The Central Nervous System

THE CENTRAL NERVOUS SYSTEM The brain and spinal cord make up the central nervous system, which occupy the dorsal body cavity and acts as the integrating and command centers of the nervous system. They interpret incoming sensory information and issue instructions based on past experience and current conditions. The spinal cord attaches to the brain through a hole at the base of the skull, the magnum foramen, and extends all the way down to the lumbar spine (lower back).

PERIPHERAL NERVOUS SYSTEM The part of the nervous system outside the CNS, consist mainly of the nerves that extend from the brain and spinal cord. The 12 pairs of cranial nerves carry impulses to and from the brain and 31

pairs of spinal nerves

carry impulses to and from the spinal cord.

FUNCTIONAL CLASSIFICATION SENSORY OR AFFERENT DIVISION Consist of nerve system from sensory receptors located in various parts of the body. Sensory fibers delivering impulses from the skin, skeletal muscles and joints are called somatic sensory fibers, whereas those transmitting impulses from the visceral organs are called visceral sensory fibers.

MOTOR OR EFFERENT DIVISION Carries impulses from the CNS to effectors organs, the muscles and glands. These impulses activate muscles and glands that is they effect a motor response.

TWO MOTOR SUBDIVISIONS 1. SOMATIC NERVOUS SYSTEM (voluntary nervous system) Allows us to consciously, or voluntarily, control our skeletal muscles

2. AUTONOMIC NERVOUS SYSTEM (involuntary nervous system) Regulates events that are automatic or involuntary, such as the activity of smooth and cardiac muscles and glands. Two parts: sympathetic and parasympathetic

BRAIN CELLS OR THE SUPPORTING CELLS

Brain tissue is composed of several different types of cells. These include neurons and specialized cells called glial cells, such as astrocytes, oligodendrocytes, ependymal cells, and

microglial. Brain tumor types are determined by the type of cell in which the tumor originated. Astrocytes—Astrocytes are small star-shaped glial cells. This cell type is one of the few types that maintain their ability to reproduce in the mature brain, and it is thought that they might be susceptible to agents that alter cellular replication. This may explain why most primary tumors in the central nervous system have an astrocytic origin.

Oligodendrocytes—Oligodendrocytes are highy specialized glial cells that form the myelin insulation, or myelin sheath, around the axons in nerve cells.

Ependymocytes—Ependymocytes are the glial cells that make up the ependyma, the membrane that lines the ventricles of the brain and the central canal of the spinal cord.

Microglial—Microglial cells function chiefly as scavengers. When central nervous system tissue is damaged, microglial cells migrate to the site where they proliferate and devour the cellular debris.

NEURONS A neuron also known as a neurone or nerve cell) is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves. A number of specialized types of neurons exist: sensory neurons respond to touch, sound, light and numerous other stimuli affecting cells of the sensory organs that then send signals to the spinal cord and brain. Motor neurons receive signals from the brain and spinal cord and cause muscle contractions and affect glands. Interneurons connect neurons to other neurons within the same region of the brain or spinal cord. Neurons respond to stimuli, and communicate the presence of stimuli to the central nervous system, which processes that information and sends responses to other parts of the body for action. Neurons do not go through mitosis, and usually cannot be replaced after being destroyed, although astrocytes have been observed to turn into neurons as they are sometimes pluripotent.

BRAIN

1.CEREBRUM In the cerebrum, there are fifty hundred to one hundred thousand neurons, the telegram of information is sent from place to place like a telegram. The cerebrum is divided in to two hemispheres, the right and left hemispheres. The dividing point is a deep grove called the longitude cerebral fissure. The different sides of the cerebrum do different things for the opposite sides of the body. The right side of the cerebrum controls things such as imagination and 3-D forms. The other side of the brain, the left side, controls numbering skills, posture, and reasoning. The hemispheres also consist of many other parts such as the lobes.

