Neuroanatomy: Spinal Cord - PDF

In two weeks 12 min quiz – on all five lectures! The Central Nervous System The central nervous system: Cerebrum: Cerebral hemisphere Diencephalon Brain stem: midbrain, pons, medulla Cerebellum Spinal cord 2  Spinal C...

In two weeks 12 min quiz – on all five lectures! The Central Nervous System The central nervous system: Cerebrum: Cerebral hemisphere Diencephalon Brain stem: midbrain, pons, medulla Cerebellum Spinal cord 2  Spinal Cord The spinal cord is a long, thin, tubular bundle that extends from the base of the brain down the back – transmits messages between the brain and the rest of the body. 3 The spinal cord is protected by bones, discs, ligaments, and muscles. The spine is made of bones called vertebrae. Why are there different shapes of vertebrae? Give high flexibility of motion and yet very strong and stable. 4 The spinal cord is running along the vertebral foramen front Where is front? Placing vertebra on top of each other create a space allowing the spinal nerves to exit/enter How many segments are there? Co1-Co4 are fused 7+12+5+5+1=30 S1-S5 are fused how many nerves do we have? 7 Longitudinal organization to the spinal cord cervical region 8 pairs thoracic region 12 pairs lumbar region 5 pairs sacral region 5 pairs 1 coccygeal at the very bottom Together: 31 spinal segments of the spinal cord each of which gives rise to a pair of spinal nerves  bilateral symmetric 8 The spinal cord occupied only 2/3 of the vertebral canal Average length of vertebral column in a male is about 71cm. The spinal cord occupied only 2/3 of the vertebral canal  the spinal cord is about 42-45 cm long Any ideas of why the spinal cord only ? occupied 2/3 of the vertebral canal? 9 Development of spinal cord  the Cauda equina (Latin for "horse's tail") Principal neurons (pyramidal) have a peak time rate at 3–4 months In the fetus, the spinal cord and the vertebral column are the same length up until the third month. Therefore at this early stage the spinal cord extends throughout the entire length of the embryo, and spinal nerves pass through the immediately adjacent neural foramina. 10  Development of spinal cord  extension of the Lumbosacral spinal nerves roots Conception At birth Adult In the fetus, at the 2nd third, the spinal cord gradually recedes from below, as the growth of the bones composing the canal is more rapid in proportion than that of the cord, resulting in extension of the spinal nerve roots. 11 Human brain grows much less than the rest of the body after birth and so it is proportionally smaller in adults (relative to the body size) than in children 10 In the adult, the conus thus lies at the level of the L1–L2 intervertebral disc and nerve roots must descend to leave from their once-adjacent neural foramina The Cauda equina (Latin for "horse's tail") long nerve routes extend like a horses tail The inferior highly branched out part of the spinal cord, starting at the Conus medullaris; Cauda equina a bundle of 10 spinal nerve roots from 2nd lumbar till the end: 4 lumbar region + 5 pairs sacral region + 1 coccygeal Human caudal spinal cord anterior view 14 The location of the inferior end of the spinal cord is not at the bottom of the vertebral column, but at the level of L1 or L2. 1st lumbar vertebra 2nd lumbar vertebra spinal tap – taking CSF sample The spinal cord ends at the conus modularis at the level of L1-L2 Lecture #12 15 From immediately after the medulla oblongata to the 2nd lumbar vertebrae The spinal originates immediately after the medulla oblongata and ends at approx. the 2nd lumbar vertebrae up to the conus modullaris  the spinal cord occupied only 2/3 of the vertebral canal 16 Cross section of the spinal cord – the shape of a butterfly anterior/ventral The spinal cord is well protected within the vertebrae, has similar protection to that of the brain. 17 Cross section of the spinal cord Under Nissl staining a cross section of the spinal cord shows white and gray areas Grey matter collection of neuron cell Gray matter White matter bodies within the CNS  butterfly (or H) shape Central canal White matter collection of bundles of myelinated nerve fibers/axons Central canal has CSF - this canal is going all the way up to the ventricular system of the brain Ventral anterior front 18  Different shapes of butterfly along the spinal cord Cervical enlargement Different shapes of the butterflies along the spinal cord Gray matter is central to the cord and is surrounded by white matter. Lumbosacral enlargement In the cervical and lumbosacral regions the diameter of the spinal cord is enlarged Any ideas why? 19  Longitudinal organization to the spinal cord bilateral symmetric