The Nervous System: The Basic Structure

The Nervous System & The Brain: The Basic StructurePsychology 12

Have you ever experienced a runners high?Its almost like running is this great friend we both shareAnyways, thats what Id like to talk to you aboutrunning as a friend, a companionin other words, the relationship of running. WHAT!? many of you will be saying, I thought that I was going to learn about how to improve my 10k time. Go read Runners World for that. You see, I dont view running as what I DO or what I AM, but as this thing, this force, that changes me over time

---from Running and Me: A Love Story by Joan Nesbit, 1999

Runners HighWhy does the writer love running so much? One of the reasons may be that people who do a lot of runningespecially long-distance running, often talk of an effect called a runners high. The longer they run, the more tired they get, of course; but at some point, the runners will push through the wall and get their second wind. Why does this happen? Endorphins, which are neurotransmitters, produce the euphoria of a runners high. As the body deals with a very physically stressful situationrunning---the runners body reacts to stress.

Question for DiscussionWhat other types of physically stressful situations may the human body encounter? How does the nervous system react?How the Nervous System WorksThe nervous system controls your emotions, movements, thinking and behaviour.Structurally, it is divided into two partsthe central nervous system [CNS] ( the brain and the spinal cord) and the peripheral nervous system [PNS] (the smaller branches of nerves that reach the other parts of the body.

How the Nervous System WorksAll parts of the nervous system are protected: the brain by the skull and several layers of sheathing, the spinal cord by the vertebrae, and the peripheral nerves by layers of sheathing. The bony protection of the spinal cord is vital. An injury to the spinal cord could prevent the transmittal of messages between the brain and the muscles, and could result in paralysis.

NeuronsMessages to and from the brain travel along nerves, which are strings of long, thin cells called NEURONS. Chemical-electrical signals travel down the neurons much as a flame travels along a firecracker fuse. The main difference is that the neuron can fire (burn) over and over again, hundreds of times a minute. Transmission between the neurons, or nerve cells, occur whenever the cells are stimulatedthe neuron fires according to the all-or-none principle (when it fires, it fires at full strength).

The Neuron ConnectionThe space between neurons is called the SYNAPSE. The synapse is a junction or connection between the neurons. A neuron transmits its impulse or message to another neuron across the synapse by releasing chemicals called NEUROTRANSMITTERS. These neurotransmitters open chemical locks or excite receptors

Neurons do not touch each othera neuron sends a message across a gap called a synapse by releasing a neurotransmitter. These neurotransmitters are received by the dendrite of another neuron.

FYI [the synapse is less than one millionth of an inch wide and is filled with fluid that transmits the chemical from one neuron to another]

NeurotransmittersThere are many types of neurotransmitters; for example,Norepinephrine: involved in learning and memoryEndorphin: inhibits painAcetylcholine: movement and memory. An undersupply is associated with paralysis and Alzheimers diseaseDopamine: Learning, emotional arousal and movement. An oversupply is linked to schizophreniaan undersupply is linked to Parkinsons diseaseSerotonin: cognitive functionsmemory and learning. It also regulates intestinal movements and mood, appetite, sleep, as well as muscle contraction. An undersupply of serotonin and norepinephrine may result in depression

Learning ActivityComplete questions 1-5 on page 159.

A Tour of the BrainWe begin our exploration of the brain at the lower end, where the spinal cord joins the base of the brain, and then continue upward toward the skull.Note that as we move from bottom to top, lower, basic processes like breathing generally give way to higher, more complex mental processes.

Tour of the BrainThe brain is the control center of the body. Made up of dense "grey matter" consisting of complicated networks of interconnected neurons, the brain can be superficially divided into three main parts: the hindbrain, the midbrain and the forebrain.

Tour of the BrainThe brain can be divided into THREE major sections: the hindbrain, midbrain, and forebrain.

Also, the large section labeled as the BRAINSTEM includes parts of all three of these3 sections and helps regulate reflex activities important to survival (ie, heartbeat and respiration)

Tour of the BrainThroughout the tour, note that certain brain structures are specialized to perform certain tasks, a process known as localization of function, but also note that most parts of the brain are not so specializedthey perform overlapping functions.

Tour of the Brain: The HindbrainHave you ever wondered what allows you to automatically breathe and your heart to keep pumpingautomatic behaviours and survival responses like these are either controlled by or influenced by parts of your hindbrain, which includes the medulla, pons and cerebellum.

