The Nervous SystemThe Nervous System

Neurons: Basic Unit of the Nervous Neurons: Basic Unit of the Nervous SystemSystem

The basic unit of structure and function in The basic unit of structure and function in the nervous system is the neuron, or nerve the nervous system is the neuron, or nerve cellcell

They conduct impulses throughout the They conduct impulses throughout the nervous systemnervous system

They are long cells that consists of three They are long cells that consists of three regions: cell body, dendrites and an axonregions: cell body, dendrites and an axon

NeuronsNeurons

Dendrites are branch-like extensions of Dendrites are branch-like extensions of the neuron that receives impulses and the neuron that receives impulses and carry them toward the cell bodycarry them toward the cell body

Axon is an extension of the neuron that Axon is an extension of the neuron that carries impulses away from the cell body carries impulses away from the cell body and towards other neurons, muscles, or and towards other neurons, muscles, or glandsglands

NeuronsNeurons

Neurons Neurons

Neurons fall into three categories: Neurons fall into three categories: Sensory neuronsSensory neurons Motor Neurons Motor Neurons Interneurons Interneurons

NeuronsNeurons Sensory neurons carry impulses from the Sensory neurons carry impulses from the

body to the spinal cord and brainbody to the spinal cord and brain Interneurons are found within the brain Interneurons are found within the brain

and spinal cord, they process the incoming and spinal cord, they process the incoming impulses and pass response impulses on impulses and pass response impulses on to motor neurons to motor neurons

Motor Neurons carry the response Motor Neurons carry the response impulses away from the brain and spinal impulses away from the brain and spinal cord to muscles or glandscord to muscles or glands

Relaying an ImpulseRelaying an Impulse

Receptors in your skin sense a tap or Receptors in your skin sense a tap or other stimulusother stimulus

Sensory neurons transmit the touch Sensory neurons transmit the touch messagemessage

The message is interpreted by the brain, a The message is interpreted by the brain, a response is sent to the motor neuronsresponse is sent to the motor neurons

Relaying an ImpulseRelaying an Impulse

Motor neurons transmit a response Motor neurons transmit a response message to the neck musclesmessage to the neck muscles

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

A Neuron at RestA Neuron at Rest

In a neuron at rest, the sodium/potassium In a neuron at rest, the sodium/potassium pump (Na+/K+) and the presence of many pump (Na+/K+) and the presence of many negatively charged ion within a cell keeps negatively charged ion within a cell keeps the inside of a cell more negatively the inside of a cell more negatively charged than the outsidecharged than the outside

How an Impulse is TransmittedHow an Impulse is Transmitted

When a stimulus excites a neuron, gated When a stimulus excites a neuron, gated sodium channels in the membrane open sodium channels in the membrane open up and sodium ions rush into the cellup and sodium ions rush into the cell

As the positive charge builds up inside the As the positive charge builds up inside the membrane, the inside of the cell becomes membrane, the inside of the cell becomes more positively charged than the outsidemore positively charged than the outside

How an Impulse is TransmittedHow an Impulse is Transmitted

This change in charge- called This change in charge- called depolarization- moves like a wave down depolarization- moves like a wave down the length of the axonthe length of the axon

As the wave passes, gated channels and As the wave passes, gated channels and the Na+/K+ pump act to return the neuron the Na+/K+ pump act to return the neuron to its resting stateto its resting state

How an Impulse is TransmittedHow an Impulse is Transmitted

An impulse can move down the complete An impulse can move down the complete length of an axon only when stimulation of length of an axon only when stimulation of the neuron is strong enoughthe neuron is strong enough

White Matter and Gray MatterWhite Matter and Gray Matter

Most axons are surrounded by a white Most axons are surrounded by a white covering of cells called the myelin sheath, covering of cells called the myelin sheath, it insulates the axon, hindering the it insulates the axon, hindering the movement of ions across its plasma movement of ions across its plasma membranemembrane

