7/10/18. Introduction. Nervous System. Physiology. Anatomy. Organization of the Nervous System. Central Nervous System

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1 Introduction Nervous System Chapter 23 Nervous system uses transmitted electrical signals called impulses to relay messages and to stimulate change Body s master communication and regulating system Every thought, action, and sensation reflects nerve activity 1 2 Anatomy Physiology Brain Spinal cord Cranial and spinal nerves Sense organs Neurotransmitters Sensory input Interpretive functions Motor output Higher mental functioning and emotional responsiveness 3 4 Organization of the Nervous System Central Nervous System Interprets sensory information Issues instructions in the form of motor responses Governs thoughts and emotional responses Surrounded by bones of skull and spinal column FromPatton physiology, KT, ed 7, ThibodeauGA: St. Louis, 2010, Anatomy Mosby. & 5 6 1

2 Major Components of the Central Nervous System Brain Spinal cord Meninges Cerebrospinal fluid (CSF) Peripheral Nervous System Cranial nerves: Exit brain Spinal nerves: Exit spinal cord Subdivisions of PNS are: SNS: Voluntary (responses consciously controlled) ANS: Involuntary ANS contains sympathetic and parasympathetic divisions 7 8 Cells of the Nervous System Neuroglia Nervous system made up of billions of cells Two types: Neurons Neuroglia Supports, protects, and insulates neurons Smaller and more numerous than neurons Makes up more than 50% of CNS 9 10 Neuroglia Neurons Glial cells in CNS are: Astrocytes Microglia Oligodendrocytes Glial cells in PNS are: Schwann cells Satellite cells Impulse-conducting cells Properties include: Excitability: Converts stimulus into impulse Conductibility: Transmits impulses to neurons, muscles, and glands Secretion: Secretes neurotransmitters

3 Parts of a Neuron Structures Associated with Axons Cell body Contains nucleus and other organelles Dendrite Transmits impulses to cell body Axon Transmits impulses away from cell body Synaptic bulbs Located at end of axon Contain synaptic vesicles Synaptic vesicles Contain neurotransmitters Parts of a Neuron FromApplegate E: The anatomy and physiology learning system, ed 4, St. Louis, 2011, Saunders. Functional Classification of Neurons Afferent (sensory): Carry impulses to CNS Efferent (motor): Carry impulses from CNS to muscles or glands Interneurons (association): Carry impulses between sensory and motor neurons and perform integrative functions Connective Tissue Layers of Nerves Nerve Impulses Epineurium Outer layer around entire nerve Perineurium Surrounds fascicles Endoneurium Surrounds individual neurons and their extensions Electrical signals that convey information along neurons Action potential Change in the electrical charge of a cell membrane Needed to conduct an impulse Caused by movement of charged particles (ions)

4 Polarization Sodium-Potassium Pump Neuron is resting and not conducting an impulse Inside has negative ( ) charge Outside has positive (+) charge Produces and maintains polarization Pumps ions in opposite directions at an unequal rate Ions are: Sodium (Na + ) Potassium (K + ) All-or-None Response Refractory Period Impulse is conducted along entire neuron at maximum capacity No fluctuations or decrease in magnitude Impulse continues until it reaches end of neuron Inability of a neuron to conduct another impulse Essentially, a neuron's unresponsive period Nerve Impulse Synapse Junction between: Neuron and neuron Neuron and muscle Neuron and gland Impulses are transmitted across synapse by with help of neurotransmitters

5 Synaptic Structures Neurotransmitters Synaptic bulbs Located at end of axon Contain neurotransmitters Synaptic gap (cleft) Space between synaptic bulb and plasma membrane Chemical messengers involved in synaptic transmission Stored in vesicles of presynaptic neuron Can be excitatory or inhibitory Examples of Neurotransmitters Synapse Acetylcholine is most common Epinephrine and norepinephrine Serotonin Dopamine Endorphins Central Nervous System Brain Brain and spinal cord Protected by Skull Vertebral column Meninges Cerebrospinal fluid (CSF) It interprets sensory information and governs intellectual activity, consciousness, memories, and emotions Uses glucose as an energy source Cerebrum Diencephalon Cerebellum Brainstem

