Nervous SystemNervous SystemObjectivesObjectives

1.1. ExplainExplain the general functions (3 Functions) of the nervous the general functions (3 Functions) of the nervous system.system.

2.2. IdentifyIdentify the two main parts of the Nervous System the two main parts of the Nervous System

3.3. DescribeDescribe the structure of a neuron and the function of each the structure of a neuron and the function of each major part.major part.

4.4. Distinguish Distinguish between sensory neurons, motor neurons, and between sensory neurons, motor neurons, and interneurons.interneurons.

5.5. SummarizeSummarize the electrical and chemical conditions of resting the electrical and chemical conditions of resting potential.potential.

6.6. OutlineOutline the electrical and chemical changes during an action the electrical and chemical changes during an action potential.potential.

7.7. ExplainExplain the role of neurotransmitters in transmitting a signal the role of neurotransmitters in transmitting a signal across a synapse.across a synapse.

8.8. DescribeDescribe the role of sensory and motor divisions of the the role of sensory and motor divisions of the peripheral nervous system.peripheral nervous system.

9.9. DistinguishDistinguish between the autonomic and somatic nervous between the autonomic and somatic nervous systems.systems.

10.10. SummarizeSummarize a spinal reflex. a spinal reflex.

IntroductionIntroduction

► The nervous system controls and coordinates all The nervous system controls and coordinates all essential functions of the human body.essential functions of the human body.

► The Nervous System has The Nervous System has 3 main functions3 main functions1.1. SENSORY FUNCTIONSENSORY FUNCTION – gather information and – gather information and

transmit to brain and spinal cordtransmit to brain and spinal cord

2.2. INTEGRATIVE FUNCTIONINTEGRATIVE FUNCTION - - Processes the Processes the informationinformation to determine the best response.  to determine the best response. 

3.3. MOTOR FUNCTIONMOTOR FUNCTION - Sends information to - Sends information to muscles, glands, and organs (effectors) so they can muscles, glands, and organs (effectors) so they can respond by muscular contraction or glandular respond by muscular contraction or glandular secretions. secretions. 

Divisions of the Nervous Divisions of the Nervous SystemSystem

► Central Nervous SystemCentral Nervous System Consists of the Spinal Cord and BrainConsists of the Spinal Cord and Brain Spinal cord carries messages to the brain where they are Spinal cord carries messages to the brain where they are

analyzed and interpretedanalyzed and interpreted Response messages are sent from the brain to the spinal Response messages are sent from the brain to the spinal

cord and the rest of the bodycord and the rest of the body

Peripheral Nervous SystemPeripheral Nervous System Consists of the neurons not found in the brain and spinal Consists of the neurons not found in the brain and spinal

cordcord Divided into 2 divisions:Divided into 2 divisions: Sensory Sensory and and MotorMotor Afferent NeuronsAfferent Neurons – Collect info and send it – Collect info and send it towardtoward the CNS the CNS Efferent NeuronsEfferent Neurons – Transmit info – Transmit info awayaway from the CNS from the CNS

The Vertebrate Nervous The Vertebrate Nervous SystemSystem

LE 48-LE 48-33

Sensor

Sensory input

Motor output

Integration

EffectorPeripheral nervous

system (PNS)Central nervous

system (CNS)

LE 48-LE 48-44

Quadricepsmuscle

Cell body ofsensory neuron in dorsal rootganglion

Sensory neuron

Spinal cord(cross section)

Whitematter

Hamstringmuscle

Graymatter

Motor neuron

Interneuron

Neuron StructureNeuron Structure

► Neurons are the basic functional units of the nervous systemNeurons are the basic functional units of the nervous system► All consist of a cell body, dendrites, and one axonAll consist of a cell body, dendrites, and one axon► Messages take the form of electrical signals known as impulses – Messages take the form of electrical signals known as impulses –

Neurons carry impulses in one directionNeurons carry impulses in one direction

Schwann Cell

Types of NeuronsTypes of Neurons

► Sensory NeuronsSensory Neurons Carry messages from sense organs to the CNSCarry messages from sense organs to the CNS Receptors detect stimuli from external or internal Receptors detect stimuli from external or internal

changes and send info to CNS by way of Afferent changes and send info to CNS by way of Afferent neuronsneurons

