Nervous System Division Study Guide

NERVOUS SYSTEM Topic Outline 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Nervous System Division Nerve Tissue Types of Neurons Nerve and Nerve Tracts Nerve Impulse Spinal Cord The Brain Meninges and Cerebrospinal Fluid Cranial Nerves The Autonomic Nervous System Learning Objectives • • • • • • • • • • • • After studying this topic, you will be able to: Name the division of the nervous system and the parts of each, and state the general functions of the nervous system Name the parts of a neuron and state the function of each Explain the importance of Schwann cells in the peripheral nervous system and neuroglia in the central nervous system Describe the electrical nerve impulses, and describe impulse transmission at synapses Describe the types of neurons, nerves, and nerve tracts State the name and numbers of the spinal nerves and their destinations State the functions of the parts of the brain and be able to locate each part on a diagram Name the meninges and describe their locations State the location and functions of cerebrospinal fluid Name the cranial nerves, and state their functions Explain how the sympathetic division of the autonomic nervous system enables the body to adapt to a stressful situation Explain how the parasympathetic division of the autonomic nervous system promotes normal body functioning in a relaxed situation. Introduction The nervous system, a remarkable creation of God, orchestrates our body's activities, from basic functions to complex thoughts. It uses nerve impulses to control tissues, organs, and systems, allowing us to perceive and react to our surroundings and internal changes. This intricate system reflects divine design and intelligence. This study guide describes the anatomy and physiology of the nervous system. The general functions of the nervous system are to detect changes and feel sensations, initiate appropriate responses to changes, and organize information for immediate or later use. These functions of the nervous system are directly related to the normal physiology of other organ systems and to the homeostasis of the body as a whole. Activating Prior Knowledge 1. The nervous system sends signals at speeds up to 268 miles per hour, allowing instant communication throughout the body. 2. The brain contains about 86 billion neurons, forming a vast network that controls every thought, movement, and sensation. 3. The brain can adapt and reorganize itself, a feature known as neuroplasticity, allowing learning and recovery from injuries. 4. The nervous system enables reflex actions, which are automatic and protect the body from harm without conscious thought. 5. The brain can store vast amounts of information, with some estimates suggesting it can hold up to 2.5 petabytes, showcasing God's intricate design. Discussion of Key Concepts Functions of the Nervous System 1. Detect changes & feel sensations 2. Organize & store information 3. Initiate responses to changes Division of the Nervous System 1. Central Nervous System (CNS): Brain and Spinal cord 2. Peripheral nervous System (PNS): Cranial Nerves & Spinal Nerves Nerve Tissue 1. Neurons: nerve cells; the functional unit of the nervous system. a. Cell body: contains the nucleus & other organelles. Regulates the functioning of the neuron. b. Nerve cell processes (extensions): i. Dendrites: carry impulses toward the cell body ii. Axon: carries impulses away from the cell body Myelin Sheath: multilayered lipid & protein covering formed by Schwann cells in the PNS & oligodendrocytes in the CNS, around axons of many peripheral & CNS neurons. It allows rapid conduction of impulses. Nodes of Ranvier: the spaces between the individual Schwann cells, or segments of the myelin sheath. 2. Neuroglia (glial cells): the non-neuronal cells of the CNS. a. Oligodendrocytes: produce the myelin sheath to electrically insulate axons of the CNS neurons. b. Microglia: capable of movement & phagocytosis of pathogens & damaged tissue. c. Astrocytes: support neurons, help maintain proper chemical environment for generation of impulses; help form the blood-brain barrier to prevent potentially harmful substances from affecting brain neurons. d. Ependyma: line the ventricles of the brain & central canal of the spinal cord; involved in the circulation of the cerebrospinal fluid (CSF). White matter: nerve tissue within the CNS that consists primarily of myelinated axons of many neurons. Gray matter: nerve tissue within the CNS that consists primarily of cell bodies of neurons. Types of Neurons 1. Sensory (afferent) neurons: carry impulses from receptors to the CNS. 2. Motor (efferent) neurons: carry impulses from the CNS to muscles & glands. Effectors: any organ such as muscle or gland, activated by motor neurons. Nerve: a bundle of neuronal axons & or dendrites and associated connective tissues located outside the CNS. 1. Sensory nerve: made only of sensory neurons. 