Chapter 11: Nervous System – Structure, Function, and Integration

General Functions of the Nervous System

Overview of Nervous System Functions

The nervous system is responsible for coordinating and regulating bodily activities through rapid communication and integration of signals. It is essential for sensation, movement, cognition, and homeostasis.

• Main Functions: Sensory input, integration, motor output, and regulation of homeostasis.

• Example: Reflex actions such as withdrawal from a painful stimulus.

Organization of the Nervous System

Central vs. Peripheral Nervous System

The nervous system is divided into the central nervous system (CNS) and peripheral nervous system (PNS). Each has distinct structures and functions.

• CNS: Composed of the brain and spinal cord; responsible for processing and integrating information.

• PNS: Consists of nerves and ganglia outside the CNS; transmits signals between the CNS and the rest of the body.

• Comparison: CNS is the main control center, while PNS acts as a communication network.

Afferent vs. Efferent Divisions

The PNS is further divided into afferent (sensory) and efferent (motor) divisions.

• Afferent Division: Transmits sensory information to the CNS.

• Efferent Division: Carries motor commands from the CNS to effectors (muscles and glands).

Somatic vs. Autonomic Nervous System

The efferent division is subdivided into the somatic and autonomic nervous systems.

• Somatic Nervous System: Controls voluntary movements via skeletal muscles.

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

• Autonomic Subdivisions: Sympathetic and parasympathetic divisions.

General Anatomy of the Nervous System

Structural Organization

The nervous system consists of gray and white matter, nuclei, and ganglia, each with specific roles.

• Gray Matter: Contains neuron cell bodies; involved in processing information.

• White Matter: Composed of myelinated axons; responsible for signal transmission.

• Nuclei: Clusters of neuron cell bodies within the CNS.

• Ganglia: Clusters of neuron cell bodies in the PNS.

Protective Roles of Cranial Bones, Vertebral Column, Meninges, and Cerebrospinal Fluid (CSF)

Protection of the CNS

The CNS is protected by bony structures, meninges, and cerebrospinal fluid.

• Cranial Bones & Vertebral Column: Provide rigid protection for the brain and spinal cord.

• Meninges: Three layers (dura mater, arachnoid mater, pia mater) that encase the CNS.

• Cerebrospinal Fluid (CSF): Cushions the CNS, removes waste, and provides nutrients.

Protective Structure	Main Function
Cranial Bones	Protect the brain from mechanical injury
Vertebral Column	Protects the spinal cord
Meninges	Enclose and protect CNS tissues
CSF	Cushions, nourishes, and removes waste

Neuroglial (Glial) Cells

Types and Functions

Neuroglial cells support neurons structurally and functionally. They are essential for maintaining the environment of the nervous system.

• Astrocytes: Maintain the blood-brain barrier, regulate ion balance.

• Oligodendrocytes: Form myelin sheaths in the CNS.

• Schwann Cells: Form myelin sheaths in the PNS.

• Microglia: Act as immune cells within the CNS.

• Ependymal Cells: Line ventricles and produce CSF.

Neurons: Structure and Function

Neuron Anatomy

Neurons are the functional units of the nervous system, specialized for communication.

• Key Parts: Cell body (soma), dendrites, axon, axon terminals.

• Types: Unipolar, bipolar, multipolar neurons.

• Function: Transmit electrical and chemical signals.

Membrane Potentials and Action Potentials

Resting Membrane Potential

The resting membrane potential is the electrical charge difference across the neuron's membrane.

• Typical Value: About -70 mV in neurons.

• Maintained by: Sodium-potassium ATPase pump and selective permeability of the membrane.

Equation:

$V_m = V_{inside} - V_{outside}$

Action Potentials

Action potentials are rapid changes in membrane potential that propagate along axons.

• Phases: Depolarization, repolarization, hyperpolarization.

• Key Channels: Voltage-gated sodium and potassium channels.

• Propagation: Saltatory conduction in myelinated axons; continuous in unmyelinated axons.

Synaptic Transmission: Neurotransmitters and Neuromodulators

Synapse Structure and Function

Synapses are junctions where neurons communicate via neurotransmitters.

• Types: Chemical (most common) and electrical synapses.

• Neurotransmitters: Acetylcholine, dopamine, serotonin, GABA, glutamate, etc.

• Neuromodulators: Substances that modify synaptic transmission (e.g., neuropeptides).

Integration of Neural Information

Neural Circuits and Pathways

Neural integration involves processing and combining signals from multiple sources to produce coordinated responses.

• Neural Circuits: Diverging, converging, reverberating, and parallel after-discharge circuits.

• Purpose: Allows complex processing such as reflexes, learning, and memory.

Structural and Functional Organization of the Brain

Major Brain Regions

The adult brain consists of several major regions, each with specialized functions.

• Cerebrum: Responsible for higher cognitive functions, voluntary movement, and sensory perception.

• Diencephalon: Includes the thalamus and hypothalamus; involved in sensory relay and homeostasis.

• Brainstem: Controls basic life functions (e.g., breathing, heart rate).

• Cerebellum: Coordinates movement and balance.

Brain Region	Main Function
Cerebrum	Conscious thought, memory, voluntary movement
Diencephalon	Sensory relay, homeostasis
Brainstem	Autonomic functions
Cerebellum	Coordination, balance

Homeostasis: The Role of the Brain

Brain and Homeostasis

The brain maintains homeostasis by integrating sensory information and regulating physiological processes.

• Endocrine vs. Nervous System: Both systems maintain homeostasis, but the nervous system acts rapidly while the endocrine system acts more slowly.

• Example: Regulation of body temperature, blood pressure, and fluid balance.

Structural and Functional Organization of the Spinal Cord

Spinal Cord Anatomy

The spinal cord is organized into segments, each with specific functions and anatomical features.

• Gray Matter: Central region containing neuron cell bodies.

• White Matter: Surrounds gray matter; contains ascending and descending tracts.

• Roots: Dorsal (sensory) and ventral (motor) roots connect the spinal cord to the PNS.

Role of CNS in Sensation

Sensory Pathways

The CNS processes sensory stimuli through specific pathways.

• First-, Second-, Third-Order Neurons: Relay sensory information from receptors to the brain.

• Example: Pain, touch, and proprioception pathways.

Role of CNS in Voluntary Movement

Motor Pathways

Voluntary movement is controlled by the CNS through complex motor pathways.

• Upper and Lower Motor Neurons: Coordinate muscle contraction.

• Key Structures: Cerebral cortex, basal nuclei, cerebellum.

• Pathway: Decision to move → initiation → execution → monitoring.

*Additional info: Some details were inferred and expanded for clarity and completeness based on standard Anatomy & Physiology curriculum topics.*