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Chapter 12 The Central Nervous System

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1 Chapter 12 The Central Nervous System

2 Central Nervous System (CNS)
CNS consists of the brain and spinal cord Cephalization Evolutionary development of a head and CNS Increased number of neurons in the head Highest level is reached in the human brain

3 Regions and Organization of the CNS
Adult brain regions Cerebral hemispheres Diencephalon Brain stem (midbrain, pons, and medulla) Cerebellum Cerebral Hemispheres – the superior part of the brain – 83% of the total brain Diencephalon – situated internally between the hemispheres and includes the thalamus, epithalamus, and hypothalamus Brain stem – below the diencephalon and include the midbrain, pons, and medulla Cerebellum – Distal, posterior aspect of the brain

4 Regions and Organization of the CNS
Spinal cord Central cavity of gray matter core External white matter composed of myelinated fiber tracts

5 Ventricles of the Brain
Connected to one another and to the central canal of the spinal cord Lined by ependymal cells

6 Ventricles of the Brain
Contain cerebrospinal fluid Two C-shaped lateral ventricles in the cerebral hemispheres Third ventricle in the diencephalon Fourth ventricle in the hindbrain, above the pons, develops from the lumen (opening) of the neural tube Ventricles are continous with one another and with the central canal of the spinal cord Lateral ventricles connect to third ventricle by the interventricular foramen Third ventricle is continuous with the fourth ventricle through the cerebral aqueduct

7 Cerebral Hemispheres Surface markings
Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures) Five lobes Frontal Parietal Temporal Occipital Insula gyri are elevated ridges on the brain Sulci are grooves Deeper grooves are called fissures All separate the regions of the brain

8 Cerebral Hemispheres Surface markings Central sulcus
Separates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobe Longitudinal fissure Separates the two hemispheres Transverse cerebral fissure Separates the cerebrum and the cerebellum Central sulcus almost seperates front to back Longitudinal is left and right division Transverse is cerebellum from rest of brain

9 Anterior Longitudinal Frontal lobe fissure Cerebral veins and arteries
covered by arachnoid mater Parietal lobe Left cerebral hemisphere Right cerebral hemisphere Occipital lobe (c) Posterior Figure 12.6c

10 Left cerebral hemisphere Transverse cerebral fissure Brain stem
Cerebellum (d) Figure 12.6d

11 Cerebral Cortex Thin (2–4 mm) superficial layer of gray matter
40% of the mass of the brain Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding Each hemisphere connects to contralateral side of the body There is lateralization of cortical function in the hemispheres Concious mind is found here Billions of neurons arranged in six layers Lateralization – right controls left and visce versa

12 Functional Areas of the Cerebral Cortex
The three types of functional areas are: Motor areas—control voluntary movement Sensory areas—conscious awareness of sensation Association areas— learning, decision making, complex movements Conscious behavior involves the entire cortex

13 Motor Areas Primary (somatic) motor cortex Premotor cortex
Frontal lobe Consciously control precise/skilled movements Spatial representation Premotor cortex Learned motor skills (repetitions, patterns) Planned movement Broca’s area Usually only in one hemisphere Motor speech area (thinking, planning, and performing) Frontal eye field Voluntary eye movement Spatial representation means that the movements for foot are in one area and the movements for hand are in another – mapping of these areas is called somatotropy – this leads to hominiculi Motor Hominiculus – upside down representation of the human body as represented by the mapping of brain areas Premotor cortex is the memory bank for skilled movement and also for planning movements

14 Sensory Areas Primary somatosensory cortex
Somatosensory association cortex Visual areas Auditory areas Olfactory cortex Gustatory cortex Visceral sensory area Vestibular cortex

15 Primary Somatosensory Cortex
Located just behind the primary motor cortex In the postcentral gyri Receives sensory information from the skin, skeletal muscles, and joints Capable of spatial discrimination: identification of body region being stimulated

