Anatomy 5.7A CNS_Esguerra
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Anatomy 5.7a
January 17, 2012 Dr. Esguerra
The Central Nervous System
OUTLINE I. Introduction and Organization of the CNS A. Type of Cells B. Anatomical Division C. Ascending and Descending Tracts II. Central Nervous System A. Cerebrum B. Cerebellum C. Brainstem D. Midbrain E. Hindbrain F. Spinal Cord G. Spinal Nerves Objectives: • Enumerating the general characteristics and functions of nervous tissue • Classify neurons • Identify areas of the nervous system where the different type of neurons are located • Identifying the neuroglia • Naming principal divisions of the Nervous System • Identifying the component parts of the CNS, ANS and PNS • Enumerating subdivisions of the brain • Identify lobes of the brain and the major sulci that form the boundaries • Describe the composition of gray and white matter • Enumerating in successive order the parts of brainstem • Identifying important landmarks on the anterior and posterior aspects of the brainstem, especially the cranial nerves • Stating the functions and divisions of the ANS • Describing the origin and general distribution of each of the principal division of the ANS • Differentiating the principal divisions of the ANS and their systemic effects • Identifying the neurotransmitters involved in the ANS
I. INTRODUCTION AND ORGANIZATION OF THE CNS A. Type of Cells • Neuron -‐are excitable cells that are specialized for the reception of stimuli and the conduction of the nerve impulse. -‐From the tip of dendrite all the way to the end of the axon. o Axons-‐ carry impulses away (except in pseudo-‐unipolar neurons where there is no dendrite, only an axon with two processes). o Dendrites-‐ carry impulses towards the body. o Synapses-‐ sites of communication between neurons. o Myelin sheath-‐ a particular feature of the axon, which is a glycoprotein that covers the nerve cell. It increases axonal conduction velocity of nerves. • CNS-‐ oligodendrocytes • PNS-‐ Schwann cells *normal neurons in the mature individual do not undergo division th and replication.(Snell, 7 Ed. 2010) • Neuroglial cells -‐varieties of nonexcitable cells which supports the neurons of CNS. -‐Supporting cells, protect neurons and participate in neural activity, neural nutrition, and defense of cells in the CNS o 4 Types: • Microglia -‐derived from monocyte phagocyte system. -‐the smallest of the neuroglial cells -‐More evenly distributed in the gray and white matter -‐Constitute major defense mechanism in CNS tissues
• Astrocytes -‐are of two types: fibrous and protoplasmic. -‐may serve as phagocytes by taking up degenerating synaptic axon terminals. • Oligodendrocytes -‐responsible for the formation of the myelin sheath of nerve fibers in the CNS. • Ependyma -‐assist in the circulation of the cerebrospinal fluid within the cavities of the brain and the central canal of the spinal cord by the movements of the cilia.
B. Anatomical Division •Central Nervous System -‐Consist of brain and spinal cord. -‐Both the brain and spinal cord are covered with a system of membranes, called meninges, and are suspended in the cerebrospinal fluid. -‐Function: integrate information that passes through it and from the PNS. •Peripheral Nervous System -‐conduct information to and from the central nervous system. -‐surrounded by fibrous sheaths as they run to different parts of the body -‐are relatively unprotected and are commonly damaged by trauma. -‐Made up of nerves that comes out of it; o Brain – cranial nerves (12 pairs) o Spinal cord-‐ spinal nerves (31 pairs) • 8 cervical • 12 thoracic • 5 lumbar • 5 sacral • 1 coccygeal o Ganglia-‐ both from brain and spinal cord. Sympathetic ganglia Paravertebral ganglia Ganglia on the walls of GI tract Note: Spinal nerves are made up of ventral and dorsal roots that came out from spinal cord and exits through intervertebral foramina. Cervical nerves are named after the vertebra below it. Since there is no C8 vertebra, the nerve above T1 vertebra is called C8. After that, the cranial nerves are named on the vertebra above it. Collection of nerve cell bodies: •Nuclei-‐ within the CNS. •Ganglia-‐ within the PNS. Bundles of nerve fibers with common origin and termination: •Tract/Fascicle-‐ CNS •Peripheral nerve-‐ PNS • Autonomic Nervous System -‐Components arising from both central and peripheral NS -‐Involved with regulation of “Internal” Environment outside conscious control -‐Comprised of two divisions: Sympathetic and Parasympathetic
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o White VS. Grey Matter -‐“white” myelinated axons: tracts, peduncles, brachia (arm-‐ like projection), lemnisci, fasciculi, funiculi -‐“grey” nerve cell bodies (unmyelinated): nuclei(middle), cortex(periphery), basal ganglia(important for motor coordination)
II. CENTRAL NERVOUS SYSTEM • Brain (3 Divisions) o Forebrain Cerebrum Diencephalon – made up of thalamus and hypothalamus, mammary bodies and epithalamus o Midbrain-‐ middle part that connects the forebrain to the hindbrain o Hindbrain Pons
Note: Peduncles are connection between two areas on the CNS. Ex. Cerebral peduncle -‐ connects the brain stem to the cerebrum; Three cerebellar peduncles -‐ connects the brain stem into the cerebellum. Lemnisci are ribbon-‐like or band of nerve fibers, usually used for tracts that transmit sensory impulses from the spinal cord towards the cerebrum or within the brain stem to the cerebrum. Funiculi are organizations within the spinal cord that groups together these tracts. No cortex in the Spinal cord, the grey matter is all central. Two divisions of Nuclei are found within it. The Dorsal horn which is found on the posterior part and the Ventral horn that is on the anterior part.