Motor NeuronsMotor Neurons Carry impulses from the CNS to muscles and Carry impulses from the CNS to muscles and

glandsglands InterneuronsInterneurons

Connect Sensory and Motor NeuronsConnect Sensory and Motor Neurons Found entirely in the CNSFound entirely in the CNS

Anatomy of a NeuronAnatomy of a Neuron

► Neuron Video► Cell BodyCell Body

Contains nucleus and most of the cytoplasmContains nucleus and most of the cytoplasm Site of most of the metabolic activity including ATP production Site of most of the metabolic activity including ATP production

and protein synthesisand protein synthesis

► DendritesDendrites Short branch extensions spreading out from the cell body.Short branch extensions spreading out from the cell body. Receive impulses (action potentials) and carry them Receive impulses (action potentials) and carry them

towardtoward the cell body the cell body► AxonAxon

Carries action potential Carries action potential awayaway from the cell body from the cell body Each neuron only has one axonEach neuron only has one axon Axon ends with a series of swellings called Axon ends with a series of swellings called axon axon

terminalsterminals

Anatomy cont.Anatomy cont.

► Myelin SheathMyelin Sheath Lipid layer that insulates the axonLipid layer that insulates the axon Speeds up the transmission of action potentialsSpeeds up the transmission of action potentials Multiple Sclerosis Video

► Schwann CellsSchwann Cells In peripheral nervous systemIn peripheral nervous system Produce the myelin that surrounds the axonProduce the myelin that surrounds the axon

► Nodes of RanvierNodes of Ranvier Gaps in the myelin sheath along the axonGaps in the myelin sheath along the axon

SynapsesSynapses Point of contact where impulses are passed from Point of contact where impulses are passed from

one neuron to anotherone neuron to another

Supporting Cells (Glia)Supporting Cells (Glia)

► Glia are essential for structural integrity of the Glia are essential for structural integrity of the nervous system and for functioning of neuronsnervous system and for functioning of neurons

► Types of glia: astrocytes, radial glia, Types of glia: astrocytes, radial glia, oligodendrocytes, and Schwann cellsoligodendrocytes, and Schwann cells

► In the CNS, astrocytes provide structural support In the CNS, astrocytes provide structural support for neurons and regulate extracellular for neurons and regulate extracellular concentrations of ions and neurotransmittersconcentrations of ions and neurotransmitters

Nerve ImpulsesNerve Impulses

► Resting potential -Resting potential --70 mV -70 mV potential potential

In a non-conducting neuronIn a non-conducting neuron Result of an imbalance of charged Result of an imbalance of charged

particles (ions) between the particles (ions) between the extracellular and the intracellular extracellular and the intracellular fluids – positive charge on the outer fluids – positive charge on the outer surface and negative on inner surface and negative on inner surfacesurface

Remember the Na/K pump? Remember the Na/K pump? Well, if not…Well, if not…

Mechanism for Resting potentialMechanism for Resting potential1.1.Na/K pump pumps 3 Na+ ions to the Na/K pump pumps 3 Na+ ions to the

outside while bringing in 2 K+ ionsoutside while bringing in 2 K+ ions2.2.Cell membrane is more permeable to K+ Cell membrane is more permeable to K+

than to Na+ so that K+ diffuses out faster than to Na+ so that K+ diffuses out faster than Na+ diffuses inthan Na+ diffuses in

3.3.Cell membrane is basically impermeable to Cell membrane is basically impermeable to large negatively charged anions present large negatively charged anions present inside the neuron, therefore fewer negative inside the neuron, therefore fewer negative particles move out than positiveparticles move out than positive

Resting PotentialResting Potential

ION CONCENTRATION

Action PotentialAction Potential

► Nerve impulses carry info from one Nerve impulses carry info from one point of the body to another by point of the body to another by progression along the neuron progression along the neuron membrane of an abrupt change in membrane of an abrupt change in resting potential.resting potential.

