Key Concepts in Neurobiology, Muscle Contraction, and Genetics

Steps of synaptic transmission

1. AP reaches axon terminal 2. Voltage-gated Ca²⁺ channels open 3. Ca²⁺ enters 4. Vesicles release neurotransmitters 5. NTs cross synaptic cleft 6. Bind to ligand-gated ion channels on postsynaptic membrane 7. Depolarization of postsynaptic cell

Where does summation occur in the neuron

At the axon hillock of the postsynaptic neuron

What is spatial summation

Multiple synapses fire at once, combining weak signals into a strong one

What is temporal summation

One synapse fires repeatedly over time to build up potential

How does long-term potentiation (LTP) strengthen a synapse

Repeated stimulation increases receptor numbers on the postsynaptic cell, making it easier to reach threshold

What are EPSPs and IPSPs

EPSPs = excitatory, cause depolarization; IPSPs = inhibitory, cause hyperpolarization

What determines whether an action potential is triggered in the postsynaptic cell

The net effect of all EPSPs and IPSPs at the axon hillock

Steps of long-term potentiation

1. Frequent APs 2. Temporal/spatial summation 3. More ligand-gated ion channels inserted in postsynaptic membrane 4. Synapse becomes stronger

Steps of hearing

1. Pinna catches sound → auditory canal → tympanic membrane vibrates 2. Ossicles vibrate → oval window vibrates 3. Cochlear hair cells detect vibrations → depolarize → AP generated 4. Signal sent to brain

Steps of muscle contraction

1. AP in motor neuron → acetylcholine released 2. Signal spreads across muscle fiber and T-tubules 3. Sarcoplasmic reticulum releases Ca²⁺ 4. Ca²⁺ binds to troponin → tropomyosin shifts 5. Actin binding sites exposed → myosin binds (cross-bridge) 6. ADP released → powerstroke 7. ATP binds → cross-bridge breaks 8. ATP hydrolysis resets myosin head

What are sarcomeres made of

Thin actin filaments and thick myosin filaments

What role does calcium play in muscle contraction

Ca²⁺ binds to troponin, which causes tropomyosin to move and expose binding sites on actin

What is the function of ATP in muscle contraction

ATP breaks the cross-bridge and resets the myosin head for another contraction

What are the energy sources for muscle contraction in order

1. Immediate: ATP 2. Short-term: Creatine phosphate 3. Intermediate: Glucose metabolism 4. Long-term: Glycogen, then lipids

Compare the three types of muscle tissue: Skeletal vs Cardiac vs Smooth

Skeletal: Voluntary, striated, multinucleated; Cardiac: Involuntary, striated, branched, intercalated discs; Smooth: Involuntary, non-striated, spindle-shaped

Which muscle types have sarcomeres

Skeletal and cardiac muscles (smooth muscle does not)

Which muscle types use motor neurons to initiate contraction

Skeletal only (cardiac and smooth are controlled involuntarily)

Steps of food processing in digestion

1. Mouth: Mechanical digestion and salivary amylase breakdown carbs 2. Esophagus: Peristalsis 3. Stomach: Pepsin breaks down proteins 4. Small intestine: Lipases, nucleases, bile aid digestion and absorption

What are the enzymes responsible for digesting specific macromolecules

1. Carbs: Amylase (mouth, small intestine) 2. Proteins: Pepsin (stomach), enzymes in small intestine 3. Lipids: Lipase (small intestine), bile (emulsifies lipids) 4. Nucleic acids: Nucleases (small intestine)

Which organs are involved in digestion and what do they do

1. Mouth: Salivary amylase 2. Stomach: HCl (parietal cells), Pepsin (chief cells) 3. Liver: Makes bile

Stomach

HCl (parietal cells), Pepsin (chief cells)

Liver

Makes bile

Gallbladder

Stores bile

Pancreas

Enzymes and bicarbonate

Small intestine

Absorption site

Sphincters

Sphincters (e.g., esophageal, pyloric, ileocecal) regulate the flow of food and digestive juices between different parts of the digestive system.

Water-soluble vitamins

Dissolve in water, like Vitamin C and B-vitamins.

Lipid-soluble vitamins

Dissolve in fats, like Vitamins A, D, E, K.

Vitamin C deficiency

Leads to scurvy.

Vitamin B3 deficiency

Causes pellagra.

Vitamin B9 deficiency

Causes spina bifida.

Vitamin D deficiency

Leads to osteomalacia or rickets.

Ghrelin

Stimulates hunger.

PYY

Suppresses appetite.

Insulin

Reduces appetite and regulates blood sugar.

Leptin

Suppresses appetite.

Gastrin

Stimulates acid secretion.

CCK

Stimulates bile and enzyme release, slows digestion for fatty meals.

Secretin

Neutralizes acid in the small intestine.

Gills

Found in fish and crustaceans, use countercurrent exchange.

