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Nervous System. Chapter 9 Pages 211-257. Chapter 9 Wordbytes. af - = toward 11. - ferrent = carried arachn - = spider 12. gangli - = swelling astro - = star 13. - glia = glue auto- = self 14. mening - =membrane dendro - = tree 15. micro- = small

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nervous system

Nervous System

Chapter 9

Pages 211-257

chapter 9 wordbytes
Chapter 9 Wordbytes
  • af- = toward 11.-ferrent = carried
  • arachn- = spider 12.gangli- = swelling
  • astro- = star 13. -glia = glue
  • auto- = self 14.mening- =membrane
  • dendro- = tree 15. micro- = small
  • di- = 2, through16.neuro- = nerve
  • ef- = away from 17. –oid = similar to
  • encephalo- = brain18.oligo- = few
  • enter- = intestines 19. peri- = around
  • epen- = above 20.somat- = body
nervous system overview
Nervous System Overview
  • Master controller and communicator for the body
  • Responsible for all behavior
  • 3 functions:
    • Sensory input monitors changes inside/outside of body
    • Integration processes and interprets, then decides what should be done
    • Motor output causes a response in effector organs
organization 2 main parts
Organization—2 main parts:
  • Central Nervous System (CNS) = brain and spinal cord
    • Interprets incoming sensory info. and dictates motor responses
  • Peripheral Nervous System (PNS) = nerves from brain & in spinal cord
    • INPUT-Afferent or Sensory division
    • OUTPUT- Efferent or Motor division
    • Subdivided: Somatic (SNS—from CNS to skeletal muscles=voluntary) & Autonomic (ANS—regulate smooth & cardiac muscle, glands=involuntary)
histology
Histology
  • Highly cellular—densely packed & tightly intertwined
  • 2 types of cells:
    • Neuron= nerve cell
      • Specialized for signal carrying & information processing
    • Neuroglia cells support, nourish & protect neurons
      • Neuroglia critical for homeostasis of interstitial fluid around neurons
supporting cells neuroglia
Supporting cells (Neuroglia)
  • ~ half the volume of CNS
  • Cells smaller than neurons
  • Can multiply and divide and fill in brain areas
  • Do not conduct nerve impulses
supporting cells in cns
Supporting Cells in CNS
  • Astrocytes most abundant and most versatile; blood-brain barrier
  • Oligodendrocytes have fewer branches; produce insulating myelin sheath in CNS
  • Microglia ovoid cells with thorny processes; provide defense (because immunity cells not allowed in CNS)
  • Ependymal cells squamous/columnar cells with cilia; produce cerebrospinal fluid (CSF)
supporting cells in pns
Supporting Cells in PNS
  • Schwann cells PNS cell support; produce & maintain myelin sheath, regenerate PNS axons
  • Satellite cells in PNS ganglia; support neurons in ganglia, regulate exchange of materials between neurons and interstitial fluid
neuron characteristics
Neuron Characteristics
  • They conduct nerve impulses from one part of the body to another
  • They have extreme longevity live/function for a lifetime
  • They are amitotic lose their ability to divide
  • They have a high metabolic rate = need O2 and glucose
neuronal structure
Neuronal Structure
  • Cell body nucleus, cytoplasm with typical organelles; most within CNS = protected by cranial bones & vertebrae
  • Dendrites short, highly branched input structures emerging from cell body = high surface area to receive signals
  • Axon may be short or long, only one per neuron; conducts away from cell body toward another neuron or effector
    • Emerges at cone-shaped axon hillock
  • Axon terminals at end of axon with synaptic bulbs
figure 9 3
Figure 9.3

(Neurilemma)

= impulse direction

Pg. 391

myelination
Myelination
  • Axons covered with a myelin sheath
    • Many layered lipid & protein creating insulations
    • Increases speed of nerve conduction.
    • Formed by:
      • Schwann cells in PNS (pg. 393 fig. 11.5)
      • Oligodendrocytes in CNS
  • Nodes of Ranvier= gaps in the myelin
    • Nodes are important for signal conduction
  • Some diseases destroy myelin multiple sclerosis & Tay-Sachs
gray and white matter
Gray and White Matter
  • White matter- primarily myelinated axons
  • Gray matter- nerve cell bodies, dendrites, unmyelinated axons, axon terminals & neuroglia
    • Spinal cord gray matter is centrally located
classification of neurons
Classification of Neurons
  • Structural according to # of processes:
    • Multipolar 3 or more; most common, especially in CNS
    • Bipolar 2 processes (an axon and a dendrite) that extend from opposite sides; found in special sense organs
    • Unipolar 1 process that divides like a T; found in ganglia in PNS
slide18
Functional according to the direction impulse travels (Table 11.1)
    • Sensory (afferent) neurons transmit impulses from sensory receptors toward or into the CNS; mostly unipolar, with cell bodies in ganglia outside CNS
    • Motor (efferent) neurons carry impulses away from CNS to muscles and glands; multipolar, usually with cell bodies in CNS
    • Interneurons (association neurons) between motor & sensory neurons; most in CNS; 99% of neurons in body; mostly multipolar
neurophysiology
Neurophysiology
  • Neurons are highly irritable = responsive to stimuli
  • When stimulated, an electrical impulse (action potential) is conducted along its axon
    • Action potential underlies all functional activities of the nervous system
action potentials
Action Potentials
  • Action potentials = nerve impulses
  • Require a membrane potential
    • electrical charge difference across cell membrane – like a battery
  • Ion Channels allow ions to move by diffusion = current
  • If no action potential then resting cell has resting membrane potential
ion channels
Ion Channels
  • Allow specific ions to diffuse across membrane
    • Move from high concentration to low