2. Motor nerve: made only of motor neurons 3. Mixed nerve: contains both sensory & motor neurons. Nerve Tract: a bundle of nerve axons within the CNS. Often referred to as White Matter: a tract may be ascending (sensory) or descending (motor) Nerve Impulse (nerve action potential): self-propagating wave of electrical current, which carries information along the nerve. Stimulus: any change in the internal or external environment that excites a sensory receptor, a neuron, or a muscle fiber. 1. 2. 3. 4. State or Events Polarization (the neuron is not carrying an electrical impulse): the neuron membrane has a (+) charge outside and a (-) charge inside. Depolarization (generated by a stimulus): entry of Na+ ions and reversal of charges on either side of the membrane. Propagation of the impulse from the point of stimulus. Saltatory Conduction: the rapid transmission of a nerve impulse from one node of Ranvier to the next; characteristic of myelinated neurons. Repolarization (immediately follows depolarization): exit of K + ions & restores the (+) charge outside & (-) charge inside the membrane. The Na+ ions are returned outside & the K+ ions are returned inside by the sodium & potassium pump. Synapse: point of junction for the transmission of nerve impulses. The space between the axon of one neuron & dendrites or cell body of the next neuron. Neurotransmitter: chemical released from the ending of an axon that enables a nerve impulse to cross a synaptic junction (acetylcholine, norepinephrine, GABA, dopamine, serotonin). Spinal Cord Enclose in the vertebral canal. Length extends from the foramen Magnum to the I.V. disc between the 1 st & 2nd lumbar vertebrae. (Cross-section) Internal H of gray matter contains primarily cell bodies of motor neurons & interneurons; external white matter consists primarily of myelinated axons of neurons. Central canal: contains Cerebrospinal Fluid (the liquid that circulates around the brain & spinal cord) & is continuous with the ventricles of the brain. Functions of the spinal cord 1. Conduct sensory impulses through the ascending (sensory) tracts to the brain. 2. Conduct motor impulses from the brain through the descending (motor) tract to the motor (efferent) neurons that supply the muscles or glands. 3. Reflex activities. A reflex is a simple, rapid, and autonomic response involving very few neurons. Spinal Nerves: 31 pairs Cauda Equina: the lumbar & sacral nerves that extend below the end of the spinal cord. Each nerve is attached to the spinal cord by two roots. The Posterior (dorsal) Root: is made of sensory neurons that carry impulses into the spinal cord. On each posterior root is a Posterior (Dorsal) root ganglion: an enlarged part of the posterior root that contains the cell bodies of sensory neurons. Ganglion: means a group of cell bodies outside the CNS. The Anterior (Ventral) Root is a motor root: it is made of motor neurons carrying impulses from the spinal cord to muscle and glands. The cell bodies of motor neurons are in the gray matter of the spinal cord. Because posterior (sensory) & anterior (motor) roots are combined to form the spinal nerve, all spinal nerves are mixed nerves. Distribution of Spinal Nerves Plexus: a network of nerves, which then distribute branches to the body parts. 1. Cervical plexus: supplies motor impulses to muscles of the neck & receives sensory impulses from the neck to the back of the head. Phrenic nerve: arises from the cervical plexus that activates the diaphragm. 2. Brachial plexus: supply shoulder, arm, forearm, wrist and hand. 3. Lumbosacral plexus: supplies nerve to the lower extremities. Sciatic nerve: the largest branch. Reflex: is an involuntary response to a stimulus Reflex arc: the most basic conduction pathway through the nervous system, connecting a receptor & an effector. Basic Components: 1. Receptor: detects changes (the stimulus) & generates impulses. 2. Sensory neuron or Afferent neuron: a cell that transmits impulses from receptor toward CNS. 3. Integrating center: one or more regions of gray matter in the CNS. Contains one or more synapses. 4. Motor neuron or Efferent neuron: a cell that carries impulses from CNS to the effector 5. Effector: a muscle or a gland outside the CNS that carries out a response. Brain: the part of the central nervous system within the cranial cavity Main Parts: 1. Cerebrum: the largest part of the brain. Divided into right and left cerebral hemispheres by a deed groove called a Longitudinal fissure. 