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The Nervous System The Nervous System
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The Nervous SystemThe Nervous System

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A. Neurons: Basic Units of the A. Neurons: Basic Units of the Nervous SystemNervous System

The basic unit of structure and function in the The basic unit of structure and function in the nervous system is the neuron (nerve cell).nervous system is the neuron (nerve cell).

Neurons conduct impulses throughout the Neurons conduct impulses throughout the nervous system.nervous system.

Neuron consists of three parts:Neuron consists of three parts:1.1. cell bodycell body

2.2. dendrites: branchlike extensions of the neuron that receive dendrites: branchlike extensions of the neuron that receive impulses and carry them toward the cell bodyimpulses and carry them toward the cell body

3.3. axon: extension of the neuron that carries impulses away axon: extension of the neuron that carries impulses away from the cell body and toward other neurons, muscles, or from the cell body and toward other neurons, muscles, or glands.glands.

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Example: Example:

Neuron StructureNeuron Structure

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There are three types of neurons:There are three types of neurons:1.1. sensory neurons: carry impulses from the body to sensory neurons: carry impulses from the body to

the spinal cord and brainthe spinal cord and brain

2.2. motor neurons: carry the response impulses motor neurons: carry the response impulses away from the brain and spinal cord to a muscle away from the brain and spinal cord to a muscle or glandor gland

3.3. interneurons: found within the brain and spinal interneurons: found within the brain and spinal cord, and process incoming impulses and pass cord, and process incoming impulses and pass response impulses on to motor neurons response impulses on to motor neurons

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Relaying an impulseRelaying an impulse The nervous system sorts and interprets The nervous system sorts and interprets

incoming information before directing a incoming information before directing a response.response.

Example: Shoulder TapExample: Shoulder Tap Question: How does a shoulder tap get your Question: How does a shoulder tap get your

attention?attention? Answer: Answer:

Receptors in the skin sense a tap or other stimulus.Receptors in the skin sense a tap or other stimulus. Sensory neurons transmit the sensory impulse (touch Sensory neurons transmit the sensory impulse (touch

message) to your spinal cord and then to your brain.message) to your spinal cord and then to your brain. The message is interpreted by the brain. A response is sent The message is interpreted by the brain. A response is sent

to the motor neurons.to the motor neurons. Motor neurons transmit the impulse (response message) to Motor neurons transmit the impulse (response message) to

the neck muscles.the neck muscles. The neck muscles are activated, causing the head to turn.The neck muscles are activated, causing the head to turn.

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Example:Example:

Sensory neuron and motor neuronSensory neuron and motor neuron

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A neuron at restA neuron at rest A resting neuron is a neuron that is not transmitting an A resting neuron is a neuron that is not transmitting an

impulse (electrical message).impulse (electrical message). The neuron membrane contain four important transport The neuron membrane contain four important transport

systems:systems:1.1. Ion channel: allows ions in and out of the cellIon channel: allows ions in and out of the cell2.2. Gated Na+ channel: allows sodium ions into the cellGated Na+ channel: allows sodium ions into the cell3.3. Na+/K+ Pump: uses ATP to pump three sodium ions out of the cell Na+/K+ Pump: uses ATP to pump three sodium ions out of the cell

for every two potassium ions it pumps in.for every two potassium ions it pumps in.4.4. Gated K+ channel: allows potassium ions to move out of the cellGated K+ channel: allows potassium ions to move out of the cell

In a neuron at rest, the Na+/K+ pump and the presence In a neuron at rest, the Na+/K+ pump and the presence of many negatively charged ions within the cell keeps of many negatively charged ions within the cell keeps the inside of the neuron cell more negatively charged the inside of the neuron cell more negatively charged than the outside.than the outside.

These conditions cause the plasma membrane of the These conditions cause the plasma membrane of the resting neuron cell to be polarized (inside of the cell is resting neuron cell to be polarized (inside of the cell is negative, outside of the cell is positive).negative, outside of the cell is positive).

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Example: Resting Neuron CellExample: Resting Neuron Cell

This polarization of a neuron cell allows it to This polarization of a neuron cell allows it to transmit an impulse.transmit an impulse.

