The Central Nervous System

Transcription

1 The Central Nervous System 1 The Central Nervous System Brain Spinal Cord Components 2 Protection of the Brain The brain is protected from injury by The skull enough said! You already know this. What else protects your Brain? 3 1

2 Protection of the Brain The Meninges Cover and protect the CNS Enclose and protect the vessels that supply the CNS Contain the cerebrospinal fluid Consists of three layers Dura Mater Arachnoid Layer Pia Mater 4 The Meninges 5 Protection of the Brain Cerebrospinal Fluid (CSF) Provides a liquid cushion for the brain and spinal cord The brain floats in CSF Formed in choroid plexuses in the brain ventricles 6 2

3 Protection of the Brain CSF Circulation of CSF 7 Protection of the Brain CSF Reabsorption of CSF 8 Protection of the Brain Blood Brain Barrier Prevents most blood borne toxins from entering the brain Impermeable capillaries, surrounded by astrocyte projections creating a double layer, throw in some tight junctions and it works pretty effectively! Not an absolute barrier Nutrients such as oxygen pass through Allows alcohol, nicotine, and anesthetics through 9 3

4 Brain Ventricles Ventricles General Information Expansions of the brain s central cavity Filled with cerebrospinal fluid Lined with ependymal cells Continuous (interconnected) with each other Though flow of CSF is unidirectional Continuous with the central canal of the spinal cord 10 Brain Ventricles The brain s ventricles and associated structures: Lateral ventricles located in cerebral hemispheres Horseshoe shaped from bending of the cerebral hemispheres Third ventricle lies in diencephalon Connected with lateral ventricles by interventricular foramen Cerebral aqueduct connects 3rd and 4th ventricles Fourth ventricle lies in hindbrain Connects to the central canal of the spinal cord Contains median and lateral aperatures 11 Brain Ventricles 12 4

5 Brain Components & Organization Brain is divided into four general regions: Cerebral hemispheres Diencephalon Brain stem Cerebellum All of which contains gray & white matter 13 Brain Components & Organization Organization of neural matter (gray vs. white) Deeply (internally) located gray matter Intermediately located white matter Additional layer of gray matter superficial to white matter Due to groups of neurons migrating externally Forms the Cortices outer layers of gray matter Formed from neuronal cell bodies Located in cerebrum and cerebellum (the cerebral cortex & cerebellar cortex respectively) 14 The Cerebral Hemispheres General Information & Terminology Account for 83% of brain mass Superficial thin (1 2 mm) cortex & a deep cortex Deep white matter with localized centers of gray matter (basal ganglia) Fissures deep grooves separate major regions of the brain, generally have dura mater in the fissure Transverse fissure separates cerebrum and cerebellum Longitudinal fissure separates cerebral hemispheres 15 5

6 The Cerebral Hemispheres Sulci shallow grooves on the surface of the cerebral hemispheres, does not contain dura mater in the sulci Several deep sulci define the lobes (which are named according to the overlying skeletal structures) Central sulcus» Separates the frontal and parietal lobes Parieto occipital sulcus» Separates the occipital from the parietal lobe Lateral sulcus» Separates temporal lobe from parietal and frontal lobes 16 The Cerebral Hemispheres Gyri twisted ridges between sulci Important gyri Prominent gyri and sulci are similar in all people Insula deep region within the lateral sulcus Has it s own cortex 17 The Cerebral Hemispheres Frontal section through forebrain showing organization of gray and white matter Cerebral cortex Cerebral white matter Deep gray matter of the cerebrum (basal nuceli/ ganglia) 18 6

7 The Cerebral Cortex Composed of gray matter Neuronal cell bodies, dendrites, and short axons, axon terminals, synapses Folds in cortex triples its size Unfolded gives a surface about that of a pillowcase Approximately 40% of brain s mass Brodmann areas 52 structurally distinct areas 19 Functional and Structural Areas of the Cerebral Cortex Figure 13.11a 20 Functional and Structural Areas of the Cerebral Cortex Figure 13.11b 21 7

