Psychology Neurons, Hormones, and the Brain Studying the Brain Structure, Functions & Review
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Studying the Brain
To examine the brain’s functions, researchers have to study a working brain, which means they can’t use cadavers. Invasive studies, in which researchers actually put instruments into the brain, can’t be done in humans, though they can be done occasionally during medically necessary brain surgery. Researchers usually use invasive techniques in animal studies. There are two main types of invasive animal studies:
- Lesioning studies: Researchers use an electrode and an electric current to burn a specific, small area of the brain.
- Electric stimulation of the brain: Researchers activate a particular brain structure by using a weak electric current sent along an implanted electrode.
Because they cannot use such invasive techniques on humans, researchers study human brains in two ways:
- They examine people with brain injuries or diseases and see what they can and can’t do.
- They use electroencephalographs (EEGs), which can record the overall electrical activity in the brain via electrodes placed on the scalp.
Recently, high-tech innovations have made studying human brains easier. Researchers use three types of imaging equipment to study the brain:
- Computerized tomography (CT): In CT, a number of x-rays are taken of the brain from different angles. A computer then combines the x-rays to produce a picture of a horizontal slice through the brain.
- Magnetic resonance imaging (MRI): Both brain structure and function can be visualized through MRI scans, which are computer-enhanced pictures produced by magnetic fields and radio waves.
- Positron emission tomography (PET): For PET scans, researchers inject people with a harmless radioactive chemical, which collects in active brain areas. The researchers then look at the pattern of radioactivity in the brain, using a scanner and a computer, and figure out which parts of the brain activate during specific tasks, such as lifting an arm or feeling a particular emotion.
Structure and Functions of the Brain
The brain is divided into three main parts: the hindbrain, the midbrain, and the forebrain.
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Structure and Functions of the Brain[/caption]The Hindbrain
The hindbrain is composed of the medulla, the pons, and the cerebellum. The medulla lies next to the spinal cord and controls functions outside conscious control, such as breathing and blood flow. In other words, the medulla controls essential functions. The pons affects activities such as sleeping, waking, and dreaming. The cerebellum controls balance and coordination of movement. Damage to the cerebellum impairs fine motor skills, so a person with an injury in this area would have trouble playing the guitar or typing a term paper.
The Midbrain
The midbrain is the part of the brain that lies between the hindbrain and the forebrain. The midbrain helps us to locate events in space. It also contains a system of neurons that releases the neurotransmitter dopamine. The reticular formation runs through the hindbrain and the midbrain and is involved in sleep and wakefulness, pain perception, breathing, and muscle reflexes.
The Forebrain
The biggest and most complex part of the brain is the forebrain, which includes the thalamus, the hypothalamus, the limbic system, and the cerebrum.
Thalamus
The thalamus is a sensory way station. All sensory information except smell-related data must go through the thalamus on the way to the cerebrum.
Hypothalamus
The hypothalamus lies under the thalamus and helps to control the pituitary gland and the autonomic nervous system. The hypothalamus plays an important role in regulating body temperature and biological drives such as hunger, thirst, sex, and aggression.
Structure and Functions of the Brain
Limbic System
The limbic system includes the hippocampus, the amygdala, and the septum. Parts of the limbic system also lie in the thalamus and the hypothalamus. The limbic system processes emotional experience. The amygdala plays a role in aggression and fear, while the hippocampus plays a role in memory.
Cerebrum
The cerebrum, the biggest part of the brain, controls complex processes such as abstract thought and learning. The wrinkled, highly folded outer layer of the cerebrum is called the cerebral cortex. The corpus callosum is a band of fibers that runs along the cerebrum from the front of the skull to the back. It divides the cerebrum into two halves, or hemispheres. Each hemisphere is divided into four lobes or segments: the occipital lobe, the parietal lobe, the temporal lobe, and the frontal lobe:
- The occipital lobe contains the primary visual cortex, which handles visual information.
- The parietal lobe contains the primary somatosensory cortex, which handles information related to the sense of touch. The parietal lobe also plays a part in sensing body position and integrating visual information.
- The temporal lobe contains the primary auditory cortex, which is involved in processing auditory information. The left temporal lobe also contains Wernicke’s area, a part of the brain involved in language comprehension.
- The frontal lobe contains the primary motor cortex, which controls muscle movement. The left frontal lobe contains Broca’s area, which influences speech production. The frontal lobe also processes memory, planning, goal-setting, creativity, rational decision making, and social judgment.
Brain Hemispheres
Lateralization refers to the fact that the right and left hemispheres of the brain regulate different functions. The left hemisphere specializes in verbal processing tasks such as writing, reading, and talking. The right hemisphere specializes in nonverbal processing tasks such as playing music, drawing, and recognizing childhood friends.
Roger Sperry, Michael Gazzaniga, and their colleagues conducted some of the early research in lateralization. They examined people who had gone through split-brain surgery, an operation done to cut the corpus callosum and separate the two brain hemispheres. Doctors sometimes use split-brain surgery as a treatment for epileptic seizures.
Control of the Body
Because of the organization of the nervous system, the left hemisphere of the brain controls the functioning of the right side of the body. Likewise, the right hemisphere controls the functioning of the left side of the body.
Vision and hearing operate a bit differently. What the left eye and right eye see goes to the entire brain. However, images in the left visual field stimulate receptors on the right side of each eye, and in-formation goes from those points to the right hemisphere. Information perceived by the right visual field ends up in the left hemisphere.
