Central Nervous System

1. Central Nervous System Chapter 13

2. CNS Coverings • Bone • Meninges • Dura Mater: white fibrous tissue • Arachnoid membrane: cobweb-like layer • Pia Mater: adheres to outer surface of brain & cord; contains blood vessels • Spaces surrounding meninges • Epidural space: (“on the dura”) btwn dura mater and bone coverings • Subdural space: (“under the dura”) btwn dura mater and arachnoid space • Subarachnoid space: under arachnoid; outside pia mater

3. http://faculty.irsc.edu/FACULTY/TFischer/AP1/meninges.jpg

4. Cerebral Spinal Fluid (CSF) • Protective cushion of fluid • Brain monitors CSF to help maintain homeostasis • Ex: CO2 levels • Fluid spaces • Subarachnoid space • Spinal cord • Ventricles (4)

5. Formation of CSF • Fluid separated from blood in choroid plexuses • Choroid plexus: network of capillaries that project into ventricles • Lined with ependymal cells • Circulation: • Separation in choroid plexuses  ventricles  central canal of spinal cord & subarachnoid spaces  blood

7. Diagnostic Study – Lumbar Puncture • Removal of CSF from subarachnoid space in lumbar region of spinal cord • Above/below L4, locate iliac crest • Side-lying, knees to chest • Sterile technique • CSF tested for abnormalities • Blood counts, bacteria, pressure • Administer diagnostic agents or medications

8. http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19078.jpghttp://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19078.jpg

9. Hydrocephalus • Internal hydrocephalus • Obstruction blocks drainage of CSF from ventricles (1-3) • Ex: tumor • External hydrocephalus • Obstruction in subarachnoid space causes build up of CSF in subarachoid space • Hemorrhage  blood clots • Treatment • Infants • Unfused sutures  cranium swells • Shunt placement btwn lateral and 4th ventricles • Adults • Pressure compresses brain  coma, death

10. http://bryanking.net/wp-content/uploads/2009/02/national_hydrocephalus_foundation.jpghttp://bryanking.net/wp-content/uploads/2009/02/national_hydrocephalus_foundation.jpg http://www.choa.org/images/graphics/hydrocephalus.jpg http://www.articleslounge.com/wp-content/uploads/2009/06/Hydrocephalus.jpg

11. Spinal Cord - Structure • Extends from foramen magnum to L1 • Fissures • Anterior median fissure (larger) • posterior median sulcus • Nerve Roots – Project from each side of spinal cord • Dorsal nerve root: carry sensory information to spinal cord • Unipolar neurons • Cell bodies make up dorsal root ganglion • Ventral nerve root: carry motor information that exits spinal cord • Dorsal + ventral nerve roots = spinal nerve • Gray matter (“H” in the center of the spinal cord) • Anterior, posterior, lateral horns (or columns) • Contains interneurons and cell bodies of motor neurons • White matter (surrounds gray matter) • Anterior, posterior, lateral columns • Contains bundles of axons (tracts)

13. Spinal Cord - Functions Two main functions: • Conduction routes to/from brain • Integration or reflex center for all spinal reflexes

14. Spinal Cord – Conduction Routes • Ascending tracts – conduct sensory impulses up to the brain • Lateral spinothalamic: pain, temperature, crude touch opposite side • Anterior spinothalamic: crude touch and pressure • Fasciculi gracilis and cuneatus: discriminating touch & pressure sensations (vibrations, stereognosis, two-point discrimination), conscious kinesthesia • Anterior & posterior spinocerebellar: unconscious kinesthesia • Spinotectal: touch that triggers visual reflexes

15. Spinal Cord – Conduction Routes • Descending tracts – conduct motor impulses down from the brain • Lateral corticospinal: voluntary movement, contraction of small muscle groups (hands, fingers, feet, toes of opposite side) • Anterior corticospinal: same as above but affect muscles on same side • Reticulospinal: maintain posture during movement • Rubrospinal: coordination of body movement & posture • Tectospinal: head and neck movement during visual reflexes • Vestibulospinal: coordination of posture & balance

17. Spinal Cord – Reflex Centers • Center of reflex arc • Switching from afferent to efferent • 3 neuron arc  interneuron • 2 neuron arc  synapse btwn afferent & efferent • Located in gray matter (“H”)

18. Brain • Consists of: • 100 billion neurons • 900 billion glial cells • Weighs approx 3 lbs in an adult • Mature neurons are incapable of cell division • Only during prenatal and beginning months of life • Malnutrition hinders neuron growth/development