8 The Cerebral Cortex Motor Areas Primary Motor Cortex Controls motor functions Located in precentral gyrus (Brodmann area 4) Pyramidal cells large neurons of primary motor cortex Corticospinal tracts descend through brainstem and spinal cord Axons signal motor neurons to control skilled movements Contralateral pyramidal axons cross over to opposite side of the brain 22 The Cerebral Cortex Motor Areas Primary Motor Cortex Motor homunculus body map of the motor cortex Specific pyramidal cells control specific areas of the body Face and hand muscles controlled by many pyramidal cells Somatotopy body is represented spatially in many parts of the CNS 23 The Cerebral Cortex Sensory Areas Primary Somatosensory Cortex Located at/on/in the postcentral gyrus Corresponds to Brodmann areas 1 3 Involved with conscious awareness of general somatic senses Spatial discrimination precisely locates a stimulus 24 8

9 Cerebral Cortex Sensory Areas Primary Somatosensory Cortex Projection is contralateral In that the cerebral hemispheres receive sensory input from the opposite side of the body Sensory homunculus a body map of the sensory cortex Cerebral White Matter Figure 13.13a 27 9

10 Deep Gray Matter of the Cerebrum Consists of: Basal forebrain nuclei (Meynert s nucleus) Basal nuclei (ganglia) Caudate nucleus Lentiform nucleus Putamen Globus pallidus Claustrum Amygdala located in cerebrum but is considered part of the of the limbic system 28 The Diencephalon Forms the center core of the forebrain Surrounded by the cerebral hemispheres Composed of three paired structures: Thalamus, hypothalamus, and epithalamus Border the third ventricle Primarily composed of gray matter 29 The Diencephalon 30 10

11 The Diencephalon The Thalamus Makes up 80% of the diencephalon Contains approximately a dozen major nuclei Send axons to regions of the cerebral cortex Nuclei act as relay stations for incoming sensory messages Afferent impulses converge on the thalamus Synapse in at least one of its nuclei Is the gateway to the cerebral cortex Nuclei organize and amplify or tone down signals 31 The Thalamus 32 The Diencephalon The Hypothalamus Lies between the optic chiasm and the mammillary bodies Pituitary gland projects inferiorly Contains approximately a dozen nuclei Main visceral (autonomic) control center of the body 33 11

12 The Diencephalon The Epithalamus Forms part of the roof of the third ventricle Includes the pineal gland (pineal body) Secretes the hormone melatonin Under influence of the hypothalamus Epithalamus highlighted in red 34 The Brain Stem and Diencephalon Figure 13.20a, 35b The Brain Stem Includes the Midbrain Pons medulla oblongata Several general functions Produces automatic behaviors necessary for survival Passageway for all fiber tracts running between the cerebrum and spinal cord Heavily involved with the innervation of the face and head 10 of the 12 pairs of cranial nerves attach to it 36 12

13 The Brain Stem The Midbrain Lies between the diencephalon and the pons Central cavity the cerebral aqueduct with gray matter surrounding (periaqueductal gray matter) Cerebral peduncles located on the ventral surface of the brain Contain pyramidal (corticospinal) tracts Superior cerebellar peduncles Connect midbrain to the cerebellum Corpora quadrigema large nuclei Superior & Inferior colliculi visual and auditory reflex centers 37 The Brain Stem The Pons Located between the midbrain and medulla oblongata Contains the nuclei of cranial nerves V, VI, and VII Contains the pneumotaxic and apneustic centers of respiration 38 The Brain Stem The Medulla Oblongata Most caudal level of the brain stem Continuous with the spinal cord Choroid plexus lies in the roof of the fourth ventricle Pyramids of the medulla lie on its ventral surface Decussation of the pyramids crossing over of motor tracts Cranial nerves VIII XII attach to the medulla 39 13

