1. Nervous System
Chapter 38
Pages

2. Nerve Cell
Neurons or nerve cells - receive, process, transmit information
Glia - which assist neuron function.
Provide nutrients
Regulate the composition of the extracellular fluid (brain & spinal cord)
Regulate communication between neurons
Speed up the movement of electrical signals within neurons

3. Functions of Nerve Cells
Localized in separate parts of the cell
A neuron must perform four functions:
Receive information from the environment
Process the information and produce electrical signals
Conduct electrical signals to a junction where it meets another cell
Transmit information to other neurons, muscles, or glands

4. Structures of Nerve Cells
Typical neurons have four distinct parts that carry out the functions:
Dendrites
A cell body
An axon
Synaptic terminals

5. Dendrites – respond to stimuli
Dendrites are branched tendrils protruding from the cell body
Perform the “receive information” function
Branches provide a large surface area for receiving signals
Dendrites of sensory neurons respond to specific stimuli- pressure, odor, light, body temperature, blood pH, or position of a joint
Dendrites of neurons in the brain and spinal cord respond to chemicals or neurotransmitters, released by other neurons

6. Cell Body – processes dendrite signals
Performing the “process information” function
Electrical signals travel down the dendrite to the cell body, which integrates incoming information
If incoming signals are strong enough, a large, rapid electrical signal called an action potential is produced
Contains other organelles - nucleus, endoplasmic reticulum, and Golgi apparatus

7. Axon – conducts action potentials
In a typical neuron, a long, thin axon extends outward from the cell body and conducts action potentials from the cell body to synaptic terminals at the axon’s end
Single axons may stretch from our spinal cord to our toes, a distance of about 3 feet
Axons are typically bundled together into nerves, much like wires are bundled within an electrical cable

8. Synapses – transmit signals between cells
The site where a neuron communicates with another cell is a synapse
A synapse consists of:
The synaptic terminal - a swelling at the end of an axon of the “sending” neuron
A dendrite or cell body of a “receiving” neuron, muscle, or gland cell
A small gap separates the two cells
Contain neurotransmitters that are released in response to an action potential reaching the terminal
The plasma membrane of the receiving neuron has receptors that bind the neurotransmitters and stimulate a response in this cell
So the output of the first cell becomes the input to the second

9. A Neuron Dendrites: Receive signals from other neurons 2
Synaptic terminals:
Transmit signals from
other neurons 1
Cell body:
Integrates signals;
coordinates the
neuron’s metabolic
activities 3
An action
potential starts here 4
neurotransmitters
dendrite
synaptic
terminal
Axon: Conducts
the action potential 5
receptors
Synaptic terminals:
Transmit signals to
other neurons 6
synapse
Dendrites
(of other neurons):
Receive signals 7

10. How is information carried?
Information is carried within a neuron by electrical signals and is transmitted between neurons by neurotransmitters released from one neuron and received by a second
An unstimulated, inactive neuron maintains a constant electrical voltage difference, or potential, across its plasma membrane, called a resting potential
The voltage inside the cell is always negative and ranges from about – 40 to –90 millivolts (mV)

11. Produce and Transmit Information
If the membrane potential becomes less negative, it reaches a threshold level and triggers an action potential
During action potential, the membrane potential rises rapidly to +50 mV inside the cell, then returns to resting potential
The action potential signal flows down the axon to the synaptic terminals with no change in voltage from the cell body to the synaptic terminals

12. Electrical Events During an Action Potential4
action potential
threshold
resting
potential 3 1 2 5
less
negative
more
negative
time
(milliseconds)

13. Myelin
Myelin speeds up the conduction of action potentials
The thicker an axon, the faster the action potential moves
Neurons increase the rate of action potential conduction by covering portions of the axon with a fatty insulation called myelin
Formed by glial cells that wrap themselves around the axon, leaving nodes between myelin segments
In myelinated neurons, action potentials “jump” from node to node, traveling at a rate of ft/ second

14. A Myelinated Axon An action potential jumps from node to node, greatly
speeding up conduction
down the axon
Schwann cell
node
myelin
myelin
sheath
axon
axon

