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Human Nervous System - CNS, Spinal cord

by 우당탕탕 is me 2024. 9. 2.

1. Anatomical Terminology Overview

  • Directional Terms:
    • Anterior: Refers to the front side of the body.
    • Posterior: Refers to the back side of the body.
    • Superior: Positioned above or towards the head.
    • Inferior: Positioned below or towards the feet.
    • Medial: Closer to the midline of the body.
    • Lateral: Farther from the midline of the body.
    • Proximal: Closer to the trunk or the center of the body.
    • Distal: Farther away from the trunk or the center of the body.
  • Relative Positioning Terms:
    • Ipsilateral: Refers to structures on the same side of the body (e.g., left arm and left leg).
    • Contralateral: Refers to structures on opposite sides of the body (e.g., left arm and right leg).
  • Anatomical Planes:
    • Sagittal Plane: Divides the body into left and right parts.
    • Coronal (Frontal) Plane: Divides the body into anterior (front) and posterior (back) parts.
    • Transverse (Horizontal) Plane: Divides the body into superior (upper) and inferior (lower) parts.

2. Central Nervous System (CNS) vs. Peripheral Nervous System (PNS)

  • Nervous System Overview:
    • The human nervous system is divided into two main subsystems:
      • Central Nervous System (CNS): Consists of the brain and spinal cord. Represented in gray in illustrations.
      • Peripheral Nervous System (PNS): Includes all nerves outside the CNS, represented in yellow.
  • Differences between CNS and PNS:
    • CNS:
      • Located in the superior part of the body.
      • Encased and protected by bones (the skull for the brain and vertebrae for the spinal cord).
      • Responsible for processing and integrating information.
    • PNS:
      • Extends from the CNS to the limbs and other body parts.
      • Involves nerves that transmit sensory and motor signals between the CNS and the rest of the body.
      • Consists of two subsystems: Autonomic Nervous System (ANS) and Somatic Nervous System (SNS).

3. Peripheral Nervous System (PNS) Subsystems

  • Autonomic Nervous System (ANS):
    • Involuntary system that regulates internal organs and glands without conscious control.
    • Divided into:
      • Sympathetic Nervous System: Activated in stress ("fight or flight" response).
      • Parasympathetic Nervous System: Activated in relaxation ("rest and digest" response).
  • Somatic Nervous System (SNS):
    • Voluntary system that controls skeletal muscles.
    • Allows conscious control over movements (e.g., walking, picking up objects).

4. Structure and Function of the Spinal Cord

  • Spinal Cord Anatomy:
    • Part of the Central Nervous System.
    • Located within the vertebral column.
    • Acts as a conduit for signals between the brain and the peripheral nerves.
    • Facilitates reflex actions independently of the brain.
  • Functional Regions of the Spinal Cord:
    • Gray Matter: Contains neuron cell bodies, dendrites, and synapses.
      • Involved in reflexes and interneuron communication.
    • White Matter: Composed of myelinated axons.
      • Responsible for transmitting signals to and from the brain.

5. Role of the Nervous System in Body Function

  • CNS (Central Nervous System):
    • Processes sensory information.
    • Coordinates voluntary and involuntary actions.
    • Integrates data from various parts of the body and generates appropriate responses.
  • PNS (Peripheral Nervous System):
    • Transmits sensory information to the CNS.
    • Carries motor commands from the CNS to muscles and glands.
    • Divided into Somatic (voluntary control) and Autonomic (involuntary control) subsystems.

6. Key Points for Understanding the Nervous System

  • Remember the anatomical terms for discussing body orientation and positioning.
  • Understand the different planes used to view and analyze anatomical structures.
  • Recognize the roles and differences between the CNS and PNS.
  • Differentiate between the Autonomic Nervous System (involuntary) and the Somatic Nervous System (voluntary).
  • Appreciate how the CNS (brain and spinal cord) is protected and functions to process and relay information throughout the body.

