Biological Psychology and Vision Lecture

Foundations of Biological Psychology

Biological psychology is defined as the scientific study of the influence of biological systems on behavior. This field explores how the physical structures and physiological processes of the body, particularly the nervous system, relate to psychological functions.

Santiago Ramón y Cajal is a foundational figure in neuroscience. He is best known for his work demonstrating that neurons are discrete cells that generate and utilize electrical signals to communicate. This finding was a departure from earlier theories that suggested the nervous system was a continuous, reticulated web.

Techniques for Studying the Nervous System

The pathways of the brain can be effectively mapped using specific staining techniques. Myelin stains are utilized to highlight the lipid-rich insulation surrounding axons, while horseradish peroxidase can be used as a tracer to follow neuronal pathways from their origin to their termination.

To investigate the active functioning of the brain, researchers use advanced neuroimaging techniques. Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) are primary tools for observing metabolic activity and blood flow changes associated with cognitive tasks.

While Electroencephalograms (EEGs) are a common diagnostic tool, the claim that they were first developed and used by Raymond Damadian in Germany in 1924 is false. Furthermore, the use of repeated transcranial magnetic stimulation (rTMS) to treat auditory hallucinations associated with schizophrenia was identified as false in the provided material.

Microdialysis is a specific biochemical technique used to assess the presence and concentration of neurochemicals. It is capable of measuring chemicals within a very small, localized area of the brain by sampling the extracellular fluid.

Neuroanatomy and Anatomical Directional Terms

The cranial nerves serve as the primary conduits between the brain and the head/neck region. However, it is false to state that every cranial nerve carries both sensory and motor information; some are specialized for only one type of information. Within the autonomic nervous system, the neurons comprising the parasympathetic division are located specifically in the brain (cranial) and the sacral divisions of the spinal cord.

From an evolutionary perspective, the brain has undergone significant changes. It is false to claim that the brain size has remained virtually unchanged from early hominin versions to the current species, Homo sapiens.

Standard directional terms are essential for navigating neuroanatomy:

  • Caudal: Refers to a direction away from the head of the body, or toward the tail.
  • Ventral: Refers to the front side of the body, specifically the belly side.
  • Rostral: Refers to a direction toward the nose, the oral region, or the nasal region. In the context of a four-legged animal, the term rostral is associated with an upright or anterior position.

Glial Cells and Myelination

Glial cells provide essential support to neurons. Myelination in the Central Nervous System (CNS) is performed by oligodendrocytes (OLs). A single oligodendrocyte is highly efficient, capable of myelinating axons from an average of 3030 different neurons. In contrast, myelination in the Peripheral Nervous System (PNS) is managed by Schwann cells. A single Schwann cell provides myelin for the axon of only 11 neuron.

Nervous system demyelination, the loss of the insulating myelin sheath, is a central feature of multiple sclerosis (MS). Beyond myelination, other glia play diverse roles. Microglia are primarily responsible for phagocytosis, which involves removing waste, damaged cells, and pathogens. Following an injury, Schwann cells facilitate recovery by guiding the regrowth of axons.

Synaptic Transmission: Neuropeptides and Small Molecules

Neurotransmitters are categorized by their molecular size and storage methods. Small-molecule transmitters are stored in small synaptic vesicles located near the presynaptic membrane for rapid release. Neuropeptides, however, are stored in large dense-core vesicles found further away from the membrane.

The release of vesicles containing neuropeptides requires high-frequency stimulation and a significant influx of calcium (Ca2+Ca^{2+}). Once released into the synapse, neuropeptides differ from small-molecule transmitters because they produce slower, longer-lasting effects and typically require repeated stimulation for release.

Acetylcholine Synthesis and Degradation

Acetylcholine (ACh) is the specific neurochemical used by vertebrates at the neuromuscular junction. It is synthesized within the neuron according to the following relationship:

Choline+Acetyl-CoA→Acetylcholine\text{Choline} + \text{Acetyl-CoA} \rightarrow \text{Acetylcholine}

The enzyme Choline Acetyltransferase (ChAT) is a unique marker for this process, as it is found only in neurons that produce ACh. Once ACh is released into the synaptic gap, it must be deactivated to prevent constant stimulation. This deactivation is performed by the enzyme Acetylcholinesterase (AChE), which breaks down acetylcholine back into its constituent parts: choline and acetate.

Principles of Genetics and Heredity

Genetic information is encoded in DNA. A sequence of three nucleotides that specifies a particular amino acid is known as a codon. Mutations are defined as differences in DNA resulting from the deletion, insertion, or duplication of genomic sections. A specific example of a genetic disorder is Huntington disease, which is caused by an expansion of CAG repeats within the huntingtin gene.

In terms of phenotypic expression, partial dominance occurs when a heterozygous offspring (carrying two different alleles) displays an intermediate phenotype between the two homozygous parents. Genetic diversity is immense; a single human can produce eggs or sperm with more than 8 million8 \text{ million} (2232^{23}, or 8,388,6088,388,608) different combinations of their chromosomes. Because of this random assortment and the sheer number of combinations, siblings often do not share many alleles.

Inheritance is also affected by physical chromosome structure. Linkage refers to the tendency of genes located close together on the same chromosome to be inherited together. This is occasionally disrupted by crossing over, the process during meiosis where homologous chromosomes exchange segments of DNA. Additionally, while the X and Y chromosomes are different, some small percentage of genes found on the X chromosome are duplicated on the Y chromosome.

The Anatomy and Physiology of Vision

Vision begins with light entering the eye and striking the retina. The path of light is as follows:

  • Blind Spot: Every eye has a blind spot caused by the optic disk, the location where the optic nerve exits the eye. This area contains no photoreceptors.
  • Macula and Fovea: When an individual stares directly at an object, the light is projected onto the macula. Within the macula is a small pit called the fovea, which is specialized for detailed vision and contains only cones.
  • Retinal Pigment Epithelium (RPE): This layer of pigmented cells supports photoreceptors and absorbs random light to prevent visual blurring.
  • Red Eye Effect: In flash photography, "red eye" is caused by the camera flash reflecting off the blood vessels in the retina.

The retinal layers are organized complexly. The cell bodies of bipolar, amacrine, and horizontal cells are situated in the inner nuclear layer. The dendrites of ganglion cells connect with amacrine and bipolar cells in the inner plexiform layer. Ultimately, the axons of the ganglion cells bundle together to form the optic nerve, which carries visual information to the brain.