Nervous Evolution Home

Spinal Cord


1: The Skull

The primary function of the skull is to protect the brain, which is the headquarters of the central nervous system and controls the behavior of the organism.
Figure 1.1: Skull in Fetal Pig A
Figure 1.2: Skull in Fetal Pig B

From the two photographs above one can see the skull and its four plates. The plates, which are divided along the dotted lines above in the shape of an X, have not yet fused together in the fetus stage.

2: Functions of the Brain

The brain controls both voluntary and involuntary movement. It enables living creatures to voluntary movements such as walking, breathing, and eating, which are all consciously controlled, as well as complex mental activity, such as thought and reasoning.
Furthermore, it controls involuntary actions, such as heart rate, respiration, and digestion.

3: Parts of the Brain

Cerebrum: (Latin term for "brain".) It is the largest part of the brain that controls many important functions of the body, such as perception, thought, imagination and action. The cerebrum is divided into two halves lengthwise, called cerebral hemispheres, by a line called the longitudinal cerebral fissure (See Fig. 3.6). The cerebrum is also divided into four lobes, shown in the picture below:
Figure 3.1: Lobes of the Brain
Figure 3.1: Lobes of the Brain

Each lobe controls different functions of the body.
Frontal lobe: provides the subject with reasoning, movement, emotions, problem-solving and speech.
Parietal lobe: allows the subject to recognize and respond to a small stimulus such as touch, pain, or a change in temperature or pressure
Occupitial lobe: controls visual processing.
Temporal lobe: controls responses to a verbal stimulus (hearing), enables the subject to verbalize its thoughts and ideas, and helps store memories.

Figure 3.2: Sketh of the top view of the brain

Medulla Oblongata: conveys signals from the brain to the spinal cord and vise versa; it sends the motor signals back and forth between the brain and spinal cord.
Cerebellum: controls voluntary movements, balance, equilibrium, muscle tone, and learning as well as remembering physical skills. There are neural pathways that join the cerebrum to the cerebral motor cortex which is what enables the cerebellum to control the muscle
movements of the body; by sending signals through these neural pathways the muscles are thus caused to move. The cerebellum also is able to
control balance by the spinocerebellar tract which is located on the spinal cord. The spinocerebellar tract is composed of four nerves that send
messages to the brain of the body's position.

(See the pictures below for parts of the brain in the fetal pig, top, and the frog, bottom.)
Figure 3.3: Parts of Fetal Pig Brain
Figure 3.4: Parts of Frog Brain

Figure 3.5: Brain of the Perch

Each animal has their brain divided into different sections to perform different activities. All of the above pictured organisms are vertebrates, which are highly complex organisms that need specialized parts of the brain to process and keep up with their advanced behavior (see elaboration on home page).

Sulci: the narrow fissures separating the adjacent convolutions (gyri, see below).
Gyri: also known as convolution, is the most prominent part of the brain. These compose the ridges on the brain's surface and each convolution is surrounded by sulci.

Figure 3.6: Parts of Fetal Pig Brain B

A starfish does not have a brain; instead it has many nerve networks. See the "Nerves" page for explanation of these networks.

A mussel does not have a brain; it has a rather undeveloped nervous system. See the "Francois the Mussel" page for more information regarding a mussel's nervous system.