14 The Brain Stem The Medulla Oblongata The core of the medulla contains: Additional nuclei of the reticular formation Nuclei influence autonomic functions Cardiac center Vasomotor center The medullary respiratory center Centers for hiccupping, sneezing, swallowing, and coughing 40 The Cerebellum Located dorsal to the pons and medulla Consists of two cerebellar hemispheres Surface folded into ridges called folia Separated by fissures Hemispheres each subdivided into: Anterior lobe Posterior lobe Flocculonodular lobe Functionally Smoothes and coordinates body movements Helps maintain equilibrium & body posture 41 The Cerebellum Cerebellar Peduncles Thick tracts connecting the cerebellum to the brain stem Superior cerebellar peduncles Middle cerebellar peduncles Inferior cerebellar peduncles Fibers to and from the cerebellum are ipsilateral Run to and from the same side of the body 42 14

15 The Spinal Cord Runs through the vertebral canal Extends from the foramen magnum to the level of the vertebra L 1 or L 2 Protected by bone, meninges, and CSF Dura mater of the spinal cord The spinal dural sheath only one layer 43 The Spinal Cord Conus medullaris the inferior end of the spinal cord Filum terminale long filament of connective tissue Attaches to the coccyx inferiorly Cervical and lumbar enlargements Where nerves for upper and lower limbs arise Cauda equina collection of nerve roots 44 The Spinal Cord Denticulate ligaments anchor spinal cord to vertebrae Two deep grooves run the length of the cord Posterior median sulcus Anterior median fissure 45 15

16 Anatomy of the Spinal Cord Figure 13.30a 46 Anatomy of the Spinal Cord Figure 13.30b 47 Gray Matter of the Spinal Cord and Spinal Roots Shaped like the letter H, or a butterfly Gray commissure contains the central canal Anterior horns contain cell bodies of motor neurons Posterior & lateral horns consist of interneurons Gray matter divided according to somatic and visceral regions 48 16

17 Gray Matter of the Spinal Cord and Spinal Roots Figure White Matter of the Spinal Cord Composed of myelinated and unmyelinated axons Three types of fibers Ascending, Descending & Commissural 50 Sensory and Motor Pathways Most motor pathways: Decussate at some point along their course Consist of a chain of two or three neurons Exhibit somatotopy Tracts arranged according to the body region they supply All pathways are paired One of each on each side of the body 51 17

18 Ascending (Sensory) Pathways Conduct general somatic sensory impulses Chains of neurons composed of: First, second, and third order neurons Four main ascending pathways Dorsal column pathway Spinothalamic pathway Spinocerebellar Pathway Composed of anterior & posterior spinocerebellar pathways 52 A s c e n d i n g P a t h w a y s 53 Descending (Motor) Pathways Deliver motor instructions from the brain to the spinal cord Divided into two groups Pyramidal, or corticospinal, tracts Other motor pathways Tectospinal tracts responsible for coordinating head and eye movements Vestibulospinal tract responsible for equilibrium and balance movements Rubrospinal tract responsible for large movements of the appendages (mostly in other primates nearly absent in humans) Reticulospinal tract regulate muscle tone in the anti gravity muscles (postural) 54 18

19 D e s c e n d i n g P a t h w a y s 55 Neat Brain Atlas (real!)

20 Additional Detail & Interesting Reading Material (Hint READ IT) 58 Disorders of the Central Nervous System Brain dysfunction Traumatic brain injuries Concussion brain injury is slight Contusion marked destruction of brain tissue Degenerative brain diseases Cerebrovascular accident (stroke) Blockage or interruption of blood flow to a brain region Alzheimer s disease Progressive degenerative disease leading to dementias 59 Disorders of the Central Nervous System Spinal cord damage Paralysis loss of motor function Parasthesia loss of sensation Paraplegia injury to the spinal cord is between T 1 and L 2 Paralysis of the lower limbs Quadriplegia injury to the spinal cord in the cervical region Paralysis of all four limbs 60 20

