For Professor Tommy

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Chapter 2 Brain and Behavior

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Gateway Theme

Brain activity is the source of human consciousness, intelligence, and behavior.

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Gateway Questions

What are the major divisions of the nervous system?

How do neurons operate and communicate with each other?

How does the nervous system change and grow?

How are different parts of the brain identified, and what do they do?

How do the left and right hemispheres of the cerebral cortex differ?

What are the different functions of the lobes of the cerebral cortex?

What are the major parts of the subcortex?

How does the endocrine system affect behavior?

How can self-regulation help me in my personal and professional life?

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An Overview of the Human Nervous System

Divisions of the nervous system

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The human nervous system is what allows communication to take place within the body, as the brain needs to be able to send and receive messages from different organs, systems, and structures.

The most basic unit of this system is the neuron, which transmits that information. If you bundle many neurons together, you create a nerve.

All nervous tissue contained in the brain and spinal cord comprise the central nervous system, while nerve cells anywhere else in the body make up the peripheral nervous system. Typically nerves from the brain flow through the spinal cord to the body (and back again), but the twelve cranial nerves do not pass through the spinal cord.

The Peripheral Nervous System

Branches of the ANS

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The peripheral nervous system can be broken down into two additional systems:

The somatic nervous system brings sensory information from our sense organs back to the central nervous system. It also facilitates messages to voluntary muscles for volitional movement.

The autonomic nervous system controls the “automatic” functions in the body, most notably those that occur in organs and glands. It is divided into: (a) sympathetic nervous system, which is the “fight or flight” function that takes over during times of crisis; and (b) the parasympathetic nervous system, which quiets our functions down and helps us to restore calm after a crisis has been resolved.

Parts of a Neuron

A stylized neuron

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To understand communication, you must be familiar with the parts and functions of the neuron. Refer to your text to make sure you are familiar with the following structures of a neuron:

- dendrites

- cell body

- axon

- axon terminal

- myelin sheath

- synaptic vesicle

- neurotransmitters

- synaptic gap

- receptor sites

Neural Function

Measuring electrical activity in the neuron

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Once neurons are adequately stimulated, they move from their negative charged state (the resting potential) to a positively charged state (the action potential). This is caused by the position of positive or negative ions on the outside or inside of the neuron’s cellular membrane.

This process happens in an all or nothing fashion, which is to say that a neuron either generates a full action potential or none at all. There is no “partial firing” of a neuron.

If you’ve ever heard of a brain tissue called white matter, you were hearing about neurons that are covered in a myelin sheath. In addition to protecting the neuron, this sheath facilitates a process called saltatory conduction. Read in your text about how this speeds up the rate at which an action potential can travel down an axon.

Synaptic Transmission and Neurotransmitters (1 of 2)

The synapse

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The tiny gap that separates two neurons is the synapse, and chemicals that traverse that gap are called neurotransmitters. They cross the gap and fill in receptor sites on the surface of postsynaptic neurons.

If you look at Table 2.1, you’ll see that there are a number of different neurotransmitters, each of which helps to regulate specific functions or processes. There is some overlap, but we do need them all on one level or another. Some stimulate functions (excitatory neurotransmitters) and some decrease functions (inhibitory neurotransmitters).

A class of neurotransmitters called neuropeptides includes endorphins and enkephalins. Review how these two chemicals are important in pain management functions.

Synaptic Transmission and Neurotransmitters (2 of 2)

Table 2.1 Major Neurotransmitters

Neurotransmitter	Main Mode of Action	Function in the Brain	Effects of Imbalance
Acetylcholine	Excitatory neurotransmitter	Participates in movement, autonomic function, learning and memory	Deficiency may play a role in Alzheimer’s disease
Dopamine	Excitatory neurotransmitter	Participates in motivation, reward, planning of behavior	Deficiency may lead to parkinson’s disease, reduced feelings of pleasure; excess may lead to schizophrenia
GABA	Inhibitory neurotransmitter	Major inhibitory effect in the CNS; participates in moods	Deficiency may lead to anxiety
Glutamate	Excitatory neurotransmitter	Major excitatory effect in the CNS; participates in learning and memory	Excess may lead to neuron death and autism; deficiency may lead to tiredness
Norepinephrine	Excitatory neurotransmitter	Participates in arousal, vigilance, and mood	Excess may lead to anxiety
Serotonin	Inhibitory neurotransmitter	Participates in mood, appetite, and sleep	Deficiency may lead to depression and/or anxiety

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A class of neurotransmitters called neuropeptides includes endorphins and enkephalins. Review how these two chemicals are important in pain management functions.

Neural Networks

A simple reflex

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Instead of thinking of neurons as individual units, think of them as interconnected communication networks. If you imagine the tremendous complexity of the internet, and then massively increase that complexity, you’ll have an idea for how this system exists.

Three different types of neurons—motor neurons, sensory neurons, and interneurons—comprise the reflex arc, which sometimes initiate activities without involving the brain. Can you imagine a time when having this system work so quickly—faster than it can operate when the brain gets involved—can be adaptive, or even life-saving?

Repair and Growth

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The ability of the brain to change is called neuroplasticity, and this has important implications for how it works. Connections between neurons can strengthen, and new ones can form. This is most true during our younger years, though plasticity can continue into adulthood.

