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Transcript
Introduction to Central Nervous System • Located btwn the diencephalon and the pons. – 2 bulging cerebral peduncles on the ventral side. These contain: • Descending fibers that go to the cerebellum via the pons • Descending pyramidal tracts – Running thru the midbrain is the hollow cerebral aqueduct which connects the 3rd and 4th ventricles of the brain. – The roof of the aqueduct ( the tectum) contains the corpora quadrigemina • 2 superior colliculi that control reflex movements of the eyes, head and neck in response to visual stimuli Midbrain •Cranial nerves 3&4 (oculomotor and trochlear) exit from the midbrain •Midbrain also contains the headquarters of the reticular activating system Midbrain • On each side, the midbrain contains a red nucleus and a substantia nigra – Red nucleus contains numerous blood vessels and receives info from the cerebrum and cerebellum and issues subconscious motor commands concerned w/ muscle tone & posture – Lateral to the red nucleus is the melanin-containing substantia nigra which secretes dopamine to inhibit the excitatory neurons of the basal nuclei. • Damage to the Pons • Literally means “bridge” • Wedged btwn the midbrain & medulla. • Contains: – Sensory and motor nuclei for 4 cranial nerves • Trigeminal (5), Abducens (6), Facial (7), and Auditory/Vestibular (8) – Respiratory nuclei: • Apneustic & pneumotaxic centers work w/ the medulla to maintain respiratory rhythm – Nuclei & tracts that process and relay info to/from the cerebellum – Ascending, descending, and transverse tracts that interconnect other portions of the CNS • Medulla Oblongata Most inferior region of the brain stem. • Becomes the spinal cord at the level of the foramen magnum. • Ventrally, 2 ridges (the medullary pyramids) are visible. – These are formed by the large motor corticospinal tracts. – Right above the medullaSC junction, most of these fibers cross-over (decussate). • Medulla Oblongata Nuclei in the medulla are • associated w/ autonomic control, cranial nerves, and motor/sensory relay. Autonomic nuclei: – Cardiovascular centers • • Cardioinhibitory/cardioacc eleratory centers alter the rate and force of cardiac contractions Vasomotor center alters the tone of vascular smooth muscle – Respiratory rhythmicity centers • Receive input from the pons – Additional Centers • Emesis, deglutition, coughing, hiccupping, and Medulla Oblongata • Sensory & motor nuclei of 5 cranial nerves: – • Auditory/Vestibular (8), Glossopharyngeal (9), Vagus (10), Accessory (11), and Hypoglossal (12) Relay nuclei – – Nucleus gracilis and nucleus cuneatus pass somatic sensory information to the thalamus Olivary nuclei relay info from the spinal cord, cerebral cortex, and the brainstem to the cerebellar cortex. What brainstem structures are visible here? Limbic System • • • Includes nuclei and tracts along the border btwn the cerebrum and the diencephalon. Functional grouping rather than anatomical Functions include: 1. 2. 3. • • Establishing emotional states Linking conscious cerebral cortical functions w/ unconscious functions of the brainstem Facilitating memory storage and retrieval Limbic lobe of the cerebrum consists of 3 gyri that curve along the corpus callosum and medial surface of the temporal lobe. Limbic system the center of emotion – anger, fear, sexual arousal, pleasure, and sadness. Reticular Formation • Extensive network of neurons that runs thru the medulla and projects to thalamic nuclei that influence large areas of the cerebral cortex. – Midbrain portion of RAS most likely is its center • Functions as a net or filter for sensory input. – Filter out repetitive stimuli. Such as? – Allows passage of infrequent or important stimuli to reach the cerebral cortex. – Unless inhibited by other brain regions, it activates the cerebral cortex – keeping it How might the “sleep centers” of your brain work? Why does alcohol make you tired? Protection • What is the major protection for the brain? • There are also 3 connective tissue membranes called the meninges: • Cover and protect the CNS • Protect blood vessels • Contain cerebrospinal fluid • The 3 meninges from superficial to deep: • Dura mater • Arachnoid mater • Pia mater Skin Galea Aponeurotica Connective Tissue Bone Dura Mater Arachnoid mater Spinal Cord • Functions to transmit messages to and from the brain (white matter) and to serve as a reflex center (gray matter). • Tube of neural tissue continuous w/ the medulla at the base of the brain and extends about 17” to just below the last rib. (Ends at L1) • Majority of the SC has the diameter of your thumb • Thicker at the neck and end of the cord (cervical and lumbar enlargements) b/c of the large group of nerves connecting Spinal Cord • Surrounded by a single layered dura mater and arachnoid and