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.