Cervical The spinal cord is enlarged in the enlargement cervical region, and in the lumbosacral region. This is where our arms are attaching to the body axis and the legs. This thickening is for an increase in the circuitry that is required to govern the activities of the arms and the legs. Lumbosacral enlargement 20 Some terms Horn  gray matter Column  white matter Dorsal horn Dorsal column Intermediate Lateral column zone Ventral horn Ventral Ventral column front The columns/horns are called based on their location (ventral horn, dorsal horn) 21  In the thoracic and upper lumbar (T1-L2) there is a triangular field  lateral horn Lateral horn Motor neurons The lateral grey column is primarily involved with activity in the sympathetic division of the autonomic motor system, providing outflow from the nervous system to the viscera-smooth muscles.  The sympathetic system comes entirely from neurons in the thoracic cord. The parasympathetic system comes from two places: cranial nerves, and from the sacral cord therefore often called the craniosacral system.  Autonomic Nervous System/ visceral motor system The autonomic nervous system is a control system that acts largely unconsciously in order to maintains the internal environment of the body by regulating the activity of visceral organs, glands and blood vessels Governs circulation, respiration, digestion, metabolism, bodily secretions, thermal regulation and reproduction  keeping the homeostatic while allowing radical changes when needed The autonomic nervous system has two main divisions: (1) Sympathetic nervous system (2) Parasympathetic nervous system 24 19th century view of the brain Nerves are unidirectional or bidirectional? First thought- bidirectional – when a nerve in the body is cut, both sensation and movement are lost 1810 by experimental ablation method Charles Bell and Francois Magendie When cut dorsal root  sensation is lost When cut ventral root muscle paralysis ventral Ganglia (single: ganglion)- Sensory collection of neuron cell bodies input located outside the CNS 26 Motor output  A way to memo: Dichotomy in the gray matter sensory/dorsal Sensory and motor zones! motor/ventral Dorsal root Sensory input Dorsal/Posterior Dorsal root ganglion horn Mixed spinal nerve Central nervous system Peripheral Nervous Motor output system Ventral/Anterior horn Ventral root The roots get together to form a mixed spinal nerve- a damage to this part will cause symptoms from both sensory and motor symptoms. 27 Many fibers join together to form each root How many dorsal root ganglions do we have? Side view rootlets Dorsal root Dorsal root ganglion Spinal nerve Ventral root 6-8 rootlets combine to form a root of spinal nerves 28 29  cut trough Spinal nerve Axons are grouped together in spatially arranged motor or sensory bundles called fascicles Spinal nerve one axon  Dorsal root ganglion Ventral root Spinal nerve Ventral ramus Dorsal root Dorsal ramus The sensory/dorsal and motor/ventral roots get together to form a mixed spinal nerve- a damage to this part will cause to both sensory and motor symptoms. 31 Dermatomes and Myotomes A dermatome is an area of skin that is supplied by sensory neurons that arise from a single spinal nerve. A myotome is the group of muscles innervated by motor neurons that arise from a single spinal nerve.  Dermatomes From the word dermis == skin A dermatome is an area of skin that is supplied by sensory neurons that arise from a single spinal nerve. There are dermatomes of 7 cervical nerves (C1 being an exception with no dermatome – carries predominantly motor fibers), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. Each of these nerves relays sensation (including pain) from a particular region of skin to the brain. is there any logic to this dermatome organization? 33 http://dictionary.reference.com/browse/dermatome Think evolutionarily: our ancestors walked on all four limbs How do we know that this is the arrangement ? 34  How can we check in human spinal cord what is the skin area of each dermatome? Pure anatomy- careful dissection of the fibers, how they innervate the skin/muscle using cadavers. Looking at the extent of cutaneous lesions caused by infection of different spinal ganglia (i.e. clinical observations of herpes zoster eruptions - the lifetime A case of shingles that demonstrates risk of developing herpes zoster is the typical dermatomal distribution, approximately 30%). in this case C8/T1 In the early 20th century rhizotomy Rhizotomy (resection of the dorsal roots of spinal nerves) was used to treat intractable pain referred from the viscera (internal organs) and to reduce spasticity in cases of cerebral palsy, as well as in central nervous system trauma. Dermatomes have some overlap Myotomes Myotome - A group of muscles primarily innervated by the motor fibers of a single nerve root. Most muscles in the upper and lower limbs receive innervation from more than one spinal nerve root. They are therefore comprised of multiple myotomes.  