16 Somatosensory Association Cortex
Posterior to the primary somatosensory cortex Integrates sensory input from primary somatosensory cortex – pressure, temperature, etc. Determines size, texture, and relationship of parts of objects being felt Allows you use stored memories to help with perceptions of objects

17 Visual Areas - Sight Primary visual (striate) cortex
Extreme posterior tip of the occipital lobe Receives visual information from the retinas Visual association area Surrounds the primary visual cortex Uses past visual experiences to interpret visual stimuli (e.g., color, form, and movement) Visual streams-2 of them Dorsal stream-motion, representation of object locations, and control of the eyes and arms – “where pathway” Ventral Stream -form recognition and object representation – “what pathway”

18 Auditory Areas - Hearing
Primary auditory cortex Superior margin of the temporal lobes Interprets information from inner ear as pitch, loudness, and location Auditory association area Located posterior to the primary auditory cortex Stores memories of sounds and permits perception of sounds

19 OIfactory Cortex - Smell
Medial aspect of temporal lobes Region of conscious awareness of odors Closely associated with the limbic system so there are emotional ties to odors

20 Gustatory Cortex - Taste
In the insula just below the temporal lobe Involved in the perception of taste

21 Visceral Sensory Area – Physical Feeling
Posterior to gustatory cortex Conscious perception of visceral sensations, e.g., upset stomach or full bladder, lungs bursting

22 Vestibular Cortex - Balance
Posterior part of the insula and adjacent parietal cortex Responsible for conscious awareness of balance (position of the head in space)

23 Multimodal Association Areas
Receive inputs from and sends outputs to multiple sources Give meaning to information received Store it as memory compare it to previous experience, and decide on action to take Area where sensations, thoughts, and emotions become conscious Three parts Anterior association area (prefrontal cortex) Posterior association area Limbic association area

24 Anterior Association Area (Prefrontal Cortex)
Most complicated cortical region Involved with intellect, cognition, recall, and personality Contains working memory needed for judgment, reasoning, persistence, and conscience Development depends on feedback from social environment This area is very slow to develop and requires continous training and input. Tumors of this region are thought to cause many personality disorders – loss of judgements, physcotic disorders

25 Posterior Association Area
Large region in temporal, parietal, and occipital lobes Plays a role in recognizing patterns and faces and localizing us in space Wernicke’s area - Involved in understanding written and spoken language Also plays a role in attention to ones space in an area or attention to a specific area Tumors in this region may cause a person to not wash or care for themselves because the brain may be telling them that doesn’t belong to me

26 Limbic Association Area
Part of the limbic system Provides emotional impact that helps establish memories Tells you if something is dangerous or pleasant with a situation Also associated with the olfactory system so odors do give a strong emotional response

27 Lateralization of Cortical Function
Division of labor between hemispheres Cerebral dominance Designates the hemisphere dominance (left hemisphere in 90% of people) Left hemisphere Controls language, math, and logic Right hemisphere Insight, visual-spatial skills, intuition, and artistic skills Left and right hemispheres communicate via fiber tracts in the cerebral white matter Left hemisphere has greater dominance over language, math, and logic – works to make sentences, balance check books, or memorize lists Right hemisphere is free spirited – visual spatial skills, intuition, emotion, and artistic skills

28 Cerebral White Matter Responsible for communication
Commissures (in corpus callosum)—connect gray matter of the two hemispheres Association fibers — connect different parts of the same hemisphere Projection fibers — (corona radiata) connect the hemispheres with lower brain or spinal cord

29 Diencephalon Three paired structures Encloses the third ventricle
Thalamus Hypothalamus Epithalamus Encloses the third ventricle Thalamus Hypothalamus Pineal Gland (part of epithalamus)

30 Thalamus 80% of diencephalon
Superolateral walls of the third ventricle Sorts, edits, and relays information Mediates sensation, motor activities, cortical arousal, learning, and memory Relay station for information coming into cerebral cortex