Tour of the Brain: The HindbrainMedulla: Essentially is an extension of the spinal cord, with many nerve fibers passing through it carrying information to an from the brain. It also controls many essential automatic brain functions like respiration and heartbeat.

Tour of the Brain: The HindbrainCerebellum: (little brain) is evolutionarily, a very old structure. It coordinates fine muscle movement and balance. The cerebellum coordinates the muscles so that movement is smooth and precise. It is also crucial for our sense of balance and equilibrium

Tour of the Brain: The HindbrainPons: Located above the cerebellum and medulla, is involved in respiration, movement, sleeping, waking, and dreaming (among other things). It also contains many axons that cross from one side to the other (pons is Latin for bridge)

Remember Axons: Long, tube like structures that convey impulses away from the neurons cell body toward other neurons 18Tour of the Brain: The MidbrainThe midbrain is the small part of the brain that helps orient our eye and body movements to visual and auditory stimuli, and works with the pons to help control sleep and level of arousal. It also contains a small structure involved with the neurotransmitter dopamine, while deteriorates in Parkinsons disease.

19Tour of the Brain: The MidbrainRunning through the core of the hindbrain, midbrain, and brainstem is the reticular (netlike) formation (RF). This finger-shaped network of neurons filters incoming sensory information and alerts the higher brain centers to important events. Without your RF, you would not be alert or perhaps even conscious. In fact, some general anesthics target the RF so pain sensations never register in the brain.

20Tour of the Brain: The ForebrainThe Forebrain is the largest and most prominent part of the human brain. It includes the thalamus, hypothalamus, limbic system, and cerebral cortex.The first three structures are located near the top of the brainstem. Wrapped around them is the cerebral cortex (cerebrum is Latin for brain, and cortex is Latin for covering)

21Tour of the Brain: The ForebrainThalamus: Resembling two little footballs jointed side by side, the thalamus serves the major sensory relay center for the brain. Like an air traffic control centre that receives information from all aircraft and then directs them to the appropriate landing or takeoff areas, the thalamus receives input from nearly all the sensory systems and then directs this information to the appropriate areas. For example, while you are reading this, your thalamus sends incoming visual signals to the visual area of your cortex. While listening to music, the information is transferred to the auditory area of the cortex.

22Tour of the Brain: The ForebrainThalamus: In addition to relaying sensory information to the cortex it also integrates information from various senses and maybe involved in learning and memory. Injury to the thalamus can cause deafness, blindness, or loss of any other sense (except smell). Damage may cause the cortex to misinterpret or not receive vital sensory info. Interestingly, brain-imaging research links thalamus abnormalities to schizophrenia (a serious psychological disorder involving problems with sensory filtering and perception).

Thalamus: Integrates input from the senses23Tour of the Brain: The ForebrainHypothalamus: Beneath the thalamus lies the hypothalamus (hypo meaning under). Although no larger than a kidney bean, it has been called the master control centre for basic drives such as hunger, thirst, sex, and aggression. It also helps govern hormonal processes by regulating the endocrine system. Hanging down from the hypothalamus, the pituitary gland is considered the key endocrine gland because it releases hormones that activate the other endocrine glands.The endocrine system is a system of glands, each of which secretes a type of hormone into the bloodstream to regulate the body.

Hypothalamus: Controls basic drives, such as hunger24

Tour of the Brain: The ForebrainLimbic System: An interconnected group of forebrain structures, known as the limbic system, is located roughly along the border between the cerebral cortex and the lower-level brain structures (hence the term limbic, which means edge or border). Structures include the hippocampus, amygdala, thalamus, hypothalamus. Responsible for emotions, drives, and memory, and involved in forming and retrieving memories.Limbic System: Regulates fear and other emotions

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Tour of the Brain: The ForebrainLimbic System: The major focus of interest in the limbic system, and particularly the amygdala, has been its production and regulation of emotions (e.g.. aggression and fear)Also known for its role in pleasure or reward. A study done with ratsstimulating certain areas of the limbic systemcause a pleasure response. The feeling was so rewarding that he rats would cross electrified grids, swim through water (which they normally avoid), and press a lever thousands of times until they collapsed from exhaustionjust to have this area of their brains stimulated.Limbic System: Regulates fear and other emotions

