ANPH 1001 Unit 3 Topic 1 Nervous System Vi!. ola Manokore

Nervous System Overview

• Course: ANPH 1001 Unit 3 presented by Viola Manokore at Norquest College.

References

• Rizzo, D.C. (2016). Fundamentals of Anatomy and Physiology (4th ed.). Cengage Learning.

Chapter 10: The Nervous System

• Introduces the spinal cord and spinal nerves as fundamental components.

Importance of the Nervous System

• Questions to Reflect On:

  • Why do we need a nervous system?

  • Identify organs constituting the nervous system.

  • Name the two main divisions of the nervous system.

  • Discuss disorders associated with the nervous system.

Functions of the Nervous System

• Acts as a control center and communication network.

• Directs body functions and interprets external environments.

• Coordinates reactions to changes to maintain homeostasis alongside the endocrine system.

Divisions of the Nervous System

• Central Nervous System (CNS):

  • Comprises the brain and spinal cord.

• Peripheral Nervous System (PNS):

  • Includes ganglia and nerves.

Functions of the Nervous System

• Sensory Input:

  • Perception of stimuli via sensory receptors.

• Integration:

  • Processing of sensory information within brain and spinal cord.

• Motor Output:

  • Activation of effectors in response to stimuli.

Peripheral Nervous System Structure

• Afferent (Sensory) Division:

  • Responsible for transmitting sensory information to the CNS.

• Efferent (Motor) Division:

  • Divided into:

    • Somatic Nervous System: Voluntary control over skeletal muscles.

    • Autonomic Nervous System: Involuntary control over organs, subdivided into:

      • Sympathetic: Stimulates fight or flight response (uses norepinephrine).

      • Parasympathetic: Restores body to rest state (uses acetylcholine).

Nervous Tissue Classification

• Nerve Cells (Neurons):

  • Transmit nerve impulses via electrochemical changes.

• Neuroglia (Glial Cells):

  • Provide support and protection for neurons; comprise about 60% of brain cells.

Types of Neuroglia Cells

• Astrocytes:

  • Support network in the brain and spinal cord; regulate nutrients and ions.

• Oligodendrocytes:

  • Form myelin sheath in CNS.

• Microglia:

  • Act as phagocytes, destroying microbes and debris.

• Ependymal Cells:

  • Line brain ventricles; involved in cerebrospinal fluid (CSF) production/movement.

• Schwann Cells:

  • Form myelin sheaths in the PNS.

Neuron Structure

• Cell Body: Contains nucleus and organelles for protein synthesis (Nissl bodies).

• Dendrites: Short and branched; receive signals.

• Axon: Long fiber that transmits impulses; may be myelinated, enhancing speed.

Types of Neurons

• Multipolar Neurons:

  • Multiple dendrites; common in the CNS.

• Bipolar Neurons:

  • One dendrite and one axon; found in sensory systems like eye and ear.

• Unipolar Neurons:

  • One process with both dendritic and axonal properties; typical in sensory neurons.

Functional Neuron Classification

• Afferent Neurons:

  • Relay signals from sensory receptors to the CNS.

• Efferent Neurons:

  • Carry commands from the CNS to effectors (muscles/glands).

• Interneurons:

  • Connect afferent and efferent pathways.

Physiology of the Nerve Impulse

• Resting Potential:

  • Na+ concentration higher outside; K+ concentration higher inside.

• Depolarization:

  • Na+ rushes into cells causing a change in charge.

• Repolarization:

  • Restores original ionic distribution utilizing Na+/K+ pumps.

• Myelinated vs. Unmyelinated Fibers:

  • Myelinated fibers transmit impulses faster (120 m/s).

Synaptic Transmission

• Synapses: Connections between neurons allowing impulse transfer.

• Neurotransmitters: Chemicals that facilitate nerve signal transmission (e.g., acetylcholine, norepinephrine).

• Synaptic Cleft: Space between presynaptic and postsynaptic neurons.

Reflex Arcs

• Definition: Involuntary responses to stimuli.

• Components: Sensory receptor, afferent neuron, interneurons, efferent neuron, and effector organ.

• Examples of reflex actions: Heartbeat regulation, digestion, withdrawal reflexes.

