Nervous SystemNervous System
Transmission of Nerve Signals forTransmission of Nerve Signals forCommunicationCommunicationCoordination and Regulation of Coordination and Regulation of Body Systems Body Systems
Structure of a NeuronStructure of a NeuronCell Body(maintains
cell metabolism)
Cell Body(maintains
cell metabolism)
Dendrites(receive signals)
Dendrites(receive signals)
Axon of anotherneuron
Axon of anotherneuron
Axon(conducts signals)
Axon(conducts signals)
Myelin Sheath(insulator)
Myelin Sheath(insulator)
Dendrite of anotherneuron
Dendrite of anotherneuron
Axon bulbAxon bulb
Types of NeuronsTypes of NeuronsReceives
information from
environment
Generates a response
Carries signal between sensory
and motor neurons
gaps in myelin sheath
formed by Schwann cells
axon
bundle of nerve fibers
Transmission of Nerve Impulse Transmission of Nerve Impulse
Along a NeuronAlong a Neuron • Involves a change in charge across Involves a change in charge across
the neuron’s membrane, caused by the neuron’s membrane, caused by the movement of ionsthe movement of ions
• Action Potential = rapid Action Potential = rapid depolarization depolarization and repolarizationand repolarizationof membraneof membrane
Electrical Events During AnElectrical Events During AnAction PotentialAction Potential
80
40
0
-40
-80
Rec
orde
d Po
tent
ial
(mill
ivol
ts)
Time (milliseconds)
RestingPotential
Extracellular Fluid(uncharged)
Threshold
IPSPEPSP
1
2
3
Action PotentialAction Potential
dep
ola
riza
tio
n
repo
larization
polarized
OrgOrg --
OrgOrg --
OrgOrg --
Org
Org -- O
rgO
rg--
Org
Org--
OrgOrg--
Org
Org
--OrgOrg
--
Resting Potential Depends on Ionic GradientsResting Potential Depends on Ionic Gradients
KK++
KK++
KK++KK++
KK++
KK++
KK++
NaNa++
NaNa++
NaNa++
NaNa++
NaNa++NaNa++
ClCl--
ClCl--
ClCl--
ClCl--
ClCl--
ClCl--
Inside: Inside: • Potassium ionsPotassium ionsare pumped intoare pumped intocell cell
• Large organic Large organic moleculesmoleculescannot pass cannot pass through through membranemembrane
Outside: Outside:
• Sodium ions areSodium ions arepumped out pumped out
• Chloride ionsChloride ionsfound in extra-found in extra-cellular fluid cellular fluid
Net negative charge insideNet negative charge inside neuronneuron
2
Resting PotentialResting Potential
SodiumChannel(closed)
SodiumChannel(closed)
PotassiumChannel(closed)
PotassiumChannel(closed)
Action PotentialAction Potential1. Sodium flows
into neuron through open channel, causing depolarization
1. Sodium flows into neuron through open channel, causing depolarization
2. Potassium flows out of neuron through open channel, causing repolarization
2. Potassium flows out of neuron through open channel, causing repolarization
inside
outside
inside
outside
Propagation of an Action Potential Along an Axon
15
Transmission of Nerve Impulses Transmission of Nerve Impulses
Between NeuronsBetween Neurons • Signal is carried by Signal is carried by
neurotransmitters that diffuse neurotransmitters that diffuse across the space between across the space between neuronsneurons
– Synapse: junction between Synapse: junction between neuronsneurons
– Synaptic cleft: space between Synaptic cleft: space between neuronsneurons
• Neurotransmitters bind to Neurotransmitters bind to receptors on next neuron, receptors on next neuron, opening ion channels opening ion channels
syna
pse
14
Structure Structure and and
OperationOperationof the of the
SynapseSynapse
1 Actionpotential isinitiated
2 Action potentialreaches axon bulb
3 Synaptic vesiclesreleaseneurotransmitter
4 Neurotransmitter binds to receptor and opens ion channel
5 Action Potential can be triggered in post-synaptic cell
Pre-synaptic cell
Post-synaptic cell
Transmission Between NeuronsTransmission Between Neurons
• Neurotransmitters can be Neurotransmitters can be – Stimulatory: initiate action potentialStimulatory: initiate action potential
• AcetylcholineAcetylcholine
– Inhibitory: prevent action potentialInhibitory: prevent action potential• DopamineDopamine
• After acting on the post-synaptic After acting on the post-synaptic neuron, neurotransmitters are neuron, neurotransmitters are removed from the synaptic cleft removed from the synaptic cleft
– Acetylcholinesterase breaks down Acetylcholinesterase breaks down acetylcholineacetylcholine
Neurotransmitters carry signals to Neurotransmitters carry signals to muscle cells to stimulate contraction. muscle cells to stimulate contraction.