White Matter and Gray MatterWhite Matter and Gray Matter The myelin sheath gives axons a white The myelin sheath gives axons a white

appearanceappearance 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 masses of The absence of myelin in masses of neurons accounts for the grayish color of neurons accounts for the grayish color of “gray matter” in the brain“gray matter” in the brain

Connections Between NeuronsConnections Between Neurons

Although neurons lie end to end- axons to Although neurons lie end to end- axons to dendrites- they don’t actually touchdendrites- they don’t actually touch

A tiny space lies between one neuron’s A tiny space lies between one neuron’s axon and another’s dendritesaxon and another’s dendrites

This junction b/t neurons is called a This junction b/t neurons is called a synapsesynapse

Connections Between NeuronsConnections Between Neurons

Impulses traveling to and from the brain Impulses traveling to and from the brain must move across the synaptic space that must move across the synaptic space that separates the axon and dendritesseparates the axon and dendrites

As an impulse reaches the end of an axon, As an impulse reaches the end of an axon, calcium channels open and calcium enters calcium channels open and calcium enters the end of the axonthe end of the axon

Connections Between NeuronsConnections Between Neurons Neurotransmitters- are chemicals that Neurotransmitters- are chemicals that

diffuse across the space of a synapse to diffuse across the space of a synapse to the dendrites of the next neuronthe dendrites of the next neuron

Enzymes in the synapse typically break Enzymes in the synapse typically break down the neurotransmitters shortly after down the neurotransmitters shortly after transmission, preventing the continual transmission, preventing the continual firing of impulsesfiring of impulses

Central Nervous SystemCentral Nervous System Two systems work together- Central Two systems work together- Central

nervous system and peripheral nervous nervous system and peripheral nervous systemsystem

Central nervous system (CNS)- brain and Central nervous system (CNS)- brain and spinal cord- coordinates all your body’s spinal cord- coordinates all your body’s activitiesactivities

Peripheral nervous system (PNS)- is made Peripheral nervous system (PNS)- is made up of all the nerves that carry messages to up of all the nerves that carry messages to and from the central nervous systemand from the central nervous system

Anatomy of the BrainAnatomy of the Brain

Cerebrum- is divided into two halves, Cerebrum- is divided into two halves, called hemispheres, that are connected by called hemispheres, that are connected by bundles of nervesbundles of nerves

Your conscious activities intelligence, Your conscious activities intelligence, memory, language, skeletal muscle memory, language, skeletal muscle movement, and senses are controlled by movement, and senses are controlled by the cerebrumthe cerebrum

Anatomy of the BrainAnatomy of the Brain

The outer surface, called cerebral cortex is The outer surface, called cerebral cortex is made of gray mattermade of gray matter

Contains the countless folds and grooves Contains the countless folds and grooves that increase surface area, plays a role in that increase surface area, plays a role in intelligence intelligence

Anatomy of the BrainAnatomy of the Brain

Cerebellum- located at the back of your Cerebellum- located at the back of your brain, controls balance, posture, and brain, controls balance, posture, and coordinationcoordination

If injured movements become jerky If injured movements become jerky

Anatomy of the BrainAnatomy of the Brain Brain stem- made up of the medulla Brain stem- made up of the medulla

oblongata, the pons, and the midbrain oblongata, the pons, and the midbrain Medulla oblongata- is the part of the brain Medulla oblongata- is the part of the brain

that controls involuntary activities such as that controls involuntary activities such as breathing and heart ratebreathing and heart rate

The pons and midbrain act as pathways The pons and midbrain act as pathways connecting various parts of the brain with connecting various parts of the brain with each othereach other

Peripheral Nervous SystemPeripheral Nervous System Can be separated into two divisionsCan be separated into two divisions The somatic nervous system The somatic nervous system The autonomic nervous systemThe autonomic nervous system

Somatic Nervous SystemSomatic Nervous System Somatic nervous system- is made up of Somatic nervous system- is made up of

