Mini-Textbook Study Notes: Nervous System Structure and Function

Nervous System Structure and Function

Overview of Nervous System Organization

The nervous system is a complex network responsible for coordinating the body's activities by transmitting signals between different parts. It is divided into central and peripheral components, each with specialized functions.

• Central Nervous System (CNS): Consists of the brain and spinal cord. It processes information and directs responses.

• Peripheral Nervous System (PNS): Composed of nerves and ganglia outside the CNS. It transmits sensory and motor signals to and from the CNS.

• Somatic Nervous System: Controls voluntary movements and transmits sensory information.

• Autonomic Nervous System: Regulates involuntary functions (e.g., heart rate, digestion).

Example: The CNS interprets sensory input from the PNS and initiates motor output.

Types of Nervous Tissue

Nervous tissue is specialized for communication and consists of two main cell types: neurons and glial cells.

• Neurons: The functional units of the nervous system, responsible for transmitting electrical impulses.

• Glial Cells: Support, nourish, and protect neurons. Types include astrocytes, oligodendrocytes, Schwann cells, and microglia.

Example: Schwann cells form myelin sheaths around peripheral nerves, increasing signal transmission speed.

Neuron Structure and Function

Neurons have specialized structures for receiving and transmitting signals.

• Dendrites: Receive incoming signals from other neurons.

• Cell Body (Soma): Contains the nucleus and organelles; integrates signals.

• Axon: Conducts electrical impulses away from the cell body.

• Synapse: Junction between neurons where neurotransmitters are released.

Example: Motor neurons transmit signals from the CNS to muscles, causing contraction.

Action Potential and Signal Transmission

Neurons communicate via electrical impulses called action potentials, which are generated by changes in membrane potential.

• Resting Potential: The membrane potential of a neuron at rest, typically around -70 mV.

• Depolarization: Sodium ions (Na+) enter the cell, making the inside more positive.

• Repolarization: Potassium ions (K+) exit the cell, restoring negative charge.

• Propagation: Action potentials travel along the axon to the synapse.

Equation:

$\Delta V = V_{final} - V_{initial}$

Example: Action potentials allow rapid communication between distant parts of the body.

Synaptic Transmission

At the synapse, electrical signals are converted to chemical signals via neurotransmitters.

• Neurotransmitters: Chemical messengers released from synaptic vesicles.

• Postsynaptic Receptors: Bind neurotransmitters, triggering a response in the next neuron.

• Excitatory vs. Inhibitory: Excitatory neurotransmitters promote action potentials; inhibitory prevent them.

Example: Acetylcholine is an excitatory neurotransmitter at neuromuscular junctions.

Classification of Neurons

Neurons are classified based on structure and function.

• Sensory Neurons: Carry information from sensory receptors to the CNS.

• Motor Neurons: Transmit signals from the CNS to effectors (muscles/glands).

• Interneurons: Connect neurons within the CNS, facilitating integration.

Example: Reflex arcs involve sensory, interneuron, and motor neuron pathways.

Organization of the Peripheral Nervous System

The PNS is divided into somatic and autonomic branches, each with distinct roles.

• Somatic: Controls voluntary movements and sensory input.

• Autonomic: Regulates involuntary functions; subdivided into sympathetic and parasympathetic systems.

Example: The sympathetic system increases heart rate during stress; the parasympathetic system slows it down.

Summary Table: Nervous System Components

The following table summarizes the main components and functions of the nervous system:

Component	Main Function	Example
Central Nervous System	Integration and processing	Brain interprets sensory input
Peripheral Nervous System	Transmission of signals	Nerves carry signals to/from CNS
Somatic Nervous System	Voluntary control	Movement of skeletal muscles
Autonomic Nervous System	Involuntary regulation	Heart rate, digestion

Additional info:

Some diagrams and handwritten notes were interpreted and expanded for clarity. The included images are directly relevant to neuron structure, action potential, synaptic transmission, and PNS organization.