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How an impulse is transmittedHow an impulse is transmitted The following steps summarizes how an The following steps summarizes how an

impulse gets transmitted throughout the body:impulse gets transmitted throughout the body:1.1. When a stimulus excites a neuron, the gated Na+ channels When a stimulus excites a neuron, the gated Na+ channels

in the membrane open up and sodium ions go inside into in the membrane open up and sodium ions go inside into the cell.the cell.

2.2. The inside of the cell now becomes positively charged and The inside of the cell now becomes positively charged and the outside negatively charged. This change in charge is the outside negatively charged. This change in charge is called depolarization.called depolarization.

3.3. This depolarization moves like a wave down the length of This depolarization moves like a wave down the length of the axon.the axon.

4.4. As the impulse passes, gated sodium channels close, so As the impulse passes, gated sodium channels close, so that sodium ions to not enter inside the cell. The gated K+ that sodium ions to not enter inside the cell. The gated K+ channels open, letting potassium ions out of the cell. This channels open, letting potassium ions out of the cell. This action repolarizes the cell.action repolarizes the cell.

5.5. As gated potassium channels close, the Na+/K+ pump As gated potassium channels close, the Na+/K+ pump restores the ion distribution.restores the ion distribution.

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Example:Example:

Transmitting an impulseTransmitting an impulse

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An impulse can move down the complete An impulse can move down the complete length of an axon only when the threshold length of an axon only when the threshold level is reached.level is reached.

Threshold level: the level at which Threshold level: the level at which depolarization of the neuron occurs.depolarization of the neuron occurs.

If the threshold level is not reached, the If the threshold level is not reached, the impulse quickly dies out impulse quickly dies out

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White matter and gray matterWhite matter and gray matterMost axons are surrounded by white Most axons are surrounded by white

covering of cell call the myelin sheath.covering of cell call the myelin sheath.The myelin sheath insulates the axon, The myelin sheath insulates the axon,

preventing the movement of ions across preventing the movement of ions across its plasma membrane.its plasma membrane.

The ions move quickly down the axon until The ions move quickly down the axon until they reach a gap in the sheath, where the they reach a gap in the sheath, where the ions pass through the plasma of the nerve ions pass through the plasma of the nerve cell and depolarization occurs.cell and depolarization occurs.

As a result, the impulse jumps from gap to As a result, the impulse jumps from gap to gap, greatly increasing the speed at which gap, greatly increasing the speed at which the impulse travels.the impulse travels.

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The myelin sheath gives axons a white The myelin sheath gives axons a white appearance.appearance.

In the brain and spinal cord, masses of In the brain and spinal cord, masses of myelinated axons make up what is called myelinated axons make up what is called “white matter.”“white matter.”

The absence of myelin in axons accounts The absence of myelin in axons accounts for the grayish color of “gray matter” in the for the grayish color of “gray matter” in the brain.brain.

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Connections between neuronsConnections between neurons Neurons lay end to end, meaning axons to Neurons lay end to end, meaning axons to

dendrites and these parts do not touch.dendrites and these parts do not touch.

A tiny space, called the synapse, lies between A tiny space, called the synapse, lies between one neuron’s axon and another neuron’s one neuron’s axon and another neuron’s dendrites. dendrites.

Impulses must move across the synaptic space.Impulses must move across the synaptic space.

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How do impulses move across the How do impulses move across the synaptic space?synaptic space?

1.1. As an impulse reaches the end of an axon, As an impulse reaches the end of an axon, calcium channels open, allowing calcium to enter calcium channels open, allowing calcium to enter the end of the axon.the end of the axon.

2.2. The calcium causes vesicles in the axon to fuse The calcium causes vesicles in the axon to fuse with the plasma membrane, releasing with the plasma membrane, releasing neurotransmitters into the synaptic space by neurotransmitters into the synaptic space by exocytosis.exocytosis.

3.3. These neurotransmitters diffuse across the These neurotransmitters diffuse across the synapse to the dendrites of the next neuron and synapse to the dendrites of the next neuron and binds to receptors.binds to receptors.

4.4. This causes ion channels to open which changes This causes ion channels to open which changes the polarity in the neuron, initiating a new the polarity in the neuron, initiating a new impulse.impulse.

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Example: SynapsesExample: Synapses

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Enzymes in the synapse break down the Enzymes in the synapse break down the neurotransmitters preventing continual neurotransmitters preventing continual firing of impulses.firing of impulses.