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Applying Your KnowledgeApplying Your Knowledge
Which one is responsible for Which one is responsible for
A.A. Transmission of a nerve impulse across Transmission of a nerve impulse across a synapse?a synapse?
B.B. Depolarization of a neuron’s membrane? Depolarization of a neuron’s membrane?
C.C. Transmission of a nerve impulse along Transmission of a nerve impulse along an axon?an axon?
D.D. Repolarization of a neuron’s membrane?Repolarization of a neuron’s membrane?
1.1. Potassium Ions (K+)Potassium Ions (K+)2.2. NeurotransmittersNeurotransmitters3.3. Sodium Ions (Na+)Sodium Ions (Na+)
Nervous System OrganizationNervous System Organization
Central Central Nervous SystemNervous System
Peripheral Peripheral Nervous SystemNervous System
BrainBrain Spinal Spinal CordCord
Somatic Somatic Nervous Nervous SystemSystem
(voluntary)(voluntary)
Autonomic Autonomic Nervous Nervous SystemSystem
(involuntary)(involuntary)
Sympathetic Sympathetic DivisionDivision
(stress or activity)(stress or activity)
Parasympathetic Parasympathetic DivisionDivision
(maintenance or (maintenance or relaxation)relaxation)
Parts of the BrainParts of the Brain
musclecoordination
Cortex: thinking, learning, memory, speech movement,
senses
breathing, heart rate, blood pressure
sends sensory input to cerebrum
homeostasis
Spinal Cord Spinal Cord and Reflex Arcsand Reflex Arcs
Involve the Somatic Nervous System
Autonomic Nervous SystemAutonomic Nervous System
speeds heart slows heart
dilates air passages
constricts bronchioles
decreases stomach and
intestinal activity
increases stomach and
intestinal activity
dilates pupils constricts pupils
Applying Your KnowledgeApplying Your Knowledge
Which one Which one
A.A. Is responsible for increasing breathing Is responsible for increasing breathing rate when you start running?rate when you start running?
B.B. Includes the spinal cord? Includes the spinal cord?
C.C. Controls skeletal muscle movement?Controls skeletal muscle movement?
1.1. Central Nervous SystemCentral Nervous System2.2. Somatic Nervous SystemSomatic Nervous System3.3. Autonomic Nervous SystemAutonomic Nervous System
Nervous System DisordersNervous System Disorders• Alzheimer Disease: Alzheimer Disease: gradual loss of neural gradual loss of neural
function due to tangles and plaques associated function due to tangles and plaques associated with axonswith axons
• Parkinson Disease: Parkinson Disease: deficiency of dopamine deficiency of dopamine causes tremors, rigidity, shuffling gaitcauses tremors, rigidity, shuffling gait
• Huntington Disease: Huntington Disease: uncoordinated movements uncoordinated movements and degenerative neurological symptoms and degenerative neurological symptoms beginning at middle age, due to autosomal beginning at middle age, due to autosomal dominant inheritancedominant inheritance
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