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NERVOUS SYSTEM CENTRAL & PERIPHERAL NERVOUS SYSTEMS Structural Divisions of Nervous System Central Nervous System (CNS) - Brain, Spinal Cord Peripheral Nervous System (PNS) - Cranial Nerves - Spinal Nerves CNS – Brain Four Major Brain Regions: - Cerebrum - Diencephalon - Brainstem - Cerebellum CNS – Cerebrum Cerebrum - Largest, Superior - Two Hemispheres *Separated By Longitudinal Fissure *Connected by Corpus Callosum (myelinated axons) - Two Layers: Outer Cortex (gray matter) & Inner White matter Cerebrum continued Cerebral Cortex - Neuron Cell Bodies & Unmyelinated processes - Gyri (ridges) & Sulci (grooves) White Matter (Myelinated axons) Nuclei (gray matter imbedded in white) Lobes of Cerebrum Each Cerebral Hemisphere has 5 Lobes: - Frontal – Personality, concentration, problem solving, voluntary control of skeletal muscle - Parietal – Skin sensation, speech & language, expression of thought - Temporal – Hearing, smell - Occipital – Vision - Insula – Bodily self-awareness; sense of disgust to smells, contamination, mutilation CNS - Diencephalon Diencephalon - Enclosed by Cerebrum Between Cerebrum & Brainstem Epithalamus Thalamus Hypothalamus Diencephalon: Epithalamus Superior to Thalamus & Third Ventricle Contains the Pineal Gland, Produces Hormones Diencephalon: Thalamus “Relay station” for all sensory impulses to cerebral cortex Consists of 2 lobes (may be joined by “Intermediate Mass” (a bridge of gray matter) Third ventricle is superior & medial to thalamus Diencephalon: Hypothalamus Below thalamus Controls pituitary function Controls regulatory functions - Helps regulate body temperature - Feeding/Thirst CNS - Brain Stem Between Diencephalon & Spinal Cord Three parts: - Midbrain * Colliculi – visual & auditory nuclei - Pons – Below midbrain; joins cerebellum to brainstem - Medulla Oblongata – Below Pons, Regulates heartbeat & breathing; has role in consciousness; joins brain & spinal cord CNS - Cerebellum Inferior to Cerebrum, Posterior to Brain Stem Joined to brainstem by Pons Two hemispheres with convoluted surfaces - Outer Gray Matter - Arbor Vitae (Inner, Branching White Matter) Provides involuntary coordination of body movements Protection of the CNS CNS Protected by: - Bone *Skull (Brain) *Vertebrae (Spinal Cord) - Meninges (C.T. membranes) - Cerebrospinal Fluid (CSF) - Blood-Brain barrier (harmful substances in blood) CNS – Meninges 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 – Meninges * Arachnoid Mater Thin, Spidery, Middle Extends past spinal cord Subdural Space – Between Dura & Arachnoid Subarachnoid Space – Between Arachnoid & Pia; Contains CSF * Pia Mater Innermost, Delicate Attached to Surface of Brain & Spinal Cord Highly Vascular CNS - Brain Ventricles 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 & ependymal cells 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) Spinal Tap 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 Outer White Matter – Bundles of Myelinated Axons Ascending Tracts or Pathways - Sensory Descending Tracts or Pathways - Motor CNS – Spinal Cord continued Inner Gray Matter - Neuron Cell Bodies (somas) & unmyelinated processes - Dorsal Gray Horn – Interneuron Somas - Ventral Gray Horn – Somas of Motor Neurons - Central Canal in Gray Commissure Peripheral Nervous System PNS Consists of: - Peripheral Nerves: * Cranial Nerves * Spinal Nerves & Nerve Plexuses - Ganglia - Sensory Receptors Carries Sensory Information & Motor Commands PNS – Nerves Bundles of Axons Sensory, Motor or Mixed CT Reinforced - Endoneurium – Surrounds each axon - Perineurium – Around each fascicle (group of axons) - Epineurium – Tough, Fibrous C.T. around Nerve PNS – Cranial Nerves Twelve Pairs 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) Attach to Spinal Cord by Ventral & Dorsal Root Fig. 8.21 Reflex Arcs Simple Pathway May not involve brain Results in Reflex - Fast, Predictable - Automatic motor response Five Components: - Receptor * End of dendrite of sensory neuron (or more complex) * Responds to specific stimuli - Sensory Neuron (Receptor to CNS) 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) Types of Reflexes Somatic reflexes: - Skeletal muscle Involuntary (Autonomic) reflexes: - Smooth muscle Heart and blood pressure Glandular secretion Digestive system regulation