o part of the brainstem between the midbrain rostrally and the medulla oblongata caudally o anterior part of the posterior cranial fossa o associated with CN V
Cerebellum
o Large brain mass posterior to pons and medulla o W 2 lateral hemispheres united by vermis
Medulla oblongata
o Most caudal subdivision of brainstem w/c is continuous with the spinal cord o Lies in the post cranial fossa o Associated with CN IX, X , XII
C. Ascending and Descending Tracts • Ascending Tract -‐Stimulus comes from the periphery to the spinal cord or brainstem going to the cerebrum or cortex -‐Usually sensory -‐Ex. Anterior Spinal thalamic tract • Descending Tract -‐Impulse comes from the CNS going to the spinal cord and exit to other tissues, ex. Skeletal muscle -‐Ex. Lateral CorticoSpinal Tract -‐Nomencalture: 1st term – origin; 2nd term-‐ termination o Spinalthalamic tract – impulse comes from the spinal cord and terminates in to the thalamus o Corticospinal tract – from cortex to spinal cord
Figure 1. (a) Simplest form of the ascending sensory pathway from the sensory nerve ending to the cerebral cortex. (b)Simple form of the descending motor pathway from the cerebral cortex to the skeletal muscle.
Note: In development, the pons and cerebellum are called the Metencephalon, the medulla the Myelencephalon and the cerebrum is known as the telencephalon.
A. CEREBRUM
• 6 lobes: o Seen on the lateral aspect: Frontal Parietal Temporal Occipital o Synthetic lobes: Central (insular lobe/island of Reil) • Seen when the lips of the lateral sylvian fissure are separated(frontal opercular, parietal opercular and temporal opercular) • Roundish part of the brain • More important in lower life forms Limbic • Related to singulate gyrus, parahypocampal gyrus, isthmus, hippocampus and dentate gyrus • Sulci o Central sulcus -‐border between frontal and parietal lobe -‐Also called the Rolandic sulcus or sulcus of Rolando o ParietoOccipital Sulcus -‐Marks the separation of the parietal lobe with the occipital lobe o Pre central sulcus -‐Anterior to pre-‐ central gyrus o Post central Sulcus -‐Posterior to post-‐central gyrus • Fissure o Lateral Sylvian/Lateral longitudinal fissure -‐separates the temporal from frontal and part of the parietal lobe o Interhemispheric sagittal fissure -‐ median fissure dividing the two hemispheres o Calcarine Sulcus – associated with the occipital lobe
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• Gyrus: In between two sulci: o Pre-‐central gyrus -‐Anterior to Rolandic Sulcus -‐Primary motor cortex o Post-‐central gyrus -‐Posterior to Rolandic Sulcus -‐Primary somatosensory cortex Note: Primary visual cortex – area around calcarine fissure Brodmann area –been correlated closely to diverse cortical functions • Corpus Callosum -‐Represents axons connecting the two hemispheres -‐Parts: Rostrum, Genu, Body, Splenium (from front-‐back)
Figure 2. Illustration of a brain presenting the different lobes, sulcus and gyrus on a typical human brain.
Figure 3. Brain Homunculus.
