Understanding Neural Cells - AP Biology

It is the influx of calcium ions into the axon terminal that causes vesicles to fuse with the cell membrane, releasing the neurotransmitters held within the vesicles into the synapse.

Potassium ion (K+) influx happens during the refractory period, when the neuron returns to its membrane potential via action of the sodium-potassium pump. Potassium influx requires active transport. Sodium ion (Na+) influx is most closely linked with action potential propagation down the axon. It eventually triggers the calcium influx, but is not directly linked to vesicle fusion and neurotransmitter release.

Chloride (Cl-) influx occurs when the neuron receives inhibitory signals, causing the cell to be hyperpolarized and not fire an action potential.

The refractory period is caused by two processes: the secondary gate closing the voltage-gated sodium channel to prevent sodium influx and the hyperpolarization of the neuron caused by potassium ion efflux.

The period of potassium efflux is closely linked to action by the sodium-potassium pump, which is responsible for importing potassium and ejecting sodium from the cell. During the refractory period, then, sodium is exiting the cell and potassium is entering. The cell is also It also removing the calcium ions that entered the axon terminal, inducing the neurotransmitter release, to prepare for further neurotransmitter release. This prepares it to fire another action potential once the refractory period is over.

The influx of sodium ions is linked to the propagation of action potentials, and would not occur during the refractory period due to the secondary gate on the voltage-gated sodium channel.

The Corpus callosum resides beneath the cortex in the brain and bridges the gap between the left and right cerebral hemispheres. It is involved in the transfer of information from these hemispheres, helping to integrate and coordinate bilateral responses.

The cerebrum is located in the cortex and is involved in higher brain function, such as thought and processing. The hypothalamus is involved in survival processes, such as the instinct to eat, drink, or reproduce. The cerebellum coordinates balance and fine-tuned movement. Purkinje cells are found in the cerebellum; Purkinje fibers are found in the heart.

The resting potential of a cell is the relatively static membrane potential that serves as the baseline voltage of a cell, which is about in neurons. The resting potential stands in opposition to the action potential.

The threshold potential of a cell is a specific membrane potential that is needed in order to initiate action potential. Therefore, threshold potential precedes action potential. Note that reaching the threshold potential triggers a positive feedback loop, causing more sodium to rush into the cell, further depolarizing the membrane potential.

The axon hillock is the area of a neuron that connects the soma and axon. This is also the area of the of the neuron that "decides" whether an action potential would be initiated or not, depending on whether the cell has reached threshold or not.

In the presynaptic terminal, the action potential causes an influx of calcium. Rising calcium levels stimulates exocytosis of neurotransmitters, which bind to post-synaptic receptors. Unused neurotransmitters are recycled by the pre-synaptic cell or degraded in the synaptic cleft.

After neurotransmitters bind to the post-synaptic neuron, ion gated channels open. This allows for depolarization and the generation of another action potential.

The autonomic nervous system is a part of the peripheral nervous system that controls the function of internal organs including the heart, lungs, and gastrointestinal organs. This is done through the use of nerves that activate and/or inactivate glands and muscles.

The somatic nervous system is a part of the peripheral nervous system and controls voluntary body movements. The central nervous system involves only the brain and spinal cord. The autonomic nervous system is not under voluntary control.

Glial cells are important in maintaining nervous system homeostasis. The major functions of glial cells include insulating neurons, holding them in place, and supplying them with nutrients and oxygen. Glial cells also degrade pathogens and dead neurons.

Neuron cells are functional units of nervous tissue that transmit electrical signals. Neurons typically are composed of a soma, dendrites, and an axon. The soma is the body of the cell, the dendrites are branched projections that receive signals, and the axon conducts signals away from the cell body.

Axons are the parts of neurons that transmit electrical signals away from the cell body and to other neurons. The axon branches off of the soma and is long with a constant radius. Parts of the axon are myelinated, meaning that it is insulated to allow for salutatory conduction. Gaps in insulation are referred nodes of Ranvier.

In neurons and many other cells, electrical signal transmission requires action potential. Action potential can be defined as the rapid rise and fall of membrane potential that allows for signal propagation. In the case of neurons, reaching action potential allows the electrical signal to travel down to axon, which permits signal transduction.

Ganglia are described as clusters of nerve cells that are found in the autonomic nervous system.

Dendrites are branched projections of the neuron that receive electrical signals from other cells. The dendrites are connected to the soma—cell body.

The soma is the cell body of a neuron. The nucleus and many organelles are located within the soma. The soma has a specialized region called the axon hillock, which is where the soma transitions into the axon.

Neurotransmitters are chemicals that transmit signals from one neuron to another across the synapse. This transport is conducted through exocytosis and endocytosis of neurotransmitters in vesicles. Common neurotransmitters are norepinephrine, dopamine, epinephrine, and histamine.

The synapse is the junction between two nerve cells through which neurotransmitters conduct an electrical signal.