NERVOUS SYSTEM

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NERVOUS SYSTEM

• NEURONS

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ENDOCRINE VS. NERVOUS SYSTEM

• Speed
• endocrine -slow
• nervous - fast
• Energy
• endocrine - cheap
• nervous - expensive
• Control
• endocrine - all tissues
• nervous - muscle and glands

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ORGANIZATION OF THE NERVOUS SYSTEM

• Central Nervous System
• brain and spinal cord
• completely encased in bone
• integrative and control center of the nervous
  system

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ORGANIZATION OF THE NERVOUS SYSTEM

• Peripheral Nervous System (PNS)
• 31 pairs of spinal nerves
• leave neural canal thru intervertebral foramina
• 12 pairs of cranial nerves
• leave brain thru foramina in the skull
• two parts
• afferent or sensory division
• efferent or motor division

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ORGANIZATION OF THE NERVOUS SYSTEM

• PNS - afferent division - sensory nervous system
• three parts
• 1. somatic sensory nerves
• from receptors in the skin, fascia, and around
  joints
• 2. visceral sensory nerves
• from receptors from organs, wall of vessels
• 3. special sensory nerves
• from receptors for smell, taste, vision and
  balance

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ORGANIZATION OF THE NERVOUS SYSTEM

• PNS - efferent division - motor nervous system
• 2 parts
• 1. Somatic Nervous System
• voluntary nervous system
• carrying impulses to skeletal muscle
• 2. Autonomic Nervous System
• involuntary nervous system
• carrying impulses to smooth muscle, cardiac
  muscle and glands
• 2 divisions
• a. Sympathetic
• b. Parasympathetic

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COMPONENTS OF THE NERVOUS SYSTEM

• 1. neurons
• carry impulses
• 2. supporting cells or neuroglia
• CNS
• astrocytes
• oligodendrocytes
• microglia
• ependymal cells
• PNS
• satellite cells
• schwann cells or neurolemmocytes

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NEURON STRUCTURE

• a. cell body or soma
• contains the nucleus
• contains unique structures called ________ bodies
• dense staining, parallel layers of rough ER
• lack ________________
• lysosomes, mitochondria, golgi, ribosomes
• neurofibrils and neurofilaments
• form cytoskeleton
• in CNS tend to cluster to form structures called
  _____________
• in PNS cluster in groups called _________

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NEURON STRUCTURE

• b. dendrite
• means tree
• process that picks up information
• contains _______________ regulated gates for Na
  and K

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NEURON STRUCTURE

• c. axon
• makes up most of the length of a neuron
• has _______________ regulated gates 1 for Na and
  1 for K
• carries information from the dendrites to the
  terminal branches
• arises from a cone-shaped process on the cell
  body called the __________________
• may branch - called collaterals

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NEURON STRUCTURE

• d. axon terminal, telodendrite, or terminal
  arborization
• passes information on to other neurons or
  effectors
• contain synaptic vesicles which release
  neurotransmitters

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MYELINATED NEURONS (PNS)

• myelin sheath- Schwann cell (PNS)
• Schwann cells contain a fatty material called
  __________
• great insulator- prevents flow of ions
• other Schwann cells may not contain myelin
• called ___________________ neurons
• neurilemma
• external to the myelin sheath
• contains nucleus and most of the cytoplasm
• external to neurilemma is the basement membrane
  and a thin sleeve of fibrous connective tissue
  called the ____________
• neither neurilemma nor endoneurium are found in
  neurons in the CNS

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MYELINATED NEURONS (PNS)

• nodes of Ranvier
• bare areas between myelin sheaths
• 500X more permeable as membranes than are
  unmyelinated neurons
• saltatory conduction
• increases velocity
• conserves energy

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VELOCITY OF CONDUCTION

• 1. diameter
• - _____________ the diameter, the _____________
  the resistance, the faster the conduction
• 2. myelin
• increases the speed of conduction

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NEURONS BASED ON SPEED OF CONDUCTION

• C fibers
• slowest fibers, 1 meter per second (2 mph)
• _____________ diameter, _______________
• located in visceral efferent nerves
• found in neurons constricting and dilating pupils
• in neurons increasing and decreasing heart rate

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NEURONS BASED ON SPEED OF CONDUCTION

• A fibers
• fastest fibers, up to 140 meters per second (300
  mph)
• ___________ diameter, ________________
• large sensory neurons that relay information
  associated with touch, pressure, position of
  joints
• in all motor neurons carrying impulses to
  skeletal muscle

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NEURONS BASED ON STRUCTURE

• 1.. Unipolar
• 2 processes are fused together and only a single
  process arises from the cell body
• 2. Bipolar
• 2 processes, one from each end of the cell body
• 3. Multipolar
• one long process arises from the cell body - axon
• many small processes make up the dendritic zone
• 4. Anaxonic
• no anatomical clues
• some found in retina and brain

