Reflex action - class-VIII

Conditioned reflex is automatic responses to certain stimuli learnt during lifetime/training. It was studied by Russian physiologist Ivan Pavlov during his experiment on induction of salivation in dogs. Thus, the correct answer is option C.

Reflex is an involuntary and instantaneous action in response to a stimulus.

Luigi Galvani was an Italian physician who demonstrated what we now understand to be the electrical basis of nerve impulses when he made frog muscles twitch by jolting them with a spark from an electrostatic machine. So, the correct option is "D" (Luigi Galvani).

Cerebral reflexes involve the brain. Spitting out a fly (ii) and pupil contraction (iv) are controlled by centers in the brainstem (midbrain/medulla), whereas pulling a hand away (i) and lifting a foot (iii) are spinal reflexes.

Reflex action is induced by the motor nerves. It is an involuntary and instant movement in response to a stimulus. A reflex action is done by neural pathway of reflex arc. In this, the action is done before the impulse reaches the brain. Out of the given options, sweating is not a reflex action. Salivation is a reflex action in which smell of food activate neural pathway and activates muscles and glands. This releases salivary juices. When someone is pinched by a needle, it activates neural pathway to evoke a response. The skin receptors quickly send nerve impulses to the spinal cord and response is relayed back. Apart from these, coughing, sneezing and blinking of eyes are also reflex actions.

Monosynaptic Reflex is a simple reflex that involves the transmission of an impulse from a sensory neuron to a motor neuron across a single synapse in the spinal cord. The knee-jerk reflex action is an example of such type of reflex.

• Involuntary actions in response to external or internal stimuli are termed as reflex actions. Peripheral nervous system and the spinal cord are involved in controlling the reflex actions. Here, the brain is not involved.
• The reflex action was discovered by Marshall. He proposed the theory explaining the body's reflex, or involuntary, actions.
  
• So, the correct answer is 'Marshall'.

• A stimulus is anything that can be perceived by a given organism including sight, sound, touch, smell, taste, etc.
•  A response is generally characterized as the behaviour proximal to the stimulus. So if a bell rings and a person jumps the stimulus is the bell and the response is the jump. 
• The ability of an organism or organ to respond to external stimuli is called sensitivity. When a stimulus is applied to a sensory receptor, it normally influences by a simple reflex. Hence, Simple reflex is best to characterize the simple response to simple stimuli. 

A reflex arc consists of a receptor (detects stimulus), a sensory neuron, an integration center (spinal cord), a motor neuron, and an effector (muscles).

The reflex action is defined as the sudden and involuntary movements that are controlled directly by the spinal cord. These actions do not require memory generation most of the time, like blinking of the eyes when something comes close to them. These are called the unconditional reflexes. Some reflex actions may involve learning and these are call the conditional reflexes. For example release of saliva at the sight of the food. Obeying the orders is the voluntary set of actions performed under the command of the somatic nervous system. It involves memory generation so as to remember the tasks and voices.

Simple withdrawal reflexes, such as pulling a hand away from a hot object, are mediated by the spinal cord to ensure the fastest possible response time.

Reflex actions are involuntary responses controlled by the central nervous system (CNS), specifically the spinal cord for most somatic reflexes.

For a standard withdrawal reflex to occur, the spinal cord must be intact to process the sensory input and generate the motor output.

The auditory nerve (vestibulocochlear nerve) transmits sensory information from the inner ear to the brain, which is part of the central nervous system.

Closing eyes in response to bright light is a classic example of a simple, involuntary reflex action designed to protect the eyes.

A reflex action is defined as a spontaneous, involuntary, automated, nerve-mediated activity produced at the unconscious level  by stimulating specific receptors. In other words, a reflex action is a sensory impulse, automatically converted into a motor effect with the involvement of the central nervous system. These actions are sudden and automatic and take place even before one can feel the stimulus through the brain. The quick pulling of the hand on touching a hot object is an automated response to stimuli and is controlled and regulated by the spinal cord along with the sensory and motor neurons which connect the receptor and effector organs. Thus, the correct answer is option C.

Reflex actions are involuntary actions that are either performed when learnt or innately performed. A complex reflex action is made up of a polysynaptic pathway, wherein, more than one synaptic junctions are involved. Swallowing of food bolus is a reflex activity that involves a polysynaptic pathway and is under reflexive or involuntary control. This stage of the swallow begins after food which has been masticated has been gathered together in the mouth and formed into a bolus which is passed from the posterior tongue. It is controlled by medulla oblongata.

The midbrain contains reflex centers for visual and auditory stimuli, such as tracking moving objects or turning the head toward a sound.

There are 4 types of spinal reflex action, namely the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex and the withdrawal reflex. The direction of response is opposite in withdrawal reflex action. The withdrawal reflex is also called as flexor withdrawal reflex. It protects the body from damaging stimuli. It is polysynaptic. Hence, it causes the stimulation of sensory, association and motor neurons.  For example, when a person touches a hot iron, he withdraws his hand from it within fraction of seconds. In this, the heat stimulates temperature and danger receptors in the skin, triggering a sensory impulse that travels to the central nervous system. The sensory neuron synapses with interneurons and connects to motor neurons. These motor neurons send motor impulses to the flexors and allows withdrawal.

A person experiences goose bumps in the presence of extremely cold temperatures. Tiny muscles attached to each hair follicle contracts because of the stimulus of cold surroundings. The hair strands stand on the end due to this contraction of muscles. The contracted tiny muscles cause bunching of the skin around hairs, which results in bumps in the goose bumps. The goose bumps are helpful to reduce the heat loss from the body and it is a way of preserving body's heat by causing the hairs on the skin to stand up. 

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• Receptor - sense organ in the skin, muscle, or another organ.
• Sensory neuron - carrier impulse within CNS

• Motor neuron - carrier impulse towards CNS
• Effector - structure by which an animal responds.