The Central Nervous System

The Central Nervous System There are two main structures that make up the central nervous system (CNS): – Brain – Spinal Cord

Coverings of the Brain and Spinal Cord The brain and spinal cord are both delicate and vital, nature has provided them with two protective coverings: – Bone (cranium and vertebrae) – Meninges (3 layers of connective tissues)

Dura mater – made of strong white fibrous tissue The Meninges Arachnoid membrane – delicate cob-web like layer Pia mater – transparent innermost layer of the meninges that covers the brain and spinal cord and contains blood vessels

Spaces Between & Around the Meninges

Epidural Space Outside the dura and inside the bony coverings of the brain and spinal cord. Contains supporting cushion of fat and other connective tissues.

Subdural Space Between the dura mater and the arachnoid membrane Contains a small amount of lubricating fluid

Subdural Hematoma

Subarachnoid Space Under the archnoid space and outside of the pia mater Contains a significant amount of cerebrospinal fluid

Menenges and Spaces

Histology of the Meninges

Meningitis An infection or inflammation of the meninges Most commonly caused by bacteria, however, it may also be caused by viral or fungal infections or tumors Usually complain of fever and severe headaches Can be fatal

Cerebrospinal Fluid (CSF) Acts as additional cushion Reservoir of circulating fluid that, along with blood, the brain monitors for changes in the internal environment. If CO 2 content in the CSF goes up, a homeostatic response is triggered in the respiratory control centers of the brainstem

Fluid Spaces Found in the subarachnoid space Within cavities and canals of the brain and spinal cord The large, fluid-filled cavities of the brain are called

ventricles .

Ventricles of the Brain

Formation and Circulation of CSF

The Spinal Cord About 45 cm long Extends from the foramen magnum to the border of the first lumbar vertebrae Two nerve roots project from each side of the spinal cord – Dorsal carries sensory information – Ventral carries motor information out

Structure of the Spinal Cord

Spinal Cord Function Two main functions – Provides conduction routes to and from the brain – Serves as an integrator for all spinal reflexes Tracts provide conduction paths to and from the brain (composed of axon bundles) – Ascending tracts conduct sensory impulses up the cord to the brain – Descending tracts conduct motor impulses down the cord from the brain

Spinal Tracts

The Brain Weighs about three pounds in adults Neurons can grown in size, but not increase in number Grows rapidly during the first nine years and matures at about 18 years 6 Major divisions

Medulla Oblongata Attaches to the spinal cord Contains control centers —for example, the cardiac, respiratory, and vasomotor control centers

Pons Lies just above the medulla Passes information from the brain to the body and vice versa, controls facial expression.

Midbrain Also called the mesencephalon Forms the midsection of the brain Involved in auditory and visual function as well as some muscular control functions

Functions of the Brainstem Sensory, motor and reflex functions Reflexes such as those for vomiting, coughing, sneezing, hiccupping and swallowing are located in the brain stem

Cerebellum 2 nd largest part of the brain Gray matter makes up the outer portion, or cortex and white matter makes up the interior portions Has numerous grooves (sulci) and raised areas (gyri)

Functions of the Cerebellum Acts with cerebral cortex to produce skilled movements by coordinating activities of groups of muscles Helps control posture Controls movements so they are not jerky Controls skeletal muscles to maintain balance

Diencephalon Located between the cerebrum and midbrain The main structures of the diencephalon are the: – Thalamus – sensations, relay info to cerebrum, emotions, complex reflex movements – Hypothalamus – link between mind and body and links the nervous system and endocrine system – Optic chiasma – optic nerves cross – Pineal body – seems to be important in regulating the body’s biological clock

Cerebrum Largest division of the brian Consists of two hemispheres Surface (cerebral cortex) is made up of gray matter only 2 – 4 mm thick Each hemisphere is divided into 5 lobes

Functional Areas of the Cerebral Cortex

Primary Somatic Sensory and Motor Areas of the Cortex