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Chapter 11

Chapter 11. The Brain & Spinal Cord. Introduction. Brain & s.c. comprise the CNS Brain is protected by cranium & meninges – membranes that surround brain Consists of 3 layers: 1. dura mater 2. arachnoid mater 3. pia mater. Meninges.

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Chapter 11

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  1. Chapter 11 The Brain & Spinal Cord

  2. Introduction • Brain & s.c. comprise the CNS • Brain is protected by cranium & meninges – membranes that surround brain • Consists of 3 layers: 1. dura mater 2. arachnoid mater 3. pia mater

  3. Meninges 1. Dura mater – outermost; tough, fibrous; attached to inside of cranium; contains many b.v. & nerves Arachnoid mater – thin & weblike; no b.v. or nerves SUBARACHNOID SPACE – contains cerebrospinal fluid (CSF) 3. Pia mater – delicate; w/b.v. & nerves; attached directly to brain & follows contours

  4. Importance of Meninges • dural sinus – space formed when d.m. splits into 2 layers • subdural hematoma – fluid & blood collects under d.m. from trauma • Meningitis – inflammation of arachnoid or pia mater from bacteria or virus

  5. Partitions of Dura mater • Falx cerebelli – b/t rt. & lt. cerebellar hemispheres 2. Falx cerebri – b/t rt. & lt. cerebral hemispheres • Tentorium cerebelli – b/t cerebrum & cerebellum

  6. Protection of Spinal Cord • S.C. protected by bony vertebrae & same 3 meninges • Epidural space – b/t vertebrae & d.m.; contains b.v. and connective tissue for protection

  7. The Spinal Cord • Consists of 31 segments • Each gives rise to a spinal nerve • Provides 2-way communi- cation b/t brain & body • 2 main functions: 1. center for reflexes 2. conducts impulses to & from brain

  8. The Spinal Cord • Beginning pt. – foramen magnum • Ending pt. – conus medullaris (narrow pt. b/t L1-L2) • Cauda equina – cord of connective tissue (a.k.a. filium terminale)

  9. Cross Section – Spinal Cord • Gray matter – horns • White matter – funiculi • 2 grooves divide s.c. into rt. & lt. halves: posterior median sulcus anterior median fissure

  10. Cross Section - S.C. • Central canal – contains CSF; continuous w/spaces in brain • Gray commissure – connects “wings” of “butterfly”

  11. Nerve Tracts • White matter in s.c. consists of fibers called nerve tracts; provide 2-way communication b/t brain & s.c.; • 2 types: 1. ascending – sensory fibers carry impulses to brain *In the medulla, fibers cross over

  12. Nerve Tracts 2. descending – motor fibers carry impulses to muscles * In the medulla, fibers cross over

  13. Reflexes • S.C.- center for reflexes (automatic, subconscious responses) • Reflexes control many involuntary actions (HR, resp.rate, swallowing, sneezing, etc.) • Pathway that neurons follow in a reflex - reflexarc. • One of the simplest – patellar reflex (helps maintain an upright position) • Involves only 2 neurons, sensory & motor (no interneuron)

  14. Parts of a Reflex Arc • Most reflexes include 5 structures: 1. receptor 2. sensory n. 3. interneuron 4. motor neuron 5. effector • Other examples: withdrawal reflex (occurs when a person touches something painful) plantar reflex, Babinski reflex (abnormal in adults), biceps, triceps & ankle jerk reflexes

  15. Ventricles of Brain • Ventricles - Interconnected cavities in brain - continuous w/central canal & subarachnoid space of s.c. ; filled w/CSF • 4 ventricles: 1st (left hemisphere) 2nd (rt. hemisphere) 3rd (midline of brain) 4th (in brainstem)

  16. Ventricles of Brain

  17. Pathway of CSF Circulation 1. Most CSF produced in lat. ventr. by choroid plexuses 2. Interventricular foramina – openings; allow CSF to flow from lat. to 3rd ventr. 3. 3rd ventricle 4. Cerebral aqueduct – narrow canal; connects 3rd to 4th ventr. 5. 4th ventricle

  18. CSF Circulation • Flows into central canal & SA space of s.c. & back to subarachnoid space of brain 7. CSF reabsorbed by arachnoid granulations 8. Drain into blood-filled dural sinus into circ. sys. Humans secrete approx. 500ml of CSF daily. Only about 150 ml in CNS at any given time (continuously reabsorbed) CSF - clear fluid; nourishes cells of the CNS; completely surrounds brain & s.c. for protection.

