Nervous System and Neuron Overview

Nervous System Functions

Sensory Input: Gathers information from sensory receptors (skin, eyes, interoceptors) detecting internal and external changes.
Integration: Brain and spinal cord process sensory input, make decisions, coordinate actions incorporating thinking and planning.
Motor Output: Sends commands via motor neurons to muscles and glands for specific responses (movement, sweating, hormone release).

Anatomical: Central Nervous System (CNS) and Peripheral Nervous System (PNS).
Functional(PNS):
- Autonomic: Self-regulation of internal organs and glands (sympathetic - arousing, parasympathetic - calming).
- Somatic: Conscious control of skeletal muscles.
Afferent vs Efferent:
- Afferent: Sensory information towards the CNS (visceral and somatic senses).
- Efferent: Motor commands from the CNS to muscles and glands.
Motor Division: Somatic (conscious control), visceral (automatic).

Ependymal Cells: Produce and circulate cerebrospinal fluid; line ventricles in brain and spinal cord.
Oligodendrocytes: Form myelin sheaths around nerve fibers in the CNS, enhancing signal speed.
Astrocytes: Support neurons, maintain blood-brain barrier, provide nutrients.
Satellite Cells: Structural support and regulate extracellular environments and also modulate the neuronal signaling as well.
Schwann Cells: Produce myelin in the PNS, support nerve regeneration.
- Nerves (PNS) vs. Tracts (CNS).

Sensory Neurons (Afferent): Transmit information from sensory receptors to the CNS.
Motor Neurons (Efferent): Transmit information from the CNS to muscles and glands.
Interneurons: Connect sensory and motor neurons within the CNS.

Cell Body (Soma): Contains nucleus and organelles.
Dendrites: Receive sensory information and transmit it to the cell body.
Axon Hillock: Integrates excitatory and inhibitory signals to decide whether to fire an action potential.
Axon: Carries electrical activity (action potential) from the cell body to synaptic terminals; can be myelinated for faster transmission.
Myelin Sheaths: Insulate the axon, facilitating rapid transmission.
Synaptic Terminals: Release neurotransmitters to communicate with postsynaptic neurons across the synaptic cleft.

Plasma membrane acts as a semi-permeable barrier, maintaining charge difference.
Resting Membrane Potential (RMP):
- Neurons have more negatively charged proteins inside, leading to a negative charge (-50 to -70 mV).
- Maintained by sodium-potassium pump, moving 3 Na^+ out and 2 K^+ in, using ATP.
- Measured in millivolts (mV).

Depolarization: Membrane potential becomes less negative, moving towards zero (excitatory).
Hyperpolarization: Membrane potential becomes more negative, moving further from zero (inhibitory).
Repolarization: Return to resting membrane potential after depolarization.