Coordination and Response Yayyu The nervous system CNS PNS Human nervous system Nerve cells ( Neurones ) • The nervous system allows us to make sense of our surroundings and respond to them and to coordinate and regulate body functions • Information is sent through the nervous system as nerve impulses - electrical signals that pass along nerve cells known as neurones • A bundle of neurones is known as a nerve. Neurones • Neurones have a long fibre ( axon ) • This means that less time is wasted transferring the impulse from one cell to another • The axon is insulated by a fatty sheath with small uninsulated sections along it (called nodes) • This means that the electrical impulse does not travel down the whole axon, but jumps from one node to the next • Their cell body contains many extensions called dendrites • This means they can connect to many other neurones and receive impulses from them, forming a network for easy communication Types of neurones Motor Relay Sensory Function Carry impulses from CNS to effector (muscle, glands) (act when they receive impulses or hormones) Found in the CNS and connects to other neurones Carry impulses from sense organs to CNS Length Long Short Long Difference in shape Large cell body at one end with long dendrites ( makes contact with other neurons) Small cell body at one end with many dendrites Cell body branches off the middle of the axon (long fibre ) Voluntary and involuntary responses A voluntary response is one where you make a conscious decision to carry out a particular action therefore it starts with your brain An involuntary (or reflex) response does not involve the brain as the coordinator of the reaction and you are not aware you have completed it until after you have carried it out Involuntary actions are usually ones which are essential to basic survival and are rapid , whereas voluntary responses often take longer as we consider what the response might be before doing it. The Reflex Arc: reflex actions are automatic, fast and protective Synapse • Neurones never touch each other • The junctions (gaps) in between them are called synapses • The electrical impulse arrives at the synapse • Then vesicles are stimulated to release tiny amounts of neurotransmitter molecules. • The neurotransmitter molecules diffuse across the synaptic gap and bind with receptor molecules on the membrane of the other neurone (known as the post synaptic membrane ) • This stimulates a new impulse in the neurone. • Impulses only travel in one direction. Synapses control the direction. • Synapses slow down the speed. • It is the only place where drugs can act to affect the nervous system - ex: this is where heroin works How an impulse is passed on at a synapse