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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


Nervous system

  • 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