Nervous System Study Guide 7 PDF

Nervous System Study Guide 7 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...

Nervous System Study Guide 7 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. Division of the Nervous System 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 Neuron 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. Saltatory Conduction 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 Neuroglia 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 & Gray Matter 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.. Sensory Neurons 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 Tract 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. State or Events 1.Polarization (the neuron is not carrying an electrical impulse): neuron membrane has a (+) charge outside and a (-) charge inside. 2.Depolarization (generated by a stimulus): entry of Na+ ions and reversal of charges on either side of the membrane Nerve Impulse  State or Events 3. 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. 4. 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). Synapse  Spinal Cord. Enclose in the vertebral canal. Length extends from the foramen Magnum to the I.V. disc between the 1st & 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. Spinal Cord Cross- section of the Spinal Cord 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. Reflex Arc Spinal Cord Spinal Nerves: 31 pairs Cauda Equina: the lumbar & sacral nerves that extend below the end of the spinal cord Cauda Equina Spinal Nerves 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 has, 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. Spinal Nerves 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: 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. Spinal Nerves 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 of a Reflex 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: cell that carries impulses from CNS to the effector 5.Effector: a muscle or a gland outside the CNS that carries out a response. Basic Components of a Reflex Knee Jerk or Patellar Reflex  Brain The part of the central nervous system within the cranial cavity Main Parts of the Brain. 1.Cerebrum: largest part of the brain. Divided into right and left cerebral hemispheres by a deep groove called Longitudinal fissure 2.Diencephalon: area between the cerebral hemisphere and brain stem. Includes the thalamus, hypothalamus & pineal gland Longitudinal fissure Diencephalon Main Parts of the Brain 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. Main parts of the Brain Main Parts of the Brain 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: 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 Meninges 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. 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: 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 3rd and 4th ventricles. CSF Flow Foramen of Luschka and Magendie Four 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.  Hydrocephalus An abnormal increase in the amount of CSF within the ventricles of the brain. In childhood, before the sutures of the skull have fused, make head enlarged In adult, because of the unyielding nature of the skull, increase intracranial pressure, causing drowsiness, vomiting and headache Cause: obstruction to the outflow of the CSF from the ventricles or failure of its reabsorption into cranial veins. Surgical Management 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  Cerebrum 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.  Cerebrum 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 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. Corpus Callosum  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: 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. Lobes of Cerebral Hemisphere Decussation of nerve tracts Lobes of Cerebral Hemisphere 2. Parietal Lobe: occupies the upper part of each hemisphere and lies behind the central sulcus. Contains the Sensory Area: area that receives impulses from receptors in the skin, such as touch, pain, and temperature, and interprets cutaneous sensation. These areas also receive impulses for proprioception (joint & muscle position). The estimation of distances, sizes, and shapes also takes place in the parietal lobe. Lobes of Cerebral Hemisphere 3. Temporal Lobe: lies below the lateral sulcus and folds under the hemisphere on each side Auditory Area: receives and interprets impulses from receptors in the inner ear for hearing. Olfactory Area: located in the medial part of the temporal lobe: receives impulses from receptors from the nose for the sense of smell. Lobes of Cerebral Hemisphere Lobes of Cerebral Hemisphere 4. Occipital Lobe: lies behind the parietal lobe and extends to the cerebellum Visual Area: receives and interprets impulses from the retina of the eye. Association areas In all lobes, for abstract thinking, reasoning, will, judgment, learning, memory, and personality. Hippocampus: part of the temporal lobe located under the lateral ventricles. It is essential for the formation of memory. Lobes of Cerebral Hemisphere  Diencephalon: located between the cerebral hemisphere and the brain stem 1.Thalamus: superior to the hypothalamus and inferior to the cerebrum. Main relay center for sensory impulses ascending to the cerebral cortex. Sensory impulses going to the brain (except for the sense of smell) follow the neuron pathways that first enter the thalamus and direct them to a particular area of the cerebral cortex. The thalamus may also suppress unimportant sensations. Diencephalon  Hypothalamus: located superior to the pituitary gland and inferior to the thalamus. a.Control the Autonomic Nervous System (ANS). b.Production of antidiuretic hormone (ADH) and oxytocin. These hormones are then stored in the posterior pituitary gland. ADH: enables the kidney to reabsorb water back to the blood and thus help maintain blood volume. Oxytocin: causes contraction of the uterus to bring about labor and delivery. c.Production of releasing hormones that stimulate the secretion of hormones by the anterior pituitary gland. Hypothalamus d. Regulation of the body temperature by promoting responses such as sweating in a warm environment and shivering in a cold environment. e. Regulation of food & water intake. The hypothalamus responds to changes in blood nutrient levels. f. Regulation of body (circadian) rhythm such as secretion of hormones, sleep cycles, changes in mood or mental alertness. Pineal Gland Located on the posterior wall of the third ventricle of the brain; secretes melatonin.  