The Secret Life of the Brain : VideoThe Secret Life of the Brain : VideoThe Secret Life of the Brain : VideoThe Secret Life of the Brain : Video

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B. The Central Nervous SystemB. The Central Nervous System

The control center of the nervous system The control center of the nervous system is the brain.is the brain.

An impulse traveling through neurons in An impulse traveling through neurons in your body usually reaches your brain your body usually reaches your brain before being rerouted.before being rerouted.

The central nervous system is made up The central nervous system is made up of two parts:of two parts:

1.1. BrainBrain

2.2. Spinal cordSpinal cord

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Central Nervous SystemCentral Nervous System

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Two systems work togetherTwo systems work together The nervous system is made up two The nervous system is made up two

important systems working together:important systems working together:1.1. Central Nervous System (CNS): brain and spinal Central Nervous System (CNS): brain and spinal

cordcord

2.2. Peripheral Nervous System (PNS): all the nerves Peripheral Nervous System (PNS): all the nerves that carry messages to and from the CNSthat carry messages to and from the CNS

The CNS and PNS work together to The CNS and PNS work together to respond to stimuli from the external respond to stimuli from the external environment.environment.

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Anatomy of the brainAnatomy of the brain The brain is the control center of the The brain is the control center of the

entire nervous system.entire nervous system. The brain is divided into three main The brain is divided into three main

sections:sections:1.1. CerebrumCerebrum

2.2. CerebellumCerebellum

3.3. Brain stemBrain stem

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The cerebrumThe cerebrum Divided into two halves, called hemispheres, Divided into two halves, called hemispheres,

that are connected by bundles of nerves.that are connected by bundles of nerves. Controls conscious activities, intelligence, Controls conscious activities, intelligence,

memory, language, skeletal muscle memory, language, skeletal muscle movements, and senses.movements, and senses.

The cerebral cortex, is the outer surface of the The cerebral cortex, is the outer surface of the cerebrum, is made up of gray matter.cerebrum, is made up of gray matter.

The cerebral cortex has folds and grooves The cerebral cortex has folds and grooves that increase its total surface area, and allows that increase its total surface area, and allows complex thought processes to occur.complex thought processes to occur.

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CerebrumCerebrum

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The cerebellumThe cerebellum Located at the back of the brainLocated at the back of the brain Controls your balance, posture, and Controls your balance, posture, and

coordinationcoordination Injury causes your movements to become Injury causes your movements to become

jerky.jerky.

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The brain stemThe brain stem Brain stem is divided into three parts:Brain stem is divided into three parts:

A.A. Medulla oblongata: part of the brain that controls Medulla oblongata: part of the brain that controls involuntary activitiesinvoluntary activities

B.B. Pons: pathway connecting various parts of the Pons: pathway connecting various parts of the brain with each otherbrain with each other

C.C. Midbrain: pathway connecting various parts of Midbrain: pathway connecting various parts of the brain with each otherthe brain with each other

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C. The Peripheral Nervous C. The Peripheral Nervous SystemSystem

The peripheral nervous system (PNS) The peripheral nervous system (PNS) carries impulses between the body and carries impulses between the body and the central nervous system.the central nervous system.

The PNS is divided into two parts:The PNS is divided into two parts:1.1. Somatic nervous systemSomatic nervous system

2.2. Autonomic nervous systemAutonomic nervous system

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Peripheral Nervous SystemPeripheral Nervous System

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Somatic Nervous SystemSomatic Nervous System Portion of the nervous system composed of Portion of the nervous system composed of

cranial nerves, spinal nerves, and all of their cranial nerves, spinal nerves, and all of their branchesbranches

Contains 12 pairs of cranial nerves from the Contains 12 pairs of cranial nerves from the brain, 31 pairs of spinal nerves from the spinal brain, 31 pairs of spinal nerves from the spinal cord, and all of the their branches.cord, and all of the their branches.

These nerves are bundles of neuron axons These nerves are bundles of neuron axons bound together by connective tissue, and the bound together by connective tissue, and the cell bodies are found along the spinal column.cell bodies are found along the spinal column.

Voluntary pathway that relays information Voluntary pathway that relays information between the CNS and skeletal muscles.between the CNS and skeletal muscles.

