ANS + NT

• Divisions of the autonomic nervous system


  • Sympathetic
  • Parasympathetic

  
• Dual innervation: Most effector organs are innervated by both sympathetic and parasympathetic divisions
• The autonomic nervous system divisions can work independently or together, and have opposing effects, with one division dominating in specific circumstances

  
• The autonomic nervous system divisions counterbalance to control organ function and maintain homeostasis
• Sympathetic function


  • Prepares the body for heightened activity (exercise, excitement, emergency, embarrassment) -> fight-or-flight
• Parasympathetic function


  • Stimulates abdominal visceral activity, conserves energy -> rest and digest
• Organ-specific sympathetic and parasympathetic responses

  • Heart: Sympathetic - Increased rate and strength of contraction, blood pressure increase. Parasympathetic - Decreased heart rate, blood pressure decreases.

  Blood vessels: Sympathetic - Vasodilation in cardiac & skeletal muscle, vasoconstriction in non-essential areas.

  Lung: Sympathetic - Bronchiole dilation. Parasympathetic - Bronchiole constriction.

  Liver: Sympathetic - Stimulates release of glucose. Parasympathetic - Increases glucose uptake.

  Sweat glands: Sympathetic - Stimulates sweating.

  Salivary glands: Sympathetic - Stimulate secretion of thick saliva. Parasympathetic - Increased secretion of watery saliva.

  Stomach: Sympathetic - Decreased secretion and motility. Parasympathetic - Increased secretion and motility.

  Intestine: Sympathetic - Decreased secretion and motility. Parasympathetic - Increased secretion and motility.

  Kidney: Sympathetic - Reduced blood flow, reduced urine formation. Parasympathetic - Increased blood flow, increased urine formation.

  Urinary bladder: Sympathetic - Micturition (urination) inhibited. Parasympathetic - Micturition promoted.

  Adrenal gland: Sympathetic - Secretion of adrenalin, noradrenalin.

  Spleen: Sympathetic - Release of stored blood.

  Rectum: Sympathetic - Defecation inhibited. Parasympathetic - Defecation promoted.

  Eye: Sympathetic - Iris (pupil) dilates, lens flattens (adjusts for distance vision). Parasympathetic - Iris (pupil) constricts, lens thickens (adjusts for near vision).
• The somatic nervous system controls voluntary movement and somatic reflexes, while the autonomic nervous system controls involuntary visceral organ function and glandular activity

  
• The somatic nervous system has lower motor neurons with cell bodies in the spinal cord or brainstem, while the autonomic nervous system has preganglionic and postganglionic neurons

  
• The somatic nervous system releases acetylcholine (ACh) at the neuromuscular junction, which is always excitatory, while the autonomic nervous system releases ACh or noradrenaline (NA) at postganglionic synapses, which can be excitatory or inhibitory

  
• Neurotransmitter binding to different receptor subtypes (nicotinic, muscarinic, alpha, beta) mediates the differential effects of ACh and NA on target organs

  
• Neurotransmitters are the language of the nervous system, with more than 50 identified, and neurotransmitter imbalances are implicated in many neuropsychological disorders

  
• Divisions of the autonomic nervous system


  • Sympathetic
  • Parasympathetic
• Dual innervation


  • Most effector organs are innervated by both sympathetic and parasympathetic divisions
  • ANS divisions can work independently/together
  • Divisions have opposing effects
  • One division dominates in specific circumstances
  • Division counterbalances to control organ function and maintain homeostasis
• Sympathetic function


  Prepares the body for heightened activity (exercise, excitement, emergency, embarrassment -> fight-or-flight)
• Parasympathetic function


  Stimulate abdominal visceral activity (Conserves energy -> rest and digest)
• Organ responses


  • Sympathetic response
  • Parasympathetic response
• Somatic vs autonomic nervous systems

  • Both are efferent divisions that distribute motor commands
  • Differ in: Neural (efferent) pathway, Effectors (target organs), Organ response, Neurotransmitters
• Somatic nervous system overview

  • Control centre: Primary motor cortex (input from cerebellum and basal nuclei)
  • Central neurons: Upper motor neuron
  • Peripheral motor neurons: Lower motor neuron
  • Target: Skeletal muscles
  • Function: Voluntary movement, Somatic reflexes
• Autonomic nervous system overview

  • Control centre: Hypothalamus (input from limbic system and cerebrum)
  • Central neurons: CNS interneuron(s)
  • Peripheral motor neurons: Preganglionic neuron, Postganglionic neuron
  • Target: Cardiac muscle, Smooth muscle, Glands
  • Function: Involuntary control of visceral organ function, Glandular activity, Visceral reflexes
• Peripheral motor neurons


