CNS vs. PNS Overview

Central Nervous System (CNS) vs. Peripheral Nervous System (PNS)

• CNS Structure: Brain (cerebrum, cerebellum, brainstem) and spinal cord, protected by skull and vertebrae, meninges, and cerebrospinal fluid.
• PNS Structure: All neural tissue outside the CNS, including cranial nerves (12 pairs), spinal nerves (31 pairs), and sensory/motor fibers.
• CNS Function: Integration and control center; interprets sensory input, coordinates motor output, and stores information.
• PNS Function: Transmits sensory input to the CNS and motor commands from the CNS to effectors. Sensory division transmits sensory input, and the motor division transmits motor commands.

Sensory (Afferent) vs. Motor (Efferent) Components

• Sensory (Afferent): Input pathways; carry signals from sensory receptors to the CNS. Divided into somatic sensory (external stimuli like pain, temperature, pressure) and visceral sensory (internal stimuli like organ stretch, chemical changes).
• Motor (Efferent): Output pathways; carry commands from the CNS to muscles/glands. Divided into somatic motor (voluntary; skeletal muscle activation) and autonomic motor (involuntary; smooth muscle, cardiac muscle, gland regulation).

Nervous System as a Control System

• Functional Steps: Sensory receptors detect stimuli, afferent pathways send signals to the CNS, control centers process input and formulate responses (reflex centers in spinal cord or higher brain processing).

Spinal Cord Anatomy and Reflexes

• Gross Anatomy: Cervical and lumbar enlargements (contain motor neurons for limbs); conus medullaris (tapered end of spinal cord), and cauda equina (nerve roots extending below spinal cord).
• Reflex Arc: Receptor → Sensory neuron → Integration center → Motor neuron → Effector.

Memory & Alzheimer's Disease

• Memory: Short-term memory involves temporary increase in synaptic efficiency; long-term memory involves synaptic remodeling and new dendritic spines.
• Alzheimer's Disease: Characterized by amyloid plaques, tau protein tangles, neuron death, and impaired memory and cognition.

Neuron Anatomy

• Components: Cell body (soma) containing the nucleus and organelles, including chromatophilic substance (nissl bodies). Dendrites receive incoming signals. Axon transmits action potentials; the axon hillock initiates action potentials.

Types of Neurons

• Sensory (Afferent): Transmit sensory input to CNS; structure is pseudounipolar.
• Interneurons (Association Neurons): Connect sensory and motor neurons; process information; entirely within the CNS.

Neuroglial (Glial) Cells

• CNS Glial Cells: Astrocytes (blood-brain barrier); Oligodendrocytes (myelinate CNS axons); Microglia (phagocytes); Ependymal cells (line ventricles, produce/circulate CSF).
• PNS Glial Cells: Schwann cells (myelinate PNS axons, aid in repair), satellite cells (support cell bodies in ganglia). Myelination: CNS oligodendrocytes wrap multiple axons, PNS Schwann cells wrap a single axon with nodes of Ranvier enabling saltatory conduction.

Resting Membrane Potential (RMP)

• Established by: Sodium-potassium ATPase pump (moves 3 Na+ out, 2 K+ in); K+ leak channels.
• Key Concepts: Depolarization (membrane potential becomes more positive due to Na+ influx); repolarization (membrane returns to resting state due to K+ efflux); hyperpolarization (membrane potential becomes more negative).

Graded vs. Action Potentials

• Graded Potentials: Localized changes in membrane potential; varying in size.
• Action Potentials: Rapid, all-or-none depolarization; signals propagate along axons.

Synaptic Transmission

• Steps: Action potential arrives at axon terminal, voltage-gated Ca2+ channels open, synaptic vesicles release neurotransmitter into cleft, neurotransmitter binds to postsynaptic receptors; excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) create depolarizing or hyperpolarizing signals.