Neuroanatomy
Fall 2002

The 100 billion neurons in the brain are not randomly distributed, but are organized in a very precise manner. Today's goal is to learn some of the parts of the nervous system.

The nervous system is divided into two parts:

1. Central nervous system (CNS): Includes the brain & spinal cord

The CNS is very well protected by:
a) Bones--cranium & vertebrae
b) Cerebrospinal fluid (CSF)
c) Meninges--3 layers (Dura mater; arachnoid; pia mater; Figure 7.6) 2. Peripheral nervous system (PNS)--Includes all neurons not in the CNS
The PNS carries messages between the skin, muscles, organs, glands, etc. and the CNS.
These neurons are not very well protected, but grow back when severed.
 
Somas tend to be grouped together and axons tend to be grouped together.
Terminology changes depending on the location:
 
CNS
PNS
somas (gray)
nucleus
ganglion
axons (white)
tract
nerve

These terms can be used to identify the location of structures (e.g., the dorsal root ganglion is a group of somas located in the PNS).
 

Given that the nervous system has 3 dimensions, it is necessary to use terminology that recognizes these 3 dimensions (Figure 7.2)
(the textbook and class whiteboard can only show things in 2 dimensions).
The proper terms to describe:

front & back are anterior & posterior (or rostral & caudal)
top & bottom are dorsal & ventral
side to side are medial & lateral
  The brain can be cut in three different planes (Figure 7.3). 1) coronal--same plane as the front of your face (cut nose off).
2) horizontal--same plane as the top of your head (cut hair off).
3) sagittal--same plane as the side of your head (cut ear off). The inside of brain has large hollow cavaties called ventricles (Figure 7.7 & 7.23)
The middle of the spinal cord is also hollow. This space is called the central canal.
The ventricles and central canal are filled with cerebrospinal fluid (CSF)
 

The brain can be divided into three main sections (Figure 7.21):

1) Forebrain--very large part in front of midbrain. Includes the cerebral cortex which is divided into four lobes: frontal, temporal, parietal, occipital (Figure 7.22). Underneath the cortex are nuclei such as the thalamus and caudate nucleus.
2) Midbrain--a relatively small structure in humans compared to rats (see Figure 7.21)
3) Hindbrain--located between the midbrain and spinal cord. The hindbrain includes the medulla oblongata, pons, and cerebellum.


Peripheral nerves

Cranial nerves--there are 12 pairs of nerves connected directly to the brain. These nerves are numbered 1 to 12 from anterior to posterior (Table 7.1) and are involved in carrying information about the head and some visceral controls. For example, five of the cranial nerves contribute to vision (II, III, IV, VI, & XI).
 

Spinal cord--there are 31 pairs of spinal nerves. These nerves enter and exit the spinal cord between the 31 vertebrae (Figure 7.5).
 

The spinal cord has two primary functions:

1) connects brain & body
2) executes reflexes
A cross section view of the spinal cord reveals a butterfly shaped pattern of neurons in the middle (gray matter) surrounded by fibers (white matter). You should be able to identify the dorsal and ventral sides (Figure 7.19). Sensory information enters the spinal cord on the dorsal side, whereas motor output exists the spinal cord on the ventral side.
 

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