► This traveling disturbance is called an This traveling disturbance is called an action potential.action potential.

ACTION POTENTIAL ANIMATION

LE 48-LE 48-1010

CYTOSOL EXTRACELLULARFLUID

[Na+]15 mM

[K+]150 mM

[A–]100 mM

[Na+]150 mM

[K+]5 mM

[Cl–]120 mM

[Cl–]10 mM

Plasmamembrane

LE 48-LE 48-1111

150 mMKCl

Innerchamber

Outerchamber

–92 mV

Potassiumchannel

Membrane selectively permeable to K+ Membrane selectively permeable to Na+

5 mMKCl

Artificialmembrane

K+

Cl–

150 mMNaCl

Innerchamber

Outerchamber

+62 mV

Sodiumchannel

15 mMNaCl

Na+

Cl–

Steps of Action PotentialSteps of Action Potential

1.1. A stimulus A stimulus (chemical-electrical-(chemical-electrical-mechanical) is mechanical) is sufficient to alter the sufficient to alter the resting membrane resting membrane potentialpotential

2.2. The membrane’s The membrane’s permeability to Na+ permeability to Na+ increases at the increases at the point of stimulationpoint of stimulation

3.3. Na+ moves into the Na+ moves into the cell rapidly; the cell rapidly; the membrane becomes membrane becomes locally locally depolarizeddepolarized

1.

2.

3

4.4. Na+ continues Na+ continues to move inward; to move inward; inside of cell inside of cell becomes becomes positively positively charged relative charged relative to outside to outside (reverse (reverse polarization or polarization or depolarization)depolarization)

5. 5. Reverse Reverse polarization at polarization at original site acts original site acts as a stimulus to as a stimulus to adjacent region adjacent region of membraneof membrane

1.

2.

3

5

4

Action Potential cont.Action Potential cont.

6.6. At the point originally stimulated, the At the point originally stimulated, the membrane’s permeability to sodium membrane’s permeability to sodium decreases, and its permeability to K+ decreases, and its permeability to K+ increases.increases.

7.7. K+ rapidly moves outward, again making K+ rapidly moves outward, again making the outside of the membrane positive in the outside of the membrane positive in relation to the inside (relation to the inside (repolarizationrepolarization))

8.8. Na+/K+ pumps transport Na+ back out Na+/K+ pumps transport Na+ back out of, and K+ back into the cell. The cycle of, and K+ back into the cell. The cycle repeats itself, traveling in this manner repeats itself, traveling in this manner along the neuron membrane.along the neuron membrane.

Threshold StimulusThreshold Stimulus

An action potential is produced in An action potential is produced in response to a response to a threshold stimulus. threshold stimulus. Resting potential is about -70mVResting potential is about -70mV If the stimulus raises the potential to -If the stimulus raises the potential to -

55mV, a threshold potential has been 55mV, a threshold potential has been reachedreached

Complete depolarization and Complete depolarization and repolarization occur and an action repolarization occur and an action potential is generatedpotential is generated

Impulses cont.Impulses cont.

► An impulse is self-propagating – once it starts it An impulse is self-propagating – once it starts it continues, and moves in one directioncontinues, and moves in one direction

Impulses cont.Impulses cont.

► Synapse and Synaptic TransmissionSynapse and Synaptic Transmission1.1. AP reaches the axon terminalAP reaches the axon terminal

2.2. Influx of Ca2+ causes synaptic vesicles with Influx of Ca2+ causes synaptic vesicles with neurotransmitter to fuse with presynaptic membraneneurotransmitter to fuse with presynaptic membrane

3.3. Neurotransmitter is released by exocytosis into synaptic cleftNeurotransmitter is released by exocytosis into synaptic cleft

4.4. Neurotransmitter binds to receptors in postsynaptic Neurotransmitter binds to receptors in postsynaptic membranemembrane

5.5. Permeability of postsynaptic membrane is altered initiating Permeability of postsynaptic membrane is altered initiating on impulse on the second neuronon impulse on the second neuron

