Basic Neuroanatomy and Neurophysiology

Basic Neuroanatomy and NeurophysiologyElaine M. Hull, PhD, Florida State University

“What is the soul?”

• I grew up in a very conservative Christian family and believed in the soul, which would outlive our earthly body and go to Heaven. I prayed many times each day and had profound religious experiences. I “saw” Jesus in the forest at my religious summer camp.

• I went to a Christian college and was part of an experimental program that studied all aspects of every civilization, beginning before written history and continuing to the present.


• We learned that even primitive people were religious and believed that gods were in charge of fertility, war, crops, and every aspect of life.

• We also learned that many of the stories in the Bible, including the Flood, the Virgin Birth, and resurrection from the dead were found in religions hundreds of years before the Bible. They were part of the general culture.


• Different groups believed in different gods, and their own gods were supposed to be the only “true” gods.

• I also took biology and psychology courses, which provided explanations for how the brain works and for the physiological problems that give rise to specific psychological disorders.


• I discovered that consciousness depends on a neural system in the brain stem that projects throughout the brain to wake it up.

• Other systems promote sleep, and still others allow us to learn, speak, and feel empathy for others.

• Damage to those areas can abolish speech, or the ability to sleep, to form memories, or to feel emotionally close to other people.


• One topic of our weekly essays was, “What is the soul.”

• In that essay, I said that I believed that the soul IS our conscious awareness, our memories of what we have done and what we hope to do, and our relationships with others.

• I would like to share with you a basic understanding of how the brain works. At the end, I will ask YOU, “What is the soul?”

Functional Neuroanatomy: The Nervous System and Behavior

• Our brains contain 100 to 150 BILLION neurons that make 1015 connections!

• Unlike cells of other structures, neurons are extremely varied in shape.

Nineteenth-Century Drawings of Neurons

The Major Parts of the Neuron

The cell body contains the nucleus with our genetic material. It is also where proteins are made and electrical potentials are integrated.

The axon conducts action potentials to terminals

Terminals release transmitter to other neurons, muscles, or organs

The axon hillock generates action potentials that can travel long distances

Dendrites receive incoming messages.

Synapses

Synapses

Neurons communicate with one another by sending an electrical potential down their long axon, which releases a chemical transmitter to activate or inhibit the next neuron.

There is a tiny gap between the neurons, called a synapse.

Synapses

Synapses

Small packets of transmitter are released when an electrical potential reaches the axon terminal.

• How do neurons produce electrical signals?

• The inside is negatively charged.This is due in part to negatively charged proteins.

• There are small channels in the cell membrane that allow one kind of ion, potassium (K+), to pass through. However, channels for another ion, sodium (Na+), are normally closed.

The inside of neurons is negatively charged, relative to the outside.

K+ is attracted in by the negative proteins. But not enough can stay in to cancel the negative charge, because the concentration gradient results in some K+ leaving.

K+ is pumped in and Na + is pumped out by an ion pump.

K+ can enter through K+ channels, but Na+ channels are closed.

Action potential

• Because Na+ is mostly outside the cell, and because the inside is negative, positively-charged Na+ is attracted to the inside.

• If a neurotransmitter opens Na+ channels, Na+ will rush in, carrying a positive charge.

• If there is enough positive charge, an action potential will be produced, which spreads down the axon by opening adjacent voltage-dependent Na+ channels.

Some axons are covered with many fatty sheaths, with uncovered areas between the sheaths. These sheaths force the action potential to “jump” from one node to the next, resulting in much faster conduction.

• At the end of the axon are many vesicles (packets) that contain neurotransmitter molecules. The action potential opens calcium (Ca++) channels, and Ca++ causes the vesicles to merge with the cell membrane, releasing the transmitter molecules into the synapse (space) between the two neurons.

A few neurotransmitters and their major effects:• Glutamate: major excitatory transmitter

• GABA (Gamma-amino-butyric acid): major inhibitory transmitter

• Acetylcholine: activates muscles; arousal, dreaming

• Dopamine: several tracts promote motor activity (degeneration Parkinson’s disease); motivated behaviors(including drug addiction); endocrine control; sexual behavior

• Norepinephrine: several tracts arousal

• Serotonin: several tracts antidepressant, energy

The Agonistic and Antagonistic Actions of Drugs

Neuroanatomy• The brain is somewhat like a mushroom:

The brain stem and spinal cord are the most primitive, responsible for life-preserving reflexes, basic movements and sensations, arousal & sleep.On top of that are the thalamus (“switchboard”)and hypothalamus (eating, drinking, reproductive & aggressive behaviors, temperature regulation).

Neuroanatomy

Surrounding that are the limbic system, (emotions, learning), and basal ganglia (motor ability, motivation).The outer covering is the cortex (planning, motor coordination, sensations, language).Beneath the cerebral hemispheres is the cerebellum (“little brain”). It coordinates rapid skilled movements and contributes to conscious perception.

Lobes of the cortex

Planning, motor control

Body sensations

Vision

HearingComplex vision

Somatosensory and motor areasPostcentral gyrus: Somatosensory

Precentral gyrus: Motor

HOW DO WE MEASURE BRAIN ACTIVITY?

• Electroencephalograph (EEG)

Computerized axial tomography (CAT)

• CAT (or CT) scans use an X-ray source that is moved around the head by steps.

• Detectors on the opposite side detect the amount of radiation that is absorbed.

