THE NERVOUS SYSTEM

1. THE NERVOUS SYSTEM

2. Divisions of the nervous system • Afferent • Sensory information from receptors to CNS • Efferent • Motor commands to muscles and glands • Somatic division • Voluntary control over skeletal muscle • Autonomic division • Involuntary regulation of smooth and cardiac muscle, glands • Central Nervous System • Brain and spinal cord • Peripheral Nervous System • All neural tissue outside CNS

3. Nervous system organization

4. Major Regions of the Brain

5. Neuronal Organization: CNS • Two kinds of neural tissue found in both brain and spinal cord: • 1. Gray matter – 60% of brain • 2. White matter – 40% of brain

6. Neuronal Organization: CNS • Gray matter: • -two kinds: • a.neural or cerebral cortex – several layers of unmyelinated neurons + neuroglia • -forms the outer layer of the cerebrum • b. nuclei = clusters of neuronal cell bodies and dendrites • -found throughout the cerebrum, thalamus, hypothalamus, brain stem and cerebellum -collections of nuclei can form a center (higher brain function)

7. Neuronal Organization: CNS • 2. White matter = myelinated axons of neurons • cell bodies are found in the gray matter • axons are bundled together to form White matter tracts • conduct nerve impulses from gray region to gray region • Brain – three types of tracts (commisural, association, projection) • Spinal cord - two types: sensory and motor tracts (ascending and descending)

8. Cerebrum • Cerebrum= largest portion of the brain – 75% of the brain’s mass -left and right cerebralhemispheresdivided by the longitudinal fissure -hemispheres connected by the corpus callosum, anterior and posterior commissure -left hemisphere has more neurons than the right (language comprehension)

9. The Cerebral Cortex -cerebral cortex is divided into lobes & is folded into ridges and grooves -grooves = sulci -the larger sulci divide the cerebrum into lobes -ridges = gyri(gyrus) -specific gyri are for the processing of sensations, for areas of voluntary movement, for speech, for all thought processes -called motor and sensory areas

10. The Cerebral Cortex • many gyri and sulci have specific names e.g. central sulcus • between the frontal and parietal lobes e.g. pre-central gyrus • in front of central sulcus

11. No – you don’t have to know all of these!!!

12. The Cerebral Cortex lateral sulcus

13. Cerebrum -cerebrum contains three categories of white matter tracts: • commissural – join areas between hemispheres e.g. corpus callosum, anterior & posterior commissures b. association – joins areas within a hemisphere c. projection – joins cerebrum to brain stem

14. Gray Matter Nuclei: Basal Ganglia • modifies motor commands that have originated from the cerebral cortex • comprised of several nuclei including the: • 1. caudate nucleus: role in posture and limb movement • 2. putamen:precedes or anticipates body movements • 3. globus pallidus:regulates muscle tone for movements • 4. substantia nigra:role in eye movements (located in the brain stem) • high concentration of dopanergic neurons (make and release dopamine)

15. Diencephalon: Thalamus • 80% of the diencephalon • Two oval masses connected by a commissural tract = intermediate mass • each oval mass is comprised of gray matter organized into multiple nuclei • white matter tracts run in and out to connect to other areas of the brain • major relay station for most sensory impulses from the SC & brain stem • also relays motor information from cerebellum into the cerebrum • relays nerve impulses to and from different areas of the cerebrum, the brain stem & cerebellum

16. Diencephalon: Hypothalamus • 20% of the diencephalon • located below the thalamus and above the optic chiasma • comprised of multiple nuclei that control various functions

17. Diencephalon: Hypothalamus -functions of the nuclei: 1. controls the ANS – role in regulating smooth & cardiac muscle contraction 2. regulates emotional and behavioral patterns– rage, aggression, pain and pleasure + sexual arousal 3. regulates eating & drinking 4. controls body temperature

18. Diencephalon: Hypothalamus -functions of the nuclei: 5. hormone production – hypothalamus produces 9 hormones • oxytocin and anti-diuretic hormone (ADH) – stored in the posterior pituitary prior to release • releasing and inhibiting hormones – that control the anterior pituitary

19. Pituitary Gland • sits in the sella turcica of the sphenoid bone • physically connected to the hypothalamus via an infundibulum • also connected by a portal system of blood vessels • divided into anterior and posterior lobes • anterior lobe is larger and makes hormones • posterior lobe is smaller and STORES hormones

20. Anterior Pituitary Gland • anterior pituitary responds to the releasing and inhibiting hormones of the hypothalamus • releasing hormones tell the anterior pituitary to make and release hormones • e.g. Corticotropin Releasing Hormone tells the AP to make and release Corticotropin (aka ACTH) • inhibiting hormones tell the anterior pituitary to stop making and releasing hormones

21. Anterior Pituitary Gland • releasing and inhibiting hormones from the hypothalamus travel to the anterior pituitary via a system of blood vessels between the hypothalamus and the anterior pituitary releasing/inhibiting hormones pituitary hormones

22. Posterior Pituitary Gland • posterior pituitary does NOT make hormones • stores & releases the hormones made by the hypothalamus • oxytocin – smooth muscle contraction • anti-diuretic hormone/vasopressin – decreases water loss from body • hormones are made by the neurons of the hypothalamus • axons extend into the posterior pituitary • end bulbs release these 2 hormones into the posterior pituitary for storage and release

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

24. BRAIN STEM • comprised of three structures: • midbrain • pons • medulla oblongata

25. Medulla Oblongata • inferior most part of the brain stem • connects to the spinal cord • made up of gray matter nuclei with white tracts running in and out to connect to brain and spinal cord • white matter - sensory/ascending and motor/descending tracts • many cross over as they pass through the medulla oblongata