Keep in mind that even though limbic system structures and neurotransmitters are instrumental in emotional behaviour, emotion in humans is also tempered by higher brain centers in the cerebral cortex. Damage to the front part of the cortex which connects to the amygdala and other parts of the limbic system, can permanently impair social and emotional behaviour. This is yet another example of the inseperable interconnectivity of the brain.26Tour of the Brain: The ForebrainCerebral Cortex: The centre for higher processing.The gray, wrinkled cerebral cortex is responsible for most complex behaviours and higher mental processes. It plays such a vital role in human life that may consider it the essence of life. Without a functioning cortex, we would be almost completely unaware of ourselves and our surroundings. Cerebral Cortex: Governs higher mental processes, such as thinking

27Tour of the Brain: The ForebrainCerebral Cortex: ConvolutionsAlthough it is only about inch thick, it is made up of approximately 30 billion neurons and nine times as many supporting cells. When spread out, the cortex would cover an area almost the size of a standard newspaper page. How does your cortex, along with all your brain structures fit inside your skull? Imagine crumpling and rolling a newspaper sheet into a ballyou would retain the same surface area, but in a much smaller space. The cortex contains wrinkles called convolutions allowing it to hold billions of neurons in the restricted space of the skull.

28Tour of the Brain: The ForebrainCerebral Cortex: HemispheresIf youve ever watch brain surgery on TVonce the skull has been opened, youll first see a gray, wrinkled, cerebral cortex that closely resembles an oversized walnut. Like a walnut, the cortex has a similar division (fissure) down the centre, which marks the left and right hemispheres of the brain. They hemispheres are connected by a band of fibers called the corpus callosum. The two hemispheres make up about 80% of the brains weight and they are mostly filled with axon connections between the cortex and other brain structures. Each hemisphere controls the opposite side of the body

29Cerebral Cortex: Hemispheres & Lobes of the BrainThe two cerebral hemispheres are divided into eight distinct areas, or lobesfour in each hemisphere. Like the lower-level brain structures, each lobe specializes in somewhat different tasksanother example of localization of function. However, some functions overlap between lobes.

30Tour of the Brain: The ForebrainCerebral Cortex: LobesFrontal Lobe: Receives and coordinates messages from other lobes; motor control, speech production, and higher functions. Includes the motor cortex which controls voluntary movements and Brocas area which controls speech productionParietal Lobe: Receives information about pressure, pain, touch, and temperature. Includes the Somatosensory cortex which receives sensory messages.Occipital Lobe: visual perception and visionincludes the Visual cortex that receives and processes visual informationTemporal Lobe: Hearing, language, comprehension, memory, and some emotional controlincludes Wernickes area that controls language comprehension

31Tour of the Brain: The ForebrainCerebral Cortex: Frontal LobesThe largest of the lobes, the two frontal lobes are located at the top front portion of the brain hemispheresright behind your forehead. They receive and coordinate messages from all other lobes, while also being responsible for at least 3 other functions:1. Higher functionsfunctions that distinguish us from other animals, such as thinking, personality, emotion, and memory. Damage to the frontal lobes affect motivation, drives, creativity, self-awareness, initiative, reasoning, and emotional behaviour. Abnormalities in FL are often observed in patients with schizophrenia

32Tour of the Brain: The ForebrainCerebral Cortex: Frontal Lobes2. Speech Production: In the left frontal lobe, on the surface of the cortex near the bottom of the motor control area lies Brocas area, which is known to play a crucial role in speech production.3. Motor Control: At the very back of the frontal lobes lies the motor cortex, which sends messages to the various muscles that instigate voluntary movement. When you call a friend on a cell phone, the motor control area of your frontal lobes guides your fingers to press the desired sequence of numbers.

In 1865, French physician Paul Broca discovered that damage to this area causes difficulty in speech, but not language comprehension. This type of impaired language ability is known as Brocas aphasia33Tour of the Brain: The ForebrainCerebral Cortex: Parietal LobesAt the top of the brain, just behind the frontal lobes, are the two parietal lobes. They contain the somatosensory cortex, which interpret bodily sensations including pressure, pain, touch, temperature, and location of body parts.When you step on a sharp nail, you quickly (and reflexively) withdraw your foot because the messages travel directly to and from your spinal cord. However, you do not experience pain until the neural messages reach the parietal lobes of the brain.

34Tour of the Brain: The ForebrainCerebral Cortex: Temporal LobesThe two temporal lobes (Latin for pertaining to the temples)are responsible for auditory perception (hearing), language comprehension, memory, and some emotional control. The auditory cortex (which processes sound) is located at the top front of each temporal lobe. This area processes incoming sensory information from the ears and sends it to the parietal lobes, where it is combined with visual and other sensory info.In the LEFT temporal lobe, Wernickes area is involved in language comprehension.

