Chapter 28Chapter 28

NERVOUS SYSTEMNERVOUS SYSTEM

Functions of Nervous TissueFunctions of Nervous Tissue1. Sensory Input:1. Sensory Input: Conduction of signals from Conduction of signals from

sensory organs (eyes, ears, nose, skin, etc.) to sensory organs (eyes, ears, nose, skin, etc.) to information processing centersinformation processing centers ( (brainbrain and and spinal spinal cordcord).).

2. Integration:2. Integration: Interpretation of sensory signals and Interpretation of sensory signals and development of a development of a responseresponse. Occurs in brain and . Occurs in brain and spinal cord.spinal cord.

3. Motor Output:3. Motor Output: Conduction of signals from brain Conduction of signals from brain or spinal cord to or spinal cord to effectoreffector organs (muscles or organs (muscles or glands). Controls the activity of muscles and glands). Controls the activity of muscles and glands, and allows the animal to glands, and allows the animal to respondrespond to its to its environmentenvironment..

Nervous System Processes and Responds to Sensory Input

Cells of Nervous TissueCells of Nervous Tissue1. Neuron1. Neuron: Nerve cell. Structural and functional : Nerve cell. Structural and functional

unit of nervous tissue. unit of nervous tissue. Carry signals from one part of the body to another.Carry signals from one part of the body to another.

2. Supporting cells2. Supporting cells: : Nourish, protect, and insulate Nourish, protect, and insulate neurons.neurons. There are roughly 50 supporting cells for every There are roughly 50 supporting cells for every

neuron.neuron. In humans, In humans, Schwann cellsSchwann cells wrap around the axons of wrap around the axons of

neurons, forming a neurons, forming a myelin sheathmyelin sheath that is essential for that is essential for transmission of nerve impulses.transmission of nerve impulses.

Neuron StructureNeuron Structure Cell body Cell body : Contains nucleus and most organelles.: Contains nucleus and most organelles.

DendritesDendrites: Extensions that convey signals : Extensions that convey signals towardstowards

the cell body.the cell body. Short, numerous, and highly branched Short, numerous, and highly branched

Axon:Axon: Extension that transmits signals Extension that transmits signals awayaway from from

the cell body to another neuron or effector cell.the cell body to another neuron or effector cell. Usually a long single fiber. Usually a long single fiber.

Axon is covered by a Axon is covered by a myelin sheathmyelin sheath made up of many made up of many

Schwann cellsSchwann cells that are separated by small spaces that are separated by small spaces

((Nodes of RanvierNodes of Ranvier). ).

Structure of the Neuron

Neuron StructureNeuron Structure Myelin sheath and nodes of Ranvier greatly speed up Myelin sheath and nodes of Ranvier greatly speed up

nerve impulses, which jump down axon from node to nerve impulses, which jump down axon from node to

node.node.

Speed of signalSpeed of signal

Myelinated axonMyelinated axon 100 meters/second100 meters/second

Unmyelinated axonUnmyelinated axon 5 meters/second 5 meters/second

Multiple sclerosisMultiple sclerosis: A disease in which a person’s : A disease in which a person’s

immune system destroys the myelin sheaths on their immune system destroys the myelin sheaths on their

neurons. neurons.

• Loss of muscle controlLoss of muscle control

• Impaired brain functionImpaired brain function

• DeathDeath

Central vs. Peripheral Nervous SystemCentral vs. Peripheral Nervous System

Central Nervous System (CNS)Central Nervous System (CNS): Brain & spinal : Brain & spinal

cord. Processing centers of nervous system.cord. Processing centers of nervous system.

Peripheral Nervous System (PNS)Peripheral Nervous System (PNS): Nerves that : Nerves that

carry signals in and out of the nervous system.carry signals in and out of the nervous system.

Human Nervous System

Three Types of NeuronsThree Types of Neurons

1. Sensory Neurons1. Sensory Neurons: Carry information from the : Carry information from the

stimulation of sensory organs (eyes, ears, etc.) to stimulation of sensory organs (eyes, ears, etc.) to

the central nervous system (CNS). the central nervous system (CNS).