21 Disorders of the Central Nervous System Congenital malformations Hydrocephalus Neural tube defects Anencephaly cerebrum and cerebellum are absent Spina bifida absence of vertebral lamina Cerebral palsy voluntary muscles are poorly controlled Results from damage to the motor cortex 61 Development of the Brain Brain arises from Secondary the brain vesicles Nueral tube formed rostral part of the neural tube develop from primary brain during week three of Three primary brain vesicles embyronic vesicles in 4 week development embryo telencephalon & diencephalon Prosencephalonfrom the prosencephalon If you want a the forebrain Mesencephalon remains refresher, go back and Mesencephalonundivided review this week s the midbrain metencephalon and developmental events. Rhombencephalon myelencephalon develop from the hindbrain the rhombencephalon Leading to Brain grows rapidly, and changes occur in the relative position of its parts Cerebral hemispheres enlarge & envelop the diencephalon and midbrain Wrinkling of the cerebral hemispheres?? Development of the Brain (Week 5 Birth) 63 21

22 Structure Location Functions Hindbrain Medulla Pons Cerebellum Reticular Formation Midbrain superior & inferior colliculus at the top of the spinal cord above the medulla at the lower rear a network of nerves extends from the medulla to the cerebrum above the pons between the hindbrain and forebrain controls breathing, heart rate, and blood pressure. regulates sensory information and facial expressions. controls movement, coordination, balance, muscle tone, and learning motor skills. monitors the general level of activity in the hindbrain and maintains a state of arousal; essential for the regulation of sleep and wakefulness. relays sensory information from the spinal cord to the forebrain. Pineal Gland on top of the midbrain behind the thalamus involves in circadian and circannual rhythms; possibly involves in maturation of sex organs. 64 Limbic System Thalamus Hypothalamus, Pituitary Gland Optic Chiasm Septum Hippocampus Amygdala Mammillary Body, Fornix Caudate Nucleus, Putamen, Globus Pallidus, Basal Ganglia (Striatum) in the middle of the limbic system beneath thalamus in front of the pituitary gland adjacent to hypothalamus within the temporal lobe in front of the hippocampus linked to the hippocampus outside the thalamus relays incoming information (except smell) to the appropriate part of the brain for further processing. regulates basic biological drives, hormonal levels, sexual behavior, and controls autonomic functions such as hunger, thirst, and body temperature. left-right optic nerves cross-over point. stimulates sexual pleasure mediates learning and memory formation. responsible for anxiety, emotion, and fear have a role in emotional behavior, learning, and motivation. involves in movement, emotions, planning and in integrating sensory information 65 Cingulate Gyrus Corpus Callosum Forebrain Frontal Lobe (Conscious Brain) Prefrontal Cortex Parietal Lobe Occipital Lobe Temporal Lobe above corpus callosum under the cingulate gyrus in front of the head in front of the frontal lobe in top rear of the head in the back of the head on each side of the head above the temples concentrates attention on adverse internal stimuli such as pain, contains the feeling of self. is a bundle of nerve fibers linking the cerebral hemispheres, involve in language learning. controls voluntary movement, thinking, and feeling. inhibits inappropriate actions, forms plans and concepts, helps focus attention, and bestows meaning to perceptions. contains the primary somatosensory area that manages skin sensation. contains the visual cortex to manage vision. contains the auditory cortex to manage hearing and speech

23 Lateralization of Cortical Functioning The two hemispheres control opposite sides of the body Hemispheres are specialized for different cognitive functions Left cerebral hemisphere more control over: Language abilities, math, and logic Right cerebral hemisphere more involved with: Visual spatial skills Reading facial expressions Intuition, emotion, artistic and musical skills 67 Female/Male Brain Differences 1.Men's brains are larger, but as they age, they also shrink faster than women's brains. 2. Women's brains operate at a higher temperature, due to burning more glucose. 3. Women use more of their brains when they think. 4. Men's brains contain roughly 6.5 times the amount of grey matter related to general intelligence as women's brains, while women's brains contain about 10 times as much white matter related to general intelligence as men's. Researchers point to this finding to explain the controversial belief that in general, men may naturally excel at math while women tend to excel in areas like language. 5. Men tend to score an average of 4 to 5 points higher on intelligence tests, as reported by the journal Intelligence in Sept The average man will think about sex as often as once a minute, while the average woman will think of sex much less often, as infrequently as once every one or two days. 7. Why do women always want to talk? Researchers have found that connecting with another through talking will trigger the pleasure centers in a woman's brain, a high second only to an orgasm. 8. Baby girls have been observed to typically have stronger reactions than boys to disturbing or distressful sounds. 9. A 20 second hug will trigger the release of oxytocin in a woman's brain. The effect of this chemical will often give the woman a feeling of trust in the person hugging her. 10. Many authors and researchers have said that men use fewer words per day than women. Depending on which study you believe (if any), the "word gap" can be anywhere from 1,000 to 10,000 words a day. 68 The Cerebral Cortex Motor Areas Premotor Cortex Located anterior to the precentral gyrus Involved in the planning of movements Receives processed sensory information Visual, auditory, and general somatic sensory Controls voluntary actions dependent on sensory feedback 69 23