Cerebral Cortex Lobes •

Frontal Lobes -involved with decision-making, problem solving, and planning

•

Occipital Lobes-involved with vision and color recognition

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Parietal Lobes - receives and processes sensory information

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Temporal Lobes - involved with emotional responses, memory, and speech

Cingulate Gyrus - a fold in the brain involved with sensory input concerning emotions and the regulation of

aggressive behavior.

Fissure of Sylvius (Lateral Sulcus) - Deep grove that separates the parietal and temporal lobes Central Sulcus (Fissure of Rolando) - Deep grove that separates the parietal and frontal lobes

Wernicke's Area Region of the brain where spoken language is understood

Broca’s Area Found at the base of the precentral gyrus

Corpus Callosum Thick band of fibers that connects the left and right brain hemispheres

Basal Ganglia Involved in cognition and voluntary movement Diseases related to damages of this area are Parkinson's and Huntington's

2.DIENCEPHALON Limbic System Structures

Thalamus - mass of grey matter cells that relay sensory signals to and from the spinal cord and the cerebrum

Hypothalamus - directs a multitude of important functions such as body temperature, hunger, and homeostasis Epithalamus – reflex centers involved in olfaction of the third ventricle. Important part of the epithalamus are the pineal gland which are endocrine gland involved in biological rhythms,secretes the hormone melatonin

3. BRAIN STEM

The size of a thumb in diameter and approximately 3 inches.

Medulla Oblongata - Lower part of the brainstem that helps to control autonomic functions such as control of heart rate,blood pressure, breathing, swallowing and vomiting. Pons - Relays sensory information between the cerebrum and cerebellum. Important nuclei involved in the control of breathing. Reticular Formation - Nerve fibers located inside the brainstem and regulate awareness and sleep. Midbrain – small part of the brain stem. It extends from the mammillary bodies to the pons inferiorly. These bulging nuclei are reflex centers involved with vision and hearing.

4. CEREBELLUM The large cauliflower projects dorsally from under occipital lobe of the cerebrum. It provides the precise timing for skeletal muscle activity and controls our balance and equilibrium.

PROTECTION OF THE CENTRAL NERVOUS SYSTEM Ventricles and Cerebrospinal Fluid-

There are four chambers in the brain, the ventricles, that contain structures (called the choroid plexus) that produce cerebrospinal fluid. The cerebrospinal fluid flows through the ventricles and bathes the brain and spinal cord.

Meninges-

The meninges is the thin, protective membranous covering that suspends the brain within the skull and prevents the brain from pressing against the skull's inner surface. The meninges is a laminated, or layered, structure. The outermost layer is the dura mater ("tough mother" in Latin), a fibrous membrane that stabilizes the CNS within the skull and the spinal column. The middle layer, the arachnoid mater, contains cerebrospinal fluid, arteries, veins, and cranial nerve roots. It also secures the dura to the innermost layer, the pia mater, a delicate membrane that clings to the contours of the brain, thereby distributing the forces that suspend the brain within the skull.

Blood-brain barrier-

Protection from harmful substances in the blood is provided by the so-

called blood-brain barrier.

SPINAL CORD 17 inches glistening white continuation of the brain stem. The spinal cord provides a two-way conduction pathway to and from the brain and it is a major reflex center (the spinal reflexes are completed at this level).

Cranial Nerves

There are 12 pairs of cranial nerves that control sensory and motor activities:

I

OLFACTORY- Smell

II

OPTIC-Vision

III

OCULOMOTOR-Eye movement

IV

TROCHLEAR- Eye movement

V

TRIGEMINAL- Facial sensation

VI

ABDUCENS- Eye movement

VII

FACIAL- Face movement

VIII

VESTIBULOCOCHLEAR- Hearing and balance

IX

GLOSSOPHARYNGEAL- Taste and gag reflex

X

VAGUS- Involuntary muscles: heart, stomach, intestines, throat, chest

XI

ACCESSORY- Voluntary muscles of the neck

XII

HYPOGLOSSAL- Tongue movement