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Brennan’s Cardiology Notes

This is how I not only passed but learned to understand cardiology. I took my chaotic notes and put them into an easy to read pocket guide. There are 10 steps to quickly reading an EKG but I’ve broken it up because some of the steps are long. I’m open to corrections,additions, helpful hints, etc.

The central nervous system (which includes the brain and spinal cord) is made up of two basic types of cells: neurons and glia. 

Neurons are information messengers. 

Use electrical impulses and chemical signals to transmit information between different areas of the brain, and between the brain and the rest of the nervous system. 

Supported by glial cells called astrocytes and oligodendrocytes

Within the cell body is a nucleus: controls the cell’s activities and contains the cell’s genetic material. 

Axon transmits messages from the cell. 

Dendrites receive messages for the cell. 

Neurons communicate sending neurotransmitters across a tiny space, (synapse) between the axons and dendrites of adjacent neurons.

There are three classes of neurons:

Sensory neurons carry information from the sense organs (such as the eyes and ears) to the brain.

Motor neurons control voluntary muscle activity such as speaking.

All the other neurons are  interneurons.

Birth

The extent to which new neurons are generated in the brain is a controversial subject. 

Mmajority of neurons are already present at birth

There is evidence to support that neurogenesis (creation of neurons) is a lifelong process.

Neurons are created in areas of the brain that are rich in concentrations of neural precursor cells (also called neural stem cells). These cells have the potential to generate most, if not all, of the different types of neurons and glia found in the brain.

Neural stem cells increase by dividing in two and producing either two new stem cells, or two early progenitor cells, or one of each.

Stem cell divides to produce another stem cell = self-renew. 

Stem cell divides to produce an early progenitor cell = differentiate. -> the new cell is more specialized in form and function. 

An early progenitor cell does not have the potential of a stem cell to make many different types of cells. It can only make cells in its particular lineage.

Early progenitor cells can self-renew or go in either of two ways. One type will give rise to astrocytes. The other type will ultimately produce neurons or oligodendrocytes.

Migration

Neurons use at least two different methods to travel to the area they need to work in:

Some neurons migrate by following the long fibers of cells called radial glia. These extend from the inner layers to the outer layers of the brain. 

Neurons also travel by using chemical signals. Adhesion molecules on the surface of neurons bind with similar molecules on nearby glial cells or nerve axons. These chemical signals guide the neuron to its final location.

Only a third reach their destination. Some cells die during the process of neuronal development. Some neurons survive the trip, but end up where they shouldn’t be. Mutations in the genes that control migration create areas of misplaced or oddly formed neurons that can cause disorders such as childhood epilepsy. 

Differentiation

In the developing brain, a neuron depends on molecular signals from other cells, such as astrocytes, to determine its shape and location, the kind of transmitter it produces, and to which other neurons it will connect. These freshly born cells establish neural circuits - or information pathways connecting neuron to neuron - that will be in place throughout adulthood.

Death

Although neurons are the longest living cells in the body, large numbers of them die during migration and differentiation.

The lives of some neurons can take abnormal turns. Some diseases of the brain are the result of the unnatural deaths of neurons.

- In Parkinson’s disease, neurons that produce the neurotransmitter dopamine die off in the basal ganglia, an area of the brain that controls body movements. This causes difficulty initiating movement.

- In Huntington’s disease, a genetic mutation causes over-production of a neurotransmitter called glutamate, which kills neurons in the basal ganglia. As a result, people twist and writhe uncontrollably.

- In Alzheimer’s disease, unusual proteins build up in and around neurons in the neocortex and hippocampus, parts of the brain that control memory. When these neurons die, people lose their capacity to remember and their ability to do everyday tasks. Physical damage to the brain and other parts of the central nervous system can also kill or disable neurons.

- Blows to the brain, or the damage caused by a stroke, can kill neurons outright or slowly starve them of the oxygen and nutrients they need to survive.