• This measures the density of brain tissue.

Magnetic Resonance Imaging (MRI)• More detailed than CAT scans.

• The head is placed into a powerful magnetic field (strong enough to lift a car!).

This aligns all the brain’s protons in one direction.

• The protons are then knocked over by a powerful pulse of radio waves (loud!).

• The pulse is turned off and protons relax back to their original position, giving off radio waves.

• Detectors around the head detect those waves.

Positron Emission Tomography (PET)

• Measures activity, not structure.

• A radioactive form of glucose is injected into the bloodstream.

• A ring of detectors maps the location of the radioactivity, as the glucose is taken up for energy.

• Subject may perform a task.

• Color is used to distinguish different levels of radioactive emissions.

Functional MRI (fMRI)• Similar to regular MRI, except that high-

powered, rapidly alternating magnetic fields are used to detect small changes in oxygen use.

• Good spatial and temporal resolution

Activity changes while viewing images of romantic partner

Transcranial Magnetic Stimulation

Brain regions implicated in emotion:Yellow: orbitofrontal prefrontal cortex; Blue: Anterior cingulate cortexGreen: Posterior cingulate cortex; Purple: Insula; Red: amygdala

Summary

• Neurons have specialized areas for receiving (dendrites), integrating (cell body), and transmitting (axon) information.

• Neurons are negatively charged at rest. When a dendrite or cell body receives a transmitter that opens Na+ channels, the neuron becomes depolarized. If the depolarization is great enough, an action potential is generated and travels down the axon to the terminal, where it releases transmitters stored in vesicles.

Summary

• Receptors on the recipient neuron may either open ion channels or activate enzymes for longer-lasting changes.

• The brain stem and spinal cord organize life-preserving reflexes, promote arousal or sleep, and process sensory input and motor output.

• The thalamus is the “switchboard” for the cortex.

• The hypothalamus (below the thalamus) regulates eating, drinking, sexual behavior, aggression, temperature, and the endocrine system.

Summary

• The limbic system, including the amygdala, septal area, hippocampus, cingulate gyrus(above the corpus callosum), and several other structures control emotions.

• The basal ganglia contribute to movements and to motivation.

Summary

• The cortex surrounds the rest of the brain and is divided into 4 major lobes:

• Frontal lobesPrefrontal cortex: planning or inhibiting actions, considering consequences, perceiving others’ emotions, humor.Frontal cortex: primary motor cortex

• Parietal lobes: primary somatosensory cortex, sense of one’s place in the environment.

Summary• Temporal lobes: primary auditory cortex;

complex visual integration, speech perception

• Occipital lobes: primary visual cortex

• Several ways to measure brain activity or structure:

Electroencephalogram (EEG)Computerized tomography (CT)Magnetic resonance imaging (MRI)Positron emission tomography (PET)

Practical applications

• Oliver Sachs reports on numerous patients with localized brain damage.

• One was a musician who had damage in the lower part of both temporal lobes, which integrate complex visual images. He can see and describe things, but does not know what they are.

Lobes of the cortex


Body sensations

Vision



• For example, Oliver Sachs asked him to describe a glove. He reported that it was “a continuous surface with five out-pouchings.” Sachs asked what it could be used for. The man said it could be a container for coins of five different sizes!

• When he and his wife left Sach’s office, he tried to lift his wife’s head, because he thought it was his hat!


• Another patient was an artist who had a stroke in the visual cortex that took away his color vision. Everything appeared black, white, or gray. He forgot what color even was.

• Another patient lost the ability to perceive motion. She saw the world as a series of still pictures. She had trouble crossing a street, because she would first see a car some distance away, but then it would be very close.

Lobes of the cortex


Body sensations

Vision



• Another patient had damage to a posterior part of her parietal lobe, which integrates our sense of our body in the rest of the world. She would put make-up on only the right side of her face, because she did not perceive that her left side existed. She was in a wheel chair, and when she ate a meal, she would eat food only on the right side of the plate.

Lobes of the cortex


Body sensations

Vision



• If she was still hungry, she would spin the wheelchair around so that the remaining half of the plate came into view. She would again eat half of what remained. This would continue until she had enough food. It seemed easier to her to spin the wheelchair than to look into a world that seemed to her not to exist. She was not blind in her left visual field, and could report correctly when Oliver Sachs would shine a light there. She simply did not integrate sensory input from the left half of the world into her perceived world.


• We now know that there are neurons in the prefrontal cortex that produce action potentials both when we move our own body parts and when someone else makes the same movement. They are called “mirror neurons.” They may help us to feel empathy with others. In a nearby area a peptide transmitter (oxytocin) is released that promotes feelings of trust and affection for others.

Lobes of the cortex


Body sensations

Vision



• There was a report last year that brain damage to the insula, especially on the left side, completely erased several people’s addiction to smoking. One person said that his “body simply forgot”the addiction. (There will be more about this in a later lecture.)


• A final patient had his hippocampus (in the inner part of the temporal lobe) destroyed in an attempt to cure his severe epilepsy. It did cure the epilepsy, but it left him unable to store new factual memories. (More about him in a later lecture.)


• So, activity in specific parts of the brain produce color and motion vision, addiction, affection and trust in others, and our sense of ourselves in the world. Other parts wake us up and put us to sleep. What else, besides these, constitutes the soul?

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Basic Neuroanatomy and Neurophysiology