divisions of the nervous system

• CNS


  The central nervous system, consisting of the brain and the spinal cord
• Brain


  • Provides conscious awareness
  • Involved in all psychological processes
  • Consists of many regions responsible for different functions
• Main lobes of the brain

  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe
• Occipital lobe


  Processes visual information
• Temporal lobe


  Processes auditory information
• Parietal lobe


  Integrates information from the different senses and plays an important role in spatial navigation
• Frontal lobe


  Associated with higher-order functions, including planning, abstract reasoning and logic
• Brain stem


  Connects the brain and spinal cord and controls involuntary processes, including our heartbeat, breathing and consciousness
• Spinal cord


  • Transfers messages to and from the brain, and the rest of the body
  • Responsible for simple reflex actions that do not involve the brain
• Peripheral Nervous System (PNS)


  Relays messages (nerve impulses) from the CNS (brain and spinal cord) to the rest of the body
• Components of the PNS

  • Somatic nervous system
  • Autonomic nervous system
• Somatic nervous system


  • Facilitates communication between the CNS and the outside world
  • Made up of sensory receptors that carry information to the spinal cord and brain, and motor pathways that allow the brain to control movement
  • Carries sensory information from the outside world to the brain and provides muscle responses via the motor pathways
• Autonomic nervous system


  • Plays an important role in homeostasis, which maintains internal processes like body temperature, heart rate and blood pressure
  • Only consists of motor pathways
  • Has two components: sympathetic nervous system and parasympathetic nervous system
  • Controls automatic responses
• Sympathetic nervous system


  • Typically involved in responses that prepare the body for fight or flight
  • Impulses travel to organs in the body to help us prepare for action when faced with a dangerous situation
  • Increases heart rate, blood pressure and breathing rate, while suppressing less important functions like digestion, salivation and the desire to urinate
• Parasympathetic nervous system


  • Relaxes the body and returns us to our 'normal' resting state: rest and digest
  • Slows down heart rate and breathing rate, and reduces blood pressure
  • Starts up any functions that were previously slowed down during a fight or flight reaction (e.g. digestion)
• Types of neurons


  • Sensory
  • Relay
  • Motor
• Sensory neurons


  • Found in receptors such as the eyes, ears, tongue and skin
  • Carry nerve impulses to the spinal cord and brain
  • When nerve impulses reach the brain, they are translated into 'sensations' such as vision, hearing, taste and touch
  • Some sensory neurons stop at the spinal cord, allowing for quick reflex actions
• Relay neurons


  • Found between sensory input and motor output/response
  • Found in the brain and spinal cord
  • Allow sensory and motor neurons to communicate
• Motor neurons


  • Found in the central nervous system (CNS)
  • Control muscle movements
  • When stimulated, they release neurotransmitters that bind to receptors on muscles to trigger a response, leading to movement
• Neurons


  • Dendrites receive signals from other neurons or from sensory receptor cells
  • Cell body is the 'control centre' of the neuron and contains the nucleus
  • Axon is a long slender fibre that carries nerve impulses, in the form of an electrical signal known as action potential, away from the cell body towards the axon terminals
  • Most axons are surrounded by a myelin sheath which insulates the axon so that the electrical impulses travel faster along the axon
  • Axon terminal connects the neuron to other neurons (or directly to organs), using a process called synaptic transmission
• Parts of a neuron

  • Dendrites
  • Cell body
  • Axon
  • Axon terminals
• All three neurons consist of similar parts
• Synaptic transmission


  1. Information passed down axon as electrical impulse (action potential)

  2. Action potential reaches end of axon

  3. Synaptic vesicles release neurotransmitters across synaptic gap

  4. Neurotransmitters bind to receptors on post-synaptic cell
• Synaptic transmission


  Process by which one neuron communicates with another
• Synaptic vesicles


  • Contain chemical messengers (neurotransmitters)
• Excitatory neurotransmitter (e.g. adrenaline) binds to post-synaptic receptors

  Causes positive electrical charge in cell membrane, making post-synaptic cell more likely to fire
• Inhibitory neurotransmitter (e.g. serotonin) binds to post-synaptic receptors


  Results in negative charge, making post-synaptic cell less likely to fire
• Excitation


  1. Receptor stimulation results in an increase in the positive charge of the postsynaptic neuron

  2. Increases the likelihood of the neuron firing
• Inhibition


  1. Receptor stimulation results in an increase in the negative charge of the postsynaptic neuron

  2. Decreases the likelihood of the neuron firing
• Summation


  The addition of positive and negative post-synaptic potentials
• A nerve cell can receive both positive and negative potentials simultaneously
• These potentials are summed and if the net effect on the postsynaptic neuron is inhibitory, the neuron will be less likely to fire, and if the net effect is excitatory, the neuron will be more likely to fire
• Explaining summation is necessary for full marks