The Nervous System

The Haitian Zombie

http://www.youtube.com/watch?v=cXcjioLLvRQ

The Function of the Nervous System

Major control and communication system of the body

What other body systems communicate with the nervous system?

• Works with the muscular system

• Works with the endocrine system

•Works with the circulatory system

•Works with the integumentary system

•Works with the digestive system

There’s more…

Urinary systemSkeletal systemRespiratory systemReproductive systemImmune system

Functions of the Nervous SystemSensory Input

◦Gathering information by sensing stimuli

Integration◦Processes and interprets that

information

Motor Output◦Response to the stimulus◦May activate muscles or glands

Organization of the Nervous SystemCentral Nervous System

◦Brain◦Spinal Cord

Peripheral Nervous System◦Nerves that connect the brain and

spinal cord to the rest of the body

Breakdown of the PNSSensory Division

◦AKA: Afferent Division◦Carry information to the CNS

Motor Division◦AKA: Efferent Division◦Carry impulses away from the CNS

Breakdown of the Motor (efferent) Division of the PNSSomatic Nervous System

◦Voluntary◦Skeletal muslces

Autonomic Nervous System◦Involuntary◦Cardiac & smooth muscles; glands;

hormones

Breakdown of the Autonomic Nervous System

Sympathetic Division ◦Fight or Flight

Parasympathetic Division◦Rest and Digest

DRAW IT OUT!

Let’s make a flow chart to organize the complicated nervous system.

The Cells of the Nervous SystemsSupporting cells called neuroglia

◦Support, insulate, & protect neurons ◦CNS & PNS have different “glia” or

supporting cells◦CANNOT transmit nerve impulses

Nerve cells called neurons◦Same for the CNS and PNS

Neuroglia of the CNSAstrocytes

◦ Form a barrier between neurons and the blood capillaries

◦ Brace the neurons to the blood supply

◦ Control the chemical environment of the brain

Microglia◦ Spiderlike

phagocytes◦ Dispose of

bacteria, dead cells, and other debris

Neuroglia of the CNSEpendymal cells

◦ Ciliated cells◦ Line the cavities

of the brain and spinal cord

◦ Circulate the cerebrospinal fluid

Oligodendrocytes◦ Wrap their

extensions tightly around nerve fibers

◦ Form insulation around neurons called myelin sheaths

Neuroglia of the PNSSatellite Cells

◦ Protect the neuron cell bodies

◦ Provide cushion

Schwann Cells◦ Form insulation

around the neurons (myelin sheaths)

◦ Increases the speed of nerve impulses!

Neurons = Nerve CellsHighly specialized cells that

transmit messages in the form of electrical impulses

Every neuron has:1. Cell Body2. Dendrites3. Axon

NeuronsCell Body

◦ Metabolic center of the cell

◦ Contains cell organelles, except centrioles

◦ Neurofibrils (cellular filaments) and the rough endoplasmic reticulum called Nissl Substance give the cell its shape

Processes (Extensions)◦ Dendrites

Can have hundreds of branching dendrites

◦ Axons Only ONE axon

protruding from the cell body,

BUT axon can branch Can have many axon

terminals

NeuronDendrites

◦ Conduct impulses toward the cell body

Axon◦ Conduct impulses

away from the cell body

◦ Axon terminals contain hundreds of tiny vesicles containing neurotransmitters

SynapseJunction where the axon terminal

of the PRESYNAPTIC neuron meets the dendrites of the POSTSYNAPTIC neuron

The two neurons don’t actually touch◦Synaptic Cleft- gap between

adjacent neurons

Schwann CellsEnvelopes and rotates around an axonMost of the cell cytoplasm is toward the

outside of the cell◦ Neurilemma

Tight coil of plasma membrane closest to the axon◦ Myelin Sheath

Nodes of Ranvier◦ Gaps in the myelin

sheath along the

axon

Neuron Cell Body LocationMost are found in the CNS

◦Nuclei- clusters of cell bodies in the CNS

◦Tracts- bundles of nerve fibers running through the CNS

Ganglia- collections of cell bodies in the PNS◦Nerves- bundles of nerve fibers

running through the PNS

Neuron ClassificationSensory Neurons

◦Carry impulses from sensory receptors TO the CNS

◦AKA Afferent Neurons◦Cell body is found in ganglion outside

the CNS◦What are Sensory Receptors?

