by the contraction of a muscle which it innervates. Nerve function is supposed to depend upon the peculiarities inherent in the central and peripheral end-organs, regardless of its construction and the character of the stimuli (Brubaker's Physiology). Special Stimuli. — These comprise the group which act upon the nerves of special sense and give rise to conscious sensations, through the highly specialized end-organs, which transfer the nerve impulse to the filaments of the nerves in relation with them. The afferent nerves (sensor) convey the impulse to the higher conscious centres, in response to the special stimuli, as follows: (1) Light or etheral vibrations act upon the end-organs of the optic nerve in the retina (sight and light); (2) sounds act upon the end-organs of the auditory nerve (hearing) in the ear; heat or vibrations of the air act upon the end-organs in the skin; chemic agents act upon the end-organs of the olfactory (smell) and gustatory (taste) nerves of the nose and tongue respectively. The efferent nerves (motor) convey impulses to the muscles, glands, etc., in response to stimuli which are supposed to arise as a result of a molecular disturbance in the central nerve cell, a combination of physical and chemic processes attended by the liberation of energy, which passes from molecule to molecule. The passage of the nerve impulse is accompanied by changes of electric tension. Thus, to sum up, all nerve impulses have their origin in the nerve cells or neurones, and these millions of associated neurones are the basis of all nerve activity. A theory has been created to simplify the understanding of nerve cell activity. It is called the neurone theory of Waldeyer, who explains it, based on the works of Golgi, Cajal, Forel, and others, as follows: (1) Each neurone is a distinct and separate entity; (2) the collaterals and other terminals of the neurones form no connections among themselves; (3) neurones are associated, and impulses conveyed, by contact or contiguity of the axonic terminals of one axone with the cell body or dendrites of another neurone. The central nerve system or cerebrospinal axis consists of the brain (encephalon) and its cranial nerves and associated ganglia; the spinal cord and its spinal nerves and associated ganglia.
Key Takeaways
- Nerve function depends on the unique characteristics of end-organs, not just their structure or stimuli.
- Special stimuli act upon sensory nerves to produce conscious sensations like sight and hearing.
- Efferent (motor) nerves transmit impulses from nerve cells to muscles and glands.
Practical Tips
- Understand how special stimuli affect the nervous system for better response in survival situations.
- Recognize the importance of motor nerves in controlling muscle contractions during emergencies.
Warnings & Risks
- Ignoring the complexities of sensory and motor nerve functions can lead to ineffective emergency responses.
- Misunderstanding reflex actions may result in improper treatment or intervention.
Modern Application
While this chapter's detailed anatomical descriptions are foundational, modern survival preparedness emphasizes practical application. Understanding how nerves respond to stimuli remains crucial for effective triage and first aid. However, today’s medical advancements offer more precise tools and techniques for assessing and treating nerve-related injuries.
Frequently Asked Questions
Q: What is the neurone theory according to Waldeyer?
The neurone theory posits that each neurone is a distinct entity with no connections among collaterals or terminals, and impulses are conveyed by contact between axonic terminals of one neurone and cell bodies or dendrites of another.
Q: How does the spinal cord function in reflex actions?
The spinal cord plays a crucial role in reflex actions by receiving nerve impulses from sensory nerves, transmitting them to motor cells, which then send impulses through efferent nerves to muscles or glands, causing them to act.
Q: What are the main components of the central nervous system?
The central nervous system includes the brain (with cranial nerves and ganglia) and the spinal cord (with spinal nerves and ganglia).