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

Nerves relay info mainly b/t your skin, the Nerves relay info mainly b/t your skin, the CNS, and skeletal muscleCNS, and skeletal muscle

Voluntary pathwayVoluntary pathway

Somatic Nervous SystemSomatic Nervous System Sometimes a stimulus results in an Sometimes a stimulus results in an

automatic, unconscious response w/in the automatic, unconscious response w/in the somatic systemsomatic system

Reflex- an automatic response to a Reflex- an automatic response to a stimulus- travels to the spinal column or stimulus- travels to the spinal column or brain stem where it sends a response brain stem where it sends a response directly to the muscle directly to the muscle

The brain is aware only after the reflex has The brain is aware only after the reflex has occurred occurred

Autonomic Nervous SystemAutonomic Nervous System

Carries impulses from the CNS to internal Carries impulses from the CNS to internal organsorgans

These impulses produce responses that These impulses produce responses that are involuntary, or not under conscious are involuntary, or not under conscious controlcontrol

Autonomic Nervous SystemAutonomic Nervous System

There are two divisions of the autonomic There are two divisions of the autonomic nervous system:nervous system:

Sympathetic Nervous SystemSympathetic Nervous System Parasympathetic Nervous SystemParasympathetic Nervous System

Sympathetic Nervous SystemSympathetic Nervous System

Controls many internal functions during Controls many internal functions during times of stresstimes of stress

Causes the release of epinephrine and Causes the release of epinephrine and norepinephrine when given a stimulusnorepinephrine when given a stimulus

Fight or flightFight or flight

Parasympathetic Nervous SystemParasympathetic Nervous System

Controls many of the body’s internal Controls many of the body’s internal functions when it is at restfunctions when it is at rest

During times that you are relaxingDuring times that you are relaxing Both systems send signals to the same Both systems send signals to the same

internal organs, just under different internal organs, just under different conditionsconditions

Sensing Smell and TasteSensing Smell and Taste

Sensing chemicals- chemicals acting on Sensing chemicals- chemicals acting on nerve endings initiate impulses in the nerve endings initiate impulses in the smell or taste receptorssmell or taste receptors

These two senses are closely linked, These two senses are closely linked, much of what you taste depends on your much of what you taste depends on your sense of smellsense of smell

Sensing Smell and TasteSensing Smell and Taste Taste buds- chemicals will dissolve in Taste buds- chemicals will dissolve in

saliva and come into contact with sensory saliva and come into contact with sensory receptorsreceptors

Taste is divided into four basic categories:Taste is divided into four basic categories: SourSour SaltySalty BitterBitter SweetSweet

Sensing LightSensing Light

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 neuronsreceptors and sensory neurons

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

Sensing LightSensing Light

Two types of receptors found in the retina:Two types of receptors found in the retina: Cones- adapted for sharp vision in bright Cones- adapted for sharp vision in bright

lightlight Rods- adapted for vision in dim lightRods- adapted for vision in dim light

Sensing Mechanical StimulationSensing Mechanical Stimulation

Sound causes the air around it to vibrateSound causes the air around it to vibrate These vibrations travel outward from the These vibrations travel outward from the

source in waves, called sound wavessource in waves, called sound waves Sound waves enter your outer ear and Sound waves enter your outer ear and

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

Sensing Mechanical StimulationSensing Mechanical Stimulation

The vibrations then pass to three small The vibrations then pass to three small bones in the middle ear- the malleus, the bones in the middle ear- the malleus, the incus, and the stapesincus, and the stapes

Also within the ear, cochlea, a snail-Also within the ear, cochlea, a snail-shaped structure in the inner earshaped structure in the inner ear

Semicircular canals- maintains balance Semicircular canals- maintains balance

Sensing TouchSensing Touch

Receptors in the dermis of the skin Receptors in the dermis of the skin respond to changes in temperature, respond to changes in temperature, pressure, and painpressure, and pain