6.6. Neurotransmitter is removed from the synapse (reuptake) Neurotransmitter is removed from the synapse (reuptake)

► Refractory PeriodRefractory Period A period when a neuron is unable to conduct an impulseA period when a neuron is unable to conduct an impulse Na+/K+ pumps are restoring the resting potentialNa+/K+ pumps are restoring the resting potential

SYNAPSE FUNCTION VIDEO

LE 48-LE 48-1717

Postsynaptic cellPresynaptic cell

Synaptic vesiclescontainingneurotransmitter

Presynaptic membrane

Voltage-gatedCa2+ channel

Ca2+Postsynaptic membrane

Postsynaptic membrane

Neuro-transmitter

Ligand-gatedion channel

Na+

K+

Ligand-gatedion channels

Synaptic cleft

NeurotransmittersNeurotransmitters

► Ach - Ach - acetylcholineacetylcholine

► NorepinephrineNorepinephrine► EpinephrineEpinephrine► DopamineDopamine► SerotoninSerotonin► GABAGABA

► Derived from Derived from amino acidsamino acids

Neuroglia Neuroglia

►Make up more than half the volume of Make up more than half the volume of

the vertebrate nervous systemthe vertebrate nervous system

►A variety of cells that metabolically A variety of cells that metabolically

assist, structurally support, and assist, structurally support, and

protect the neuronsprotect the neurons

Fig. 34-14, p.583

Peripheral Nervous SystemPeripheral Nervous System

► All nerves not in the spinal cord and brainAll nerves not in the spinal cord and brain► Sensory Division (Afferent)Sensory Division (Afferent)

Transmits impulses from the sense organs (e.g. ears and Transmits impulses from the sense organs (e.g. ears and eyes) to the CNSeyes) to the CNS

► Motor Division (Efferent)Motor Division (Efferent) Transmits impulses from the CNS to the muscles and Transmits impulses from the CNS to the muscles and

glandsglands Two divisions: Somatic and AutonomicTwo divisions: Somatic and Autonomic

Somatic SystemSomatic System

►Regulates activities that are under Regulates activities that are under conscious control (ex: skeletal muscle conscious control (ex: skeletal muscle movement)movement)

►Many nerves are part of reflexes and Many nerves are part of reflexes and can act automaticallycan act automatically Patellar reflex – By passes the brain Patellar reflex – By passes the brain

completelycompletely

ReflexesReflexes

►Automatic movements made in Automatic movements made in

response to stimuliresponse to stimuli

► In the simplest reflex arcs, sensory In the simplest reflex arcs, sensory

neurons synapse directly on motor neurons synapse directly on motor

neuronsneurons

►Most reflexes involve an interneuronMost reflexes involve an interneuron

Stretch ReflexStretch Reflex

STIMULUSBiceps

stretches.

ResponseBiceps

contracts.

Figure 34.16Page 585

motor neuron

sensory neuron

Central and Peripheral Central and Peripheral Nervous SystemsNervous Systems

►Central nervous system (CNS)Central nervous system (CNS)

BrainBrain

Spinal cordSpinal cord

►Peripheral nervous systemPeripheral nervous system

Nerves that thread through the Nerves that thread through the

body body

Peripheral Peripheral Nervous Nervous SystemSystem

► Somatic nerves- Somatic nerves- externalexternal Motor functionsMotor functions (Shown in green)(Shown in green)

► Autonomic nerves Autonomic nerves - internal- internal Visceral functionsVisceral functions (Shown in red)(Shown in red)

Two Types of Two Types of Autonomic NervesAutonomic Nerves

►Sympathetic Sympathetic

►Parasympathetic Parasympathetic

►Most organs receive input from both Most organs receive input from both

►Usually have opposite effects on organUsually have opposite effects on organ

Sympathetic NervesSympathetic Nerves

►Originate in the thoracic and lumbar Originate in the thoracic and lumbar

regions of the spinal cordregions of the spinal cord

►Ganglia are near the spinal cordGanglia are near the spinal cord

►Promote responses that prepare the Promote responses that prepare the

body for stress or physical activity body for stress or physical activity

(fight-or-flight response)(fight-or-flight response)

