The Structure and Function of the Nervous System

1. Basic Functions of the Nervous System:

The nervous system is a complex system that plays a crucial role in controlling and coordinating the body’s activities. The basic functions of the nervous system include:

• Sensation: Receiving information from the internal and external environment through sensory organs.
• Movement: Controlling muscle contractions, enabling the body to move and perform other actions.
• Autonomic (Visceral): Regulating the body’s automatic functions, such as heartbeat, breathing, digestion, excretion, etc.
• Cognition (Higher Nervous System): Performing activities related to thinking, memory, language, emotions, etc.

2. Classification of the Nervous System Based on Anatomy:

• Central Nervous System (CNS): Consists of the brain and spinal cord, which are the control centers for bodily functions.
  • Brain: The highest control center of the nervous system, comprising the forebrain, midbrain, hindbrain, cerebellum, and brainstem.
  • Spinal cord: A bundle of nerve fibers connecting the brain to other organs and parts of the body, responsible for transmitting information and controlling reflexes.
• Peripheral Nervous System (PNS): Includes nerves that connect the CNS to other parts of the body.
  • 31 pairs of spinal nerves: Originating from the spinal cord, controlling the functions of the body, organs, and parts located in the trunk and limbs.
  • 12 pairs of cranial nerves: Originating from the brain, controlling the functions of the body, organs, and parts located in the head and neck.
  • Ganglia: Clusters of nerve cells scattered throughout the PNS, responsible for controlling some of the body’s automatic functions.

3. Classification of the Nervous System Based on Physiology:

• Somatic Nervous System: Controls voluntary activities, including conscious movement and sensation.
• Autonomic Nervous System (ANS): Controls involuntary, automatic functions of the body, further divided into two branches:
  • Sympathetic ANS: Activated when the body is in a state of stress or excitement, for example: increased heart rate, increased blood pressure, dilation of pupils, etc.
  • Parasympathetic ANS: Activated when the body is in a state of rest or relaxation, for example: decreased heart rate, decreased blood pressure, constriction of pupils, etc.

4. Nerve Cells (Neurons):

• Number: Over 1000 billion nerve cells in the human body.
• Types:
  • Neurons: The structural and functional units of the nervous system, consisting of three main parts: cell body, axon, and dendrites.
  • Glial cells: Supporting cells that surround and nourish nerve cells, ensuring the normal functioning of the nervous system.

5. Functions of Glial Cells:

• Supporting and Maintaining Environment: Providing nutrients, oxygen, and removing waste products for neurons.
• Protecting Nerve Cells: Supporting the regeneration and repair of damaged nerve cells.
• Facilitating Rapid Signal Transmission: Forming myelin sheaths around axons, enabling faster nerve signal transmission.

6. Classification of Neurons by Function:

• Sensory Neurons: Receive information from the internal and external environment, transmitting information to the CNS.
• Motor Neurons: Transmit information from the CNS to organs, muscles, and glands, controlling bodily functions.
• Interneurons: Connect sensory and motor neurons, processing information and generating responses.

7. Ion Channels in the Nerve Cell Membrane:

• 3 types of ion channels:
  • Passive ion channels: Always open, allowing ions to pass through the cell membrane freely.
  • Chemically-gated ion channels: Open when chemical substances act upon them.
  • Voltage-gated ion channels: Open when there is a change in the membrane potential.
• Chemically-gated ion channels are present on the axon and cell body membrane: WRONG, chemically-gated ion channels are present on the cell body and dendrites.
• Voltage-gated ion channels are responsible for generating and propagating action potentials: CORRECT.

8. Myelin Sheath:

• Schwann cells are responsible for surrounding the axon and protecting it from interstitial fluid, forming the myelin sheath in the PNS: CORRECT.
• Role of satellite cells: Surrounding ganglia outside the CNS.

9. Types of Glial Cells in the CNS:

• 4 types:
  • Oligodendrocytes: Form myelin sheaths in the CNS.
  • Astrocytes: Support the regeneration and repair of damaged nerve cells.
  • Microglia: Provide nutrients, oxygen, and remove waste products for neurons.
  • Schwann cells: Surround axons, helping to conduct signals faster.

10. Resting Membrane Potential:

• The resting membrane potential is around -70mV: CORRECT.

11. Resting Nerve Cell Membrane:

• The resting nerve cell membrane is more permeable to K+: CORRECT.

12. Nerve Impulse Transmission:

• Local transmission is 50 times faster than saltatory conduction: WRONG, saltatory conduction is faster than local transmission.
• When will the speed of saltatory conduction be faster? When the distance between the Nodes of Ranvier is shorter.
• The larger the diameter of the fiber, the faster the conduction: CORRECT.
• In a living organism, an axon can conduct in both directions: WRONG, in a living organism, nerve impulses only travel in one direction from the terminal bouton of one cell to another.

13. Meninges and Cerebrospinal Fluid:

• How many layers of connective tissue are there in the meninges? List them: 3 layers: Dura mater, arachnoid mater, pia mater.
• The spinal meninges have a structure similar to the cranial meninges: CORRECT.
• Where is the cerebrospinal fluid produced? Choroid plexuses in the ventricles.
• How many ventricles are there? 4: Left ventricle, right ventricle, third ventricle, fourth ventricle.
• The cerebrospinal fluid is located in the subarachnoid space: WRONG, cerebrospinal fluid is located in the ventricles and subarachnoid space.
• Cerebrospinal fluid composition differs from plasma (more protein and glucose, less Cl- and K+): WRONG, cerebrospinal fluid has less protein and glucose, more Cl- and K+ than plasma.

14. Blood-Brain Barrier:

• The blood-brain barrier is primarily composed of astrocytes: CORRECT.

15. Cerebral Arterial System:

• The cerebral arteries originate from the basilar artery and internal carotid arteries: WRONG, the cerebral arteries originate from the vertebral arteries and internal carotid arteries.
• Damage to which artery in the cerebral arterial system is most dangerous? Basilar artery, as there is only one branch.
• What arteries constitute the Circle of Willis? Anterior cerebral arteries, posterior communicating arteries, posterior cerebral arteries, sometimes the anterior communicating artery.

16. Origin of Nervous Tissue:

• In terms of origin, nervous tissue is formed from the ectoderm of the embryo: CORRECT.

Notes:

• The information in this article is general in nature and may not be entirely accurate.
• To gain a deeper understanding of the structure and function of the nervous system, consult specialized materials.
• This article is for reference purposes only and cannot replace the advice of a qualified medical professional.