Explain the function and process of a neuron’s refractory period.
Describe how the brain transports essential chemicals.
Describe the key aspects of the resting potential.
Provide a summary of the all-or-none law of action potentials.
Describe the structure of the blood-brain barrier and explain why it is important.
Although the electrical potential across the membrane is returning from its peak toward the resting point, it is still above the threshold. Why doesn’t the cell produce another action potential during this period? (If it did, of course, it would endlessly repeat one action potential after another.) Immediately after an action potential, the cell is in a refractory period during which it resists the production of further action potentials. In the first part of this period, the absolute refractory period, the membrane cannot produce an action potential, regardless of the stimulation. During the second part, the relative refractory period, a stronger-than-usual stimulus is necessary to initiate an action potential. The refractory period depends on two facts: The sodium channels are closed, and potassium is flowing out of the cell at a faster-than-usual rate. In most of the neurons that researchers have tested, the absolute refractory period is about 1 millisecond (ms), and the relative refractory period is another 2 to 4 ms.
The brain has several transport mechanisms. Small, uncharged molecules, including oxygen and carbon dioxide, cross freely. Water crosses through special protein channels in the wall of the endothelial cells. Also, molecules that dissolve in the fats of the membrane cross easily. Examples include vitamins A and D and all the drugs that affect the brain—from antidepressants and other psychiatric drugs to illegal drugs such as heroin. How fast a drug takes effect depends partly on how readily it dissolves in fats and therefore crosses the blood– brain barrier.
For a few other chemicals, the brain uses active transport, a protein-mediated process that expends energy to pump chemicals from the blood into the brain. Chemicals that are actively transported into the brain include glucose (the brain’s main fuel), amino acids (the building blocks of proteins), purines, choline, a few vitamins, iron, and certain hormones.
All parts of a neuron are covered by a membrane about 8 nanometers (nm) thick (just less than 0.00001 mm), composed of two layers (free to float relative to each other) of phospholipid molecules (containing chains of fatty acids and a phosphate group). Embedded among the phospholipids are cylindrical protein molecules through which various chemicals can pass. The structure of the membrane and its proteins controls the flow of chemicals between the inside and outside of the cell. When at rest, the membrane maintains an electrical gradient, also known as polarization—a difference in electrical charge between the inside and outside of the cell. The neuron inside the membrane has a slightly negative electrical potential with respect to the outside, mainly because of negatively charged proteins inside the cell. This difference in voltage is called the resting potential.
Once a neuron reaches the threshold of activation, the action potential is conducted all of the way down the axon without loss of intensity. Furthermore, the magnitude of the action potential is roughly the same every time and is independent of the intensity of the stimulus that initiated it.
Tightly joined endothelial cells form the capillary walls in the brain, making the blood-brain barrier. This protects the brain from harmful viruses, bacteria, and chemicals that might otherwise be able to enter the brain and cause damage.
What are nerve cells and nerve impulses? - Exams 1aThe difference in voltage in a resting neuron is called the resting potential.
Neurons receive information and transmit it to other cells.
Glial cells serve many functions.
Glial cells transmit information across long distances.
The blood-brain barrier is made up of closely packed glial cells.
The difference in voltage in a resting neuron is called the resting potential.
Increasing the electrical gradient for potassium will reduce the tendency for potassium ions to exit the neuron.
Dendrites contain the nuclei, ribosomes, mitochondria, and other structures found in most cells.
A prolonged increase in the permeability of the membrane to sodium ions would interfere with a neuron's ability to have an action potential.
An afferent axon brings information into a structure.
Neurons are distinguished from other cells by their shape.
Both dendrites and cell bodies are capable of producing action potentials.
At the resting potential, the potassium channels are completely closed and the sodium channels are almost closed.
Schwann cells build the myelin sheaths in the periphery of the body.
An efferent axon carries information away from a structure.
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What are nerve cells and nerve impulses? - Exams 1bNeurons differ most strongly from other body cells in their ____.
The two basic kinds of cells in the nervous system are _____.
Water, oxygen, and ____ most freely flow across a cell membrane.