CNS Overview

  • The Central Nervous System (CNS) is composed of the brain and the spinal cord.
  • The CNS is protected by a three-part protection system: the meninges, the cerebrospinal fluid (CSF), and the bony structures (cranium and vertebrae).

Meninges

  • The meninges are three protective layers that cover the brain and spinal cord:
    1. Dura Mater: The outermost, tough layer that provides primary protection.
    2. Arachnoid Mater: The middle layer, which has a spiderweb-like appearance. The space beneath it, called the subarachnoid space, contains CSF.
    3. Pia Mater: The innermost, delicate layer that closely adheres to the surface of the brain and spinal cord.
  • These three layers together form the protective covering of the brain and spinal cord.

Cerebrospinal Fluid (CSF)

  • Cerebrospinal Fluid (CSF) is a clear, colorless fluid that:
    • Provides physical protection by acting as a cushion for the brain and spinal cord.
    • Offers chemical protection by maintaining a stable environment, free of proteins and blood cells.
    • CSF is produced by the choroid plexus in the brain's ventricles at a rate of approximately 500 mL per day.
    • It circulates through the ventricles, the central canal of the spinal cord, and the subarachnoid space.
    • CSF is absorbed into the blood through structures called arachnoid villi.

 

Brain Ventricles

  • The ventricles are interconnected cavities within the brain filled with CSF:
    • Two lateral ventricles (right and left)
    • Third ventricle
    • Fourth ventricle
  • These ventricles are involved in the production and circulation of CSF, which provides cushioning and nutrients to the brain and spinal cord.

Spinal Cord Structure

  • The spinal cord is an extension of the CNS and is protected by the same meninges (dura mater, arachnoid mater, and pia mater) as the brain.
  • It consists of two types of matter:
    • Gray Matter: Located in the center, containing neuron cell bodies, dendrites, and unmyelinated axons. It forms an "H" or butterfly shape.
    • White Matter: Surrounds the gray matter, consisting of myelinated axons that form tracts to transmit signals to and from the brain.

Spinal Cord Function

  • The spinal cord is responsible for:
    • Relaying sensory and motor information between the body and the brain.
    • Controlling reflexes that require quick responses, such as the withdrawal reflex (e.g., stepping on a sharp object).

Spinal Nerves and Roots

  • Spinal nerves are 31 pairs of nerves that emerge from the spinal cord:
    • Dorsal Root: Contains sensory neurons that carry information from the body to the CNS.
    • Ventral Root: Contains motor neurons that carry commands from the CNS to muscles.
  • Dorsal Root Ganglion: A cluster of sensory neuron cell bodies located in the dorsal root.

Reflex Arcs

  • Reflex actions, such as the knee-jerk reflex, are processed at the level of the spinal cord and do not require input from the brain.
  • Reflex arcs involve:
    • Sensory Neurons: Detect stimuli and transmit signals to the spinal cord.
    • Interneurons: Located in the spinal cord, connect sensory neurons to motor neurons.
    • Motor Neurons: Carry signals from the spinal cord to muscles to initiate movement.

CNS vs. Peripheral Nervous System (PNS)

  • CNS: Comprises the brain and spinal cord.
  • PNS: Consists of nerves and ganglia outside the CNS, including:
    • Somatic Nervous System: Controls voluntary movements and conveys sensory information.
    • Autonomic Nervous System (ANS): Regulates involuntary body functions and is divided into:
      • Sympathetic Nervous System: Activates 'fight or flight' response.
      • Parasympathetic Nervous System: Promotes 'rest and digest' state.

Cranial Nerves

  • There are 12 pairs of cranial nerves that emerge directly from the brain:
    • Cranial Nerve I: Olfactory nerve - sense of smell.
    • Cranial Nerve II: Optic nerve - vision.
    • Cranial Nerves III to XII: Include various nerves controlling eye movements, facial muscles, hearing, balance, taste, and functions related to the head and neck.
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