B3.1 - Coordination and control , the nervous system

• The human nervous system consists of the central and peripheral nervous system
• The nervous system enables humans to react to their surroundings and to coordinate their behavior.
• Information is sent through the nervous system as electrical impulses – electrical signals that pass along nerve cells known as neurons. A bundle of neurons is known as a nerve.
• Nervous system consists of:

  A)

  B)

  
• A nerve

  A)

  B)

  
• Neurone


  A nerve cell, specially adapted to carry electrical charges, called nerve impulses from one part of the body to another
• Sensory neurone


  A neurone which carries nerve impulses from receptors to the central nervous system
• Motor neurone


  A neurone which carries nerve impulses from the central nervous system to effectors
• Relay neurone


  A neurone that acts as a coordinator, transmitting impulses from the sensory to the motor neurone in the spinal cord
• Effector


  A cell, tissue, organ or organ system that responds to a stimulus
• Voluntary response


  A nerve pathway which produces a conscious response to a stimulus
• Reflex response


  A nerve pathway which produces an automatic response to a stimulus
• Synapse

  A gap between two neurones
• Axon


  A single long fibre within a neurone which carries a nervous impulse away from the cell body
• Electrical impulse


  A signal which is passed through the nervous system as electrical charge to instigate a response
• Central nervous system (CNS)


  The part of the nervous system which includes the brain and spinal cord
• Stimulus


  A detectable change in the internal or external environment of an organism e.g. light, sound, or temperature.
• Receptor


  A cell or organ which detects a stimulus.
• The central nervous system (CNS) consists of the brain and spinal cord. It is responsible for coordinating the response by directing the electrical impulse to the correct effector.
• Voluntary responses move through the nervous system via the brain, while automatic responses move through the unconscious part of the brain or the spinal cord. The neurones found in the CNS are relay neurones.
• Neurons

  • Reach all parts of the body to coordinate responses
  • Each neuron is made up of key components
• Axon


  The long fiber which transmits electrical impulses away from the cell body
• Axons


  • Adapted to ensure fast transmission of the electrical impulse
  • A fatty layer called the myelin sheath may cover the axon to insulate it and increase the speed of the impulse
  • Some axons are very long (more than a meter in length), this reduces the number of synapses and speeds up transmission
• Dendrites

  Branched endings that create links between neurons
• One neuron can link with many other neurons which increases the response from a stimulus
• Nerve

  A) Dendrites

  B) Axon

  C) nerve

  
• Synapse

  A synapse is a gap between two neurons found between the terminal end of the axon of one neuron and the membrane of a dendrite of another.
• Electrical impulses cannot cross synapses; instead, chemicals called neurotransmitters (such as dopamine and serotonin) transmit the impulse from one neuron to the next. This is the only part of the nervous system where messages are chemical as opposed to electrical.
• Neurotransmitters diffuse across the synapse, which slows down the transmission of electrical impulses. Synapses ensure that impulses only travel in one direction.
• Synapse

  A) Neurotransmitters

  
• Electrical impulse travels


  Along the first axon
• Electrical impulse arrives at terminal end of axon on presynaptic neurone


  Chemical messengers (neurotransmitters) are released from vesicles
• Neurotransmitters diffuse across synaptic gap


  Bind with receptor molecules on membrane of dendrite of second neurone (postsynaptic membrane)
• Binding of neurotransmitters on postsynaptic membrane


  Stimulates second neurone to generate electrical impulse
• Electrical impulse travels

  Down the second axon
• Neurotransmitters are destroyed or recycled


  To prevent continued stimulation of second neurone and repeated impulses
• Voluntary response

  A conscious decision to carry out a particular action, starting with the brain
• Voluntary responses

  • Take longer than involuntary responses as we consider the response before doing it
• Involuntary (or reflex) response

  Does not involve the brain as the coordinator, you are not aware you have completed it until after
• Involuntary (reflex) response

  Passage of information is called a reflex arc