pia mater. • Terminates in cone shaped structure called the conus medullaris. – The filum terminale, a fibrous extension of the pia mater, extends to the posterior surface of the coccyx to anchor the spinal cord. • The cord does not extend the entire length of the vertebral column – so a group of nerves leaves the inferior spinal cord and extends downward. It resembles a horses tail and is called the cauda equina. Spinal Cord • Notice the gross features of the spinal cord on the right. • 31 pairs of spinal nerves attach to the cord by paired roots and exit from the vertebral canal via the intervertebral foramina. Cross Sectional Anatomy of the Spinal Cord • Flattened from front to back. • Anterior median fissure and posterior median sulcus partially divide it into left and right halves. • Gray matter is in the core of the cord and surrounded by white matter. • Resembles a butterfly. • 2 lateral gray masses connected by the gray commissure. • Posterior projections are the posterior or dorsal horns. • Anterior projections are the anterior or ventral horns. • In the thoracic and lumbar cord, there also exist lateral Gray Matter • Posterior horns contain interneurons. • Anterior horns contain some • interneurons as well as the cell bodies of motor neurons. – These cell bodies project their axons via the ventral roots of the spinal cord to the skeletal muscles. – The amount of ventral gray matter at a given level of the spinal cord is proportional to the amount of skeletal muscle innervated. Gray Matter • Lateral horn neurons are sympathetic motor neurons serving visceral organs. – Their axons also exit via the ventral root. • Afferent sensory fibers carrying info from peripheral receptors form the dorsal roots of the spinal cord. The somata of these sensory fibers are found in an enlargement known as a dorsal root ganglion. • The dorsal and ventral roots fuse to form spinal nerves. White Matter • Myelinated nerve fibers. • Allows for communication btwn the brain and spinal cord or btwn different regions of the spinal cord. • White matter on each side of the cord is divided into columns or funiculi. – Typically, they are ascending or descending. • What does that mean? Spinal Nerves • 31 nerves connecting the spinal cord and various body regions. • 8 paired cervical nerves • 12 paired thoracic nerves • 5 paired lumbar nerves • 5 paired sacral nerves Spinal Nerves • Each connects to the spinal cord by 2 roots – dorsal and ventral. • Each root forms from a series of rootlets that attach along the whole length of the spinal cord segment. • Ventral roots are motor while dorsal roots are • Spinal Nerves The 2 roots join to form a spinal nerve prior to exiting the vertebral column. • Roots are short and horizontal in the cervical and thoracic regions while they are longer and more horizontal in the sacral and lumbar • regions. Almost immediately after emerging from its intervertebral foramen, a spinal nerve will divide into a dorsal ramus, a ventral ramus, and a meningeal branch that reenters and innervates the meninges and associated blood vessels. • Each ramus is mixed. • Joined to the base of the ventral rami of spinal nerves in the thoracic region are the rami communicantes. These are sympathetic fibers that we’ll deal with shortly. • Dorsal rami supply the posterior body trunk whereas the thicker ventral rami supply the rest of the body trunk and the limbs. The Brain • 3 primary divisions: – Forebrain • cortex (folded stuff) • limbic system, etc (stuff around brain stem) – Midbrain (top of brainstem) – Hindbrain (bottom of brainstem + cerebellum) Hindbrain Medulla Pons Cerebellum Pons Medulla Cerebellum http://wwwunix.oit.umass.edu/~psyc335c/lectures/hindbrain.gif Medulla: Controls vital reflexes: breathing, heart rate, vomiting, salivation, coughing, sneezing - Via cranial nerves Damage to medulla can be fatal Large doses of opiates can be fatal b/c suppress activity of medulla…why…?...b/c receptors there! Pons: Also has cranial nerves Location of axon decussation (where axons cross from one side of the brain to the other…so left brain controls right body and vice versa) Reticular formation: motor control, arousal, consciousness Midbrain: Cerebral aqueduct More cranial nerves Superior colliculus (visual info) Inferior colliculus (auditory info) Substantia nigra: dopamineproducing cells, structure that is lost in Parkinson’s Disease http://en.wikipedia.org/wiki/Midbrain Brainstem Medulla Pons Midbrain Some forebrain structures Senses: Information comes in the cranial nerves and eventually ends up in the cortex Cranial Nerves Table 4.4, page 87 Olfactory nerve: Smell http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Optic nerve: Vision http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Occulomotor nerve: Eye movement, pupil constriction