Neurobiology and Nervous System Organization Notes

Dendrites: These structures are responsible for receiving signals from the presynaptic neuron.
Synaptic Cleft: The physical gap between the Dendrites of the post-synaptic neuron and the presynaptic terminal.
Cell Body: A single neuron typically contains $1$ cell body.
Axon: The long projection that conducts electrical impulses away from the cell body.
Nerve: Defined as multiple neurons bundled together.
Peripheral Nervous System (PNS): Contains all nerves in the body except for the cranial nerves.
Axon Hillock: The site where summation occurs. It processes both Inhibitory and Excitatory signals. If the signal strength is high enough ("sight pass on"), an action potential is generated.
Myelination: * Schwann cells: Responsible for making myelin in the PNS; these are composed of Fats. * Oligodendrocytes: Responsible for making myelin in the CNS.
Ganglia: Collections of cell bodies in the PNS.

General Function: Support, nourishment, and myelination of neurons.
$1$ Astrocytes: Provide nourishment to neurons and contribute to the Blood-Brain Barrier (BBB).
$2$ Ependymal cells: Line the ventricles of the brain and are responsible for producing Cerebrospinal Fluid (CSF).
$3$ Microglia: Phagocytic cells that ingest cellular waste and pathogens.
$4$ Oligodendrocytes / Schwann cells: Support the neurons through the process of myelination.

Summation Types: * Spatial Summation: Summation based on the physical location of the inputs. * Temporal Summation: Summation based on the timing/frequency of inputs.
Steps of Signal Transmission: 1. The cell reaches the threshold potential. 2. Voltage-gated $Na^+$ channels open. 3. $Na^+$ influx occurs, causing further depolarization. 4. The membrane potential reaches a peak of approximately $+35\,mV$ . 5. The $Na^+$ channel inactivates at this peak. 6. $K^+$ flows out of the cell as voltage-gated $K^+$ channels open. 7. Repolarization begins as the cell loses positive charge. 8. $K^+$ channels close slowly, leading to an overshoot of the resting membrane potential, known as hyperpolarization (dropping below $-70\,mV$ ). 9. The resting potential will be restored. 10. $Na^+/K^+$ ATPase activity restores and maintains the resting potential.
Saltatory Conduction: The specific way an electrical impulse "skips" down a myelinated axon, jumping from node to node.

Storage: Neurotransmitters are stored in vesicles inside the presynaptic nerve terminals.
Release: A signal (referenced in transcript as "IE.gssIikIsiy1") leads to vesicle release via the process of exocytosis.
Post-Synaptic Impact: The NT acts on the effector (post-synaptic receptor) and can be either Excitatory or Inhibitory.
Inhibitory Examples: * GABA. * Alcohol. * Barbiturates. * Midazolam. * Lorazepam.
Methods to Modulate NT Activity: 1. Enzymatic Breakdown: For example, Acetylcholine (ACh) in the synaptic cleft is rapidly broken down by the enzyme Acetylcholinesterase (AChE). 2. Reuptake Carriers: For example, SSRIs (Selective Serotonin Reuptake Inhibitors). The body naturally attempts to bring neurotransmitters back into the presynaptic neuron; SSRIs block this ability, allowing Serotonin to act longer on the postsynaptic receptor. 3. Diffusion: Neurotransmitters can simply diffuse out of the synaptic cleft.

Central Components: The Brain and the Spine.
Autonomic Nervous System: Responsible for functions humans cannot consciously control, such as temperature regulation. * Sympathetic Nervous System. * Parasympathetic Nervous System.
Spinal Column Divisions: * Cervical. * Thoracic. * Lumbar. * Sacral spine.
Nerve Architecture in the Spine: * Dorsal Root Ganglion: Contains Sensory neurons; located at the Back of the spinal cord. * Motor Neurons: Located at the Front of the spinal cord.