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

a. Definition

Support cells in the nervous system that assist and protect neurons.

b. Function

Maintain homeostasis, form myelin, and provide support and protection for neurons.

c. Example

• Astrocytes: Maintain the blood-brain barrier and regulate blood flow and nutrient transport.

• Microglia: Function as immune defense in the central nervous system, clearing debris through phagocytosis.

• Ependymal Cells: Line the brain's ventricles and produce cerebrospinal fluid (CSF).

• Oligodendrocytes: Create the myelin sheath around CNS axons, enhancing signal conduction speed.

• Schwann Cells: Myelinate peripheral nerves by wrapping around a single axon, providing electrical insulation.

IV. Parts of a Motor Neuron

a. Definition

Components that make up a motor neuron which transmits impulses.

b. Function

Facilitate the transmission of nerve impulses from the neuron to the effectors (muscles or glands).

c. Example

• Dendrites: Receive incoming signals and transmit them to the cell body.

• Axon: Conducts impulses away from the cell body to communicate with other neurons or effectors.

• Myelin Sheath: Insulating fatty layers that increase the speed of electrical impulses along the axon.

• Synaptic Knobs: Release neurotransmitters to communicate with the next cell in the pathway.

V. Classification of Neurons

a. Definition

Different types of neurons based on structure and function.

b. Function

Classify the role of neurons in sensory and motor functions.

c. Example

• Multipolar Neurons: Predominantly motor neurons with many dendrites and one axon, allowing for extensive connections.

• Bipolar Neurons: One axon and one dendrite, primarily found in sensory systems for direct transmission of signals.

• Unipolar Neurons: One process that splits into two branches, typically involved in sensory transmission to the CNS.

VI. Nerves and Tracts

a. Definition

Bundles of axons in the peripheral nervous system or pathways in the central nervous system.

b. Function

Facilitate communication between neurons in different regions.

c. Example

• Epineurium: The outermost layer that provides protection and structure to the entire nerve.

• Perineurium: Surrounds individual fascicles of nerve fibers, supplying additional protection and support.

• Endoneurium: The innermost layer wrapping around each nerve fiber, providing a nurturing environment for individual neurons.

VII. Cell Membrane Potential

a. Definition

The electrical potential difference across a cell membrane.

b. Function

Important for the generation and conduction of action potentials.

c. Example

• Voltage-gated channels: Open or close in response to changes in membrane potential, critical for action potential propagation.

• Ligand-gated channels: Open upon binding a specific chemical, initiating cellular responses, including action potentials.

VIII. Synapses: Neurochemical Transmission

a. Definition

The junction between two neurons where neurotransmission occurs.

b. Function

Facilitates communication between neurons through the release of neurotransmitters.

c. Example

• Synaptic Vesicles: Containers that store neurotransmitters released into the synaptic cleft upon action potential arrival.

• Synaptic Cleft: The gap between presynaptic and postsynaptic neurons where neurotransmitter diffusion occurs to transmit signals.

IX. Brain & Spinal Cord Coverings

a. Definition

Layers of protective tissue surrounding the brain and spinal cord.

b. Function

Provide protection and support to the CNS.

c. Example

• Dura Mater: The tough outermost layer that helps protect against injury.

• Arachnoid Mater: The middle layer with a web-like structure that supports blood vessels and contains CSF.

• Pia Mater: The delicate innermost layer that directly adheres to brain and spinal cord tissues.

X. Cerebrospinal Fluid (CSF)

a. Definition

Clear fluid surrounding the brain and spinal cord.

b. Function

Cushions and nourishes the brain and spinal cord.

c. Example

• Choroid Plexus: Structure in the ventricles that produces and regulates the flow of CSF.

XI. Spinal Cord

a. Definition

A cylinder of nerve tissue extending from the brain down the vertebral column.

b. Function

Conducts impulses between the brain and the body, and coordinates reflexes.

c. Example

• Cervical Enlargement: The thickening of spinal cord segments due to nerve supply for the upper limbs.

• Lumbar Enlargement: The thickening for nerves servicing the lower limbs.

• Cauda Equina: A bundle of spinal nerves that extend beyond the termination of the spinal cord.

XII. Reflex Arc Components

a. Definition

The neural pathway involved in a reflex action.

b. Function

Enables quick responses to stimuli without direct involvement of the brain.

c. Example

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

• Sensory Neuron: Transmits impulses to the integrating center.

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

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

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

XIII. Cranial Nerve V - Trigeminal

a. Definition

A cranial nerve responsible for sensation in the face and motor functions like chewing.

b. Function

Enables facial sensation and motor control for chewing.

c. Example

• Clinical assessments: Evaluating responses to facial stimuli to assess trigeminal nerve function.

XIV. Functions of the Spinal Cord

a. Definition

The roles performed by the spinal cord in the nervous system.

b. Function

Processes and transmits sensory and motor information between the body and brain.

c. Example

• Ascending tracts: Pathways responsible for conveying sensory information to the brain.

• Descending tracts: Pathways for transmitting motor commands from the brain to the body.