Reflex action of the nerve
There is no denying the fact that Nerves are the cables of the nervous system. Each nerve is packed with hundreds of wire like cells called neurons, which carry electric signals to and from the brain. The brain and spinal cord form the central nervous system, and the nerves outside them are the peripheral nervous system.
It is evident that Neurons work like wires, transmitting electric signals. When the neuron is resting, an electric charge builds up inside it. If triggered, a nerve impulse rushes to the end of the cell, where a chemical called a neurotransmitter passes the signal to the next neuron across a gap, or synapse.
There are three main types of neurons.
Sensory neurons carry incoming signals from sense organs to the central nervous system. Motor neurons carry outgoing signals from the brain to the body, usually to muscle cells.
Association neurons form a complex maze of connections in the brain and spinal cord, linking sensory neurons to motor neurons.
MOTOR NEURON
All neurons are similar in structure to a motor neuron. The cell body contains the nucleus that controls the cell. Filaments called dendrites branch out from the cell body and pick up signals from other neurons. The nerve fiber, or axon, takes the signal and passes it on to other neurons, muscles, or glands.
WHAT IS A REFLEX ACTION?
Reflex actions are involuntary—they happen before you have time to think. When they happen, a nerve signal takes a shortcut through the spinal cord, rather than involving the brain. If we touch a very hot object, a sensory neuron sends a signal shooting from the hand to the spinal cord. There an association neuron transmits the signal to a motor neuron, which tells a muscle in the arm to move the hand.
"Reflex Arc" is the internal neural activity and pathway in the brain and/or spinal cord. "Reflex Action" is the motor movement of muscle that produces the actions described below.
A reflex arc is a neural pathway that controls an action reflex. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs. There are two types of reflex arc: autonomic reflex arc (affecting inner organs) and somatic reflex arc (affecting muscles).
A reflex action is an automatic and inborn response to a stimulus that involves a nerve impulse passing from a sensory nerve cell to a muscle or gland without reaching the level of consciousness. Simple reflexes include sucking, swallowing, blinking, scratching, and the knee jerk. Most reflexes consist of complex patterns of many unconsciously coordinated muscular actions that form the basis of much instinctive behavior in animals. Examples include walking, standing, vision of the object and its reflection arc through the passage up to the people of the eye, the cat's righting reflex, and basic sexual acts.
The anatomical pathway of a reflex is called the reflex arc. It consists of an afferent (or sensory) nerve, usually one or more inter-neurons within the central nervous system, and an efferent (motor, secretory, or secret-motor) nerve.
Most reflexes have several synapses in the reflex arc. The stretch reflex is exceptional in that, with no inter neuron in the arc, it has only one synapse between the afferent nerve fibre and the motor neuron (see below Movement: The regulation of muscular contraction). The flex-or reflex, which removes a limb from a noxious stimulus, has a minimum of two inter neurons and three synapses.
Probably the best-of both eyes contract. Light is the stimulus; impulses reach the brain via the optic nerve; and the response is conveyed to the pupillary musculature by autonomic nerves that supply the eye. Another reflex involving the eye is known as the lacrimal reflex. When something irritates the conjunctiva or cornea of the eye, the lacrimal reflex causes nerve impulses to pass along the fifth cranial nerve (trigeminal) and reach the midbrain. The efferent limb of this reflex arc is autonomic and mainly parasympathetic. These nerve fibres stimulate the lacrimal glands of the orbit, causing the outpouring of tears. Other reflexes of the midbrain and medulla oblongata are the cough and sneeze reflexes. The cough reflex is caused by an irritant in the trachea and the sneeze reflex by one in the nose. In both, the reflex response involves many muscles; this includes a temporary lapse of respiration in order to expel the irritant.
The first reflexes develop in the womb. By seven and a half weeks after conception, the first reflex can be observed; stimulation around the mouth of the fetus causes the lips to be turned toward the stimulus. By birth, sucking and swallowing reflexes are ready for use. Touching the baby’s lips induces sucking, and touching the back of its throat induces swallowing.
Although the word stereotyped is used in the above definition, this does not mean that the reflex response is invariable and unchangeable. When a stimulus is repeated regularly, two changes occur in the reflex response—sensitization and habituation. Sensitization is an increase in response; in general, it occurs during the first 10 to 20 responses. Habituation is a decrease in response; it continues until, eventually, the response is extinguished. When the stimulus is irregularly repeated, habituation does not occur or is minimal.