Which scientific work did Cajal apply to his study of infant brains?
The structure that contains a cell’s chromosomes is called the ____.
What do neurons have that other cells do not?
Small, charged molecules can cross the cell membrane through ____.
Santiago Ramon y Cajal demonstrated that ____.
What structure is composed of two layers of fat molecules that are free to flow around one another?
The cell membrane is composed of two layers of _____.
Dendrites ____.
The branching fibers that form the information-receiving pole of the nerve cells are called _____.
Many dendrites contain short outgrowths called spines that _____.
Protein channels allow ____ molecules to cross the cell membrane.
As compared to dendrites, axons usually ____.
The surface of a dendrite is lined with specialized junctions through which the dendrite receives information from other neurons. What are these junctions called?
What are nerve cells and nerve impulses? - Exams 1cExplain the function and process of a neuron’s refractory period.
Describe how the brain transports essential chemicals.
Describe the key aspects of the resting potential.
Provide a summary of the all-or-none law of action potentials.
Describe the structure of the blood-brain barrier and explain why it is important.
Although the electrical potential across the membrane is returning from its peak toward the resting point, it is still above the threshold. Why doesn’t the cell produce another action potential during this period? (If it did, of course, it would endlessly repeat one action potential after another.) Immediately after an action potential, the cell is in a refractory period during which it resists the production of further action potentials. In the first part of this period, the absolute refractory period, the membrane cannot produce an action potential, regardless of the stimulation. During the second part, the relative refractory period, a stronger-than-usual stimulus is necessary to initiate an action potential. The refractory period depends on two facts: The sodium channels are closed, and potassium is flowing out of the cell at a faster-than-usual rate. In most of the neurons that researchers have tested, the absolute refractory period is about 1 millisecond (ms), and the relative refractory period is another 2 to 4 ms.
The brain has several transport mechanisms. Small, uncharged molecules, including oxygen and carbon dioxide, cross freely. Water crosses through special protein channels in the wall of the endothelial cells. Also, molecules that dissolve in the fats of the membrane cross easily. Examples include vitamins A and D and all the drugs that affect the brain—from antidepressants and other psychiatric drugs to illegal drugs such as heroin. How fast a drug takes effect depends partly on how readily it dissolves in fats and therefore crosses the blood– brain barrier.
For a few other chemicals, the brain uses active transport, a protein-mediated process that expends energy to pump chemicals from the blood into the brain. Chemicals that are actively transported into the brain include glucose (the brain’s main fuel), amino acids (the building blocks of proteins), purines, choline, a few vitamins, iron, and certain hormones.
All parts of a neuron are covered by a membrane about 8 nanometers (nm) thick (just less than 0.00001 mm), composed of two layers (free to float relative to each other) of phospholipid molecules (containing chains of fatty acids and a phosphate group). Embedded among the phospholipids are cylindrical protein molecules through which various chemicals can pass. The structure of the membrane and its proteins controls the flow of chemicals between the inside and outside of the cell. When at rest, the membrane maintains an electrical gradient, also known as
.....read more What is the function of synapses? - Exams 2aOnly sensory neurons are found in a reflex arc.
The amount of temporal summation depends on the rate of stimulation.
At synapses, the cell that receives the message is called the presynaptic neuron.
Electrical communication between neurons is faster than chemical communication within neurons.
Transmission of information between neurons occurs in the same way as transmission along an axon.
Most of the known neurotransmitters are synthesized from amino acids.
Inhibitory synapses actively suppress excitatory responses.
Neurotransmitter levels in the brain can be affected by changes in diet.
Gases can be used as neurotransmitters.
Spatial summation is the result of synaptic inputs from different locations arriving at the same time.
Most neurons release more than one kind of neurotransmitter.
Most of the brain’s excitatory ionotropic synapses use the neurotransmitter glutamate.
Generally speaking, a neuron will release a greater number of neurotransmitters than what it will respond to with its own receptors.
Metabotropic synapses use a large variety of transmitters.
Whether or not a neurotransmitter is excitatory depends on the response of the postsynaptic receptor.
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