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L Nervous  System
 

L Nervous System

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  • Buoyancy : brain weight in air: about 1.4 kg – in CSF about 50 g (= 97% lighter) because it is only a little denser than the CSF. Protects brain from crushing itself. Arachnoid granulations only appear at about 3 years of age. Infants are therefore especially sensitive to alterations or hyperactivity of the choroid plexuses.l
  • Alcohol, nicotine and anesthetics can diffuse through BBB. Blood borne toxins (urea, food toxins, bacterial toxins) cannot get through. Recent discovery: During prolonged emotional stress the tight junctions of the BBB are opened.
  • In 90-95% of people left side has more control over language, math and logic. Right side is more involved withy visual-spatial skills, intuition, emotion, artistic and musical skill.
  • Substantia nigra is in mesencephalon
  • Thalamus = 80% of diencephalon. Gateway (relay station) to the cerebral cortex not just for sensory input but for all info. Processing and editing also takes place. About 12 nuclei Hypothalamus also about 12 nuclei. Main visceral control center of the body
  • Scm = sternocleido mastoid muscle
  • 31 pairs of spinal nerves – designated as are vertebrae a. 8 cervical b. 12 thoracic c. 5 lumbar d. 5 sacral
  • Plexus - plexuses
  • do NOT require cerebral processing but can be modified by cerebral control
  • General functions 1. excitatory of digestive organs 2. depresses heart rate and blood pressure 3. constricts pupils of eyes 4. sexual arousal 5. slows breathing 6. constricts urinary bladder

L Nervous  System L Nervous System Presentation Transcript

  • Central Nervous System www.freelivedoctor.com
  • Neural Tissue Anatomical subdivisions of NS Made up of neurons and neuroglia cells www.freelivedoctor.com
  • Functional Overview of NS
    • CNS
    • Integration, processing and coordination of sensory data and motor commands
    • Higher functions
    • PNS
    • Sensory or afferent division with sensory neurons. Brings sensory info to CNS. Begins as receptors, ends in?
    • Motor or efferent division with motor neurons. Brings motor commands to peripheral tissue. Ends at effector cells.
    www.freelivedoctor.com
  • Peripheral Nervous System www.freelivedoctor.com
  • Cellular Organization of Neural Tissue
    • Two cell types:
    • Neurons
    • Neuroglia
      • Schwann cells
      • Satellite cells
      • Astrocytes
      • Oligodendrocytes
      • Microglial cells
      • Ependymal cells
    www.freelivedoctor.com
  • General Neuron Structure
    • Cell body or Soma with Perikaryon
    • Dendrites
    • Axon with axon hillock
    • Synaptic terminals
    www.freelivedoctor.com
  • Astrocytes : largest & most numerous
    • Function: BBB
      • structural framework & repairs
      • regulation of ions, nutrients, gases
    www.freelivedoctor.com
  • Oligodendrocyte
    • Smaller than astrocyte
    • Produce myelin in CNS (white matter vs. gray matter!)
    • Myelin = ?
    www.freelivedoctor.com
  • Microglia cells
    • Smallest
    • Phagocytosis of ?
    •  # during infection or injury
    www.freelivedoctor.com
  • Ependymal cells
    • Lining of ventricles & central canal
    • Some regions ciliated
    • Some specialized to produce CSF
    www.freelivedoctor.com
  • Schwann Cells and Peripheral Axons
    • Responsible for myelination, but surround all peripheral axons!
    • Involved in repair mechanism after injury Wallerian Degeneration
    myelinated www.freelivedoctor.com
  • Structural Neuron Classification
    • Anaxonic
      • In CNS
    • Unipolar
      • Also called pseudounipolar
      • Sensory neurons
    Axon hillock See fig. 13-10 www.freelivedoctor.com
  • Structural Neuron Classification cont. . .
    • Bipolar
      • Unmyelinated
      • Rare, but important in special senses
    • Multipolar
      • Most common
      • All motor neurons
    www.freelivedoctor.com
  • Functional Neuron Classification
    • 1) somatic vs. visceral sensory or afferent
    • monitoring of ?
    • 2) somatic vs. visceral motor or efferent carry instructions to ?
    • 3) Inter- or association neurons
    www.freelivedoctor.com
  • Synapse
    • Site of communication between two nerve cells or nerve cell and effector cell
    • neuro-effector junctions (example?)
    • Electrical vs. chemical synapses
    www.freelivedoctor.com
  • Chemical Synapse vs. Electrical Synapse
    • Space between two cells
    • Signal transduction via NT
    • Most common
    • Direct physical contact between cells = gap junctions
    • Direct signal transduction
    • Rare, but occurs in CNS and heart
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  • Chem. Synapse Structure
    • Axon terminal of presynaptic cell
    • Synaptic cleft
    • Dendrite or cell body of postsynaptic cell
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  • Neuron Organization
    • Divergence - One neuron synapses with several, effectively "spreading the word".