24 The Cerebral Cortex Motor Areas Frontal Eye Field & Broca s Area Frontal Eye Field Lies anterior to the premotor cortex In Brodmann area 8 Controls voluntary movement of the eyes Especially when moving eyes to follow a moving target Broca s Area Located in left cerebral hemisphere In Brodmann areas 44 and 45 Manages speech production Corresponding region in the right cerebral hemisphere Controls emotional overtones to spoken words 70 Cerebral Cortex Sensory Areas Somatosensory Association Area Lies posterior to the primary somatosensory cortex Corresponds to Brodmann areas 5 and 7 Integrates different sensory inputs Touch, pressure, and others Draws upon stored memories of past sensory experiences 71 Cerebral Cortex Sensory Areas Visual Areas Primary visual cortex Corresponds to Brodmann area 17 Located deep within the calcarine sulcus On the posterior and medial part of the occipital lobe Receives visual information that originates on the retina First of a series of areas that interprets visual input 72 24

25 Cerebral Cortex Sensory Areas Visual Areas Visual association area Surrounds the primary visual area Coincides with Brodmann areas 18 and 19 Continues the processing of visual information Complex visual processing extends into: Temporal and parietal lobes Approximately 30 cortical areas have been identified 73 Cerebral Cortex Sensory Areas Visual Areas 74 Cerebral Cortex Sensory Areas Visual Areas Visual information proceeds in two streams Ventral stream into inferior part of the temporal lobe Responsible for recognizing objects, words, and faces Dorsal stream extends to the postcentral gyrus Perceives spatial relationships Ventral and dorsal streams The what and where pathways 75 25

26 Cerebral Cortex Sensory Areas Auditory Areas Primary auditory cortex Function conscious awareness of sound Location superior edge of the temporal lobe Corresponds to Brodmann areas 41 and Cerebral Cortex Sensory Areas Auditory Areas Auditory association area Lies posterior to the primary auditory cortex Located within Brodmann area 22 Permits evaluation of different sounds Lies in the center of Wernicke s area Involved in recognizing and understanding speech 77 Cerebral Cortex Sensory Areas Gustatory Cortex Involved in the conscious awareness of taste stimuli Corresponds to Brodmann area 43 Located on the roof of the lateral sulcus 78 26

27 Cerebral Cortex Sensory Areas Vestibular Cortex Located in the posterior part of the insula Deep to the lateral sulcus Responsible for sensing changes in equilibrium 79 Cerebral Cortex Sensory Areas Olfactory Cortex Lies on the medial aspect of the cerebrum Located in a region called the piriform lobe Olfactory nerves transmit impulses to the olfactory cortex Provides conscious awareness of smells 80 Cerebral Cortex Sensory Areas Olfactory Cortex Part of the rhinencephalon nose brain Includes the piriform lobe, olfactory tract, and olfactory bulb Connects the brain to the limbic system Explains why smells trigger emotions Orbitofrontal cortex Involved with consciously identifying and recalling specific smells 81 27

28 Cerebral Cortex Association Areas Make associations between different types of sensory information Associate new sensory input with memories of past experiences New name for association areas higher order processing areas 82 Association Areas Prefrontal Cortex Large region of the frontal lobe anterior to motor areas Performs cognitive functions All aspects of thinking and perceiving Remembering and recalling information Also related to mood Has close links to the limbic part of the forebrain 83 Association Areas Prefrontal Cortex Functional neuroimaging techniques Reveal functions of specific parts of the prefrontal cortex Anterior pole of frontal cortex Active in solving the most complex problems Functional areas located on the medial side of the frontal lobe Regions near the corpus callosum Involved in complex personal and social interactions Involved in mentalization 84 28

