UNIT 1: 

 

LECTURE 4    Tuesday, September 8, 2009

 
Text Assignment: Chapter 3      pp 77-108

 

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.

 

II. Three Types of Neurons

 

  1. Sensory Neurons: cells specialized to receive input from the senses
  2. Motor Neurons: cells which transmit impulses to the muscles and control muscular movements
  3. Interneurons: interconnecting neurons which link or stand between other neurons. The brain is comprised primarily of interneurons.

 

 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.

 

IV. Neuron Components and Neural Impulses

 

  1. Cell Body and Cell Membrane: the cell body contains the nucleus of the cell and is encompassed by a cell membrane
  2. Axon: a long fiber like structure that is specialized for the transmission of neural impulses. Each neuron has only one axon. Near the end of the axon there are typically branching out fibers called terminals which end in little knob-like structures called terminal buttons
  3. Myelin Sheath: a fatty like substance that covers most of the length of long motor axons. Myelinated axons have fast transmission as the nerve impulse travels along their surface over small openings called Nodes of Ranvier. An impulse jumps from one node to the next at a rate as fast as 120 meters per second and is referred to as Saltatory transmission or conduction. Disorders that are associated with the destruction of the myelin sheath such as Multiple Sclerosis (MS) have dramatic effects on the muscular system as well sensations in the arms and legs and vision.
  4. Dendrites: multiple fiber like structures specialized for the reception of neural impulses
  1. Neural Impulses and Transmission:  Neurons fire when there is sufficient

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.

 

V.Neurotransmitters and Neuromodulators

           

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.

 

The Central Nervous System (CNS)

 

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.

 

VII. Subcortical Areas of the Brain

 

  1. Thalamus: sometimes referred to as the switchboard of the brain. In a sense, neuronal fibers from the thalamus “coordinate” cortical and subcortical areas . The thalamus plays a major role in motor functions.
  2. Hypothalamus: critically involved in a number of life sustaining activities – eating, drinking, control of body temperature and blood pressure. Generally the anterior portion of the hypothalamus regulates parasympathetic division of the autonomic nervous system day-to-day activities such as eating, heart rate and digestion, whereas the posterior portion regulates the sympathetic division of the Autonomic Nervous System, such as strong emotions and sexual behavior.
  3. Hippocampus: remotely (very remotely) resembles a seahorse in appearance. Heavily involved in entering new memories into storage. Patients with damage may remember past events but have extreme difficulty in acquiring new learning. The hippocampus does not store new memories but it is directly involved in processes that transmit new memories to other areas of the brain for storage.
  4. Amygdala: a key structure of the limbic system involved in basic emotions and sexual behavior.
  5. Basal Ganglia: located on the outer sides of the thalamus. Plays a highly significant role in planning and producing movement. Its function is highly dependent on the neurotransmitter dopamine. Example: Parkinson’s Disease – neurosurgical efforts to control abnormal movements by making lesions in the basal ganglia.
  6. Brainstem: The brainstem is directly involved in vital functions such as breathing and circulation. A key system in the brainstem is the medull oblongata, which regulates involuntary functions such as breathing, heartbeat, and body temperature. Another important brain system is the reticular formation – an area that is arousal or alertness.
  7. Cerebellum: the very back portion of the brain that controls body balance and equilibrium. Damage to this area can cause cerebellar ataxia.

 

VIII. The Neuroendocrine System

 

  1. Pituitary Gland: located in the sphenoid bone over the roof of the mouth. It is a small gland connected to the hypothalamus by the pituitary stalk. The Pituitary Gland is sometimes referred to as the master gland of the endrocrine system because it regulates the functions of other hormone secreting glands.
  2. Testosterone: male hormones – facial hair and secondary sex characteristics, muscular system
  3. Estrogen: female hormone – causes breasts to develop and regulates the menstrual cycle
  4. Cortisol: secreted by the outer layer of the adrenal glands and is provides help in meeting energy demands by converting protein and fat to sugar.

 

 

 

 

 

 

 

__________________________________________________________________________________ 

 

CHAPTER 3

 

UNIT 1: 

 

LECTURE 5    Thursday, September 10, 2009

 

Text Assignment: Chapter 3       pp 109-126

 

Probing the Brain/Genetics and the Nervous System
 
I. Measurements of Neurological Function

 

  1. Electroencephalograph (EEG): when neurons fire, the produce electrical fields. The EEG can record the electrical activity of the brain. If there is no electrical activity, the EEG tracing will be flat and, if it persists, the person will be considered “brain dead”.
  2. Computer Assisted Tomography (CT): involves a series of x-rays, which builds a three-dimensional image, section by section.
  3. Magnetic Resonance Imaging (MRI): “makes use of the magnetic properties of different atoms to take even sharper pictures of the brain (Text definition, p. 69). Generally, it is the most precise, clear form of neuroimaging which has greatly improved neurological research and research in neuropsychology.
  4. Positron Emission Tomography (PET): allows for the measurement of blood flow or energy consumption in the brain. Very small amounts of radiation (a harmless amount) are administered by IV. As the radiation enters the brain, the amount in different parts is recorded. The computer generates three-dimensional  images of the brain.

 

II The Damaged Brain: Some types of Neurological Impairment

 

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)