31 Hypothalamus Forms the inferolateral walls of the third ventricle
Main visceral control center Center for emotional response: Involved in perception of pleasure, fear, and rage and in biological rhythms and drives Regulates body temperature, food intake, water balance, and thirst Regulates sleep and the sleep cycle Controls release of hormones by the anterior pituitary Produces posterior pituitary hormones Digestive tract motility

32 Brain Stem Three regions Midbrain Pons Medulla oblongata
Midbrain would be behind the structures

33 Brain Stem Similar structure to spinal cord
Controls automatic behaviors necessary for survival Contains fiber tracts connecting higher and lower neural centers Associated with 10 of the 12 pairs of cranial nerves

34 Midbrain Located between the diencephalon and the pons
Visual reflex centers Auditory relay centers Relay centers for some of the motor pathways

35 Pons Forms part of the anterior wall of the fourth ventricle
Fibers of the pons Connect higher brain centers and the spinal cord Relay impulses between the motor cortex and the cerebellum Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial) Some nuclei of the reticular formation Nuclei that help maintain normal rhythm of breathing

36 Joins spinal cord at foramen magnum
Medulla Oblongata Joins spinal cord at foramen magnum Forms part of the ventral wall of the fourth ventricle Relay center for information from muscles and joints to cerebellum Mediates responses to help with equilibrium Other relay centers for sensory information

37 Autonomic reflex centers Cardiovascular center
Medulla Oblongata Autonomic reflex centers Cardiovascular center Cardiac center adjusts force and rate of heart contraction Vasomotor center adjusts blood vessel diameter for blood pressure regulation

38 Medulla Oblongata Respiratory centers Generate respiratory rhythm
Control rate and depth of breathing, with pontine centers Additional centers regulate Vomiting Hiccuping Swallowing Coughing Sneezing

39 The Cerebellum 11% of brain mass Dorsal to the pons and medulla
Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction Two hemispheres connected by vermis Each hemisphere has three lobes Anterior, posterior, and flocculonodular Cerebellum receives impulses from the cerebral cortex of the intent to initiate voluntary muscle contraction Signals from proprioceptors and visual and equilibrium pathways continuously “inform” the cerebellum of the body’s position and momentum Cerebellar cortex calculates the best way to smoothly coordinate a muscle contraction A “blueprint” of coordinated movement is sent to the cerebral motor cortex and to brain stem nuclei

40 Cognitive Function of the Cerebellum
Recognizes and predicts sequences of events during complex movements Plays a role in nonmotor functions such as word association and puzzle solving

41 Functional Brain Systems
Networks of neurons that work together and span wide areas of the brain Limbic system Reticular formation

42 Limbic System Emotional or affective brain
Cingulate gyrus Emotional or affective brain Amygdala — recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response Cingulate gyrus — plays a role in expressing emotions via gestures, and resolves mental conflict Puts emotional responses to odors Example: skunks smell bad The limbic system interacts with the prefrontal lobes, therefore: We can react emotionally to things we consciously understand to be happening We are consciously aware of emotional richness in our lives Hippocampus and amygdala—play a role in memory Most limbic system output is through the hypothalamus (where visceral functions are controlled) can cause physcosomatic illnesses – HBP, heartburn Admygdala

43 Reticular Formation: RAS and Motor Function
RAS (reticular activating system) Sends impulses to the cerebral cortex to keep it conscious and alert Filters out repetitive and weak stimuli (~99% of all stimuli!) Severe injury results in permanent unconsciousness (coma) Reticular Formation Three broad columns along the length of the brain stem Raphe nuclei Medial (large cell) group of nuclei Lateral (small cell) group of nuclei Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord LSD interferes with RAS which promotes sensory overload Alcohol and other drugs depress the RAS becasuse the RAS system is inhibited by the sleep center of the hypthalamus Motor function Helps control coarse limb movements Reticular autonomic centers regulate visceral motor functions Vasomotor Cardiac Respiratory centers

44 Language Language implementation system
Broca’s area and Wernicke’s area (in the association cortex on the left side) Analyzes incoming word sounds Produces outgoing word sounds and grammatical structures Corresponding areas on the right side are involved with nonverbal language components Lesions in Broca’s area can understand language, but have difficulty speaking Lesions in Wernicke’s area cause words to be jarballed