15. Neurotransmitters Neurons use chemicals to communicate at synapses
A synapse is where the synaptic terminal of one neuron meets the dendrite of another. They do not actually touch at a synapse
A tiny gap or synaptic cleft, separates the first or presynaptic neuron, from the second or postsynaptic neuron
The presynaptic neuron sends neurotransmitter chemicals across the gap to the postsynaptic neuron
There are many types of neurotransmitters
A synaptic terminal contains vesicles, each full of neurotransmitter molecules
When an action potential is initiated, it travels down an axon until it reaches its synaptic terminal

16. Across the Synapse
The inside of the terminal becomes positively charged and triggers a cascade of changes that cause the vesicles to release neurotransmitters into the synapatic cleft
The outer surface of the plasma membrane of the postsynaptic neuron is packed with receptor proteins that are specialized to bind the neurotransmitter released by the presynaptic neuron
The neurotransmitter molecules diffuse across the gap and bind to these receptors

17. Synapses produce excitatory or inhibitory postsynaptic potentials
The binding of neurotransmitter molecules to receptors on a postsynaptic neuron opens ion channels in the neuron’s plasma membrane
Depending on which channels are associated with the receptors, ions such as Na+, K+, Ca2+, or Cl– may move through these channels causing a small, brief change in voltage, called a postsynaptic potential or PSP
If the postsynaptic neuron becomes more negative, its resting potential moves farther away from threshold, reducing the likelihood of firing an action potential
This change in voltage is an inhibitory postsynaptic potential (IPSP)
If the postsynaptic neuron becomes less negative, then its resting potential will move closer to threshold, and it will be more likely to fire an action potential
This voltage change is an excitatory postsynaptic potential (EPSP)

18. Signaling in Neurons

19. Neurotransmitter action is brief
Some neurotransmitters are rapidly broken down by enzymes in the synaptic cleft
acetylcholine, the transmitter that stimulates skeletal muscle cells
Many other neurotransmitters are transported back into the presynaptic neuron

20. How Do Neurons Produce and Transmit Information?
Summation of postsynaptic potentials determines the activity of a neuron
The dendrites and cell body of a single neuron receive EPSPs and IPSPs from the synaptic terminals of presynaptic neurons
The voltages of all the PSPs that reach the postsynaptic cell body are added up, a process called integration
If the excitatory and inhibitory postsynaptic potentials added together raise the electrical potential inside the neuron above threshold, the postsynaptic cell produces an action potential

22. Nervous System Must be able to perform four operations:
Determine the type of stimulus
Determine and signal the intensity of a stimulus
Integrate information from many sources
Initiate and direct appropriate responses

23. Determine the type of Stimulus
The nature of a stimulus is determined by connections between the senses and the brain
All nervous systems interpret what a stimulus is by monitoring which neurons are firing action potentials
For example, the brain interprets action potentials that occur in the axons of the eye and travel to the visual areas of the brain as the sensation of light
Therefore, you distinguish the sound of music from the taste of coffee, or the bitterness of coffee from the sweetness of sugar, because these different stimuli result in action potentials in different axons that connect to different areas of the brain

24. Intensity is coded for by frequency of action potentials
Because all action potentials are the same size and duration, no information about the strength or intensity of a stimulus can be encoded in a single action potential
Intensity is coded in two ways:
First, the intensity can be signaled by the frequency of action potentials in a single neuron—the more intense the stimulus, the faster the neuron fires action potentials
Second, most nervous systems have many neurons that respond to the same input
Stronger stimuli excite more of neurons, whereas weaker stimuli excite fewer neurons that fire at the same time
A gentle touch may cause a single touch receptor in the skin to fire action potentials very slowly; a hard poke may cause several touch receptors to fire, some very rapidly

25. Signaling Stimulus Intensity
sensory neuron 1
Sensory neuron 1
fires slowly;
sensory neuron 2
is silent
sensory
neuron 2
sensory
neuron 1
sensory neuron 2
(a) Gentle touch
sensory neuron 1
Sensory neurons
1 and 2 both fire
sensory
neuron 2
sensory
neuron 1
sensory neuron 2
(b) Hard poke
time

26. The nervous system processes information from many sources
The brain is bombarded by sensory stimuli from inside and outside the body
The brain evaluates inputs, determines which are important, and decides how to respond
A number of neurons may funnel their signals to fewer neurons
Many sensory neurons may converge onto a small number of brain cells
Some brain cells act as “decision-making” cells, adding up the PSP that result from the synaptic activity of the sensory neurons
Depending on their strength (and other factors, as hormones or metabolic activity), they produce appropriate outputs

