Monday, March 20, 2006

Peripheral Nervous System/ Structure of Vertebral Column

The Peripheral Nervous System (PNS) is the nervous system outside of the Central Nervous System (CNS) and consists of bundles of axons (nerve fibers) which are known as fascicles. The axons extend from the brain and spinal cord. These fascicles are surrounded by perineurium. A peripheral nerve is arranged similar to a muscle in terms of connective tissue. It has an outer covering which forms a sheath around the nerve called the epineurium. Between individual nerve fibers is an inner layer of endoneurium. The myelin sheath in peripheral nerves is made up of Schwann cells wrapped in multiple layers around the axons. This applys mostly of the voluntary nerve fibers. Impulses travel along these Schwann cells. In the PNS, spinal nerves are responsible for sending messages by electric impulses to and from the spinal cord. Cranial nerves do the same from the brain. The PNS in our body is responsible for all communication lines that link to the CNS.
The PNS has 2 subdvisions:
Sensory or afferent, which take in information and motor or efferent, which carry out commands. Two kinds of sensory information can be retrieved. They are touch or feeling. Then there is propreoception, which is positional information. For example a person could be blind but know that their hand is out in front of them or by their side. Motor or efferent consists of the somatic nervous system, responsible for it's axons to conduct impulses from the CNS to skeletal muscles. This is voluntary movement in the voluntary nervous system. We are conciously controlling them. The autonomic nervous system (ANS) is almost like it sounds "automatic". The ANS is refered to as the involuntary nervous system. Reactions that are uncontrolled that our body takes care of for us. These are such things as pumping the heart, or activity in the glands and smooth muscles. ANS has 2 functional subdivisions:
Sympathetic- allows the body to mobilize or react in emergency situations. (the more high-strung of the two)
parasympathetic- more of a conservative type, saving energy. Promotes evryday, non-emergency functions.

The vertebral column (spine) is formed from 26 irregular bones that connect to allow for flexability. This is why the spine is curved. There are 5 major divisions of the vertebral column:
7 cervical vertebrae- the vertebral bodies are small compared to the heavier work that the lower spine does, however they have an extensive range of movement.
12 thoracic vertebrae- rib bearing. In order to simplify breathing by the chest expanding, the thoracic vertebrae remains stiff even if the mody is moving.
5 lumbar vertebrae- this is where the main weight of the body is carried. Lumbar vertebrae has a lumbar disk with 2 major components. The outer ring is called the annulus fibrosus made up of strong layers of ligaments. This part helps hold the vertebrae together, limits movement, and contains the inner core and elasticity of the disk. The inner part is called the nucleus pulposus, also known as the shock absorber between vertebrae.
5 sacrum vertebrae- this is important because this is where the sciatic and femoral nerves are located.
4 coccyx- tiny and fused at the terminus of the vertebrae.(tail bone)


Blogger Stephan said...

Looks great,Heidi! Lots of information,wonderful pics and love the use of many colors.
My critique is mainly that the second pic does not enlarge when you open it, and that you should indent your paragraphs, so it is easier to read them(easier on the eyes,also). good work!

7:25 PM  
Blogger Melissa's Anatomy Blog said...

Hi Heidi,
Good job on presenting the info needed in a precise explanation. Also, the pictures you used were really great. The main thing I think you could do to improve your blog is to post the pictures within the text, so they better explain what you are describing. Also, maybe you could have included some info on how the nerves come out of the spinal column. Other than that, I think you did a great job!

6:56 AM  
Blogger Courtney Allard said...

Hi Heidi,

I can definately tell you put alot of hard work into this one. Hopefully the little lesson on picture posting will help you with your next blog. I guess we all didn't focus to much on the nerves coming out of the spinal cord. Heidi I think you are getting a lot better at this whole blog thing, keep up the good work!

1:39 PM  
Blogger Larry Frolich said...

I agree with all your colleagues said. NIce pictures. nice original style, clearly in your own words with a narrative that makes sense to you. I would go back and review action potentials and how neurons work. Remmeber the impulse actually moves down the neuron axon and the Schwann cells are like insulation and help the message move down the neuron. Maybe do a little review on neuron function, action potentials and the role of the Schwann and neuroglial cells. Otherwise great work--keep it up,

3:27 PM  

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