Chapter 14 ANS Flashcards
The Autonomic Nervous System (Fig. 14.1)
Involuntary, general visceral motor system that innervates cardiac, smooth muscle, and glands
Differences from somatic nervous system (Fig 14.2):
Effector
Effector:
ANS innervates cardiac and smooth muscles and glands
Somatic system innervates skeletal muscle
Differences from somatic nervous system:
Motor unit:
Motor unit:
ANS = 2 motor neurons + effector
1st neuron = **pre-ganglionic neuron with cell body in **CNS
2nd neuron = **post-ganglionic neuron with cell body in **autonomic ganglion outside CNS
Somatic = 1 motor neuron with cell body in CNS + effector (skeletal muscle)
Differences from somatic nervous system:
Axon Fibers
Axon fibers:
ANS – 1st axon = myelinated but smaller diameter (Aβ), 2nd = unmyelinated (C fiber)
Somatic – large myelinated (Aα)
Differences from somatic nervous system:
Neurotransmitter
Neurotransmitter:
ANS – ACh and norepinephrine (NorEpi)
depending on receptor of effector tissue - can be excitatory or inhibitory
Somatic – ACh – always excitatory
ANS has two divisions:
Parasympathetic division
Sympathetic division
Parasympathetic division
Parasympathetic division
Promotes maintenance functions and conserves energy (rest and digest)
• reduces heart rate
• stimulates digestion, elimination of feces and urine
**craniosacral origins – cell bodies for preganglionic neuron in brain and sacral spinal cord
Fibers in cranial nerves:
III – oculomotor - supplies iris and ciliary bodies of eye
VII – facial – supplies nasal and lacrimal glands
IX – glossopharyngeal – supplies parotid and salivary glands
**X - right and left vagus nerves
- account for 90% of all preganglionic parasympathetic fibers
- supply almost every organ and gland in thoracic and abdominal cavities
Sacral nerves – supply pelvic organs and distal half of large intestine
Ganglion in or near effector organ:
Long pre-ganglionic **cholinergic fiber releases **ACh at ganglion
Excitatory at nicotinic receptors
Short post-ganglionic **cholinergic fiber releases **ACh at effector
**Muscarinic receptors – can be excitatory or inhibitory depending on receptor sub-type
Sympathetic division
Sympathetic division
Mobilizes the body during activity (fight or flight)
• temporally reduces nonessential activities
• increases both heart rate and force of its contraction
• constricts certain blood vessels allowing blood to be diverted to active tissues
• dilates bronchioles in lungs – increasing air flow
• stimulates release of glucose from liver
**Thoracolumbar origins – cell bodies for preganglionic neuron in thoracic and lumbar spinal cord
• cell bodies form **lateral horns of spinal cord
• nerves innervate more organs than parasympathetic division
• dilate smooth muscle of iris
• inhibit nasal and salivary glands
• supplies visceral organs
• supplies sweat glands and arrector pili muscles of skin
• supplies smooth muscle in walls of blood vessels
Sympathetic division
Sympathetic trunk ganglion
Sympathetic trunk ganglion close to spinal cord
•**collateral ganglia (prevertebral) – located anterior of vertebral column
preganglionic fibers form several **splanchnic nerves (greater, lesser, lumbar and sacral)
•short pre-ganglionic **cholinergic fiber releases **ACh at ganglion
**excitatory at **nicotinic receptors
• long post-ganglionic **adrenergic fiber **releases NorEpi at effector
**alpha and beta receptors – can be excitatory or inhibitory depending on sub-type
Sympathetic division
Adrenal Medulla
Adrenal medulla – center portion of the adrenal gland
• **modified sympathetic ganglion
• post-ganglionic fibers (Chromaffin cells) do not leave medulla
• releases **NorEpi and epinephrine (Epi) into the blood
Sympathetic division
Dual innervation
Dual innervation – when an organ innervated with both parasympathetic and sympathetic fibers
Actions antagonistic to one another – one divisions excites, one division suppresses activity
Visceral reflex arcs (Fig. 14.8)
Visceral reflex arcs – same components as somatic division but motor output involves pre and post ganglionic neurons
e.g. stretch of bladder initiating micturation reflex
**sympathetic reflexes – responsible for thermoregulatory responses to heat (sweating, vasodilation), release of renin from the kidneys, metabolic effects (increased rate and blood glucose levels, mobilization of fats) through activation of adrenal medulla
**enteric nervous system = **reflex arcs found completely within the walls of the gastrointestinal system
Hypothalamus (Check Fig 14.9)
Hypothalamus = primary controller of ANS