  • Somatic NS: Lower motor neuron cell body in spinal cord motor nucleus (anterior gray horn) or brainstem nucleus
  • Autonomic NS: Preganglionic neuron cell body in motor nucleus (lateral grey horn/matter) or brainstem nucleus, Postganglionic neuron cell body in peripheral ganglion
• Peripheral motor neurons neurotransmitters

  • Somatic NS: Acetylcholine (ACh) released by lower motor neuron, always excitatory
  • Autonomic NS: Preganglionic neuron - release of ACh, always excitatory, Postganglionic neuron - release of ACh or Noradrenalin (NA), may be excitatory or inhibitory
• Parasympathetic (craniosacral) division


  • Preganglionic neurons arise from brain stem (axons exit via cranial nerves) and sacral region of spinal cord (axons exit via spinal nerves)
  • Ganglia located close to, or within, the target region
  • Preganglionic axon: long, Postganglionic axon: short
  • Cranial pathways: CN III, VII, IX, X
  • Sacral pathways: Sacral spinal cord segments S2-S4 (innervate pelvic organs and distal portion of large intestine)
• Sympathetic (thoracolumbar) division


  • All preganglionic fibres arise within spinal cord segments T1-L2
  • Cell bodies in motor nuclei of lateral gray horns, axons exit spinal cord via spinal nerves
  • Ganglia located close to the spinal cord, Preganglionic axon: short, Postganglionic axon: long
  • Segments T1-T6 innervate the head and thorax, Segments T5-L2 innervate abdominopelvic organs
  • Ganglia: Chain of 23 connected by fibres to form sympathetic trunk, Flank both sides of the vertebral column, Extend from neck to pelvis
• The Adrenal Medulla


  1. Preganglionic neuron releases ACh

  2. ACh binds to nicotinic receptors on adrenal medulla cells

  3. ACh stimulates medullary cells to release Adrenalin(A) and Noradrenalin(NA) into bloodstream

  4. A and NA released into the blood affect any cell bearing adrenergic receptors, enhancing and prolonging the sympathetic response
• Sympathetic effects


  • Widespread, Occur during exercise, excitement, emergency, embarrassment
  • Adrenal medulla releases A and NA to the blood, enhancing and prolonging sympathetic effects
  • Single preganglionic neuron can synapse with many postganglionic neurons to activate multiple effectors
• Neurotransmitters


  • Preganglionic neurons: release ACh

  Postganglionic neurons: Sympathetic - release NA, Parasympathetic - release ACh
• Neurotransmitter receptors


  • Cholinergic receptors: Nicotinic, Muscarinic

  Adrenergic receptors: Alpha (α), Beta (β)
• Cholinergic receptors


  Nicotinic - always excitatory, Muscarinic - excitatory or inhibitory
• Adrenergic receptors


  Alpha (α) and Beta (β) subtypes can be excitatory or inhibitory
• Synaptic transmission


  Preganglionic neuron releases NT

  NT binds receptors on postganglionic neuron, producing graded depolarisation

  Action potential in postganglionic neuron leads to release of NT

  NT binds receptors on target cell/organ, producing graded depolarisation or hyperpolarisation

  Target cell is excited or inhibited
• Postsynaptic potentials


  • Excitatory postsynaptic potential (EPSP): NT binds, opens ion channels, graded depolarisation, increased target activity

  Inhibitory postsynaptic potential (IPSP): NT binds, opens ion channels, graded hyperpolarisation, decreased target activity
• Agonists and antagonists


  Agonists: Drugs that mimic the reaction of the NT, promote normal response

  Antagonists: Drugs that bind the receptor and block the action of the NT, prevent normal response
• Neurotransmitters


  • Acetylcholine: Motor control outside CNS, Cognition, Memory, Consciousness within CNS

  Biogenic amines: Emotional behaviour, Regulate biological clock

  Noradrenaline: Stimulates brain reward and pleasure centres, Involved in reducing stress and enhancing attention

  Dopamine: Stimulates brain reward and pleasure centres, High levels in schizophrenia, Deficient in Parkinson's

  Serotonin: Mood regulation, sleep, appetite, nausea, migraine headaches

  GABA: Main inhibitory NT in brain, Helps regulate sleep/wakefulness, Involved in motor control

  Glutamate: Involved in learning and memory, Excessive release causes excitotoxicity

  Substance P: Produced by damaged tissue, Stimulates peripheral nociceptors, Mediates pain transmission

  Endorphins: Natural opiates, Inhibits perception of pain in CNS