The Central Nervous System The central nervous system (CNS) consists of the spinal cord and brain.

Organization of the Nervous System The CNS, composed of the spinal cord and brain, communicates with the PNS, which contains nerves. In the somatic system, nerves conduct impulses from sensory receptors to the CNS and motor impulses from the CNS to the skeletal muscles. In the autonomic system, consisting of the sympathetic and parasympathetic divisions, motor impulses travel to smooth muscle, cardiac muscle, and the glands.

-protected by bone -wrapped in protective meninges -surrounded and cushioned with cerebrospinal fluid

The ventricles: -produce and store cerebrospinal fluid - interconnecting cavities The CNS receives and integrates sensory input and formulates motor output.

Gray matter contains cell bodies and short, nonmyelinated fibers; white matter contains myelinated axons that run in tracts.

The Spinal Cord The spinal cord extends from the base of the brain through the vertebral canal.

Structure of the Spinal Cord A central canal holds cerebrospinal fluid. Gray matter of the spinal cord forms an “H” and contains interneurons and portions of sensory and motor neurons. White matter consists of ascending tracts (dorsally) taking sensory information to the brain and descending tracts (ventrally) carrying motor information from the brain. Tracts cross just before entering the brain.

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The spinal cord has a central canal filled with cerebrospinal fluid, gray matter in an H-shaped configuration, and white matter around the outside. The white matter contains tracts that take nerve impulses to and from the brain. The photomicrograph shows a cross section of the spinal cord.

Functions of the Spinal Cord -centre for many reflex arcs. -sends sensory information to the brain -receives motor output from the brain, -extending communication from the brain to the peripheral nerves for both control of voluntary skeletal muscles and involuntary internal organs. Severing the spinal cord produces paralysis.

The Brain The brain has four cavities called ventricles. The cerebrum has two lateral ventricles, the diencephalon has the third ventricle, and the brain stem and cerebellum have the fourth ventricle.

The Cerebrum The cerebrum has two cerebral hemispheres connected by the corpus callosum. . SEE THE “C”

Cerebral Lobes Learning, memory, language and speech take place in the cerebrum. Sulci divide each hemisphere into lobes including the frontal, parietal, occipital, and temporal lobes Viewed from above, the cerebrum has left and right cerebral hemispheres that are connected by the corpus callosum.

“FAsT - Frontal PEOPLE - Parietal TAKE - Temporal OUT - Occipital CHEESE - Cerebellum BURGERS” - Brain Stem

The Cerebral Cortex The cerebral cortex = thin, outer layer of gray matter covering both hemispheres. The primary motor area is in the frontal lobe; this controls skeletal muscle. The primary somatosensory area is dorsal to the central sulcus or groove. The primary visual area is at the back occipital lobe. The temporal lobe has the primary auditory area.

Language and Speech Language and speech are dependent upon Broca’s area (a motor speech area) and Wernicke’s area (a sensory speech area) that are involved in communication. These two areas are located only in the left hemisphere; the left hemisphere functions in language in general and not just in speech. The left brain and right brain have different functions. Functions associated with the left brain center around those that are verbal, logical, analytical, and rational; functions associated with the right hemisphere are nonverbal, visuo-spatial, intuitive, and creative. Recent studies in hemisphere dominance suggest that rather than hemisphere dominance, the hemispheres simply process the same information differently.

The Diencephalon (Two in the Head) The hypothalamus and thalamus are in the diencephalon that encircles the third ventricle. The hypothalamus controls homeostasis and the pituitary gland, and the thalamus receives all sensory input except smell and integrates it and sends it to the cerebrum. The hypothalamus is an integrating center that helps maintain homeostasis by regulating hunger, sleep, thirst, body temperature, and water balance. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems.

The Cerebellum – “little brain” The cerebellum receives sensory input from eyes, ears, joints and muscles and receives motor input from the cerebral cortex. It integrates this information to maintain posture, coordination and balance. The cerebellum is involved in learning of new motor skills, such as playing the piano or hitting a golf ball.

The Brain Stem The brain stem contains the medulla oblongata, pons, and midbrain. The medulla oblongata and pons have centers for vital functions such as breathing, heartbeat, and vasoconstriction (blood vessel narrowing) The medulla also coordinates swallowing and some other automatic reactions (many reflex centers for heartbeat, breathing and BP) The midbrain acts as a relay station between the cerebrum and spinal cord or cerebellum. The medulla oblongata contains reflex centers for vomiting, coughing, sneezing, hiccupping, and swallowing.

The Reticular Formation The reticular formation is a complex network of nuclei and fibers that extend the length of the brain stem. One portion of the reticular formation, called the reticular activating system, arouses the cerebrum via the thalamus causing alertness. It is believed to act as a filter for incoming sensory impulses. A severe injury to the reticular activating system can cause a person to be comatose.