The Nervous System

• The Nervous System


  The roles of different subdivisions of the central and peripheral nervous systems in responding to, and processing and coordinating with, sensory stimuli received by the body to enable conscious and unconscious responses, including spinal reflexes
• Central Nervous System

  • It comprises the brain and the spinal cord
  • Its primary role is to process information received from the body's internal and external environments and to activate appropriate responses
• Brain


  • Is responsible for basically everything we think, feel and do
  • The brain interprets the information and decided how it will respond
• Spinal cord


  • Long, thin bundle of nerve fibres that extends from the base of the brain to the lower back
  • Receives sensory information from the Peripheral NS and sends to brain for processing
  • Receives motor information from the brain and sends it to the relevant part of the body (via the Peripheral NS)
• Peripheral Nervous System


  • Is the entire network of nerves located outside the Central NS
  • It extends from the top of the head to the tips of our fingers and toes
  • Carries information to the Central NS from the body's muscles, organs and glands (about our internal environment) and from the sensory organs (about the external environment)
• Somatic Nervous System


  • Is a sub-division of the Peripheral NS comprising a network of nerves that carries sensory information to the Central NS and motor information from the Central NS
  • Our Somatic NS is only active when we voluntarily move
  • Involved in the activity of our skeletal muscles
• Autonomic Nervous System


  • Is a sub-division of the peripheral NS that connects the Central NS to the body's internal organs (such as the heart, stomach, liver) and glands (such as sweat, salivary and adrenal glands), providing feedback to the brain about their activities
  • Self-regulates and occurs without conscious effort and not typically under voluntary control – even when we are sleeping!
• Sympathetic Nervous System


  • Sub-division of the Autonomic NS
  • Activates internal muscles, organs and glands to prepare the body for exercise or to deal with a stressful or threatening situation
  • This is often initiated by a stressor to enhance survival by providing an immediate response
• Parasympathetic Nervous System


  • Sub-division of the Autonomic NS
  • Helps to maintain the internal body environment in a steady, balanced state of normal functioning
  • Also counterbalances the effects of the Sympathetic NS by restoring our body to a state of calm
  • It's calming effects aren't as immediate and intense at the Sympathetic NS
  • Also the prominent system when doing regular everyday activities like eating your lunch
• Enteric Nervous System


  • Is embedded within the walls of the gastrointestinal tract and is dedicated to its functioning
  • Neurons and ganglia detect the physiological condition of the gastrointestinal tract whilst also controlling gut movement
  • Works with the Central NS to control the digestive system (direct link via Vagus Nerve)
  • Sometimes referred to as the 'second brain' due to the level of autonomy, it's memory abilities and the high number of neurons found
• Pathway of a Conscious Response

  1. The sensory receptors register the sensory stimulus

  2. Sensory messages are sent along the peripheral nervous system (PNS) to the brain via the spinal cord

  3. The brain coordinates the conscious motor response by sending motor messages out via the PNS

  4. The skeletal muscles of the body receive the motor message and respond accordingly
• Spinal Reflexes


  1. It is sometimes referred to as a reflex arc because the response to an incoming stimulus is automatically 'reflected back' from the spinal cord without any initial input from the brain

  2. Spinal reflexes are adaptive as they save us time in situations that may be harmful to us

  3. Is an unconscious, automatic reflex controlled solely by neural circuits in the spinal cord
• Scenario: Putting your hand under the cold water tap

  1. The sensory receptors on an individual's hand register the feeling of cold water.

  2. The sensory neural messages travel to the brain via the spinal cord.

  3. The brain will have registered the unpleasantness of the cold water and will then initiate a response to move the hand.

  4. The skeletal muscles of the hand register the motor message and moves.
• Scenario: Accidently touching the hot coals of the BBQ

  1. The sensation of the hot coals from the BBQ are detected by the body's sensory receptors, which send a signal via sensory neurons to the spinal cord.

  2. The spinal cord, via interneurons, immediately relays a signal via motor neurons to initiate an unconscious motor response in the skeletal muscles in response to the hot coals.

  3. As the motor neurons send messages to unconsciously remove the hand, sensory neurons send their neural impulses to the brain to make it aware of any pain or sensation. The brain's conscious awareness is not necessary for the reflex response, but the brain will register the sensations independently and after the reflex response has occurred. Which is why the pain was of the burn was not registered until after
• Neural Basis of Learning & Memory

  Synaptic plasticity – resulting from long-term potentiation and long-term depression, which together act to modify connections between neurons (sprouting, rerouting and pruning) – as the fundamental mechanism of memory formation that leads to learning
• Synaptic Plasticity


  • Refers to the ability of the synapse to change in response to experience
  • Enables change involving the strengthening or weakening of connections between the neurons at a synapse
• Hebb (1949)


  • "neurons that fire together wire together"
  • Repeated neural transmission - presynaptic and postsynaptic neurons simultaneously active
  • Repeated activation changes the structure or chemistry of synapse, strengthening the connection
  • Makes them more likely to fire together again – signals become stronger and more efficient
• Sprouting


  • Is the creation of new extensions on a neuron to allow it to make new connections with other neurons
  • This occurs through the growth of nerve endings on axons or dendrites
• Rerouting


  • Occurs when new connections are made between neurons to create alternate neural pathways
  • These alternate 'routes' may be entirely new neural pathways or connections to other pathways in the brain
  • The rerouting may involve the existing synaptic connections and/or new connections from the sprouts
• Pruning


  • Refers to the process of eliminating or trimming away old synaptic connections between neurons
  • When certain connections are not activated or used, they are eliminated
  • This is necessary to make way for more essential connections in our brain, thereby fine-tuning our brain's functioning and making it more efficient
• Long Term Potentiation (LTP)

  • Long-lasting strengthening of synaptic connections
  • Neurons communicate with each other more easily
  • Postsynaptic neuron becomes more responsive
  • The more often the neural pathway is used the stronger it becomes
• Long Term Depression (LTD)


  • A long-lasting decrease in the strength of synaptic transmission
  • Results from a lack of stimulation of pre and post synaptic neurons
  • Unused neural pathways eventually disappear...
  • Believed to also be a helpful part of learning as it only leaves behind the important and necessary information
• Glutamate


  • Main excitatory neurotransmitter – makes postsynaptic neurons more likely to fire
  • Promotes growth and strengthening of synaptic connections – leading to LTP
  • Also initiates growth of new dendritic spines on postsynaptic neurons (sprouting) –> more synaptic connections (bushy dendrites)