Parasympathetic NervesParasympathetic Nerves

►Originate in the brain and the Originate in the brain and the

sacral region of the spinal cordsacral region of the spinal cord

►Ganglia are in walls of organsGanglia are in walls of organs

►Promote housekeeping responses Promote housekeeping responses

such as digestion “Rest & Digest”such as digestion “Rest & Digest”

Both Systems Are Both Systems Are Usually ActiveUsually Active

►Most organs are continually receiving Most organs are continually receiving both sympathetic and both sympathetic and parasympathetic stimulationparasympathetic stimulation

►For example, sympathetic nerves For example, sympathetic nerves signal heart to speed up; signal heart to speed up; parasympathetic stimulate it to slow parasympathetic stimulate it to slow downdown

►Which dominates depends on situationWhich dominates depends on situation

Function of the Spinal CordFunction of the Spinal Cord

►Expressway for signals between brain Expressway for signals between brain

and peripheral nervesand peripheral nerves

►Sensory and motor neurons make Sensory and motor neurons make

direct reflex connections in the spinal direct reflex connections in the spinal

cordcord

►Spinal reflexes do not involve the brainSpinal reflexes do not involve the brain

Structure of the Spinal CordStructure of the Spinal Cord

spinal cord

ganglion

nerve

vertebra

meninges(protectivecoverings)

Figure 34.18Page 587

Anatomy of the BrainAnatomy of the Brain

Cerebrospinal FluidCerebrospinal Fluid

► Surrounds the spinal Surrounds the spinal cordcord

► Fills ventricles within Fills ventricles within the brainthe brain

► Blood-brain barrier Blood-brain barrier controls which controls which solutes enter the solutes enter the cerebrospinal fluidcerebrospinal fluid

Figure 34.20Page 588

The BrainstemThe Brainstem

►““Lower Brain”Lower Brain”►Medulla oblongata – controls Medulla oblongata – controls

automatic, homeostatis functions automatic, homeostatis functions (breathing, hear and blood vessels, (breathing, hear and blood vessels, swallowing, vomiting, digestionsswallowing, vomiting, digestions

►Pons – breathing regulation & other Pons – breathing regulation & other homeostatic functionshomeostatic functions

►Midbrain – recipt and integeration of Midbrain – recipt and integeration of sensory infosensory info

CerebellumCerebellum

►Coordination, error checking in motor, Coordination, error checking in motor, perceptual & cognitive functions perceptual & cognitive functions (learning, consciousness)(learning, consciousness)

►Sensory info about joint position and Sensory info about joint position and length of muscle – how you “know” length of muscle – how you “know” where your parts arewhere your parts are

►Auditory & visual informationAuditory & visual information

CerebrumCerebrum

►Right and Left Cerebral Hemispheres Right and Left Cerebral Hemispheres which are responsible for opposite which are responsible for opposite sides of bodysides of body

►Gray matter outside; white matter Gray matter outside; white matter insideinside

►CORPUS CALLOSUM – connection CORPUS CALLOSUM – connection between two halvesbetween two halves

Sensory ReceptorsSensory Receptors

Convert the energy of a stimulus into Convert the energy of a stimulus into

action potentialsaction potentials

Mechanoreceptors Mechanoreceptors

Thermoreceptors Thermoreceptors

Pain receptors Pain receptors

Chemoreceptors Chemoreceptors

Osmoreceptors Osmoreceptors

Photoreceptors Photoreceptors

Assessing a StimulusAssessing a Stimulus

►Action potentials don’t vary in Action potentials don’t vary in amplitudeamplitude

►Brain tells nature of stimulus by:Brain tells nature of stimulus by: Particular pathway that carries the Particular pathway that carries the

signalsignal Frequency of action potentials along Frequency of action potentials along

an axonan axon Number of axons recruited Number of axons recruited

Somatic SensationsSomatic Sensations

►TouchTouch

►PressurePressure

►TemperatureTemperature

►PainPain

►MotionMotion

►PositionPosition