Anatomy Week Two

The first week we learned about the nervous system and how it was divided into 2 main systems, the central nervous system and the peripheral nervous system.  In this week we learned how they work together to convey information.  The peripheral nervous system is further divided into the autonomic nervous system and the somatic nervous system.  

The somatic nervous system consists of the sensory neurons that are responsible for conveying the information from somatic receptors in the head, body wall, and limbs, and also from the receptors for the special senses of vision, hearing, taste, and smell to the CNS.  The somatic nervous system also includes the motor neurons that conduct impulses from the CNS to only skeletal muscles.  The action of these motor responses can be controlled, so these are considered voluntary.  

The autonomic nervous system consists of sensory neurons and motor neurons.  The sensory neurons convey information to the CNS from autonomic sensory receptors that are located primarily in the visceral organs such as the stomach and lungs.  The motor neurons conduct nerve impulses from the CNS to smooth muscle, cardiac muscle and glands.  Because its motor responses are not normally under conscious control, the actions of the autonomic nervous systems are considered involuntary.  The ANS (autonomic nervous system) is made up of three divisions: the sympathetic, parasympathetic, and the enteric.  

With a few exceptions, effectors are innervated by both the sympathetic and parasympathetic divisions, usually with opposing actions.  An example of this would be that the sympathetic neurons work to increase heart rate, and the parasympathetic neurons work to slow the heart rate down.  The Enteric division consists of enteric plexuses that extend the length of the gastrointestinal tract.  The enteric sensory neurons monitor the chemical changes within the GI tract and the stretching of its walls.  The enteric motor neurons monitor and govern the contraction of the of the smooth muscle that lines the GI tract, the secretions of the GI tract organs (such as the acid secretion by the stomach), and the activity of the GI tract endocrine cells.  The Enteric plexuses also communicate with the CNS by the sympathetic system and parasympathetic neurons, although many of the neurons in the enteric plexuses function independently of the CNS to some extent.  The enteric plexuses are sometimes thought of as the 'brain' of the gut, and there are there are over 100 million sensory, motor, and interneurons which is as many as the spinal cord. 

So all these things are happening in your body every second of our lives and we don't even know its happening.  Our  nervous systems are extremely complex and we never really stop to think about all the processes that go on in it even when you do something as simple as touching something.  Our bodies being able to perceive external stimuli as well as making sure that all our bodily functions are running smoothly is simply amazing.