Reflex action and reflex arc - class-XII

Reflex actions are rapid, involuntary responses to stimuli that are primarily processed by the spinal cord, allowing for a faster reaction time than if the signal had to travel to the brain.

An automatic (involuntary) neuromuscular action excited by a defined stimulus is called reflex action. Sweating is not a reflex action. It is primarily a means of temperature regulation. But, Salivation and hand withdrawal because of the needle both are reflex actions.

Option 'D' is correct

Voluntary movements are movements that are in direct control of the will of a person. These are controlled by skeletal muscles. For example walking, talking, dancing, etc. Involuntary movements are movements that are not in control of a person. They are generated by smooth striated muscle. For example, heart pumping, digestion, etc. 

Medulla oblongata is the part of hindbrain. It is located in the brainstem, anterior to the cerebellum. It controls the involuntary functions . It is linked to the autonomic system and has cardiac, respiratory, vomiting and vasomotor centres. It also controls breathing heart rate and blood pressure.

Each kind of a change in the environment evokes an appropriate movement in
response. When we want to talk to our friends in class, we whisper, rather than shouting
loudly. So, the movement to be made depends on the event triggering it. Hence, such
controlled movement must be connected to the recognition of various events in the
environment, followed by only the correct movement in response. Therefore, the correct answer is option A.

Reflex action is an action which is given in response to something in the environment. It is an immediate action taken without much thinking and it does not have our control. The spinal cord is responsible for the response of the body because the impulse has not reached the brain till then. Therefore, the correct answer is option A.

• Voluntary actions are those which can be controlled by us like clapping, dancing, jumping, running, etc. 
• Whereas, involuntary actions are those which cannot be regulated or stopped by us like the circulation of blood, heartbeat, etc. Hence, reflex actions are involuntary actions that are done to save oneself from danger. 

• The best-known reflex is the pupillary light reflex. If a light is flashed near one eye, the pupils 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. 

Swallowing food is a complex process involving both voluntary and involuntary muscle coordination, but it is not classified as a simple reflex action in the same way as blinking or shivering.

Ivan Pavlov is famous for his experiments on classical conditioning, which involves the formation of conditioned reflexes in dogs.

A reflex arc follows the pathway: Stimulus -> Receptor -> Sensory neuron -> Integration center (spinal cord) -> Motor neuron -> Effector -> Response.

Involuntary actions are the actions which are happening without the conscious choice of an organism. The examples for involuntary actions are: Vomiting, yawning, salivation, heart beats, coughing, sneezing, etc.  Whereas chewing is a voluntary action, which is controllable.

Reflex action is an involuntary action and it is a sudden reaction against the stimulus. e.g. removal of hand on being touched by hot or insertion of a pin in a skin, coughing, closing of the eyelid when any object enters in the eye

There are two types of reflex arcs namely, autonomic (visceral) reflex arc, affecting inner organs and somatic reflex arc, affecting muscles. 

• The movement of animals towards or away from the stimulus is called as the taxis. The taxis may be negative or positive. 
• The movement away from a stimulus is called negative taxis and the movement towards the stimulus is called positive taxis.

• A simple reflex arc consists of only one sensory neuron and one motor neuron, hence the name is the monosynaptic reflex. A complex reflex arc or polysynaptic reflex is formed when the sensory neuron influences several motor neurons through intermediate (association) neurons of the spinal cord. Complex reflex arc consisting of two sensory neurons and one motor neuron.

A sleeping cat suddenly gets up and chases a rat. The movement involved is similar to the movement of train on green signal, because it is involuntary action.

So, the correct option is ‘the
movement of train on green signal’.

The somatic reflex arc affects the muscles and the receptor organ is skin whereas, the effector organ is skeletal muscles. The visceral reflex arc affects the internal organs and the receptor organ is epithelial lining of the gut whereas, the effector organ is smooth muscles. 

The reflex arc is a simple nervous pathway and consists of the sensory receptor, afferent neuron, centre, efferent neuron and effector organ. The afferent/sensory neurons transmit the sensory information from sensory receptors to the spinal cord (sensory pathway). Reflex arc starts with sensory receptors, not with muscles. The interneurons of spinal cord integrate the incoming information and signal is relayed to motor/efferent neurons.  The motor pathway transmits the signal from motor neurons to the effector organs (muscles and glands etc). Thus, reflex arc transmits the information from receptor to effector via the spinal cord which. The brain is not the part of reflex arc. Thus, the correct answer is option C.

Reflex arc transmits the sensory information from receptor to effector via spinal cord. It consists of sensory receptor, afferent (sensory) neuron, centre, efferent (motor) neuron and effector organ. The afferent/sensory neurons transmit the sensory information from sensory receptors to spinal cord (sensory pathway). Detection of environmental stimulus by receptors forms the first step of reflex arc. 

