Human Histology: Nervous Tissue

• The lecture covers Human Histology MT120225, specifically Unit 4 on Nervous Tissue
• The lecture takes place in the second semester of the academic year 2024-2025, at the UST General Santos School of Health Sciences, Department of Medical Technology
• The course content includes an overview of the nervous tissue, the central and peripheral nervous systems, and neural plasticity and regeneration

Unit Intended Learning Outcome

• Students are to identify the different types of nervous tissue and their functions

Pre-test questions

• Enumerate two types of cells in the nervous tissue
• State whether nervous tissue originates from the ectoderm (True / False)
• State whether the dura mater is the outermost layer covering the brain (True / False)
• Identify which glial cell produces myelin for nerve fibers in the PNS
• Identify which glial cell produces myelin to insulate nerve fibers of the CNS

Overview of Nervous Tissue

• Nervous tissue consists of a network of billions of nerve cells
• Glial cells support the network of nerve cells

Properties and Functions of the Nervous Tissue

• The Central Nervous System (CNS) collects and sends information throughout the body
• The Peripheral Nervous System (PNS) detects stimuli, sends data to the CNS, and relays messages from the CNS to the body
• Irritability: Nervous tissues react to diverse stimuli
• Conductivity: Nervous tissues transmit impulses

Development of Nervous Tissue

• Information missing

Anatomical Division of the Nervous System

• Information missing

Functional Division of the Nervous System

• Sensory nervous system detects stimuli and transmits information from receptors to the CNS
• Motor nervous system initiates and transmits information from the CNS to effectors
• Somatic sensory input is consciously perceived from receptors (e.g., eyes, ears, skin)
• Visceral sensory input is not consciously perceived from receptors of blood vessels and internal organs
• Somatic motor output is consciously or voluntarily controlled, with skeletal muscle as the effector
• Autonomic motor output is involuntarily controlled; effectors include cardiac muscle, smooth muscle, and glands

Cells of the Nervous Tissue: Neurons

• Neurons are the structural and functional unit of the nervous system
• Neurons receive stimuli and transmit electrical impulses to effector cells
• Neurons have lost the ability to undergo mitotic division; damage leads to long-term effects
• Neurons are capable of maintaining and renewing their subcellular components
• Neurons exhibit neural plasticity

Main Parts of a Neuron

• Cell body (soma)
• Dendrites
• Axons

Cell Body (Soma)

• The cell body is the trophic center
• It contains the nucleus and nucleolus
• Cytoplasmic organelles include free ribosomes, highly developed rough endoplasmic reticulum (RER), Golgi apparatus, mitochondria, and lysosomes
• Lipofuscin, a hallmark of cellular aging, is present
• The cytoskeleton is comprised of microtubules, actin filaments, and intermediate filaments

Dendrites

• They are the primary sites for signal reception and processing on neurons
• The plasmalemma of dendrites contains receptor sites for binding chemical signals
• Dendrites are short, tapering, and highly branched
• Dendritic arborization increases the receptor surface area
• Dendritic spines contribute to synaptic plasticity, learning, and memory formation

Axon

• The axon serves as a long projection that propagates nerve impulses to another neuron, muscle fiber, or glandular cell
• The axon hillock serves as the attachment site for the cell body
• Axon collaterals are branches along the length of the axon
• TeTerminal boutons are end of the axon
• Collaterals coordinate complex neural circuits
• The axon initial segment is the region between the apex of the axon hillock and the beginning of the myelin sheath

Structural Classes of Neurons

• Information missing

Functional Classification of Neurons

• Sensory / Afferent neurons convey action potentials into the CNS and are mostly unipolar in structure
• Motor / Efferent neurons use cranial and spinal nerves to convey action potential away from the CNS to PNS effectors and are mostly multipolar in structure
• Interneurons / Association neurons form a communicating and integrative network between sensory and motor neurons; most are multipolar

Glial Cells

• Glial cells or neuroglia support, nourish, and protect neurons
• Glial cells maintain the interstitial fluid of the nervous system
• Glial cells can continuously divide throughout their lifetime

Types of Neuroglia

• Astrocytes
• Oligodendrocytes
• Microglia
• Ependymal cells
• Schwann cells
• Satellite cells

Astrocytes

• Have many short branching processes and are found in gray matter
• Fibrous Astrocytes: Have many long unbranched processes and are located mainly in white matter

Oligodendrocytes

• Information missing

Microglia

• Information missing

Ependymal Cells

• Information missing

Schwann Cells

• Information missing

Satellite Cells

• Information missing

Myelin Sheath

• Multi-layered lipid-rich covering around some axons
• Formed by concentric layers of the plasma membrane of oligodendrocyte / Schwann cells
• Functions include insulation, speeding up nerve impulses, and reducing the total amount of ion exchange during action potential

Synapses

• A synapse is the site of communication between two neurons or a neuron and an effector cell
• Elements of the synapse includes a presynaptic axon terminal, synaptic cleft, and postsynaptic cell membrane

Classification of Synapses

• Axodendritic: axon to dendrite
• Axosomatic: axon to cell body
• Axoaxonic: axon to axon

Postsynaptic Responses

• Release of neurotransmitters can cause either excitation or inhibition at the postsynaptic membrane

Excitatory Neurotransmitters

• Acetylcholine stimulates muscle contraction
• Glutamine promotes cognitive function in the brain
• Serotonin affects sleep, appetite, cognition, and mood
• Excitatory neurotransmitters cause depolarization, making the postsynaptic neuron more likely to fire impulses

Inhibitory Neurotransmitters

• GABA is the primary inhibitory neurotransmitter.
• Glycine inhibits activity between neurons in the CNS, including the retina
• Excitatory neurotransmitters cause hyperpolarization, making the postsynaptic neuron less likely to fire impulses

Central Nervous System (CNS)

Major Structures

• Cerebrum
• Cerebellum
• Brain stem
• Spinal cord