurones (carry signals from CNS to muscles).
The action potential is where the magic happens - it's an electrical signal that travels along the neurone. Your neurone starts at resting potential (about -60mV), but when stimulated strongly enough, sodium channels open and the inside becomes positive . This creates a wave of electrical activity that zooms along the axon. The refractory period afterwards ensures signals only travel in one direction - pretty clever, right?
Key Insight: Reflex actions bypass your brain entirely, travelling through the spinal cord for lightning-fast protective responses - that's why you pull your hand away from something hot before you've even consciously realised it's burning!
2
of 2
Nerve Impulse Speed and Synaptic Transmission
Ever wondered why some nerve signals are faster than others? Three main factors control the speed of nerve impulses: temperature (warmer = faster ion movement), axon diameter (bigger = less resistance), and most importantly, myelination - those Schwann cells wrapped around axons that make signals jump between nodes of Ranvier.
Synapses are the gaps between neurones where the real communication happens. Unlike electrical synapses (direct connection), chemical synapses use neurotransmitters - chemical messengers that cross the synaptic cleft to pass on the signal.
Here's how synaptic transmission works with acetylcholine: when an action potential arrives at the presynaptic button, calcium channels open and Ca²⁺ floods in. This causes vesicles full of acetylcholine to fuse with the membrane and dump their contents into the synaptic cleft. The acetylcholine then binds to receptors on the postsynaptic membrane, opening sodium channels and generating a new impulse.
The process doesn't end there - acetylcholinesterase quickly breaks down the acetylcholine into choline and ethanoic acid, which get recycled back into the presynaptic neurone. This cleanup is crucial for preventing continuous stimulation.
Exam Tip: Many drugs work by interfering with synaptic transmission - some amplify signals (like opening more calcium channels), while others inhibit them (like blocking neurotransmitter production or receptor binding). Understanding this mechanism helps explain everything from antidepressants to nerve gases!
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Biology280 views·Updated 12 Jul 2026·2 pagesWJEC A Level Biology: Nervous System Overview
Caitlin Ellis@caitlinellis0312
Your nervous system is basically your body's electrical network, constantly processing information and controlling everything from your heartbeat to your exam stress responses. Understanding how nerve impulses travel and how synapses work is crucial for A-level biology - and it's...
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of 2
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The Nervous System Structure and Function
Think of your nervous system as your body's personal internet - it detects changes (called stimuli), processes the information, and sends out responses faster than you can blink. The whole system is split into two main parts that work together seamlessly.
The Central Nervous System (CNS) includes your brain and spinal cord - basically your body's command centre. Meanwhile, the Peripheral Nervous System consists of all the nerves branching out from your CNS, including the somatic nerves (which you control consciously) and the autonomic nerves (which handle unconscious stuff like your heartbeat).
Neurones are the specialised cells that carry these electrical messages around your body. You've got three types: sensory neurones (carry signals from receptors to your CNS), relay neurones (connect things up in your CNS), and motor neurones (carry signals from CNS to muscles).
The action potential is where the magic happens - it's an electrical signal that travels along the neurone. Your neurone starts at resting potential (about -60mV), but when stimulated strongly enough, sodium channels open and the inside becomes positive . This creates a wave of electrical activity that zooms along the axon. The refractory period afterwards ensures signals only travel in one direction - pretty clever, right?
Key Insight: Reflex actions bypass your brain entirely, travelling through the spinal cord for lightning-fast protective responses - that's why you pull your hand away from something hot before you've even consciously realised it's burning!
2
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Nerve Impulse Speed and Synaptic Transmission
Ever wondered why some nerve signals are faster than others? Three main factors control the speed of nerve impulses: temperature (warmer = faster ion movement), axon diameter (bigger = less resistance), and most importantly, myelination - those Schwann cells wrapped around axons that make signals jump between nodes of Ranvier.
Synapses are the gaps between neurones where the real communication happens. Unlike electrical synapses (direct connection), chemical synapses use neurotransmitters - chemical messengers that cross the synaptic cleft to pass on the signal.
Here's how synaptic transmission works with acetylcholine: when an action potential arrives at the presynaptic button, calcium channels open and Ca²⁺ floods in. This causes vesicles full of acetylcholine to fuse with the membrane and dump their contents into the synaptic cleft. The acetylcholine then binds to receptors on the postsynaptic membrane, opening sodium channels and generating a new impulse.
The process doesn't end there - acetylcholinesterase quickly breaks down the acetylcholine into choline and ethanoic acid, which get recycled back into the presynaptic neurone. This cleanup is crucial for preventing continuous stimulation.
Exam Tip: Many drugs work by interfering with synaptic transmission - some amplify signals (like opening more calcium channels), while others inhibit them (like blocking neurotransmitter production or receptor binding). Understanding this mechanism helps explain everything from antidepressants to nerve gases!
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