July 6, 2021
In I/GCSE Biology, nervous system is commonly asked in the exam! 👍
The nervous system
- Reaction time ➡️ Time between hearing the gun and reacting to it
- Nervous system ➡️ brain, spinal cord and neurons (or nerve cells)
- Receptors ➡️ cells that detect stimuli or change in environment
Features of neurons
It is important to memorize the following features of neurons in I/GCSE Biology!
- Neurons not joined together ➡️ small gap between them = synapse
- When impulse reaches end of neuron ➡️ chemical released
- Chemical travels across gap and starts an impulse in next neuron
- Message can only travel in one direction
3 types of neurons
You should also remember 3 types of neurons in I/GCSE Biology,
- Sensory neurons = carry impulses from receptor to spinal cord
- Relay neurons = carry impulses through spinal cord, up to the brain and from the brain back down the spinal cord
- Motor neurons = take impulses from spinal cord to an effector
👇 Look at the diagram showing the 3 types of neurons below! 👇
Receptor and effector
Receptors in the:
- Eyes – sensitive to light
- Ears – sensitive to sound + change in position (help keep out balance)
- Tongue – sensitive to chemicals (enables us to taste)
- Nose – sensitive to chemicals (enables us to smell)
- Skin – sensitive to touch, pressure, pain and temperature change
- Each receptor cell ➡️ nucleus + cytoplasm surrounded by cell membrane (animals and humans)
Effectors in the:
- Muscle = made to contract
- Gland = secretes a chemical (e.g. hormone)
Nervous system pathway:
It is important to memorize the nervous system pathway in I/GCSE Biology!
- Step 1 – Receptors cells detect stimuli or change in environment
- Step 2 – Information from receptor (e.g. something burning – nose) passes info along neurons to brain
- Step 4 – Information passes along the neurons as signals called impulses
- Step 5 – Brain coordinates a response – sends information to appropriate organ
Reflex actions
In I/GCSE Biology, reflex actions is also a commonly asked topic!
Reflex actions:
- Automatic + very quick response
- Needed to protect us from being hurt or damage a tissue
Reflex arc:
- Step 1 – Pain detected by receptor
- Step 2 – Sends impulse along sensory neurone to relay in spinal cord
- Step 3 – Relay neuron sends impulse via an arc to motor
- Step 4 – Motor neuron sends impulse to effector
- Step 5 – Muscle contracts or gland secrets
*Other types: e.g. coughing or blinking
References
- "Nervous System: Central Nervous System", https://slideplayer.com/slide/12851261/78/images/3/3+main+types+of+Neurons%3A+sensory+neuron+motor+neuron+relay+neuron.jpg
- "Igcse biology edexcel 2.77 2.90", https://image.slidesharecdn.com/igcsebiologyedexcell2-140916213251-phpapp01/95/igcse-biology-edexcel-277-290-6-638.jpg?cb=1410905825
- "Muscle Stimulus And Response", https://4.bp.blogspot.com/-8VzDTk4OAxY/WZpyjpUeZKI/AAAAAAAAFtk/aaC_CH0dDckjTSGmF9fUVpyut4K2B_bCACLcBGAs/s620/Picture7.png
- "The Nervous System and Reflex Arcs IGCSE Biology", https://images.slideplayer.com/39/10938436/slides/slide_15.jpg
And we're done with this topic! Well Done!
Drafted by Alyssa (Biology)