26. Medulla Oblongata • nuclei regulate autonomic functions • gray matter nuclei are known as reflex centersfor regulating heartbeat and BP (cardiovascular center), respiration (respiratory center), plus vomiting, coughing, sneezing, hiccupping and swallowing -associated with 5 pairs of cranial nerves VIII IX X XI XII

27. Pons • “bridge” • connection from cerebrum to cerebellum • consists of multiple nuclei with white matter tracts • nuclei control both somatic (voluntary) and visceral (involuntary) motor responses

28. Midbrain • relay station between the cerebrum, cerebellum and rest of brain stem • vision, hearing, sleep/awake and motor control • substantia nigra = part of the basal ganglia • motor control • cerebral peduncles = connection between thalamus and midbrain • white matter tracts that run from midbrain to the thalamus • motor and sensory tracts cerebral peduncle pons medulla oblongata

29. Midbrain thalamus pineal gland • Posterior portion = tectum • -midbrain also connects the cerebrum to cerebellum via cerebellar peduncles • -white matter tracts (motor & sensory) • -Corpora quadrigemina = superior & inferior colliculi • -reflex centers for eye movement, head and neck movement (protection), pupil size and eye tracking corpora quadrigemina median eminence cerebellar peduncle medulla oblongata

30. Cerebellum • 10% of brain’s total volume; 50% of its neurons! • divided into hemispheres with lobes - like the cerebrum • connected by a vermis • has a superficial layer of gray matter called the cerebellar cortex - like the brain • deep to this gray matter are tracts of white matter = arbor vitae (tree of life) • also contains gray matter nuclei – like the cerebrum

31. Cerebellum • evaluates and coordinates involuntary and voluntary motor activities initiated by the cerebrum and corrects problems by sending info back to the cerebrum • regulates posture & balance • uses sensory data and stored memories – “muscle memory”

32. The Limbic System cingulate gyrus hypothalmic nuclei anterior thalmic nuclei • called the emotional brain • involved in linking olfaction and memory to basic emotional behaviors fornix corpus callosum olfactory tract mamillary body amygdala parahippocampal gyrus hippocampus

33. main components: • 1. limbic lobe: includes the hippocampus (within the parahippocampal gyrus), the cingulate gyrus, the insulaand the dentate gyrus • 2. amygdala: integration center between the limbic system, cerebrum and various sensory systems • 3. olfactory bulbs • 4. mammillary bodiesof the hypothalamus • 5. fornix - tract of white matter that connects the hippocampus to the hypothalamus • fibers end at the mammillary bodies • 6. hypothalmic nuclei • other areas The Limbic System

34. Spinal Cord • length in adults = 16 to 18 inches • 31 segments – each with a pair of spinal nerves • Cervical and lumbar enlargements • cervical = C4 to T1, nerves to and from upper limbs • lumbar = T9 to T12, nerves to and from lower limbs • Cervical • and lumbar enlargements

35. Spinal Cord • Tapers to conus medullaris at lumbar area • fragments into a cauda equinae as it runs through the sacral canal • dorsal & ventral roots of lowest spinal nerves • filium terminalearises from the conus medullaris • extension of the pia mater that anchors the SC to the coccyx

36. Histology of the Spinal Cord • Central gray matter • Contains cell bodies of neurons and glial cells + unmyelinated axons • Gray matter projections are called gray horns • Peripheral white matter • Myelinated axons organized as tracts • white matter areas are called white columns

37. Histology of the Spinal Cord • Organization of Gray Matter • 1. Posterior gray horns • sensory neurons • 2. Anterior gray horns • somatic motor neuronal cell bodies • 3. Lateral gray horns • visceral motor neuronal cell bodies • Gray commissure • axons of interneurons crossing cord

38. Histology of the Spinal Cord • Organization of White matter • Anterior, lateral and posterior white columns • tracts of myelinated axons • ascending = sensory information up • descending = motor information down

39. Protection: The Cranial & Spinal Meninges • Cranium & spinal cord are covered with protective membranes = meninges • Cranial meninges are continuous with spinal meninges • 3 layers: • 1. outer, fibrous dura mater • 2. middle arachnoid mater • 3. inner, thin pia mater

40. Protection: The Cranial & Spinal Meninges • the dura mater around the cranium differs from the dura mater around the spinal cord • cranium = dura mater forms sheets (falx cerebri) that separate the cerebrum into hemispheres and the cerebellum from the cerebrum • is also comprised of an outer endosteal layer and an inner meningeal layer • large thin –walled veins called sinuses can be found between these two layers • for the circulation of blood • e.g. superior sagittal sinus • spinal cord = dura mater is one layer thick

41. Cranial & Spinal Meninges • there are spaces between these membranes: • A. subarachnoid space:between the arachnoid and pia maters • connects to pia mater • B. subdural space:between the arachnoid and the dura mater • potential space in the cranial & spinal regions • C. epidural space– between the dura mater and the vertebral canal in the spinal column

42. Protection: The Cranial & Spinal Meninges • the spaces around the cranium differ from the spaces around the spinal cord • A. Subarachnoid space: • cranium = large space filled with used CSF; also contains cerebral veins; connects to pia mater through multiple arachnoid trabeculae • spinal cord = large space filled with used CSF; connects to pia mater through denticulate ligaments • B. Subdural space • no differences between cranium and spinal cord • C. Epidural space • cranium = potential space • spinal cord = large space filled with adipose tissue and blood vessels

43. 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 • contain cerebrospinal fluid • made by specialized cells in the ventricles – choroid plexus (capillaries + ependymal cells)

44. Flow of CSF • CSF continually circulates –from the ventricles down the central canal and into subarachnoid space • CSF is gradually reabsorbed into the blood through fingerlike projections into the dural venous sinuses = arachnoid granulations (arachnoid villi)