The Pathway of a Nerve Impulse
Impulses traveling in the peripheral nervous system can be traveling in one of two directions. They can be traveling toward the central nervous system as sensory information. Or they can be traveling away from the central nervous system as motor impulses .
A sensory pathway is divided into three sections.
First order neuron – carries the sensory impulse from the sensory receptor to the central nervous system.
Second order neuron – carries the information from the central nervous system to the thalamus. Information traveling along second order neurons decussates from one side of the CNS to the other side of the CNS.
Third order neuron – carries sensory information from the thalamus to the cerebral cortex.
Sensory Pathways
Information that is relayed to the brain can be coded in several ways. The strength of the stimulus can be coded for by the number of sensory receptors stimulated. The type of receptor activated. For example chemoreceptors for levels of oxygen in the blood. Or thermoreceptors for thermal sensations such as hot or cold Spinothalamic pathway. There are actually two spinothalamic pathways. The lateral spinothalamic and the anterior spinothalamic pathways. The lateral spinothalamic pathway relays the sensations of pain and temperature. The anterior spinothalamic pathway carries the sensations of crude touch, pressure, tickling and itching.
Motor pathways
Are efferent and travel from the central nervous system to an effector organ, gland or muscle. There are two main types the pyramidal pathways and the extrapyramidal pathways. The pyramidal pathways are considered direct while the extrapyramidal pathways are considered indirect. Motor pathways Both of these pathways consist of upper motor neurons and lower motor neurons. The upper motor neurons start in the primary area of the motor cortex and synapse with lower motor neurons in the ventral horn of the spinal cord. The upper motor neurons to not innervate the effector organ, gland or muscle.The lower motor neurons start in the ventral horn of the spinal cord and actually innervate the effector organ, muscle or gland. Motor pathways .The pyramidal pathways are considered direct motor pathways because 90 % of the axons cross-over in the medulla. The lower motor neurons of the pyramidal pathways innervate the muscles of the limbs, hands and feet. The pyramidal pathways control precise motor movements such as buttoning a shirt or playing the piano. receptors can be characterized as chemo-, mechanic-, thermo-, or photoreceptorsA variety of sensory receptors scattered throughout the body can become activated by exteroceptive, interoceptive, or proprioceptive input. Exteroceptive input relays sensory information about the body’s interaction with the external environment. Interoceptive input relays information about the body’s internal state, whereas proprioceptive input conveys information about position sense from the body and its component parts. Each receptor is specialized to detect mechanical, chemical, nociceptive (L. nocere, “to injure,” “painful”), or thermal stimuli.
●Examples of pyramidal pathways are the lateral corticospinal tract anterior corticospinal tract and corticobulbar tract.
• sensory systems inform CNS about the external (exteroceptors) and about the internal (interceptors) environment
• a special group is formed by the proprioceptors, informing about the position of the body and the body parts within exteroceptors we can distinguish between tele receptors (vision, audition, olfaction) and contact receptors (taste [gustation], touch) – interceptors are also contact receptors the role of tele- and contact receptors also differ in the regulation of behavior (preparative and consummator stage) sensory systems react specifically to a given modality, type of energy – adequate stimulus
FUNCTIONS OF THE pathway impulses
Individual neurons carry incoming signals, or communicate with an array of neurons, or carry signals to effectors that produce an action. The nervous system thus carries out a complex assortment of tasks, such as sensing smells, producing speech, remembering past events, providing signals that control body movements and regulating the operation of internal organs. These diverse activities are grouped into three basic functions: sensory, integrative and motor.
Sensory function
The sensory receptors detect many different types of stimuli, both within your body, such as an increase in blood temperature, and outside your body, such as a touch on your arm. Sensory or afferent neurons carry this sensory information into the brain and spinal cord through cranial and spinal nerves.
Integrative function.
The nervous system integrates (processes) sensory information by analyzing and OVERVIEW OF THE NERVOUS SYSTEM Nervous tissue is one of the four main tissue types. It acts together with the endocrine system to regulate homeostasis in the body. The nervous system has many similarities with the endocrine system, and they control of the activities of the body to keep it within optimal limits. However, the nervous system is extremely fast-acting, but shorter lived in action than the endocrine (hormonal) system. Think of how quickly you reflexively move when you accidentally put your hand on a hot stove or step on a tack. The nervous system uses a series of electrochemical signals to receive information from the receptors of the body in the peripheral nervous system (PNS) regions and sends them to the central nervous system (CNS), the brain and spinal cord, to coordinate our actions. A new message is then sent to an effector organ or muscle to take action. This whole process of sending information from receptor to coordinator to reactor takes only a fraction of a second. That would not sound so amazing, if not for the fact that this is happening at millions of places in the body at once. Nervous tissue monitors everybody activity, including breathing, digestion and the beating of your heart. You do not even need to actively think about these things since they are done for you automatically (or autonomic ally) without your conscious thought. Certain of the manual therapies may utilize routine sensory, motor and reflex tests to assess the role of the nervous system in maintaining homeostasis. Even in this age of technology and computers, no computer built today can rival the complexity of the human nervous system. The nervous system is a network of billions of interconnected nerve cells (neurons) that receive stimuli, coordinate this sensory information and cause the body to respond appropriately. The individual neurons transmit messages by means of a complicated electrochemical process. With a mass of only 3 percent of the total body weight, the nervous system is one of the smallest yet most complex of the 11 body systems. The two main subdivisions of the nervous system are the central nervous system (CNS), which consists of the brain and spinal cord, and the peripheral nervous system (PNS), which includes all nervous tissue outside the CNS.
