Introduction to the Nervous System

Introduction to the Nervous System

• Overview of the nervous system as a complex network responsible for communication within the body.

I. Cells of the Nervous System

A. Neurons: Glia

• Astrocytes: Support cells that maintain the blood-brain barrier, regulate blood flow and nutrient transport.

• Microglia: Modified monocytes functioning as the immune defense of the CNS, acting as phagocytes to clear debris.

• Ependymal Cells: Ciliated cells that line the ventricles of the brain and are involved in the production of cerebrospinal fluid (CSF).

• Oligodendrocytes: Cells with multiple processes that create the myelin sheath around CNS axons, facilitating faster nerve impulse conduction.

• Schwann Cells: Responsible for myelination of peripheral nerves, wrapping around a single axon to isolate it electrically.

Page Repetition

A. Neurons: Glia (Repeated Content from Page 2)

• Information is identical and reiterates the types of glial cells.

IV. Parts of a Motor Neuron

B. Neurons: "Typical" Also parts of Model

• Dendrite: Branching structures that receive signals from other neurons.

• Nucleus: Contains genetic material; regulates cellular activities.

• Axon Hillock: The point of initiation for action potentials.

• Axon: Long projection that transmits impulses away from the cell body.

• Schwann Cell: Insulates axon with myelin sheath, essential for signal transmission efficiency.

• Myelin Sheath: Fatty layers that increase the speed of electrical impulses.

• Axon Collateral: Branches of the axon that allow signals to reach multiple targets.

• Node of Ranvier: Gaps in the myelin sheath enabling rapid signal conduction through saltatory conduction.

• Telodendria/Terminal Processes: End branches of axon that form synaptic connections.

• Synaptic Knobs/Boutons: End structures of neurons where neurotransmitters are released.

V. Classification of Neurons

C. Types of Neurons

• Multipolar Neurons: Characterized by one axon and multiple dendrites, typical of motor neurons.

• Bipolar Neurons: Have one axon and one dendrite, commonly found in sensory systems (e.g., retina).

• Unipolar Neurons: Feature a single process that splits into two branches, one for sensory input and one for output to the CNS.

VI. Nerves and Tracts

• A. Epineurium: Protective layer around nerves, consisting of dense connective tissue.

• B. Perineurium: Surrounds fascicles of nerve fibers, maintaining structure and support.

• C. Endoneurium: Innermost layer surrounding individual nerve fibers, providing a microenvironment for neurons.

• D. Fascicles: Bundles of axons within a nerve, organized for efficient communication.

VII. Cell Membrane Potential - Anatomic Features

A. Voltage-Gated Channels

• Voltage-gated K+ Channels: Open in response to changes in membrane potential, allowing K+ to exit the cell.

B. Ligand-Gated Channels

• Open due to binding of chemicals (e.g., neurotransmitters), critical for initiating action potentials.

• Example: Acetylcholine causing Na+ channels to open, resulting in depolarization.

VIII. Synapses: Neurochemical Transmission

A. Neurotransmitters

• Chemicals released by neurons to communicate with other neurons across synapses.

B. Pre/Post Synaptic Potential

• Changes in membrane potential occurring at the presynaptic and postsynaptic neurons during synaptic transmission.

C. Synaptic Vesicles

• Contain neurotransmitters, released upon electrical activation of the presynaptic terminal.

D. Synapse - The Space

• The synaptic cleft is the gap between presynaptic and postsynaptic neurons where neurotransmitter diffusion occurs.

IX. Brain & Spinal Cord Coverings

A. Meninges

• Dura Mater: Tough outer layer providing protection against injury.

• Arachnoid Mater: Middle layer with a web-like structure; contains cerebrospinal fluid.

• Pia Mater: Delicate inner layer directly adherent to brain and spinal cord tissues.

Related Spaces

• Epidural Space: Space between the dura mater and the inner walls of the vertebral canal; contains fat and blood vessels.

• Subdural Space: Space filled with serous fluid to protect the brain and spinal cord.

• Subarachnoid Space: Contains cerebrospinal fluid, cushioning the CNS structures.

X. Cerebrospinal Fluid (CSF)

A. Choroid Plexus

• Structure in the ventricles that produces CSF.

B. Ependymal Cells

• Specialized cells that form the lining of the ventricles, aiding in the secretion and circulation of CSF.

C. Fluid Spaces: Ventricles

• Open spaces in the brain filled with cerebrospinal fluid, critical for cushioning and nourishing brain tissue.

XI. Spinal Cord

A. Spinal Anatomy

• Cervical Enlargement: Increased thickness due to the number of nerves servicing the upper limbs.

• Lumbar Enlargement: Enlarged area for nerves servicing the lower limbs.

• Cauda Equina: Bundle of spinal nerves extending below the termination of the spinal cord.

• Conus Medullaris: The tapered end of the spinal cord.

• Filum Terminale: Fibrous extension anchoring the spinal cord to the coccyx.

• Columns and Fissures/Sulci: Structural divisions within the spinal cord that separate ascending and descending tracts.

• 31 pairs of Spinal Nerves: Spinal nerves categorized into cervical, thoracic, lumbar, sacral, and coccygeal regions.

B. Definition of a Spinal Nerve

• Formed by the merger of dorsal and ventral roots from the spinal cord, each serving specific body regions.

C. Dorsal and Ventral Primary Ramus

i. Dorsal Primary Ramus

• Serves the muscles and skin of the back.

ii. Ventral Primary Ramus

• Supplies the anterior and lateral skin and muscles of the trunk and the limbs.

XII. Reflex Arc Components

1. Sensory Receptor: Detects a stimulus and generates an action potential.

2. Sensory Neuron: Transmits impulses to the integrating center.

3. Integrating Center: Processes information (usually in the spinal cord).

4. Motor Neuron: Carries impulses away from integrating center to effector.

5. Effector: Muscle or gland that responds to motor nerve impulses.

XIII. Cranial Nerve V - Trigeminal

• Key functions include sensation to the face and motor functions like chewing, important for clinical assessments involving facial stimuli.

XIV. Functions of the Spinal Cord

A. Ascending Tracts - Sensory Pathways

• Responsible for conveying sensory information to the brain.

B. Descending Tracts - Motor Pathways

• Convey motor commands from the brain to the body.