Tag: reflex action and reflex arc

Questions Related to reflex action and reflex arc

Put the following parts of a reflex arc in the correct order beginning with the sensory receptor.
A. Motor neuron    B. Interneuron    C. Effector    D. Sensory neuron     E. Sensory receptor

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. E, D, B, A, C

  2. E, D, A, B, C

  3. A, B, C, D, E

  4. A, E, D, B, C

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Correct Option: A
Explanation:

Most reflex arcs have five main components:  receptors, sensory neurons,interneurons, motor neurone and muscles.
Neurons have special proteins called receptors. Receptors respond to signals in the environment like pressure, pain, vibrations, light etc.
Sensory neurons have sensory receptors, they get activated by the signal from the environment. The activated sensory neurons extend into spinal cord sending an electrical signal to another neuron, the interneuron.
Interneuron then relays the signal to the motor neuron. Motor neuron run out of spinal cord and connect with the muscle or effector.
Thus the correct sequence is a sensory receptor, sensory neuron, interneuron, motor neuron and last effector.

In spite of the presence of complex neuron  networks, reflex arcs continue to be more efficient for quick responses.

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. True

  2. False

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Correct Option: A
Explanation:
The process of response to a peripheral nervous stimulation that occurs involuntarily, that I without conscious effort or thought and requires the involvement of a part of the central nervous system, is called a reflex action. These actions are very rapid, automatic, stereotyped behaviour or responses in which same kind of stimulus evokes a short-lived response. The stimulus is detected by sensory receptors present in the skin. These  initiate nerve impulses in the sensory or afferent neurons leading from them to the spinal cord. These impulses enter the spinal cord and initiate impulses in one or more interneurons. Interneurons initiate impulses in one or more motor or efferent neurons. The motor neurons then carry these impulses to the effectors or skeletal muscles in which response will be shown. This entire pathway from sensory receptor to sensory neuron to spinal cord (having interneurons) to motor neuron to effectors is called the reflex pathway or reflex arc.
So, the correct answer is 'True'.

Reflex arcs are formed in the 

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. Brain

  2. Spinal cord

  3. Heart

  4. Eye

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Correct Option: B
Explanation:
The process of response to a peripheral nervous stimulation that occurs involuntarily, that I without conscious effort or thought and requires the involvement of a part of the central nervous system, is called a reflex action. These actions are very rapid, automatic, stereotyped behaviour or responses in which same kind of stimulus evokes a short-lived response. The stimulus is detected by sensory receptors present in the skin. These  initiate nerve impulses in the sensory or afferent neurons leading from them to the spinal cord. These impulses enter the spinal cord and initiate impulses in one or more interneurons. Interneurons initiate impulses in one or more motor or efferent neurons. The motor neurons then carry these impulses to the effectors or skeletal muscles in which response will be shown. This entire pathway from sensory receptor to sensory neuron to spinal cord (having interneurons) to motor neuron to effectors is called the reflex pathway or reflex arc. Therefore, reflex arc is formed in spinal cord.
So, the correct answer is 'Spinal cord'.

The components of a reflex arc are

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. Sensory neuron, receptor, motor neuron

  2. Receptor, sensory neuron, center, motor neuron

  3. Receptor, sensory neuron, center, motor neuron, effector organ

  4. Motor neuron, sensory neuron, center, effector organ

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Correct Option: C
Explanation:

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.

Therefore, the correct answer is option C.

Reflex arc made of two neurons is

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. Asynaptic

  2. Monosynaptic

  3. Disynaptic

  4. Polysynaptic

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Correct Option: B

Which one of the following reflex do not include innervation of brain?

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. Spinal reflex

  2. Cranial reflex

  3. Afferent reflex

  4. Efferent reflex

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Correct Option: A
Explanation:

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

For example- the withdrawal of the hand on touching a hot object
So, the correct answer is 'spinal reflex'

Which one of the following is the component of reflex arc?

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. Sensory neuron

  2. Brain

  3. Motor neuron

  4. Both A and C

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Correct Option: D
Explanation:

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. 

Therefore, the correct answer is option D.

What is the correct path of a reflex arc?

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. $Sensory stimulus \rightarrow Dendrite \rightarrow Axon$

  2. $ Motor nerves \rightarrow Acetylcholine \rightarrow Adjustor neuron$

  3. $ Efferent nerves \rightarrow Connector nerves \rightarrow Motor nerves$

  4. $Afferent nerves \rightarrow Efferent nerves \rightarrow Connector nerves$

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Correct Option: A

The delay in transmission from the dorsal to the ventral root across the spinal cord for the reflex pathways 'A', 'B', 'D' and 'C' respectively is 0.5 ms,1.0 ms, 1.5 ms, and 2.0 ms.Identify the correct option: (Average synaptic delay =0.5 ms)

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. A=monosynaptic , B=bisynaptic , C=trisynaptic

  2. A=monosynaptic , B= trisynaptic , D=bisynaptic

  3. A=monosynaptic , C=trisynap tic , D=quadrisynaptic

  4. A=monosynaptic , D=trisynaptic , C=quadrisynaptic

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Correct Option: D
Explanation:

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 correct answer is option D.

Reflex arc consists of 

biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

  1. Motor nerve

  2. Sensory nerve

  3. Both sensory and motor nerves

  4. None of the above

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Correct Option: C
Explanation:

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.