Notes Ch. 11A Nervous System II Anatomy and Physiology

Overview of Divisions of the Nervous system The central nervous system (CNS) is made of the brain and the spinal cord. The brain is the largest and most complex part of the nervous system. The brain oversees sensation and perception, movement, and thinking. The brain has 2 cerebral hemispheres, the diencephalon, the brainstem, and the cerebellum. The brain has about 100 billion multipolar neurons. Remember that gray matter is neuron cell bodies with unmyelinated axons. White matter has myelinated axons.

The brain connects to the spinal cord by the brainstem The brain connects to the spinal cord by the brainstem. The brain and spinal cord coordinate with the peripheral nervous system (PNS). Membranes called meninges are located between the bone and soft tissues of the nervous system.

Meninges The meninges have 3 layers - dura mater, arachnoid mater, and pia mater. The dura mater is the outermost layer. It is made of tough, white,dense connective tissue and contains many blood vessels and nerves. It attaches to the inside of the cranial cavity and forms the internal periosteum of the surrounding skull bones.

In some areas the dura mater splits into two layers, forming channels called dural sinuses. Blood flows through these channels as it returns from the brain to vessels leading to the heart. The dura mater continues into the vertebral canal and surrounds the spinal cord.

The arachnoid mater is a thin, weblike membrane that does not have blood vessels and is located between the dura and pia maters. The space between the arachnoid and pia maters contains the clear, watery cerebrospinal fluid (CSF). The CSF allows the brain and spinal cord to float and protects them by absorbing forces that might jar and damage the tissue.

The pia mater is thin and contains many nerves and blood vessels that nourish underlying cells of the brain and spinal cord. This attaches to the surface of brain and spinal cord and follows the contours of them.

Ventricles and Cerebrospinal Fluid CSF is formed in four interconnected cavities called ventricles. They are found in the cerebral hemispheres of the brain and the brainstem. There are 2 lateral ventricles that are the largest. The first is in the left cerebral hemisphere and the second is in the right cerebral hemisphere. There is a narrow space that makes up the third ventricle. The fourth ventricle is in the brain stem.

Choroid plexuses make CSF Choroid plexuses make CSF. They are tiny, reddish, cauliflower like masses of specialized capillaries from the pia mater. CSF is a clear, somewhat viscous liquid. It contains a large amount of sodium and lesser concentrations of glucose and potassium than other extracellular fluids. CSF is both nutritive and protective. Humans secrete almost 500 milliliters of CSF every day. Only about 140 milliliters are in the nervous system at any time.