27. The nervous system produces outputs to muscles and glands
Action potentials from the decision-making neurons may travel to other parts of the brain, the spinal cord, or the sympathetic and parasympathetic nervous system
Ultimately, the output of the nervous system will stimulate activity in the muscles or glands that produce behaviors
The same principles of connectivity and intensity coding for sensory inputs are used for the brain’s outputs
Which muscles or glands are activated is determined by their connections to the brain or spinal cord
How hard a muscle contracts is determined by how many neurons connect to it and how fast those neurons fire action potentials

28. How are behaviors controlled?
Most behaviors are controlled by pathways composed of four elements:
Sensory neurons respond to a stimulus, either internal or external
Interneurons receive signals from sensory neurons, hormones, or neurons that store memories; based on this input, interneurons often activate motor neurons
Motor neurons receive information from sensory neurons or interneurons and activate muscles or glands
Effectors, usually muscles or glands, perform the response directed by the nervous system

29. Reflexes are simple behaviors
Simple behaviors, such as reflexes, may be controlled by activity in as few as two or three neurons—a sensory neuron, a motor neuron, and an interneuron in between, usually stimulating a single muscle
In humans, simple reflexes such as the knee-jerk or pain- withdrawal reflexes are produced by neurons in the spinal cord

30. Complex behaviors
Complex behaviors are organized by interconnected neural pathways in which several types of sensory input converge on a set of interneurons
By integrating the postsynaptic potentials from multiple sources, the interneurons “decide” what to do and stimulate motor neurons to direct the appropriate activity in muscles and glands
Hundreds, or even millions of neurons, mostly in the brain, may be required to perform complex actions such as playing the piano

31. Simple nervous systems
In the animal kingdom, there are two nervous system designs.
A diffuse nervous system
Cnidarians (Hydra, jellyfish, and their relatives)
Radially symmetrical cnidarians have no “front end,” so there is no evolutionary pressure to concentrate the senses in one place
Cnidarian nervous systems are composed of a network of neurons, called a nerve net, woven through the animal’s tissues, with a cluster of neurons, called a ganglion, but nothing like a real brain

32. Nervous System Organization
ring of ganglia
diffuse network
of neurons
(a) Hydra

33. More Complex A centralized nervous system, in more complex organisms
Most animals are bilaterally symmetrical, with head and tail ends
The head is usually the first part of the body to encounter food, danger, and potential mates. It is advantageous to have sense organs concentrated there
Sizable ganglia evolved that integrate the information gathered by the senses and direct appropriate actions
Over evolutionary time, the major sense organs of became localized in the head, and the ganglia became centralized into a brain
This process, called cephalization, reached a peak in the vertebrates

34. Nervous System Organization
brain
nerve cords
cerebral
ganglia
(brain)
(b) Flatworm
(c) Octopus

35. Nervous system divided into 2 parts
The central nervous system (CNS) - brain and spinal cord
The peripheral nervous system (PNS) - neurons that lie outside the CNS and axons that connect them with CNS
The cell bodies of neurons of the PNS are often located in ganglia alongside the spinal cord or in ganglia near target organs, such as ganglia in the head and neck that control the salivary glands

36. Organization and Functions of the Vertebrate Nervous System

37. The PNS links the CNS to the Body
Nerves of the PNS –
Connect the brain and spinal cord with muscles, glands, sensory organs, and digestive, respiratory, urinary, reproductive, and circulatory systems
Contain axons of sensory neurons, bringing sensory information to the CNS from all parts of the body
These nerves also contain the axons of motor neurons that carry signals from the CNS to glands and muscles
The motor portion of the PNS consists of 2 parts:
The somatic and Autonomic nervous systems

38. Somatic Nervous System
Controls voluntary movement
Motor neurons of the somatic nervous system form synapses with skeletal muscles and control voluntary movement
Lifting a cup of coffee or adjusting your iPod
The cell bodies of somatic motor neurons are located in the spinal cord, and their axons go directly to the muscles they control

39. Autonomic Nervous System
Controls involuntary actions
Motor neurons of the autonomic nervous system innervate the heart, smooth muscles, and glands, and produce involuntary actions
It is controlled by the hypothalamus, medulla, and pons—parts of the brain
It consists of two divisions that innervate the same organs, but with opposing actions:
The sympathetic division
The parasympathetic division

