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In I/GCSE Biology, the nervous system consists of the brain and spinal cord. Impulses from receptors pass along nerves containing nerve cells called sensory neurons to the CNS. Motor neurons transmit impulses to the muscles and glands.
Motor Neurones
- The cell body of the neurone is at one end of the fibre, in the CNS.
- Dendrons are cytoplasmic extensions which form further extensions called dendrites.
- Synapses are junctions to other nerve cells.
- The axon terminals carry impulses to the effector organ. The axon is covered with myelin sheath – a type of fat which insulates the axon, preventing short circuits and speeds up the impulses.
Sensory Neurones
- A sensory neurone has a similar structure to the motor neurone, but the cell body is located on the side branch of the fibre, just outside the CNS.
- The neurone is also covered in myelin sheath.
Synapses 🦴🦴
- In I/GCSE Biology, synapses are gaps between nerve cells.
- The gap is not crossed by electrical impulses, but by chemicals. Impulses arriving at the synapse cause the ends of the axon to secrete a chemical called a neurotransmitter, which diffuses across the gap and attaches to the membrane of the second neurone.
- This starts off impulses in the second cell. There are tons of synapses in the body to ensure an infinite number of possible pathways through the system.
Reflex Arc
- The stimulus is detected by pain receptors in the skin, generating impulses in the sensory neurones. These enter the CNS through the dorsal root ganglion.
- In the spinal cord, the sensory neurons are connected by synapses to relay neurones (interneuron), which in turn, connect to the motor neurones.
- They emerge from the spinal cord through the ventral root and send impulses back to the muscles of the arm. These muscles contract, pulling the finger away from the painful stimulus.
That's the end of the topic!
Drafted by Joey (Biology)
Reference:
https://www.earthslab.com/physiology/sensory-motor-functions-and-neurons/