A Journey Through the Central Nervous System

1. A Journey Through the Central Nervous System Biology 2121 Chapter 12

2. Incoming Nerve Impulse • Stimulus travels towards the spinal cord • Via somatic sensory neuron • Dorsalrootganglion • Collection of sensory nerve nuclei • Anteriorhorns of gray • Synapse with interneurons

4. Inside the Spinal Cord • 17 inches long and ¾ inch thick • Bone and epiduralspace • Fat and veins • Spinalduramater • Subdural space and arachnoid mater • Subarachnoidspace • Between arachnoid and pia mater • CSF

5. A sagittal view of the human thoracic spinal cord, showing the (1) intervertebral discs, (2) vertebral bodies (3) dura mater (4) epidural space (5) spinal cord (6) subdural space. bodies.

6. Lumbar Tap

7. Inside the Spinal Cord • Terminates at the conusmedullaris • Ends at L1 – L2 • FilumTerminale • Extension of conus (covered by pia mater) • anchors spinal cord to coccyx • Denticulate ligaments (saw-tooth like pia mater) attach to dura mater • SpinalNerves • 31 pairs move out through intervertebralformaina • CaudaEquina • Nerve roots exit terminal end of spinal cord

9. Gray Matter of the Spinal Cord

10. Inside the Spinal Cord – Gray Matter

11. White Matter of the Spinal Cord • Composed of myelinated and unmyelinated nerve fibers • Run in threedirections • 1. ascending (sensory inputs) • 2. decending (motor inputs) • 3. Transversely (side to side in spinal cord) • Our sensoryinputmovestowardthebrain • Ascending fiber tracts

12. White Matter of the Spinal Cord- Ascending Tracts • The ascendingtracts are called: • 1. DorsalWhiteColumns • Skin (touch, pressure, limb and joint position, upper limbs and trunk, neck) • 2. Anterior/posteriorspinalcerebellartracts • Trunk and lower limb impulses to cerebellum • 3. Anteriorspinothalamictract • Touch and pressure to somatosensory cortex • 4. Lateralspinothalamictract • Pain and temperature info to the somatosensory cortex • Several neuronchains synapse in the ascending tracts • 1st , 2nd and 3rd order neurons

13. White Matter

14. Nonspecific Pathway • Anterolateral Pathways - lateral and anterior • Lateral and anterior spinothalamic tracts • Older pathway

15. Specific Pathway • Relays precise transmissions of inputs from a single type of sensory receptor (touch and vibration) • Includes • Dorsal white column • Medial lemniscal tracts • Terminates in the thalamus – continues onto the somatosensory cortex

16. Specific Pathway

17. Spinocerebellar Tracts • Muscle tendon stretch to cerebellum • Coordinates skeletal muscle activity • No conscious sensation

18. Trauma and Disorders • Trauma • Paralysis and Flaccid Paralysis • Spastic paralysis • Quadriplegia • Disorders • Polio • Amyotropic Lateral Sclerosis

20. Cerebellum • Processesinputsfrom: • Cerebral motor cortex • Bran stem nuclei • Sensory receptors (via spinocerebellar tracts) • Functions • Precise timing and patterning skeletal muscle contractions • Smooth and coordinated movements • Agility

21. Cerebellum • Anatomy • 11% of total brain mess • Dorsal to the pons and medulla • Two hemispheres connect via the ‘vermis’ • Folia: convoluted surface (“leaves”) • Largest neurons: Purkinje cells (multineurons) • White matter: arbor vitae (“tree of life”)

22. Cerebellum

23. Peduncles • Fiber tracts connect the cerebellum to the brain stem • 1. Superiorpeduncles: midbrain and cerebellum • Neurons inside cerebellum to motor cortex (via thalamus) • 2. Middlepeduncles: one-way, pons to cerebellum • Pons notifies the cerebellum of voluntary motor activity initiated by voluntary motor cortex • 3. Inferiorpeduncles: medulla and cerebellum • Sensory information to cerebellum from muscles in the body and vestibular nuclei of brain stem (balance and equilibrium)