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NEURONS BASED ON FUNCTION

• 1. Motor or efferent neurons - 0.5 million
• to an effector away from the CNS
• muscle or gland
• all _____________
• 2. Sensory or afferent neurons - 10 million
• from a receptor to the CNS
• most are ______________
• bipolar - retina, inner ear, taste buds,
  olfactory neurons

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NEURONS BASED ON FUNCTION

• 3. Interneurons, association neurons,
  internuncial neurons - 20 billion
• completely within the CNS
• distribution of sensory information and
  coordination of motor activity
• involved in higher brain functions
• all ____________________

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Axonal Transport

• all of proteins made in the soma
• some are needed in the axon
• others are transported from axons terminals back
  to the soma
• two-way passage of protein, organelles and other
  materials along an axon is called axonal
  transport
• movement from soma to axon is called
  _______________ transport
• movement from axon to soma is called
  _______________ transport
• materials travel along microtubules

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Axonal Transport

• Two types of axonal transport
• 1. Fast axonal transport, either direction
• moves organelles, enzymes, calcium ions and small
  molecules such as glucose and amino acids
• returns used synaptic vesicles and other
  materials to the soma
• some pathogens travel this pathway to invade
  neurons including tetanus toxin and herpes
  simplex, rabies, and polio viruses
• 2. Slow axonal transport or axoplasmic flow
• always a_____________________
• moves enzymes and cytoskeletal components down
  axon, renews worn-out axoplasmic components in
  mature neurons, and supplies new axoplasm for
  developing or regenerating neurons

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CONNECTIVE TISSUE COVERINGS

• A. Endoneurium
• around individual neurons
• B. Perineurium
• around fascicles of neurons
• C. Epineurium
• around entire nerve

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REGENERATION - PNS

• about 6 months after birth all developing
  neurons lose ability to undergo mitosis
• Schwann cells - participate in repair
• Wallerian degeneration - axon distal to the
  injury degenerates and macrophages migrate into
  area to phagocytize debris
• Schwann cells do not degenerate
• _____________ and ______________ form a solid
  cellular cord, the regeneration tube, that
  follows path of original axon
• axon grows into the tube and the schwann cells
  wrap around the axon

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REGENERATION - CNS

• Limited regeneration
• astrocytes
• produce scar tissue that prevents axon growth
• release chemicals that block the regrowth of
  axons
• some success
• grafts from PNS
• embryonic neurons

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NEUROGLIA - CNS

• 1. Astrocytes
• outnumber neurons 501
• two types
• A. protoplasmic astrocytes
• maintain blood brain barrier
• controls the interstitial environment
• Na, K, CO2 rapid transport controls volume of
  blood flow absorbs and recycles some
• B. fibrous astrocytes
• form supportive framework for the CNS
• form scar tissue when neurons are damaged

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Astrocytes
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NEUROGLIA - CNS

• 2. Oligodendrocytes
• forms _______________ sheaths
• tip of processes expand to form a pad that wraps
  around the axon, may have as many as 15 arm-like
  processes
• myelinated neurons _________ matter
• unmyelinated neurons __________ matter

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Oligodendrocytes
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NEUROGLIA - CNS

• 3. Microglia
• least numerous and smallest neuroglia
• capable of migrating thru neural tissue
• engulf cellular debris, waste products and
  pathogens
• small _________________ which develop from
  __________________

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Microglia
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NEUROGLIA - CNS

• 4. Ependymal cells
• line central canal and ventricles of the brain
• cuboidal cells but have no basement membrane
• have _____________ when lining the ventricles
• other areas - scattered ________________
• specialized ependymal cells participate in the
  secretion of CSF (______________ plexus)

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Ependymal cells
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SYNAPSE

• 1. Electrical
• current can pass from one neuron to next via gap
  junctions
• may go both ways
• found in smooth and cardiac muscle
• rare in neurons and neuroglia

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SYNAPSE

• 2. Chemical
• synaptic bulbs contain synaptic vesicles that
  contain a neurotransmitter
• neurotransmitter is released in the synaptic
  cleft
• causes excitation or inhibition of neuron or
  effector

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CHEMICAL SYNAPSE - EXCITATORY

• Synaptic vesicles
• contain 3000 molecules of ACh or acetyl choline
• formation of Ach
• acetyl CoA __________ ---gt ACh
• uses enzyme acetyl transferase
• uses ATP from mitochondria
• ______________ leak from extracellular fluid
• causes synaptic vesicles to move to the membrane
  and dump ACh into synaptic cleft

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CHEMICAL SYNAPSE - EXCITATORY

• Postsynaptic membrane receptors for ACh
• ACh binds to ligand-regulated gates on dendritic
  zone
• increases permeability to Na and K -- Na diffuses
  across (in) much faster
• opens chemical regulated gates
• EPSP - excitatory postsynaptic potential
• lasts up to 15-20 msec
• not an action potential
• carried to the axon by the cable properties of
  the dentritic membrane

