Neural Structure, Function, and Physiology: Study Notes for Anatomy & Physiology

Nervous System Organization

Overview of Nervous System Organization

The nervous system is a complex network responsible for coordinating body activities and responding to internal and external stimuli. It is organized into central and peripheral divisions.

• Central Nervous System (CNS): Consists of the brain and spinal cord; processes information and issues commands.

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS; transmits signals between the CNS and the rest of the body.

• Functional Divisions: Sensory (afferent), motor (efferent), and integrative functions.

Neuroglia (Glial Cells)

Types, Locations, and Roles

Neuroglia are non-neuronal cells that support, protect, and nourish neurons. They are found throughout the CNS and PNS.

• Astrocytes: CNS; maintain blood-brain barrier, regulate nutrients.

• Oligodendrocytes: CNS; form myelin sheaths.

• Microglia: CNS; act as immune cells.

• Ependymal cells: CNS; line ventricles, produce cerebrospinal fluid.

• Schwann cells: PNS; form myelin sheaths.

• Satellite cells: PNS; support neuron cell bodies.

Neuron Structure and Classification

General Features of a Neuron

Neurons are specialized cells for transmitting electrical and chemical signals.

• Cell body (soma): Contains nucleus and organelles.

• Dendrites: Receive signals from other neurons.

• Axon: Transmits impulses away from the cell body.

• Axon terminals: Release neurotransmitters.

• Myelin sheath: Insulates axon, increases conduction speed.

Structural and Functional Classifications

• Structural: Multipolar, bipolar, unipolar neurons.

• Functional: Sensory (afferent), motor (efferent), interneurons.

Ohm’s Law and Its Relation to the Body

Application in Neurophysiology

Ohm’s Law describes the relationship between voltage, current, and resistance in electrical circuits, including biological membranes.

• Formula: $V = IR$

• Application: Explains how ion flow (current) across neuron membranes generates electrical signals.

Ion Channels in Neuron Membranes

Roles and Types of Ion Channels

Ion channels regulate the movement of ions across the neuronal membrane, crucial for generating electrical signals.

• Leak channels: Always open; maintain resting potential.

• Voltage-gated channels: Open in response to changes in membrane potential.

• Ligand-gated channels: Open in response to chemical signals.

• Mechanically-gated channels: Open in response to physical deformation.

Resting Membrane Potential

Generation of Resting Membrane Potential

The resting membrane potential is the electrical charge difference across the neuron membrane at rest, typically around -70 mV.

• Generated by: Unequal distribution of ions (Na+, K+) and selective permeability of the membrane.

• Sodium-potassium pump: Maintains ion gradients by pumping 3 Na+ out and 2 K+ in.

Depolarization vs. Hyperpolarization

Differences Explained

• Depolarization: Membrane potential becomes less negative (closer to zero).

• Hyperpolarization: Membrane potential becomes more negative.

Graded Potentials

Definition and Characteristics

Graded potentials are small changes in membrane potential that vary in size and decay with distance.

• Occur in: Dendrites and cell body.

• Can be: Depolarizing or hyperpolarizing.

Action Potentials

Generation and Propagation

An action potential is a rapid, all-or-none electrical signal that travels along the axon.

• Generated by: Opening of voltage-gated Na+ and K+ channels.

• Propagation: Sequential depolarization along the axon.

• Saltatory conduction: In myelinated axons, action potentials jump between nodes of Ranvier.

Conduction Velocity Factors

Factors Affecting Action Potential Speed

• Axon diameter: Larger diameter increases speed.

• Myelination: Myelinated axons conduct faster.

• Temperature: Higher temperature increases speed.

Nerve Fiber Classifications

Types of Nerve Fibers

Nerve fibers are classified based on diameter, myelination, and conduction velocity.

Type	Diameter	Myelination	Conduction Velocity
A fibers	Large	Myelinated	Fast
B fibers	Medium	Lightly myelinated	Moderate
C fibers	Small	Unmyelinated	Slow

Chemical Synapses

Structure and Function

Chemical synapses are specialized junctions where neurons communicate via neurotransmitters.

• Presynaptic neuron: Releases neurotransmitter.

• Synaptic cleft: Gap between neurons.

• Postsynaptic neuron: Receives signal via receptors.

Postsynaptic Potentials

Types and Effects

• Excitatory postsynaptic potential (EPSP): Depolarizes postsynaptic membrane, increases likelihood of action potential.

• Inhibitory postsynaptic potential (IPSP): Hyperpolarizes postsynaptic membrane, decreases likelihood of action potential.

Neurotransmitter Receptors

Types of Receptors

• Ionotropic receptors: Directly control ion channels; fast response.

• Metabotropic receptors: Indirectly affect ion channels via second messengers; slower, longer-lasting effects.

Neurotransmitter Classification

Functional Classifications

• Excitatory neurotransmitters: Promote action potentials (e.g., glutamate).

• Inhibitory neurotransmitters: Suppress action potentials (e.g., GABA).

• Modulatory neurotransmitters: Influence neuron activity (e.g., dopamine).

Neural Integration

Integration of Neural Signals

Neural integration refers to the process by which neurons combine multiple synaptic inputs to produce a coordinated output.

• Summation: Temporal and spatial summation of EPSPs and IPSPs.

• Threshold: If the combined input reaches threshold, an action potential is generated.

Additional info: Some content was inferred and expanded for completeness and clarity based on standard Anatomy & Physiology curriculum.