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Nervous System Overview

I’m going to try a new type of post here, probably not very interesting to most, but it will be helpful for me and other paramedic students out there.

Inspired by: http://www.rhmedicclass.com, another medic student in NYC, although I’m not sure which school he/she attends, it isn’t mine.

The Nervous System Organization

The nervous system (NS) is our quick-acting/short-lasting¬†system to maintain homeostasis (the endocrine being slower-acting/long-lasting system). It contains the central nervous system (CNS), brain and spinal cord, which is our processing, storage, and command center. It also has the peripheral nervous system (PNS), which is what actually makes us “do stuff” (like makes muscles move) and “sense stuff” (touch, pain, etc).

The CNS and PNS are connected by afferent or efferent nerves. Afferent sends signals away from the PNS and to the CNS, while efferent nerves enter the PNS and receive signals from the CNS.

The PNS has two divisions: somatic and autonomic. Somatic controls our muscles, and does what we tell it to. Autonomic is… automatic… it controls processes that don’t require thought and can’t typically be voluntarily controlled, even if we wanted to (smooth/cardiac muscle, glands, fat tissue). Of course, the autonomic is further divided: sympathetic and parasympathetic. Sympathetic is the proverbial “fight-or-flight” side. If we need to fight, it will affect homeostasis to favor that (i.e. increase heart rate and contractility, respirations, blood flow to muscles, dialate the pupils). Parasympathetic is our lazy side (decrease heart rate, respirations, blood flow to muscles, increase blood flow to kidneys, gut, constrict pupils).

Neural Tissue

Alright, before going into more detail, gotta cover the various types of neural tissues and their functions.

Neurons are cells that communicate with each other and other cells, and are the basic unit of the nervous system. They have spindly dendrites (receive information), a cell body (nucleus, no centrioles so they can’t regenerate), an axon (long extension which carries the transmission), and a synaptic terminal (where the transmission ends and is passed onto the next neuron or other target cell).

Types:

  1. Multipolar (dendrites > axons,  found in CNS and motor neurons)
  2. Unipolar (“cell body on stick” or “lollipop neuron”, found mostly in sensory PNS neurons)
  3. Bipolar (cell body in-between dendrites/axon, found in some sense organs such as sight/smell/hearing)

Functional types:

  1. Sensory: self-explanatory. Includes external somatic sensory (sight, smell, hearing, touch), proprioceptors (position/movement of muscle/joints), and visceral or internal (monitor GI, respiratory, cardio, urinary, reproductive, taste, and deep pain/pressure).
  2. Motor: somatic motor (skeletal muscle), and visceral motor (i.e. cardiac/smooth muscle, glands, adipose tissue)
  3. Interneurons: Coordination of sensory/motor activity. They interconnect with other neurons.

Neuroglia are cells that help out the neurons.

Four types in CNS:

  1. Astrocytes: Most numerous. Maintain the triple B (blood-brain-barrier), provide structure, repair damaged neural tissue.
  2. Oligodendrocytes: create myelin (insulatory matter, which speeds conduction and reduces signal loss allowing signals to travel further)! This is “white matter” (cell bodies are “gray matter”). Gaps of myelin (which wraps around an axon) are called nodes of Ranvier.
  3. Microglia: small/rare. Phagocytes derived from WBC’s.
  4. Ependymal: line central canal of the spinal cord (CSF is here!) and ventricles of brain (CSF is here in brain! along with subarachnoid layer). Within brain can produce CSF or circulate it.

Two types in PNS:

  1. Satellite cells: surround/support neuron cell bodies (analogous to astrocytes in CNS).
  2. Schwann cells: In addition to being a fun word to say, it is the myelin of the PNS.

Anatomical CNS vs. PNS:

CNS:

  1. Centers: neurons with common function
  2. Neural cortex: gray matter covering the brain
  3. Higher centers: most complex
  4. Tracts: axons with common destination/function
  5. Columns: groups of tracts in spinal cord
  6. Pathways: link brain with rest of body

PNS:

  1. Ganglia: gray matter (cell bodies)
  2. Nerves: white matter (myelinated axons), either cranial (12 pairs) or spinal (31 pairs).

Next post I’ll do neuron functions, including membrane potential and propogation of an action potential.

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Categories: Educational