Nervous System 101
The nervous system is divided into two parts:
(1)  Central Nervous System (CNS) – brain and spinal cord
(2)  Peripheral Nervous System (PNS) – cranial and spinal nerves.
Nerves pass messages to and from the CNS
Sensory (afferent) Neurons
Transmit impulses TO the CNS from the sense organs
Motor (efferent) Neuron System
- Transmits impulses FROM the CNS to effectors.
Motor neurons act by conscious decision or “behind the scenes”
a) Somatic (voluntary) Nervous System – directs contraction of skeletal muscles
b)Â Â Autonomic (involuntary) Nervous System – controls activities of organs and various involuntary muscles, such as cardiac and smooth muscles. Has 2 systems that generally target the same organs but are antagonistic.
 i.   Parasympathetic Nervous System – “Rest and Digest” or “Brake” – activates tranquil functions. E.g. secretion of saliva or digestive enzymes.
 ii.  Sympathetic Nervous System – “Fight or Flight” or “Accelerator” –    prepare body for action. E.g. increasing heart rate, increasing sugar release from liver to blood.
