The communication system Cerbrospinal fluid (CSF) formed by

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Chapter 8 The Nervous System

• The communication system

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Summary

• Divisions of the nervous system
• Nervous system cells
• Nerves and nerve impulses
• Central Nervous System
• Brain and spinal cord
• Membranes and fluids
• Peripheral Nervous System

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Divisions of the Nervous System

• Central Nervous System (CNS)
• Peripheral Nervous System (PNS)
• Sensory (afferent) division transmits information
  to toward the CNS.
• Motor (efferent) division transmits impulses away
  from the CNS.

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Divisions of the Nervous System

• PNS
• Motor division
• Somatic Motor
• Autonomic nervous system (ANS)

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Cells of the Nervous System

• Neuron 3 parts
• Cell body - main part of the neuron
• Dendrites branching projections that transmit
  impulses toward the cell body.
• Axon single large process that transmits
  impulses away from the cell body.
• Myelin sheath segmented material wrapped around
  the dendrites and axons of the PNS. The space
  between the segments are called Nodes of Ranvier
  (rahnveeAY).

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Cells of the Nervous System

• Schwann cells produce myelin, a white fatty
  substance that insulates the axons and dendrites
  like insulation around electrical wires.
• Neurolemma outer membrane of the Schwann cell
  that is essential for regenration of cut/injured
  axons.
• Axons in the CNS do not have a neurolemma and the
  potential for regeneration is less.

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Cells of the Nervous System

• Neurons 3 types
• Sensory (afferent) neurons transmit sensory
  information (impulses) to the spinal cord and
  brain from all parts of the body.
• Motor neurons (efferent) neurons transmit
  impulses away from the CNS to effectors (muscles,
  glands, etc).
• Interneurons (connectors) found only in the
  CNS integrate sensory and motor functions,
  involved in learning, etc.

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Cells of the Nervous System

• Neuroglia special types of connective tissue
  cells (glia glue). A common type of brain
  tumor glioma originates in these cells.
• Astrocytes large cells that look like stars
  threadlike extensions. Astrocytoma
• Microglia usually stationary but when brain
  tissue is inflamed or degenerating they act as
  microbe - eating scavengers (phagocytosis).
• Oligodendrocytes (oligodendroglia) hold nerve
  fibers together and produce the myelin sheath
  found in the CNS.

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Cells of the Nervous System

• Multiple Sclerosis destruction of myelin,
  replaced with hard, plaque-like lesions and
  invasion by inflammatory cells.
• Manifestations include impaired nerve conduction,
  weakness, incoordination, visual impairment, and
  speech disturbances.
• An autoimmune disease attacking females more than
  males.

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Nerves and Nerve Impulses

• Nerves are groups of axons /or dendrites bundled
  together like the stands of a cable. 3 types
• Sensory
• Motor
• Mixed
• Nerve tracts groups of neurons within the CNS.
  Because they are myelinated and appear white
  White Matter.
• Neural Tissue composed of cell bodies and
  unmyelinated axons and dendrites is called Gray
  Matter.

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Nerves and Nerve Impulses

• Nerve Impulses are generated in the following
  sequence (like that for muscle).
• Polarization neuron at rest, i.e. not carrying
  an impulse, electrical charge is negative.
• Depolarization neuron receives a stimulus and
  discharges an impulse electrical charge
  reversed, i.e. becomes more positive. The
  impulse is called an Action Potential.

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Nerves and Nerve Impulses

• Nerve impulse generation
• Propagation impulse travels over the nerve and
  down the axon
• Repolarization return toward resting state,
  neuron can respond to a stimulus.
• Nerve impulse may be transmitted to another nerve
  or another type of cell like a muscle.

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Nerves and Nerve Impulses

• Transmission of nerve impulse from an axon to the
  dendrites of another neuron.
• Synapse
• Neuron before synapse
• Neuron after
• Impulse causes the release of a neurotransmitter
  at the end of the presynaptic neuron. The
  neurotransmitter then stimulates the postsynaptic
  neuron. One way transmission.

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Nerves and Nerve Impulses

• Neurotransmitters contained in small sacs
  within the synaptic knob. Examples
• Acetylcholine found at the neuromuscular
  junction.
• Dopamine, serotonin, and norepinephrine feel
  good neurotransmitters.
• Endorphins and enkephalins morphine like
  active in pain conduction pathways in the CNS.
  Natural pain killers

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CNS Brain Divisions and Functions

• Brain stem
• Medulla Oblongata enlarged upward extension of
  the spinal cord lying just inside the cranial
  cavity above the large hole in the cranium???

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CNS Brain Divisions and Functions

• Brain Stem
• Pons located anteriorly from the upper part of
  the medulla.
• Midbrain superior to the pons.

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CNS Brain Divisions and Functions

• Cerebellum located inferiorly to the occipital
  lobes of the cerebrum. Functions concerned with
  movement coordination, muscle tone, posture and
  equilibrium (unconscious).

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CNS Brain Divisions and Functions

• Diencephalon located between the midbrain and
  the cerebrum, 2 parts
• Thalamus - inferior to the cerebrum.
• Produces sensations and associates sensations
  with emotions.
• Also associated with awareness.
• Hypothalamus inferior to the thalamus
• Regulates secretion of hormones by the anterior
  pituitary gland.
• Produces ADH hormone that affects urine volume.
• Involved in maintenance of body temperature.

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CNS Brain Divisions and Functions

• Cerebrum largest, uppermost part of the brain.
• Cerebral cortex surface has ridges or folds
  gyri and grooves sulci and fissures (deeper).
  This allows for more surface area within the
  cranium.
• 2 separated hemispheres connected at the base by
  the corpus callosum.
• Divided into lobes same name as the bones of
  the cranium that lie over them.