How can we check in human what is the map for motor innervation- the myotome? 1) Pure anatomy- careful dissection of the fibers, how they innervate the muscle using cadavers. 2) Study patients with poliomyelitis to deduce the map of motor innervation In humans, poliovirus infection usually begins with oral ingestion of the virus. After oral ingestion, the virus multiplies in the alimentary mucosa. The virus then moves into the blood stream (viremia) through the putative barrier(s) that virulent poliovirus strains cross more efficiently than attenuated strains. The circulating virus invades the CNS and replicates in neurons, particularly motor neurons. Molecular aspects of poliovirus pathogenesis, Akio Nomoto Proc Jpn Acad Ser B Phys Biol Sci. 2007 Dec; 83(8): 266–275. 3) Human myotomal maps  in vivo direct ventral root stimulation This study investigates the myotomal innervation patterns of cervical and lumbar nerve roots through in vivo stimulation during surgeries for spinal decompression C4-T1 nerves : Innervate the upper limbs L1-S3 nerves: Innervate the lower limbs 40 Expansion of the amount of gray matter that is present in the ventral horns of the cervical and lumbar/sacral regions more grey matter volume means more neurons, more local circuits  there are more muscles to be active arms A myelin stain section: stain with legs silver salts or gold chloride. The inverse appearance of Nissl stain: Dark== white matter 41 Light == gray matter  Communication at the horizontal level of the spinal cord Sometimes we need a really quick response  Spinal reflexes What do we need for a spinal reflex? Sensory neuron i.n. m.n.  effector (muscle) There are connections between the Dorsal horn and the Ventral horn made by local circuit interneurons 42 In some places we have a direct connection between the Dorsal horn and the Ventral horn the stretch (myotactic) reflex Efferent contraction of Afferent impulses from muscle spindle the stretched muscle (stretch receptors) to spinal cord to resists the stretch tendon Inhibit contraction of antagonist muscles When the tendon in the knee is tapped, the extensor muscle is stretched slightly. This stretch activates the Group I sensory afferent axons Afferent: arrives Ascending- providing information 43 Efferent: exits; descending- commands  Vertical communication in the spinal cord The information is also being send to the brain- so that we will get the sensation of pain. And then the brain can also send orders down by activating the m.n. directly Afferent: Ascending- providing information 45 Efferent: descending- commands What if the spinal cord was injured right at the neck? Would u feel the touch? What about the reflexes?  Spinal reflex does not require any input from the brain On May 27, 1995, Reeve became paralyzed after being thrown from a horse during a riding competition. Had reflexes but no sensation Christopher Reeve, 1952-2004 47 Vertical communication White matter in the spinal cord In the spinal cord information runs in tracts. tracts are bundle of axons which have common origin and common termination. Connecting the upper part of the CNS and the lower part of the CNS  by white matter! Ascending tracts- those that connects the lower part to the upper part called ascending tract. Descending tracts- those that connect the upper part to the lower part called descending tracts 48 Vertical communication in the spinal cord Three zones in White matter in spinal cord white matter Dorsal column Why do white matter sensory zone Lateral column decrease from mixture of both superior to inferior sensory and motor pathways (ex. lateral sections? cortical spinal tract, motor pathway) Ventral column mixture of both Dark== white matter sensory and motor Light == gray matter pathways (ex. pain pathways; anterior corticospinal tract) Representative cross-sections that are taken from different levels of the spinal cord 49  White matter in the spinal cord White matter decrease from superior to inferior sections for 2 reasons: (i) Descending axons: axons that are coming down from the brainstem and cerebral cortex in the lateral and anterior column of white matter are simply terminating along the way. (ii) Ascending axons: axons that are sending signal from the periphery (temperature, pain, mechanosensation) to the brain are adding up The higher we go in the spinal cord  