Study Guide: Nervous System Structure and Function lesson 11

Nervous System Overview

Functions of the Nervous System

The nervous system is responsible for coordinating and regulating bodily activities by processing sensory information, integrating data, and producing motor responses.

• Sensory Input: The process of receiving information from sensory receptors about internal and external environments.

• Integration: The interpretation and processing of sensory input within the central nervous system (CNS).

• Motor Output: The transmission of signals from the CNS to effector organs (muscles or glands) to elicit a response.

Example: Touching a hot surface activates sensory receptors, the CNS processes the information, and motor output causes withdrawal of the hand.

Structural Divisions of the Nervous System

• Central Nervous System (CNS): Composed of the brain and spinal cord; responsible for integration and command.

• Peripheral Nervous System (PNS): Consists of nerves and ganglia outside the CNS; transmits signals between the CNS and the rest of the body.

Nerves and Ganglia

Cranial Nerves vs. Spinal Nerves

• Cranial Nerves: Emerge from the brain; primarily serve the head and neck.

• Spinal Nerves: Emerge from the spinal cord; serve the rest of the body.

Ganglia: Clusters of neuron cell bodies located in the PNS; act as relay points for transmitting signals.

Afferent vs. Efferent Signals

• Afferent (Sensory) Signals: Carry information from sensory receptors to the CNS.

• Efferent (Motor) Signals: Transmit commands from the CNS to effectors (muscles/glands).

Somatic vs. Visceral Sensory

• Somatic Sensory: Relates to sensations from skin, muscles, and joints.

• Visceral Sensory: Involves sensations from internal organs.

Structural Organization of the Nervous System

The nervous system is organized into the CNS and PNS, with further subdivisions based on function and structure.

Functional Divisions of the Nervous System

Somatic and Visceral Functions

Division	Function (General)	Function (Special)	Structures Innervated
Somatic Sensory	Detects stimuli from skin, muscles, joints	Touch, pain, temperature, proprioception	Skin, skeletal muscles, joints
Visceral Sensory	Detects stimuli from internal organs	Stretch, pain, chemical changes	Viscera (organs)
Somatic Motor	Voluntary control of skeletal muscles	Movement	Skeletal muscles
Visceral Motor (Autonomic Nervous System)	Involuntary control of smooth muscle, cardiac muscle, glands	Regulation of organ function	Viscera, glands, heart

Autonomic Regulation of the Heart

• Autonomic Nervous System (ANS): Regulates contraction of cardiac muscle in the heart.

Types of Sensation

• Pain from a pulled muscle: Somatic sensory

• Nausea: Visceral sensory

• Taste: Special sensory

Cells of the Nervous System

Types of Cells

• Neurons: Excitable cells that transmit electrical signals.

• Neuroglia (Glial Cells): Support, protect, and nourish neurons.

Functional Characteristics of Neurons

• Excitability: Ability to respond to stimuli.

• Conductivity: Ability to transmit electrical impulses.

• Secretion: Release of neurotransmitters.

Neuron Structures

• Cell Body (Soma): Contains nucleus and organelles.

• Dendrite: Receives incoming signals.

• Axon: Transmits impulses away from the cell body.

• Axon Hillock: Region where action potentials are initiated.

• Nerve Fiber: General term for a long axon.

• Terminal Bouton (Axon Terminal): Releases neurotransmitters to communicate with other cells.

Structural Types of Neurons

Type	Number of Processes	Location in Body	Function
Multipolar Neuron	Many dendrites, one axon	CNS, motor neurons	Motor function, integration
Bipolar Neuron	One dendrite, one axon	Special senses (retina, olfactory epithelium)	Sensory function
Unipolar Neuron	Single process splits into two branches	PNS, sensory neurons	Sensory function

Central process vs. peripheral process: In unipolar neurons, the peripheral process receives sensory input, while the central process transmits signals to the CNS.

Functional Classes of Neurons

Type	Function	Structural Type	Location in Body
Sensory Neuron	Transmit sensory information to CNS	Unipolar (mostly)	PNS
Motor Neuron	Transmit motor commands from CNS	Multipolar	CNS, PNS
Interneuron	Integrate information within CNS	Multipolar	CNS

Neuron Cell Bodies and Signal Direction

• Neuron cell bodies in CNS: Located in gray matter (nuclei).

• Neuron cell bodies in PNS: Located in ganglia.

• Signals through dendrites: Always toward the cell body.

• Signals through axons: Always away from the cell body.

Neuroglia (Glial Cells)

Type	Structural Characteristics	Function	CNS or PNS?	Special Characteristics
Astrocytes	Star-shaped, many processes	Support neurons, regulate environment	CNS	Blood-brain barrier
Microglial Cells	Small, mobile	Phagocytosis (immune defense)	CNS	Remove debris
Ependymal Cells	Line ventricles, ciliated	Produce and circulate cerebrospinal fluid	CNS	Form choroid plexus
Oligodendrocytes	Few processes	Form myelin sheaths	CNS	Myelinate multiple axons
Satellite Cells	Surround neuron cell bodies	Support and protect neurons	PNS	Regulate environment
Schwann Cells	Wrap around axons	Form myelin sheaths	PNS	Myelinate single axon

Myelin and Myelin Sheaths

• Myelin: Fatty substance that insulates axons, increasing speed of impulse transmission.

• Myelin Sheath: Layer formed by glial cells around axons.

• Role in PNS: Schwann cells form myelin sheaths around peripheral axons.

• Role in CNS: Oligodendrocytes form myelin sheaths around central axons.

Additional info: Myelinated axons conduct impulses faster than unmyelinated axons.

Nerve Structure and Connective Tissue

• Endoneurium: Surrounds individual axons.

• Fascicle: Bundle of axons.

• Perineurium: Surrounds each fascicle.

• Epineurium: Encloses the entire nerve.

Connective tissue wrapping a bundle of axons into a fascicle: Perineurium.

Key Equations

• Resting Membrane Potential:

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

• Ohm's Law (for neurons):

$I = \frac{V}{R}$

Summary Table: Neuroglia Myelination

Glial Cell	Location	Myelination Role
Oligodendrocyte	CNS	Myelinates multiple axons
Schwann Cell	PNS	Myelinates single axon

Additional info: These study notes cover the foundational structure and function of the nervous system, including neuron types, neuroglia, and the organization of nerves. Understanding these concepts is essential for further study in anatomy and physiology.