6 Regions of Brain Cerebrum Largest area of brain Language centers interpret written/spoken words as well as speech Cerebral cortex covers outer region of cerebrum Sulci and gyri separate cerebrum into lobes FromHerlihyB: The human body in health and illness, ed 4, St. Louis, 2011, Saunders Cerebral Hemispheres Hemispheric Specialization Cerebrum contains right and left hemispheres Research indicates they possess specialized functions Longitudinal fissure Separates hemispheres Corpus callosum Transverse fibers connecting hemispheres Left hemisphere Language: Receptive and expressive Governs many mathematical abilities, as well as reasoning and analytical skills Right hemisphere specializes in sounds Melodies Art Emotional expression Spatial relationships Cerebral Lobes Frontal lobe Motor function Personality/mood Intellect Speech Parietal lobe Sensation Speech Understanding

7 Cerebral Lobes Cerebral Lobes Temporal lobe Auditory Naming Memory Occipital lobe Vision Whole object integration FromHerlihyB: The human body in health and illness, ed 4, St. Louis, 2011, Saunders Brain Waves and States of Consciousness Brain Wave Patterns Consciousness: Degree of mental alertness and responsiveness Levels of consciousness recorded as brain wave patterns Beta Alpha Theta Delta Beta Wakeful consciousness and mental activity High-intensity waves are associated with extreme stress Alpha Awake and relaxed Brain Wave Patterns Diencephalon Theta Drowsiness and dreamlike awareness, subconscious, out-of-body experiences Delta Deep sleep from which the subject is not easily aroused Located in center of brain Contains two primary structures: Thalamus Hypothalamus

8 Thalamus and Hypothalamus Diencephalon Thalamus Relays sensory information (except olfaction) to appropriate parts of cerebrum Hypothalamus Regulates ANS Controls hunger and thirst, anger and aggression, hormones, sexual behavior, and sleep patterns Diencephalon, Cerebellum, and Brainstem Cerebellum Located posterior and inferior to cerebrum Concerned with muscle tone Coordinates complex muscular movements Regulates posture and balance FromHerlihyB: The human body in health and illness, ed 4, St. Louis, 2011, Saunders Brainstem Cerebellum Vegatative function Continuous with spinal cord Three divisions: Midbrain Pons Medulla oblongata

9 Midbrain and Pons Brainstem Midbrain Conducts nerve impulses from cerebrum to pons Conducts sensory impulses from spinal cord to thalamus Pons Connects cerebellum and cerebrum with spinal cord Medulla Oblongata Spinal Cord Transmits sensory and motor impulses between brain and spinal cord Contains: Respiratory center Cardiovascular center Vasomotor center Exits skull via foramen magnum Integrating center and information highway Cauda equina Lower portion of cord fans out like a horse tail Spinal Cord Spinal Cord Cross section reveals: White matter: Located on periphery Gray matter: Located in deeper regions H-shaped Central canal Center of spinal cord; contains circulating CSF FromPatton KT, ThibodeauGA: Anatomy &physiology, ed 7, St. Louis, 2010, Mosby

10 Spinal Cord: Tracts Meningeal Layers Two types: Ascending Sensory (afferent) impulses travel up cord Descending Motor (efferent) impulses travel down cord Pia mater Innermost delicate layer Attaches to surface of CNS Arachnoid Middle layer; forms loose covering around CNS Dura mater Outermost dense layer; lies against bones of CNS Meninges in Skull Region Cerebrospinal Fluid Fluid circulating around brain and spinal cord Functions include: Supplies oxygen and nutrients to tissues of brain and spinal cord Removes metabolic waste during sleep Acts like a shock absorber FromLeonard P: Building a Medical Vocabulary, ed 7, St. Louis, 2009, Saunders Peripheral Nervous System Cranial Nerves Cranial nerves Arise from inferior surface of brain 12 pairs Spinal nerves Arise from spinal cord 31 pairs CN I: Olfactory - smell CN II: Optic - sight CN III: Oculomotor - eye movement CN IV: Trochlear - eye movement CN V: Trigeminal - face sensation and chewing CN VI: Abducens - eye movement CN VII: Facial - facial expression

11 Cranial Nerves Cranial Nerves CN VIII: Vestibulocochlear - hearing and equilibrium CN IX: Glossopharyngeal - oral sensation, taste and salivation CN X: Vagus - 90% of parasympathetic nervous system CN XI: Accessory (spinal accessory) - trapezius and SCM CN XII: Hypoglossal - tongue movement FromPatton KT, ThibodeauGA: Anatomy &physiology, ed 7, St. Louis, 2010, Mosby Spinal Nerves Structure of Spinal Nerves 31 pairs 8 cervical nerves 12 thoracic nerves 5 lumbar nerves 5 sacral nerves 1 coccygeal nerve Part of spinal nerve that connects to spinal cord Two types: Ventral (anterior) Contains motor neurons Dorsal (posterior) Contains sensory neurons Ganglion Nerve Plexuses Cluster of nerve cell bodies Ventral and dorsal roots merge to form a single nerve Network of intersecting nerves in PNS Major plexuses: Cervical Brachial Lumbosacral