2. Interneurons:2. Interneurons: Found only in CNS. Integrate and Found only in CNS. Integrate and

process data from sensory neurons and send process data from sensory neurons and send

commands to motor neurons.commands to motor neurons.

3. Motor Neurons3. Motor Neurons: Receive information or : Receive information or

commands from the CNS, and relay them to commands from the CNS, and relay them to

effector cells (muscles or glands) to elicit a effector cells (muscles or glands) to elicit a

response.response.

Central Nervous SystemCentral Nervous System BrainBrain: Master control center. Over 100 billion : Master control center. Over 100 billion

neurons and many more supporting cells. neurons and many more supporting cells. EmotionEmotion IntellectIntellect Controls some muscles and spinal cordControls some muscles and spinal cord Homeostatic centersHomeostatic centers

BrainBrain: Protected by:: Protected by: SkullSkull MeningesMeninges: Three layers of tissue covering brain.: Three layers of tissue covering brain. Cerebrospinal FluidCerebrospinal Fluid: Liquid surrounding brain.: Liquid surrounding brain. Blood-brain barrierBlood-brain barrier: Maintains stable environment and : Maintains stable environment and

protects brain from infection and many harmful protects brain from infection and many harmful chemicals.chemicals.

Central Nervous SystemCentral Nervous System Cerebral CortexCerebral Cortex: :

Less than 5 mm thickLess than 5 mm thick Highly folded, occupies over 80% of total brain mass.Highly folded, occupies over 80% of total brain mass. Contains 10 billion neurons and billions of synapses.Contains 10 billion neurons and billions of synapses. Left and right hemispheres are divided into 4 lobesLeft and right hemispheres are divided into 4 lobes Intricate neural circuitry is responsible for many Intricate neural circuitry is responsible for many

unique human traits:unique human traits:• ReasoningReasoning• Mathematical abilityMathematical ability• Language skillsLanguage skills• ImaginationImagination• Personality traitsPersonality traits• Artistic talentArtistic talent• Sensory perceptionSensory perception• Motor functionMotor function

Cerebral Cortex is the Most Complex and Largest Part of Human Brain

Cerebral Cortex Controls Sensory and Motor Functions

Central vs. Peripheral Nervous SystemCentral vs. Peripheral Nervous System

Central Nervous System (CNS)Central Nervous System (CNS)::

Spinal CordSpinal Cord: Lies inside vertebral column.: Lies inside vertebral column.

Receives sensory information from skin and muscles.Receives sensory information from skin and muscles.

Sends out motor commands for movement.Sends out motor commands for movement.

ReflexesReflexes: Unconscious responses to a stimulus. Only : Unconscious responses to a stimulus. Only

sensory and motor neurons are involved.sensory and motor neurons are involved.

Knee-Jerk Reflex Involves Spinal Cord, not Brain

What is a Nerve Impulse?What is a Nerve Impulse?An An electrical signalelectrical signal that depends on the flow that depends on the flow

of ions across the neuron plasma of ions across the neuron plasma membrane.membrane.

Resting PotentialResting Potential: A neuron at rest has a : A neuron at rest has a net net

negative chargenegative charge (-70 mV, equivalent to 5% of the (-70 mV, equivalent to 5% of the

voltage in AA battery).voltage in AA battery).

The net negative charge is due to different ion The net negative charge is due to different ion

concentrations across the neuron membrane.concentrations across the neuron membrane.

Resting Potential is Caused by Differences in Ion Concentrations Across Neuron Membrane

What is a Nerve Impulse?What is a Nerve Impulse?An An electrical signalelectrical signal that depends on the flow of ions that depends on the flow of ions

across the neuron plasma membrane.across the neuron plasma membrane. Action PotentialAction Potential: When a neuron is stimulated above a : When a neuron is stimulated above a

certain threshold, this causes:certain threshold, this causes:

1. Depolarization1. Depolarization: An : An influx of positive ionsinflux of positive ions (Na(Na++)) into the into the

cell, caused by the opening of sodium channels.cell, caused by the opening of sodium channels.