or toward area of opposite charge

  • Leakage channels
  • Gated channels- require trigger to open
  • Voltage- Gated channels respond to a change in membrane potential
resting membrane potential
Resting Membrane Potential
  • Leakage channels
  • Cytosol high in K+ & interstitial fluid high in Na+(sodium –potassium pumps)
  • Leakage lets K+ through easily and Na+ poorly
  • inside is negative relative to outside
  • actual value depends on the relative leakage channel numbers
graded potentials
Graded Potentials
  • Short-lived, local changes to membrane potential
  • Cause current flows that decrease with distance
  • Magnitude varies with strength of stimulus
action potential ap
Action Potential (AP)
  • Generated by neurons and muscle cells
  • Series of active events
  • Channels actively open & close
  • Some initial event is required to reach a voltage threshold (~ = - 55 mv)
  • Stimulus = any event bringing membrane to threshold
action potential
Action Potential
  • Resting state
    • voltage-gated channels closed
  • Depolarizing phase-
    • membrane potential rises and becomes positive
  • Repolarizing phase-
    • potential restored to resting value ( PNa,  PK)
  • Undershoot
    • Potassium permeability continues
active events
Active Events
  • Stimulus to reach threshold
  • Na+ channel opens=>
  • Na+ ions enter=>
  • positive potential=>
  • Causes K+ channel opening =>
  • repolarization
all or none phenomenon
All- or –None Phenomenon
  • This sequence is always the same
  • If threshold then the same size of changes occur no larger or smaller APs
  • Stimulus must reach threshold to start
  • After one AP there is a short period before next can be triggered= absoluterefractory period each AP is a separate, all-or-none event; enforces one-way transmission of AP
conduction of nerve impulses
Conduction of Nerve Impulses
  • Each section triggers next locally
  • Refractory period keeps it going the right direction
  • unmyelinated fiber- continuous conduction
  • With myelin- saltatory conduction
    • Can only be triggered at nodes of Ranvier
  • Myelinated fibers faster & larger neurons faster
the syanpse
The Syanpse
  • Synapse (to clasp or join)- junction that mediates information transfer from 1 neuron to another or from a neuron to an effector cell
  • Axodendritic or axosomaticsynapses – most synapses occur between the axonal ending of a neuron and the dendrites or cell body of other neurons
synaptic transmission electrical synapse
Synaptic Transmission – Electrical synapse
  • Sequence of events at synapse
  • Triggered by voltage change of the Action Potential
  • Sending neuron = presynaptic
  • Receiving neuron = postsynaptic
  • Space between = synaptic cleft
  • Neurotransmitter carries signal across cleft
events at synapse chemical synapse
Events at Synapse – Chemical synapse
  • AP arrives at presynaptic end bulb=>
  • Opens voltage gated Ca2+ channels=>
    • Ca2+ flows into cell
  • increased Ca2+ concentration =>
  • exocytosis of synaptic vesicles=>
  • Neurotransmitter released into cleft
  • Diffuse across and bind to receptors in postsynaptic cell membrane
synaptic transmission
Synaptic Transmission
  • Binding at receptors
  • Chemical trigger of ion channels
  • May depolarize or hyperpolarize postsynaptic cell membrane
  • If threshold reached at axon hillock then postsynaptic cell action potential results
synaptic transmission1
Synaptic Transmission
  • Finally the neurotransmitter must be removed from the cleft-
  • Diffusion away
  • Destroyed by enzymes in cleft
  • Transport back into presynaptic cell
  • Neuroglia destruction
neurotransmitters
Neurotransmitters
  • AcetylCholine (Ach)- common in PNS
  • Biogenic amines - Norepinephrine (NE), Dopamine (DA), serotonin, Histamine
  • Amino Acids-
    • Glutamate, Aspartate, gamma aminobutyric acid (GABA), glycine
  • Neuropeptides – endorphins
  • Novel Messengers - ATP/ Nitric oxide (NO)/ Carbon monoxide (CO)
development of neurons
Development of Neurons
  • P. 422-424
  • Neuroblasts
  • Growth cone
  • Programmed cell death
web sites
Web sites:
  • http://www.sciencecases.org/chin/chin.asp
  • http://www.pbs.org/wgbh/nova/sciencenow/3204/01.html
  • http://www.getbodysmart.com/ap/nervoussystem/menu/menu.html
  • http://www.bbc.co.uk/science/humanbody/body/interactives/3djigsaw_02/index.swf?startPosition=nervous
  • http://learn.genetics.utah.edu/units/addiction/reward/madneuron.cfm
  • http://www.gpc.edu/~bbrown/peril/neurons/level1.htm
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