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THE NERVOUS SYSTEM

This text provides an overview of the divisions and organization of the nervous system, including the central and peripheral nervous systems. It also explores the major regions of the brain, such as the cerebrum, basal ganglia, diencephalon, brain stem, and midbrain.

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THE NERVOUS SYSTEM

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  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

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