Neural Tissue Grouping

• White Matter: Composed of myelinated axons, forms nerve tracts in CNS.

• Gray Matter: Consists of nerve cell bodies and dendrites; involved in processing.

• Nerves and Ganglia: Nerves are fiber bundles outside CNS, and ganglia are collections of nerve cell bodies outside the CNS.

Spinal Cord Anatomy

• Begins at the medulla oblongata, extends 16-18 inches, and has 31 segments connected to pairs of spinal nerves.

• Covered by protective meninges: dura mater, arachnoid mater, and pia mater.

Summary

• The nervous system's major divisions include the CNS and PNS. It involves varied neuron structures and classifications focused on their functions. The physiology of nerve impulses encompasses resting potentials, synaptic transmission, and reflex arcs that facilitate immediate responses.

Nervous System Overview

Course: ANPH 1001 Unit 3 presented by Viola Manokore at Norquest College.

References

• Rizzo, D.C. (2016). Fundamentals of Anatomy and Physiology (4th ed.). Cengage Learning.

Chapter 10: The Nervous System

This chapter introduces the spinal cord and spinal nerves, which are fundamental components of the nervous system. It emphasizes their roles in sensory and motor functions, illustrating how they connect the central nervous system (CNS) with the peripheral nervous system (PNS).

Importance of the Nervous System

The nervous system is critical for survival and functioning in both simple and complex organisms. It serves as the body's control center, enabling communication between different body parts, processing information, and executing appropriate responses.

Questions to Reflect On:

• Why do we need a nervous system?

• What organs constitute the nervous system?

• What are the two main divisions of the nervous system?

• What disorders are commonly associated with the nervous system?

Functions of the Nervous System

• Acts as a control center and comprehensive communication network.

• Directs and regulates body functions, interprets external and internal environments, and initiates responses.

• Coordinates the body’s reactions to changes, maintaining homeostasis alongside the endocrine system, which utilizes hormones for regulation.

Divisions of the Nervous System

• Central Nervous System (CNS):

  • Composed of the brain and spinal cord, it is responsible for processing and integrating information as well as coordinating activity throughout the body.

• Peripheral Nervous System (PNS):

  • Includes all neural structures outside the CNS, such as ganglia (clusters of nerve cell bodies) and nerves that facilitate communication between the CNS and the rest of the body.

Functions of the Nervous System

1. Sensory Input:

   • Involves the perception of stimuli via specialized sensory receptors located throughout the body, including skin, muscles, and organs.

2. Integration:

   • The brain and spinal cord process sensory information, making sense of it and determining appropriate responses.

3. Motor Output:

   • Involves the activation of effectors, such as muscles and glands, in response to stimuli, facilitating movement and physiological changes.

Peripheral Nervous System Structure

• Afferent (Sensory) Division:

  • Responsible for transmitting sensory information from receptors to the CNS, enabling perception of the environment.

• Efferent (Motor) Division:

  • Divided into:

  • Somatic Nervous System:

    • Controls voluntary movements and the reflex arcs involving skeletal muscles.

  • Autonomic Nervous System:

    • Regulates involuntary actions and is subdivided into:

      • Sympathetic Division:

        • Prepares the body for the 'fight or flight' response during stressful situations, utilizing norepinephrine for quick, short-term reactions.

      • Parasympathetic Division:

        • Restores the body to a state of calm and rest, primarily using acetylcholine to manage energy-conservation processes including digestion and rest.

Nervous Tissue Classification

• Nerve Cells (Neurons):

  • Specialized for transmitting nerve impulses through electrochemical changes, differing in structure based on their function and signal direction.

• Neuroglia (Glial Cells):

  • Supportive cells that provide protection, nourishment, and structure for neurons; comprising about 60% of brain cells, they are crucial for maintaining homeostasis, forming myelin, and managing inflammatory responses.

Types of Neuroglia Cells

1. Astrocytes:

   • Star-shaped cells that maintain the blood-brain barrier, support neural structure, and regulate nutrient transport and ion balance in the CNS.

2. Oligodendrocytes:

   • Form the myelin sheath around axons in the CNS, facilitating faster impulse transmission.

3. Microglia:

   • Act as the immune defense in the CNS, removing damaged neurons and pathogens through phagocytosis.