In the case of auditory information, both hemispheres receive input about what each ear hears. However, information first goes to the opposite hemisphere. If the left ear hears a sound, the right hemisphere registers the sound first.
The fact that the brain’s hemispheres communicate with opposite sides of the body does not affect most people’s day-to-day functioning because the two hemispheres constantly share information via the corpus callosum. However, severing the corpus callosum and separating the hemispheres causes impaired perception.
Split-Brain Studies
If a researcher presented a picture of a Frisbee to a split-brain patient’s right visual field, information about the Frisbee would go to his left hemisphere. Because language functions reside in the left hemisphere, he’d be able to say that he saw a Frisbee and describe it. However, if the researcher presented the Frisbee to the patient’s left visual field, information about it would go to his right hemisphere. Because his right hemisphere can’t communicate with his left hemisphere when the corpus callosum is cut, the patient would not be able to name or describe the Frisbee.
The same phenomenon occurs if the Frisbee is hidden from sight and placed in the patient’s left hand, which communicates with the right hemisphere. When the Frisbee is in the patient’s left visual field or in his left hand, the patient may not be able to say what it is, although he would be able to point to a picture of what he saw. Picture recognition requires no verbal language and is also a visual-spatial task, which the right hemisphere controls.
The Endocrine System
The endocrine system, made up of hormone-secreting glands, also affects communication inside the body. Hormones are chemicals that help to regulate bodily functions. The glands produce hormones and dump them into the bloodstream, through which the hormones travel to various parts of the body. Hormones act more slowly than neurotransmitters, but their effects tend to be longer lasting.
The pituitary gland, which lies close to the hypothalamus of the brain, is often called the master gland of the endocrine system. When stimulated by the hypothalamus, the pituitary gland releases various hormones that control other glands in the body. The chart below summarizes the better known hormones along with some of their functions.
| Hormone | Produced by | Involved in regulating |
| Thyroxine | Thyroid gland | Metabolic rate |
| Insulin | Pancreas | Level of blood sugar |
| Melatonin | Pineal gland | Biological rhythms, sleep |
| Cortisol, Norepinephrine, Epinephrine, Adrenaline | Adrenal glands | Bodily functions during stressful and emotional states |
| Androgens | Testes (and ovaries and adrenal glands to a lesser extent) | Male secondary sex characteristics, sexual arousal in males and females |
| Estrogens | Ovaries (and testes and adrenal glands to a lesser extent) | Breast development and menarche in females |
| Progesterone | Ovaries (and testes and adrenal glands to a lesser extent) | Preparation of uterus for implantation of fertilized egg |
Quick Review
The Nervous System
- The nervous system comprises the central nervous system and the peripheral nervous system.
- The central nervous system consists of the brain and the spinal cord. The spinal cord connects the brain to the rest of the body.
- The peripheral nervous system consists of the somatic nervous system and the autonomic nervous system. The somatic nervous system affects voluntary muscles and organs. The autonomic nervous system affects the heart, blood vessels, glands, and smooth or involuntary muscles.
- The autonomic nervous system contains the sympathetic nervous system, which prepares the body for emergency action, and the parasympathetic nervous system, which helps the body conserve energy and relax.
Neurons: Cells of the Nervous System
- Glial cells support neuron function.
- Neurons, the other type of cell in the nervous system, receive, integrate, and pass along information.
- A neuron contains the soma, dendrites, axon, and myelin sheath.
- Terminal buttons at the ends of axons release neurotransmitters or chemicals that cross over to neighboring neurons.
- The space between neurons is the synapse.
- The resting potential of a neuron is the stable negative charge inside the neuron when it is inactive.
- The action potential is a temporary change in electric charge inside a neuron.
- Neural impulses conform to the all-or-none law, which means that neurons fire to generate an action potential only if stimulation reaches a minimum threshold.
- In neural communication, receptor sites on postsynaptic cells can be excitatory or inhibitory.
Neurotransmitters
- Neurotransmitters are chemicals that enable neurons to communicate with each other.
- Major neurotransmitters include acetylcholine, dopamine, serotonin, endorphins, norepinephrine, GABA, and glutamate.
- Agonists are chemicals that mimic the action of neurotransmitters.
- Antagonists are chemicals that block the action of neurotransmitters.
Studying the Brain
- Researchers use lesioning and electric stimulation of the brain to study animals.
- To study human brains, researchers use electroencephalographs, computerized tomography, magnetic resonance imaging, and positron emission tomography. Researchers also study the impact of brain injuries and diseases.
Structure and Functions of the Brain
- The brain consists of the hindbrain, midbrain, and forebrain. Each section of the brain contains subsections, which control different functions.
- The hindbrain contains the medulla, the pons, and the cerebellum.
- The midbrain contains a dopamine-releasing system and helps us to locate events in space.
- The forebrain is the largest part of the brain and includes the thalamus, the hypothalamus, the limbic system, and the cerebrum.
- Lateralization refers to how the right and left sides of the brain specialize in different functions. The left hemisphere processes verbal skills, while the right side processes nonverbal tasks.
- The left side of the brain affects the functioning of the right side of the body. Conversely, the right side of the brain affects the functioning of the left side of the body.
The Endocrine System
- The endocrine system, which consists of glands that release hormones, also helps communication within the body.
- Hormones are chemicals that regulate body functions.
- The pituitary gland is the master gland of the endocrine system.
- Major hormones include thyroxine, insulin, melatonin, adrenal hormones, androgens, estrogens, and progesterone.