B. CEREBELLUM • Gyri = folia • Anatomical features o Anterior and posterior lobes o Flocculonodular lobe o Vermis o Hemspheres (right and left) • Cerebellar cortex • Deep cerebellar nuclei C. BRAINSTEM • Serves as conduit for ascending and descending tracts • Contains important reflex controls (respiratory, cvs, consciousness) • Contains cn iii – xii nuclei PARTS OF THE BRAINSTEM • Midbrain • Pons • Medulla oblongata Note: pons + medulla = bulbar region BRAINSTEM: DORSAL VIEW • 4 MAJOR LANDMARKS a) DORSAL COLUMNS (Fasciculus-‐bundle) o Fasciculus Gracilis (2) -‐ medial o Fasciculus CUNEATUS (2) -‐ lateral b) DORSAL COLUMN TUBERCLES (tuberculus-‐ prominence) – represents internal location of nucleus of f. Gracilis and f. cuneatus o CLAVA/ T. Gracilis o T. CUNEATUS TH c) 4 VENTRICLE -‐ Between brain stem and cerebellum -‐ filled with cerebrospinal fluid -‐ floor: rhomboid fossa d) 4 COLLICULI – above rhomboid fossa o SUPERIOR-‐ important for vision and hearing o INFERIOR-‐ sound processing Note: Rhomboid fossa-‐ seen when the cerebellum is removed. • CEREBELLAR PEDUNCLES -‐connect brainstem to cerebellum -‐superior (brachium conjunctivum), middle (brachium pontis), inferior (restiform body and juxtarestiform body) • ORIGIN – CN IV (trochlear nerve) – only CN that comes off the dorsal aspect of brainstem • MEDULLARY Velum (superior and inferior) – not part of cerebellum in area of the rhomboid fossa th o closes off 4 ventricle • MEDIAL EMNENCE-‐ column on either side from midline of rhomboid fossa. o Represents the fiber tract • FACIAL COLLICULUS-‐ prominence on the most caudal end • SULCUS LIMITANS-‐ groove on the lateral aspect of medial eminence and facial colliculus • STRIAE MEDULLARES-‐ extends from the midline towards the lateral recesses on corners of rhomboid fossa • LATERAL RECESSES -‐FORAMEN OF LUSCHKA-‐ hole where the cerebrospinal fluid from th 4 ventricle exits • TRIGONES (4) – prominence below striae medullares -‐HYPOGLOSSAL (medially located) -‐VAGAL (laterally located)
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th
• OBEX(funnel-‐shaped area, most inferior part of 4 ventricle) -‐FORAMEN OF MAGENDIE –hole where cerebrospinal fluid exits th from 4 ventricle to cisterna magna BRAINSTEM: VENTRAL VIEW • FOUR MAJOR LANDMARKS -‐PYRAMIDS (most medial) -‐OLIVES (lateral) -‐BASE OF PONS (basis pontis) -‐CEREBRAL PEDUNCLES (basis pedunculi) • ORIGINS OF CN III – XII (EXCEPT IV) Note: pyramidal decussation-‐ where fibers crossed the midline BRAINSTEM: BLOOD SUPPLY • Posterior cerebral artery • Basilar artery • Superior cerebellar artery • Anterior inferior cerebellar artery (aica) • Posterior inferior cerebellar artery (pca) • Vertebral artery D. MIDBRAIN ROSTRAL MIDBRAIN (Compare to a short pants) • 3 regions 1. Tectum “roof” 2. Tegmentum “cover” 3. Basis pedunculi “base stalk” -‐-‐ 2-‐3 cerebral peduncle-‐made up of the base stalk and the tegmentum • Superiorcolliculus • Cerebral aqueduct (of sylvius) • Peraqueductal grey matter-‐ area around the cerebral aqueduct • Occulomotor nucleus -‐ for cn iii • Edinglewestphan nucleus – for cn iii • Medial longitudinal fascicullus -‐ located usually on the medial aspect of brainstem • Pyramidal tract-‐ made up of fibers for corticospinal and corticobulbar tract • Substancia nigra • Red nucleus • Medial lemniscus-‐ important for sensory transmission from the spinal cord to the thalamus CAUDAL MIDBRAIN (Darth vader) • Inferior colliculus • Cerebral aqueduct (of sylvius) • Periaqueductal grey matter • Mesenphalic (midbrain) nucleus of cn v • Motor nucleus of cn iv • Sup. Cerebellar peduncle decussation • Pyramidal (corticospinal and corticobulbar) tract • Substancia nigra • Medial lemniscus
