Human Physio Autonomic & Somatic Nervous System

PNS

Efferent → Somatic (concious) → Skeletal muscle

→ Autonomic (unconcious) → Sympathetic OR Parasympathetic

Sympathetic → Cardiac muscle, smooth muscle, glands

Parasympathetic → Enteric nervous system → Gastro-intestinal tract

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Efferent division of PNS

A schematic of the somatic nervous system (SNS), which provides conscious and subconscious control over skeletal muscles.

\ A schematic of the autonomic nervous system (ANS), which controls visceral funcstions largely outside of our awareness

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Autonomic nervous system

  • Parasympathetic and sympathetic branches
  • action via ANS is by dual innervation (antagonistic control of internal organs)
  • Parasympathetic division is most active at rest   * “==rest and digest==” functions
  • Sympathetic division is most active in emergency or threatening situations   * “^^fight-or-flight^^” response
ANS: Homeostasis

Parasympathetic

  • conserve energy
  • digestion
  • diuresis
  • defacation

Sympathetic

  • exercise
  • emergency
  • embarassment
Anatomy of ANS

Preganglionic neuron

  • originates in CNS (spinal cord) and projects to autonomic ganglion outside CNS

Ganglion

  • sympathetic chain ganglion runs along vertebral column

Postganglionic neuron

  • cell body in ganglion and projects axons to target tissue/effector organ

Target tissue

  • cardiac muscle, smooth muscle or glands

 

Sympathetic vs Parasympathetic

Anatomical difference of two autonomic branches characterised by:

  • Origin in the CNS
  • Location of the autonomic ganglia
  • Length of fibres
<<Sympathetic:<<
  • Originate in the thoracic and lumbar region of spinal cord
  • Ganglia close to spinal cord
  • Short preganglionic neurons
  • Long postganglionic neurons to target tissues
[[Parasympathetic:[[
  • Originate in brain stem (cranial nerves) and sacral region
  • Ganglia on or near target organs
  • Long preganglionic neurons
  • Short postganglionic neurons
SNS vs PNS pathways

Sympathetic and parasympathetic branches also differ in their ^^neurotransmitter^^ released from preganglionic & postganglionic neurons and receptors.

 

SNS vs PNS responses

<<Sympathetic divison<<

  • Dilates pupil of eye
  • inhibits salivary gland secretion
  • relaxes bronchi in lungs
  • accelerates hearts
  • inhibits activity of stomach and intestines
  • inhibits activity of pancreas
  • stimulates glucose release from liver; inhibits gallbladeer
  • stimulates adrenal medulla
  • inhibits emptying of bladder
  • promotes ejaculation and vaginal contractions

[[Parasympathetic division[[

  • constricts pupil of eye
  • stimulate salivary gland secretion
  • constricts bronchi in lungs
  • slows heart
  • stimulates activity of stomach and intestine
  • stimulates activity of pancrease
  • stimulates gallbladder
  • promotes emptying of bladder
  • promotes erection of genitalia

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