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CNS Brain Divisions and Functions

• Cerebrum - lobes
• Frontal lobe generates impulses for voluntary
  movement, left area controls the right side,
  right controls the left.
• ? Effect of a CVA in the right frontal area
• Special areas for different functions, example
  damage to Brocas motor speech area causes
  aphasia.

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CNS Brain Divisions and Functions

• Parietal Lobes general sensory areas.
• Receive impulses from receptors in the skin and
  interpret cutaneous sensations.
• Receive impulses from stretch receptors in
  muscles for conscious muscle sense.
• Temporal lobes
• Auditory areas receive impulses from receptors in
  the inner ear hearing.
• Olfactory areas receive impulses from receptors
  in the nasal cavities smell.

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CNS Brain Divisions and Functions

• Occipital lobe visual areas that receive
  impulses from the retinas of the eyes. Impulses
  travel over the Optic nerve vision/interpretatio
  n.
• Summary of cerebral functions

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CNS Spinal Cord

• The spinal cord extends from the occipital lo
  lobe to the bottom of the 1st lumbar vertebra -
  about 17-18 inches. It is contained in the
  spinal cavity formed by the vertebral column.
• Functions connects the brain and PNS.
• Ascending tracts carry sensory information to the
  brain.
• Descending tracts carry motor impulses away from
  the brain.

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CNS Spinal Cord

• Functions also include reflexes involuntary
  response to a stimulus.
• Reflex arc pathway of nerve impulses during a
  reflex
• Receptor - stimulus
• Sensory neurons carry impulse to CNS
• CNS with 1 or more synapse - integration
• Motor neurons carry impulse toward effector
• Effector responsible for a response

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CNS Spinal Cord

• Reflexes
• Stretch reflex when a muscle is stretched it
  will automatically contract. This type of reflex
  helps keep us upright against gravity patellar
  reflex.
• Flexor reflex painful stimulus will cause
  withdrawal of a body part (protective mechanism).
• ? Why do doctors test reflexes?

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Membranes and Fluids of the CNS

• Meninges tough, fluid-containing membranes that
  protect the brain and spinal cord. 3 Layers
• Dura Mater
• Arachnoid
• Pia Mater
• ?Where is the subarachnoid space

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Membranes and Fluids of the CNS

• Cerbrospinal fluid (CSF) formed by the choroid
  plexus (network of capillaries in the brain).
  CSF is continually formed, circulated and
  reabsorbed into the blood. Production
  reabsorption normally. NPH and hydrocephalus
• Functions of the CSF

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CNS

• Ventricles spaces in the brain which contain
  CSF.
• 2 lateral ventricles one each half of the
  cerebrum.
• Third and fourth ventricles are below the lateral
  ventricles.
• Fluid moves through the ventricles and out of the
  fourth ventricle to the arachnoid space which
  covers the brain and spinal cord.
• ? How do we sample CSF

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PNS

• Includes nerves that connect the CNS to other
  parts of the body (cranial, spinal and ANS
  nerves).
• Cranial nerves Nerves 1-12 (I XII)
• I Olfactory
• II Optic
• III Oculomotor
• IV Trochlear
• V Trigeminal
• VI Abducens

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PNS

• Cranial nerves
• VII Facial
• VIII Acoustic
• IX Glossopharyngeal
• X Vagus
• XI Accessory
• XII Hypoglossyl
• On Occasion Our Trusty Truck Acts Funny A Good
  Vehicle AnyHow

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PNS

• Spinal nerves
• 31 pairs conduct impulses between the spinal cord
  and those parts of the body not served by cranial
  nerves.
• Named according to the vertebrae from which they
  emerge.
• Involved in sensations and movements.
• Skin surface areas that are supplied by a single
  spinal nerve are called dermatomes.

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PNS

• Spinal nerves Major nerves
• Phrenic diaphragm
• Radial posterior arm, forearm, hand
• Ulnar little and ring finger
• Intercostal intercostal muscles
• Sciatic posterior thigh
• Cauda equina lumbar and sacral nerves that
  extend past the end of the spinal cord.

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PNS Motor divisions

• Somatic motor serves skeletal muscles
• ANS motor neurons that conduct impulses from the
  spinal cord or brain stem to cardiac muscle,
  smooth muscle tissue, and glandular tissue
  involuntary functions.
• 2 divisions parasympathetic and sympathetic.
  Both serve about the same tissues but cause
  opposite actions.

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PNS Motor Division

• ANS Sympathetic fight or flight response.
  Active during stressful situations fear, anger,
  exercise. Our built in emergency system.
  Stimulation causes
• Increased HR, dilation of the bronchioles and
  blood vessels in the skin and skeletal muscles.
• Decreased peristalsis, urination and defecation.
• Increased sweating, secretion of epinephrine from
  the adrenal gland.
• Dilation of the pupils.

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PNS Motor Division

• ANS Parasympathetic division resting and
  digesting. Active during non-stressful normal
  situations. Stimulation causes
• Decreased heart rate
• Increased peristalsis and secretion of digestive
  juices.
• Stimulates urination and defecation
• Pupil constriction

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ANS Motor Division

• Neurotransmitters
• ANS nerve pathways consist of 2 nerve
  preganglionic and postganglionic. (Ganglion
  collections of neuron cell bodies)
• All preganglionic neurons secrete acetylcholine
  which stimulates
• Postganglionic neuron. The sympathetic
  post-neurons secrete norepinephrine while the
  parasympathetic post-neurons secrete
  acetylcholine.