The nervous system is also responsible for our perceptions, behaviors and memories, as well as initiating all voluntary movements. Because the nervous system is quite complex, it’s commonly considered in several chapters of a typical textbook. We will consider the organization of the nervous system, the structure and functions of the spinal cord and spinal nerves, as well as certain applications to the manual therapies. storing some of it and making decisions for appropriate responses. An important integrative function is perception, the conscious awareness of sensory stimuli. Perception occurs in the brain. Many of the neurons that participate in integration are interneurons (association neurons), whose axons extend for only a short distance and contact nearby neurons in the brain or spinal cord. Interneurons comprise the vast majority of neurons in the body
Motor function
Once a sensory stimulus is received, the nervous system may elicit an appropriate motor response, such as muscular contraction or glandular secretion. The neurons that serve this function are motor (efferent) neurons. Motor neurons carry information from the brain toward the spinal cord, or out of the brain and spinal cord to effectors (muscles and glands) through cranial and spinal nerves. Stimulation of the effectors by motor neurons causes muscles to contract and glands to secrete.
ORGANIZATION OF THE NERVOUS SYSTEM
The CNS integrates and correlates many different kinds of incoming sensory information, as well as being the source of thoughts, emotions and memories. Most nerve impulses that stimulate muscles to contract and glands to secrete originate in the CNS. Structural components of the PNS are cranial nerves and their branches, spinal nerves and their branches, ganglia and sensory receptors. The PNS is further subdivided into a
Somatic nervous system (SNS),
an autonomic nervous system (ANS),
And an enteric nervous system (ENS).
The somatic nervous system consists of
1) Sensory neurons that convey information from somatic receptors in the head, body wall, viscera, and limbs and from receptors for the special senses of vision, hearing, taste, and smell to the CNS.
2) Motor neurons that conduct impulses from the CNS to skeletal muscles only. Because these motor responses can be consciously controlled, the action of this part of the PNS is voluntary. The ANS consists of motor neurons that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands. Because its motor responses are not normally under conscious control, the action of the ANS is involuntary. The ANS consists of two divisions.Sympathetic and parasympathetic. With a few exceptions, effectors are innervated by both divisions, and the two divisions usually have opposing action. Its neurons extend most of the length of the gastrointestinal (GI) tract. Sensory neurons of the enteric nervous system monitor chemical changes within the GI tract and the stretching of its walls. Enteric motor neurons govern contraction of GI tract smooth muscle, secretions of the GI tract organs, such as acid secretion by the stomach, and activity of GI tract endocrine cells.
Conclusions
1. Motor behavior involves a coordinated contraction of many muscles and is controlled by motor control systems. CNS contains neuronal networks mediating different types of motor coordination. A typical network consists of a group of interneurons that activate a specific group of motoneurons in a certain sequence and inhibit other motoneurons that may counteract the intended movement. There are preformed networks that allow performance of a basic movement repertoire (e.g. locomotion, posture, breathing, eye movements, etc.), In addition, we are able to learn new motor coordinations through plastic changes taken place in genetically expressed motor infrastructure.
2. It also contains neuronal systems whose axons project to the spinal networks. Cortical motor areas are responsible for voluntary movements, as well as for corrections of motor patterns generated by the spinal cord and brainstem. Cerebellum, basal ganglia and thalamus do not participate directly in generation of movements, but are involved in motor coordination. Cerebellum improves a "quality" of movements by coordinating activity of motor cortex, brainstem and spinal cord on the basis of peripheral and central feedback signals. Basal ganglia are responsible for selection and initiation of proper type of motor behavior. Thalamus is a "relay station" transmitting different type of signals to the cortex.
3. Each level of motor control affects its subordinate level via descending pathways. The spinal cord receives commands via five descending tracts. The vestibulo-, reticulo-, rubro- and tectospinal tracts originate from vestibular, reticular, and red nuclei of the brainstem and from tectum, respectively. The corticospinal tracts originate from the primary motor cortex, and to a lesser extent from the premotor and supplementary motor areas. Descending tracts have different basic functions.