THE NERVOUS SYSTEM

1. THE NERVOUS SYSTEM

2. Divisions of the nervous system

3. Anatomical Organization of the Nervous System

4. Major Regions of the Brain Figure 15.1 Major Divisions of the Brain

5. Neuronal Organization: CNS • Two kinds of neural tissue found in both brain and spinal cord: • Gray matter = neuroglia & unmyelinated axons, and dendrites of motor neurons • -forms the outer layer of the cerebrum = cerebral cortex • Gray matter also contains nuclei deep in the brain = clusters of neuronal cell bodies in CNS • Collections of nuclei can form a center (higher brain function)

6. Neuronal Organization: CNS • 2. White matter = myelinated axons • Cell bodies found in gray matter • White matter tracts = bundles of axons • For the conduction of nerve impulses • Brain – three types of tracts (commisural, association, projection) • Spinal cord - Two types: sensory and motor tracts (ascending and descending)

7. Figure 15.13b Sectional Views of the Brain

8. An Introduction to the Organization of the Brain

9. Cerebrum • Cerebrum= largest portion -left and right cerebralhemispheres divided by the longitudinal fissure -connected by the corpus callosum -folded into ridges and grooves: grooves = sulci -sulci divide the cerebrum into lobes -ridges = gyri(gyrus) • many gyri and sulci have specific names e.g. Central sulcus • Frontal and parietal lobes

10. Cerebrum -cerebrum is comprised of white and gray matter: 1. white matter - neurons with long, myelinated axons -organized into tracts -three categories of tracts • commisural – join areas between hemispheres e.g. corpus callosum b. association – joins areas within a hemisphere c. projection – joins cerebrum to brain stem

11. 2. gray matter: cerebral cortex -outermost layer of the cerebrum -contains gyri for specific processing of sensation, -area of voluntary movement, speech, all thought processes -called motor and sensory areas e.g. primary somatosensory area (postcentral gyrus): touch, proprioception, pain, itching, thermal - forms a “map” of the entire body e.g. primary visual, auditory & gustatory areas e.g. primary motor area(precentral gyrus): controls voluntary contractions -also contains gyri that are called association areas for integration and analysis of incoming info & help in making of “decisions” e.g. somatosensory, visual, auditory, language and common integrative areas

12. -2. gray matter: basal ganglia: - multiple nuclei found deep within the cerebrum -first described by Thomas Wells - 1664 - links to the midbrain -1. receives input from the cortex & provides output to the motor areas of the cortex via the thalamus -2. integrates motor commands -3. regulates the initiation & termination of muscle mve. -4. also functions to anticipate body movements & controls subconscious contraction of skeletal muscle

13. Basal Ganglia • comprised of the: • 1. striatum • caudate nucleus: activity occurs prior to eye movements • putamen: precedes or anticipates body movements • nucleus accumbens • 2. globus pallidus: regulates muscle tone for movements • 3. claustrum • 4. substantia nigra: high concentration of dopanergic neurons • 5. subthalmic nucleus

14. Medical application: Basal Ganglia -damage to the basal ganglia: -results in uncontrollable, abnormal body movements -muscle rigidity may develop and tremors -Parkinson – neurons that extend from the substantia nigra to the caudate nucleus and putamen degenerate -loss of dopamine releasing neurons – increase in muscle tone and stiffness -Huntington - hereditary disorder -caudate nucleus and putamen degenerate with loss of neurons that release GABA or ACh -spasmatic muscle contractions and loss of mental status

15. Diencephalon • Diencephalon • includes the hypothalamus, thalamus, epithalamus and subthalamus • thalamus: 80% of the diencephalon • paired oval masses of gray matter organized into nuclei, interspersed with white matter tracts • major relay station for most sensory impulses from the SC, brain stem • crude perception of pain, heat and pressure (refined in cerebrum) • transmits motor information from cerebellum to the cerebrum • relays nerve impulses to and from different areas of the cerebrum plus cerebrum into the brain stem/cerebellum

16. Thalmic nuclei • reticular • pulvinar • geniculate – medial and lateral • anterior • medial • ventral – lateral, posterior and anterior • lateral – posterior and dorsal

