Notes, abstracts, papers, exams and problems of Biology

Phases of Neuromuscular Transmission

Motor Neuron Transmission:

1. The action potential occurs in the axonal cone and travels along the axon (nodes of Ranvier). When it reaches the presynaptic membrane, voltage-gated Ca channels open.
2. Ca enters the neuron, and the presynaptic membrane attracts vesicles of acetylcholine (ACh) found in the axon's cytosol.
3. Acetylcholine is released into the synapse.
4. Chemical-gated channels open when coupled to ACh, allowing Na to enter the cell.
5. An action potential occurs in the muscle cell membrane and spreads throughout the plasmolemma.
6. In the triad, dihydropyridine receptors (DHPR) are close to the terminal cisternae. When stimulated by the action potential, they stimulate ryanodine receptors. Ryanodine receptors (calcium

Sympathetic Nervous System (SNS) vs. Parasympathetic Nervous System (PNS)

The Parasympathetic Nervous System (PNS) prepares the body for changes, influencing heart rate and respiration. The Sympathetic Nervous System (SNS) restores the body to a resting state.

Nervous System Cells

• Neurons: The basic units of the Central Nervous System (CNS) and the peripheral nervous system.
• Glial cells: Support cells within the nervous system.

Peripheral Nervous System

The peripheral nervous system forms neural networks.

• Soma (neuronal body): Contains the cell nucleus and organelles. It provides energy to the cell. Lysosomes degrade cellular waste.
• Dendrites: Branching extensions that receive signals from other neurons.
• Axon: A long, slender projection that conducts

The Cells and Tissues of Plants

Plant Cell: Plant cells have eukaryotic cell structures except for the animal centrosome and possess a cell wall surrounding the membrane. They have chloroplasts and vacuoles.

Cell Types

Parenchymal Cells: These cells secrete substances and store hormones. They can undergo differentiation to perform specific functions, such as tracheids, which die and become woody vessels to circulate crude sap.

Simple and Complex Tissues

Tissues are groups of cells that perform a specific activity. They are classified according to the number of cell types (one or more) into simple and complex tissues.

• Simple Tissues: Parenchyma, collenchyma, and sclerenchyma.
• Complex Tissues: Formed by different cell types performing various functions,

Arteries and Superficial Veins of the Skull and Face

Neck Origin:

• **Arteries:** Common carotid, internal and external carotid.
• **Veins:** Internal and external jugular vein.

Jugular Vein Origin:

• Retromandibular vein (posterior to the jaw)
• Posterior auricular vein (behind the ear)
• Occipital vein (in the occipital region)
• Emissary vein (by the occipital region)
• Parietal emissary vein (parietal and occipital region)
• Nasofrontal vein (frontal nose and region)
• Dorsal nasal vein
• Zygomaticotemporal vein
• Angular vein (eye)
• Zygomaticofacial vein
• Infraorbital vein

Carotid Artery Origin:

• Posterior auricular artery
• Occipital artery
• Anterior auricular artery
• Superficial temporal artery
• Zygomatico-orbital artery
• Supraorbital artery
• Supratrochlear artery
• Dorsal nasal artery
• Zygomaticotemporal

Subclavian Artery

The subclavian artery is divided into three portions: pre-scalenic, intra-scalenic, and post-scalenic. It originates several branches:

• Vertebral Artery: Both vertebral arteries join to form the basilar artery, which contributes to the posterior cerebral circulation.
• Internal Thoracic Artery: Gives off mediastinal branches, thymic branches, bronchial branches, the pericardiacophrenic artery, sternal branches, perforating branches, lateral costal branches, and anterior intercostal branches. The internal thoracic artery then divides into the musculophrenic artery and the superior epigastric artery.

Thyrocervical Trunk

The thyrocervical trunk gives rise to:

• Inferior Thyroid Artery: Which further branches into the inferior laryngeal

DNA vs. RNA: Key Differences

DNA (Deoxyribonucleic Acid)

• Composition: The pentose sugar is D-deoxyribose. Contains the nitrogenous bases Adenine (A), Guanine (G), Thymine (T), and Cytosine (C) in similar proportions.
• Structure: DNA is a double-stranded molecule consisting of two polynucleotide chains.
• Configuration: Forms a double helix structure with the two chains connected by base pairing (A-T and C-G).
• Location: In eukaryotic cells, DNA is located in the nucleus, forming chromosomes. In prokaryotic cells, it forms a single, circular chromosome located in the cytoplasm.
• Function: DNA encodes the information that determines the order of amino acids required to synthesize all cellular proteins. A gene, a defined segment of DNA, contains the information

Metabolism

Metabolism is the set of chemical reactions that occur inside the cell. The different sequences of reactions or routes are called metabolic pathways, and the molecules involved are metabolites.

There are two phases:

1. Catabolism: Transformation of complex organic molecules into simpler ones (degradation). This process releases energy stored in ATP's phosphate bonds.
2. Anabolism: Synthesis of complex molecules from simple ones (construction), requiring energy provided by ATP.

Structure of Metabolic Pathways

• Linear: Intermediates are only used in a particular pathway.
• Branched: Metabolic routes intersect or cross at two or more points.
• Cyclical: After a series of transformations, the initial molecule is regenerated.

Types of Metabolism Based on

Methods for Studying Cellular Composition and Function

Biochemical Methods: To understand the composition and function of cellular structures.

• Cell Fractionation: Homogenization and deep freezing.
• Chromatography and Electrophoresis: Used to separate macromolecules.

Isotopic Methods: Incorporating radioactive isotopes into molecules to track their evolution within the cell, followed by autoradiography. Fluorescent markers are also used.

Cytosol and Cytoplasmic Inclusions

Cytosol: The internal liquid medium composed of water, salts, organic molecules, and macromolecules.

Cytoplasmic Inclusions: Accumulations of substances in eukaryotic and prokaryotic cells. Functions include reserve storage (e.g., glycogen and fat in animal cells, vegetable oils and... Continue reading "Cellular Structures: Composition, Function, and Methods" »

Apoptosis: Cellular Suicide

Apoptosis, or programmed cell death, is a crucial mechanism in multicellular organisms. It plays a vital role in development, removing unnecessary cells during embryonic stages (e.g., interdigital tissue), and in adulthood, eliminating damaged or potentially harmful cells. This process involves a series of changes leading to cell death. The cell shrinks, loses water, and forms bubble-like protrusions. The nucleus fragments, and the resulting apoptotic bodies are ingested by neighboring cells. Apoptosis is triggered by signals that activate endonucleases, which in turn produce lethal proteins, hydrolases, and proteases.

The Interphase Nucleus

The interphase nucleus houses the genetic material and controls all cellular... Continue reading "Apoptosis: Cellular Suicide Mechanisms and Nuclear Components" »

Molecular Level: Chemical Composition of Living Beings

1.1. Bioelements

Bioelements are all chemical elements that, in greater or lesser proportions, form living matter. There are six that qualify as the primary bioelements: C (Carbon), H (Hydrogen), O (Oxygen), N (Nitrogen), P (Phosphorus), and S (Sulfur). These make up most of living matter.

Others are involved in smaller quantities but are still essential for cellular metabolism. These are called secondary bioelements, which include Mg (Magnesium), Ca (Calcium), K (Potassium), Na (Sodium), and Cl (Chlorine).

Even smaller quantities of other elements are essential for living beings. These are called trace elements, and their lack causes serious illness and even death. Examples include Fe (Iron)... Continue reading "Chemical Composition of Living Beings: Bioelements and Biomolecules" »