Nervous System Overview and Classification

Nervous System Overview

• The nervous system is comprised of neurons and neuroglia
• Structures of the brain and spinal cord are arranged in two layers
• Gray matter is composed of nerve cell bodies and proximal parts of nerve fibers arising from nerve cell bodies.
• White matter is composed of the remaining parts of nerve fibers

Nervous System Classification

• Anatomical classification: based on the structures of the brain, spinal cord, and peripheral nerves
• Functional classification: based on the function of the system, somatic and autonomic systems.

Nervous System Components

• Central Nervous System (CNS): includes the brain and spinal cord
  • Brain: is subdivided into the cerebral cortex, cerebellum, brain stem and others
  • Spinal cord: extends from the foramen magnum to the vertebral column
• Peripheral Nervous System (PNS): consists of cranial nerves and spinal nerves, divided into
  • Somatic nervous system
  • Autonomic nervous system: includes sympathetic and parasympathetic nervous systems

Synapse

• Synapse is the junction between two neurons
• It is not an anatomical continuation, only a physiological continuity
• Anatomical classification methods include:
  • Axoaxonic synapse: axon of presynaptic neuron ends on axon of postsynaptic neuron
  • Axodendritic synapse: axon of presynaptic neuron connects with dendrite of postsynaptic neuron
  • Axosomatic synapse: axon of presynaptic neuron ends on the soma (cell body) of postsynaptic neuron
• Functional classification
  • Electrical synapse: the physiological continuity between both neurons is provided by gap junctions.
  • Chemical synapse: neurotransmitter is released from one neuron, crosses the synaptic cleft. and triggers a response in the postsynaptic neuron.

Protection and Nourishment of the Brain

• Central nervous tissue is delicate
• Encased by hard, bony structures (cranium and vertebral column)
• Protected by meninges (three layers):
  • Dura mater
  • Arachnoid mater
  • Pia mater
• Surrounded by cerebrospinal fluid (CSF) a cushioning fluid
• Blood-brain barrier (BBB) selective limits substances entering the brain from the blood stream

Cerebrospinal Fluid (CSF)

• CSF surrounds the brain and spinal cord
• Acts as a shock absorber against mechanical injury
• Facilitates the exchange of materials between neural cells and interstitial fluid
• CSF differs in composition from blood

Blood-Brain Barrier (BBB)

• Neuroprotective structure that prevents entry of many substances and pathogens into the brain tissues from blood
• Exists in capillary membrane of all parts of the brain, except some areas of hypothalamus.

Functions of the Blood-Brain Barrier (BBB)

• Acts as a mechanical barrier and transport mechanisms
• Prevents potentially harmful chemical substances from entering the brain tissue
• Permits entry of essential materials
• BBB provides a healthy environment for nerve cells

Reflex Activity

• Reflex activity is the nervous systems response to stimulation that occurs without consciousness.
• Reflex arc is the anatomical nervous pathway for a reflex action, consisting of: Stimulus, Receptor, Afferent Nerve, Center, Efferent Nerve, Effector Organ

CNS Functional Levels

• Three major levels with specific functional characteristics:
  • Spinal cord level: responsible for walking movements, reflexes, and control of local blood vessels
  • Lower brain or subcortical level: responsible for control of subconscious activities, such as arterial pressure, respiration, equilibrium cerebellum
  • Higher brain or cortical level, including the cerebral cortex, responsible converting the functions of lower brain centers into definitive operations including memory, intelligence, and higher functions

Explore the intricate structures and classifications of the nervous system, including its central and peripheral components. This quiz covers the key aspects of neurons, neuroglia, gray and white matter, and the functional divisions of the nervous system.