The nervous system contains more than 100 billion nerve cells (neurons), as well as an even greater number of supporting cells (glial cells). Each nerve cell has a cell body (soma) and several extensions (axon, nerve fiber). Neurons are cells specialized in receiving, conducting, and transmitting nerve impulses. The glial cells that wrap around the axons form insulating myelin sheaths (fat sheaths). Myelinated axons have a higher conduction velocity than unmyelinated ones.
Anatomy of the Nervous System
Anatomically, the nervous system can be divided into the central nervous system (CNS), which consists of the brain (cerebrum) and the spinal cord (medulla spinalis), and the peripheral nervous system (PNS), which consists of 32 pairs of spinal nerves and 12 pairs of cranial nerves.
The nervous system performs various functions, including controlling our muscles (the somatic-motor nervous system), transmitting sensory information from sensory cells in the skin, etc. (the sensory nervous system), and regulating functions such as heart rate and breathing, which are controlled by the autonomic nervous system. The autonomic nervous system can, in turn, be divided into the sympathetic and parasympathetic nervous systems.
Sensory nervous system
Sensory nerve fibers transmit impulses from sensory cells to the CSN. This occurs automatically.
The somatic-motor nervous system
Motor nerve fibers transmit impulses from the central nervous system to the skeletal muscles. Voluntary.
Autonomic nervous system
- Motor nerve fibers transmit impulses to the glands, the heart, and smooth muscle. This occurs automatically
- The sympathetic nervous system is activated in crisis situations— increasing heart rate, blood pressure, and blood flow to our major muscle groups. Flight response. This happens automatically.
- Parasympathetic nervous system – Activated during rest, has the opposite effect of the sympathetic nervous system: lowers heart rate and blood pressure, has a calming effect. Occurs automatically