About a decade after Brocas area was discovered, a German neurologist Carl Wernicke noted patients with damage to this area could not understand what they read or heard, but they could speak quickly and easily. Unfortunately, their speech was often unintelligible. It contained made-up words, sound substitutions (girl became curl) and word substitutions (bread became cake). This syndrome is now referred to as Wernickes aphasia.35Tour of the Brain: The ForebrainCerebral Cortex: Occipital Lobes(Latin oh, in the back of, and caput, head)located at the lower back of the brain. Occipital lobes are responsible for vision and visual perception. Damage to this area can produce blindness, even though the eyes and their neural connection to the brain are perfectly healthy. The occipital lobes are involved in shape, colour, motion, and perception.

36Split-Brain ResearchSplit-Brain Surgery: Cutting of the corpus callosum to separate the brains two hemispheres. When used medically to treat severe epilepsy, split-brain patients provide data on the functions of the two hemispheres.

This information has profoundly improved our understanding of how the two halves of the brain function.

One split-brain patient found that when he dressed himself, he sometimes pulled his pants down with his left hand and up with his right. However, generally most patients show very few outward changes in behaviour, other than fewer epileptic seizures. The subtle changes normally appear only with specialized testing.37Split-Brain ResearchHemispheric Specialization: although complex activities occur in both hemispheres, specialization of function occurs in some areas Right HemisphereNonverbal Abilities: Music, art, perceptual and spatiomanipulative skills, recognition of faces, patterns and melodies, some language comprehensionEmotions: Associated with negative emotions, emotion expression, and emotion perceptionSynthetic: figures things out by combining to form wholesControls and senses the left side of the body.Left Hemisphere: Language Functions: speaking, reading, writing, and understanding languageEmotions: Associated with positive emotionsAnalytical: Figures things out step by stepControls and senses the right side of the body

In general, for most adults the left hemisphere is specialized not only for language functions (speaking, reading, writing, and understanding language), but also for analytical functions, such as mathematics. In contrast, the right hemisphere is specialized primarily for nonverbal abilities. This includes art and musical abilities and perceptual and spatiomanipulative skills, such as maneuvering through space, drawing or building model cars, painting pictures, and recognizing faces and facial expressions. In addition, the right hemisphere also contributes to complex word and language comprehension.A study reported that different aspects of personality appear in different hemispheresin one patient, the right hemisphere seemed more disturbed by childhood memories of being bullied than did the left. In other studies, the right hemisphere experienced more negative emotions, such as loneliness and sandness than did the left.38Traumatic Brain InjuriesImagine yourself as a high school football player (not too difficult for some!). If you suffered a concussion while playing a game, would you tell your coach?

Traumatic Brain InjuriesThere is mounting evidence linking multiple concussions with permanent (and possibly fatal) brain damageAccording to a report, many of the 1.2 million teenagers who play high school football either dont know what a concussion is or they simply dont care. They continue to play on and get hurt much worsesometimes fatally.Traumatic Brain InjuriesMillions of people suffer head injuries each year, and most of these injuries are minorthanks to the bony skulls protection for the brain. This is not the case for traumatic brain injuries (TBI). TBI is defined as an injury to the brain caused by significant traumaSymptoms: (range from mild to severe): headache, loss of consciousness, convulsions, coma and death. Two most common brain injuries are concussions (result from significant blow to the head) and contusions (bruises to the brain). Either TBI can result in prolonged or nonreversible brain damage and serious problems, such as extreme changes in personality, significant loss of motor skills, emotional control, and mental abilitiesThe BrainA) Questions: Answer questions 3, 4 & 5 on page 168.

B) Read the Case Study on page 169

Answer the following questions:How does split-brain surgery benefit both the patient and humans in general? Should split-brain surgery ever be performed on a person with no brain disorders?Complete questions 1-3 from the case study.

The Model BrainLets work with our right hemispheric spatiomanipulative skillswe are going to build a 3-D version of the brain. Objective: To gain a better understanding of the location and function of the parts of the brain

Using your textbook, the slides and the chart you created yesterday as guides, create a 3-D cross section of the left side of the brain, making sure to include all the structures listed in your charts (obviously, none from the right hemisphere)Use a numbering system on the appropriate sections of the brain (attached with sticky notes & toothpicks) and write the corresponding names of the structures and their functions on card stock (recipe cards)..

43Cross-section of the Brain

Time Reports: Lots of Action in the Memory GameRead the Time article on page 180-1. Answer the Analyzing the Article Questions 1-2