40. Sympathetic Division
The neurons of the sympathetic division release the neurotransmitter norepinephrine onto their target organs, preparing the body for stressful or energetic actions, “fight or flight”
During these activities, it directs some of the blood supply from the digestive tract to the muscles of the arms and legs
The heart rate accelerates, the pupils of the eyes open wider, and the air passages in the lungs expand

41. Parasympathetic Division
The neurons of the parasympathetic division release acetylcholine onto their target organs
The parasympathetic division controls maintenance activities that can be carried out at leisure, often called “rest and digest”
Under parasympathetic control, the digestive tract becomes active, the heart rate slows, and air passages in the lungs constrict, because the body requires less blood flow and less oxygen

42. The Autonomous Nervous System
PARASYMPATHETIC
DIVISION
SYMPATHETIC
DIVISION
constricts pupil
eye
dilates pupil
stimulates
salivation
and tears
salivary and
lacrimal glands
inhibits
salivation
and tearing
cranial
cranial
constricts
airways
lungs
relaxes
airways
cervical
reduces
heartbeat
cervical
heart
increases
heartbeat
stimulates
pancreas to
release insulin
and digestive
enzymes
liver
stimulates glucose
production and
release
pancreas
stimulates
secretion of
epinephrine and
norepinephrine
from adrenal
medulla
thoracic
kidney
thoracic
stomach
stimulates
digestion
inhibits
digestion
spleen
kidney
lumbar
dilates blood
vessels in gut
small
intestine
large
intestine
lumbar
rectum
urinary
bladder
sacral
sacral
stimulates bladder
to contract
relaxes
bladder
sympathetic
ganglia
uterus
stimulates
sexual arousal
external
genitalia
stimulates
orgasm

43. Central Nervous System
Receives and processes sensory information, generates thoughts, directs responses
The brain and spinal cord are protected from physical damage in 3 ways:
The skull surrounds the brain, and vertebrae protect the spinal cord
The triple connective tissue layer of meninges lies between the bone and spinal cord
Between the meninges layers is the cerebrospinal fluid that cushions the brain and spinal cord, and nourishes the cells

44. Extra Brain Protection
Protected from damaging chemicals by the blood–brain barrier
Capillary system is less permeable than in the rest of the body and selectively transports needed materials into the brain while keeping many dangerous substances out
The blood–brain barrier keeps water-soluble substances from diffusing from the blood into the brain, but many lipid-soluble substances can still diffuse across the capillary walls

45. Spinal Cord
Controls reflexes, conducts information to and from the brain
Nerves carrying axons of sensory neurons emerge from the dorsal part of the spinal cord, and nerves carrying axons of motor neurons emerge from the ventral part
Merge to form the spinal nerves that innervate the body
Resemble tree roots tree that merge into a single trunk, the branches are called the dorsal and ventral roots of the spinal nerves

46. Swellings on each dorsal root - dorsal root ganglia, contain the cell bodies of sensory neurons
In the center of the spinal cord is a butterfly-shaped area of gray matter
Contain cell bodies of motor neurons that control voluntary muscles and the autonomic nervous system, plus interneurons that communicate with the brain and other parts of the spinal cord

47. The Spinal Cord gray matter dorsal root contains the cell contains the
bodies of motor
neurons and
interneurons
dorsal root
contains the
axons of
sensory
neurons
white matter
contains
myelinated
axons
dorsal root
ganglion
contains the
cell bodies of
sensory neurons
spinal
nerve
ventral root
contains the axons
of motor neurons

48. White Matter
The gray matter is surrounded by white matter - contains myelin-coated axons of neurons that extend up or down the spinal cord
These axons carry sensory signals from internal organs, muscles, and the skin up to the brain
Axons also extend downward from the brain, carrying signals that direct the motor portions of the peripheral nervous system
If the spinal cord is severed, body parts innervated by motor and sensory neurons located below the injured area are paralyzed and feel numb, though the motor and sensory neurons, the spinal nerves, and the muscles remain intact

49. The Spinal Cord gray matter dorsal root contains the cell contains the
bodies of motor
neurons and
interneurons
dorsal root
contains the
axons of
sensory
neurons
white matter
contains
myelinated
axons
dorsal root
ganglion
contains the
cell bodies of
sensory neurons
spinal
nerve
ventral root
contains the axons
of motor neurons

50. Reflexes
The neuronal circuits for many reflexes reside in the spinal cord
The simplest type of behavior is the reflex, an involuntary movement of a body part in response to a stimulus
In vertebrates, many reflexes are produced by the spinal cord and peripheral neurons, and do not include the brain