The brain’s ability to produce new cells is called neurogenesis, and this is part of our ability to learn as well as to remember information. Scientists hope to capitalize on neurogenesis in order to help people with different types of injuries regain lost functions in the future.

Mapping Brain Structure and Exploring Brain Function

An EEG recording

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There are many ways that scientists and medical experts can study a living brain without even removing it from your skull!

Please study carefully the techniques, advantages, and limitations of the following neuroimaging and assessment approaches for examining brain structures:

- Computer Tomography (CT)

Magnetic Resonance Imaging (MRI)

Refer also to the text to understand these techniques for examining brain functions:

- Studying neurological soft signs

- Electrical Stimulation of the Brain (ESB)

- Ablation and Deep Lesioning

- Electroencephalography (EEG)

- Positron Emission Tomography (PET)

- Functional Magnetic Resonance Imaging (fMRI)

The Cerebral Hemispheres

The corpus callosum

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The cerebral cortex is so large that it is divided into two halves, called hemispheres, which are connected by a thick band of neurons called the corpus callosum. Certain functions are controlled more by the left or right hemispheres in a pattern called lateralization, but this does not mean that people are “right-brained” or “left-brained.”

Spatial neglect is a condition that can emerge in response to damage to one of the hemispheres.

Is it true that right-handed people are left-brain dominant and that left-handed people are right-brain dominant? Not exactly. See how your author describes the curious and complex issue of hemispheric dominance.

The Split Brain

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When severe epilepsy does not respond to other forms of treatment, a split-brain operation might be performed in which the corpus callosum is severed to decrease communication between the cerebral hemispheres. Clearly this will result in certain forms of impairment, but patients can live for a long time after such a procedure.

The left and right hemispheres tend to have different basic areas of skill and process information differently, but we use both of our hemispheres at the same time for most tasks, even though we may lean on one more than the other.

Sex Differences: His and Her Brains?

Male and female brains

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There are basic differences between male and female brains that have been identified by research:

1. Women’s brains have more interconnection between the hemispheres than men’s brains.

2. Women tend to use both hemispheres more for a variety of tasks, while men seem to rely more on activity in one hemisphere for the same task.

3. Men have a more “front to back” orientation of connections in the brain, which may explain why they go quickly from perception to action. Women have a more “side to side” configuration, which some believe explains why they are more likely to use rationality and intuition in their processing.

The Frontal Lobes and Mirror Neurons

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Just behind your forehead are the frontal lobes of the cerebral cortex. They contain the following areas and functions:

1. Prefrontal cortex (executive functioning)

2. Association areas (combining and processing input)

3. Broca’s area (speech production center)

4. Primary motor cortex (directing muscular activity)

Mirror neurons are contained in the motor cortex, and they fire when we perform an action or when we observe someone perform an action. Do you ever find yourself tensing up when you watch a fight on television? This may be due to mirror neuron activity.

Review the proposed relationship between mirror neurons and autism spectrum disorder.

The Parietal, Temporal, and Occipital Lobes

Functions of the lobes of cerebral cortex

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The parietal lobes, at the crown of your head, contain the somatosensory cortex which processes body sensations such as temperature, pressure, and touch.

The temporal lobes contain the primary auditory cortices, which light up when we’re listening to sounds. They also have Wernicke’s Area, which is a primary language comprehension center.

In the back of your head, the occipital lobes contain the primary visual cortices that allow you to see. If this area is injured you may still be able to see things but not recognize them. This is called visual agnosia.

The Hindbrain and Midbrain

Main structures of the human brain

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While the cerebral cortex is the highest level of human brain functioning, other areas are crucial to function and survival.

The earliest level of brain structure is the hindbrain, which includes the medulla, pons, and cerebellum.

The midbrain connects the hindbrain to the forebrain.

The forebrain contains the cerebral cortex, as well as the limbic system, thalamus, and hypothalamus.

The reticular formation flows from the hindbrain through the midbrain, and is important in our attentional processes as well as a variety of other functions, including several reflexes and alertness.

Damage to the brainstem can lead to locked-in syndrome, in which a person is unable to move or communicate but is still cognizant of what is happening around them.

The Forebrain

Parts of the limbic system

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The forebrain contains many of the structures that distinguish human beings from lower animals. Review in your text how these structures work.

The thalamus directs sensory input (excluding smell) to their processing centers in the cortex.

The hypothalamus controls many functions, including but not limited to sexual behavior, thirst, hunger, and temperature regulation.

Emotions and memory as well as sexual urges and arousal can be understood by studying the limbic system, which includes amygdala and hippocampus among other structures.

Glands of the Endocrine System

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The endocrine system is comprised of a variety of glands that exist throughout the body. Each is responsible for secreting hormones that can be released into the bloodstream to affect distant parts of the body.

The hypothalamus controls the endocrine system by sending messages to the pituitary gland, which secretes growth hormone and also tells other glands what they need to do.

Study the functions and hormones secreted by the other endocrine glands:

- the pineal gland

- the thyroid gland

- the adrenal glands (including the adrenal medulla and the adrenal cortex)

- the pancreas

- the gonads (testes in men and ovaries in women)