Central Nervous System

Central Nervous System Learning Objectives

Nervous System Organization

  • Overview of the Nervous System

    • The nervous system is divided into two main parts:

    • Central Nervous System (CNS)

      • Comprises the brain and spinal cord.

    • Peripheral Nervous System (PNS)

      • Consists of all neural tissue outside the CNS, including sensory and motor neurons.

  • Flow of Information

    • The flow of information within the nervous system follows a specific path:

    • Sensory input is received by sensory neurons (afferent), processed by interneurons in the CNS, and results in an appropriate response sent out through motor neurons (efferent).

  • Identifying Neuron Types

    • There are three main types of neurons based on the location of their cell bodies and axons:

    • Afferent Neurons (Sensory Neurons)

      • Cell bodies located in the peripheral ganglia; axons project towards the CNS.

    • Interneurons

      • Found entirely within the CNS; their cell bodies and axons are located within the spinal cord and brain, facilitating communication between afferent and efferent neurons.

    • Efferent Neurons (Motor Neurons)

      • Cell bodies located in the CNS; axons extend to effectors in the periphery (muscles and glands).

  • Protection of the CNS

    • The CNS is protected through various means:

    • Bone Encasement: The skull protects the brain, and the vertebral column shields the spinal cord.

    • Meninges: Three protective layers (dura mater, arachnoid mater, pia mater) surround the CNS.

    • Cerebrospinal Fluid (CSF): Acts as a cushion and provides nutrients to the CNS while removing waste.

  • Blood Brain Barrier (BBB)

    • Definition: The BBB is a selective barrier that regulates the entry of substances from the bloodstream into the brain.

    • Formation:

    • Composed of tightly joined endothelial cells of the brain's capillaries, astrocytic end-feet, and the basement membrane.

    • Protects the brain from potentially harmful substances while allowing essential nutrients to pass.

  • Types of Glial Cells and Their Functions

    • Oligodendrocytes and Schwann Cells

    • Responsible for myelination of axons in the CNS (oligodendrocytes) and PNS (Schwann cells), enhancing signal transmission speed.

    • Astrocytes

    • Support neurons, maintain ion balance, transport nutrients, and contribute to the blood-brain barrier's integrity.

    • Microglia

    • Act as immune cells in the CNS, responding to injury and disease by clearing debris and pathogens.

    • Ependymal Cells

    • Line the ventricles of the brain and spinal cord, producing and circulating cerebrospinal fluid (CSF).

The Brain

  • White Matter vs. Gray Matter

    • White Matter: Contains myelinated axons; facilitates communication between different brain regions and between the brain and spinal cord.

    • Gray Matter: Composed of neuronal cell bodies, dendrites, and unmyelinated axons; involved in processing and cognition.

  • Lobes of the Cerebral Cortex

    • The cerebral cortex is divided into four lobes, each responsible for different functions:

    • Frontal Lobe

      • Responsible for planning, reasoning, problem-solving, and voluntary motor function.

    • Parietal Lobe

      • Processes sensory information such as touch, temperature, and pain; involved in spatial orientation.

    • Temporal Lobe

      • Functions in auditory processing, memory, and speech comprehension.

    • Occipital Lobe

      • Primarily responsible for visual processing, including perception and interpretation of visual stimuli.