- Spinal cord injury can disrupt communication between the brain and muscles when neurons lose their connection to axons located below the site of injury. These neurons may still live, but they lose their ability to communicate.

Types of Spinal Cord Injury (SCI)

Typical complications of SCI include: Autonomic Dysreflexia (AD) Orthostatic Hypotension (OH) Spinal Shock Spasticity and Hypertonia Contracture Pain Deep Vein Thrombosis (DVT) Heterotopic Ossification Osteoporosis and Risk of Fracture Pressure Sores Impaired Temperature Control Pulmonary Impairment Bladder, Bowel and Sexual Impairments

You’re lucky I keep a file of interesting stuff. Here goes (I definitely have posts in the archive about some of these things):

Genetic: Marfan Syndrome, Type 1 Ehler’s Danlos, Mayer-Rokitansky-Kuster-Hauser (Müllerian agenesis) syndrome, Treacher-Collins Syndrome, Turner Syndrome, Osteogenesis Imperfecta, Rett Syndrome, Huntington’s disease, Apert Syndrome, Neurofibromatosis, Tuberous Sclerosis, Cornelia de Lange Syndrome

Neuro: Too much ALS, Progressive Supranuclear Palsy, Chronic Immune Demyelinating Polyneuropathy, a bilateral occipital stroke causing complete blindness (pretty rare), Guillain-Barré syndrome, Lennox-Gastaut Syndrome, Wernicke-Korsakoff Syndrome, Reflex Sympathetic Dystrophy as a late sequella of venomous snakebite

Heme-Onc: Bilateral Wilms Tumors, an intra-aorta tumor, Retinal Metastases of Breast cancer, Carcinoid Syndrome, Paraneoplastic Parkinson’s from Small cell lung cancer, hemophilia, systemic mastocytosis, Kaposi’s Sarcoma, Sézary Syndrome, Cutaneous B cell Lymphoma

Infectious (remember that I’ve done a good bit of tropical medicine):  Tertiary Syphillis + HSV Encephalitis in an AIDS patient, tons of Cerebral Malaria (and regular malaria) and typhoid, Elephantiasis, Onchocerciasis, Fournier’s Gangrene, Pericarditis, Endocarditis, Rheumatic Fever, Brucellosis, Sporotrichosis, Histoplasmosis, Pasturella Multocida infection of a tendon, MAC, disseminated MAC, lots of Pulmonary TB/Scrofula/Pott’s Disease, Congenital Rubella, Congenital Syphillis, lots of Zika and Chikungunya, Necrotizing Fasciitis, Empyemas, Giardia, Campylobacter infections, cutaneous leishmaniasis, Buruli ulcer, a possible case of Monkeypox (though we couldn’t test this…definitely a poxvirus tho), lots of intestinal worms, pulmonary nocardiosis, joint infection with Leuconostoc

Endocrine: Thyroid storm, Myxedema Coma, Addisonian Crisis, Cushing’s Disease, Pheochromocytoma, MEN Syndrome, Precocious puberty in a 5 year old

Nephro: Bartter and Gitelman Syndromes, Malaria-induced Nephrotic syndrome, Synthetic marijuana-induced end stage renal failure requiring dialysis

Toxic: Serotonin Syndrome, Neuroleptic Malignant Syndrome, tons of venomous snakebites including a few causing consumption coagulopathy and death, Carbon monoxide poisoning, Organophosphate poisoning, Formaldehyde poisoning from homemade vape juice gone wrong, lots of pica (although it’s sort of a cultural thing to eat clay)

Psych: Fixed Erotomanic Delusion, Cotard’s Delusion, Conversion Disorder, Depressive Pseudodementia, Menopausal psychosis, post-partum psychosis

Cardiac: Long QT Syndrome (congenital and acquired), HOCM, Takotsubo Cardiomyopathy, Prinzmetal angina secondary to diet pills, isolated dextrocardia, Tetralogy of Fallot - corrected and once uncorrected in an adolescent! Hypoplastic Left Heart, WPW, Dextrocardia + transposition of the great vessels.