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Reflexes in the somatic systemReflexes in the somatic system Sometimes a stimulus results in an automatic, Sometimes a stimulus results in an automatic,

unconscious response within the somatic unconscious response within the somatic nervous system.nervous system.

Reflex: an automatic response to a stimulusReflex: an automatic response to a stimulus

Example: Hand jerks when you touch Example: Hand jerks when you touch something hotsomething hot

A reflex impulse travels to the spinal column A reflex impulse travels to the spinal column or brain stem where it causes an impulse to or brain stem where it causes an impulse to be sent directly back to a muscle. (message is be sent directly back to a muscle. (message is not interpreted)not interpreted)

The brain becomes aware of the reflex only The brain becomes aware of the reflex only after it occurs.after it occurs.

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Somatic Nervous System: ReflexSomatic Nervous System: Reflex

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The autonomic nervous systemThe autonomic nervous system Portion of the peripheral nervous system that Portion of the peripheral nervous system that

carries impulses from the CNS to internal organs.carries impulses from the CNS to internal organs. The impulses produce responses that are The impulses produce responses that are

involuntary. (unconscious control)involuntary. (unconscious control) The autonomic nervous system is divided into The autonomic nervous system is divided into

two parts:two parts:1.1. Sympathetic nervous system: controls many internal Sympathetic nervous system: controls many internal

functions during times of stress.functions during times of stress.

2.2. Parasympathetic nervous system: controls many of the Parasympathetic nervous system: controls many of the body’s internal functions when it is at rest.body’s internal functions when it is at rest.

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Autonomic Nervous SystemAutonomic Nervous System

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Sympathetic nervous system releases Sympathetic nervous system releases hormones such as epinephrine and hormones such as epinephrine and norepinephrine, that results in the fight – or – norepinephrine, that results in the fight – or – flight response.flight response.

Both the sympathetic and parasympathetic Both the sympathetic and parasympathetic systems send signals to the same internal systems send signals to the same internal organs.organs.

The resulting activity of the organ depends on The resulting activity of the organ depends on the intensities of the opposing signals.the intensities of the opposing signals.

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Parasympathetic Nervous System and Parasympathetic Nervous System and Sympathetic Nervous SystemSympathetic Nervous System

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Outline of the Nervous SystemOutline of the Nervous System

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D. Sensing ChemicalsD. Sensing Chemicals

How are you able to smell and taste?How are you able to smell and taste? Answer: Chemical molecules of a substance Answer: Chemical molecules of a substance

stimulate receptors in your nose and mouth.stimulate receptors in your nose and mouth. How does your sense of smell get activated?How does your sense of smell get activated?

1.1. The receptors for smell are hair like nerve endings The receptors for smell are hair like nerve endings located in the upper portion of your nose.located in the upper portion of your nose.

2.2. Chemicals acting on these nerve endings initiate Chemicals acting on these nerve endings initiate impulses in the olfactory nerve, which is connected to impulses in the olfactory nerve, which is connected to your brain.your brain.

3.3. In the brain, this signal is interpreted as a particular In the brain, this signal is interpreted as a particular odor.odor.

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Olfactory SystemOlfactory System

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The senses of taste and smell are closely linked.The senses of taste and smell are closely linked.Example: Stuffed noseExample: Stuffed noseYou can smell a little, if anything, and since your sense You can smell a little, if anything, and since your sense of taste depends on your sense of smell, your sense of of taste depends on your sense of smell, your sense of taste is dulled.taste is dulled.

How does your sense of taste get activated?How does your sense of taste get activated?1.1. Chemicals dissolved in saliva contact sensory receptors on Chemicals dissolved in saliva contact sensory receptors on

your tongue called taste buds.your tongue called taste buds. Taste buds: sensory receptors located on the tongue that result in Taste buds: sensory receptors located on the tongue that result in

taste perception.taste perception. There are four different tastes:There are four different tastes:

1.1. SourSour2.2. SaltySalty3.3. BitterBitter4.4. SweetSweet

2.2. Taste bud cells are depolarized, signals from your taste buds Taste bud cells are depolarized, signals from your taste buds are sent to the cerebrum.are sent to the cerebrum.

