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NERVOUS SYSTEM CENTRAL & PERIPHERAL NERVOUS SYSTEMS General – CNS CNS Protected by Bone - Skull (Brain) - Vertebrae (Spinal Cord) Protected by Meninges CNS – General continued Meninges - CT Membranes between Bone & CNS * Dura Mater Outer, Tough, Fibrous, Double Extends down vertebral cavity, beyond end spinal cord Dural Sinuses – Veins between layers Dural Folds – Innermost layer extents into fissures Epidural Space – Between walls of vertebral cavity & Dura of spinal cord CNS – General continued * Arachnoid Mater Thin, Spidery, Middle Extends past spinal cord Subdural Space – Between Dura & Arachnoid Subarachnoid Space – Between Arachnoid & Pia; Contains CSF; Sampled via spinal tap * Pia Mater Innermost, Delicate Attached to Surface of Brain & Spinal Cord Highly Vascular CNS – Brain Structure Cerebrum Diencephalon Brainstem Cerebellum CNS – Brain Structure Cerebrum - Largest, Superior - Two Hemispheres Separated By Longitudinal Fissure & Bridged by Corpus Callosum (myelinated fibers) * Cerebral Cortex (Higher Thought Processes) Outer, Convoluted Gray Matter Gyri (Ridges); Sulci – Grooves * White Matter (Surrounds Nuclei) * Nuclei (Basal helps with posture & movement) Brain Structure continued - Each Cerebral Hemisphere has 5 Lobes: * Frontal – Personality, Judgment, Behavior, motor areas assoc. with skeletal muscle * Parietal – Sensory Input from Skin & Organs * Temporal – Hearing, Smell * Occipital - Vision * Insula – Monitors Internal Organs & Responsible for Aversions Brain Structure continued Diencephalon - Enclosed by Cerebrum Between Cerebrum & Brainstem Epithalamus Thalamus Hypothalamus Epithalamus Part of Diencephalon Superior to Thalamus & Third Ventricle Contains the Pineal Gland, Produces Hormones Thalamus “Switchboard” for all Sensory Impulses to Cerebral Cortex Hypothalmus * Coordinates Neural & Endocrine Functions * Regulates Basic Visceral Functions Fig. 8.24 Brain Structure continued Brain Stem - Inferior to Diencephalon; Mergers with Spinal Cord - Controls visceral functions - Midbrain * Colliculi – Visual & Auditory Nuclei - Pons – Below Midbrain, Fiber Tracts, Joins Cerebellum to brainstem - Medulla Oblongata – Below Pons, Cardiovascular & Resp. Rhythmicity Centers, Joins Brain & Spinal Cord Fig. 8.23 Brain Structure continued Cerebellum - Inferior to Cerebrum, Posterior to Brain Stem Connects to brainstem at Pons Outer Gray Matter Arbor Vitae (Inner, Branching White Matter) Controls learned motor skills Coordinates Skeletal Muscles, Maintains Body Tone & Equilibrium, Posture Brain Structure continued Ventricles - Cavities within Brain, Filled with CSF - Continuous with Subarachnoid Space & Central Canal of Spinal Cord - Lateral – Largest Two, within Cerebral Hemispheres - Third – Narrow, Midline, Diencephalon - Fourth – Brain Stem, Continuous with Central Canal of Spinal Cord Fig. 8.36 CNS - Cerebrospinal Fluid (CSF) Secreted by Choroid Plexuses (capillaries in ventricles) Clear, Similar to Blood Plasma Most CSF produced by Lateral Ventricles Circulates through Ventricles, Subarachnoid Space, Central Canal Supports, Absorbs Shocks, Provides Nutrients Sample via Spinal Tap (Subarachnoid Space, L-4) CNS – Spinal Cord Protected by Bone, Meninges, CSF Vertebral Cavity Extends from Medulla Oblongata (Through Foramen Magnum) to L2 16-18 