Figure 4. The midbrain. A: Anterior View B: Lateral View E. HINDBRAIN A) PONS ROSTRAL PONS (princess leia) th • 4 ventricle • Roof: cerebellum • Floor: pontine tegmentum • Sup. Medullary velum • Sup. And middle cerebellar peduncle-‐ connect pons to the cerebellum • Middle longitudinal fasciculus • Pontine reticular formation • Motor and sensory nuclei of cn v -‐> cn v fibres • Sup. Vestibular nucleus-‐ important for cn viii • Medial, spinal and lat. Lemnisci Note: medial and spinal for somatic sensation and lateral for vestibular inputs. • Basis pontis • Pyramidal (corticospinal and corticocbulbar) tract • Pontine nuclei • Pontocerebellar fibres CAUDAL PONS (ship) • Facial colliculus (centrally located) • Motor nuclei of cn vi and vii • Medial longitudinal fasciculus • tectospinal tract • vestibular nuclei • spinal nucleus of cn v-‐ spans the pons, medulla, and upper spinal tract. Also has inputs from cn vii, ix, and x. • medial lemniscus • trigeminothalamic tract • spinal lemniscus • lateral lemniscus • pontine nuclei • pyramidal (corticospinal and corticocerebular) tract • middle cerebellar peduncle
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B) MEDULLA OBLONGATA ROSTRAL MEDULLA (shirt and tie) th • 4 ventricle • hypoglossal nucleus of cn xii • medial longitudinal fasciculus • tectospinal tract • medial lemnisci • pyramidal tract • dorsal motor nucleus of cn x • solitary nucleus • vestibular nuclei • solitary tract • spinal nucleus and tract of cn v • reticular formation-‐ located in the tegmentum part • nucleus umbiguus-‐ important for cn ix and x • spinocerebellar and rubrospinal tracts • spinal lemniscus • Olivary Nucleus (inferior, dorsal and medial) -‐ important for balance with association on cerebellum Note: Sulcus medial to olivare nucleus is the pre olivare sulcus. It is where the CN XII exits. Rostral Medulla is called the open medulla because of the presence th of the 4 ventricle. MIDDLE MEDULLA (butterfly) • Closed Medulla • dorsal motor nucleus of cn x • hypoglossal nucleus • nucleus and fasciculus gracus • nucleaus and fascicullus cuneatus • lat. (accessory) cuneate nucleusinternal arcuate fibres (sensory decussation) • internal arcuate fibers (sensory decussation) • reticular formation • nucleus ambiguus • spiral nucleus and tract of cn v • rubrospinal tract • spinal lemniscus CAUDAL MEDULLA (yoda) • pyramidal (motor) decussation-‐ crossing of fibers of pyramidal tract • medial longitudinal fascicullus • tectospinal tract • accessory nucleus of cn xi and fibres of the pyramidal tract • Nucleus Gracilis and Nucleus Cuneatus • Fasciculus gracilis and cuneatus • Lateral Accessory Cuneat Nucleus-‐ important for cerebellar (motor) function for the upper limbs • Internal Arcuate Fibers • Nuclear decussation from N. Gracilis and N. Cuneatus • spinal nucleus and tract of cn v • rubrospinal tract • ant. post spinocerebellar tracts • ant. lat. spinothalamic tracts • sympathetic tract RETICULAR FORMATION – Net like • Located on the tegmental part of brainstem • Part of primitive brain • Composed of loosely defined nuclei and tracts • Extends from midbrain -‐> medulla • Input from and output to virtually all parts of CNS
RETICULAR FORMATION NUCLEI • PRECEREBELLAR NUCLEI -‐ responsible for response to movement • RAPHE NUCLEI • LAT. NUCLEI -‐ receptive role • CENTRAL NUCLEI • CATHECOLAMINE NUCLEI o LOCUS CERULEUS-‐ secretes norepinephrine to modulate responses o SUBSTANTIA NIGRA-‐ regulation of movement RETICULAR FORMATION FUNCTIONS CONTROL OF MOVEMENT -‐ because of the connection of the spinal cord to the cerebellum Modulation of pain information AUTONOMIC REFLEX CIRCUIT (respiratory and cardiovascular reflex) AROUSAL AND CONSCIOUSNESS-‐ rostral nuclei (ARAS) F. SPINAL CORD
• major reflex center and conduction pathway between the body and the brain EXTERNAL FEATURES • Elongated cylindrical structure in vertebral canal • 35 to 40 cm long • Extends from foramen magnum (continuous with medulla) to the lower border of L1 vertebra • 2 enlargements: cervical and lumbar
