Zach Ganska
Level 5 Valued Member
Every time I think I'm out; they pull me back in....
Scientist,
I follow your argument, however many of the statements you made sounded contradictory to what I was taught as an undergrad in college, so insomnia and curiosity has lead me to pull out my old texts and brush up on the subject.
Brett, Brandon, Scientist -
please provide updated texts if the following quotes are outdated and no longer considered valid in the study of A & P. I would be grateful if so as I haven't studied at the collegiate level in a few years and will be doing so at some near point in time.
Scientist-
These are direct quotes pulled from "Fundamentals of Anatomy & Physiology 8th edition" by Martini & Nath (2009), and "Exercise Physiology , Energy, Nutrition & Human Performance 6th Edition" by McArdle, Katch & Katch (2007). They oppose several statements you have made regarding what a reflex is and is not (emphasis mine). Please provide academic support of your claims to disprove these sources.
Reflexes are rapid, automatic responses to specific stimuli .........
The “wiring” of a single reflex is called a reflex arc A reflex arc begins at a receptor and ends at a peripheral efector, such as a muscle fiber......(Martini 448).
Reflexes are classified on the basis of (1) their development, (2) the nature of the resulting motor response, (3) the complexity of the neural circuit involved, or (4) the site of information processing. The categories are not mutually exclusive - they represent different ways of describing a single reflex
Innate reflexes result from the connections that form between neurons during development. Such reflexes generally appear in a predictable sequence, from the simplest reflex responses (withdrawal from pain) to more complex motor patterns (chewing, sucking, or tracking objects with the eyes). The neural connections responsible for the basic motor patterns of an innate reflex are genetically or developmentally programmed (Martini 449).
More complex, learned motor patterns are called acquired reflexes. An experienced driver steps on the brake when trouble appears ahead; a professional skier must make equally quick adjustments in the body while racing. These motor responses are rapid and automatic, but they were learned rather than preestablished. Such reflexes are enhanced by repetition. The distinction between innate and acquired reflexes is not absolute: Some people can learn motor patterns more quickly than others, and the differences probably have a genetic basis.
Most reflexes, whether innate or acquired, can be modified over time or suppressed through conscious effort .......
Polysnaptic reflexes can produce far more complicated responses than monosynaptic reflexes, because the interneurons can control motor neurons that activate several muscle groups simultaneously
Spinal reflexes range in complexity from simple to monosynaptic reflexes involving a single segment of the spinal cord to polysynaptic reflexes that involve many segments. In the most complicated spinal reflexes, called intersegmental reflex arcs, many segments interact to produce a coordinated, highly variable response (Martini 450).
The best-known monosynaptic reflex is the stretch reflex, which provides automatic regulation of skeletal muscle length (Martini 450).
Many stretch reflexes are postural reflexes - reflexes that help us maintain a normal upright posture. Standing for example involves a cooperative effort on the part of many muscle groups. Some of these muscles work in opposition to one another, exerting forces that keep the body’s weight balanced over the feet, If the body leans forward, stretch receptors in the calf muscles are stimulated. Those muscles then respond by contracting, thereby returning the body to an upright position. If the muscles overcompensate and the body begins to lean back, the calf muscles relax. But then stretch receptors in the muscles of the shins and thighs are stimulated, and the problem is corrected immediately.
Postural muscles generally have a firm muscle tone and extremely sensitive stretch receptors. As a result, very fine adjustments are continually being made, and you are not aware of the cycles of contraction and relaxation that occur. Stretch reflexes are only one type of postural reflex, there are many complex polysynaptic postural reflexes (Martini 452).
General Characteristics of Polysynaptic Reflexes
1. They involve Pools of Interneurons......
2. They are intersegmental in Distribution. The interneuron pools extend across spinal segments and may activate muscle groups in many parts of the body.
3. They involve Reciprocal Inhibition. Reciprocal inhibition coordinates muscular contractions and reduces resistance to movement. In the flexor and crossed extensor reflexes, the contraction of one muscle group is associated with the inhibition of opposing muscles.
4. They Have Reverberating Circuits, Which Prolong the Reflexive Motor Response.
Several Reflexes May Cooperate to Produce a Coordinated, Controlled Response. As a reflex movement gets under way, antagonistic reflexes are inhibited...... In complex polysynaptic reflexes, commands may be distributed along the length of the spinal cord, producing a well-coordinated response (Martini 454).
The brain can affect spinal cord-based reflexes
Reflex motor behaviors occur automatically, without instructions from higher centers. However, higher centers can have a profound effect on the performance of a reflex. Processing centers in the brain can facilitate or inhibit reflex motor patterns based in the spinal cord. Descending tracts originating in the brain synapse on interneurons and motor neurons throughout the spinal cord (Martini 454).
Voluntary Movements and Reflex Motor Patterns
Spinal reflexes produce consistent, stereotyped motor patterns that are triggered by specific external stimuli. However, the same motor patterns can also be activated as needed by centers in the brain. By making use of these preexisting patterns, relatively few descending fibers can control complex motor functions. For example, the motor pattens for walking, running, and jumping are directed primarily by neuronal pools in the spinal cord. The descending pathways from the brain provide appropriate facilitation, inhibition, or “fine-tuning” of the established patterns. This is a very efficient system that is similar to an order given in a military drill: A single command triggers a complex, predetermined sequence of events.