  19. Lumbar Puncture • Needle inserted into subarachnoid space of s.c. & CSF is withdrawn • Site is usually b/t L1-L2 or L3-L4 (a.k.a. spinal tap) • A manometer used to measure CSF pressure • CSF can be analyzed for viruses, bacteria, bleeding, tumors of the n.s., MS, & early-onset Alzheimers

  20. Normal vs. Hydrocephalic Brain ←Normal Normal Brain Hydrocephaly Normal intracranial Excessive accumulation pressure 7-15 mm Hgof CSF causes ventricles in brain to dilate; infant’s skull expands & incr. in circumference (bulging fontanels possible)

  21. Treatment of Hydrocephaly • Shunt placed in brain to regulate pressure & reabsorb CSF into subarachnoid space

  22. The Human Brain • 5 Major Areas: 1. Cerebrum 2. Basal ganglia 3. Diencephalon 4. Brain stem 5. Cerebellum

  23. Cerebrum • Largest part of brain • Consists of 2 halves (hemi- spheres) • Connected by corpus callosum (collection of nerve fibers) • Convolutions – raised ridges • Sulci – shallow grooves • Fissures – 2 deep grooves 1. Longitudinal – divides brain into rt. & left halves

  24. Cerebrum • Transverse – separates cere- brum from cere- bellum • Cerebral cortex – thin, outer gray matter; contains cell bodies • White matter – under gray; makes up most of the cerebrum

  25. Functions of Cerebrum • 3 basic functions: 1. Motor area – sends impulses to muscles 2. Sensory area – interpret impulses from sensory receptors 3. Association area – not primarily motor or sensory; interprets, analyzes, reasons, memory, problem solving, etc.

  26. Lobes of the Brain • Sulci divide each cerebral hemisphere into 5 functional areas called lobes (named for skull bones). • 5th lobe - insula (not shown) located deep w/in lateral sulcus & covered by parts of frontal, parietal & temporal lobes

  27. Lobes of the Brain • Frontal • Association areas – problem solving, planning, analyzing, etc. • Motor areas – (ant. to central sulcus) – control of voluntary muscles • Broca’s area – ant. to motor cortex & in left hemi.; coordinates muscles of speech

  28. Lobes of the Brain 2. Parietal – • Somato- sensory area – cutaneous & other senses • Association area – under- standing speech & using words

  29. Lobes of the Brain 3. Occipital – visual area 4. Temporal – auditory area & auditory memories • Wernicke’s area – in left temporal lobe; controls analysis of spoken language 5. Insula – deep w/in lateral sulcus & includes parts of frontal, parietal & temporal lobes; associated w/emotions

  30. Basal Ganglia • Also called basal nuclei • Consist of gray matter deep within the cere- bral hemispheres • Relay info from cortex to brainstem & s.c. • Produce the ntm dopamine that inhibits motor functions (decr. levels assoc. w/Parkinson’s disease)

  31. Diencephalon • Includes 2 regions: • Thalamus – receives all sensory info & channels it to correct region on cerebral cortex for interpret- ation • Hypothalamus – maintains homeo- stasis (i.e. heart rate, b.p., temp., hunger, sleep & wake cycles, growth)

  32. Limbic System • Also located in the diencephalon is the limbic system • This area controls emotions & is also assoc.w/memory

  33. Pineal & Pituitary Glands • Also located in diencephalon • Pineal gland – secretes melatonin in absence of light • Controls sleep & wake cycles • Pituitary gland – regulates growth & reproductive cycles under direction of hypothalamus

  34. Brainstem • Connects brain to s.c. • Includes 3 regions: 1. midbrain 2. pons 3. medulla

  35. Midbrain • 1st, short section of brainstem • Relays info. from lower parts of b.s. & s.c. to higher brain • Contains corpora quadrigemina – structure that allows movement of eyes & head at same time

  36. Pons • Rounded bulge on underneath side of b.s. • Sends impulses to & from medulla & cerebellum

  37. Medulla Oblongata • Enlarged contin- uation of s.c. • All nerve tracts pass thru here & many cross over • Acts as relay center b/t s.c. & cerebral cortex

  38. Medulla • Contains 3 centers: 1. Cardiac center – area that controls heart rate 2. Vasomotor center – constricts or dilates b.v. 3. Respiratory center – regulates rate & depth of breathing • Nonvital centers – coughing, sneezing, swallowing, vomiting also located in medulla

  39. Reticular Formation • Nerve fibers scattered throughout the b.s. • When sensory impulses reach the r.f., it responds by activating the cerebral cortex into wakefulness • The cerebral cortex can also activate the r.f. (intense cere- bral activity keeps a person awake) • If the r.f. is destroyed, a person remains in a comatose state

  40. Reticular Formation • The r.f. filters incoming sensory info & decides what is important • Decreased activity in the r.f. results in sleep • Types of Sleep: 1. Slow-wave (non-REM)- restful, dreamless; reduced b.p. & resp. rate; lasts from 70-90 min. & alternates w/REM sleep

  41. Sleep • REM sleep (rapid eye movement) – “paradoxical sleep”; dream sleep; lasts 5-15 min.; heart & resp. rate irregular; so important that if a person lacks it one night, it is made up for the next night

  42. Cerebellum • Composed mostly of white matter • A treelike pattern is visible called the arbor vitae • Integrates info about body position • Coordinates skeletal muscle activity • Maintains posture & equilibrium

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