17. Diencephalon • hypothalamus -emotions, autonomic functions, hormone production -made of numerous nuclei and tracts 1. control of the ANS – integrates signals from the ANS (regulated smooth and cardiac muscle contraction) major regulator of visceral activities (heart rate, food movements, contraction of bladder) 2. produces hormones & connects with pituitary to regulate its activity 3. regulates emotional and behavioral patterns – rage, aggression, pain and pleasure + sexual arousal 4. regulates eating & drinking – hypothalamus contains a thirst center which responds to a rise in osmotic pressure in the ECF (dehydration) 5. controls body temperature – monitors temp of blood flowing through the hypothalamus

18. Hypothalmic nuclei • mamillary bodies • supraoptic • preoptic • dorsomedial • ventromedial • anterior hypothalmic • posterior hypothalmic • paraventricular • suprachiasmatic • arcuate

19. Diencephalon • epithalamus – consists of the pineal gland and habenular nuclei -pineal gland – part of the endocrine system -secretes the hormone melatonin -increased secretion in dark -promote sleepiness and helps set the circadian rhythms of the body (awake/sleep period) • subthalamus – works with the cerebrum and cerebellum to control body movements

20. BRAIN STEM • comprised of three structures: midbrain, pons & medulla

21. BRAIN STEM • Medulla oblongata • continuation of the SC • forms the inferior part of the brain stem • relays sensory information and controls automatic motor functions • white matter contains sensory/ascending and motor/descending tracts – continuous with spinal cord • contains several nuclei also • these nuclei regulate autonomic functions - reflex centers for regulating heartbeat and BP (cardiovascular center), respiration (respiratory center), plus vomiting, coughing, sneezing, hiccuping and swallowing • nuclei in the posterior part of medulla are associated with sensations of touch, proprioception, pressure and vibration -injury to the medulla: hard blow to the back of the head or upper neck can be fatal -damages the medullary rhythmicity area of the respiratory center (disrupts pattern of breathing) -non-fatal injury: paralysis and loss of sensation, irregular breathing and heart rate

22. BRAIN STEM • Pons = “bridge” • connection point from cerebrum to cerebellum - via projection tracts • consists of multiple nuclei and tracts • also controls both somatic (voluntary) and visceral (involuntary) motor responses • Pontine nuclei – relays information from cerebrum into the cerebellum • Pneumotaxic area – controls breathing (with medulla) • Apneustic area– controls breathing (with medulla)

23. BRAIN STEM • Midbrain (Mesencephalon) • relay station between the cerebrum and the spinal cord and cerebellum • sends motor tracts to the SC (via the medulla) and pons & conducts sensory tracts into the thalamus • anterior portion contains a pair of white tracts = cerebral peduncles • White matter tracts that conduct impulses from the cerebrum to the pons and medulla • nuclei of anterior portion generate involuntary somatic motor responses • anterior portion also releases dopamine from substantia nigra (nuclei) - loss of these neurons = Parkinsons • anterior portion - red nuclei forms synapses with cerebellum to coordinate muscle movements - posterior portion = tectum - white matter tracts = cerebellar peduncles - four round elevations = colliculi -reflex centers for visual activities (tracking, scanning) pupillary reflex, shape of the lens -reflexes that mediate movements of the eyes, head and neck - the startle reflex -relays impulses from hearing receptors to the thalamus

24. Cerebellum • divided into hemisphere with lobes - like the cerebrum • anterior and posterior lobes • has a superficial layer of gray matter called the cerebellar cortex - like the brain • deep to this gray matter are tracts of white matter and gray matter nuclei • controls voluntary and involuntary motor activities • evaluates and coordinates motor activities initiated by the cerebrum and corrects problems by sending info back to the cerebrum • regulate posture & balance • uses sensory data and stored memories

25. The Limbic System corpus callosum cingulate gyrus anterior thalmic nuclei hypothalmic nuclei fornix • called the emotional brain • group of structures that surround the brain stem • involved in olfaction and memory • emotion – anger, fear, happiness… • associated with specific responses – behavioral patterns • basic behavioral patterns • preparing for attack, laughing, crying, blushing • also includes sexual behaviors for the continuation of the species • connects with the hypothalamus to regulate these behaviors olfactory tract mamillary body amygdala parahippocampal gyrus hippocampus

26. The Limbic System • main components: • 1. limbic lobe: rim of cerebral cortex on the medial surface of each hemisphere – includes the hippocampus (parahippocampal gyrus), the cingulate gyrus, the insula and the dentate gyrus • 2. amygdala: integration center between the limbic system, cerebrum and various sensory systems • stimulation – rage • fear recognition • social interaction • recognition of familiar objects, facial expression • interpretation of facial expressions • 3. olfactory bulbs • 4. septal nuclei • 5. mammillary bodies of the hypothalamus • 6. fornix - tract of white matter that connects the hippocampus to the hypothalamus • fibers end at the mammillary bodies • 7. hypothalmic nuclei • other areas include the anterior nuclear group of the thalamus and the reticular system within the brain stem

