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What are the 3 branches of the PNS?
- Somatic Nervous System (SNS)
- Autonomic Nervous System (ANS)
- Enteric Nervous System (ENS)
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What is SNS?
The somatic nervous system is under voluntary control (Skeletal Muscle).
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What is ANS?
The autonomic nervous system under involuntary control that can be further subdivided into sympathetic and parasympathetic responses.
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What are the two branches of the ANS?
Sympathetic (fight or flight response) & Parasympathetic (rest and digest)
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What is ENS?
The enteric nervous system in involved in regulating the digestive system.
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Major features of somatic and autonomic nervous system: Sensory input
- SNS: Somatic senses and special senses.
- ANS: Mainly from interoceptors; some from somatic senses and special senses.
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Major features of somatic and autonomic nervous system: Control of motor output
- SNS: Voluntary control from cerebral cortex, with contributions from basal ganglia, cerebellum, brain stem, and spinal cord.
- ANS: Involuntary control from hypothalamus, limbic system, brain stem, and spinal cord; limited control from cerebral cortex.
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Major features of somatic and autonomic nervous system: Motor neuron pathway
- SNS: One-neuron pathway: Somatic motor neuros extending from CNS synapse directly with effector.
- ANS: Usually two-neuron pathway: Preganglionic neurons extending from CNS synapse with postganglionic neurons in an autonomic ganglion, and postganglionic neurons extending from ganglion synapse with a visceral effector. *Alternatively, preganglionic neurons may extend from CNS to synapse with chromaffin cells of adrenal medullae.
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Major features of somatic and autonomic nervous system: Neurotransmitters and hormones
- SNS: All somatic motor neurons release ACh.
- ANS: All sympathetic and parasympathetic preganglionic neurons release acetylcholine (ACh). Most sympathetic postganglionic neurons release norepinephrine (NE); those to most sweat glands release ACh. All parasympathetic postganlionic neurons release ACh. Chromaffin cells of adrenal medullae release epinephrine and norepinephrine.
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Major features of somatic and autonomic nervous system: Effectors
- SNS: Skeletal muscle.
- ANS: Smooth muscle, cardiac muscle and glands.
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Major features of somatic and autonomic nervous system: Responses
- SNS: Contraction of skeletal muscle.
- ANS: Contraction of relaxation of smooth muscle; increased or decrease rate and force of contraction of cardiac muscle; increased or decrease secretions of glands.
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What is meant by the term preganglionic autonomic neuron?
- First of two motor neurons in autonomic motor pathway.
- Its cell body is in the brain or spinal cord, and its axon exits the CNS as part of a cranial or spinal nerve.
- The axon is small-diameter, myelinated type B fiber that usually extends to an autonomic ganglion, where it synapses with a postganglionic neuron.
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What is meant by the term postganglionic autonomic neuron?
- Second neuron in the autonomic motor pathway.
- Lies entirely outside the CNS
- Its cell body and dendrites are located in an autonomic ganglion, where it forms synapses with one or more preganglionic axons.
- The axon is small-diameter, unmyelinated type C fiber that terminates in a visceral effector.
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Where are the sympathetic preganglionic neuron cell bodies?
They are located in the lateral horns of gray matter in T1 - T12 and L1 - L2 and sometimes also L3.
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Where do the axons exit the spinal cord?
It emerge through the anterior root of the spinal cord.
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What is Sympathetic Ganglia?
Its the sites of synapses between sympathetic preganglionic and postganglionic neurons.
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What are the names of the two groups of sympathetic ganglia?
1. Sympathetic Trunk Ganglia: near the spinal cord - therefore most of the preganglionic axons are short. Mostly innervate organs above the diaphragm.
2. Prevertebral Ganglia: Lie close to large abdominal arteries. Generally innervate organs below diaphragm.
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Name some of the specific ganglia as indicated in lecture.
- Celiac ganglion: on either side of the celiac trunk, an artery inferior to the diaphragm.
- Superior mesenteric ganglion: near the beginning of the superior mesenteric artery in the upper abdomen.
- Inferior mesenteric ganglion: near the inferior mesenteric artery in the middle of the abdomen.
- Aorticorenal ganglion: near the renal artery of each kidney.
- Renal ganglion: near the renal artery of each kidney.
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