2. Diencephalon: the area between the cerebral hemisphere and brain stem. Includes the thalamus, hypothalamus & pineal gland. 3. Brain Stem: connects the cerebrum and diencephalons with the spinal cord. 3 Parts: a. Midbrain: upper portion of the brain stem b. Pons: connects the midbrain with the medulla c. Medulla Oblongata: connects the brain with the spinal cord 4. Cerebellum: located below the back part of the cerebral hemisphere; and is connected with the cerebrum, brain stem, and spinal cord by means of pons. Covering of the Brain and the Spinal Cord: Meninges 1. Dura mater: the thickest and the toughest outermost layer of the meninges. Lines the skull and the vertebral canal. 2. Arachnoid mater: the middle layer of the meninges. Loosely attached to the pia mater by web-liked fibers allowing a space for the movement of the cerebrospinal fluid (CSF) between the two membranes. 3. Pia mater: is a very thin membrane and it is the innermost layer on the surface of the brain and spinal cord. Made of delicate connective tissue in which there are many blood vessels. The blood supply to the brain is carried, to a large extent, by the pia mater. Subarachnoid space: space between the arachnoid and the pia mater. It contains the CSF, the fluid that circulates in and around the brain and spinal cord. The functions of CSF are: 1. Support neural tissue 2. Act as a cushion for the CNS 3. Carries nutrients to CNS neurons and transports or removes waste products from the cells. Ventricles: space within the brain that forms CSF Choroid Plexus: a network of capillaries in each ventricle that forms the CSF by filtration of blood plasma. Four Ventricles: 1. Two Lateral Ventricles: largest ventricles located in the two cerebral hemispheres. Interventricular Foramen: opening that will communicate ® & (L) Lateral ventricles to 3rd ventricle. 2. Third Ventricle: is surrounded by diencephalon. Cerebral Aqueduct: a tunnel through the midbrain that permits CSF to flow from the 3 rd and 4th ventricles. 3. Fourth Ventricle: located at the back of the pons → Central canal of the spinal cord→ Cranial & Spinal Subarachnoid space that surrounds the brain and the spinal cord → Arachnoid villi: fingerlike extensions of the arachnoid mater → Cranial venous sinuses (superior sagittal sinus) reabsorbs back into the blood → CSF becomes plasma again. Cerebrum Cerebral Cortex: the gray matter on the surface of the cerebral hemisphere, consists of cell bodies of neurons, that impulses are received and analyzed. Form the basis of knowledge. Responsible for conscious thought, reasoning, and abstract mental functions; conscious and voluntary actions originate. Internal to gray matter is white matter, made primarily of myelinated axons that connect the lobes of the cerebrum to one another and to all parts of the brain. The cerebral cortex is folded extensively, forming elevated portions known as gyri or convolution, which are separated by shallow & deep groves called sulci or fissures. This folding permits the presence of millions of more neurons in the cerebral cortex. Important Sulcus: 1. Central sulcus: lies between the frontal and parietal lobes at each hemisphere at a right angle to the longitudinal fissure. 2. Lateral sulcus: curves along the side of each hemisphere and separates the temporal lobe from the frontal and parietal lobes. Corpus Callosum: is a band of nerve fiber that connects the left and right hemispheres. Located at the bottom of the longitudinal fissure. Acts as a bridge between the right and left hemispheres, permitting impulses to cross from one side of the brain to the other. Basal Ganglia: masses of gray matter located deep within the white matter of the cerebral hemisphere. Help initiate & terminate movements. Help regulate the muscle tone required for specific body movements & control subconscious contractions of skeletal muscles, such as automatic arm swings while walking. Dopamine: neurotransmitter secreted by the neurons of basal ganglia. Lesion of the basal ganglia results in movement disorder. Limbic System: a part of the cerebrum, sometimes called the “emotional brain”, concerned with various aspects of emotion and behavior. Lobes of Cerebral Hemisphere 1. Frontal Lobe: lies in front of the central sulcus. Contains the Motor Area: an area that generates the impulses for voluntary movements. Because of the way in which motor fibers cross the opposite sides in the CNS. The left motor area controls movement on the right side of the body and the right motor area controls the left side of the body. Broca’s area (motor speech area): located in front of the lowest part of the motor cortex. Controls the movement of the mouth involved in speaking.