51. Pain-withdrawal Reflex, an example
The pain-withdrawal reflex involves neurons of both the central and peripheral nervous systems
If you put your hand on a tack, tissue damage activates pain sensory neurons
Action potentials in the axons of pain sensory neurons travel up the spinal nerve and enter the spinal cord through a dorsal root
Within the gray matter of the cord, the pain sensory neuron stimulates an interneuron, which stimulates a motor neuron
Action potentials in the axon of the motor neuron leave the spinal cord through a ventral root and travel in a spinal nerve to a skeletal muscle
The action potential stimulates the muscle, which contracts, and you withdraw your hand from the tack

52. The Pain-withdrawal Reflex
stimulus
sensory
neuron
spinal
cord
motor
dorsal root
interneuron
ventral
root
The motor
neuron stimulates
the effector muscle
The effector
muscle causes a
withdrawal response
A painful
stimulus activates
a pain sensory
The signal is
transmitted by the
pain sensory neuron
to the spinal cord
transmitted to an
interneuron and then
to a motor neuron 4 3 2 1 5

53. Animation: Reflex Arcs

54. Many spinal cord interneurons also have axons that extend to the brain
Action potentials in these axons inform the brain about stuck hands and may trigger more complex behaviors, such as shrieks and learning about the dangers of thumbtacks
The brain sends action potentials down axons in the spinal cord white matter to interneurons and motor neurons in the gray matter, which modify spinal reflexes
With enough training, or motivation, you can suppress the pain-withdrawal reflex

55. Some complex actions coordinated within the spinal cord
The wiring for some complex activities resides within the spinal cord
All the neurons needed for basic movements of walking and running are contained in the spinal cord
The advantage of the semi-independent arrangement between brain and spinal cord increases speed and coordination, because messages do not travel up to the brain and back down, just to swing a leg forward while walking
The brain’s role in these semi-automatic behaviors is to initiate, guide, and modify spinal motor neuron activity

56. The Brain All vertebrate brains consist of three major parts:
The hindbrain - medulla, pons, and cerebellum
The midbrain
The forebrain - thalamus, hypothalamus, and cerebrum
In the earliest vertebrates, these three anatomical divisions were also functional divisions:
The hindbrain governed breathing and heart rate
The midbrain controlled vision
The forebrain dealt with the sense of smell

57. In nonmammalian vertebrates, the three divisions remain prominent
However, in mammals—particularly humans—the brain regions are significantly modified
Some have been reduced in size; others, especially the forebrain, are greatly enlarged

58. A Comparison of Vertebrate Brains
optic lobe
thalamus
cerebellum
cerebrum
medulla
midbrain
cerebrum
forebrain
midbrain
hindbrain
cerebellum
(a) Embryonic vertebrate brain
midbrain
cerebrum
cerebellum
(d) Horse brain
(b) Shark brain
cerebrum
midbrain
cerebrum
cerebellum
midbrain
(inside
cerebellum
(c) Goose brain
(e) Human brain

59. Hindbrain - Medulla
In structure and function, the medulla is like an enlarged extension of the spinal cord
Like the spinal cord, the medulla has neuron cell bodies at its center, surrounded by a layer of myelin-covered axons
It controls automatic functions - breathing, heart rate, blood pressure, swallowing

60. Hindbrain - Pons Located above the medulla,
Neurons influence transitions between sleep and wakefulness, affect the rate and pattern of breathing

61. Hindbrain - Cerebellum
Coordinates body movements
Receives information from command centers in the forebrain and position sensors in muscles and joints. By comparing information from these two sources, the cerebellum guides smooth, accurate motions and body position
The cerebellum is also involved in motor learning as a result of practice of a repeated activity

62. The Cerebral Cortex
The thin outer layer of each cerebral hemisphere, with billions of neurons packed in a highly organized way into a sheet just a few mm. thick
Folded into convolutions - raised, wrinkled ridges that increase its surface area to over two square yards
Neurons in the cortex receive sensory information, process it, direct voluntary movements, create memories, and allow us to be creative and even envision the future
The cortexes in each hemisphere communicate with each other through a band of axons, the corpus callosum