Motor control therefore involves a series of interacting levels. At the lowest level are monosynaptic reflexes that are rapid, but stereotyped and relatively inflexible. At the highest level are centers in the brain that can modulate or build on reflexive motor patterns.
Reinforcement and Inhibition
A single EPSP may not depolarize the postsynaptic neuron sufficiently to generate an action potential, but it does make that neuron more sensitive to other excitatory stimuli, known as facilitation. Alternatively, an IPSP will make the neuron less responsive to excitatory stimulation, through the process of inhibition. By stimulating excitatory or inhibitory interneurons within the brain stem or spinal cord, higher centers can adjust the sensitivity of reflexes by creating EPSPs or IPSPs at the motor neurons involved in reflex responses.
When many excitatory synapses are chronically active, the postsynaptic neuron can enter a state of generalized facilitation. This facilitation of reflexes can result in reinforcement, and enhancement of spinal reflexes. If a stimulus fails to elicit a particular reflex response during a clinical exam, there can be many reasons for the failure: The person may be consciously suppressing the response, the nerves involved may be damaged, or there may be underlying problems inside the CNS. The clinician may then ask the patient to perform an action designed to provide reinforcement. Reinforced reflexes are usually too strong to suppress consciously (Martini 455).
Reflex actions in the spinal cord and other subconscious areas of the CNS control many muscle functions. Hundreds of hours of practicing a particular skill “grooves” the neuromuscular movements to become automatic, requiring little to no conscious control. Unfortunately, improper practice can also automate a task to produce less than optimal neuromuscular actions (McArdle 402).
Summary
1. Neural control mechanisms located in the CNS finely regulate human movement. In response to external and internal stimuli, bits of sensory input automatically become coded, routed, organized, and transmitted to the effector organ - the skeletal muscles.
2. Tracts of neural tissue descend from the brain to influence spinal cord neurons. Neurons in the extrapyramidal tract control posture and provide a continual background level of neuromuscular tone; the pyramidal tract neurons stimulate discrete muscular movements.
3. The cerebellum fine tunes muscle activity through its function as the major comparing, evaluating, and integrating center.
4. The spinal cord and other subconscious areas of the CNS control diverse muscle functions. The reflex arc provides the basic mechanism to process “automatic” muscle actions.
(McArdle 414-415)
Scientist,
I follow your argument, however many of the statements you made sounded contradictory to what I was taught as an undergrad in college, so insomnia and curiosity has lead me to pull out my old texts and brush up on the subject.
Brett, Brandon, Scientist -
please provide updated texts if the following quotes are outdated and no longer considered valid in the study of A & P. I would be grateful if so as I haven't studied at the collegiate level in a few years and will be doing so at some near point in time.
Scientist-
These are direct quotes pulled from "Fundamentals of Anatomy & Physiology 8th edition" by Martini & Nath (2009), and "Exercise Physiology , Energy, Nutrition & Human Performance 6th Edition" by McArdle, Katch & Katch (2007). They oppose several statements you have made regarding what a reflex is and is not (emphasis mine). Please provide academic support of your claims to disprove these sources.
Reflexes are rapid, automatic responses to specific stimuli .........
The “wiring” of a single reflex is called a reflex arc A reflex arc begins at a receptor and ends at a peripheral efector, such as a muscle fiber......(Martini 448).
Reflexes are classified on the basis of (1) their development, (2) the nature of the resulting motor response, (3) the complexity of the neural circuit involved, or (4) the site of information processing. The categories are not mutually exclusive - they represent different ways of describing a single reflex
Innate reflexes result from the connections that form between neurons during development. Such reflexes generally appear in a predictable sequence, from the simplest reflex responses (withdrawal from pain) to more complex motor patterns (chewing, sucking, or tracking objects with the eyes). The neural connections responsible for the basic motor patterns of an innate reflex are genetically or developmentally programmed (Martini 449).
More complex, learned motor patterns are called acquired reflexes. An experienced driver steps on the brake when trouble appears ahead; a professional skier must make equally quick adjustments in the body while racing. These motor responses are rapid and automatic, but they were learned rather than preestablished. Such reflexes are enhanced by repetition. The distinction between innate and acquired reflexes is not absolute: Some people can learn motor patterns more quickly than others, and the differences probably have a genetic basis.
Most reflexes, whether innate or acquired, can be modified over time or suppressed through conscious effort .......
Polysnaptic reflexes can produce far more complicated responses than monosynaptic reflexes, because the interneurons can control motor neurons that activate several muscle groups simultaneously
Spinal reflexes range in complexity from simple to monosynaptic reflexes involving a single segment of the spinal cord to polysynaptic reflexes that involve many segments. In the most complicated spinal reflexes, called intersegmental reflex arcs, many segments interact to produce a coordinated, highly variable response (Martini 450).