45 Storage and retrieval of information Two stages of storage
Memory Storage and retrieval of information Two stages of storage Short-term memory (STM, or working memory)—temporary holding of information; limited to seven or eight pieces of information Long-term memory (LTM) has limitless capacity Capacity of STM is about 7-8 digits However, long term memory can be deleted

46 Transfer from STM to LTM
Factors that affect transfer from STM to LTM Emotional state—best if alert, motivated, surprised, and aroused Rehearsal—repetition and practice Association—tying new information with old memories Automatic memory—subconscious information stored in LTM Damage to hippocampus and temporal region can result in either slight memory loss (if one side) or massive loss Old memories may not be lost, but association to new ones does nt occur and the person lives in the now (anterograde) Retrograde is loss of past memories (can not recover old memories)

47 Categories of Memory Declarative memory (factual knowledge)
Explicit information Related to our conscious thoughts and our language ability Stored in LTM with context in which it was learned Nondeclarative memory Less conscious or unconscious Acquired through experience and repetition Best remembered by doing; hard to unlearn Includes procedural (skills) memory, motor memory, and emotional memory

48 Protection of the Brain
Bone (skull) Membranes (meninges) Watery cushion (cerebrospinal fluid) Blood-brain barrier

49 Meninges Cover and protect the CNS
Protect blood vessels and enclose venous sinuses Contain cerebrospinal fluid (CSF) Form partitions in the skull Three layers Dura mater Arachnoid mater Pia mater Dura Strongest meninx Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses Arachnoid Middle layer with weblike extensions Separated from the dura mater by the subdural space Subarachnoid space contains CSF and blood vessels Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption Pia mater Layer of delicate vascularized connective tissue that clings tightly to the brain

50 Cerebrospinal Fluid (CSF)
Composition Watery solution Less protein and different ion concentrations than plasma Constant volume Functions Gives buoyancy to the CNS organs Protects the CNS from blows and other trauma Nourishes the brain and carries chemical signals Volume in adults is about 150ml or half a cup Replaced about every 8 hours CSF reduces brain weight by 97% Choriod plexus Produce CSF at a constant rate If not drained creates a condition known as hydrocephalus which can cause the head to expand in infants, but in adults can be a serious and deathly condition – pressure can be relieved with a shunt which drains the fluid into the abdominal cavity

51 Helps maintain a stable environment for the brain
Blood-Brain Barrier Composition Continuous endothelium of capillary walls Basal lamina Astrocytes Helps maintain a stable environment for the brain Separates neurons from some bloodborne substances

52 Blood-Brain Barrier: Functions
Selective barrier Allows nutrients to move by facilitated diffusion Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics Absent in some areas, e.g., vomiting center and the hypothalamus, where it is necessary to monitor the chemical composition of the blood

53 Homeostatic Imbalances of the Brain
Traumatic brain injuries Concussion—temporary alteration in function Contusion—permanent damage Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death Cerebral edema—swelling of the brain associated with traumatic head injury

54 Homeostatic Imbalances of the Brain
Cerebrovascular accidents (CVAs)(strokes) Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot Typically leads to hemiplegia, or sensory and speed deficits Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia Tissue plasminogen activator (TPA) Tissue plaminogen activator These statements must be true in order to consider tPA administration: Ischemic stroke onset within 3 hours of drug administration. Measurable deficit on NIH Stroke Scale examination. Patient's computed tomography (CT) does not show hemorrhage or nonstroke cause of deficit. Patient's age is >18 years. tPA ContraindicationsDo NOT administer tPA if any of these statements are true: Patient's symptoms are minor or rapidly improving. Patient had seizure at onset of stroke. Patient has had another stroke or serious head trauma within the past 3 months. Patient had major surgery within the last 14 days. Patient has known history of intracranial hemorrhage. Patient has sustained systolic blood pressure >185 mmHg. Patient has sustained diastolic blood pressure >110 mmHg. Aggressive treatment is necessary to lower the patient's blood pressure. Patient has symptoms suggestive of subarachnoid hemorrhage. Patient has had gastrointestinal or urinary tract hemorrhage within the last 21 days. Patient has had arterial puncture at noncompressible site within the last 7 days. Patient has received heparin with the last 48 hours and has elevated PTT. Patient's prothrombin time (PT) is >15 seconds. Patient's platelet count is <100,000 uL. Patient's serum glucose is <50 mg/dL or >400 mg/dL.

