Tony's Blog

What does dopamine do?

Tony — Mon, 30 Nov 2009 02:50:30 +0000

Dopamine is a neurotransmitter,* and pretty doggone fun as neurotransmitters go. It works with serotonin and norepinephrine to regulate various components of your well-being: mood, attention, motivation, desire, pleasure, and as you might imagine from the rest, sexuality. Dopamine itself helps to generate the feeling of pleasure associated with rewarding experiences — food, sex, and drugs can set it to flowing. Consequently, it can kick-start motivation, desire, and other reactions that naturally follow a pleasurable experience.

Dopamine helps you to think, too. In the frontal lobe, it plays a part in memory and problem-solving. Also, you know the good feeling you can get from learning something new? That’s dopamine at work, encouraging you to continue, and thereby helping to thicken the myelin sheath that makes brain signals zip along faster.

Sweet stuff, huh? But get too much of it and you can go schizophrenic or even psychotic. Too little of it, on the other hand, and your basal ganglia can malfunction, leading to Parkinson’s disease. No fun. So if you were thinking of eating a chocolate truffle while snorting coke off the thigh of a Cuban virgin, you might want to reconsider.

* Its chemical formula is C₆H₃(OH)₂-CH₂-CH₂-NH₂. You wanted to know that.

Dopamine

What do the basal ganglia do?

Tony — Sun, 01 Nov 2009 19:36:22 +0000

First off: As I’ve mentioned before, clusters of neural co-laborers in the brain are called nuclei. However, certain nuclei are referred to en masse as the basal ganglia. That’s just the way it is. We may as well learn to live with the situation.

Anyway. The basal ganglia are functionally related nuclei, comprising the putamen, globus pallidus, substantia nigra, nucleus accumbens, and the caudate and subthalamic nuclei. They’re involved in the inhibition of movement (so that we don’t flail around all the time), and consequently in motivation and appetitive behavior: when you’re hungry, you don’t want your movement inhibited — you need to get to that bag of pork rinds before your jobless brother-in-law notices them.

Irregularities in the basal ganglia most often manifest themselves as disorders in movement, notably:

Parkinson’s Disease, characterized by tremors and trouble with initiating movement, and
Huntington’s Disease, characterized by uncontrollable spastic movements called chorea.

Both of these sound roundly irritating, not to mention life-threatening. My heart goes out to the people who have to wake up to them every day.

Basal ganglia

What does the hypothalamus do?

Tony — Sun, 18 Oct 2009 01:28:16 +0000

The hypothalamus lies quietly under the thalamus,* but it doesn’t mind its own business: Together with the pituitary gland, it links the nervous system to the endocrine system. In that capacity it’s quite the busybody, playing a role in fear and anger, hunger and thirst, blood pressure and pulse rate, fatigue, body temperature, and circadian rhythms. It gets involved in sex, too, processing pheromones as olfactory stimuli. Cheeky thing.

* By the way, the word hypothalamus comes from Greek roots meaning “under the thalamus”. Go figure.

Hypothalamus

What are neurotransmitters?

Tony — Sun, 11 Oct 2009 17:49:08 +0000

Neurotransmitters are chemicals used to transmit signals between neurons. (Makes sense, doesn’t it?) They’re emitted from the axon of the sender, cross the synapse to the receiver, and attach to a receptor site on a dendrite there. If the receiver is properly excited by the intrusion, it sends its own neurotransmitters to its neighbors; and so on. In this way, long concatenations of impulses are sent coursing through you, and you yelp when you stab your finger with the needle. Again.

Some gripping examples of neurotransmitters are dopamine, serotonin, and norepinephrine. You really should look them up.

Neurotransmitters

What does the nucleus accumbens do?

Tony — Mon, 28 Sep 2009 00:06:05 +0000

The nucleus accumbens — Latin for leaning nucleus — is a cluster of neurons* that acts as a liaison between the limbic system and the central gray nuclei. It’s a paired structure, like the hippocampus, and is involved in the brain’s reward system, releasing dopamine and other neurotransmitters that produce a feeling of pleasure. For this reason, it also plays a large part in addictive behavior, appetitive eating, and behavioral motivation in general. It has a role in fear responses and the placebo effect as well. Feel free to blame it for the bad things you do.

* In brain physiology, a nucleus is a cluster of neurons that perform functions together. Outside of the brain, such a cluster is called a ganglion. Inside of the brain, it’s too dark to read.

Nucleus accumbens

What does the hippocampus do?

Tony — Tue, 22 Sep 2009 23:17:54 +0000

The hippocampus (Greek for seahorse, someone’s idea of its shape) is a paired structure, with mirror-image parts on both sides of the brain. Part of the limbic system, it lurks beneath the surface of the temporal lobe. It’s involved in:

The perception and navigation of space
Behavioral inhibition
Memory of experienced events

Its role in memory is important but not clearly defined. Deterioration of the hippocampus can result in age-related memory loss, and damage to it can result in amnesia, both retrograde and anterograde. There’s an interesting Wikipedia entry on an example of what happens when the hippocampus is removed. It reminds me of the movie 50 First Dates.

You’ll note that I omitted any references to hippopotamuses in college. I think my restraint is to be congratulated.

Hippocampus

What does the amygdala do?

Tony — Fri, 18 Sep 2009 20:57:00 +0000

Or rather, the amygdalae — there are two of them. They’re part of the limbic system (about which more later), and each consists of several nuclei. The nuclei are roughly almond-shaped; the Greek word for almond is “amygdale” (αμυγδαλη); you see the connection. Together they are involved in many brain functions, including:

Fear conditioning
Appetitive conditioning
Processing and memory of emotions
Memory consolidation
Neurotransmitter activation
Sympathetic nervous system activation
Facial muscle movement

Irregularities in the amygdalae have been linked to borderline personality and bipolar disorders, schizophrenia, and autism. Damage to them can cause a general wacky fearlessness. So keep yours safe.

Amygdala

What is the hindbrain?

Tony — Sun, 13 Sep 2009 01:41:46 +0000

The hindbrain comprises the cerebellum, pons, and medulla oblongata. It is the rearmost of the three primary divisions of the brain; namely, the:

Hindbrain (rhombencephalon),
Midbrain (mesencephalon), and
Forebrain (prosencephalon)

As the picture below shows, the hindbrain itself has two parts, the metencephalon and the myelencephalon. I may talk about them later. To labor the point just now would be unseemly.

Hindbrain et al.

What does the midbrain do?

Tony — Wed, 09 Sep 2009 07:22:44 +0000

The midbrain is the top portion of the brain stem, adjoining the diencephalon above and the pons below. It comprises the inferior and superior colliculi (together called the tectum), and the tegmentum, crus cerebri, and substantia nigra (together the cerebral peduncle). It’s involved in vision, hearing, body movement in general, and eye movement in particular.

Some language notes: The Latin word tectum can mean roof or ceiling. Tegmentum is a corruption of tegumentum, which means a covering. The midbrain is also called the mesencephalon, from Greek roots meaning — get this — “midbrain”.

Midbrain

What does the medulla oblongata do?

Tony — Sat, 05 Sep 2009 18:08:41 +0000

The medulla oblongata is the lower portion of the brain stem, adjoining the pons above and the spinal cord below. It aids in communication between the spinal cord and the brain, and between the brain hemispheres. It also plays a role in several autonomic functions, such as respiration and circulation, swallowing and vomiting, urination and defecation, and reflex responses.

A personal observation: “Medulla oblongata” is fun to say, and would be a good name for a band.

Medulla oblongata