Biology Y9 Topic 3: The Nervous System

Biology Y9 Topic 3: The Nervous System

1. How it works

   • Sensory receptor detects a stimulous
     • Information sent as an electrical impulse along neurones
       • Neurones are found in nerves
       • The Impulse travels down neurones until it reaches the CNS
         • Made up of the Brain and spinal cord
           • The brain sends the correct responses down Motor Neurones to the rest of the body
             • These carry the impulses that make the effectors do the right things
               • The effectors are either muscles or glands
                 • Muscles respond by contracting
                 • Glands respond by releasing (secreting) chemical substances
                 • Can be summed up as: Stimulus - receptor - coordinator (CNS) - effector
         • The neurones that carry the impulse to the CNS are called sensory neurones

2. Reflexes

   • What are they for?
     • Help you avoid danger or harm
       • Automatic and rapid
       • Don't involve the conscious part of the brain
     • takes care of Basic body functions
       • I.E. Breathing and moving food through digestive system
   • How do they work?
     • Sensory Neurones are connected to motor neurones by relay neurones
     • Electrical impulses are sent along the neurones until they reach the effector
       • This is the reflex arc (brief)

3. How synapses work

   • Neurones aren't joined directly
     • The junctions in between are called synapses
   • Electrical impulses travel across slower than in the neurones, but the diffusion is needed to get the impulse to the brain

4. Reflex arc in detail

   • When you touch the object, a receptor in your skin is stimuated. An elecrtical impulse from a receptor is passed along a sensory neurone to the CNS - in this case, the spinal cord
     • When an impulse from the sensory Neurone arrives at a synapse with a relay neurone, a chemical is released. The chemical diffuses across the synapse to the relay neurone, where it sets off a new impulse that travels along the relay neurone
       • When the impulse reaches the synapse between the relay neurone and a motor neurone returning to the arm, another chemical is released. Again, the chemical diffuses across the synapse and starts another impulse travelling down the motor neurone to the effector
         • When the impulse reaches the effector organ, it is stimulated to respond. In this example, the impulse arrives in the muscles, causing them to contract. This action moves the hand rapidly away from the source of pain. If the effector organ is a gland, it will respond by releasing chemical substances
           • The reflex pathway is not very different from a normal conscious action. However, in a reflex action the coordinator is a relay neurone either in the spinal cord or an unconscious part of the brain. The whole reflex is very fast
             • An impulse also travels up your spinal cord to the conscious part of your brain. You know about the reflex action, but only after it has happened