Reflex arc consists of sensory receptor, afferent neuron, centre, efferent neuron and effector organ. The reflexes that involve sensory and motor nerve fibres of cranial nerves and control the head region are known as cranial reflexes. Since, cranial reflexes involve head, eyes, nose, mouth, swallowing and facial expression, they produce the vital and involuntary responses. Spinal reflexes are the one in which spinal cord serves as centre without involvement of brain. They control the voluntary responses of other body parts via spinal cord. Salivation in response to sight/smell/thought of food, blushing and sneezing are involuntary actions, which involve mouth, facial expression and nose, and thus are categorized under cranial reflexes. Scratching is a voluntary response to itch stimulus in which brain is not involved and thus is a spinal reflex. 

• Monosynaptic reflex is a type of reflex in which the reflex arc consists of only two neurons, one sensory neuron, and one motor neuron. Monosynaptic refers to the presence of a single chemical synapse. 
• By contrast, in polysynaptic reflex arcs, more than one relay neurons connect the sensory and motor neuron. 
• Polysynaptic reflex or spinal reflex or withdrawal reflex protects the body from the damaging stimulus. It is located in the spinal cord. 

Reflex arc transmits the sensory information from receptor to effector via the spinal cord. It consists of the sensory receptor, afferent neuron, centre, efferent neuron and effector organ. The afferent/sensory neurons transmit the sensory information from sensory receptors to the spinal cord (sensory pathway). The interneurons of spinal cord integrate the incoming information and signal is relayed to motor/efferent neurons. The motor pathway transmits the signal from motor neurons to the effector organs (muscles and glands etc). 

A reflex arc follows a specific pathway: a receptor detects a stimulus, sensory neurons transmit the signal to the central nervous system (grey matter), motor neurons carry the response, and effectors perform the action. Option C correctly lists this sequence.

The path taken by the nerve impulses in a reflex is called as a reflex arc. 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. 

A reflex arc is a simple nervous pathway and consists of the sensory/afferent neuron, center (spinal cord), motor/efferent neuron and effector organ. The afferent/sensory neurons transmit the sensory information from sensory receptors to the spinal cord (sensory pathway). The interneurons of spinal cord integrate the incoming information and signal is relayed to motor/efferent neurons.  The motor pathway transmits the signal from motor neurons to the effector organs (muscles and glands etc). Thus, reflex arc transmits the information from receptor to effector via the spinal cord.

A monosynaptic reflex arc involves only one synapse between the sensory neuron and the motor neuron. This is the simplest form of a reflex arc.

Spinal reflexes are responses to stimuli arising from the  spinal cord. These responses are quick usually to protect the body from a dangerous situation.

A reflex arc is a simple nervous pathway and consists of a sensory/afferent neuron, center (spinal cord), motor/efferent neuron and effector organ. The afferent/sensory neurons transmit the sensory information from sensory receptors to the spinal cord (sensory pathway). The interneurons of spinal cord integrate the incoming information and signal is relayed to motor/efferent neurons. The motor pathway transmits the signal from motor neurons to the effector organs (muscles and glands etc). Thus, reflex arc transmits the information from receptor to effector via the spinal cord. The brain is not the part of the reflex arc. 

Monosynaptic transmission involves only two neurons, one sensory and one motor. In this, the signal is passed from one neuron to another neuron. In multisynaptic transmission, more than two neurons are involved. In this case, there is some delay in transmission of neural signal at the synapses. This is because more synapses are encountered in a reflex pathway and hence it takes more time to effect the reflex. In the given problem, it is given than average synaptic delay is 0.5 ms. Reflex pathway A is monsynaptic as it is taking 0.5 ms for transmission of signal. Reflex pathway B is disynaptic as it is taking 1.0 ms for signal transmission. This is because there are three neurons are involved. From sensory neuron each motor neuron takes 0.5 ms for transmission of signal. Reflex pathway for D is trisynaptic as it is having 1.5 ms of synaptic delay. Similarly, reflex pathway for C is quadrisynaptic as it is having 2.0 ms of synaptic delay. 

The primary components of the reflex arc are the sensory-nerve cells (or receptors), that receive stimulation, in turn connecting to other nerve cells, that activate muscle cells (or effectors), which perform the reflex action.

• Pavlov's Pouch is an artificially created pouch for experimental purposes.
• It was surgically created by a physiologist Ivan Petrovich Pavlov.
  
• It was created to study the physiology of the digestive tract.
• It was also used to study the principles of secretion of the fundal glands.
  
• It is a small portion of the stomach which is separated from the main stomach of a dog.
  
• So, the correct answer is 'Opened stomach of a dog'.

• Secretin was the first hormone to be identified. In 1902, William Bayliss and Ernest Starling were studying how the nervous system controls the process of digestion.
•  It was known that the pancreas secreted digestive juices in response to the passage of food (chyme) through the pyloric sphincter into the duodenum. Hence, The scientist who found secretion of gastric juice to be under control of the nervous system was Ernest Starling.