The inside of the cell becomes The inside of the cell becomes positively chargedpositively charged for a for a

brief moment (1-2 milliseconds).brief moment (1-2 milliseconds).

2. Repolarization:2. Repolarization: After a few milliseconds, the neuron After a few milliseconds, the neuron

allows allows otherother positive ions (Kpositive ions (K++) to leave the cell) to leave the cell so the inside so the inside

of the cell becomes negatively charged once again.of the cell becomes negatively charged once again.

Action Potential Requires Stimulus Above a Certain Threshold

Nerve Impulses are Caused by Action Potentials

Neurons Communicate at SynapsesNeurons Communicate at Synapses

Synapse: Synapse: Junction between two neurons or a Junction between two neurons or a neuron and an effector cell (muscle or gland). neuron and an effector cell (muscle or gland). There are two types of synapses:There are two types of synapses:

1. 1. Electrical SynapseElectrical Synapse:: Found in heart and digestive tract of human body.Found in heart and digestive tract of human body. Action potentials pass directly from one neuron to Action potentials pass directly from one neuron to

another.another.

2. 2. Chemical SynapseChemical Synapse:: Found in CNS, muscles, and most other organs. Found in CNS, muscles, and most other organs. Require Require neurotransmittersneurotransmitters: Chemicals that convey : Chemicals that convey

messages from one neuron to another.messages from one neuron to another. Transmitting neuronTransmitting neuron releases neurotransmitters which releases neurotransmitters which

cross synapse and cause an action potential in the cross synapse and cause an action potential in the receiving neuronreceiving neuron..

Chemical Synapses Use Neurotransmitters

Important NeurotransmittersImportant Neurotransmitters

Dopamine: Dopamine: High levels are associated with schizophrenia.High levels are associated with schizophrenia. Low levels are associated with Parkinson’s disease.Low levels are associated with Parkinson’s disease.

Serotonin and Norepinephrine: Serotonin and Norepinephrine: Affect mood, sleep, attention, and learning.Affect mood, sleep, attention, and learning. Low levels are associated with depression.Low levels are associated with depression. Prozac increases the amount of serotonin at synapses.Prozac increases the amount of serotonin at synapses.

Endorphins: Endorphins: Small peptides that decrease pain perception by CNS.Small peptides that decrease pain perception by CNS. Natural painkillers produced in times of stress (childbirth).Natural painkillers produced in times of stress (childbirth). Also decrease urine output, depress respiration, and cause Also decrease urine output, depress respiration, and cause

euphoria and other emotional effects on brain.euphoria and other emotional effects on brain. Heroin and morphine mimic action of endorphin.Heroin and morphine mimic action of endorphin.

Neurotropic DrugsNeurotropic Drugs

Stimulants: Stimulants: Include caffeine, cocaine, and amphetamines.Include caffeine, cocaine, and amphetamines. Increase the activity of the CNS by altering effect of Increase the activity of the CNS by altering effect of

neurotransmitters at chemical synapses.neurotransmitters at chemical synapses.

Depressants: Depressants: Include alcohol and Valium.Include alcohol and Valium. Decrease the activity of the CNS by altering effect of Decrease the activity of the CNS by altering effect of

neurotransmitters at chemical synapses.neurotransmitters at chemical synapses.

Diseases of the Nervous SystemI. Alzheimer’s DiseaseI. Alzheimer’s Disease Most common form of dementia in U.S. Most common form of dementia in U.S. Unknown cause, probably both genetic and environmental Unknown cause, probably both genetic and environmental

factors are important.factors are important. No effective treatmentNo effective treatment Certain diagnosis is usually only possible through discovery of Certain diagnosis is usually only possible through discovery of

typical brain lesions during autopsy.typical brain lesions during autopsy. Usually affects elderly: Over 4 million cases in U.S.Usually affects elderly: Over 4 million cases in U.S.