There are also long-term changes in reflexes, which may be seen in experimental spinal cord transections performed on kittens. Repeated stimulation of the skin below the level of the lesion, such as rubbing the same area for 20 minutes every day, causes a change in latency (the interval between the stimulus and the onset of response) of certain reflexes, with diminution and finally extinction of the response. Although this procedure takes several weeks, it shows that, with daily stimulation, one reflex response can be changed into another. Repeated activation of synapses increases their efficiency, causing a lasting change. When this repeated stimulation ceases, synaptic functions regress, and reflex responses return to their original form.
Although a reflex response is said to be rapid and immediate, some reflexes, called recruiting reflexes, can hardly be evoked by a single stimulus. Instead, they require increasing stimulation to induce a response. The reflex contraction of the bladder, for example, requires an increasing amount of urine to stretch the muscle and to obtain muscular contraction.
Reflexes can be altered by impulses from higher levels of the central nervous system. For example, the cough reflex can be suppressed easily, and even the gag reflex (the movements of incipient vomiting resulting from mechanical stimulation of the wall of the pharynx) can be suppressed with training.
The so-called conditioned reflexes are not reflexes at all but complicated acts of learned behaviour. Salivation is one such conditioned reflex; it occurs only when a person is conscious of the presence of food or when one imagines food.
In some cases to avoid damage to the body. For example, if your hand comes into contact with a hot object there is a reflex action causing it to move out of the way. This reflex action doesn't require conscious thought and can therefore be thought of as a basic survival function.
This is one example of a reflex action, but there are many others.. any involuntary and nearly instantaneous movement in response to a stimulus. These may or may not have a survival function, eg being hit on the knee causes a knee jerk reaction.
The gag reflex is there to stop you choking or putting things that are too big down your throat reflexes where someone goes to punch you are instinctive too, as this reflex tries to stop you getting hurt.
A reflex is an involuntary, spontaneous response to a stimulus. Reflexes protect your body from things that can harm it.
Prepared by Kh. Atiar Rahman
There is no denying the fact that Nerves are the cables of the nervous system. Each nerve is packed with hundreds of wire like cells called neurons, which carry electric signals to and from the brain. The brain and spinal cord form the central nervous system, and the nerves outside them are the peripheral nervous system.
It is evident that Neurons work like wires, transmitting electric signals. When the neuron is resting, an electric charge builds up inside it. If triggered, a nerve impulse rushes to the end of the cell, where a chemical called a neurotransmitter passes the signal to the next neuron across a gap, or synapse.
There are three main types of neurons.
Sensory neurons carry incoming signals from sense organs to the central nervous system. Motor neurons carry outgoing signals from the brain to the body, usually to muscle cells.
Association neurons form a complex maze of connections in the brain and spinal cord, linking sensory neurons to motor neurons.
MOTOR NEURON
All neurons are similar in structure to a motor neuron. The cell body contains the nucleus that controls the cell. Filaments called dendrites branch out from the cell body and pick up signals from other neurons. The nerve fiber, or axon, takes the signal and passes it on to other neurons, muscles, or glands.
WHAT IS A REFLEX ACTION?
Reflex actions are involuntary—they happen before you have time to think. When they happen, a nerve signal takes a shortcut through the spinal cord, rather than involving the brain. If we touch a very hot object, a sensory neuron sends a signal shooting from the hand to the spinal cord. There an association neuron transmits the signal to a motor neuron, which tells a muscle in the arm to move the hand.
"Reflex Arc" is the internal neural activity and pathway in the brain and/or spinal cord. "Reflex Action" is the motor movement of muscle that produces the actions described below.
A reflex arc is a neural pathway that controls an action reflex. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs. There are two types of reflex arc: autonomic reflex arc (affecting inner organs) and somatic reflex arc (affecting muscles).
A reflex action is an automatic and inborn response to a stimulus that involves a nerve impulse passing from a sensory nerve cell to a muscle or gland without reaching the level of consciousness. Simple reflexes include sucking, swallowing, blinking, scratching, and the knee jerk. Most reflexes consist of complex patterns of many unconsciously coordinated muscular actions that form the basis of much instinctive behavior in animals. Examples include walking, standing, vision of the object and its reflection arc through the passage up to the people of the eye, the cat's righting reflex, and basic sexual acts.