3.3. At the cerebrum, the signal is interpreted and you notice a At the cerebrum, the signal is interpreted and you notice a particular taste.particular taste.

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A young adult has approximately 10,000 A young adult has approximately 10,000 taste buds.taste buds.

As a person ages, his or her sense of As a person ages, his or her sense of smell becomes less sharp and taste buds smell becomes less sharp and taste buds may decrease in number or become less may decrease in number or become less sensitive, so it may decrease one’s sense sensitive, so it may decrease one’s sense of taste.of taste.

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E. Sensing LightE. Sensing Light

How are you able to see?How are you able to see?Your sense of sight depends on receptors Your sense of sight depends on receptors

in your eyes that respond to light energy.in your eyes that respond to light energy.The retina, found at the back of the eye, is The retina, found at the back of the eye, is

a thin layer of tissue made up of light a thin layer of tissue made up of light receptors and sensory neurons.receptors and sensory neurons.

Light enters the eye through the pupil and Light enters the eye through the pupil and is focused by the lens onto the back of the is focused by the lens onto the back of the eye, where it strikes the retina.eye, where it strikes the retina.

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The retina contains two types of light The retina contains two types of light receptors cells:receptors cells:

1.1. Rods: receptor cells adapted for vision in dim Rods: receptor cells adapted for vision in dim light; help detect shape and movement; black and light; help detect shape and movement; black and white picturewhite picture

2.2. Cones: receptor cells adapted for sharp vision in Cones: receptor cells adapted for sharp vision in bright light; help detect colorbright light; help detect color

These light receptors convert light signals These light receptors convert light signals into nerve impulses and relay them to the into nerve impulses and relay them to the brain.brain.

At the back of the eye, retinal tissue At the back of the eye, retinal tissue comes together to form the optic nerve, comes together to form the optic nerve, which leads to the brain, where images which leads to the brain, where images are interpreted.are interpreted.

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Visual SystemVisual System

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F. Sensing Mechanical F. Sensing Mechanical StimulationStimulation

Hearing and touch depend on receptors that Hearing and touch depend on receptors that respond to mechanical stimulation.respond to mechanical stimulation.

Your sense of hearingYour sense of hearing Sound waves enter your outer ear and travel Sound waves enter your outer ear and travel

down to the end of the ear canal, where they down to the end of the ear canal, where they strike a membrane called the eardrum and strike a membrane called the eardrum and cause it to vibrate.cause it to vibrate.

Sound waves: waves created by air vibrationsSound waves: waves created by air vibrations The vibrations then pass to three small bones in The vibrations then pass to three small bones in

the middle ear:the middle ear:1.1. MalleusMalleus2.2. IncusIncus3.3. stapesstapes

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Parts of the Middle EarParts of the Middle Ear

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As the stapes vibrates, it causes the membrane As the stapes vibrates, it causes the membrane of the oval window, a structure between the of the oval window, a structure between the middle and inner ear, to move back and forth.middle and inner ear, to move back and forth.

The movement from the oval window causes The movement from the oval window causes fluid in the cochlea to move.fluid in the cochlea to move.

Cochlea: snail-shaped structure in the inner ear Cochlea: snail-shaped structure in the inner ear containing fluid and hairs; produces electrical containing fluid and hairs; produces electrical impulses that the brain interprets as sound.impulses that the brain interprets as sound.

The fluid in the cochlea moves like a wave The fluid in the cochlea moves like a wave against the hair cells causing them to bend.against the hair cells causing them to bend.

The movement of the hairs produces electrical The movement of the hairs produces electrical impulses, which travel along the auditory nerve impulses, which travel along the auditory nerve to the sides of the cerebrum, where they are to the sides of the cerebrum, where they are interpreted as sound.interpreted as sound.

Hearing loss can occur if the auditory nerve or Hearing loss can occur if the auditory nerve or the hair cells in the cochlea are damaged.the hair cells in the cochlea are damaged.

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Cochlea, Oval window, Stapes, Semicircular Cochlea, Oval window, Stapes, Semicircular CanalsCanals

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Your sense of balanceYour sense of balance The inner ear also converts information about The inner ear also converts information about

the position of your head into nerve impulses the position of your head into nerve impulses which travel to your brain, informing it about your which travel to your brain, informing it about your body’s equilibrium.body’s equilibrium.

