Reflex Arc

Finger Burn

We are going to take a trip into the human body. Our destination of choice is the reflex arc. So be ready for a very fast trip, as the reflexes are very fast responses. Our itinerary consist of the following stops:

1. receptor

2. sensory neuron

3. interneuron

4. CNS

5. motor neuron

6. effector


we will also take a detour to the endocrine system to see how fear creates a response in the body.

Traveling around the body..

The first stop are the receptor in the skin they detect the stimulus. We will pretend that the host body we are traveling through has just burnt her finger by hot water. receptor are the end of particular dendrite or a specialized receptor cell in a sensory organ. The next processes that I saw is the transmission of the message. First of all, while a neuron is at rest, the inside of its cell membrane is more negatively charged than the outside. The difference in charge across the membrane is the resting potential, because it contains the potential energy needed to transmit an impulse. Then the action potential takes place when Na+ channels open quickly. Na+ rushes into the cell, and it becomes positive. The next Na+ channels down the axon spring open, and more Na+ rushes into the cell. The impulse moves forward. K+ channels open slowly. K+ flows out of the cell, and it becomes negative again. When the impulse reaches the axon terminal, vesicles in the terminal fuse to the neuron’s membrane. The fusing releases neurotransmitters into the synapse. The neurotransmitters bind to the receptors on the next neuron, stimulating the neuron to open its Na+ channels. Before an action potential moves into the next neuron, synapse crosses a tiny gap between the neurons. The axon terminal, the part of the axon through which the impulse leaves that neuron, contains chemical-filled vesicles. When an impulse reaches the terminal, vesicles bind to the terminal’s membrane and release their chemicals into the synapse. Neurotransmitters are the chemical signals of the nervous system. They bind to receptor proteins on the adjacent neuron and cause Na+ channels in that neuron to open, generating an action potential. Typically, many synapses connect neurons. Before the adjacent neuron generates an action potential, it have to be stimulated at more than one synapse. The amount a neuron needs to be stimulated before it produces an action potential is called a threshold. Once neurotransmitters have triggered a new action potential, they must be removed from the synapse so that ion channels on the second neuron will close again. These neurotransmitters will be broken down by enzymes in the synapse, or they are transported back into the terminal that released them.
reflex arc

Then..

The second stop is sensory neuron. The receptor creates an action potential that will travel along the sensory neuron. This sensory neuron transmit nerve impulses from the receptor into the spinal cord. The action potential is the stretching causes a change in charge distribution that triggers a moving electrical impulse. That means in action potential the neuron membrane will be positive.

After that..

The third stop is interneuron. The interneuron receive signals from sensory neurons and relay them within the spinal cord

more over..

The forth stop is (CNS) central nervous system which receive and process the information of what happen inside all of the parts of the body . So its consists the brain , spinal cord and neurons . This mean that they transmit signals from the different parts of the body . in our trip we will not stop at the brain at the moment, because it is a reflex , and reflexes bypass the brain it goes directly to the spinal cord.

In addition..

the fifth stop is I saw the motor neurons transmit information to the glands , muscles and organs. the glads, organs or muscles are called effectors. They will make a reaction that will oppose the stimulus.

The connection

We finished our trip to the nervous system, but let us take a small detour to the endocrine system and see how the stimulus we faced also made the endocrine system to react. showing us that system work together. I saw the hormones its a chemical signals that made by the endocrine system. Hormones are made in organs called glands and its release hormone into bloodstream. When the hormone moves through the body it interact only with a cell that has specific membrane receptors(target cells). In the brain there I saw the hypothalamus gland it is already stimulated by the nervous system and its released hormone to the pituitary gland secretes adrenocorticotropic hormone (ACTH) stimulated the adrenal gland to produce the hormone corticosteroid. The adrenal glands causes the heart to increase its strength and number of contractions, circulating blood more quickly.

The response

Finally, we saw the saw that the host body we are traveling through removed her finger from the hot water and her heart rate became normal.
Fight or Flight Response