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

4. Neuronal Organization: CNS • Gray matter = unmyelinated neurons + neuroglia • -forms the outer layer of the cerebrum = neural or cerebral cortex • also forms nuclei deep in the brain = clusters of neuronal cell bodies in CNS • collections of nuclei can form a center (higher brain function)

5. 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)

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

7. Cerebrum • Cerebrum= largest portion of the brain -left and right cerebralhemispheresdivided by the longitudinal fissure -hemispheres connected by the corpus callosum

8. many gyri and sulci have specific names e.g. Central sulcus • between the frontal and parietal lobes -cerebral cortex is folded into ridges and grooves -grooves = sulci -sulci divide the cerebrum into lobes -ridges = gyri(gyrus) -specific gyri are for the processing of sensation, area of voluntary movement, speech, all thought processes -called motor and sensory areas

9. 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

10. 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 • high concentration of dopanergic neurons

11. Diencephalon • thalamus:80% of the diencephalon • Two oval masses connected by a commissural tract = intermediate mass • each oval mass is comprised of of gray matter organized into nuclei, interspersed with white matter • major relay station for most sensory impulses from the SC & brain stem • relays motor information from cerebellum into the cerebrum • relays nerve impulses to and from different areas of the cerebrum, the brain stem & cerebellum

12. Diencephalon • hypothalamus • control of the ANS– role in regulating smooth & cardiac muscle contraction • hormone production – oxytocin and anti-diuretic hormone (ADH) • regulates emotional and behavioral patterns – rage, aggression, pain and pleasure + sexual arousal • 4. regulates eating & drinking • 5. controls body temp

13. 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

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

15. Medulla Oblongata • inferior most part of the brain stem • Connects to the spinal cord • made up of white matter tracts and gray matter nuclei • white matter - sensory/ascending and motor/descending tracts • many cross over as they pass through the 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

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

17. MIDBRAIN • relay station between the cerebrum and the medulla oblongata & spinal cord • relay station between the cerebrum and cerebellum • located behind the pons and extends to the diencephalon – as cerebral peduncles • white matter motor tracts through the pons into the SC • white matter sensory tracts up into the thalamus cerebral peduncle pons medulla oblongata

18. 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

19. Cerebellum • 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 • 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”

20. called the emotional brain • involved in linking olfaction and memory to basic emotional behaviors • main components: • 1. limbic lobe: includes the hippocampus (within the parahippocampal gyrus), the cingulate gyrus, the insula and 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 cingulate gyrus hypothalmic nuclei anterior thalmic nuclei fornix corpus callosum olfactory tract mamillary body amygdala parahippocampal gyrus hippocampus

21. 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–comprised of an outer endosteal layer and and inner meningeal layer • large spaces for the circulation of blood can be found between these two layers = sinuses • e.g. superior sagittal sinus • 2. middle arachnoid mater • 3. inner, thin pia mater • the dura mater forms sheets (falx cerebri) that separate the cerebrum into hemispheres and the cerebellum from the cerebrum

22. 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 • potential space in the cranial region • C. epidural space– between the dura mater and the vertebral canal in the spinal column • potential space in the cranial region

23. 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)

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

25. The blood supply to the brain • Arterial blood reaches brain via internal carotid and the vertebral arteries • both give rise to the Circle of Willis • made up of communicating arteries and cerebral arteries • the posterior communicating and cerebral unite to form the basilar artery • the basilar the formed from the union of the vertebral arteries • Venous blood leaves via internal jugular veins

26. 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

27. 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

28. External Anatomy of Spinal Cord

29. 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

30. Histology of the Spinal Cord • Organization of Gray Matter • 1. Posterior gray horns • sensory neurons entering the cord • 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 • Organization of White matter • Anterior, lateral and posterior white columns • tracts of myelinated neuronal axons • ascending = sensory information • descending = motor information

31. White matter tracts