Peripheral Nervous System Flashcards
What kind of innervation does the somatic nervous system provide?
Provides sensory and motor innervation to all parts of the body, except the viscera in body cavities, smooth muscles and glands.
- Somatic Sensory System transmits conscious sensations of touch, pain, temperature and proprioception from sensory receptors, whilst the Somatic Motor System innervates only skeletal muscle, stimulating voluntary and reflexive movement and carries this information from the CNS to the muscles.
What kind of innervation does the autonomic nervous system provide?
- Consists of motor fibers that stimulate smooth (involuntary muscle), modified cardiac muscle , and glandular (secretory) cells).
How do spinal nerves?
Initially arise from SC as rootlets, which converge to form two nerve roots- the anterior (ventral) nerve root and posterior (dorsal) nerve root.
What does the anterior nerve root consist of?
- Anterior nerve root consists motor (efferent) fibers passing from nerve cell bodies in anterior horn of spinal cord gray matter to effector organs.
What does the posterior nerve root consist of?
- Posterior root consists of sensory (afferent) fibers from cell bodies in the DRG that extend peripherally to sensory endings from the posterior horn of spinal cord gray matter.
How is a mixed spinal nerve formed, and what do they divide into?
Posterior and anterior nerve roots unit within (or just prox.) the IV foramen, to form a mixed spinal nerve which immediately divides into two rami- the posterior (dorsal) ramus and anterior (ventral ramus).
Sympathetic vs Parasympathetic neurons
Sympathetic:
-Fight or Flight
-Thoraco-lumbar
-Short preganglionic fibres
-Synapse with postganglionic fibres in the sympathetic trunk or visceral ganglia
-Run in the splanchnic nerves to get to ado/pelv viscera
Parasympathetic:
-Conserve energy
-Cranio-sacral
-Long preganglionic fibres
-Synapse with postganglionic fibres near the viscera
Sympathetic ganglion are often referred to as?
Paravertebral as they are adjacent to the vertebra
How do you get to the prevertebral ganglia?
To get to here, preganglionic sympathetic neurons bypass the sympathetic trunk without synapsing, continuing through an abdominopelvic splanchnic nerve to reach prevertebral ganglia.
Why do we have referred pain?
Probably due to convergence of the two inputs to the same population of neurons at a given spinal segmental level.
Describe referred pain from paired viscera
If you have symmetrical/ paired viscus that develops a
nerve supply from each side of the spinal cord and drags it out with it. Then, it is only going to get visceral afferents are only going to get it from one side of the spinal cord and therefore pain will only be referred to one side of the spinal cord.
o E.g. pain refered to from the kidney and ureter is unilateral.
Describe referred pain from unpaired viscera
GI tract + associated glands & ducts – develop in
midline but migrate away from it (associated orifices - mouth, anal canal remain in midline)
• Nerve supply from both sides of spinal cord
• Therefore even if they move out to one particular side of the
spinal cord, they still retain a sensory nerve supply that goes into both sides of the spinal cord. Therefore brain can’t distinguish whether the pain is coming from one side of the spinal cord or another and so pain will be referred to the midline for unpaired viscera.
o E.g. this is the case fort he stomach and the bladder.
Discuss example of appendix in terms of referred pain
- Appendix is an unpaired structure.
=Initially, when there is inflammation of the appendix- pain is referred to the midline of the relative dermatome.
=As it becomes really inflamed and begins to push up against the body wall, it irritates the parietal layer of serous membrane which is innervated by somatic nerves and therefore it will refer pain to its localized area on the side where it is located.