Lungs

Found in land animals, internal sacs with alveoli for gas exchange.

Body Surfaces

Found in amphibians and earthworms, gas exchange through moist skin.

Tracheal Systems

Found in insects, air tubes deliver O2 directly to tissues.

Path of an oxygen molecule

Oxygen enters through the nasal cavity → passes pharynx → larynx → trachea → bronchi → bronchioles → alveoli → diffuses into capillaries → oxygenated blood returns to heart → pumped to tissues.

Breathing regulation

Cellular respiration produces CO₂, which lowers pH. This is detected by chemoreceptors, which signal the brain to increase the breathing rate to expel more CO₂ and normalize pH.

Nitrogenous waste types

1. Ammonia: Most toxic, requires a lot of water for excretion (aquatic animals) 2. Urea: Less toxic, water-soluble, moderate energy cost (mammals) 3. Uric acid: Least toxic, requires more energy, no water loss (birds, reptiles).

Steps in the process of excretion

1. Filtration: Blood enters glomerulus → Bowman's capsule 2. Reabsorption: Useful molecules reclaimed in the tubules 3. Secretion: Unwanted solutes added to filtrate 4. Excretion: Urine flows to ureter → bladder → urethra → exits body.

Open circulatory system

Blood is not always contained in vessels (e.g., insects).

Closed circulatory system

Blood is contained in vessels (e.g., vertebrates).

Circulatory systems in fish

2-chambered heart, single circuit.

Circulatory systems in amphibians

3 chambers, dual circuits (pulmocutaneous/systemic).

Circulatory systems in mammals

4 chambers, pulmonary and systemic circuits.

Pathway of oxygenated blood

Oxygen enters pulmonary veins → left atrium → left AV valve → left ventricle → aortic valve → aorta → arteries → capillaries → tissues.

SA node

Fires, atria contract → signal pauses at AV node → travels through bundle branches → Purkinje fibers carry signal → ventricles contract

Lymphatic system

Functions: Immunity (WBCs in lymph nodes), Fluid recovery (returns plasma to circulatory system), Lipid absorption (transports lipids from the SI)

Components of blood

Plasma: Water, ions, proteins, nutrients, hormones, gases, waste; Cells: Erythrocytes (RBCs), Leukocytes (WBCs), Platelets

Blood clotting process

Platelet plug forms → Platelets release clotting factors → Prothrombin → thrombin → fibrinogen → fibrin forms clot

Innate immunity

Fast, non-specific (e.g., skin, phagocytes)

Acquired immunity

Slow, specific, memory (e.g., T/B cells)

Immune/inflammatory response steps

Pathogen enters → Histamines and cytokines released → Blood vessels dilate → WBCs destroy pathogens → Positive feedback loop until threat is eliminated

Adaptive immune response

APC engulfs pathogen → presents antigen → Helper T cell activates Cytotoxic T cells and B cells → B cells produce antibodies, T cells kill infected cells

Role of vaccines

Vaccines trigger a primary immune response, creating memory cells for faster, stronger secondary immune responses when exposed to pathogens

Vaccination process steps

Vaccine introduces antigen → Primary immune response (slow and weak) → Creates memory cells → Secondary immune response is faster, stronger

Types of pathogens

1. Bacteria (e.g., E. coli, strep) 2. Viruses (e.g., SARS-CoV2, influenza) 3. Parasites (e.g., tapeworms, malaria)

Lifecycle of malaria parasite

Mosquito injects sporozoites → liver → merozoites released → merozoites infect RBCs → gametocytes formed → mosquito picks up gametocytes → fertilization occurs → sporozoites are released

Countermeasures for SARS-CoV2

Antivirals (reduce CFR), Masks (reduce transmission), Vaccines (produce memory response, reduce spread), Contact tracing (break transmission chains)

Structure of DNA

DNA is a double helix composed of two strands of nucleotides, with adenine pairing with thymine and cytosine pairing with guanine

Steps of DNA replication

1. Helicase unwinds the DNA 2. DNA polymerase adds complementary nucleotides 3. Ligase seals gaps between fragments 4. Leading and lagging strands are formed

Central dogma of molecular biology

DNA → RNA → Protein (transcription in nucleus, translation in cytoplasm)

Genotype

Genetic makeup of an organism

Phenotype

Observable traits influenced by genotype and environment

Mendel's law of segregation

Alleles for a gene segregate (separate) during gamete formation, and each gamete carries only one allele for each gene

Mendel's law of independent assortment

Genes for different traits assort independently during gamete formation (for genes located on different chromosomes)

Types of genetic mutations

Point mutation (substitution), frameshift (insertions or deletions), silent mutation, missense mutation, nonsense mutation

Dominant traits

Expressed if at least one allele is dominant

Recessive traits

Require two copies of the recessive allele to be expressed

Natural selection

The process by which organisms with favorable traits survive and reproduce more successfully than those without, leading to adaptation to the environment