    • Convergence - Several neurons synapse with a single neuron, concentrating the input.
    • Serial processing - step-wise, sequential
    • Parallel processing - simultaneous processing of different information
    www.freelivedoctor.com
  • Anatomical Organizatin of NS
    • Collections of cell bodies - ganglion in PNS, center or nucleus in CNS
    • Bundles of axons - tracts in CNS, nerves in PNS
    • “ White” = myelinated axons, both nerves and tracts
    • “ Gray” = non-myelinated material, dendrites, synapses and cell bodies as well as nonmyelinated axons. In CNS – nucleus; in PNS - ganglia
    www.freelivedoctor.com
  • Brain and Cranial Nerves
    • Discuss the organization of the brain, including the major structures and their functions
    • Describe the meninges of the spinal cord and brain, and integrate the formation and flow of CSF with this information.
    • Describe the structures that constitute the BBB and their functions
    • Review the cranial nerves, again giving a brief function of each.
  • Major Brain Subdivisions
    • Telencephalon (= Cerebrum)
    • Diencephalon (Thalamus and hypothalamus)
    • Mesencephalon
    • Metencephalon (Pons and cerebellum)
    • Myelencephalon (= Medulla oblongata)
    Brainstem
  • Gray & White Matter Organization
    • In brain stem similar to spinal cord ( nuclei around ventricles, tracts on outside)
    • In cerebrum and cerebellum : white matter covered with layer of neural cortex (grey)
  • Cranial Meninges
    • 1. Dura mater - strong, "tough mother"
    • a. falx cerebri
    • b. falx cerebelli
    • c. tentorum cerebelli
    2. Arachnoid - spidery, holds blood vessels 3. Pia mater - "delicate mother"
  • Arachnoid granulations: This is where the CSF produced in the choroid plexuses of the ventricles and which has circulated into the subarachnoid space is reabsorbed. Longitudinal fissure
  • Four Ventricles
    • CSF filled chambers
    • Communicating with central canal of spinal cord
    Lined by ependymal cells
    • Formation in ventricles by specialized ependymal cells of choroid plexuses (~500 mL/day; total volume ~ 150 mL)
    • Functions
      • transport medium, in
      • shock absorption
      • buoyancy (floats the brain)
    • CSF circulation: Ventricles -> central canal -> subarachnoid space
    • Reabsorption into circulation via arachnoid granulations into superior sagittal sinus.
    CSF: Cerebro-Spinal Fluid Fig 15.6
  • Blood Brain Barrier (BBB)
    • what is it?
    • 3 areas in brain don’t have BBB
    • portion of hypothalamus
    • pineal gland (in diencephalon)
    • choroid plexus
    • Two hemispheres separated by longitudinal fissure
    • Gyrus (gyri) separated by sulcus (sulci)
    • Major lobes named after overlaying bones
    Cerebrum
  • Cerebral Hemispheres . . .
    • . . have functional regions (motor, sensory and association areas)
    • . . . have some functional differences (in spite of anatomical resemblance) -> Lateralization of cortical functioning
    • . . . receive information and generate commands for opposite side of body
  • Cerebral Cortex and Central White Matter
    • Gray surface (cortex) with white tracts internally
      • Commissures – connect corresponding gyri of the two hemispheres
      • 1) corpus callosum
      • 2) anterior commissure
      • Projection tracts (fibers) – connect more or less vertically
      • Association tracts (fibers) – connect one gyrus to another in the same hemisphere
  • Basal (or cerebral) Nuclei Misnomer: basal ganglia Gray matter internal to the cerebral cortex, below floor of lateral ventricles. Function: modulate motor output from the cerebral cortex. Subconscious control of skeletal muscle tone and coordination of learned movement patterns. Parkinson's disease is caused by the loss of at least 80% of the dopaminergic neurons in basal nuclei and substantia nigra (resting tremor) Fig 15.11
  • Diencephalon Epithalamus Pineal gland - produces melatonin, sets diurnal cycles Thalamus (~12 nuclei) Hypothalamus Just superior to optic chiasma Infundibulum - connects to pituitary gland Some functions: Control of autonomic nervous system Coordination of nervous and endocrine systems Secretion of hormones - ADH and oxytocin
  • Mesencephalon)
    • = Midbrain
    • Corpora quadrigemina = 2 pairs of sensory nuclei
      • Superior colliculi (relay station for visual information)
      • Inferior colliculi (relay station for auditory information
    • Substantia nigra - regulates motor output
    • Cerebral peduncles - ascending and descending tracts to thalamus
    • Nuclei of ori for CN III and IV
  • Metencephalon: Cerebellum Hemispheres and lobes Cortex -gray surface with folia - fine ridges and sulci - grooves between the ridges Purkinje cells , axons of which become arbor vitae (white matter) in center Regulation of posture and balance
  • Metencephalon: Pons Myelencephalon: Medulla oblongata
    • Mostly ascending and descending tracts
    • Nuclei of ori for many cranial nerves
    • Location of autonomic nuclei involved in respiratory and cardiovascular control
    • Relay stations for sensory and motor neurons
  • Cranial Nerves
    • Twelve pairs:
      • 2 attach to forebrain (Telen- & Diencephalon)
      • 10 attach to brainstem (Mes-, Met- and Myelencephalon)
    • Names relate to appearance or function
    • Classification ?
