Nervous System Overview

Prayer Before Study

• Request for understanding, memory and accuracy.
• Seek guidance at the start, during, and until the completion of the work.

Course Content Overview

• The unit will cover an overview of nervous tissue, the central and peripheral nervous systems, and neural plasticity and regeneration.

Unit 4: Nervous Tissue Learning Outcome

• Students will identify the different types of nervous tissue and their functions.

Pre-Test Topics

• Identifying cells in nervous tissue
• Source of nervous tissue
• Brain covering
• Glial cells and their role/function in the PNS/CNS

Overview of Nervous Tissue

• Nervous tissue comprises a network of billion nerve cells assisted by glial cells.

Properties and Function of Central and Peripheral Nervous System

• The central nervous system receives and sends bodily information.
• The peripheral nervous system detects stimuli and sends information to the CNS, communicating messages to the body.
• The two properties of Nerve Tissue Include irritability and conductivity.

Properties of Nervous Tissues

• Irritability: Reacts to various stimuli
• Conductivity: Transmits impulses

The Development of Nervous Tissue.

• Neurulation-The process by which the neural plate folds to form the neural tube, which will eventually develop into the brain and spinal cord

Anatomical Division of the Nervous System

• CNS includes
  • Brain
  • Spinal cord
• PNS include
  • Cranial nerves
  • Spinal nerves
  • Ganglia

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 (e.g., sight, hearing, touch).
• Visceral sensory input is not consciously perceived (e.g., blood vessels, internal organs).
• Somatic motor output is consciously controlled, affecting skeletal muscle.
• Autonomic motor output is involuntarily controlled, affecting cardiac muscle, smooth muscle, and glands.

Neurons

• Structural and functional units of the nervous system
• Neurons receive stimuli and conduct electrical impulses to effector cells.
• Neurons have lost the ability to undergo mitotic division.
  • Damage causes long-term effects.
• Neurons can maintain and renew their subcellular components.
• Neurons undergo neural plasticity.

3 main parts of a Neuron (Memory Check)

• Cell body
• Dendrites
• Axons

Parts of a Neuron: Cell Body

• Trophic center of the neuron
• Contains nucleus and nucleolus
• Cytoplasmic organelles include:
  • Free ribosomes
  • Highly developed rough endoplasmic reticulum (RER)
  • Golgi apparatus
  • Mitochondria
  • Lysosomes
  • Lipofuscin (hallmark of cellular aging)
• Cytoskeletal filaments include:
  • Microtubules
  • Actin filaments
  • Intermediate filaments

Parts of a Neuron: Dendrites

• Main signal reception and processing sites
• Covered by the plasmalemma which contains receptor sites for binding chemical signals.
• Dendrites are short, tapered, and highly branched.
• Dendritic arborization increases the receptor surface area.
• Dendritic spines are related to synaptic plasticity, learning, and memory formation.

Parts of a Neuron: Axon

• Long projection: Conducts nerve impulses to another neuron, muscle fiber, or glandular cell.
• Axon hillock represents the attachment site.
• Axon collateral refers to the branches along the axon's length.
• Terminal boutons represent the axon's end.
• Collaterals coordinate complex neural circuits.
• Axon initial segment marks region between apex of the axon hillock and the beginning of the myelin sheath.

Functional Classification of Neurons

• Sensory/Afferent Neurons: Action potential is conveyed into the CNS, and most are unipolar.
• Motor/Efferent Neurons: Action potential travels away from the CNS, through the cranial and spinal nerves in the PNS mostly multipolar.
• Interneurons/Association Neurons: Form a communicating and integrative network, most are multipolar.

Glial Cells: Support

• Glial cells support, nourish and protect the neurons.
• Glial cells maintain the interstitial fluid of the nervous system.
• Glial cells have the ability to continuously divide throughout their lifetime.
• Types of neuroglia, Astrocytes, oligodendrocytes, microglia, ependymal cells, Schwann cells and satellite cells
• Glias are supportive central nervous systems

Types of Glial Cells: Astrocytes

• Types:
  • Protoplasmic: Have branched processes and found in gray matter.
  • Fibrous: Possesses long processes and located in white matter.