29 Association Areas General Interpretation Area Function is currently under investigation Located at the interface of: The visual, auditory, and somatosensory association areas Newer studies show most of this region is involved in the visual processing of spatial relationships 85 Association Areas Language Area Surrounds the lateral sulcus in the left cerebral hemisphere Five parts have been identified Broca s area speech production Wernicke s area speech comprehension Lateral prefrontal cortex conceptual analysis of spoken words Most of the lateral and inferior temporal lobe Coordination of auditory and visual aspects of language Parts of the insula Initiation of word articulation Recognition of rhymes and sound sequences 86 Association Areas Insula Functions of its cortex not well understood Some parts function in language and the sense of balance Other parts visceral function Conscious perception of: Upset stomach Full bladder Some aspects of the sense of smell 87 29

30 Functional Brain Systems Networks of neurons functioning together The limbic system spread widely in the forebrain The reticular formation spans the brain stem 88 Functional Brain Systems The Limbic System Location Medial aspect of cerebral hemispheres Also within the diencephalon Composed of: Septal nuclei, cingulate gyrus, and hippocampal formation Part of the amygdala The fornix and other tracts link the limbic system together 89 Functional Brain Systems The Limbic System 90 30

31 Functional Brain Systems The Limbic System The emotional brain Cingulate gyrus Allows us to shift between thoughts Interprets pain as unpleasant Hippocampal formation Hippocampus and the parahippocampal gyrus Function in memory, declarative memory and consolidation into long term memory 91 Functional Brain Systems The Reticular Formation Runs through the central core of the medulla, pons, and midbrain Forms three columns Midline raphe nuclei Medial nuclear group Lateral nuclear group 92 Functional Brain Systems The Reticular Formation Widespread connections Ideal for arousal of the brain as a whole Forms the reticular activating system (RAS) Maintains consciousness and alertness Functions in sleep and arousal from sleep 93 31

32 Nuclei of the Hypothalamus 94 The Brain Stem The Midbrain Periaqueductal gray matter surrounds the cerebral aqueduct Involved in two related functions Fight and flight reaction Mediates response to visceral pain 95 The Brain Stem The Midbrain Corpora quadrigemina the largest nuclei Divided into the superior and inferior colliculi Superior colliculi nuclei that act in visual reflexes Inferior colliculi nuclei that act in reflexive response to sound Other important nuclei embedded in the white matter Substantia nigra neuronal cell bodies contain melanin Functionally linked to the basal nuclei Red nucleus lies deep to the substantia nigra Largest nucleus of the reticular formation 96 32

33 Cerebral White Matter Allows the different areas of the cerebral cortex communicate: With each other With the brainstem and spinal cord Fibers are usually myelinated and bundled into tracts Types of tracts Commissural Allows communication between cerebral hemispheres Corpus callosum the largest commissure Associative Connect different parts of the same hemisphere Projection Descend from the cerebral cortex Ascend to the cortex from lower regions 97 Projection Tracts Internal capsule projection fibers form a compact bundle Passes between the thalamus and basal nuclei Corona radiata superior to the internal capsule Fibers run to and from the cerebral cortex 98 Basal Forebrain Nuclei Four important structures in the cerebrum Septum Diagonal band of Broca Horizontal band of Broca Basal nucleus of Meynert Functions are related to arousal, learning, memory, and motor control 99 33

34 Basal Ganglia A group of nuclei deep within the cerebral white matter Caudate nucleus arches over the thalamus Lentiform nucleus lens shaped Divided into two parts Globus pallidus Putamen Together, these nuclei are called the corpus striatum 100 Basal Ganglia Corpus striatum combination of the lentiform and caudate nuclei 101 Basal Ganglia Cooperate with the cerebral cortex in controlling movements Receive input from many cortical areas Evidence shows that they: Start, stop, and regulate intensity of voluntary movements In some way estimate the passage of time