63. Midbrain
Clusters of neurons that contribute to movement, arousal, emotion
The midbrain is small in humans, and has an auditory relay center and clusters of neurons that control reflex movements of the eyes
For example, if you are sitting in class and someone races through the door, centers in your midbrain are alerted and direct your gaze to the new, and potentially interesting or threatening, visual stimulus

64. Midbrain The midbrain contains neurons that produce dopamine
Cluster of neurons, the substantia nigra, helps control movement
Another cluster is an essential part of the “reward circuit” that is responsible for pleasurable sensations and addiction
Contains a portion of the reticular formation that consists of dozens of interconnected clusters of neurons in the medulla, pons, and midbrain, which send axons to the forebrain

65. Reticular Formation
These neurons receive input from every sense, part of the body and many areas of the brain
Plays a role in sleep, wakefulness, emotion, muscle tone, and some movements and reflexes.
It filters sensory inputs before they reach the conscious regions of the brain
Activities of the reticular formation allow you to read and concentrate in the presence of a variety of distracting stimuli, such as music or smells
Example - mother who wakes hearing the faint cry of her infant, but sleeps through loud traffic noise

66. Forebrain - Thalamus
Complex relay station that channels all sensory information except olfaction, from all parts of the body to the cerebral cortex
Signals traveling from the spinal cord, cerebellum, medulla, pons, and reticular formation pass through the thalamus

67. Forebrain - Hypothalamus
Clusters of neurons that release hormones into the blood or control the release of hormones from the pituitary gland
Other regions direct activities of the autonomic nervous system
The hypothalamus, by hormone production and neural connections, maintains homeostasis by influencing body temperature, food intake, water balance, heart rate, blood pressure, the menstrual cycle, and circadian rhythms

68. Forebrain - Cerebrum Outer cerebral cortex
Two cerebral hemisphere
Outer cerebral cortex
Corpus Collosum - clusters of neurons beneath the cortex near the thalamus
Bundles of axons that interconnect the two hemispheres and connect the hemispheres to the midbrain and hindbrain

69. Structures of the interior cerebrum
The amygdala - clusters of neurons - produce sensations of pleasure, fear, or sexual arousal
The hippocampus plays an important role in the formation of long-term memory, particularly of places, and is required for learning
All vertebrates have a hippocampus
Birds, especially jays and nutcrackers, remember where they store seeds during the winter - have a larger hippocampus than other birds

70. The basal ganglia - deep within the cerebrum and substantia nigra in the midbrain
Important in the overall control of movement
The basal ganglia are essential to the decision to initiate a particular movement and to suppress other movements
Parkinson’s disease & substantia nigra
Huntington’s & basal ganglia

71. The Human Brain meninges skull FOREBRAIN (within dashed blue line)
cerebral
cortex
corpus
callosum
cerebral cortex
(gray matter)
hypothalamus
thalamus
pituitary
gland
myelinated axons
(white matter)
corpus
callosum
thalamus
MIDBRAIN
basal
ganglia
cerebellum
pons
HINDBRAIN
medulla
hypothalamus
spinal cord
hippocampus
substantia nigra
(a) A lateral section of the human brain
(b) A cross-section of the brain

72. Limbic System
A diverse group of structures
The hypothalamus, the amygdala, and the hippocampus, as well as nearby regions of the cerebral cortex, located in a ring between the thalamus and cerebral cortex
Helps to produce emotions and emotional behaviors - fear, rage, calm, hunger, thirst, pleasure, sexual responses
Other brain regions are involved in emotions, including other parts of the cerebral cortex, midbrain, hindbrain, and spinal cord

73. The Limbic System limbic region of cortex cerebral cortex
corpus callosum
thalamus
olfactory
bulb
hypothalamus
hippocampus
amygdala

74. 4 Anatomical Regions
The cerebral cortex is divided into four anatomical regions: frontal, parietal, occipital, and temporal
It can also be divided into functional areas:
Primary areas are regions where signals originating in sensory organs such as the eyes and ears are received and converted into subjective impressions
Nearby association areas interpret the sounds as speech or music, and the visual stimuli as recognizable objects or words

75. The Cerebral Cortex primary sensory area sensory association area
visual
auditory association
area: language
comprehension
memory
speech
motor area
higher
intellectual
functions
auditory
leg
trunk
arm
hand
face
tongue
Parietal
Lobe
Frontal
Temporal
Occipital
premotor