http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Trochlear nerve: Eye movement http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Trigeminal nerve: Skin senses from face Jaw muscles for chewing and swallowing (muscles of mastication) http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Abducens nerve: Eye movements http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Facial nerve: Taste Facial expressions Crying Salivation Dilation of head’s blood vessels http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Acoustic nerve: Aka vestibulocochlear or statoacoustic Hearing Equilibrium http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Glossopharynge al nerve: Taste Swallowing Salivation Throat movements during speech http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Vagus nerve: Sensation from neck and thorax Control of throat, esophagus, larynx Parasympathetic nerves to stomach, intestines, etc http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Spinal accessory nerve: Aka Accessory nerve Neck and shoulder movements http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial Nerves Table 4.4, page 87 Hypoglossal nerve: Muscles of tongue http://www.besthealth.com/besthealth/bodyguide/reftext/images/ cranial_nerves.jpg Cranial nerve signs help determine the location of a lesion in the brain • Essential element in clinical neuroanatomy • Neurological exam: http://www.vhct.org/case1799/neurologic_ examination.shtml • Example: patient is asked to stick out tongue. If the tongue deviates to the left, the lesion involves the nucleus of the left hypoglossal nerve. Nerve key Nerve Type of function On Optic Some = sensory Old Olfactory Say Olympus Occulomotor Marry = motor Towering Trochlear Money Tops Trigeminal But = both (S&M) A Abducens My Fin Facial Brother And Acoustic* Says German Glossopharyngeal Bad Viewed Vagus Boys Some Spinal accessory** Marry Hops Hypoglossal Money * Acoustic-vestibulocochlear, stateocochlear ** Spinal accessory = accessory Forebrain • • • • • • • Thalamus Hypothalamus Pituitary gland Basal ganglia Basal forebrain Hippocampus Limbic system Thalamus: Relay station for all sensory info on its way to brain (except olfactory info) Many specialized nuclei (ex: LGN, MGN…don’t have to know these!) Hypothalamus Communicates with pituitary gland to alter hormone release Involved in feeding, drinking, temperature regulation, sexual behavior, fighting, arousal (activity level)…4 Fs Pituitary gland Endocrine gland (hormone producing) Attached to base of hypothalamus by stalk Makes and releases hormones into bloodstream Basal Ganglia Motor control, but also memory and emotional expression Lose dopamine neurons in SN Parkinson’s Disease http://www.uni.edu/walsh/basalganglia-2.jpg thalamus.wustl.edu/ course/cbell6.gif Lose dopamine neurons in caudate & putamen Huntington’s chorea Don’t memorize image!!! Just understand that this is a very complex system! Basal forebrain Anterior and dorsal to hypothalamus Important for arousal, wakefulness, attention http://memorylossonline.com/summer2003/glo ssary/basalforebrain.jpg Lose cells in nucleus basalis decreased attention & intellect (AD, PD) Hippocampus Memory formation HM: temporal lobes removed for intractable epilepsy no longer formed new memories http://www.hermespress.com/Perennial_Tradition/hippocampus.gif http://www.umassmed.edu/bnri/graphics/crusiofig1.gif Limbic System important for motivated & emotional behaviors (eating, drinking, sexual activity, aggressive behavior) Ventricles Contain cerebrospinal fluid (CSF) CSF reabsorbed into blood vessels, so continuous turnover Protective Reservoir for hormones, nutrients http://mywebpages.comcast.net/epollak/PSY255_pix/ventricles.PNG Ventricle size can indicate problems • Enlarged ventricles as in Alzheimer’s patients (cell loss). • Lack of ventricles due to tumors etc. Cortex • 2 hemispheres – Communicate via corpus callosum & anterior commisure • 4 lobes http://pegasus.cc.ucf.edu/~Brainmd1/brmodelc.gif http://www.urmc.rochester.edu/neuroslides/slides/slide201.jpg http://trc.ucdavis.edu/mjguinan/apc100/modules/Nervous/grosscns/images/brain10.jpg 6 laminae (layers of cells) The lobes of the cortex • Frontal – Thinking – Prefrontal cortex • Planning • Working memory • Socially appropriate behavior • Delayed-response task • Lobotomies – Primary motor cortex • Broca’s aphasia The lobes of the cortex • Parietal – Sensing • Primary sensory cortex Homunculus The lobes of the cortex • Temporal – Spoken language comprehension • Wernike’s aphasia – Hearing – Vision • Movement perception • Face recognition – Emotional motivational behavior The lobes of the cortex • Occipital – Vision • Primary visual cortex • Damage causes “cortical blindness” Evolution of Gene Related to Brain's Growth • A gene that helps determine the size of the