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CHEMICAL SYNAPSE - EXCITATORY

• EPSP
• need 10 or more EPSPs to fire an action potential
  on the axon
• two ways to generate an action potential
• 1. ______________ summation
• all at the same time
• 2. ______________ summation
• over a short period of time

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CHEMICAL SYNAPSE - EXCITATORY

• AChE or acetyl cholinesterase
• enzyme associated with the postsynaptic membrane
• breaks down ACh
• ACh ---gt acetate choline
• acetate - _____________ away
• choline - __________________ back into the
  synaptic bulb
• destroys ACh within 20 msec after its arrival

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CHEMICAL SYNAPSE - INHIBITORY

• neurotransmitter -- GABA - gamma amino butyric
  acid
• increases permeability of the postsynaptic
  membrane to K and Cl ions
• opens chemical regulated gates
• causes IPSP - inhibitory postsynaptic potential
• drives the axon membrane away from threshold
  --hyperpolarization
• makes it harder for the voltage regulated gates
  to open

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OTHER NEUROTRANSMITTERS

• 1. Biogenic amines
• norepinephrine (NE)
• epinephrine (EP)
• dopamine
• deficiency in brain can cause ________________
  disease
• serotonin
• Prozac inhibits reabsorption
• LSD - activates serotonin receptors
• histamine

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OTHER NEUROTRANSMITTERS

• 2. Acetyl choline
• formed from acetate and choline
• 3. Excitatory amino acids
• glutamate
• aspartate
• 4. Inhibitory amino acids
• GABA
• used to reduce anxiety
• glycine

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OTHER NEUROTRANSMITTERS

• 5. Neuropeptides
• Substance P
• Opioids -- endorphins, enkephalins, dynorphins
• 6. Dissolved gases
• CO (carbon monoxide)
• NO (nitric oxide)
• 7. Others
• ATP, Prostaglandins, ADH, oxytocin, glucagon,
  insulin and many other hormones

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SYNAPTIC DELAY

• 0.2 - 0.5 msec
• time required to cross a chemical synapse and
  stimulate or inhibit postsynaptic membrane
• reflexes involved small number of synapses - less
  synaptic delay

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SYNAPTIC FUNCTIONS

• Fatigue
• runs out of neurotransmitter
• enough for 10,000 transmissions
• can be exhausted in seconds
• only fatigue in the nervous system
• Acidosis -- below pH 7.4
• ______________ neuronal activity
• below pH 7.0 -- acidosis coma

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SYNAPTIC FUNCTIONS

• Alkalosis -- above pH 7.4
• _________________ neuronal excitability
• above pH 7.8 -- alkalosis coma
• Chemicals
• Curare
• competes with ACh receptor on motor end plate
• Nerve gas (parathion, malathion)
• inactivates AChE for up to several weeks

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SYNAPTIC FUNCTIONS

• Chemicals
• Atropine
• blocks ACh from binding
• dilates pupils
• antidote to nerve gas
• Botulism toxin
• inhibits release of ACh
• inhibits muscle contractions
• Caffeine
• reduces threshold

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SYNAPTIC FUNCTIONS

• Chemicals
• Nicotine
• mimics ACh
• Venom of black widow spiders
• causes massive release of ACh
• Seafood neurotoxins (tetrodotoxin)
• blocks Na from entering voltage regulated gates
• Prostigmine
• inhibits AChE
• helps myasthenia gravis victims

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MODIFICATION OF NEURONAL ACTIVITY

• Presynapse
• inhibition
• inactivates _______ channels
• examples glycine, NE, GABA
• excitation or facilitation
• activates _________ channels
• example serotonin

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MODIFICATION OF NEURONAL ACTIVITY

• Neuromodulators
• chemical substances which alter neuronal activity
  indirectly
• either influence the release of neurotransmitter
  or the postsynaptic cells response to the
  neurotransmitter
• typically neuropeptides
• example - NO (nitric oxide)
• released by postsynaptic neurons in some areas of
  brain concerned with learning and memory
• diffuses into presynaptic neuron and stimulates
  it to release more neurotransmitter

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NEURONAL CIRCUITS

• 1. Converging ciruit
• same source
• Pacinian corpuscles -- pressure
• different sources
• control of respiration

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NEURONAL CIRCUITS

• 2. Divergening Circuit
• permits broad distribution of a specific input
• types
• A. amplification
• B. divergence into multiple tracts
• 3. Parallel after-charge circuit
• several neurons process same information at one
  time
• each chain has a different number of synapses,
  but eventually they all reconverge on a single
  output
• output neuron may go on firing for some time
  after input has ceased
• important in withdrawal reflexes
• longer-lasting output from small period of pain

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NEURONAL CIRCUITS

• Reverberating Circuit
• axons extend back toward the sources of an
  impulse and further stimulate the presynaptic
  neuron
• helps maintain consciousness, muscular
  coordination, normal breathing, short term
  memory...