Biological Bases of Behavior: The Nervous System – Study Notes

Overview of the Nervous System

Central and Peripheral Nervous System

The nervous system is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Each plays a crucial role in processing and transmitting information throughout the body.

• Central Nervous System (CNS): Consists of the brain and spinal cord. It is responsible for integrating sensory information and responding accordingly.

• Peripheral Nervous System (PNS): Composed of cranial and spinal nerves and peripheral ganglia. It connects the CNS to limbs and organs.

Types of Neurons

Functional Classification

Neurons are specialized cells that transmit nerve impulses. They are classified based on their function:

• Sensory Neurons (Afferent): Detect changes in the internal and external environment and carry information from sensory organs to the brain.

• Motor Neurons (Efferent): Control muscle contraction and movement by transmitting information from the brain to the organs and muscles.

• Interneurons: Relay information between sensory and motor neurons, primarily within the CNS.

Glial Cells of the Nervous System

Types and Functions

Glial cells are non-neuronal cells in the CNS that provide support and protection for neurons. They have several important functions:

• Astrocytes: Provide physical support, regulate the chemical environment, and supply nutrients (such as lactate) to neurons.

• Oligodendrocytes: Produce the myelin sheath around axons in the CNS, which increases the speed of electrical impulses.

• Microglia: Act as the immune defense in the CNS by removing debris and protecting against invading organisms via phagocytosis.

Additional info: In the PNS, Schwann cells perform a similar myelination function as oligodendrocytes.

Structure of Neurons

Basic Anatomy

Neurons have specialized structures that enable them to transmit signals efficiently:

• Soma (Cell Body): Contains the nucleus and most of the cell's organelles. It is responsible for the general metabolic functions of the neuron.

• Dendrites: Branch-like extensions that receive information from other neurons.

• Axon: A long projection that transmits electrical impulses (action potentials) away from the soma to other neurons or muscles.

• Myelin Sheath: A fatty layer that surrounds and insulates axons, increasing the speed of impulse transmission.

• Nodes of Ranvier: Gaps in the myelin sheath where action potentials are regenerated, allowing for rapid signal conduction (saltatory conduction).

• Axon Terminals (Terminal Buttons): The endpoints of axons where neurotransmitters are released to communicate with other cells.

Neuronal Communication

Synapses and Neurotransmitters

Neurons communicate with each other at specialized junctions called synapses:

• Synapse: The junction between the axon terminal of one neuron and the dendrite or soma of another neuron.

• Neurotransmitter: Chemical messengers released by neurons at the synapse, which can have excitatory or inhibitory effects on the postsynaptic cell.

Example: Acetylcholine is a neurotransmitter that stimulates muscle contraction.

Summary Table: Major Cell Types in the Nervous System

Cell Type	Location	Main Function
Neuron	CNS & PNS	Transmit electrical and chemical signals
Astrocyte	CNS	Support, nourish, and regulate environment
Oligodendrocyte	CNS	Produce myelin sheath
Microglia	CNS	Immune defense, phagocytosis
Schwann Cell	PNS	Produce myelin sheath

Key Terms and Definitions

• Myelin Sheath: Insulating layer around axons that increases the speed of nerve impulse transmission.

• Node of Ranvier: Gaps in the myelin sheath where action potentials are regenerated.

• Synapse: Site of communication between two neurons.

• Neurotransmitter: Chemical substance that transmits signals across a synapse.

• Afferent: Carrying information toward the CNS (sensory).

• Efferent: Carrying information away from the CNS (motor).

Additional info:

• Saltatory conduction, enabled by myelin and nodes of Ranvier, allows action potentials to "jump" from node to node, greatly increasing conduction speed.

• Damage to myelin (as in multiple sclerosis) can severely impair nervous system function.