Nervous system

• Homeostasis


  The process by which the body maintains a relatively stable internal environment
• Homeostatic imbalances = illness or death
• To preserve homeostasis the body must


  • Detect changes (stimuli) occurring inside & outside the body
  • Respond to these changes by altering the activities of organ systems
  • Coordinate the activities of all organ systems
• Functions of the Nervous System

  • Sensory function
  • Integrative function
  • Motor function
• Sensory function


  • Receptors detect sensory input
  • Sensory input is sent to control centre
• Integrative function


  • Analyses & interprets sensory input
  • Determines appropriate responses
  • Generates the motor output that causes the response

  
• Motor function


  • Issues motor output to activate an effector
• General sensory receptors


  • Thermoreceptors (detect changes in temperature)
  • Nociceptors (detect painful stimuli)
  • Mechanoreceptors (tactile receptors, baroreceptors, proprioceptors)
• Special sensory receptors


  • Photoreceptors (detect light)
  • Chemoreceptors (detect chemicals in solution)
  • Mechanoreceptors called hair cells (detect hearing & balance stimuli)
• Effectors


  • Skeletal muscle
  • Cardiac & smooth muscles
  • Gland secretion
• Divisions of the Nervous System

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)

  
• Central Nervous System (CNS)

  • Consists of the brain and spinal cord
  • Control centre - performs the function of integration
  • Controls our emotions, behaviours and personality
  • Performs intellectual (cognitive) functions
  • Stores memories

  
• Peripheral Nervous System (PNS)

  • Consists of sensory receptors and the cranial, spinal and peripheral nerves that link all parts of the body to the CNS
  • Cranial nerves and their branches primarily innervate structures of the head & neck
  • Spinal nerves branch to form the peripheral nerves that innervate all parts of the body below the head

  
• Functional divisions of the PNS

  • Sensory Division (afferent division)
  • Motor Division (efferent division)
• Motor Division


  • Somatic Nervous System
  • Autonomic Nervous System

  
• Somatic Nervous System


  • Conveys "somatic" motor output from the CNS to the body's skeletal muscles
  • Controls voluntary skeletal muscle movements and involuntary skeletal muscle movements (somatic reflexes)

  
• Autonomic Nervous System


  • Conveys "autonomic" motor output from the CNS to the body's glands, cardiac & smooth muscles
  • Controls involuntary (automatic) activities

  
• Divisions of the Autonomic Nervous System

  • Sympathetic Division
  • Parasympathetic Division

  
• Sympathetic Division


  • Controls "fight-or-flight" activities - activates body functions that support physical activity and inhibits those that don't
• Parasympathetic Division


  • Controls "rest and digest" activities - activates body functions that conserve and restore body energy
• Components of the Nervous System

  • Neuroglia
  • Neurons (nerve cells)

  
• Neuroglia


  Support neuron development and function
• Neurons


  Specialised cells that perform the function of communication - when stimulated they generate electrical signals called graded potentials and action potentials to conduct sensory and motor information from one part of the body to another

  
• Structural Components of a Neuron

  • Dendrites
  • Cell body
  • Axon (fiber)
  • Axon terminals
• Dendrites


  • Short processes that are the main receptive (or input) region of a neuron - act as sensory receptors and receive information from other neurons
• Cell Body


  • Contains a nucleus and organelles - receives information from other neurons and converts this information into a graded potential
• Axon


  • A single process that connects to the cell body - generates and conducts action potentials to convey information from the initial segment to the axon terminals
• Axon Terminals


  • Form a synapse with another cell - contain synaptic vesicles that store and release neurotransmitters to transmit the information to another neuron, muscle or gland
• Nucleus


  Clusters of neuron cell bodies in the CNS
• Ganglion


  Clusters of neuron cell bodies in the PNS
• Tract


  Bundles of neuron axons in the CNS
• Nerve


  Bundles of neuron axons in the PNS
• Structural Classifications of Neurons

  • Multipolar
  • Bipolar
  • Unipolar
• Functional Classifications of Neurons

  • Sensory Neurons
  • Interneurons
  • Motor Neurons
• Sensory Neurons


  • Conduct sensory input from receptors to the CNS - Unipolar in structure

  
• Interneurons


  • Conduct information within the CNS - Multipolar in structure
• Motor Neurons


  • Conduct motor output away from the CNS to a muscle or gland - Multipolar in structure
• Neurons perform the function of neural communication. Their structure allows them to detect stimuli, generate electrical signals to conduct sensory input to the CNS, sensory input or motor output within the CNS, and motor output from the CNS to an effector muscle or gland

  
• Basic Principles of Electricity: Particles can be positively or negatively charged, and as opposite charges attract, energy is required to keep them apart
• Neurons


  Perform the function of neural communication