HUBS1403 Lecture Notes - Lecture 31: Vagus Nerve, Vascular Smooth Muscle, Glycerol
8 Jun 2018
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Autonomic Nervous System
The ANS controls visceral function
• Heart rate
• Respiratory rate
• Blood pressure
• Sexual function
• Digestion
• Temperature regulation
Origins in the hypothalamus
Somatic vs Autonomic Nervous System
System
Description
Somatic
• SNS - originates in Spinal cord
• Somatic motor neuron - single myelinated axon projects from visceral horn to periphery
• In periphery - somatic motor neuron terminates at skeletal muscle fibre
• Use acetylcholine as a neurotransmitter - works on a number of different receptors
• Response: contraction of skeletal muscle
Autonomic
• Autonomic motor neurons - 2 motor atoms in series from lateral horn to periphery
• In periphery - autonomic motor neuron terminates at glands, cardiac muscle, smooth muscle,
circulation via adrenal medulla
• Use acetylcholine, adrenaline and noradrenaline as neurotransmitters
• Contraction or relaxation of smooth muscle, increased or decreased rate and force of contraction
of cardiac muscle, increased or decreased secretion of glands
The ANS Plays a Crucial Role in Regulating Homeostasis and Reproduction
1. There are 3 divisions of the autonomic NS
Sympathetic
"fight or flight"
Parasympathetic
"rest or digest"
Enteric
2. Dual innervation
When this occurs (eg heart, eye) the effects of the sympathetic and parasympathetic divisions are usually opposed
3. Autonomic tone
In many cases the autonomic input to an effector is active even at rest, eg eympathetic input to arterioles
Sympathetic and parasympathetic different with respect to:
• Physiological roles
• Sites of origin
• Lengths of fibres
• Location of ganglia
• Neurotransmitters
Peripheral Autonomic Neural Pathways
Both division if the ANS have 2 motor neurons to innervate an effector organ:
1. The preganglionic neuron
• (myelinated)
• (cell body originated in brain or spinal cord)
2. The postganglionic neuron
• Unmyelinated - slower
• Cell body and dendrites located I a peripheral autonomic ganglion where the preganglionic neuron
synapses with it
The Sympathetic Nervous System
Thoracic and Lumbar Outflow
In the sympathetic division, preganglionic neuron cell bodies originate in:
• Lateral horns T1-T12
• Lateral horns L1-L3
3 major types if sympathetic ganglia
1. Sypathetic trunk ganglia (lie in a vertical row on either side of the vertebrate column)
2. Preventable (collateral) ganglia (lie anterior to the vertebrate column and close to the large ab arteries)
3. Adrenal medulla (modified neurons)
The 1st synapse after exiting the spinal cord is at the sympathetic trunk ganglia
• Sympathetic trunk ganglia are paired
• Ganglia lie anterior and lateral to the vertebral column
• There are 2 cervical, 11-12 thoracic, 4- 5 lumbar, 4-5 sacral sympathetic trunk ganglia and 1 coccygeal ganglion
Preganglionic neurons connect with postganglionic neurons by:
1. Synapsing with postganglionic neurons in the 1st ganglion it reaches
2. Ascending to descending to higher or lower ganglion before synapsing with postsynaptic neurons
Parasympathetic Nervous System
Craniosacral Outflow
In the parasympathetic division, preganglionic neuron cell bodies originate in the brainstem nuclei of:
• Cranial nerve III (oculomotor)
• Cranial nerve VII (facial)
• Cranial nerve IX (glossopharyngeal)
• Cranial nerve X (vagal)
• Lateral gray matter of sacral segments 2-4 ot the spinal cord
Preganglionic neurons of the parasympathetic nervous system synapse in the ganglia that lie CLOSE to effector
Preganglionic - parasympathetic - very long
Autonomic Pathways
In thorax, abdomen and pelvis, autonomic plexuses contact visceral organs for autonomic control
These include
• Cardiac plexus
• Pulmonary plexus
• Celiac plexus
• Superior mesenteric plexus
• Inferior mesenteric plexus
• Renal plexus
• Hypogastric plexus
ANS Neurotransmitters
• SNS:
o Preganglionic: ACh
o Postganglionic: Nor adrenaline
- PNS:
o Preganglionic: ACh
o Postganglionic : ACh
Simplistically, the ANS uses 2 types of neurotransmitter
• Cholinergic neurons - acetylcholine
• Adrenergic neurons - adrenaline and noradrenaline
ANS Neurotransmission
• The majority of sympathetic ganglionic release NE
BUT
• Some sympathetic ganglionic release Ach not NE
• Exceptions to the rule:
• … to the brain blood vessels (dialation)
• … the skeletal muscle blood vessels (dilation)
• … to sweat glands
Document Summary
The ans controls visceral function: heart rate, respiratory rate, blood pressure. Somatic motor neuron - single myelinated axon projects from visceral horn to periphery. In periphery - somatic motor neuron terminates at skeletal muscle fibre: use acetylcholine as a neurotransmitter - works on a number of different receptors, response: contraction of skeletal muscle. Autonomic autonomic motor neurons - 2 motor atoms in series from lateral horn to periphery. The ans plays a crucial role in regulating homeostasis and reproduction: there are 3 divisions of the autonomic ns. When this occurs (eg heart, eye) the effects of the sympathetic and parasympathetic divisions are usually opposed: autonomic tone. In many cases the autonomic input to an effector is active even at rest, eg eympathetic input to arterioles. Sympathetic and parasympathetic different with respect to: physiological roles. In the sympathetic division, preganglionic neuron cell bodies originate in: The 1st synapse after exiting the spinal cord is at the sympathetic trunk ganglia.
