Neurons; The Central Nervous System
I. Neurons: neurons are individual brain cells or nerve cells – the basic unit of nervous
System. The average human brain is composed of approximately 100 billion neurons.
III. Glial Cells and Brain Circuits: Glial cells are the most numerous cells in the brain
and act as supportive cells for neuronal functioning and are critical for the formation
of neuronal connections. Brain Circuits are organizations of neurons analogous to
circuits or transmission patterns of neurons.
stimulation from other neurons. When neurons are inactive or “at rest” the state of the neuron is referred to as resting potential. During resting potential more sodium ions are outside the neuron than inside and more potassium ions are on the inside. When channels (small holes or pores in the membrane) are open there is an exchange of ions from the inside and out. When the resulting stimulation exceeds a threshold and changes the charge in an axon down the length of the axon, the shifting charge is referred to as the action potential. When the exchange of ions works its way to the end of the axon, the terminal buttons release chemicals that act on other neurons. This is what is meant by the firing of a neural impulse. The all-or-none-law of neural transmission simply means that the action potential occurs (neuron fires) or it does not – there is no in between state. For a more detailed explanation of the action potential refer to Figure 2.2 on page 48 of your text.
1. The Synapse is the general site where the release of chemicals by the terminal knobs of an axon acts on the membrane of another neuron, Between the terminal knobs of an axon and the dendrites of a neighboring neuron is a small space referred to as the Synaptic Clef or the Synaptic Gap
2. Neurotransmitters: The chemicals that send signals by crossing the synaptic gap are referred to as neurotransmitters.
3. Neuromodulators : are chemicals which reduce of modify the effects of neurotransmitters
4. Some receptors of dendrites respond to some neurotransmitters but not to others. Neurotransmitters or neuromodulators bind to receptor sites of the dendrites and either increase (excitatory) or decrease (inhibitory) the likely hood that the proximal neuron will fire.
5. As can be seen in Figure 2.1 on page 51 of your text, neurotransmitters and neuromodulators have pronounced effects on various states of the nervous system and can result in a variety of disorders and symptoms. For example, a decrease in the neurotransmitter dopamine is critically involved in the symptoms of Parkinson’s disease whereas an increase in the same transmitter is related to schizophrenia. Hence, El Dopa, an early drug used in the treatment of Parkinson’s disease, increases dopamine activity and reduces the symptoms of Parkinson’s disease. The phenylthiazines, a class of drugs used in the early treatment of schizophrenia reduces schizophrenic symptoms by directly affecting dopamine receptors and reducing the levels of dopamine.
6. Serotonin and Depression: a shortage of serotonin is believed to be one cause of clinical depression. Antidepressant medications such as Prozac
(fluoxetine), and the tricyclic medications (e.g. Adapin and Ludiomil) keep more serotonin available at the synapse. The class of drugs known as SSRIs
(Selective serotonin reuptake inhibitors) increases the available serotonin by blocking the reuptake of serotonin and making it more
available at the synapse. Examples of SSRIs include Celexa, Lexapro, Luvox, Paxil, Prozac, and Zoloft.
I. Central Nervous System (CNS): the CNS is composed of the brain and the spinal
cord. The brain and the spinal cord have linkages with the Peripheral Nervous System), which is composed of the Somatic System and the Autonomic System (ANS). Of most importance to behavior is the autonomic Nervous System.
II. The two divisions of the Autonomic nervous System are:
1. Sympathetic Division: The Sympathetic Division of the Autonomic Nervous System is involved in any heightened physiological state of the organism such as strong emotions. Consider the following expressions: 1) hot with anger, 2) sent chills up and down my spine (pilo erection), 3) cold with fear, 4) anxiety attacks
2. Parasympathetic Division: mostly regulates day-to-day activities such as eating, digestion. Generally, the Parasympathetic Division has opposite effects to the Sympathetic Division – while the Sympathetic Division plays a role in general activation and increased arousal; the Parasympathetic division tends to regulate normal day-to-day functions
3. Generally, the Sympathetic Division and the Parasympathetic Divisions of the
Autonomic Nervous System have opposite effects, but there are instances in which they work in sequence. For example, in male sexual behavior, the Parasympathetic Division causes erection but the Sympathetic Division controls ejaculation
III. Composition of the Brain:
1. The Meninges: The meninges are comprised of three layers below the skull:
the tough outer layer is called the Dura Mater, a strong fibrous membrane
that surrounds the brain and spinal cord, 2) the middle layer of the meninges is called the Arachnoid, and 3) the layer closest to the brain is called the pia mater or pia. Examples of neurological problems: meningitis and subdural hematoma
2. Cerebral Hemispheres and four Lobes: Each half of the brain is called a
cerebral hemisphere and each hemisphere has four lobes:
3.Cerebral Cortex: the outer layer of the brain vital to higher processes and
mental functioning. The wrinkled appearance results from sulci in between bulges called Gyri. All areas beneath the cortex are referred to as subcortical
areas of the brain. A band of nerve fibers that connects the two halves of the brain is called the Corpus Callosum.
