The spinal cord is divided into 31 different segments, with motor nerve roots exiting in the ventral
aspects, and sensory nerve roots entering in the dorsal aspects. The ventral and dorsal roots
later join to form paired spinal nerves, one on each side of the spinal cord.
There are 31 spinal cord segments:- 8 cervical segments
- 12 thoracic segments
- 5 lumbar segments
- 5 sacral segments
- 1 coccygeal segment
The Peripheral Nervous System (PNS)
The PNS consists of 12 cranial nerves, and 31 pairs of spinal nerves and sensory
receptors. These peripheral nerves serve two main functions:
- They provide a connection for the nervous system to activate different bodily organs, such as
muscles. Efferent (motor) information going to an effector site. - They relay information from the bodily organs back to the brain, providing a constant update of
the relation between the body and the environment. This is afferent (sensory) information.
The peripheral nerves of the efferent division are divided into two main divisions:
- The Somatic Nervous System connects to the skeletal muscles of the body, and
provides the means for nervous system to initiate and produce movement. - The Autonomic Nervous System (ANS) affects all of the other tissues and organs that
are not skeletal muscle. It is a self-regulatory system that allows people to involuntarily
adapt to the environment. It adjusts or modifies some functions in response to stress;
both physical and mental. It helps regulate: - Blood vessel diameter and blood pressure.
- The heart’s electrical conductivity and ability to contract.
- Respiratory function, such as the bronchium diameter with respiration
- Functions of the stomach, intestine, salivary glands, hormone
secretion, urinary and sexual functions.
The ANS reaches homeostasis due to its two components: the Sympathetic and
Parasympathetic Nervous System.
The Sympathetic Nervous System (SNS) is sometimes referred to as the “Fight or
Flight” system because it is activated in highly stressful situations, such as danger. It allows for
increased responses of the body under conditions of physical or psychological stress.