Sunday, 2 June 2013

Sympathetic Nervous System - brief overview

Generally involved in the fight or flight response but is constantly trying to maintain homeostasis within the body.

The sympathetic nervous system uses 2 types of neurons:

-Preganglionic / presynaptic neurons: these release the neurotransmitter acetylcholine at the ganglion

-Postganglionic / postsynaptic neurons: these typically release norepineprhine but can also use acetylcholine and epinephrine

Preganglionic neurons are the shorter of the two and reach out from the spinal cord to a ganglion, where they form synapses with postganglionic neurons. These postganglionic neurons are very long and extend across most of the body.

Examples of sympathetic stimulation:

- Iris (eye muscle): pupil dilation

- Salivary glands: saliva production reduced

- Oral / Nasal Mucosa: mucus production reduced

- Heart: heart rate and force increased

- Lungs: bronchial muscles relaxed

- Stomach: peristalsis reduced

- Small intestine: motility reduced

- Large intestine: motility reduced

- Liver: increased conversion of glycogen to glucose

- Kidneys: decreased urine secretion

- Adrenal medulla: norepinephrine and epinephrine secretion

- Bladder: wall relaxed, sphincter closed

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