1) occipital lobes – located near the base of the brain below the parietal lobes and above a structure called the cerebellum
2) temporal lobes – located beneath the side of the head in the general area of the ears and underneath the frontal and parietal lobes, and
3) parietal lobes – lobes immediately behind the frontal lobe toward the back
of the brain,
4) frontal lobes – large lobes immediately behind the forehead
IV. Functions of the Four Lobes:
1. Frontal Lobes: much larger in the humans than in other primates. The frontal lobes are involved in higher processes such as speech, retrieval of memories, reasoning, and control over precision movements such as with the hand and fingers.
2. Parietal Lobes: contain the somatosensory strip that registers sensations from the body (see figure 2.8 on page 59 of your text). The parietal lobes are involved in special vision and locating objects or places.
3. Temporal lobes: Involved in storing visual memories, comprehending language, processing sound, and entering new information to memory.
4. Occipital lobe: very much involved in vision. Generally, the occipital lobe controls our visual perception system.
V. Somatosensory Strip (Sensory Area) and Motor Strip (Motor Area)
VI. Split-Brain Research: it is possible to separate the two hemispheres of the brain
surgically by severing the connections between the two hemispheres by cutting through the Corpus Callosum. This is known as the split-brain preparation. Although rarely used, the procedure may be a last result treatment of intractable epilepsy involving severe and frequent grand mal seizures that cannot be controlled by medication. The procedure (severing the Corpus Callosum) reduces the severity of convulsions by preventing propagation from one side of the brain to the other. Generally, the functions of the two hemispheres differ primarily in degree. It is not entirely accurate to say that the left brain is analytical and verbal whereas the right brain is involved in perception and intuitions. This has led to an oversimplification in explaining behavior. For example, classifying mathematicians as left brain people and musicians as right brain people. The two hemispheres differ in their degree of involvement in these abilities. For example, damage to the right hemisphere may have more of an effect on one’s musical abilities than damage to the left. Language, however, uniquely involves the left hemisphere and damage to the left hemisphere may have significant effects on various aspects of language behavior.
1. Lesions: damage to brain tissue or cells
2. Epilepsy (petit mal; grand mal): epilepsy may or may not involve detectable damage to an area of the brain.
3. Stroke: most often due to a clot clogging a blood vessel in the brain. For example, persons who have atrial fibrillation may be at a higher risk for clots forming in that area of the heart, and then passing via the circulatory system to the brain. Usually persons who have this problem will take regular dosages of a blood thinner such as Coumadin.
4. Concussion: jarring of the brain – may be very mild or severe and life threatening
5. Contusion: actual bruising of brain tissue
6. Hematoma: bleeding in an area on or within the brain that forms varying sizes of a blood mass or clot
7. Aneurysm: ballooning of a weak area of a blood vessel that may cause increasing pressure on surrounding brain cells or may rupture and result in serious problems or death (an aneurysm may occur in any vessel – not just those in the brain).
8. Electrical stimulation of the brain: brain stimulations may be used diagnostically.
For example, stimulation of areas in the basal ganglia prior to inducing lesions to control abnormal motor movements in Parkinsonism.
III. Behavioral Genetics
1. Mendelian Inheritance: Gregor Mendel, an Augustinian monk who taught
natural science in high school in Austria.. First person to study different generations of life focusing on pea plants. Two important factors: 1) for each trait, an offspring inherits an element from each parent, and 2) if an element is dominant over the other, it is apparent. If it is recessive (not dominant) it is only apparent if the offspring receives two copies of it, one from each parent
2. Important terms:
(a) Chromosome: a twisted molecule of deoxyribonucleic (DNA) located in the
nucleus of all cells. Each cell has 23 pairs of chromosomes (except sex cells).
(b) Gene: a stretch of DNA which produces a specific protein or enzyme
(c) Genotype: the actual genetic makeup of an individual
(d) Phenotype: the observable characteristics of an individual
(e) Pruning: the elimination of neural connections with low usage
(f) Plasticity: the changes in the brain that take place as a result of experience
or environmental interactions
3. Genes and Environment Interactions
(a) Passive Interaction: genetically shaped tendencies are passively received.
For example, a person with a high activity level may prefer “fast paced” activities such as high active sports. A child of such a parent may inherit the activity level and also develop a preference for “fast paced” activities
(b) Evocative or Reactive Interaction: genetically influenced characteristics lead
to different social reactions by others. For example, persons may expect
children with glasses to be “bookworms”. Genetically influenced physical
characteristics can be a basis for cultural stereotypes
(c) Active Interaction: Constructing or modifying situations to fit genetically
influenced personal characteristics. For example, persons may put
themselves in an environmental situation in which they feel comfortable such
shy persons avoiding large crowds (genetic factors have been shown to
influence temperament characteristics such as shyness)
4. Genetic Research
(a) Heritability: how much of the variability in a particular characteristic in a
population is due to genetics (NOT the amount of a characteristic that is
inherited). For example, 90% of the variability in peoples height in a
particular culture may be a result of genetics. This does not mean that an
individual’s height is determined 90 % by heredity and 10% by environment.
(b) Twin Studies: Monozygotic (identical twins) and Dizygotic (fraternal twins)