27. Protection and Support of the Brain

28. Protection: The Cranial Meninges • Cranium is covered with protective membranes = meninges • Cranial meninges are continuous with spinal meninges • 3 layers: 1. outer, fibrous dura mater – forms sheets (falx) that separate the cerebrum and the cerebellum into the hemispheres and the cerebellum from the cerebrum • comprised of an outer endosteal layer and and inner meningeal layer • large spaces for the circulation of blood can be found between the two dural layers = sinuses • e.g. superior sagittal sinus • 2. middle arachnoid mater • 3. inner, thin pia mater

29. Cranial Meninges • -there are spaces between these membranes • A. subarachnoid space: between the arachnoid and pia maters • large veins run through the subarachnoid space • e.g. cerebral veins • B. subdural space: between the arachnoid and the dura mater • C. epidural space – between the dura mater and the vertebral canal in the spinal column

30. Protection: CSF • brain contains fluid-filled chambers = Ventricles • 2 lateral ventricles, 1 third ventricle, 1 fourth ventricle • connects to the central canal which runs into the spinal canal • These chambers contain cerebrospinal fluid • made by specialized cells in the ventricles – choroid plexus (ependymal cells) • continually circulates - ventricles and central canal to subarachnoid space

31. CSF is gradually reabsorbed into the blood through fingerlike projections into the dural venous sinuses = arachnoid granulations • interfering with the drainage of CSF into the subarachnoid space can result in accumulation of CSF in the ventricles & CSF pressure rises = hydrocephalus (implantation of a shunt – lateral ventricle into the superior vena cava or abdomen)

32. Flow of CSF

33. The blood supply to the brain • Arterial blood reaches brain via internal carotid and the vertebral arteries • give rise to the Circle of Willis • loops around the optic chiasma • the loop is formed from anterior and posterior communicating arteries • from this loop branches the anterior, middle and posterior cerebral arteries • the posterior communicating and cerebral unite to form the basilar artery • from the basilar artery branches numerous smaller arteries – e.g. cerebellar and pontine • the basilar the formed from the union of the vertebral arteries • Venous blood leaves via internal jugular veins

35. THE NERVOUS SYSTEM: THE SPINAL CORD AND SPINAL NERVES

36. Spinal Cord • length in adults = 16 to 18 inches • Cervical and lumbar enlargements • cervical = C4 to T1, nerves to and from upper limbs • lumbar = T9 to T12, nerves to and from lower limbs • Tapers to conus medullaris • filium terminale arises from the CM - extension of the pia mater that anchors the SC to the coccyx • 31 segments each with • Dorsal root ganglia • Sensory neuron cell bodies • Pair of dorsal roots • Pair of ventral roots

37. Cervical • and lumbar enlargements

38. Histology of the Spinal Cord • Central gray matter • Contains cell bodies of neurons and glial cells + unmyelinated axons • Gray matter projections are horns • Peripheral white matter • Myelinated and unmyelinated axons • Organized as tracts or columns • Organization of Gray Matter • 1. Posterior gray horns • Somatic and visceral sensory nuclei • 2. Anterior gray horns • Somatic motor control • 3. Lateral gray horns • Visceral motor neurons • Gray commissures • Axons of interneurons crossing cordated and unmyelinated axons

39. Organization of White Matter • Six columns (funiculi) • Anterior, lateral and posterior white columns • Contain tracts of myelinated neurons • Ascending tracts relay sensory information up the spinal cord to brain – in through the dorsal root of the spinal nerve • Descending tracts carry motor information down the spinal cord - out to the muscles via the ventral root of the spinal nerve

40. White matter tracts • Motor tracts/Descending tracts: • Corticospinal (lateral & anterior): cortex to spinal cord • Recticulospinal tracts (lateral & medial): RAS (brain stem) to spinal cord • Rubrospinal tract: midbrain to spinal cord • Vestibulospinal tract: inner ear to spinal cord • Tectospinal tract: tectum to spinal cord • Sensory tracts/Ascending tracts: • Spinocerebellar (posterior & anterior): spinal cord to cerebellum • Posterior column • Spinothalmic (Anterior & lateral): spinal cord to thalamus