Chapter 3_ Neuroscience 1_ The Neuron _ Top Hat

Neuroscience explores the foundational aspects of thoughts, memories, and perceptions as electrochemical events in the central nervous system (CNS).
Experience of the world is mediated by these brain processes, not direct sensations.
Fundamental importance of understanding brain physiological activity for human thought and behavior.
Two primary avenues of investigation in neuroscience:
- Structural Questions: Focus on brain anatomy—what the brain is made of, its structure, and connections.
- Functional Questions: Understanding brain activity and how different parts function together.

The CNS comprising the brain (3.0 - 3.5 lbs, about 2% of body weight) and spinal cord is encased in bone.
The PNS encompasses all nerve tissues outside the CNS, facilitating communication between the CNS and body.
Components of brain cells:
- Glial Cells: Provide structure and perform housekeeping tasks in the brain.
- Neurons: Approximately 100 billion neurons in the human brain; responsible for integrative and communicative functions.
- Neurons network forms about 100 trillion connections, showcasing the complexity of the brain.

The investigation must consider different levels of organization:
- Large-scale brain anatomy.
- Specialized systems and neural circuitry.
- The neuron as a fundamental unit of the nervous system.

Philosophical discussions around the mind-body problem, notably examined by René Descartes (dualism).
- Dichotomy between body as a machine and the immaterial mind.
- Modern investigations in neurobiology have sought to bridge these concepts with scientific inquiry.
- Assertion: Mental changes correlate with physical brain changes.

Structure of a Neuron:
- Dendrites: Receive and integrate incoming information.
- Cell Body (Soma): Contains nucleus and organelles, processes signals.
- Axon: Transmits information to other cells, potentially extends long distances.
Neurons can form numerous connections through synapses.

Action potentials are the means by which neurons communicate.
- Initiation via changes in membrane potential—resting potential typically at -70 mV.
- Resting Potential: Established due to ion concentration differences across the membrane; primarily involves Na+, K+, and organic ions.
- Sodium-Potassium Pump: Active transport mechanism maintaining resting potential by moving Na+ out and K+ in.

Depolarization: When the potential reaches the threshold (~-50 mV), sodium channels open, and Na+ rushes in.
Repolarization: After reaching a peak (~+40 mV), k+ channels open, repolarizing the cell.
Refractory Period: Absolute and relative periods that prevent backward signal propagation.

Action potentials propagate via saltatory conduction in myelinated axons, speeding up transmission significantly.
The action potential is an all-or-nothing phenomenon—it either occurs fully or not at all, coded by the firing rate rather than amplitude.

Synapse: The connection point where neurotransmitters are released from the presynaptic cell and affect the postsynaptic cell.
Post-Synaptic Potentials (PSPs):
- Excitatory PSPs (EPSPs): Depolarizing potentials that increase likelihood of neuron firing.
- Inhibitory PSPs (IPSPs): Hyperpolarizing potentials that decrease likelihood of firing.
Neural Integration:
- Temporal Summation: Accumulation of PSPs from a single neuron over time.
- Spatial Summation: Simultaneous PSPs from multiple neurons influencing firing likelihood.

Understanding the neuron structure, function, and communication through its electrical activity and synaptic transmission is crucial in the field of neuroscience, laying the foundation for studying complex behaviors and cognitive processes.