Introduction to the Nervous System

Introduction to the Nervous System

  • The nervous system will be covered over three lectures.

  • Key topics include:

    • Introduction to the nervous system.

    • Subdivisions and components.

    • Major features of the nervous system.

Objectives of the Package

  • Explain the divisions and subdivisions of the nervous system.

  • Identify different components of the central nervous system (CNS).

  • Discuss key anatomical features:

    • Cerebrum: Largest part of the brain, responsible for sensory perception, voluntary movement, and higher cognitive functions such as reasoning and problem-solving.

    • Brainstem: The part of the brain responsible for regulating essential functions such as breathing, heart rate, and blood pressure.

    • Cerebellum: Responsible for coordinating voluntary movements, balance, and motor learning.

    • Diencephalon: The part of the brain located between the cerebrum and brainstem, responsible for relaying information and regulating autonomic functions.

  • Explore the ventricles of the CNS:

    • Four ventricles that facilitate certain brain functions.

  • Discuss protective layers of connective tissue surrounding the CNS.

  • Circulation and function of cerebrospinal fluid (CSF).

Classification of the Nervous System

Structural Classification

  • Two main subdivisions:

    • Central Nervous System (CNS)

    • Peripheral Nervous System (PNS)

Components

  1. Central Nervous System (CNS):

    • Composed of the brain and spinal cord.

  2. Peripheral Nervous System (PNS):

    • Series of nerves:

      • Spinal nerves (31 pairs): Arise from the spinal cord.

      • Cranial nerves (12 pairs): Arise from the brainstem.

    • Associated with ganglia.

Grey Matter vs. White Matter

  • Grey Matter:

    • Made up of nerve cell bodies and glial cells (neuroglia).

    • Contains unmyelinated fibers.

  • White Matter:

    • Composed primarily of myelinated nerve fibers.

    • Contains few unmyelinated fibers.

Organization of Matter in CNS

  • Spinal Cord:

    • Grey matter forms the core, surrounded by white matter.

  • Cerebrum:

    • Grey matter forms a thin shell on the outside, surrounding the core of white matter.

Ganglia and Nuclei

  • Ganglion: A cluster of nerve cell bodies outside the CNS.

  • Nucleus: A cluster of nerve cell bodies within the white matter of the CNS.

  • Both serve as important structures in the nervous system, differing by their locations.

Functions of PNS and CNS

  • PNS Functions:

    • Collects sensory information.

    • Distributes motor impulses.

  • CNS Functions:

    • Processes and analyzes sensory information.

    • Initiates motor responses.

    • Higher-level cognitive functions such as learning and memory.

Proprioception

  • Proprioception is a sensory interpretation of body position and movement, falling under the somatic system.

Embryonic Development of the Nervous System

  • Begins during the third week post-fertilization.

  • Neural Tube Formation:

    • Expands into primary cerebral vesicles:

    1. Prosencephalon (forebrain)

    2. Mesencephalon (midbrain)

    3. Rhombencephalon (hindbrain)

  • Primary vesicles further divide into secondary vesicles:

    • Prosencephalon → Telencephalon (cerebrum) & Diencephalon.

    • Rhombencephalon → Metencephalon (pons & cerebellum) & Myelencephalon (medulla oblongata).

Spinal Cord Anatomy

  • Length: 43 to 45 cm, does not vary with height.

  • Enlargements:

    • Cervical Enlargement (for upper limb control)

    • Lumbar Enlargement (for lower limb control)

  • Terminates as Conus Medullaris at the L1-L2 level.

Cross-Section of the Spinal Cord

  • Grey matter organized into horns:

    • Anterior horn: Contains motor neurons.

    • Posterior horn: Contains sensory neurons.

    • Lateral horn: Contains autonomic neurons.

  • White matter divided into columns:

    • Anterior, posterior, and lateral columns.

    • Contains ascending (sensory) and descending (motor) pathways.

    • Individual bundles of sensory or motor fibers, never mixed.

Spinal Nerve Formation

  • Nerve fibers exit the spinal cord through:

    • Ventral root: Carries motor fibers.

    • Dorsal root: Carries sensory fibers.

  • Both roots combine to form the spinal nerve, which then branches out to peripheral regions.