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Lecture 2

EXSC 224 Lecture Notes - Cell Membrane, Axon Hillock, Resting Potential

5 Pages
49 Views
Fall 2016

Department
Exercise Science
Course Code
EXSC 224
Professor
Thompson
Lecture
2

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Neurons - nerve cells
Neurons have a resting membrane potential
Primary cell in the nervous system
Cell body - biosynthetic center and receptive region
*Also called the Soma*
Nissil bodies = Rough ER
Only called this is NEURONS
Rough ER does protein synthesis
Has nucleus - makes neurotransmitters (which usually secrete protein/ amino
acid)
Well-developed Golgi apparatus
Modify the proteins made in rough ER
Package protein in vesicles
Mitochondria - lots, has rough and smooth ER
Oxygen is used to produce ATP
High metabolic rate
Glucose - only use this for fuel (NOT fats)
Axon hillock - Cone-shaped area from which the axon arises
Segway between cell body and axon
Generates action potential if stimulous is big enough
Converts stimulus to impulse (AP)
Cytoskeleton (neurofibrils and neurofilaments)
Microtubules and ATP transports vesicles produced in cell body down the
axon
Gives neuron it’s shape
Clusters of cell bodies are called
1. Nuclei in the CNS
Lots of nuclei present
2. Ganglia in the PNS
Only sensory neurons have ganglia, motor neurons don’t!
Processes - Extensions from the cell body (dendrites and axons)
In CNS - tracts
Tracts are clusters of axons within CNS
In PNS - nerves
Axons within the PNS
○ Neurilemma
Schwann cell - one internode
Node of Ranvier
Terminal branches - axon terminals/secretory region
Dendrites - receive signals from other neurons
Receptive/input region from both sensory components or other neurons
Short, tapering, and diffusely branched
Allow for a large surface area for which neurons can synapse onto
Convey input toward the cell body
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Graded potentials - at the synapses (between neuron to neuron)
Between dendrites and incoming information into neuron
Axon - conducting region of a neuron
Generates and transmits impulses (aka. axon potentials)
One axon per cell arising from the axon hillock
Axon hillock generates the AP that travels down the length of the axon
AP = impulse or nerve impulse
Numerous terminal branches - knoblike axon terminals
Synaptic knobs or boutons (where neurotransmitter is secreted)
Can branch enough to synapse onto hundreds of dendrites
Myelin Sheath - dont need to know a TON about myelin
Oligodendrocytes and Schwann cells - myelin fills the volume of these
Axons have proteins, ion channels (Na/K pumps, Na & K pumps)
NO ion channels or pumps can cross the membran where myelin wraps
around axon
Myelin wraps around axon in segments, there are gaps between wrappings
Space between myelin wrapping is called Node of Ranvier
Membrane at node of Ranvier is DIFFERENT from membrane inside schwann
cell
AP jumps from one Node of Ranvier to the next
Segmented protein-lipoid sheath around most long or large-diameter axon
○ Functions:
1. Protect and insulate the axon - more difficult to injure axon
Acts as a scaffold to repair axons that have been injured
2. Increase speed of nerve impulse transmission
When in the PNS
Concentric layers of Schwann cell membrane
Not all neurons are myelinated!!
Lu gherrics disease - dead neurons
When in the CNS
Formed by processes of oligodendrocytes
Wrap around multiple axons
Nodes of Ranvier are present
Thinnest fibers are unmyelinated
White matter - dense collections of myelinated fibers
Occasionally, some axons are sometimes not myelinated
Gray matter - mostly neuron cell bodies and unmyelinated fibers
NOT MYELINATED
Cell body and dendrites are never myelinated
Neuron function -
1. Neurons are highly irritable/ excitable
There is a resting membrane potential, we can disrupt this resting
membrane potential
2. Respond to adequate stimulus by generating an action potential (AP)
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Description
