The retina and optic nerves originate from protrusions of the diencephalon known as eye vesicles during development.

Neurodevelopment: Understanding Brain Development

The development of the central nervous system begins with the neuroectoderm, a specialized region of ectoderm. The embryonic brain is divided into three areas: the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon). The prosencephalon further divides into the telencephalon and diencephalon, while the hindbrain subdivides into the metencephalon and myelencephalon.

The telencephalon, of cerebrum, consists of the cerebral cortex, underlying white matter, and the basal ganglia. The diencephalon includes the prethalamus, thalamus, hypothalamus, subthalamus, epithalamus, and pretectum. The mesencephalon comprises the tectum, tegmentum, ventricular mesocoelia, cerebral peduncles, and several nuclei and fasciculi.

The rhombencephalon includes the medulla, pons, and cerebellum, which can be subdivided into a variable number of transversal swellings called rhombomeres. In humans, eight rhombomeres can be distinguished, from caudal to rostral: Rh7-Rh1 and the isthmus. Rhombomeres Rh7-Rh4 form the myelencephalon, while Rh3-Rh1 form the metencephalon.

Understanding neurodevelopment is crucial in comprehending brain development and its complexities. By studying the different areas of the embryonic brain, we can gain insight into the formation of the central nervous system and its functions.

Long-term memories prior to anterograde amnesia are unaffected, as the condition only affects the formation of new memories. Unfortunately, amnesia cannot be treated as it involves damage to neurons. Lacunar amnesia refers to the loss of memory for a specific event, with the term lacuna meaning a gap of missing part in Latin. Retrograde amnesia typically involves damage to structures in the medial temporal lobe, such as the hippocampus, rather than the cerebellum. Source amnesia is characterized by the inability to recall the context in which previously learned information was acquired, while still retaining the factual knowledge.

Understanding Amnesia: Types and Causes

Amnesia is a memory deficit that can be categorized into two types: anterograde and retrograde. Anterograde amnesia refers to the inability to create new memories, while retrograde amnesia refers to the loss of memory for information acquired before the onset of amnesia. The damage to the hippocampus and medial temporal lobe is often associated with amnesia. Source amnesia is the inability to remember where of how previously learned information was acquired. Psychogenic amnesia is characterized by sudden retrograde episodic memory loss, while semantic amnesia affects semantic memory and language use. Transient global amnesia is a condition that affects those over 50 and spontaneously resolves within 24 hours, with no clear cause identified. Understanding the types and causes of amnesia can help in its diagnosis and treatment.

Development of the cerebellum commences from the metencephalon in the sixth week.

Neurodevelopment: Understanding Brain Development

The development of the central nervous system begins with the neuroectoderm, a specialized region of ectoderm. The embryonic brain is divided into three areas: the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon). The prosencephalon further divides into the telencephalon and diencephalon, while the hindbrain subdivides into the metencephalon and myelencephalon.

The telencephalon, of cerebrum, consists of the cerebral cortex, underlying white matter, and the basal ganglia. The diencephalon includes the prethalamus, thalamus, hypothalamus, subthalamus, epithalamus, and pretectum. The mesencephalon comprises the tectum, tegmentum, ventricular mesocoelia, cerebral peduncles, and several nuclei and fasciculi.

The rhombencephalon includes the medulla, pons, and cerebellum, which can be subdivided into a variable number of transversal swellings called rhombomeres. In humans, eight rhombomeres can be distinguished, from caudal to rostral: Rh7-Rh1 and the isthmus. Rhombomeres Rh7-Rh4 form the myelencephalon, while Rh3-Rh1 form the metencephalon.

Understanding neurodevelopment is crucial in comprehending brain development and its complexities. By studying the different areas of the embryonic brain, we can gain insight into the formation of the central nervous system and its functions.

Frontotemporal lobe degeneration (FTLD) encompasses various syndromes, such as Pick’s disease, primary progressive aphasia (which impacts speech), semantic dementia (affecting conceptual knowledge), and corticobasal degeneration (characterized by asymmetrical akinetic-rigid syndrome and apraxia). It is important to note that posterior cortical atrophy, which involves tissue loss in the posterior regions and affects higher visual processing, is not considered a part of the FTLD syndrome.

Heritability: Understanding the Concept

Heritability is a concept that is often misunderstood. It is not a measure of the extent to which genes cause a condition in an individual. Rather, it is the proportion of phenotypic variance attributable to genetic variance. In other words, it tells us how much of the variation in a condition seen in a population is due to genetic factors. Heritability is calculated using statistical techniques and can range from 0.0 to 1.0. For human behavior, most estimates of heritability fall in the moderate range of .30 to .60.

The quantity (1.0 – heritability) gives the environment ability of the trait. This is the proportion of phenotypic variance attributable to environmental variance. The following table provides estimates of heritability for major conditions:

Condition Heritability estimate (approx)
ADHD 85%
Autism 70%
Schizophrenia 55%
Bipolar 55%
Anorexia 35%
Alcohol dependence 35%
Major depression 30%
OCD 25%

It is important to note that heritability tells us nothing about individuals. It is a population-level measure that helps us understand the relative contributions of genetic and environmental factors to a particular condition.