19. Brain - Divisions • Brainstem • Medulla oblongata • Pons • Midbrain • Cerebellum • Diencephalon • Thalamus • Pineal body • hypothalamus • Cerebrum • Cortex • Corpus callosum

20. Brainstem • Medulla Oblongata • Enlarged extension of the spinal cord • Located just above the foramen magnum • Reflex centers: cardiac, vasomotor, respiratory • Pons • White matter & reticular formation • Reflex centers for CN 5-8 • Midbrain • White matter & reticular formation • Reflex centers for CN 3-4

21. Cerebellum • Structure • Lower posterior portion of brain • Outer region  cortex  gray matter • Internal areas  white matter • Grooves  sulci; raised areas  gyri • Function • Produce skilled movements by coordinating muscle groups • Posture (unconscious) • Maintains balance

22. Cerebellar Disease • Diseases of the cerebellum (tumor, abscess, trauma, hemorrhage) produce abnormalities in muscle coordination • Most common – ataxia (muscle incoordination) • Signs/symptoms: • Hypotonia • Tremors • Disturbances in gait & balance

23. Diencephalon • Thalamus • Dumbbell-shaped mass of gray matter • Forms walls of third ventricle • Functions: • Processes auditory & visual input • Conscious recognition of pain, temperature & touch • Emotional responses (associates sensory impulses with pleasantness vs unpleasantness)

24. Diencephalon • Hypothalamus • Lie beneath thalamus and forms the floor of the 3rd ventricle • Functions: • Controls responses made by autonomic effectors • Maintains water balance • Endocrine function – release hormones that regulate actions of the anterior pituitary gland • Waking state (alert and arousal) • Regulating appetite • Maintaining normal body temperature

25. Diencephalon • Pineal Body • Located just above the midbrain • Functions: • Regulates biological clock • Produces melatonin

26. Cerebrum • Largest, upper division of the brain • Two halves – right & left hemispheres • Communicate via corpus callosum • Cerebral cortex – surface of the cerebrum; gray matter • Gyri & sulci (shallow) or fissures (deep) • Frontal lobe, parietal lobe, temporal lobe, occipital lobe

28. Functional Areas of the Cerebral Cortex (fig 13-16)

29. Functions of the Cerebral Cortex • Postcentral gyrus – termination area for sensory pathways • Touch, pressure, temperature, body position • Precentral gyrus – primary motor area • Neurons in this area control individual muscles

30. Functions of the Cerebral Cortex - Language • Speech centers are located in frontal, parietal & temporal lobes • In 90% of the population these areas are found in the left hemisphere • Aphasia = language defects • Broca’s area – unable to articulate words; able to make vocal sounds • Wernicke’s area – deficit in language comprehension

31. Functions of the Cerebral Cortex - Emotions • Experiencing and expressing emotions involves the function of the limbic system • Area of the brain that surrounds the corpus callosum • For proper expression the limbic system functions with the cerebral cortex

32. Functions of the Cerebral Cortex - Memory • Temporal, parietal and occipital lobes • Limbic system also plays a role • Removal of hippocampus inhibits a person from recalling new information

33. Disorders of the Central Nervous System

34. Cerebrovascular Accident (CVA) • Aka Stroke • Hemorrhage or cessation of blood flow through cerebral blood vessels • Lack of oxygen to neurons causes cell damage or death • If motor areas are affected, patient loses function on opposite side of the body • (motor neurons cross over from side to side in the brainstem) • Hemiplegia – paralysis (loss of voluntary muscle control) on one whole side of the body http://www.strokegenomics.org/img/stroke_hem_web.jpg

35. Cerebral Palsy • Permanent, non-progressive damage to motor control areas of the brain • Damage present at birth or shortly after birth; remains throughout life • Possible causes: • Prenatal infection, trauma to head before/during/after birth, reduced oxygen supply to brain • Results in impairment to voluntary muscles • Most common  spastic paralysis: involuntary contractions of affected muslcles

36. Dementia • Dementia: degeneration of neurons that affect memory, attention span, intellectual capacity, personality & motor control

37. Alzheimer’s Disease (AD) • Lesions develop in the cortex of the brain • Result is dementia • No known cause; no effective treatment • Genetic basis http://www.crystalinks.com/alzheimersbrain.jpg

38. Seizures • Sudden bursts of abnormal neuron activity that cause temporary changes in brain function • Mild seizures • Small changes in level of consciousness, motor control & sensory preception • Severe seizures • Convulsions (jerky, involuntary movements) & sometimes unconsciousness • Treatment • Drugs (phenobarbital, valproic acid) block neurotransmitter activity in affect areas  inhibits bursts of explosive neuron activity

39. http://theness.com/neurologicablog/?p=27