55 Homeostatic Imbalances of the Brain
Degenerative brain disorders Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia Parkinson’s disease: degeneration of the dopamine-releasing neurons of the substantia nigra Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex

56 Spinal Cord Location Functions Begins at the foramen magnum
Ends as conus medullaris at L1 vertebra Functions Provides two-way communication to and from the brain Contains spinal reflex centers

57 Spinal Cord: Protection
Bone, meninges, and CSF Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater CSF in subarachnoid space

58 Spinal Cord Spinal nerves Cervical and lumbar enlargements
31 pairs Cervical and lumbar enlargements The nerves serving the upper and lower limbs emerge here Cauda equina The collection of nerve roots at the inferior end of the vertebral canal

59 Cross-Sectional Anatomy
Two lengthwise grooves divide cord into right and left halves Ventral (anterior) median fissure Dorsal (posterior) median sulcus Gray commissure—connects masses of gray matter; encloses central canal

60 Gray Matter Dorsal horns—interneurons that receive somatic and visceral sensory input Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons Dorsal root (spinal) gangia—contain cell bodies of sensory neurons

61 White Matter Consists mostly of ascending (sensory) and descending (motor) tracts Transverse tracts (commissural fibers) cross from one side to the other Tracts are located in three white columns (funiculi on each side—dorsal (posterior), lateral, and ventral (anterior) Each spinal tract is composed of axons with similar functions

62 Spinal Cord Cross Section

63 Spinal Cord Trauma Functional losses Parasthesias Sensory loss
Paralysis Loss of motor function Palsy Weakness that is reversible Nerve Palsy - Weakness or failure due to injury of a nerve; it is usually short term, but immediate support is necessary..

64 Spinal Cord Trauma Flaccid paralysis—severe damage to the ventral root or ventral horn cells Impulses do not reach muscles; there is no voluntary or involuntary control of muscles Muscles atrophy Spastic paralysis—damage to upper motor neurons of the primary motor cortex Spinal neurons remain intact; muscles are stimulated by reflex activity No voluntary control of muscles

65 Spinal Cord Trauma Transection
Cross sectioning of the spinal cord at any level Results in total motor and sensory loss in regions inferior to the cut Paraplegia—transection between T1 and L1 Quadriplegia—transection in the cervical region

66 Destruction of the ventral horn motor neurons by the poliovirus
Poliomyelitis Destruction of the ventral horn motor neurons by the poliovirus Muscles atrophy Death may occur due to paralysis of respiratory muscles or cardiac arrest Survivors often develop postpolio syndrome many years later, as neurons are lost slowly progressive muscle weakness, fatigue (both generalized and muscular), and,a gradual decrease in the size of muscles (muscle atrophy).   Pain from joint degeneration and increasing skeletal deformities such as scoliosis are common may precede the weakness and muscle atrophy

67 Amyotrophic Lateral Sclerosis (ALS)
Also called Lou Gehrig’s disease Involves progressive destruction of ventral horn motor neurons and fibers of the pyramidal tract Symptoms—loss of the ability to speak, swallow, and breathe Death typically occurs within five years Linked to glutamate excitotoxicity, attack by the immune system, or both

68 Other Spinal Cord Disorders
Cerebral Palsy Poor control of voluntary muscles May be due to a lack of oxygen during development Spina bifida Incomplete formation of vertebral arches Lumbar myelomenigocele Myelomenigocele – sac that contains CSF or meniges or even cord

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