The Autonomic Nervous System
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What are the 3 branches of the PNS?
- Somatic Nervous System (SNS)
- Autonomic Nervous System (ANS)
- Enteric Nervous System (ENS)
What is SNS?
The somatic nervous system is under voluntary control (Skeletal Muscle).
What is ANS?
The autonomic nervous system under involuntary control that can be further subdivided into sympathetic and parasympathetic responses.
What are the two branches of the ANS?
Sympathetic (fight or flight response) & Parasympathetic (rest and digest)
What is ENS?
The enteric nervous system in involved in regulating the digestive system.
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.
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.
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.
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.
Major features of somatic and autonomic nervous system: Effectors
- SNS: Skeletal muscle.
- ANS: Smooth muscle, cardiac muscle and glands.
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.
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.
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.
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.
Where do the axons exit the spinal cord?
It emerge through the anterior root of the spinal cord.
What is Sympathetic Ganglia?
Its the sites of synapses between sympathetic preganglionic and postganglionic neurons.
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.
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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