more damage in case of injury 50 Vertical information: upward the spinal cord sensory tracts Usually you need 3 neurons to get to cortex – 1st example: Spinal-thalamic tract (Anterior-Lateral System) convey sensory info about pain/temperature (also known as Anterior column) 51 Spinal-thalamic tract (Anterior-Lateral System) convey sensory info about pain/temperature. Naming of the tract: (1) The first word is the origin (spinal) the second word is the destination (thalamus) (2) Based on location within spinal cord 3nd neuron (in thalamic Anterior-Lateral The ventral posterior- VPL nucleus) lateral (VPL) nucleus of the thalamus Decussation at the level of the spinal cord (80% of the axons decussate) The axial twist hypothesis 1st neuron an axial rotation in the early embryo (the head is turned 180 with 2nd neuron respect to the body) explain the pattern of midline-crossing and non- crossing connections in the nervous system. Decussations are unique to vertebrates 52 Vertical information: upward the spinal cord sensory tracts Usually you need 3 neurons to get to cortex – the highest level/rank (awareness) 1st example: Spinal-thalamic tract convey sensory info about pain/temperature/crud touch (anterior column). 2nd example: dorsal/posterior column convey sensory information about fine touch, vibration, pressure and proprioception From Latin: "one's own" take or grasp 53 Dorsal/posterior column: Convey sensory information about fine touch, vibration, pressure and proprioception. The ventral posterior- lateral (VPL) nucleus of the thalamus 3nd neuron (in VPL) 2nd neuron 1st neuron Decussation at the level of the medulla 54 Dorsal/posterior column: Convey sensory information about fine touch, vibration, pressure and proprioception. dorsal column 1st neuron The dorsal column is made up from 2 tracts: Fasciculus Gracilis (walk on grass) Fasciculus Cuneate (eat with hands) 55 Explanation for the spatial arrangement in the dorsal column Axons enter the column from the lateral side As we go higher in the spinal cord there will be more sensory fibers added. As axons of dorsal root ganglion enter from the lateral side into the dorsal root to join the dorsal column white matter. In other words the additional white matter will be from the lateral side, therefore: Sensation from the lower parts of the body(legs, abdomen) will be positioned more medially in the Dorsal column; Sensation from higher parts of the body (hands) will be positioned more laterally in the Dorsal column. Somato-sensation arrangement in spinal cord 56  Somato-sensation arrangement All the fibers from the lower than T6 go through the medial bundle the fasciculus gracilis, and the axons coming from the upper body parts above T6 goes into the lateral bundle  the fasciculus cuneate 57 Dorsal/posterior column: Convey sensory information about fine touch, vibration, pressure and proprioception. In each side, there are 2 fasciculus up to the medulla (Fasciculus Gracilis and Fasciculus cuneate), 3nd neuron (in VPL) then they combined into one ventral posterior-lateral of the thalamus medial lemniscus Fasciculus Gracilis 2nd neuron Fasciculus Cuneate Decussation at the 1st neuron level of the medulla In this specific figure, what does the 1st neuron innervate? Leg/arm? 1) The axon goes via fasciculus cuneate 58 2) Arm area in sensory cortex Lemniscus (ribbon or band) elongated tract thalamus VPL MGB Lateral Lateral lemniscus lemniscus Medial lemniscus Fasciculus 59 Comparing the Spinal-thalamic tract and the dorsal tract Spinal-thalamic tract (Anterior-Lateral System) dorsal/posterior column 60 Dorsal column is evolutionarily more modern than the spinal-thalamic tract 1) Myelination (highway vs regular road); The dorsal tract heavy myelinated axons fast conductance -> highway 35 – 70 m/sec Spinal-thalamic tract lightly myelinated or even unmyelinated axons  slow conductance 1 – 15 m/sec 2) The type of sensation they transmit: The dorsal tract transmit new sensation  proprioception (sense of the position of the body), vibration, fine touch, 2-point discrimination Spinal-thalamic tract transmit  pain, crud touch, tickling, temperature, etching and sexual sensation 61 Vertical information: upward the spinal cord sensory tracts Usually you need 3 neurons to get to cortex – the highest level/rank (awareness) 1st example: Spinal-thalamic tract convey sensory info about pain/temperature (anterior column). 2nd example: dorsal/posterior column convey sensory information about fine touch, pressure and proprioception (dorsal column). 3rd example: Spinocerebellar tract convey proprioception (lateral column). 