The Peripheral Nervous System
In the past two installments in the series on The Amazingly Designed Human Body we started looking at the nervous system. We learned that it is divided into two major divisions, the central and peripheral nervous system. In the central nervous system, we first covered the brain in The Amazingly Designed Human Body – Part 6 and then the spinal cord in The Amazingly Designed Human Body – Part 7. This week we take a brief overview of the Peripheral Nervous System.
Where the central nervous system was the supercomputer and network router that processed all of the signals the body received, the peripheral nervous system are the cables that connect the thousands of motor and remote processing and stimuli gathering units to the network hub and supercomputer. This includes the skin, muscles, glands, heart and internal organs,
Similar to a large computer network, the main processing unit (brain) and initial bundles of trunk lines running to the network routing hub (spinal cord) are generally protected in a safe housing. The supercomputer is housed in a protective room like the brain is protected by the skull. The main trunk bundle and network routing is also usually protected in conduit and protected room, just like the spinal cord is protected by the vertebral column. However, the peripheral nervous system is similar to the miles of network cables covering a large commercial business and is not protected and more susceptible to injury and damage.
The peripheral nervous system consists of all of the nerves that branch off from the central nervous system. They are divided into the cranial and spinal nerves.
I. Cranial Nerves – Cranial nerves are those that arise directly from the brain and brain stem. There are 12 cranial nerves.
A. Olfactory Nerve – 1st Cranial Nerve – Connects to the nasal cavity and is responsible for the sense of smell. One unique feature of the olfactory nerve is that it has the capacity to regenerate itself under normal conditions.
B. Optic Nerve – 2nd Cranial Nerve – Connects to the retina of the eyes and is responsible for vision.
C. Oculomotor Nerve – 3rd Cranial Nerve – Connects to the muscles surrounding the eyes and controls eye movements and pupil dilation.
D. Trochlear Nerve – 4th Cranial Nerve – Connects to the superior oblique muscle which is involved in eye movement.
E. Trigeminal Nerve – 5th Cranial Nerve – Connects to the face and jaws and is involved in facial sensory information and the muscles associated with eating, biting, chewing and swallowing.
F. Abducens Nerve – 6th Cranial Nerve – Connects to the lateral rectus muscle of the eyes which is involved in abduction movement of the eyes.
G. Facial Nerve – 7th Cranial Nerve – Connects to numerous facial muscles and the tongue. It is involved in facial expression and the sense of taste.
H. Vestibulocochlear Nerve – 8th Cranial Nerve – Connects to the inner ear and is involved with the transmission of sound. The vestibulocochlear nerve is also known as the auditory nerve.
I. Glossopharyngeal Nerve – 9th Cranial Nerve – The glossopharyngeal nerve is involved in a number of functions most of which are sensory functions and only one motor function. Areas of sensory control include the middle ear, tongue, pharynx, tonsils, parotid glands and carotid bodies. Its motor function involves the strylopharyngeal muscle which helps in swallowing.
J. Vagus Nerve – 10th Cranial Nerve – The vagus nerve is one of the most important and complex nerves in the entire body. The name ‘vagus’ comes from Latin meaning ‘wandering’ as it wanders from the brain stem throughout the chest and abdomen to a number of the of the internal organs. It is largely involved in the autonomic nervous system control of the heart, lungs, liver, kidneys, and the rest of the internal organs. The vagus nerve has three main branches, the pharyngeal, superior laryngeal and the internal branches.
1. Pharyngeal Branch – Connects to and involves in the muscles of the soft palate and pharynx.
2. Superior Laryngeal Branch – Connected to and involved with the upper larynx, pharynx and the carotid body.
3. Internal Branch – The largest of the three branches that connects and controls the functions of the internal organs in the chest and abdomen.
K. Spinal Accessory Nerve – 11th Cranial Nerve – Connects to muscles in the head and neck that involved with head movement.
L. Hypoglossal Nerve – 12th Cranial Nerve – Connects to the tongue and involves movement of the tongue.
II. Spinal Nerves – There are 31 pairs of nerves that branch off from the spinal cord. Spinal nerves are divided into groups based upon the region of the spinal cord from where they originate: the cervical, thoracic, lumbar, sacral and coccygeal nerves.
A. Cervical Spinal Nerves – There are 8 pairs of cervical nerves which are designated C1 to C8. They branch out from between the cervical vertebra to the back of the head, neck, shoulders and arms and are involved in both motor and sensory functions.
B. Thoracic Spinal Nerves – There are 12 pairs of thoracic nerves which are designated T1 to T12. The first 11 thoracic nerves branch out from the thoracic vertebra and between the ribs. The twelfth thoracic nerve braches out from beneath the last rib. The thoracic nerves connect to arms, thoracic and abdominal regions.
C. Lumbar Spinal Nerves – There are 5 pairs of lumbar nerves. They connect to the lower abdominal region and upper and interior regions of the legs.
D. Sacral Spinal Nerves – There are 5 pairs of sacral nerves. They connect to the pelvic and urogenital regions along with the legs and feet.
E. Coccygeal Spinal Nerve – There is only 1 coccygeal nerve and it connects with the fourth and fifth sacral spinal nerves (S4, S5) to form the coccygeal plexus which is involved with the sensory functions of the lower sacral and coccyx regions.
The peripheral nervous system is also divided in two categories, somatic and autonomic, based upon their basic function.
III. Somatic Nervous System – The somatic nervous system is the system that is used to control your voluntary (skeletal) muscles and to connect the sensory receptors to the central nervous system. It allows you to consciously move your muscles as well as allowing you to touch, see, hear, taste and smell.
IV. Autonomic Nervous System – The autonomic nervous system controls all of the involuntary movements and functions of the body including the heart, internal organs and glands. Under normal conditions, you do not have direct control over any of these nerves or functions. The autonomic nervous system is further divided into two groups, the sympathetic and parasympathetic nervous systems.
A. Sympathetic Nervous System – The sympathetic nervous system is responsible for our ‘fight-or-flight’ response. It operates under stressful or frightening circumstances. The actions of the sympathetic nervous system affect a number of body organs and parts including the heart, lungs, kidneys, liver, eyes and other parts of the gastrointestinal tract. When the sympathetic nervous system is activated, it causes a release of adrenalin that increases heart and lung function and causes the liver to release excess glucose into the blood stream for extra energy.
B. Parasympathetic Nervous System – The parasympathetic nervous system is responsible for our involuntary bodily functions during normal conditions without any stress or danger. It also connects to the same organs and body parts as the sympathetic nervous system does but generally operates in the exact opposite way. For example, the sympathetic system causes an increase in heart rate and blood pressure and the parasympathetic system works to decrease the heart rate and blood pressure.
As we look at the nervous system of the human body along with the other body systems, we see a repeating theme of system within a system, unity and in diversity. We saw the same pattern of unity and diversity in the series on the Simple Cell. Only an amazingly designed system could exhibit such diversity and unity in the same thing. It reminds me of the unity and diversity in the triune Godhead. God the Father, God the Son and God the Holy Spirit. Three persons. One God. It only makes sense that God would pattern much of His Creation after His own unique character.
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