Nervous System - Biology

In the beginning of an action potential voltage-gated sodium channels begin to open, allowing sodium ions to rush into the cell. This influx of positive ions results in a change in the polarity of the cell, making the voltage become positive inside the cell. This process is called depolarization.

Hyperpolarization comes after depolarization, and is caused by potassium ions leaving the cell interior. The removal of these positive ions causes the cell to become more negative than the resting potential.

Repolarization is the final process to return the cell to its resting potential. The sodium-potassium pump brings potassium ions back into the cell and removes the sodium ions, returning the cell to its normal resting state.

Action potentials are electrical signals transmitted by neurons. When a neuron is stimulated, a signal is transmitted down the axon. This signal is the action potential.

An action potential in a neuron can help to stimulate a muscle to contract, but the muscle itself will not conduct an action potential.

The axon is wrapped in fatty bundles called myelin sheaths that promote fast transmission of an electrical signal. The other structures listed here are not myelinated.

The refractory period occurs when the cell repolarizes/hyperpolzarizes beyond the resting potential; that is, the membrane potential drops to a value more negative than when it is at rest. This prevents the firing of another action potential immediately after one has been fired. The other values represent the resting potential (), the threshold (), and values that are more positive, and are therefore incorrect.

As an action potential begins, there's a rapid influx of sodium in to cell, causing the cell's membrane potential to rapidly increase, depolarizing the cell. Once the cell has reached its action potential peak, the sodium channels begin to close. This closing activates the potassium channels. These channels allow potassium to leave the cell. Since potassium is a positive ion, as it leaves, the cell's membrane potential becomes more negative, repolarizing. The slight dip in the action potential curve, labeled as hyperpolarization, is result of the potassium channels lagging to close, and potassium loss is "overshot". As a result, too much potassium lost from the cell will cause the cell's potential to become more negative relative to its normal potential.

Action potentials are largely due to the movements of potassium and sodium across a membrane. While other ions and neurotransmitters can affect action potential firing, the movements of these two ions have the greatest effect on a neuron firing.

As an action potential is essentially an electrical current, it makes sense for it to open voltage-gated channels. Specifically, voltage-gated calcium channels are opened to allow calcium ions to flow into the cell and bind to synaptic vesicles.

The sympathetic nervous system is responsible for stress responses, while the parasympathetic nervous system is responsible for resting responses. The sympathetic nervous system causes increased heart rate, pupil dilation, suppressed digestion, inhibited salivation, and dilated bronchi.

The most basic anatomy for a neuron involves three structures: a soma, a dendrite, and an axon. The dendrite receives an electrical impulse and sends it to the cell body, or soma. The axon will then send the action potential towards its synapse with another neuron. The axon hillock is a wider region of the axon where the soma and axon join together.

While every neuron will have only one soma and one axon, some neurons have several dendrites. This means that a neuron can receive information from several different locations through different dendrites, but can only send it in one direction along the single axon.

The nervous system has two major divisions: the central nervous system and the peripheral nervous system. The peripheral nervous system is further divided into the somatic nervous system and the autonomic nervous system. The autonomic nervous system can then be divided into the sympathetic and parasympathetic branches.

General: Central and Peripheral

Peripheral: Somatic and Autonomic

Autonomic: Sympathetic and Parasympathetic

The parasympathetic nervous system is responsible for the "rest and digest" functions of the body. The sympathetic nervous system is associated with "fight or flight" responses in the body. Increased blood flow to skeletal muscles is a common result of the sympathetic nervous system being stimulated, not the parasympathetic nervous system.

The vagus nerve is responsible for slowing down the heart rate. It also increases digestive activity. Knowing this, we can conclude that the vagus nerve has a "rest and digest" function in the body. This means that it is part of the parasympathetic nervous system.

The sympathetic nervous system is responsible for stress responses, or "fight or flight." The somatic nervous system is under voluntary control, while the autonomic nervous system is involuntary. Both the sympathetic and parasympathetic divisions fall under the autonomic umbrella. The central nervous system includes only the brain and spinal cord.

Reflex arcs are unique neural pathways due to the fact they are constructed to cause voluntary muscles to move without a stimulus being integrated in the brain. Instead, the integration of the stimulus occurs in the spinal cord, where an efferent signal is immediately created towards the voluntary muscle.

The sympathetic nervous system is responsible for the "fight or flight" response. The parasympathetic nervous system does the opposite (rest and digest). The enteric nervous system helps with digestion. The remaining two answer choices are too broad and do not answer the question as well as the sympathetic nervous system. Note that the sympathetic and parasympathetic nervous systems are branches of the autonomic nervous system, which itself is a branch of the parasympathetic nervous system.

Vesicles of neurotransmitter are located at the axon terminal of the presynaptic neuron. Upon stimulation, they are released into the synapse and flow across the gap between neurons. Neurotransmitters attach to receptors located on the postsynaptic membrane after being released into the synaptic cleft. This allows the action potential to continue on to the next neuron.

In the neuron, dendrites respond to the chemical neurotransmitters released by other local neurons. These dendrites have receptors in their membranes that bind specific neurotransmitters and produce electrical signals as a result of this binding. Binding of a neurotransmitter can either excite or inhibit the neuron, influencing its ability to transmit a signal.

A hormone is a chemical that is synthesized by one group of cells, secreted, and then carried in the bloodstream to other cells whose activity is influenced by reception of the hormone. An electrolyte is a solutution that conducts electricity and generally contains ions. Enzymes are proteins that speed up chemical reactions. Proteins are organic molecules composed of amino acids that are necessary for growth and repair of tissues.

A neurotransmitter is a chemical agent that relays messages from one nerve cell to the next. An enzyme is a protein that causes other substances to change. Enzymes regulate the rate of chemical reactions. An electrolyte is a substance that, when dissolved, forms electrically charged particles. Ions have lost one or more electrons and have a positive charge, or gained one or more electrons and have a negative charge. In aqueous solutions, ions are called electrolytes because they permit the solution to conduct electricity. Interleukin is a type of protein that enables communication among cells active in inflammation or the specific immune response.

Vesicles containing neurotransmitters must bind to the membrane at the axon terminal in order to release their contents into the synapse. This binding is dependent upon an influx of calcium ions that occurs with an action potential. The other ions listed are important for other parts of the action potential, but it is calcium that is crucial for this particular step.

Voltage-gated potassium ion channels are responsible for bringing the membrane potential back to or below resting the potential. This is achieved when these channels open, which can only happen at very positive voltages (hence voltage-gated), and as the potassium ions rapidly leave the cell, the cell repolarizes to a negative potential.