62 Spinocerebellar tract convey information about proprioception This tract conveys information to the cerebellum about length and tension of muscle fibers – where are your body parts when you walk/sit Not everything goes through the thalamus to reach the cortex. The spinocerebellar tract is a set of axonal fibers originating in the spinal cord and terminating in the ipsilateral cerebellum (unconscious proprioceptive sensation). Lateral column 63 Vertical information: motor commands downward the spinal cord  motor tracts Descending tracts- Two main motor pathways in the spinal cord: (1) Pyramidal tract/cortico-spinal tract voluntarily control - starts at M1 (only 2 neurons) (2) Exctrapyramidal tract- from brainstem nuclei to spinal - have 2 or more neurons in a chain - provide involuntary commends to muscles 64 1) Pyramidal tract/cortico-spinal tract voluntarily control - starts at M1 (only 2 neurons) Two good reasons for its name: The upper motor neurons are giant The column in which it runs pyramidal neurons, called BETZ has the shape of pyramid cells (in M1), can reach 100 μm in (at the level of the Medulla). diameter 65 Pyramidal tract/cortico-spinal tract voluntarily control - starts at M1. Only 2 motor neurons Upper motor neuron (actually inter neuron) The major function of this pathway is fine voluntary motor control of the limbs. The pathway also controls voluntary body posture adjustments. 80% fibers of the corticospinal tract cross over in the medulla and form the lateral corticospinal tract; 10% of fibers travel in the anterior corticospinal tract crossing at the spinal cord level; and 10% do not cross over and join the tract ventral corticospinal tract. 80% 10% 66  Pyramidal tract arrangement Axons exit the column from the Axons coming down from the pyramidal tract medial side exit medially into the ventral horn to innervate the lower motor neuron, therefore: the first to leave (upper body parts) will be located more medially, and the last to leave (lower body) will be located more laterally. 67 The corti-cospinal tracts arise from layer V 68  The corticospinal (or pyramidal) tract arises from different regions of the cortex. The Primary Motor Cortex: Upper Motor Neurons That Initiate Complex Voluntary Movements The axons of Betz cells form part of the pyramidal or corticospinal tract; however, they are not the only source of pyramidal tract fibers. fibers arise from: MI = primary motor cortex SI = primary somatosensory SMA = supplementary motor area PMC = premotor cortex Stimulation of premotor cortex (PMC) or the supplementary motor area (SMA) requires higher levels of current to elicit movements, and often results in more complex movements than stimulation of primary motor cortex (MI usually elicit simple movement of individual body parts). 69 S1 had direct role in control of movement Vertical information: motor commands downward the spinal cord  motor tracts Two main motor pathways in the spinal cord: 1) Pyramidal tract/cortico-spinal tract voluntarily control - starts at M1 (only 2 neurons) 2) Exctrapyramidal tract- from brainstem nuclei to spinal - have 2 or more neurons in a chain - provide involuntary commends to muscles 70  Exctrapyramidal tract- from brainstem nuclei to spinal - provide involuntary (subconsciously) commends to muscles Includes the brain stem, motor nuclei, and all motor pathways that are not part of the pyramidal system (including: substantia nigra, red nucleus, subthalamic nucleus, midbrain reticular formation and the cerebellum). These motor pathways are complex and multisynaptic - indirect pathway; often described as the motor-modulation system The extrapyramidal pathway is actively involved in the initiation and selective activation of movements Lower motor neuron in performed at a subconscious level, including: ventral horn 71 posture and skeletal muscle tone and coordination.  “involuntary” movements Neuroanatomy, Extrapyramidal System by Jane Lee; Maria Rosaria Muzio. 2021 72 https://www.ncbi.nlm.nih.gov/books/NBK554542/  Watch these movies Spinal Cord - Meninges and Internal Structure - Anatomy Tutorial https://www.youtube.com/watch?v=4H_2JRRzha4 Spinal Cord - External Anatomy - 3D Anatomy Tutorial https://www.youtube.com/watch?v=xXWsQrl1N7s 73  Spinal cord summary sensory/dorsal motor/ventral Butterfly shape: Dermatomes subdivisions of gray Spinal cord part of CNS the spinal cord and white matters 31 bilateral spinal nerves Cauda equina occupied only 2/3 of (horse's tail) the vertebral canal vertical level of the spinal cord – motor tracts vertical level of the spinal cord – sensory tracts Spinal-thalamic tract (Anterior-Lateral System) Communication at the horizontal level of the spinal dorsal/posterior column 74 cord – spinal reflexes