Hardy-Weinberg Principle and Allele Frequency

Allele frequency refers to the proportion of a population that carries a specific variant at a particular gene locus. It can be calculated by dividing the number of individual alleles of a certain type by the total number of alleles in a population. The Hardy-Weinberg Principle states that both allele and genotype frequencies in a population remain constant from generation to generation unless specific disturbing influences are introduced. To remain in equilibrium, five conditions must be met, including no mutations, no gene flow, random mating, a sufficiently large population, and no natural selection. The Hardy-Weinberg Equation is used to predict the frequency of alleles in a population, and it can be used to estimate the carrier frequency of genetic diseases. For example, if the incidence of PKU is one in 10,000 babies, then the carrier frequency in the general population is 1/50. Couples with a previous child with PKU have a 25% chance of having another affected child.

Genetics plays a role in the development of Alzheimer’s disease, with different genes being associated with early onset and late onset cases. Early onset Alzheimer’s, which is rare, is linked to three genes: amyloid precursor protein (APP), presenilin one (PSEN-1), and presenilin two (PSEN-2). The APP gene, located on chromosome 21, produces a protein that is a precursor to amyloid. The presenilins are enzymes that cleave APP to produce amyloid beta fragments, and alterations in the ratios of these fragments can lead to plaque formation. Late onset Alzheimer’s is associated with the apolipoprotein E (APOE) gene on chromosome 19, with the E4 variant increasing the risk of developing the disease. People with Down’s syndrome are also at high risk of developing Alzheimer’s due to inheriting an extra copy of the APP gene.

Genomics: Understanding DNA, RNA, Transcription, and Translation

Deoxyribonucleic acid (DNA) is a molecule composed of two chains that coil around each other to form a double helix. DNA is organised into chromosomes, and each chromosome is made up of DNA coiled around proteins called histones. RNA, on the other hand, is made from a long chain of nucleotide units and is usually single-stranded. RNA is transcribed from DNA by enzymes called RNA polymerases and is central to protein synthesis.

Transcription is the synthesis of RNA from a DNA template, and it consists of three main steps: initiation, elongation, and termination. RNA polymerase binds at a sequence of DNA called the promoter, and the transcriptome is the collection of RNA molecules that results from transcription. Translation, on the other hand, refers to the synthesis of polypeptides (proteins) from mRNA. Translation takes place on ribosomes in the cell cytoplasm, where mRNA is read and translated into the string of amino acid chains that make up the synthesized protein.

The process of translation involves messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Transfer RNAs, of tRNAs, connect mRNA codons to the amino acids they encode, while ribosomes are the structures where polypeptides (proteins) are built. Like transcription, translation also consists of three stages: initiation, elongation, and termination. In initiation, the ribosome assembles around the mRNA to be read and the first tRNA carrying the amino acid methionine. In elongation, the amino acid chain gets longer, and in termination, the finished polypeptide chain is released.

Ethical theory and principles are important in medical ethics. There are three key ethical theories that have dominated medical ethics: utilitarianism, deontological, and virtue-based. Utilitarianism is based on the greatest good for the greatest number and is a consequentialist theory. Deontological ethics emphasize moral duties and rules, rather than consequences. Virtue ethics is based on the ethical characteristics of a person and is associated with the concept of a good, happy, flourishing life.

More recent frameworks have attempted to reconcile different theories and values. The ‘four principles’ of ‘principlism’ approach, developed in the United States, is based on four common, basic prima facie moral commitments: autonomy, beneficence, non-maleficence, and justice. Autonomy refers to a patient’s right to make their own decisions, beneficence refers to the expectation that a doctor will act in a way that will be helpful to the patient, non-maleficence refers to the fact that doctors should avoid harming their patients, and justice refers to the expectation that all people should be treated fairly and equally.

The superego encompasses the ‘ego ideal’, which embodies exemplary attitudes and conduct. One can liken the Superego to a moral compass of conscience.

Freud’s Structural Theory: Understanding the Three Areas of the Mind

According to Freud’s structural model, the human mind is divided into three distinct areas: the Id, the Ego, and the Superego. The Id is the part of the mind that contains instinctive drives and operates on the ‘pleasure principle’. It functions without a sense of time and is governed by ‘primary process thinking’. The Ego, on the other hand, attempts to modify the drives from the Id with external reality. It operates on the ‘reality principle’ and has conscious, preconscious, and unconscious aspects. It is also home to the defense mechanisms. Finally, the Superego acts as a critical agency, constantly observing a person’s behavior. Freud believed that it developed from the internalized values of a child’s main caregivers. The Superego contains the ‘ego ideal’, which represents ideal attitudes and behavior. It is often referred to as the conscience. Understanding these three areas of the mind is crucial to understanding Freud’s structural theory.