Chapter 2 - Everything Neurons

Golgi Staining

a dye method to label neurons in brain slices from many different animals

Reticular Theory (Camillo Golgi)

The cells of the brain are all directly connected to each other; forming a continuous network

Neuron Doctrine (Santiago Ramon y Cajal)

Each cell in the brain is independent of other cells, there are no continuous connections between the cells of the brain

Connectome

A reconstructive “map” of every neuron and its connections

Neurons

Highly specialized cell that has the same components of all other cells in our body (nucleus, mitochondria, ribosomes, etc.)

Neuron Organization: Dendrites

“input zone”

Branching offshoots from the cell body, site where information is received from neurons;

Packed full of neurotransmitter receptors where chemicals released from other neurons bind to influence activity

Dendrite Types

Basal Dendrite: near the cell body;

Apical Dendrite: far from the cell body

Neuron Organization: Soma/Cell Body

“integration zone”

Cell body of the neuron where the primary organelles are located;

Site where dendrites and axons are sprouted;

Specialized area of the soma where the axon begins is the axon hillock

The Soma/Cell Body’s Axon Hillock

Where neurons integrate the thousands of inputs and decide whether or not to “fire” (send a signal)

Neuron Organization: Axon

“conduction zone”

A long, cable-like offshoot of the soma used for transmitting electrical signals;

Wrapped tightly in myelin

Myelinated Axons

Myelin: a fatty sheath that serves as electrical insulation;

Nodes of Ranvier: Tiny gaps in the myelin sheath where electrical ions can flow into the axon

Neuron Organization: Axon Terminal

“output zone”

Specialized swelling at the end of axons where a neuron transforms an electrical signal into chemical release;

Packed full of synaptic vesicles which hold and release neurotransmitters (chemical messengers);

From ~100 billions neurons we estimate ~500 trillion synapses

Axonal Transport

Electrical signals travel unidirectionally from the cell body to the axon terminal

Direction of Flow

Anterograde Transport: from the cell body to the axon terminal;

Retrograde Transport: from the axon terminal to the cell body

Glial Cells

Non-neuronal cells in our brains

Types of Glial Cells

Oligodendrocytes: form the fatty myelin sheath around axons;

Astrocytes: form the blood brain barrier and supply neurons with energy;

Microglia: the immune cells of the brain that eat debris

The Synapse

The gap between an axon terminal and the post-synaptic neuron

Electrical Signaling

Neurons transform an electrical signal into a chemical signal, which are conveyed via the synapse

Electrochemical Gradients

The difference in electrical charge and chemical concentration between the semipermeable cell membrane

Voltage

Referential measurement that quantifies the electrical charge difference across the neuronal membrane

Resting Membrane Potential

The stable electrical charge difference across a cell’s membrane when it is not actively sending signals;

Neurons resting membrane potential is around -70 mV (more negatively charged at rest relative to surroundings)

Concentrations of chemical within and outside the cell

Inside the cell: high concentration of negatively charged proteins and potassium (K+), proteins are too big to transfer across the membrane;

Outside the cell: high concentration of sodium (Na+), chloride (Cl-), and calcium (Ca2+)