autonomic nervous system

• autonomous 


  self governing
• visceral nervous system

  control over internal organs
• subconscious control

  • heart rate
  • pupil diameter
  • blood vessel contractility
  • hormonal secretions
  • gastrointestinal motility
• afferent division

  carries instructions to the CNS
• efferent division

  carries instructions from the CNS
• somatic 


  controls striated muscle
• autonomic nervous system

  • unconscious control of cardiac, smooth muscle, and glands
  • parasympathetic, sympathetic and enteric
• somatic nervous system

  conscious control of skeletal muscles
• organisation of the somatic nervous system

  • connections between the spinal cord and effector organs
  • axons of the somatic nervous system have a single myelinated axon extending from the CNS to the effector

  A) Dorsal root

  B) dorsal root ganglion

  C) sensory fibre

  D) ventral root

  E) motor fibre

  F) cutaneous receptors

  G) skeletal muscle

  H) anterior horn of grey matter

  
• organisation of the autonomic nervous system

  axons of the autonomic nervous system have:

  • a 2 neuron chain
  • the preganglionic neurone extends to the ganglion
  • the postganglionic neuron extends from ganglion to an effector organ

  A) lateral horn of grey matter

  B) mixed spinal nerve

  C) intermediolateral column

  D) preganglionic fibre

  E) sympathetic ganglion

  F) postganglionic fibres

  G) visceral organ

  H) cutaneous blood vessels

  
• motor (efferent) pathways of ANS

  • axons that form synapses with ganglion cells = preganglionic autonomic fibres
  • axons innervating effector cells = postganglionic autonomic fibres
  • the postganglionic neurone has many varicosities from which neurotransmitter is released
• ganglia

  cell bodies of many peripheral autonomic neurones occur in clusters and form swellings on nerve trunks
• neurotransmitters of the autonomic nervous system

  preganglionic nerves

  • acetylcholine (ACh) - cholinergic transmission

  postganglionic nerves

  • acetylcholine - cholinergic transmission
  • noradrenaline (NA) - noradrenergic transmission

  both

  • noradrenergic non-cholinergic neurotransmission (NANC)
• autonomic nervous system

  1. conveys all outputs from the central nervous system to rest of body except motor innervation of skeletal muscle
  2. regulates mostly non-voluntary processes in homeostasis
  3. sympathetic and parasympathetic systems functions separately
  4. sympathetic activity increases in stress, parasympathetic activity predominates during satiation and repose
  5. influenced by sensory information via control centres in brain
• 2. non voluntary processes in homeostasis regulated by the ANS

  • heartbeat
  • contraction of smooth muscle of various organs and blood vessels
  • exocrine and some endocrine secretions
  • energy metabolism e.g. liver and skeletal muscle
• 3. sympathetic and parasympathetic systems functioning separately

  • they have opposing effects in some states (heart rate, GI tract) but non others (salivary gland secretion, blood vessels)
• 4. sympathetic activity increasing in stress

  • aroused state, fight or flight response
  • pupils dilated
  • hair erected
  • increase blood sugar
  • increase heart rate
  • increase blood flow through muscle
  • blood diverted from GI tract
• parasympathetic ganglia

  • lie near to their effector organs or within their walls
  • these ganglia are often very small
• parasympathetic nervous system

  • preganglionic axons emerge from cranial and sacral regions of CNS
  • preganglionic axons form synapses in ganglia near to effector tissues
  • sacral nerves - form pelvic plexuses containing scattered ganglia and also some ganglia within tissue
  • in general, parasympathetic preganglionic fibres are long and postganglionic fibres are short
• sympathetic nervous system

  preganglionic sympathetic axons entering sympathetic chains terminate in:

  1. paravertebral sympathetic chains
  2. pre vertebral ganglia/plexuses
  3. adrenal medulla
• paravertebral sympathetic chains

  both pre and postganglionic axons may run for some distance up or down the sympathetic chain before forming synapse/emerging
• pre vertebral ganglia/plexuses

  in the abdominal cavity, 3 main:

  • coeliac ganglion
  • superior mesenteric ganglion
  • hypogastric ganglion
• adrenal medulla

  • some preganglionic fibres emerging from 10th and 11th thoracic segments run in greater splanchnic nerve and terminate on chromaffin cells in the medullae of adrenal glands
  • chromaffin cells analogous to sympathetic ganglia cells