Maintaining balance is the function of your Maintaining balance is the function of your semicircular canals.semicircular canals.

Semicircular canal: structures in the inner ear Semicircular canal: structures in the inner ear containing fluid and hairs that help the body containing fluid and hairs that help the body maintain balance.maintain balance.Example: Tilting the headExample: Tilting the headCauses the fluid to move which bends the hair Causes the fluid to move which bends the hair and produces impulses. Neurons from the and produces impulses. Neurons from the semicircular canals carry the impulses to the semicircular canals carry the impulses to the brain, which sends an impulse to stimulate your brain, which sends an impulse to stimulate your neck muscles and readjust the position of the neck muscles and readjust the position of the head. head.

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Your sense of touchYour sense of touch Receptors in the dermis of the skin Receptors in the dermis of the skin

respond to changes in:respond to changes in:1.1. TemperatureTemperature

2.2. PressurePressure

3.3. painpain

Although some receptors are found all Although some receptors are found all over your body, those responsible for over your body, those responsible for responding to particular stimuli are responding to particular stimuli are usually concentrated within certain areas usually concentrated within certain areas of your body.of your body.

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Light pressure receptorsLight pressure receptors Found in the following areas :Found in the following areas :

1.1. dermis of the fingertipsdermis of the fingertips

2.2. EyelidsEyelids

3.3. LipsLips

4.4. tip of the tonguetip of the tongue

5.5. palmspalms

When these receptors are stimulated, When these receptors are stimulated, you perceive sensations of light touch. you perceive sensations of light touch.

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Heavy pressure receptorsHeavy pressure receptors Found in the following areas:Found in the following areas:

1.1. JointsJoints

2.2. muscle tissuemuscle tissue

3.3. certain organscertain organs

4.4. PalmsPalms

5.5. FingersFingers

6.6. soles of your feetsoles of your feet

When these receptors are stimulated, you When these receptors are stimulated, you perceive heavy pressure.perceive heavy pressure.

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Free nerve endingFree nerve ending Extend into the lower layers of the epidermis.Extend into the lower layers of the epidermis. Are receptors for the following sensations:Are receptors for the following sensations:

1.1. ItchItch2.2. TickleTickle3.3. HotHot4.4. ColdCold5.5. painpain

Heat receptors are found deep in the dermis.Heat receptors are found deep in the dermis. Cold receptors are found closer to the Cold receptors are found closer to the

surface of the skin.surface of the skin. Pain receptors can be found in all tissues of Pain receptors can be found in all tissues of

the body except those in the brain.the body except those in the brain.

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Receptors on the skinReceptors on the skin

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G. Nervous System DisordersG. Nervous System DisordersA.A. Meningitis:Meningitis: -Viral or Bacterial infection-Viral or Bacterial infection

in the brainin the brain-Bacterial meningitis is -Bacterial meningitis is

the the inflammation of the inflammation of the meninges meninges

(membranous (membranous coverings of coverings of the brain and the brain and spinal cord)spinal cord)

-Symptoms: fever, -Symptoms: fever, severe severe headache, stiff headache, stiff neck, sore neck, sore throat, and throat, and vomiting, vomiting, followed by followed by respiratory respiratory illnessillness

-Can cause permanent -Can cause permanent brain damagebrain damage

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B.B. Alzheimer’s Disease:Alzheimer’s Disease:

-Form of dementia that affects a person’s -Form of dementia that affects a person’s memory, ability to reason, make memory, ability to reason, make judgments and function in everyday judgments and function in everyday situationssituations

-brain cells -brain cells degenerate, reducing the degenerate, reducing the responsiveness of the remaining cells to responsiveness of the remaining cells to many of the chemicals that transmit many of the chemicals that transmit signalssignals

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C.C. Parkinson’s Disease:Parkinson’s Disease:

-Degenerative disorder of the nervous -Degenerative disorder of the nervous systemsystem

-Patients with this disease may exhibit -Patients with this disease may exhibit shaking, tremors, sluggish movents, or shaking, tremors, sluggish movents, or muscle rigiditymuscle rigidity

-Rigidity in muscles is one of the serious -Rigidity in muscles is one of the serious effectseffects

-May become difficult to move around-May become difficult to move around