Myelin Sheath

• Is a multi-layered, lipid-rich covering around some axons.
• Formed of concentric layers of the plasma membrane from oligodendrocytes or Schwann cells.
• Functions:
  • Insulation
  • Speeds up nerve impulses
  • Reduces the total amount of ion exchange during action potential

Synapse Structure

• The Synapse is the site of communication between 2 neurons or a neuron and an effector cell.
• Presynaptic Axon Terminal
• Synaptic Cleft
• Post-Synaptic Cell Membrane

Synapses Classification

• Axodendritic
• Axosomatic
• Axoaxonic

Postsynaptic Responses

• Release of neurotransmitters causes either excitation or inhibition at the postsynaptic membrane.

Neurotransmitters: Excitatory

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

Neurotransmitters: Inhibitory

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

Central Nervous System Structures of the CNS

• Structures include the Cerebrum, Cerebellum, Brain stem, Spinal Cord and the Meninges

CNS Tissues Structural Features

• White matter mostly includes myelinated nerve fibers, oligodendrocytes, and some astrocytes.
• Gray matter mainly contains neuronal cell bodies, dendrites, astrocytes, and microglial cells.

Connective Tissue of the CNS

• Connective tissue includes the three meningeal layers
  • Dura mater consists of a thick, dense irregular connective tissue
• Two Layers: Periosteal and Meningeal layer
• Arachnoid Mater consists a component which include of a sheet of connectives in contact with Dura Mater and System of loosely arranged trabeculae
• Pia Mater consists flattened mesenchymal cells
• Attach to glial restricting membrane

Blood Brain Barrier

• BBB regulates the substance from blood into the brain
• Consists of capillary endothelial cells, tight junctions, endothelial membrane and end-foot processes of astrocytes.
  • Functions by protecting it from toxins, meeting the metabolic needs and regulating homeostasis in the CNS

Central Nervous System: Choroid Plexuses

• Consist of specialized tissue folded into the ventricles.
• Functions of CSF:
  • Mechanical protection
  • Provides nutrients to the CNS
  • Homeostatic function
  • Circulation

Central Nervous System: Cerebrum

• Cerebral cortex is the gray matter.
• Deep to the cortex is the subcortical white matter.
• Major neuronal cell types:
  • Pyramidal
  • Stellate
  • Other (Martinotti cells)

Central Nervous System: Cerebellum

• The cerebellar cortex is organized into 3 layers.

Central Nervous System: Spinal Cord

• Key features of the gray matter include:
  • 2 Dorsal Horns and contain interneurons.
  • 2 Ventral Horns and contain multipolar motor neurons.
• White matter is peripherally located and consists of ascending and descending fibers.

Structures of Peripheral Nervous System

• Peripheral Nervous System include : Nerves, Ganglia and Nerve endings

PNS Organization

• Nerves are enclosed by epineurium, fascicles are surrounded by perineurium, and individual axons are invested by Schwann cells forming the endoneurium.

Structures of the Peripheral Nervous System: Nerve Coverings

• Epineurium: External coat of a nerve
• Perineurium: Surrounds each bundle of nerve fibers
• Endoneurium: Surrounds individual nerve fiber

Peripheral Nerves

• Made of axons sheathed by Schwann cells, these can be myelinated or unmyelinated

Myelinated Nerve Fibers

• These are enclosed by a myelin sheath.
• Circular constrictions within are called nodes of ranvier.
• Gaps between each myelin segment
• Impulse conductions are saltatory.

Unmyelinated Nerve Fibers

• Smallest diameter axons.
• There is no myelin sheath, they are wrapped by a the simple fold of the Schwann cell.
• Contains voltage gated Channels
• Impulse Conduction is not saltatory but is slower

Classification of Peripheral Nerves by Function

• Sensory nerves contain afferent fibers (to the CNS).
• Motor nerves contain efferent fibers (from the CNS).
• Mixed nerves contain both afferent and efferent fibers.

Ganglia

• Ovoid structures composed of neuronal cell bodies surrounded glial satellite cells that are closely associated with cranial and spinal nerves.
• Types: sensory and autonomic.
• Sensory: cranial and dorsal root ganglia
• Autonomic: sympathetic and parasympathetic ganglia.

Neural Plasticity

Memory Check

• Is there any damage from a long term affect from losing the ability of a neuron's ability to undergo mitotic division
• Structural components of a typical neuron
• Types and functions of glial cells found in the central and peripheral nervous systems