Human Physiology - Neural Control and Coordination (Neuron, CNS, PNS, Reflex Action, Sense Organs)

The Neuron: Comprises the cell body ($Cyton$), $Dendrites$, and $Axon$. Myelinated neurons have $Nodes\ of\ Ranvier$ for saltatory conduction.

Nerve Impulse: Generation of action potential involves $Na^+$ influx (depolarization) and $K^+$ efflux (repolarization).

Resting Potential: The membrane is polarized at approximately $-70\ mV$ due to the $Na^+/K^+$ pump and leaky channels.

Synaptic Transmission: Chemical transmission via neurotransmitters (e.g., $Acetylcholine$) across the synaptic cleft from pre-synaptic to post-synaptic membranes.

Central Nervous System (CNS): Includes the Brain (Cerebrum for intelligence, Cerebellum for balance, Medulla for involuntary actions) and the Spinal Cord.

Peripheral Nervous System (PNS): Consists of Cranial nerves ($12\ pairs$) and Spinal nerves ($31\ pairs$). Divided into Somatic and Autonomic Nervous Systems.

Autonomic Nervous System (ANS): Comprises the Sympathetic ($fight\ or\ flight$) and Parasympathetic ($rest\ and\ digest$) systems.

Reflex Action: An involuntary response to a stimulus mediated by the reflex arc: $Receptor \rightarrow$ $Sensory\ Neuron \rightarrow$ $Interneuron\ (Spinal\ Cord) \rightarrow$ $Motor\ Neuron \rightarrow$ $Effector$.

The Eye: Structure includes $Sclera$, $Choroid$, and $Retina$. The $Retina$ contains photoreceptors: $Rods$ (twilight vision/rhodopsin) and $Cones$ (daylight/color vision/iodopsin).

The Ear: Outer ear collects sound, middle ear (ossicles: $Malleus$, $Incus$, $Stapes$) amplifies it, and inner ear ($Cochlea$) converts it to electrical signals. The $Vestibular\ apparatus$ maintains body equilibrium.