25. Through the Brain Stem

26. Ascending Pathways through the base of the brain • Pathways- enter the medullaoblongata at the base of the spinal cord • Both specific and nonspecific tracts • Olives • Contain nuclei that relay state of stretch of muscles and joints to cerebellum • Nucleusgracilis and cuneatus • Associated with specific ascending pathway

28. Pons (“Bridge”) • Location • Between the medulla and midbrain • Anatomy • Composed of conduction tracts • Deep projection tracts connects higher brain centers and spinal cord

30. Midbrain • Location • Between diencephalon and pons • Functions and Anatomy - nuclei • CorporaQuadrigemina • Superior colliculi – coordinate visual reflexes like head and eye movements • Inferior colliculi – auditory relay ear to sensory cortex of cerebrum • Peduncles (associated with motor tracts)

32. Ascending Tracks move through the Diencephalon • 1. Hypothalamus • 2. Thalamus • 3. Epithalamus

33. Through the Hypothalamus • Location • Superior to brain stem • Makes walls of 3rd ventricle • Function and Anatomy • Mammillary bodies • Infundibulum and Pituitary gland • Other functions (page 446)

35. Synape at the Thalamus • Location • Superior to the hypothalamus • Function and Anatomy • Connected by intermediate mass • All ascending tracts move through the thalamus to the cerebral cortex through nuclei • Many nuclei • Ventral posterior lateral nucleus • Impulses from general somatic sensory receptors for touch, pressure , pain) • Geniculatebodies • Visual and auditory relay centers

36. Destination Somatosensory Cortex • As the fibers move up to the higher brain centers: • Form Projection tracts • Corona Radiata (radiating crown) • Tracts pass through internal capsule • Radiate out and eventually reach the cerebral cortex

38. Cerebrum • 2 CerebralHemispheres (83% of total brain mass) • Lobes and fissures • White matter and Gray Matter (Cerebral Cortex) • Giri and Sulci • CerebralCortex – The conscious mind • Composed of sensory areas • 1. Primary somatosensory cortex • 2. Somatosensory association cortex • 3. Primary visual cortex (striate) • 4. Primary auditory cortex • 5. Olfactory cortex • 6. Gustatory cortex • 7. Visceral sensory area • 8. Vestibular cortex

40. Cerebrum

41. Somatosensory Cortex

42. Association Areas • 1. Visual • 2. Auditory • 3. MultimodalAssociationAreas • (a). Anterior • (b). Posterior • (c). Limbic

43. Association Areas

44. Motor Relay • 1. Primary (somatic) motor cortex • Pyramidal cells and corticspinal tracts • 2. Premotor cortex • Skilled motor activities • Planning movements • 3. Broca’s area • Left hemisphere only • Motor speech area • 4. Frontal Eye Field • Voluntary movement of the eye

45. Motor Cortex Areas

46. Descending Motor Tracts • 1. Pyramidal (Direct) Tracts • Lateral and corticospinal tracts • 2. Extrapyramidal Pathways • Tectospinal • Motor impulses from midbrain – coordinated movment of head and eyes • Vestibulospinal • Motor impulses for muscle tone; activates limb and trunk extensor muscles that move head; balance (standing and moving) • Rubrospinal • Muscle tone of distal limbs • Reticulospinal • Muscle tones; visceral motor functions; unskilled movements

47. Descending Motor Pathways

48. Descending Pathways

49. Back through the Diencephalon and the Brain Stem • Hypothalamus- Visceral Control Center (page 446) • Midbrain • Cerebralpeduncles • Corticospinal tracts • Cerebellarpeduncles • Connect midbrain to cerebellum • Rednucleus • Relays motor pathways for limb flexion • Pons • Middle cerebellar peduncles • Connect cerebral cortex to cerebellum

50. Medulla Oblongata • CorticospinalTracts cross-over • Decussation (a “crossing”) of the pyramids • Control • 1. Cardiovascular center • 2. Respiratory centers • 3. Vomiting, hiccuping, coughing, sneezing