inches Two Enlargements (Limb Control): - Cervical (Shoulder & Arms) - Lumbar (Pelvis & Legs) CNS – Spinal Cord continued Conus Medullaris – Inferior tip of spinal cord Cauda Equina – Nerve roots inferior to cord tip Filum Terminale – Pia Mater attached to coccyx Fig. 8.21 CNS – Spinal Cord continued Outer White Matter - Bundles Myelinated Axons Ascending Tracts or Pathways - Sensory - From Sensory Receptors to CNS Descending Tracts or Pathways - Motor - From CNS to Glands or Muscles CNS – Spinal Cord continued Inner Gray Matter - Neuron Cell Bodies & unmyelinated processes - Dorsal & Ventral Horns project towards outer surface - Dorsal Gray Horn – Interneuron Somas - Ventral Gray Horn – Somas of Motor Neurons - Central Canal through Grey Commissure CNS – Spinal Cord continued 31 Pairs of Spinal Nerves (PNS) - Sensory: Dorsal Roots/Ganglia, Ascending Tracts - Motor: Ventral Roots, Descending Tracts Dermatomes – skin segments supplied by spinal nerves Peripheral Nervous System PNS Consists of: - Peripheral Nerves: * Cranial Nerves * Spinal Nerves * Nerve Plexuses - Ganglia Carries Sensory Information & Motor Commands PNS – Peripheral Nerves Nerves (PNS) - Sensory * Carries from Receptors towards CNS - Motor * Carries from CNS towards effector - Mixed * Both Sensory & Motor PNS – Peripheral Nerves Bundles of Axons Sensory, Motor or Mixed CT Reinforced - Endoneurium – Surrounds each axon - Perineurium – Around groups of axons - Epineurium – Tough, Fibrous C.T. around Nerve PNS – Cranial Nerves Twelve Pairs I Arises from Cerebrum II – XII from Brain Stem Function - Sensory - Motor - Mixed PNS – Spinal Nerves 31 Pairs: - 8 Cervical - 12 Thoracic - 5 Lumbar - 5 Sacral - 1 Coccygeal All are Mixed; both Sensory (Afferent) & Motor (Efferent) 1 Pair at each Spinal Segment Attach to Spinal Cord by Ventral & Dorsal Root Supply Dermatomes (skin segments) Fig. 8.21 PNS – Nerve Plexuses Networks of Spinal Nerve Branches - Cervical Brachial Lumbar Sacral Reflex Arcs Simple Conduction Pathway Results in Reflex - Fast, Predictable - Automatic motor response Five Components: - Receptor * End of dendrite of sensory neuron * Responds to specific stimuli - Sensory Neuron (Receptor to CNS) Fig. 8.18 Reflex Arcs continued - Interneuron * CNS Gray Matter * Usually one but may be 0 or >1 * Transmits, Inhibits, or Reroutes to Motor Neuron - Motor Neuron (CNS to Effector) - Effector * Muscle or Gland; responds to motor impulse * Response is Reflex (e.g. knee jerk, secretion of digestive juices, pain withdrawl) PNS – Somatic Nervous System Voluntary Controls Skeletal Muscles Neurotransmitter=Acetylcholine Cell Body in CNS Axons extend to Skeletal Muscles PNS - Autonomic Nervous System (ANS) Involuntary Motor/Efferent Chain of two Motor Neurons Receives info from CNS; Regulates: - Cardiac Muscle - Smooth Muscle - Glandular Activity Fig. 8.39 PNS – ANS continued Two Antagonistic Branches that Serve same Organs: - Parasympathetic * “Housekeeping” * Conserves Energy * Craniosacral Origin (CN X) * Effects include: Increased Gastrointestinal Activity, Decreased heart & resp. rates PNS – ANS continued - Sympathetic * “Fight or Flight” * Expends Energy * Thoracolumbar Origin * Effects Include: Increased heart & resp. rates, Constriction of blood vessels, Increased blood pressure, Pupil dilation, Bronchiole dilation, inhibition of G.I. activity