The Human Brain

The human brain (Figures 12-3 and 12-4) has three major subdivisions: brainstem, cerebellum, and cerebrum.

a. The Brainstem. The brainstem is the core of the brain. We consider it in three parts--the hindbrainstem, the midbrainstem, and the forebrainstem. In general, the brainstem is made up of many nuclei and fiber tracts. It is a primary coordinating center of the human nervous system.

b. The Cerebellum. Over the hindbrainstem is the cerebellum. The cerebellum is connected to both the midbrainstem and the hindbrainstem. The cerebellum is the primary coordinating center for muscle actions. Here, patterns of movements are properly integrated. Thus, information is sent to the appropriate muscles in the appropriate sequences. Also, the cerebellum is very much involved in the postural equilibrium of the body.

central sulcus precentral gyrus postcentral gyrus frontal pole frontal loi temporal p central sulcus precentral gyrus postcentral gyrus frontal pole frontal loi temporal p

Central And Precentral Sulcus Images

temporal lobe \ medulla

Figure 12-3. Human brain; sideview.

temporal lobe \ medulla

Figure 12-3. Human brain; sideview.

Brain Lobes Bottom View
Figure 12-4. Human brain; bottom view.

c. The Cerebrum. Attached to the forebrainstem are the two cerebral hemispheres (Figure 12-5). Together, these two hemispheres make up the cerebrum. Among related species, the cerebrum is the newest development of the brain.

(1) Cerebral hemispheres. The cerebrum consists of two cerebral hemispheres, right and left. They are joined together by a very large fiber tract known as the corpus callosum (the great commissure).

(2) Lobes. Each hemisphere can be divided into four lobes. Each lobe is named after the cranial bone it lies beneath--parietal, frontal, occipital, and temporal. (Actually, there are five lobes. The fifth is hidden at the bottom of the lateral fissure. It is known as the insula or insular lobe. It is devoted mainly to visceral activities.)

(3) Gyri and sulci. The cerebral cortex, the thin layer at the surface of each hemisphere, is folded. This helps to increase the amount of area available to neurons. Each fold is called a gyrus. Each groove between two gyri is called a sulcus.

(a) The lateral sulcus is a cleft separating the frontal and parietal lobes from the temporal and occipital lobes. Therefore, the lateral sulcus runs along the lateral surface of each hemisphere.

(b) The central sulcus is a cleft separating the frontal from the parietal lobe. Roughly, each central sulcus runs from the left or right side of the cerebrum to top center and over into the medial side of the cerebrum.

(c) There are two gyri that run parallel to the central sulcus. Anterior to the central sulcus is the precentral gyrus. Posterior to the central sulcus is the postcentral gyrus.

Cerebral Hemispheres Frontal Section
Figure 12-5. Left cerebral hemisphere.


Extending interiorly from the brain is the spinal cord (Figure 12-6).

Extending interiorly from the brain is the spinal cord (Figure 12-6).

Brainstem Cross Section Levels
Figure 12-6. A cross section of the spinal cord.

a. The spinal cord is continuous with the brainstem. Together, the spinal cord and the brainstem are called the neuraxis. The foramen magnum is taken as the point that divides the brainstem from the spinal cord. Thus, the brainstem is within the cranial cavity of the skull, and the spinal cord is within the vertebral (spinal) canal of the vertebral column.

b. The spinal cord has a central portion known as the gray matter. The gray matter is surrounded by the white matter.

(1) The gray matter is made up of the cell bodies of many different kinds of neurons.

(2) The white matter is made up of the processes of neurons. The white color is due to their myelin sheaths. These processes serve several purposes: Many make a variety of connections within the spinal cord. Many ascend the neuraxis to carry information to the brain. Many descend the neuraxis to carry commands from the brain.

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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.

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  • lauri
    What is each lobe of the cerebral hemisphere named after?
    8 years ago
  • Jennifer
    What are the names of the four lobes of the cerebral hemisphere what is each lobe named after?
    8 years ago
  • markus schultheiss
    Where is the cerebrum located view from top of brain?
    8 years ago
  • sara
    What is the groove that separates the hemispheres of the brain?
    8 years ago
  • clio cattaneo
    What parts make up the human brain?
    8 years ago

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