The best-known monosynaptic reflex is the stretch reflex, which provides automatic regulation of skeletal muscle length (Martini 450).
Many stretch reflexes are postural reflexes - reflexes that help us maintain a normal upright posture. Standing for example involves a cooperative effort on the part of many muscle groups. Some of these muscles work in opposition to one another, exerting forces that keep the body’s weight balanced over the feet, If the body leans forward, stretch receptors in the calf muscles are stimulated. Those muscles then respond by contracting, thereby returning the body to an upright position. If the muscles overcompensate and the body begins to lean back, the calf muscles relax. But then stretch receptors in the muscles of the shins and thighs are stimulated, and the problem is corrected immediately.
Postural muscles generally have a firm muscle tone and extremely sensitive stretch receptors. As a result, very fine adjustments are continually being made, and you are not aware of the cycles of contraction and relaxation that occur. Stretch reflexes are only one type of postural reflex, there are many complex polysynaptic postural reflexes (Martini 452).
General Characteristics of Polysynaptic Reflexes
1. They involve Pools of Interneurons......
2. They are intersegmental in Distribution. The interneuron pools extend across spinal segments and may activate muscle groups in many parts of the body.
3. They involve Reciprocal Inhibition. Reciprocal inhibition coordinates muscular contractions and reduces resistance to movement. In the flexor and crossed extensor reflexes, the contraction of one muscle group is associated with the inhibition of opposing muscles.
4. They Have Reverberating Circuits, Which Prolong the Reflexive Motor Response.
Several Reflexes May Cooperate to Produce a Coordinated, Controlled Response. As a reflex movement gets under way, antagonistic reflexes are inhibited...... In complex polysynaptic reflexes, commands may be distributed along the length of the spinal cord, producing a well-coordinated response (Martini 454).
The brain can affect spinal cord-based reflexes
Reflex motor behaviors occur automatically, without instructions from higher centers. However, higher centers can have a profound effect on the performance of a reflex. Processing centers in the brain can facilitate or inhibit reflex motor patterns based in the spinal cord. Descending tracts originating in the brain synapse on interneurons and motor neurons throughout the spinal cord (Martini 454).
Voluntary Movements and Reflex Motor Patterns
Spinal reflexes produce consistent, stereotyped motor patterns that are triggered by specific external stimuli. However, the same motor patterns can also be activated as needed by centers in the brain. By making use of these preexisting patterns, relatively few descending fibers can control complex motor functions. For example, the motor pattens for walking, running, and jumping are directed primarily by neuronal pools in the spinal cord. The descending pathways from the brain provide appropriate facilitation, inhibition, or “fine-tuning” of the established patterns. This is a very efficient system that is similar to an order given in a military drill: A single command triggers a complex, predetermined sequence of events.
Motor control therefore involves a series of interacting levels. At the lowest level are monosynaptic reflexes that are rapid, but stereotyped and relatively inflexible. At the highest level are centers in the brain that can modulate or build on reflexive motor patterns.
Reinforcement and Inhibition
A single EPSP may not depolarize the postsynaptic neuron sufficiently to generate an action potential, but it does make that neuron more sensitive to other excitatory stimuli, known as facilitation. Alternatively, an IPSP will make the neuron less responsive to excitatory stimulation, through the process of inhibition. By stimulating excitatory or inhibitory interneurons within the brain stem or spinal cord, higher centers can adjust the sensitivity of reflexes by creating EPSPs or IPSPs at the motor neurons involved in reflex responses.
When many excitatory synapses are chronically active, the postsynaptic neuron can enter a state of generalized facilitation. This facilitation of reflexes can result in reinforcement, and enhancement of spinal reflexes. If a stimulus fails to elicit a particular reflex response during a clinical exam, there can be many reasons for the failure: The person may be consciously suppressing the response, the nerves involved may be damaged, or there may be underlying problems inside the CNS. The clinician may then ask the patient to perform an action designed to provide reinforcement. Reinforced reflexes are usually too strong to suppress consciously (Martini 455).
Reflex actions in the spinal cord and other subconscious areas of the CNS control many muscle functions. Hundreds of hours of practicing a particular skill “grooves” the neuromuscular movements to become automatic, requiring little to no conscious control. Unfortunately, improper practice can also automate a task to produce less than optimal neuromuscular actions (McArdle 402).
Summary
1. Neural control mechanisms located in the CNS finely regulate human movement. In response to external and internal stimuli, bits of sensory input automatically become coded, routed, organized, and transmitted to the effector organ - the skeletal muscles.
2. Tracts of neural tissue descend from the brain to influence spinal cord neurons. Neurons in the extrapyramidal tract control posture and provide a continual background level of neuromuscular tone; the pyramidal tract neurons stimulate discrete muscular movements.
3. The cerebellum fine tunes muscle activity through its function as the major comparing, evaluating, and integrating center.
4. The spinal cord and other subconscious areas of the CNS control diverse muscle functions. The reflex arc provides the basic mechanism to process “automatic” muscle actions.
(McArdle 414-415)