10% of those over 6510% of those over 65 Almost half of those over 85Almost half of those over 85

Symptoms progress over time. Three stages:Symptoms progress over time. Three stages: Mild StageMild Stage: : Forgetfulness, minor disorientation, mild personality Forgetfulness, minor disorientation, mild personality

changes, depression, difficulty in finding right words during conversation, changes, depression, difficulty in finding right words during conversation,

and performing arithmetic calculations (e.g.: balancing checkbook).and performing arithmetic calculations (e.g.: balancing checkbook).

Diseases of the Nervous System

I. Alzheimer’s Disease (Continued)I. Alzheimer’s Disease (Continued) Stages of Alzheimer’s Disease:Stages of Alzheimer’s Disease:

Moderate Stage:Moderate Stage: Noticeable memory loss, difficulty performing Noticeable memory loss, difficulty performing

everyday tasks (bathing, dressing, cooking, driving, operating everyday tasks (bathing, dressing, cooking, driving, operating

appliances), may wander off, confuse day and night, fails to appliances), may wander off, confuse day and night, fails to

recognize acquaintances and distant relatives.recognize acquaintances and distant relatives.

Severe Stage:Severe Stage: Very limited speech (less than 12 words), eventually Very limited speech (less than 12 words), eventually

becomes mute and uncomprehending, loses all self-care ability, becomes mute and uncomprehending, loses all self-care ability,

can’t recognize closest relatives, friends, or caregivers, becomes can’t recognize closest relatives, friends, or caregivers, becomes

incontinent, progressively loses ability to walk, stand, sit up, incontinent, progressively loses ability to walk, stand, sit up,

smile, and hold head up. Many patients die from complications smile, and hold head up. Many patients die from complications

like pneumonia.like pneumonia.

Brain Atrophy in Alzheimer’s Disease

Definite diagnosis of Alzheimer’s usually requires post-mortem brain examination.Notice pronounced atrophy with wide sulci (grooves) in frontal and parietal regions.Source: www-medlib.med.utah.edu/WebPath/CNSHTML

II. AutismII. Autism Severe developmental brain disorder, starts in childhood. Severe developmental brain disorder, starts in childhood. Symptoms vary from child to child, but may include:Symptoms vary from child to child, but may include:

SpeechSpeech abnormalities or lack of speech abnormalities or lack of speech Lack ofLack of attachment attachment to parents or caretakersto parents or caretakers Lack of eye contact, interest in people, and toysLack of eye contact, interest in people, and toys Repetitive behaviors (e.g.: rocking, counting fingers repeatedly)Repetitive behaviors (e.g.: rocking, counting fingers repeatedly) Self-injurious behaviors (e.g.: head banging, screaming fits, arm flapping)Self-injurious behaviors (e.g.: head banging, screaming fits, arm flapping) Rigid adherence to specific rituals, patterns, or routinesRigid adherence to specific rituals, patterns, or routines Extreme dislike of being touched, sounds, and/or certain foodsExtreme dislike of being touched, sounds, and/or certain foods Walking on tiptoes and balancing on feet.Walking on tiptoes and balancing on feet. Low IQ (May be due to lack of cooperation) and poor social skillsLow IQ (May be due to lack of cooperation) and poor social skills Savants:Savants: May have areas of normal or advanced competence: Math skills, May have areas of normal or advanced competence: Math skills,

memory, musical talent, drawing, etc.memory, musical talent, drawing, etc.

Unknown cause, probably both genetic and environmental Unknown cause, probably both genetic and environmental factors are important (See L.A. Times article 5/4/2000).factors are important (See L.A. Times article 5/4/2000).

II. AutismII. Autism Usually affects children before the age of 3.Usually affects children before the age of 3.

Males are more susceptible: 4 males for every female.Males are more susceptible: 4 males for every female.

Occurs in 1 in 1000 births, but epidemic (6 to 7% of children) in Occurs in 1 in 1000 births, but epidemic (6 to 7% of children) in

certain areas.certain areas.

Occurs in all racial, ethnic, and social backgrounds.Occurs in all racial, ethnic, and social backgrounds.

Does not appear to be caused by psychological environment.Does not appear to be caused by psychological environment.

No cure, but some treatments may improve symptoms in No cure, but some treatments may improve symptoms in

some individuals.some individuals.