Neurons - nerve cells ● Neurons have a resting membrane potential ● Primary cell in the nervous system ● Cell body - biosynthetic center and receptive region ○ *Also called the Soma* ○ Nissil bodies = Rough ER ■ Only called this is NEURONS ■ Rough ER does protein synthesis ○ Has nucleus - makes neurotransmitters (which usually secrete protein/ amino acid) ○ Well-developed Golgi apparatus ■ Modify the proteins made in rough ER ■ Package protein in vesicles ○ Mitochondria - lots, has rough and smooth ER ■ Oxygen is used to produce ATP ○ High metabolic rate ○ Glucose - only use this for fuel (NOT fats) ○ Axon hillock - Cone-shaped area from which the axon arises ■ Segway between cell body and axon ■ Generates action potential if stimulous is big enough ■ Converts stimulus to impulse (AP) ○ Cytoskeleton (neurofibrils and neurofilaments) ■ Microtubules and ATP transports vesicles produced in cell body down the axon ■ Gives neuron it’s shape ○ Clusters of cell bodies are called ■ 1. Nuclei in the CNS ● Lots of nuclei present ■ 2. Ganglia in the PNS ● Only sensory neurons have ganglia, motor neurons don’t! ● Processes - Extensions from the cell body (dendrites and axons) ○ In CNS - tracts ■ Tracts are clusters of axons within CNS ○ In PNS - nerves ■ Axons within the PNS ○ Neurilemma ○ Schwann cell - one internode ○ Node of Ranvier ○ Terminal branches - axon terminals/secretory region ● Dendrites - receive signals from other neurons ○ Receptive/input region from both sensory components or other neurons ○ Short, tapering, and diffusely branched ■ Allow for a large surface area for which neurons can synapse onto ○ Convey input toward the cell body ■ Graded potentials - at the synapses (between neuron to neuron) ● Between dendrites and incoming information into neuron ● Axon - conducting region of a neuron ○ Generates and transmits impulses (aka. axon potentials) ○ One axon per cell arising from the axon hillock ■ Axon hillock generates the AP that travels down the length of the axon ● AP = impulse or nerve impulse ○ Numerous terminal branches - knoblike axon terminals ■ Synaptic knobs or boutons (where neurotransmitter is secreted) ■ Can branch enough to synapse onto hundreds of dendrites ● Myelin Sheath - dont need to know a TON about myelin ○ Oligodendrocytes and Schwann cells - myelin fills the volume of these ○ Axons have proteins, ion channels (Na/K pumps, Na & K pumps) ■ NO ion channels or pumps can cross the membran where myelin wraps around axon ○ Myelin wraps around axon in segments, there are gaps between wrappings ○ Space between myelin wrapping is called Node of Ranvier ○ Membrane at node of Ranvier is DIFFERENT from membrane inside schwann cell ○ AP jumps from one Node of Ranvier to the next ○ Segmented protein-lipoid sheath around most long or large-diameter axon ○ Functions: ■ 1. Protect and insulate the axon - more difficult to injure axon ● Acts as a scaffold to repair axons that have been injured ■ 2. Increase speed of nerve impulse transmission ○ When in the PNS ■ Concentric layers of Schwann cell membrane ■ Not all neurons are myelinated!! ■ Lu gherrics disease - dead neurons ○ When in the CNS ■ Formed by processes of oligodendrocytes ● Wrap around multiple axons ■ Nodes of Ranvier are present ● Thinnest fibers are unmyelinated ○ White matter - dense collections of myelinated fibers ■ Occasionally, some axons are sometimes not myelinated ○ Gray matter - mostly neuron cell bodies and unmyelinated fibers ■ NOT MYELINATED ■ Cell body and dendrites are never myelinated ● Neuron function - ○ 1. Neurons are highly irritable/ excitable ■ There is a resting membrane potential, we can disrupt this resting membrane potential ○ 2. Respond to adequate stimulus by generating an action potential (AP) ○ 3. AP is always the same regardless of stimulus ■ All the same size and duration ● Principles of Electricity (Ions) ○ 1. More positive charges outside cell than inside cell ○ 2. Energy is required to separate opposite charges across a membrane ○ 3. If opposite charges are separated, the system has potential energy
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