Vías Eferentes PDF

## Vías Eferentes The information entering or exiting the central nervous system is conducted through a set of nerves that form the peripheral nervous system. The nerves that carry information towards the brain or spinal cord form the **sensory or afferent pathways**, and the nerves that carry info...

## Vías Eferentes The information entering or exiting the central nervous system is conducted through a set of nerves that form the peripheral nervous system. The nerves that carry information towards the brain or spinal cord form the **sensory or afferent pathways**, and the nerves that carry information from the central nervous system toward the organs form the **motor or efferent pathways**. The nerves originating from the brain or **cranial nerves**, and those originating from the spinal cord or **spinal (rachitic) nerves**, are made up of afferent and efferent fibers. The efferent pathways of the peripheral nervous system can be subdivided according to the type of effector organ to which they are directed. If the efferent neurons innervate the skeletal muscles, they are part of the **somatic nervous system**. While neurons directed to the smooth muscles, cardiac muscle or glands form the **autonomic nervous system**. As its name implies, the control that the autonomic nervous system exerts over the organs it innervates is independent of will. ## Autonomic Nervous System (ANS) Almost all the tissues in the body are innervated by nerve fibers of the autonomic nervous system, which regulates the function of different organs in the face of environmental changes. Two antagonistic mechanisms exist, through which the autonomic nervous system exerts this control: the **sympathetic nervous system** and the **parasympathetic nervous system.** ### Sympathetic Nervous System In general, the sympathetic nervous system produces the “fight or flight” response; that is, it is responsible for increased activity in the body during stressful conditions. Thus, sympathetic stimulation produces an increase in blood pressure and heart rate, pupillary dilation, increased respiration, and hair standing on end. **Adrenaline and noradrenaline** act as neurotransmitters in the transmission of the nerve impulse of the sympathetic nervous system, therefore it is also called the **adrenergic system.** ### Parasympathetic Nervous System In general, the parasympathetic nervous system coordinates the normal activities of the body at rest. This is how parasympathetic stimulation lowers the respiratory rate and heart rate, stimulates the gastrointestinal system, defecation, and urine production, as well as body regeneration which takes place during sleep. **Acetylcholine** acts as a neurotransmitter during the transmission of the nerve impulse in the parasympathetic system. For this reason, the parasympathetic system is also known as the **cholinergic system.** ### Sympathetic Division: * **Pupil Dilation** * **Salivation Inhibition** * **Bronchodilation** * **Heart Rate Acceleration** * **Inhibition of Digestive Activity** * **Inhibition of Intestinal Motility and Secretion** * **Relaxation of the Urinary Bladder** * **Celiac Ganglia** * **Inferior Mesenteric Ganglia** ### Parasympathetic Division: * **Pupil Constriction** * **Salivation Stimulation** * **Bronchoconstriction** * **Heart Rate Reduction** * **Stimulation of Digestive Activity** * **Stimulation of Intestinal Motility and Secretion** * **Contraction of the Urinary Bladder** ## Neuromuscular Junction Skeletal muscle is made up of cells called **muscle fibers**, which run almost the entire length of the muscle. They are called muscle fibers due to their elongated and cylindrical shape. Each muscle fiber's cytoplasm or sarcoplasm contains bundles of protein filaments referred to as **myofibrils**, which extend along its length. Myofibrils are made up of two types of proteins: **myosin** and **actin**. Myosin forms the thick filaments, while actin forms the thin filaments. The organization of the actin and myosin filaments creates the characteristic transverse striated appearance of skeletal muscle. The different segments of these striations are labeled with letters and make up the **sarcomere.** Muscle contraction occurs when the muscle fiber shortens; that is, when the sarcomeres come together. This is due to the actin filaments sliding over the myosin filaments, increasing their overlap. As the sarcomeres approach each other, the Z-lines get closer; however, the width of the A-band stays the same. When the muscle relaxes, the Z-lines separate. Skeletal muscle contraction is controlled by motor nerve fibers of the somatic nervous system, which carry nerve impulses from specific areas of the cerebral cortex, which is the main region that controls the initiation of voluntary movements. The axons of motor neurons communicate with the muscle fiber through a chemical synapse called the **neuromuscular junction**. When nerve impulses reach the presynaptic terminal axon of the neuron, synaptic vesicles containing the neurotransmitter acetylcholine are released into the synaptic cleft from those neurons. Then, acetylcholine binds to its specific receptors located in a specific region of the muscle fiber membrane called the **motor end plate**. This opens sodium channels, which triggers a potential action that travels along the muscle fiber membrane called the **sarcolemma.** The muscle action potential triggers the release of calcium ions (Ca²+) that are stored in the **sarcoplasmic reticulum** of the muscle fiber. Increased calcium in the cytoplasm triggers the displacement of the actin filaments, which produces muscle contraction. ## Nervous and Endocrine Control The stability of the internal environment, the control and coordination between the different parts of the body, and functional integration between them is achieved through the action of the **regulating systems** corresponding to the nervous and endocrine systems. ### Comparison between the Nervous and Endocrine Systems: | Feature | Nervous System | Endocrine System | |---|---|---| | Signal | Nerve impulses | Hormones | | Signal Producing Cells | Neurons | Endocrine cells | | Effector Tissues | Muscles and glands | Target tissues that have hormonal receptors (including other endocrine glands, smooth and skeletal muscles, kidneys, liver, gonads, bones, heart, and the hypothalamus) | | Signal Transport | Neural pathways (afferent and efferent) | Blood vessels (blood) | | Signal Effect | Rapid and temporary | Slow and prolonged | ### Neuroendocrine Regulation In some cases, the nervous and endocrine systems operate independently, but in others, there is functional integration between them, known as **neuroendocrine regulation.** An example is the body's response to stressors. Both systems release specific chemical substances that prepare the body for a physiological response to stressors. The nervous system does so more quickly, at the level of the synapse, activating the sympathetic centers, which release adrenaline and noradrenaline in different parts of the body.. This includes the adrenal glands, which release the hormones adrenaline and cortisol into the blood, supplementing the action of the nervous system and keeping the body alert. If the stress response persists, this neuroendocrine response continues. **Stressors**: External or internal stimuli that trigger stress are called stressors. **Stress Response**: A defense or adaptive response to a stimulus that threatens life. * **Sympathetic Nervous System:** * **Adrenaline and Noradrenaline** * **Glándulas Suprarrenales** * **Increased Heart Rate** * **Increased State Of Alertness** * **Increased Blood Flow To The Brain And Muscles** * **Decreased Blood Flow To The Skin And Kidneys** * **Endocrine System:** * **Adrenaline** * **Cortisol** * **Increased Blood Sugar** * **Reduced Inflammation** * **Inhibited Allergic Reactions**