12 Dermatomes Dermatome Map Area of skin supplied by specific sensory nerve root Dermatomes are named by their corresponding nerve Distribution called a dermatome map Each map has its own variations FromHabif: Clinical dermatology: a color guide to diagnosis and therapy, ed 5, St. Louis, 2010, Mosby Myotomes Myotome Map Group of skeletal muscles supplied by specific motor spinal nerve root Distribution is called a myotome map Sometimes used in muscle tests Reflexes Stretch (Patellar) Reflex Involuntary and predictable Cranial reflex means the brain mediated the reflex Primitive reflexes may reappear in people with dementia Spinal reflex means the spinal cord mediated the reflex FromPatton KT, ThibodeauGA: Anatomy &physiology, ed 7, St. Louis, 2010, Mosby

13 Autonomic Nervous System Autonomic Nervous System Innervates cardiac and smooth muscles/glands, thus regulating: Heart and respiration rates Blood circulation Body temperature Gastrointestinal activity and metabolism Two divisions: Sympathetic and parasympathetic FromPatton KT, ThibodeauGA: Anatomy &physiology, ed 7, St. Louis, 2010, Mosby Dual Innervation Parasympathetic Division Innervated by both sympathetic and parasympathetic divisions Some have only sympathetic innervation Example: Adrenal glands Some have only parasympathetic innervation Example: Lacrimal apparatus Supports functions that conserve and restore energy Regulates digestion "Housekeeping" division Nerves emerge from the brainstem and sacrum Sympathetic Division Touch Dominates during physical exertion or emotional stress Effects include raises in heart rate, blood pressure, and respiration Suppresses activity of the digestive and urinary systems Also called the thoracolumbar division Many different types of many receptors, such as: Pressure Movement Temperature Nociception and pain perception

14 Taste Taste Buds on the Tongue Chemoreceptors activated when a molecule from a particular size and shape fits into a particular receptor site Five primary tastes: Salty Sweet Bitter Sour Savory Strongly influenced by smell FromApplegate E: The anatomy and physiology learning system, ed 4, St. Louis, 2011, Saunders Smell Structures Involved in Smell Olfaction: Sense of smell Scent receptors located in superior nasal cavity Molecules fit into receptor sites; information travels into olfactory bulb and the brain Plays important role in sexual behavior FromHerlihyB: The human body in health and illness, ed 4, St. Louis, 2011, Saunders Vision Vision: The Retina Photoreceptors transmit visual information and send to retina Rods are active in dim light, responsible for night vision Cones are active in bright light, specialized for detecting color

15 Vision: Rods and Cones Hearing Mediated by mechanoreceptors Detect sound waves and vibrations Sound waves vibrate tympanic membrane, causing it to vibrate Transmitted through three small bones in middle ear Oval window covers opening to cochlea Sound waves travel until they reach brain B: FromPatton C: Courtesy KT, ThibodeauGA: Dr. Scott Mittman, Anatomy Johns &physiology, Hopkins Hospital, ed 7, Baltimore, St. Louis, 2010, MD. Mosby The Ear Balance and Equilibrium Fluid-filled canals contain mechanoreceptors that resemble hair These cells move when we move Information is sent along nerves, notifying brain of body movements FromHerlihyB: The human body in health and illness, ed 4, St. Louis, 2011, Saunders Receptors Proprioceptors Respond to stimuli by creating a nerve impulse Our bodies avert harm and seek nourishment Specific receptors generally detect specific stimuli Perception: Organization, identification, and interpretation of sensory information Adaptation: Decrease in sensitivity to prolonged stimulus Found in muscles, joints, fascia, and ears Detect body movements, body position, and muscle stretch

16 Receptors Classified by Type of Stimuli Detected Chemoreceptors detect chemical stimuli or changes in chemical concentrations of fluids Nociceptors detect noxious stimuli, such as excessive heat and cold or tissue damage Mechanoreceptors detect mechanical stimuli Muscle Spindles Stretch receptors wrapped around intrafusal fibers Monitor changes in muscle length and rate of change Cause reflexive contraction when muscles are overstretched Muscle Spindle Golgi Tendon Organs Activated by muscle tension Located at musculotendinous junctions If tension is too great, motor efferent neurons are inhibited Causes inverse stretch reflex FromPatton KT, ThibodeauGA: Anatomy &physiology, ed 7, St. Louis, 2010, Mosby