76. Primary Sensory Areas
The parietal lobe - interpret sensations of touch that originate in all parts of the body
In an adjacent region of the frontal lobe, primary motor areas command movements in corresponding areas of the body by stimulating the motor neurons in the spinal cord that innervate muscles, allowing you to walk
Like the primary sensory area, the primary motor area has adjacent association areas, including the motor association area which directs the motor area to produce movements

78. Frontal Lobe
Behind the bones of the forehead lies the association areas of the frontal lobe
They are important in complex reasoning functions such as short-term memory, decision making, predicting the consequences of actions, controlling aggression, planning for the future, and working for delayed rewards

79. Damage to the Cortex
Damage to the cortex from trauma, stroke, or a tumor results in specific deficits such as problems with speech, difficulty reading, or the inability to sense or move specific parts of the body
Most brain cells of adults cannot be replaced, so if a brain region is destroyed, these deficits may be permanent
Training sometimes allows undamaged regions of the cortex to take over and restore some of the lost functions

80. Animation: The Human Brain

81. How do neuroscientists learn about the functions of brain regions?
The functions of different parts of the brain were discovered by examining the behaviors and abilities of people who suffered brain injuries
In 1848, Phineas Gage was setting an explosive charge to clear rocks from a railroad line under construction when the gunpowder triggered prematurely
The blast blew a 13-pound steel rod through Gage’s skull, severely damaging both of his frontal lobes
Gage survived his wounds, but his personality changed radically
Before the accident, Gage was conscientious, industrious, and well-liked; after his recovery, he became impetuous, profane, and incapable of working toward a goal

82. A Revealing Accident

83. Studies of other people with brain injuries have revealed that many parts of the brain are highly specialized
One patient with damage to the left frontal lobe was unable to name fruits and vegetables, although he could name everything else
Other victims of brain damage are unable to recognize faces, suggesting that the brain has regions specialized to recognize categories of things
Modern neuroscience has powerful techniques for visualizing brain structure and activity, offering insights into the functioning of the human brain

84. Left Brain or Right Brain
Specialized for different functions
The structural brain symmetry does not extend to brain function
In the 1950s, Roger Sperry of the California Institute of Technology studied people whose hemispheres had been separated by cutting the corpus callosum to prevent the spread of epilepsy from one hemisphere to the other
Severing the corpus callosum prevented the two hemispheres from communicating with each other

85. Sperry made use of the fact that axons from the eyes, which are not severed by the surgery, follow a pathway that causes the left half of each visual field to be “seen” by the high hemisphere and the right half to be seen by the left hemisphere
Sperry used a device that projected different images onto the left and right visual fields and thus sent different signals to each hemisphere
When Sperry projected an image of a nude figure onto only the left visual field, the subjects would blush and smile, but would claim to have seen nothing
The same figure projected onto the right visual field was readily described verbally

86. Specialization of Cerebral Hemispheres
Left
HEART
Right
LEFT HEMISPHERE
Controls right side of body
Input from right visual field,
right ear, left nostril
Centers for language, speech,
reading, mathematics, logic
RIGHT HEMISPHERE
Controls left side of body
Input from left visual field,
left ear, right nostril
Centers for spatial perception,
music, creativity, recognition
of faces and emotions
retina
optic nerve
optic
chiasma
corpus
callosum
visual cortex

87. In right-handed people, the left hemisphere is dominant in speech, reading, writing, language, comprehension, mathematical ability, and logical problem solving
The right side of the brain is superior in musical skills, artistic ability, recognizing faces, spatial visualization, and the ability to recognize and express emotions
Recent experiments indicate that the left–right dichotomy is not as rigid as was once believed

88. Learning and Memory
Involve biochemical and structural changes in specific parts of the brain
Learning has two phases: working memory and long- term memory
Remembering a telephone number long enough to dial it is working memory; if the number is called often enough, it becomes remembered as long-term memory
The frontal and parietal lobes of the cerebral cortex and some of the basal ganglia deep in the cerebrum are the primary sites of working memory

89. Most working memory probably requires the repeated activity of a particular neural circuit in the brain, and as long as the circuit is active, the memory stays
In contrast, long-term memory seems to be structural and the result of persistent changes in the expression of certain genes
It may require the formation of new, long-lasting synaptic connections between specific neurons, or the long-term strengthening of existing, but weak, synapses
For many memories, converting working memory into long-term memory seems to involve the hippocampus, which is believed to process new memories and transfer them to the frontal and temporal lobes of the cerebral cortex for permanent storage