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Nervous System


Peripheral Nervous System

Cranial Nerves Spinal Nerves The peripheral nervous system is outside the CNS. It consists of the various nerves that connect particular parts of the CNS with particular organs. Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves. Cranial nerves (Figure 05) are either sensory nerves, motor nerves, or mixed nerves. All of them, except the vagus nerve, control the head, the face, the neck, and the shoulders. The vagus nerve controls the internal organs. Table 04 lists the functions of the various cranial nerves. All spinal nerves (Figure 06) are mixed nerves that take impulses to and from the spinal cord. Table 05

Figure 05 Cranial Nerves [view large image]

Figure 06 Spinal Nerves
[view large image]

describes the symptom of spinal cord injury (SCI) with the particular spinal nerve(s).



Cranial Nerve CN# Brain Region Major Functions
Terminal§ 0 Near the olfactory Reception of pheromone for sex
Olfactory 1 Cerebral Cortex Smell
Optic 2 Limbic System Vision
Oculomotor 3 Midbrain Eyelid & eyeball movement; pupil dilation
Trochlear 4 Pons Control downward & lateral eye movement
Trigeminal 5 " Chewing; sensation of face & mouth
Abducens 6 " Control lateral eye movement
Facial 7 " Control most facial expressions; secretion of tears & saliva; taste; ear sensation
Auditory 8 Medulla Hearing; balance
Glossopharyngeal 9 " Taste; swallowing; sensation from tongue, tonsil, pharynx, carotid blood pressure
Vagus 10 " Sensory, motor and autonomic functions of viscera - glands, digestion,
heart rate, breathing rate, aortic blood pressure
Spinal Accessory 11 " Controls muscles used in head movement
Hypoglossal 12 " Controls tongue movements

Table 04 Functions of Cranial Nerves

§ The exact function of the terminal nerve in human is still under investigation, which is hampered by its small size and proximity to the olfactory nerve. For mouse and other animals at least, it is connected to the vomeronasal organ (vestige in human), which leads to a pathway for controlling sexual arousal.

Spinal Nerve(s) Innervated Body Part(s) Symptom(s) of SCI
C1 Head and Neck Quadriplegia
C2-C4 Diaphragm Breathing problem
C5 Deltoids, biceps No control at wrist or hand
C6 Wrist extenders No hand function
C7-T1 Triceps, hand dexterity problems with hand and fingers
T2-T8 Chest muscles Paraplegia, poor trunk control
T9-T12 Abdominal muscles Paraplegia
Lumbar and Sacral Leg muscles, bowel, bladder, sexual organs Decreasing control of hip flexors and legs, dysfunction of bowel, bladder, and sex

Table 05 Symptom(s) of Spinal Cord Injury

Note: Other effects of SCI may include low blood pressure, inability to regulate blood pressure effectively, reduced control of body temperature, inability to sweat below the level of injury, and chronic pain.

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