o Cervical -‐ extends from the C4 through T1 segments of the spinal cord; where brachial plexus arises o Lumbosacral -‐ extends from T11 through S1
segments of the spinal cord ; where lumbar and sacral plexus arise • CONUS MEDULLARES-‐ conical termination of spinal cord • FILLUM TERMINALE -‐ conn. tissue cont. of pia matter penetrate dura matter at s1-‐s2 coccygeal ligament • CAUDA EQUINA: formation of spinal n. roots descending from conus • INTRADURAL SPACE -‐ between pia matter and dura matter • 31 pairs of spinal nerves (dorsal and ventral roots) • Segments o 8 cervical o 12 thoracic o 5 lumbar o 5 sacral o 1 coccygeal DEV’T CHANGES • Occupies only 2/3 of adult vertebral canal rd • 3 month of fetal life-‐ rate of vertebral column growth greater than spinal cord • At birth: L2-‐L3 intervertebral disc • Adult: L1-‐L2 intervertebral disc G. SPINAL NERVES • C1 spinal nerve exits b/w the atlas and occipital bone • C8 emerges b/w C7 and T1 vertebrae • All other spinal nerves emerges from intervertebral foramina below vertebral column of same number • Lumbar and sacral nerve roots descend within lumbar cistern before reaching the respective intervertebral foramina and form cauda equina
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o INTERMEDIATE GREY ZONE LAMINA VII -‐ Nucleus Dorsalis-‐ cerebral proprioception -‐ Intermedial lateral Nucleus o T1-‐L2/L3 (lateral horn) – preganglionic symph. fibers o S2-‐S4 (no lateral horn) – preganglionic parasymph. fibers -‐ Intermediomedial aspect-‐ visceral afferent (input from gut, heart, lungs) LAMINA X-‐ grey matter surrounding the central canal. With visceral afferents o VENTRAL HORN LAMINA VIII-‐ contains motor interneuron coming from the cortex o Receives some descending tract fibers o Sends commissural axons to the opposite side LAMINA IX-‐ contains the main motor neurons -‐ Alpha motor neuron-‐ striated muscle -‐ Gamma motor neurons-‐ intrafusal fibers for muscle spindles -‐ Medial nuclear grp – long and short axial ms. -‐ Lateral nuclear grp – remaining musculature
WHITE MATTER -‐-‐ divided into areas called folliculi • Ventral/anterior median fissure-‐ divides anterior folliculus into right and left • Ventrolateral/anterolateral sulcus-‐ where ventral rootlets come out. Ventral rootlets are roots coming form the ventral horn. -‐ Separates the anterior folliculus to lateral folliculus • Dorsolateral/posterolateral sulcus-‐ where posterior/dorsal root fibers enter the spinal cord. -‐ Separates lateral folliculus to posterior folliculus • Dorsal/posterior median sulcus-‐ divides posterior funniculus into right and left • Dorsal intermediate sulcus-‐ divides dorsal folliculus into two; F. Gracilis (medial) and F. Cuneatus (lateral) -‐ Only present in the cervical and upper thoracic because of the inputs from the upper limbs. In the lower portion, only one column which is the F. Gracilis.
Figure 5. Transverse section of the medulla spinalis in the mid-‐ thoracic region GREY MATTER • centrally located • there are two enlargements on the sides: Poserior/dorsal horn and the Anterior/ventral horn • a lateral horn is also found in the thoracic and upper lumbar level related to preganglionic neurons in autonomic NS o DORSAL HORN LAMINA I & II-‐ high concentrations of substance P and opiate receptors (important role in pain transmission) LAMINA II & III (known as Substantia Gelatinosa)-‐ transmission of pain LAMINA IV-‐ low intensity stimuli LAMINAVI-‐ present only in cord enlargement because it receives input from limbs
Figure 6. Transverse section of the cord. Seen is the central canal around which is the H-‐shaped grey matter, surrounded in turn by the white matter which contains the long ascending and descending tracts.
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