Found in cutaneous sense organs Sense touch, pressure, pain, temperature

Proprioceptors detect stretch or tension in skeletal muscles, their tendons, and joints

Neuron ClassificationMotor Neuron

◦Carries impulses from the CNS to the body

◦AKA Efferent Neuron◦Cell body of the neuron is found in

the CNS

Neuron ClassificationInterneurons or Association

Neurons◦Small neuron that is always located

in the CNS whose job is to connect the sensory and motor neurons to complete the pathway

Structural Classification of NeuronsBased on the number of

processes extending from the cell body of the neuron

3 Types:◦Multipolar neuron- many extensions

from the cell body◦Bipolar neuron- one axon and one

dedrite◦Unipolar neuron- one short single

process leaving the cell body

Structural Classification of Neurons

What do neurons do?Irritability- ability

to respond to a stimuli and convert it into a nerve impulse

Conductivity- ability to transmit an impulse to other neurons, muscles, or glands

Nerve Impulse Videohttp://highered.mcgraw-hill.com/s

ites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

Nerve ImpulseMembrane of a

resting (inactive) neuron is polarized◦ Fewer positive

ions inside the cell than outside

◦ Major + ions that are in the cell are K+

◦ Major + ions outside the cell are Na+

Voltmeter = -70 mV

Nerve ImpulseWhen stimuli (light,

sound, touch, or neurotransmitters released from another neuron) excite a neuron, sodium channels open in the membrane allowing an inward rush of Na+

Depolarization- change in polarity of the membrane◦ Locally, the inside is more

+ and the outside is less + All or none response: Only if

the stimulus is strong enough and the Na+ influx is great enough, will the neuron transmit an impulse (message)

Nerve Impulse If signal is strong enough,

an action potential (nerve impulse) is generated

Action potential propagates over the entire axon

K+ ions rush out of the neuron after Na+ rush in, repolarizing the membrane◦ Restores electrical conditions

to the resting state (more - on the inside)

Sodium-Potassium pump then restore the neuron to the initial concentrations of Na+ and K+

5 Step Nerve Impulse1. Resting membrane potential is more – inside

the cell than outside with more K+ inside the cell and more Na+ outside the cell

2. Stimulus opens Na+ channels, allowing influx of Na+ in cell initiating local depolarization

3. Generates action potential which travels down the axon

4. Repolarization by K+ channels allowing K+ to leave the cell, making the inside of the cell more - than the outside

5. Na+/K+ pump restores ion concentrations to more K+ in cell and more Na+ outside of the cell

Nerve Impulse

What happens when the action potential reaches the axon terminals?

Ca2+ ions rush into the axon terminal of the presynaptic neuron, causing tiny vesicles containing neurotransmitters to be released into the synaptic cleft

Neurotransmitters then bind to the receptors on the dendrites of the postsynaptic neuron

If enough neurotransmitters bind to the dendrites, an action potential will result

Electrochemical Event

ACT IT OUT!http://highered.mcgraw-hill.com/s

ites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

Represent the membrane, Na+ and K+ ions, Na+ and K+ channels, Na/K pump

Why doesn’t the sodium channel let K ions pass through?Sodium Channel

◦ Negatively charged amino acids block anions from passing through

◦ Na+ is smaller than K+

◦ Only allows 1Na+ and 1 H20 molecule to pass at a time; K+ is too large

Potassium Channel◦ Negatively charged

amino acids block anions from passing through

◦ K+ is larger than Na+

◦ K channel is deeper and wider

◦ Na+ is too small and not electronegative enough to activate the channel

How does myelin sheath increase the speed of a nerve impulse?

Saltutory conduction

http://www.youtube.com/watch?v=mOgHC5G8LuI

Multiple Sclerosis (MS)Antibodies

specific for protein in myelin sheath

Damaged myelin forms scar tissue forming hard plaque or sclerosis

Neurons are short-circuited and damaged

Myelin Repair

Sodium Channel BlockersIf you block a

sodium channel and the sodium cannot get into the neuron cell… what will happen?

Does not allow neurons to transmit nerve impulses

Paralysis due to loss of nerve function

TTX (tetrodotoxin)Anesthetics Treat cardiac

arythmiasAnti-epileptic drugs

NeurotoxinsTTX (tetrodotoxin)Too large to pass through the

blood brain barrier so often does not affect mental function

Binds to Na+ channels, preventing Na+ from generating an action potential

Paralysis, slowed heart rate, slowed respiration

Potassium Channel BlockersProlong

depolarizationUse for heart

problems