human brain has been under intense Darwinian pressure in the last few million years. • It has changed its structure 15 times since humans and chimps separated from their common ancestor. • Evolution has been particularly intense in the five million years since humans split from chimpanzees Changes in the architecture of the ASPM protein over the last 18 million years are correlated with a steady increase in the size of the cerebral cortex (2002) Dr. Bruce T. Lahn at U. Chicago. A disrupted form of this gene was identified as the cause of microcephaly (people born with an abnormally small cerebral cortex). Functions • Forebrain – the cool stuff (thinking, perceiving, big part of emotion) • Midbrain – sensory pathways • Hindbrain – motor control, reflexes (breathing, heart rate, etc) Spinal Cord & Spinal Nerves • Spinal cord – Truly the pathway between body and mind – Conducts impulses to and from the brain – Carries out spinal reflexes • Spinal nerves – 31 pairs – All are mixed nerves Structure of the Spinal Cord • Extends from the foramen magnum to the first or second lumbar vertebra. • Ends in the conus medullaris • Filum terminale – Extends from conus medullaris to sacral vertebrae • Cauda equina – = filum terminale + dorsal & ventral roots from spinal nerves that extendHuman Anatomy, 3rd edition Prentice Hall, © 2001 below conus Coverings of the Spinal Cord • 3 layers called meninges • Dura mater – Outer layer • Arachnoid – Middle layer • Pia mater – Adheres tightly to the surface of the spinal cord Meninges of the Spinal Cord Human Anatomy, 3rd edition Prentice Hall, © 2001 Meninges of the Spinal Cord Human Anatomy, 3rd edition Prentice Hall, © 2001 Sectional Anatomy of the Spinal Cord • Inner part consists of gray matter – Unmyelinated cell bodies, neuroglia, & dendrites – Organized into “horns” • Outer part consists of white matter – Tracts of myelinated fibers – Ascending tracts are sensory – Descending tracts are motor Human Anatomy, 3rd edition Prentice Hall, © 2001 Example of Ascending Nerve Tracts Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Nerves • Connect to the spinal cord via a dorsal and a ventral root • Dorsal root is sensory – Contains a dorsal root ganglion • Ventral root is motor Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Nerves • The roots unite into the spinal nerve • Spinal nerves exit through intervertebral foramen • Split into branches, or rami. – Dorsal ramus – Ventral ramus – Regions of skin supplied by a spinal nerve = dermatomes (“skin Human Anatomy, 3rd edition slices”) Prentice Hall, © 2001 Dermatomes Human Anatomy, 3rd edition Prentice Hall, © 2001 Nerve Plexuses • Plexus = “braid” • Nerves supplying the limbs form plexuses when they leave the spinal cord – Cervical plexus – Brachial plexus – Lumbosacral plexus • Lumbar plexus • Sacral plexus Human Anatomy, 3rd edition Prentice Hall, © 2001 Cervical Plexus • Formed by spinal nerves C1 – C5 – Nerves innervate the neck and shoulder region – Phrenic nerve to the diaphragm Human Anatomy, 3rd edition Prentice Hall, © 2001 • Brachial Plexus Formed by spinal nerves C5 – C8 and T1 – Nerves innervate the arm and shoulder • Radial nerve • Ulnar nerve • Median nerve Human Anatomy, 3rd edition Prentice Hall, © 2001 Brachial Plexus Human Anatomy, 3rd edition Prentice Hall, © 2001 Lumbosacral Plexus Human Anatomy, 3rd edition Prentice Hall, © 2001 Lumbar Plexus • Formed by spinal nerves T12 and L1 – L4. – Innervates the medial and anterior portions of the thigh and lower abdominal regions – Lateral femoral cutaneous nerve Human Anatomy, 3rd edition Prentice Hall, © 2001 Sacral Plexus • Formed by spinal nerves L4 and L5, and S1 and S2 – Innervates the posterior portion of the hip, thigh, and leg, and the genital region – Sciatic nerve Human Anatomy, 3rd edition Prentice Hall, © 2001 Sacral Plexus Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Reflexes • Reflexes are automatic responses to stimuli • Spinal reflexes result from the stimulation of a spinal reflex arc. Human Anatomy, 3rd edition Prentice Hall, © 2001 Basic Elements of a Reflex Arc Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Cord Injuries • Can affect sensory perception; motor paralysis • Location affects severity of the injury • Spinal compression results from squeezing the spinal cord within the vertebral canal • Spinal transection is the severing of the spinal cord Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Cord Injuries • Quadriplegia • Paraplegia http://www.apparelyzed.com/paralysis.html Gracile fasc Cuneate fasc Gracile fasc Goll Burdach Cuneate fasc Flechsig Gower s Lat sp-thal Gracile fasc Goll Burdach Cuneate fasc Flechsig C(p) Rubro Mona kow Gower s Lat sp-thal c R T v Fasciculi proprii Flechsig C(p) Gower s Lat sp-thal c R T v Gel sub Zona spongiousa N p C(p) t h I-m I-lat c R T v