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.

19

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