  • Olfactory Nerve (= CN or N I)
    • 1º function?
    • Origin?
    • Destination? _____________(By way of cribiform plate of ethmoid )
    • Only CN directly attached to Cerebrum
  • Optic Nerve (N II)
    • 1º fu?
    • ori?
    • dest? - by way of optic foramen of sphenoid to Diencephalon (optic chiasma) and to occipital lobe
  • Oculomotor (N III)
    • C: Motor
    • O: Mesencephalon
    • D: Somatic motor to superior, inferior, medial recti and inferior oblique; visceral motor to intrinsic eye muscles
    • by way of superior orbital fissure
  • Trochlear (N IV)
    • C: Motor
    • O: Mesencephalon
    • D: superior oblique
    • by way of superior orbital fissure
  • Trigeminal (N V)
    • C: Mixed
    • three major branches
    • 1. ophthalmic (sensory)
    • 2. Maxillary (sensory)
    • 3. Mandibular (mixed)
    • O: face / nuclei of pons
    • D: sensory nuclei in pons / muscles of mastication
  • Abducens (CN VI) C: Motor O: Pons D: Runs lateral rectus eye muscle
  • Facial (N VII)
    • C: Mixed
    • O: sensory from taste receptors of anterior 2/3 of tongue / motor from pons
    • D: Sensory to sensory nuclei of pons / motor muscles of facial expression, visceral motor to tear gland.
  • Vestibulocochlear (N VIII)
  • Glossopharyngeal (CN IX) C: mixed O: sensory from posterior 1/3 of tongue / motor from medulla oblongata D: medulla / muscles for swallowing, parotid gland
  • Vagus (N X)
    • C: Mixed
    • O: Sensation from pharyngeal area and outer ear / motor from medulla
    • D: Sensory to medulla / visceral motor to thoracic and abdominal cavities and their organs. Major motor pathway for ANS
  • Accessory (N XI) and
    • C: Motor
    • O: Motor nuclei of medulla and spinal cord
    • D: Swallowing, trapezius & scm muscles
    • Hypoglossal (N XII)
    • C: Motor
    • O: Motor nuclei of medulla
    • D: Tongue musculature
  • Spinal Cord and Spinal Nerves Explain spinal cord anatomy, including gray and white matter and meninges (give the general functions of this organ). Discuss the structure and functions of the spinal nerves and plexuses. Describe the structural components of reflexes.
    • Resides inside vertebral canal
    • Extends to L1/ L2
    • 31 segments, each associated with a pair of dorsal root ganglia
    • Two enlargements
    Adult spinal cord:
  • 1. Cervical Enlargement Gray matter expanded to incorporate more sensory input from limbs and more cell bodies for motor control of limbs
  • Spinal Meninges 3) Pia mater 2) Arachnoid 1) Dura mater Three membranes surround all of CNS 1) Dura mater - "tough mother", strong 2) Arachnoid meninx - spidery looking, carries blood vessels, etc. Subarachnoid space 3) Pia mater - "delicate mother", adheres tightly to surface of spinal cord
  • Inferior End of Spinal Cord
    • Conus medullaris - inferior end of spinal cord proper
    • Cauda equina - individual spinal nerves within spinal canal
    • Filum terminale - filamentous end of meninges, "tie-down"
  • Lumbar Puncture (= Spinal Tap) For clinical examination of CSF or administration of radiopaque dyes, drugs and sometimes anesthetics However: mostly “epidurals” for anesthetics L3 L4
  • Organization of Cord Cross Section
    • Gray matter - interior horns
    • posterior - somatic and visceral sensory nuclei
    • anterior (and lateral) gray horns – somatic and visceral motor control
    • gray commissures - axons carrying information from side to side
    • White matter - tracts or columns
    • posterior white column -
    • anterior white column
    • lateral white column
    • anterior white commissure
    • functions
    • ascending tracts - sensory toward brain
    • descending tracts - motor from brain
  • Peripheral Nerves Definition: bundles of axons. AKA tracts in CNS Organization – coverings: Epineurium wraps entire nerve Perineurium wraps fascicles of tracts Endoneurium wraps individual axons
  • Anatomy of a Peripheral nerve Function: sensory - afferent motor - efferent mixed - contains axons of both
  • Organization of Spinal Nerves:
    • 1. Root – inside vertebral canal
    • a. dorsal sensory root with a ganglion
    • b. ventral motor
    • 2. Mixed spinal nerve
    • 3. Rami
    • a. dorsal - mixed to skin and muscles of back
    • b. ventral - mixed “spinal nerve” to ventrolateral body surfaces and limbs
    • c. white ramus communicans motor ANS
    • d. gray ramus communicans motor ANS
    1. Fig 14-7
  • Dermatomes
    • Sensory innervations by specific spinal nerves  Each pair of spinal nerves monitors specific region of body surface.
