Neurons & Glial cells

Overview of the Nervous System

  • Contains various divisions and types of neurons.

  • Structural and functional classifications of neurons.

Structure of Multipolar Neuron

  • Cell Body (Soma): Contains cell organelles similar to any other cell.

  • Dendrites: Extensions that receive impulses towards the cell body.

  • Axon: A single long extension that carries impulses away from the cell body.

  • Neurofibrils and Microtubules: Support structures that aid in the transport of vesicles containing neurotransmitters.

Neuronal Impulse Transmission

  • Impulses involve a change in charge across the membrane due to the opening of voltage-gated channels.

  • Example: In the case of voluntary movement, the relevant neuron’s cell body could be located in the spinal cord.

Organelles in the Soma

  • Mitochondria: Site of cellular respiration.

  • Golgi Complex: Involved in the production of neurotransmitters (e.g., acetylcholine).

  • Nissl Bodies: Stained structures involved in the production of proteins and neurotransmitters, appearing darkly stained due to chromatophilic substances.

Types of Neurons

Structural Classification

  • Multipolar Neurons: Multiple dendrites and one axon, common in CNS.

  • Bipolar Neurons: One dendrite and one axon.

  • Unipolar Neurons: Sensory neurons with a single process that splits axon and dendrites.

Functional Classification

  • Afferent Neurons: Carry impulses towards the CNS; sensory neurons.

  • Efferent Neurons: Carry impulses away from the CNS; motor neurons.

  • Interneurons: Connect neurons within the CNS.

Glial Cells (Neuroglia)

  • Supportive cells in the nervous system, smaller than neurons, and do not transmit impulses.

  • More numerous than neurons and can divide, potentially leading to gliomas (tumors).

  • Responsible for myelination in the CNS and PNS.

Types of Glial Cells in CNS

  • Astrocytes: Form the blood-brain barrier, regulate the environment for neurons, support nutrient exchange between neurons and capillaries.

  • Microglia: Act as immune cells, phagocytizing debris or pathogens in the CNS.

  • Ependymal Cells: Line the ventricles of the brain, produce cerebrospinal fluid (CSF).

  • Oligodendrocytes: Form myelin sheaths around axons in the CNS.

Types of Glial Cells in PNS

  • Schwann Cells (Neurolemocytes): Form myelin sheaths around axons in the PNS, facilitating faster impulse transmission.

Cerebrospinal Fluid (CSF) Production

  • Choroid Plexus: Where CSF is produced, composed of ependymal cells separating blood vessels and ventricular spaces filled with CSF.

  • CSF circulates through the ventricular system and meninges, absorbing nutrients and removing wastes.

Meninges and CSF Flow

  • Meninges: Protective coverings of the brain and spinal cord; includes dura mater, arachnoid mater, and pia mater.

  • CSF flows through the subarachnoid space and is eventually reabsorbed back into the bloodstream through arachnoid villi.

Myelination Effects on Impulse Transmission

  • Saltatory Conduction: Myelination allows impulses to 'jump' from one node of Ranvier to another, significantly speeding up conduction.

  • Damage to myelin (e.g., in multiple sclerosis) results in slower impulse transmission and potential neuronal damage.

  • Myelination supports regeneration of axons following injury, allowing damaged neurons to recover function.

  • The ventricles of the brain are lined by ependymal cells.

  • They are involved in the production of cerebrospinal fluid (CSF).

  • The choroid plexus, made of ependymal cells, separates blood vessels from ventricular spaces filled with CSF.

  • CSF circulates through the ventricular system and meninges.

  • It absorbs nutrients and removes wastes.

  • CSF flows through the subarachnoid space.

  • Eventually, CSF is reabsorbed back into the bloodstream through arachnoid villi.