Brain Stem 1.Midbrain: Extends from the pons to the hypothalamus and encloses the cerebral aqueduct. Function: acts as relay centers or integration of visual and auditory reflexes. 2.Pons: lies between the midbrain and the medulla; in front of the cerebellum. It is composed largely of myelinated nerve fibers, which serve to connect the cerebellum with the brain stem as well as the cerebrum above and the spinal cord below. Function: regulates respiration with medulla oblongata to produce normal respiration. Origination of CN: V, VI, VII, & VIII. Brain Stem  Brain Stem 3. Medulla Oblongata: located between the pons and the spinal cord. It appears white externally, like pons, it contains many myelinated nerve fibers. Internally, it contains a collection of cell bodies called nuclei or centers. Functions a.Respiratory Center: regulates breathing. b.Cardiac Center: helps regulate the rate and force of the heartbeat. c.Vasomotor Center: regulates the diameter of blood vessels by contraction of the smooth muscles in the blood vessel walls, thereby controlling blood flow and blood pressure. Also, in the medulla are the reflex centers for coughing, sneezing, swallowing, & vomiting. Origination of CN: IX, X, XI, XII. Brain Stem 4. Reticular Formation: A network of small groups of neuronal cell bodies (gray matter) intermingled with small bundles of myelinated axons (white matter) beginning in the medulla oblongata & extending superiorly through the central part of the brain stem. Reticular Activating System: a portion of the reticular formation that has many ascending connections with the cerebral cortex. Concerned with the level of consciousness – from the states of sleep, drowsiness, and relaxation to full alertness & attention.  Cerebellum Separated from the medulla and pons by the fourth ventricle and is inferior to the occipital lobes of the cerebrum. Made up of three parts: the middle portion (vernix) and the two lateral hemispheres.  Functions of the Cerebellum 1.To aid in the coordination of voluntary muscles so that they function smoothly and in an orderly fashion. 2.To aid in the maintenance of balance in standing, walking, and sitting, as well as during more strenuous activities. Message from the internal ear and from sensory receptors in tendons and muscles aid the cerebellum. 3.To aid in the maintenance of muscle tone so that all muscle fibers are slightly tensed and ready to produce necessary changes in position as quickly as may be necessary. Cranial Nerves: 12 pairs emerge from the brain stem or other parts of the brain. CN I, II, VIII: contains only sensory fibers CN III, IV, VI, XI, and XII: contain all or mostly motor fibers CN V, VII, IX, and X: contain both sensory and motor fibers (mixed nerves) Cranial Function(s) Nerves I. Olfactory Sense of Smell II. Optic Sense of Vision/ Sight III. Movement of the eyeball, elevation of the Oculomotor upper lid; constriction of pupils in bright light or for near vision Extraocular muscles IV. Movement of the eyeball (control the Trochlear superior oblique muscle) V. Sensation for the entire face, scalp & teeth; Trigeminal contraction of chewing muscle VI. Movement of the eyeball (control the lateral Abducens rectus muscle) VII. Facial Sense of taste (anterior 2/3 tongue); contraction of facial muscles; secretion of saliva. VIII. Acoustic Cochlear branch: sense of (Vestibulocochlear) hearing; Vestibular branch: sense of equilibrium. IX. Sense of taste (Posterior 1/3); Glossopharyngeal controls muscles of the throat; secretion of saliva. Acoustic (Vestibulocochlear) X. Vagus Controls muscles of the throat; PNS stimulation to thoracic and abdominal organs (decrease heart rate; contraction alimentary tube (peristalsis); increase digestive secretion) XI. Spinal Contraction of neck & shoulder muscles Accessory (sternocleidomastoid and trapezius); motor to larynx XII. Movement of the tongue Hypoglossal  Autonomic Nervous System The portion of the PNS that consists of the motor portion of some cranial & spinal nerves. Making up the ANS are visceral motor neurons to smooth muscle, cardiac muscle & glands. An ANS pathway consists of two neurons that synapse in a ganglion: Preganglionic neurons: from the CNS to the ganglia Postganglionic neurons: from the ganglia to the effectors Autonomic Nervous System Pathway  Two Divisions of the ANS. 1.Sympathetic Division (Thoracolumbar division): dominates during stress situations; responses prepare the body to meet physical demands. The sympathetic pathway begins in the spinal cord with cell bodies in the thoracic & lumbar regions. Arise from the spinal cord at the level of the 1st thoracic nerve down to the level of the 2nd lumbar spinal nerve Sympathetic Division From this part of the cord, nerve fiber extend to the sympathetic ganglia where they synapse with a 2nd set of neurons (postganglionic neurons), the fiber of which extends to the glands & involuntary muscle tissue. The postganglionic neuron of the sympathetic neurons of the sympathetic nervous system acts on the effectors by releasing the neurotransmitter norepinephrine. Two Divisions of the ANS 2. Parasympathetic Division (Craniosacral division): dominates in relaxed situations to permit normal functioning. Cell bodies of parasympathetic neurons are in the brain stem and sacral part of the spinal cord. Their axons are in the CN 3, 7, 9, 10 & some sacral nerves, and extend to the parasympathetic ganglia that are usually located near or within the walls of the effector organs. The pathway continues along the 2nd set of neurons (postganglionic neurons) that stimulate the involuntary muscle tissue and glands. These neurons released the neurotransmitter acetylcholine.  EFFECTS OF THE SYMPATHETIC AND PARASYMPATHETIC NERVOUS SYSTEM.. Effector Sympathetic Parasympathetic System.. System.. Irish of the Dilation of pupils Constriction of pupils. eye Sweat glands Stimulation None ( secretion) Heart  rate & strength of  rate & strength of beat. beat. Bronchi of Dilation Constriction. Lungs Salivary glands  secretion  secretion. Digestive glands Inhibition Stimulation Stomach &  peristalsis  peristalsis for Intestine normal digestion Kidney Decrease activity None Urinary bladder Relaxation (to prevent Contraction & urination) emptying Liver Increases released of None glucose. Penis Ejaculation Erection Adrenals Stimulation None Blood vessels to: Skeletal Dilation Constriction muscles Skin & viscera Constriction None Respiratory Constriction Dilation system Digestion Constriction Dilation Blood vessels to: Skeletal muscles Dilation Constriction Skin & viscera Constriction None Dilation Constriction Respiratory system Digestion Constriction Dilation