Ventricles And Cerebrospinal Fluid

Interconnected cavities called ventricles (ven'tri-klz) are located within the cerebral hemispheres and brain stem (fig. 11.3 and reference plates 53 and 54). These spaces are continuous with the central canal of the spinal cord and are filled with cerebrospinal fluid.

The largest ventricles are the lateral ventricles, which are the first and second ventricles (the first ventricle in the left cerebral hemisphere and the second ventricle in the right cerebral hemisphere). They extend into the cerebral hemispheres and occupy portions of the frontal, temporal, and occipital lobes.

A narrow space that constitutes the third ventricle is located in the midline of the brain beneath the corpus callosum, which is a bridge of axons that links the two parts of the cerebrum. This ventricle communicates with the lateral ventricles through openings (interventricular foramina) in its anterior end.

Intraventricular foramen

Cerebral aqueduct

Lateral ventricle

Lateral ventricle

Intraventricular foramen

Cerebral aqueduct

Lateral Aqueduct

Cerebral aqueduct

Fourth ventricle

To central canal of spinal cord

Figure 11.3

(a) Anterior view of the ventricles within the cerebral hemispheres and brain stem. (b) Lateral view.

Cerebral aqueduct

Fourth ventricle

To central canal of spinal cord

Figure 11.3

(a) Anterior view of the ventricles within the cerebral hemispheres and brain stem. (b) Lateral view.

The fourth ventricle is located in the brain stem just in front of the cerebellum. A narrow canal, the cerebral aqueduct (aqueduct of Sylvius), connects it to the third ventricle and passes lengthwise through the brain stem. This ventricle is continuous with the central canal of the spinal cord and has openings in its roof that lead into the subarachnoid space of the meninges.

Tiny, reddish cauliflowerlike masses of specialized capillaries from the pia mater, called choroid plexuses, (ko'roid plek'sus-ez) secrete cerebrospinal fluid. These structures project into the cavities of the ventricles (fig. 11.4). A single layer of specialized ependymal cells (see chapter 10, p. 372) joined closely by tight junctions covers the choroid plexuses. In much the same way that astrocytes provide a barrier between the blood and the brain interstitial fluid (blood-brain barrier), these cells block passage of water-soluble substances between the blood and the cerebrospinal fluid. At the same time, the cells selectively transfer certain substances from the blood into the cerebrospinal fluid by facilitated diffusion and transfer other substances by active transport (see chapter 3, p. 88), thus regulating the composition of the cerebrospinal fluid.

Most of the cerebrospinal fluid arises in the lateral ventricles, from where it slowly circulates into the third and fourth ventricles and into the central canal of the spinal cord. It also enters the subarachnoid space of the meninges by passing through the wall of the fourth ventricle near the cerebellum.

Humans secrete nearly 500 milliliters of cere-brospinal fluid daily. However, only about 140 milliliters are in the nervous system at any time, because cere-brospinal fluid is continuously reabsorbed into the blood. The CSF is reabsorbed through tiny, fingerlike structures called arachnoid granulations that project from the subarachnoid space into the blood-filled dural sinuses (fig. 11.4).

Cerebrospinal fluid is a clear, somewhat viscid liquid that differs in composition from the fluid that leaves the capillaries in other parts of the body. Specifically, it contains a greater concentration of sodium

Arachnoid granulations

Choroid plexus

Choroid plexus of third ventricle

Interventricular foramen

Third ventricle

Cerebral aqueduct Fourth ventricle

Choroid plexus of fourth ventricle

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Responses

  • SARAH
    What size tumor in 4th ventricle in cerebellumto block spinal fluid?
    4 years ago
  • wilma
    What structure has four interconnected cavities located in cerebral hemisphere?
    4 years ago
  • nina anderson
    Which lateral walls of which ventricle are two openings leading into the subarachnoid space?
    4 years ago
  • richard
    What passage way in the spinal cord is contiuous with the vetricles?
    4 years ago
  • harley
    Which ventricle is continuous with the central canal of the spinal cord?
    4 years ago
  • delmo
    Is cerebral spinla fluid reabsorbed into the blood by the cererbral arteries?
    4 years ago
  • Rufino
    What are the ventricles that have tiny capillaries located in the walls of?
    4 years ago
  • debra
    What is the name of the specialized capillaries that secrete cerebrospinal fluid?
    2 years ago
  • melilot
    What is the name of the specialized capallaries that secrete ceresponal fluid?
    1 year ago
  • edvige colombo
    What is the name of the specialized capillaries that sexrete cerebrospinal fluid?
    1 year ago
  • folcard
    Which ventricle is located within the brain stem?
    8 months ago

Post a comment