The anatomical pathway of a reflex is called the reflex arc. It consists of an afferent (or sensory) nerve, usually one or more inter-neurons within the central nervous system, and an efferent (motor, secretory, or secret-motor) nerve.
Most reflexes have several synapses in the reflex arc. The stretch reflex is exceptional in that, with no inter neuron in the arc, it has only one synapse between the afferent nerve fibre and the motor neuron (see below Movement: The regulation of muscular contraction). The flex-or reflex, which removes a limb from a noxious stimulus, has a minimum of two inter neurons and three synapses.
Probably the best-of both eyes contract. Light is the stimulus; impulses reach the brain via the optic nerve; and the response is conveyed to the pupillary musculature by autonomic nerves that supply the eye. Another reflex involving the eye is known as the lacrimal reflex. When something irritates the conjunctiva or cornea of the eye, the lacrimal reflex causes nerve impulses to pass along the fifth cranial nerve (trigeminal) and reach the midbrain. The efferent limb of this reflex arc is autonomic and mainly parasympathetic. These nerve fibres stimulate the lacrimal glands of the orbit, causing the outpouring of tears. Other reflexes of the midbrain and medulla oblongata are the cough and sneeze reflexes. The cough reflex is caused by an irritant in the trachea and the sneeze reflex by one in the nose. In both, the reflex response involves many muscles; this includes a temporary lapse of respiration in order to expel the irritant.
The first reflexes develop in the womb. By seven and a half weeks after conception, the first reflex can be observed; stimulation around the mouth of the fetus causes the lips to be turned toward the stimulus. By birth, sucking and swallowing reflexes are ready for use. Touching the baby’s lips induces sucking, and touching the back of its throat induces swallowing.
Although the word stereotyped is used in the above definition, this does not mean that the reflex response is invariable and unchangeable. When a stimulus is repeated regularly, two changes occur in the reflex response—sensitization and habituation. Sensitization is an increase in response; in general, it occurs during the first 10 to 20 responses. Habituation is a decrease in response; it continues until, eventually, the response is extinguished. When the stimulus is irregularly repeated, habituation does not occur or is minimal.
There are also long-term changes in reflexes, which may be seen in experimental spinal cord transections performed on kittens. Repeated stimulation of the skin below the level of the lesion, such as rubbing the same area for 20 minutes every day, causes a change in latency (the interval between the stimulus and the onset of response) of certain reflexes, with diminution and finally extinction of the response. Although this procedure takes several weeks, it shows that, with daily stimulation, one reflex response can be changed into another. Repeated activation of synapses increases their efficiency, causing a lasting change. When this repeated stimulation ceases, synaptic functions regress, and reflex responses return to their original form.
Although a reflex response is said to be rapid and immediate, some reflexes, called recruiting reflexes, can hardly be evoked by a single stimulus. Instead, they require increasing stimulation to induce a response. The reflex contraction of the bladder, for example, requires an increasing amount of urine to stretch the muscle and to obtain muscular contraction.
Reflexes can be altered by impulses from higher levels of the central nervous system. For example, the cough reflex can be suppressed easily, and even the gag reflex (the movements of incipient vomiting resulting from mechanical stimulation of the wall of the pharynx) can be suppressed with training.
The so-called conditioned reflexes are not reflexes at all but complicated acts of learned behaviour. Salivation is one such conditioned reflex; it occurs only when a person is conscious of the presence of food or when one imagines food.
In some cases to avoid damage to the body. For example, if your hand comes into contact with a hot object there is a reflex action causing it to move out of the way. This reflex action doesn't require conscious thought and can therefore be thought of as a basic survival function.
This is one example of a reflex action, but there are many others.. any involuntary and nearly instantaneous movement in response to a stimulus. These may or may not have a survival function, eg being hit on the knee causes a knee jerk reaction.
The gag reflex is there to stop you choking or putting things that are too big down your throat reflexes where someone goes to punch you are instinctive too, as this reflex tries to stop you getting hurt.
A reflex is an involuntary, spontaneous response to a stimulus. Reflexes protect your body from things that can harm it.
Prepared by Kh. Atiar Rahman
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