The autonomic nervous system (ANS)
Is the portion of the nervous system that controls most
visceral functions of the body
Divisions of ANS:
The ANS is subdivided into:
- Sympathetic nervous system
- Parasympathetic nervous system
General organization of the ANS:
- The ANS is activated by centers located in the spinal cord,
brain stem, and hypothalamus.
- The peripheral parts of the ANS are made up of
preganglionic and postganglionic neurons.
Sympathetic:
Output from the CNS:
- Originate from the thoracic and some lumbar segments
from T1 to L2 (thoraco-lumbar).
- The cell bodies of the preganglionic neurons are located in the
lateral horn of the spinal cord.
- It leave the spinal cord and
project to the paravertebral
ganglion, where it synapse with
the postganglionic neurons.
- The ratio of a preganglionic
neuron to postganglionic
neurons is about 1:20
The sympathetic ganglia
The site of cell bodies of the postganglionic neurons
1. Paravertebral ganglion:
- extends parallel to the thoracic and upper lumbar spinal segments
- are connected together to form the sympathetic trunk
2. Cervical extension:
superior, middle and stellate ganglia
3. Collateral ganglia:
- close to the viscera.
- the celiac, superior mesenteric, and inferior mesenteric ganglia
Organization of
sympathetic:
Activation of sympathetic:
Stressful stimuli:
- Emotion
- Anxiety
- Exercise
- Hypoglycemia
- Hypotension
- Infection
- Any debilitating disease
- Intense heat or cold
- Hemorrhage
- Trauma
- Surgery
Parasympathetic:
Output from the CNS
The cell bodies of the preganglionic neurons are located in:
- Motor nuclei of the cranial nerves III,VII, IX and X
- lateral horn of the sacral segment (S2, S3 and S4).
The parasmpathetic ganglia are found near or within the
wall of the target organs.
The ratio of a preganglionic neuron to postganglionic
neurons is 1:1
Organization of
Parasympathetic:
Activation of parasympathetic:
physical and mental rest.
The neurotransmitters of ANS:
- Acetylcholine
- Norepinephrine (noradrenaline).
Cholinergic neurons:
- All preganglionic neurons
- All postganglionic parasympathetic neurons
- Some postganglionic sympathetic neurons
Adrenergic neurons:
- Most postganglionic sympathetic neurons
 Postganglionic sympathetic neurons that release acetylcholine
supply:
1. the sweat glands
2. arterioles of skeletal muscles
3. pilo-erectror muscles.
Acetylcholine:
- Synthesized from acetyl co A and choline in the cell body of
cholinergic neurons
- Synthesis is catalyzed by the enzyme choline acetyltransferase.
When it released at the synaptic cleft:
- acts on its receptors.
- its action is terminated by the acetylcholinesterase enzyme
- which converts it to acetate and choline.
Norepinephrine (noradrenaline):
Synthesized from the amino acid tyrosine in noradrenergic neurons
When it released at the synaptic cleft:
- Acts on its receptors.
- Diffusion into the plasma where it is hydrolyzed by two enzymes:
- Monoamine oxidase (MAO)
- Catechol-O-methyl-transferase (COMT)