5.1 Nerves

• Nervous system


  The system that coordinates the body's activities and responses to internal and external stimuli
• Components of the nervous system

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

  The brain and spinal cord
• Peripheral Nervous System (PNS)

  • Afferent division (inputs)
  • Efferent division (outputs)
  • Somatic
  • Autonomic
  • Enteric (inputs and outputs from the gut)
• Neurons


  • Specialised cells that are long-lived, have a high metabolic rate, and cannot divide (missing centrioles)
• Structure of a neuron

  • Cell body
  • Dendrites
  • Axons
  • Telodendria
  • Axon terminals
• Types of neuroglia


  • Maintain the Blood brain barrier
  • Repair damaged neural tissue
  • Provide 3D framework
  • Guide neuron development
  • Provide myelin sheath (insulation)
  • Regulate environment
• Resting membrane potential


  Difference of ionic composition of ECF versus cytosol, maintained by the active Na+/K+ pump and differing membrane permeability
• Altering the membrane potential


  Activation leads to changes in the membrane, giving rise to a local or graded potential
• Excitation potential


  Depolarisation leads to action potentials, which have several phases and are all the same size
• Synapse


  Connections between neurons, found at the end of the axon, where neurotransmitters are released into the synaptic cleft to activate the post-synaptic cell
• Types of neurotransmitters


  • Cholinergic (Acetyl Choline)
  • Biogenic amines (Nor-epinephrene, Dopamine, Serotonin)
  • Amino acids (GABA)
  • Neuropeptides (Opioids)
  • Dissolved gases (Nitric oxide, Carbon monoxide)
• Nervous system cells


  neurons and nervous tissue supporting cells are neuroglia
• Central nervous system function


  It is responsible for integrating, processing, and coordinating sensory data and motor commands. 
• peripheral nervous system function

  The PNS delivers sensory information to the CNS and carries motor commands to peripheral tissues and systems, except those of the enteric nervous system
• Somatic nervous system


  Controls skeletal muscle contractions. Voluntary contractions are under conscious control. 
• autonomic nervous system


  visceral motor system, automatically regulates smooth muscle, cardiac muscle, glandular secretions, and adipose tissue at the sub-conscious level
• Two subdivisions of ANS

  The ANS includes a parasympathetic division and a sympathetic division, which commonly have antagonistic (opposite) effects.
• Enteric nervous system


  The enteric nervous system is an extensive network of neurons and nerve networks in the walls of the digestive tract. 
• Functional characteristics of neuron

  • Neurons lack centrioles and therefore typical CNS neurons cannot divide. 
  • Cell body, dendrite, axon and telodendria 
• Cell body 

  • Has a large nucleus with nucleolus and cytoplasm called perikaryon.   
  • Neurofibrils extend into dendrite and axon to provide support. 
• Perikaryon


  Cytoskeleton of perikaryon contain neurofilament and neurotubules. Contain organelles that provide energy and synthesize organic matieral like neurotransmitters.
• Dendrites

  • Dendrite have dendritic spines that participate in synapses. 
  • They represent 80-90% of neuron total surface area
• Axon


  Axon propagates electrical impulse (action potential).
• Axoplasm


  Contain neurofibrils, neurotubules, small vesicles, lysosomes, mitochondria and various enzymes.