    • Clinical significance ?
  • 4 Principal Plexuses Braids of ventral rami of cervical, thoracic, lumbar or sacral spinal nerves Cervical Plexus Phrenic nerve - innervates diaphragm
  • Brachial Plexus Musculocutaneous nerve - innervates biceps and brachialis muscles Median nerve - innervates lateral flexors Ulnar nerve - innervates medial flexors Radial nerve - innervates forearm extensors
  • Reflexes
    • Fast, stereotypical, inborn, protective actions
    • Occur at spinal cord or brainstem levels
    • May be either monosynaptic or polysynaptic
    • All require
    • a. stimulus at receptor
    • b. sensory information relay
    • c. processing at CNS level
    • d. activation of motor response
    • e. response of peripheral effector
  • Autonomic Division of NS Compare and contrast the structures of the sympathetic and the parasympathetic divisions, including functions and neurotransmitters. Show the levels of integration in the ANS, and compare these with the SNS. www.freelivedoctor.com
  • Overview of ANS
    • Pathway for Visceral Motor Output
    • ANS has two antagonistic divisions:
      • Sympathetic
      • Parasympathetic
    • ANS output always involves two neurons between spinal cord (CNS) and effector.
    www.freelivedoctor.com
    • Synapsing takes place in ganglia
    • Naming of neurons:
    ? www.freelivedoctor.com neuron #1 preganglionic presynaptic neuron #2 Ganglionic postsynaptic effector Preganglionic fiber (=axon): Always myelinated Postganglionic fiber: Always unmyelinated
  • Sympathetic Division
    • Thoracolumbar division
    • Preganglionic neurons (cell bodies) located between T1 & L2 of spinal cord
    • Ganglionic neurons (cell bodies) in ganglia near vertebral column
      • Paravertebral ganglia = sympathetic chain ganglia
      • Prevertebral ganglia = collateral ganglia
    • Special case: adrenal medulla
    • Effects of Sympathetic Division?
    www.freelivedoctor.com
  • Special Case: Adrenal medulla
    • Modified sympathetic ganglion
    • Terminus for neuron #1, stimulates specialized 2nd order neurons with very short axons in adrenal medulla to release NT into blood stream (= hormones)
    • Epinephrine (adrenalin) ~ 80% and norepinephrine (noradrenalin)
    • Endocrine effects are longer lasting than nervous system effects
    www.freelivedoctor.com
  • Sympathetic Neuroeffector Junctions Differ from somatic neuromuscular junctions Varicosities www.freelivedoctor.com
  • Summary of Sympathetic Division
    • A. Neuron #1 is short, neuron #2 is long
    • B. Synapsing occurs in prevertebral chain ganglia or paravertebral collateral ganglia
    • C. Neuron #1 releases Ach, usually neuron #2 releases NE
    • D. Prepares for emergency action, excitatory to many organs, inhibitory to others ( digestive for example)
    • E. Effects very widespread and somewhat persistent
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  • Para – Sympathetic Division Craniosacral division Preganglionic neurons (cell bodies) located in brain stem & sacral segments of spinal cord Ganglionic neurons (cell bodies) in ganglia near target organs: Intramural ganglia Effects of parasympathetic division ? www.freelivedoctor.com
  • Summary of Parasympathetic Division
    • A. Neurons #1 are long, come from the brain stem or sacral spinal cord, run with the spinal or pelvic nerves and produce ACh.
    • B. Neurons #2 are short, produce ACh, and may be either excitory or inhibitory.
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  • Anatomy of Dual Innervation
    • Each organ receives innervation from sympathetic and parasympathetic fibers
    • Fibers of both divisions meet & commingle at plexuses (fig 17-9) to innervate organs close to those centers
    • Names of plexuses derived from locations or organs involved
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