Special Sub-Topic: Basic Neurobiology Click Here To Play: Basic Neurobiology

Ok, we will start with a question regarding action potentials first. What accounts for the rising phase of an action potential in a typical neuron?

Influx of sodium (Na+) ions into the neuron. At resting potential the concentration of potassium is high inside the cell and the concentration of sodium is low. The opposite is true for the outside of the cell, sodium concentration is high and potassium is low. When the cell membrane becomes depolarized, sodium channels are opened and this allows sodium ions to flow across the cell membrane causing the membrane potential of the neuron to go past the threshold, or become more positive, and fire an action potential. The rising phase of this action potential is due to the increasing sodium concentration inside of the cell.

There are many severe neurological disorders out there. What disease would you be suffering from if I were to demyelinate your axons?

Multiple Sclerosis. Multiple sclerosis is a very degenerative disease that occurs when the body's own immune system attacks the protective myelin sheath that insulates the neuron. The loss of myelin causes action potentials to travel more slowly and they oftentimes do not reach their destination. Symptoms of MS can vary depending on which neurons are demyelinated.

With regards to the axons of dorsal column medial-lemniscus pathway for sending somatic information to the brain: where do these axons cross the midline?

At the level of the brain stem. The dorsal column medial-lemniscus pathway is a way to send somatic information from the upper body/lower body and parts of the head to the somatic sensory cortex. The information remains ipsilateral until the level of the brainstem where it crosses the midline at the second order nuclei; it is then sent to the thalamus and ultimately sent to the somatic sensory cortex in the parietal lobe.

If I were to damage your Edinger-Westphal nucleus what would you have trouble doing?

Moving the muscles in your iris. The Edinger-Westphal nucleus is involved in the pupillary reflex. When light hits the retina, information is sent to the pretectum which relays this information to the Edinger-Westphal nucleus, this in turn affects the ciliary ganglion which constricts the muscles in the iris.

Lower motor neurons have an interesting distribution within the ventral horn of the spinal cord. What muscles would I damage if I were to destroy the lateral most part of the ventral horn?

Motor neurons innervating distal muscles. The distribution of motor neurons in the ventral horn is interesting in the sense that motor neurons in the middle of the spinal cord innervate proximal muscles whereas motor neurons located more laterally in the ventral horn innervate more distal muscles.

The output of the basal ganglia is...

Inhibitory. The basal ganglia is very complex and its structure is not well understood; however the major function of the basal ganglia is to suppress unwanted bodily movements. Neurons in two major basal ganglia structures, the golbus pallidus and the substantia nigra pars reticulata, are constantly active and inhibiting thalamic activity and eye movement respectively. Therefore the output of the basal ganglia are inhibitory.

This disease of the basal ganglia is inherited and is caused by a glutamine repeat in a particular gene

Huntington's disease. Huntington's disease is a terribly degenerative inherited disease in which the inhibitory function of the basal ganglia is lost. This causes wild and spastic movements that cannot be controlled.

Now on to a little brain development... We all start out as a tube within a tube composed of three germ layers which give rise to all of the structures and tissues. What would be the result on the development of the nervous system if I removed the mesoderm layer?

The nervous system would not develop. Many people hear nervous system and automatically think of ectoderm. That is a logical leap seeing that the entire nervous system is composed of ectoderm; however the nervous system's induction is dependent on several signals from the notochord, which is composed of mesodermal cells. So if I were to remove the mesoderm from a developing embryo the nervous system would fail to form.

Serious diseases can develop when the neural tube fails to close properly during development. Which of the following are diseases that result from an incomplete closure of the neural tube?

Both. Spina bifida can occur in varying degrees and results when the neural plate fails to close along the length of the spinal cord. Anencephaly occurs when the neural plate fails to close along the region that will become the brain.

Because I enjoy developmental biology I will give you one more on neuro devo...Which product should a pregnant woman never use because of its link to an increased risk of birth defects?

Isotretinoin. Isotretinoin is an acne medication whose main component is a form of retinoic acid. RA is an inductive signal from the notochord that helps initiate the development of the nervous system; however too much RA can cause severe birth defects. That is why pregnant women are not prescribed accutane. I hope you enjoyed this quiz. I will, in the future, make them more entertaining for all of you.