4. Ependymal Cells:

   • Line the ventricles of the brain and the central canal of the spinal cord; involved in the production and circulation of cerebrospinal fluid (CSF).

5. Schwann Cells:

   • Form the myelin sheaths around axons in the PNS, playing a role in repairing peripheral nerve injuries.

Neuron Structure

• Cell Body (Soma):

  • Contains the nucleus and organelles necessary for protein synthesis, including Nissl bodies which play a role in neurotransmitter synthesis.

• Dendrites:

  • Short, branched extensions that receive signals from other neurons, transmitting them toward the cell body.

• Axon:

  • A long, single fiber that transmits impulses away from the cell body; can be myelinated or unmyelinated, with myelination increasing transmission speed.

Types of Neurons

1. Multipolar Neurons:

   • Characterized by multiple dendrites; primarily found in CNS, involved in motor control and complex brain functions.

2. Bipolar Neurons:

   • Have one dendrite and one axon; often found in sensory systems like the retina of the eye and the olfactory system.

3. Unipolar Neurons:

   • Possess one process that branches into a dendritic and axonal part; typically involved in sensory functions.

Functional Neuron Classification

• Afferent Neurons (Sensory Neurons):

  • Relay signals from sensory receptors to the CNS, translating stimuli into electrical signals for processing.

• Efferent Neurons (Motor Neurons):

  • Carry commands from the CNS to effectors such as muscles and glands, facilitating movement and responses.

• Interneurons:

  • Connect afferent and efferent pathways within the CNS, playing a crucial role in reflexes and higher-order processing.

Physiology of the Nerve Impulse

• Resting Potential:

  • A neuron's state at rest, with a higher concentration of Na+ ions outside and K+ ions inside, creating an electrochemical gradient.

• Depolarization:

  • A rapid influx of Na+ ions occurs, making the inside of the cell more positive and triggering an action potential.

• Repolarization:

  • Following depolarization, K+ ions exit the cell, restoring the original ionic distribution with the help of Na+/K+ pumps.

• Myelinated vs. Unmyelinated Fibers:

  • Myelinated fibers transmit impulses much faster (up to 120 m/s) due to saltatory conduction, where impulses jump between nodes of Ranvier.

Synaptic Transmission

• Synapses:

  • Junctions between neurons allowing for the transfer of impulse signals through neurotransmitters to facilitate communication.

• Neurotransmitters:

  • Chemicals such as acetylcholine and norepinephrine that cross the synaptic gap to transmit nerve signals between neurons.

• Synaptic Cleft:

  • The microscopic space between presynaptic and postsynaptic neurons where neurotransmitters diffuse to convey messages.

Reflex Arcs

• Definition:

  • Reflex arcs are involuntary responses initiated by stimuli.

• Components:

  • Comprised of a sensory receptor, afferent neuron, interneurons, efferent neuron, and effector organ, allowing for rapid responses without conscious thought.

• Examples of Reflex Actions:

  • Include heartbeat regulation, digestive processes, and withdrawal reflexes in response to pain.

Neural Tissue Grouping

• White Matter:

  • Composed of myelinated axons, forming the nerve tracts in the CNS; facilitates rapid communication between different brain areas.

• Gray Matter:

  • Contains nerve cell bodies, dendrites, and synapses, and is involved in the processing and integration of information.

• Nerves and Ganglia:

  • Nerves are bundles of axons outside the CNS that facilitate communication, and ganglia are clusters of nerve cell bodies located outside the CNS, involved in processing sensory information.

Spinal Cord Anatomy

• The spinal cord begins at the medulla oblongata, extends approximately 16-18 inches, and is divided into 31 segments, each connecting to pairs of spinal nerves that relay information to and from the body.

• It is protected by three layers of protective tissue called meninges: dura mater, arachnoid mater, and pia mater, which also contain CSF that cushions the spinal cord.

Summary

The nervous system's major divisions include the CNS and PNS, each with various structures and functions. The classification of neurons elucidates their unique roles in sensory input, integration, and motor output. Furthermore, understanding the physiology of nerve impulses, synaptic transmission, and reflex mechanisms highlights the complexity and importance of the nervous system in coordinating responses and maintaining homeostasis within the body.