Spinal cord lectures 2024.pdf

+ The Spinal Cord M&H: 488-496, 535-536, 541 Dr Elise Randle-Barrett © Monash University + Learning objectives: 1. Describe the external anatomy of the spinal cord, spinal nerves and nerve roots, and the structures that p...

+ The Spinal Cord M&H: 488-496, 535-536, 541 Dr Elise Randle-Barrett © Monash University + Learning objectives: 1. Describe the external anatomy of the spinal cord, spinal nerves and nerve roots, and the structures that protect the spinal cord. 2. Describe the internal anatomy of the spinal cord and the functions of gray and white matter. 3. Map the main somatosensory pathways (include neurons, ascending spinal cord tracts and sensory information conducted in your answer). 4. Map the main somatic motor pathways (include neurons, descending spinal cord tracts and the skeletal muscles they innervate in your answer). Warning: This material has been reproduced and communicated to you by or on behalf of Monash University under Part VB of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice. Unless otherwise stated, all images are the property of Pearson Education Limited © Monash University + Brain é ê “ The spinal cord is a two-way conduction highway” that conducts sensory input to the brain and motor output away Spinal cord from the brain é ê Sensory Motor input Output http://dailytimes.com.pk/ © Monash University + Why Study the Spinal Cord? As an allied health professional is it important that you understand the anatomy and functions of the spinal cord to successfully assess, treat and rehabilitate patient’s with spinal cord injuries. www.burke.org © Monash University +Objective 1: Describe the external anatomy of the spinal cord, spinal nerves and nerve roots, and the structures that protect the spinal cord. External Anatomy of the Spinal Cord The spinal cord: § long, thin, delicate tubular structure Cervical vertebrae -- § protected by the vertebral column Thoracic vertebrae vertebral foramen Lumbar (spinal cord passes vertebrae through vertebral foramen of each vertebra) Sacral vertebrae vertebra Coccyx Vertebrae + § ends between L1- L2 of the vertebral column in adults and L4 in infants § terminates in a cone shaped structure called the conus medullaris § anchored to L1 the coccyx L2 Conus medullaris by the filum terminale Filum terminale + § divided into 5 regions and 31 segments Cervical Cervical (C1-C8) Thoracic Thoracic (T1-T12) Lumbar (L1-L5) Located between Lumbar T12 to L2 of the Sacral (S1-S5) vertebral & 1 coccygeal column Sacral Coccyx + § a pair of spinal nerves connects to each segment 8 Cervical nerves 12 Thoracic nerves 5 Lumbar nerves 5 Sacral nerves 1 Coccygeal nerve + Spinal Nerves § Emerge from the Cervical nerves vertebral column § Branch to form the peripheral nerves that Thoracic nerves innervate all parts of the body (except the head) Lumbar nerves § Are mixed nerves à contain the axons of sensory & motor Sacral nerves (somatic & autonomic) Coccygeal nerve neurons + § Connect to the spinal cord by dorsal & ventral nerve roots Dorsal root Spinal nerve Ventral root Dorsal root Dorsal root Spinal cord Dorsal root Spinal Spinal nerve nerve Spinal nerve Ventral root Ventral root ventral root + dorsal root ganglion dorsal roots contain the contains the cell bodies axons of sensory neurons of sensory neurons Dorsal root Dorsal root (sensory) ganglion Sensory receptors Spinal nerve Motor Ventral root (autonomic) (motor) Motor ventral roots contain the (somatic) axons of motor neurons (somatic & autonomic) +§ the lumbar, sacral and coccygeal nerve roots travel beyond the conus medullaris to reach the vertebral region from which the lumbar, sacral and coccygeal spinal nerves emerge Ø this collection of nerve roots is called the cauda equina Lumbar, sacral & coccygeal regions of the spinal cord Cauda 5 Lumbar nerves equina 5 Sacral nerves Coccygeal nerve https://www.claims-medneg.co.uk + Protection of the Spinal Cord The spinal cord is protected from mechanical forces by: § vertebral column § cerebrospinal fluid à also nourishes the neural tissue & removes waste products § spinal meninges Dura mater Subdural space (serous fluid & blood vessels) Pia Mater Arachnoid mater Arachnoid Mater Subarachnoid space Dura Mater (CSF & blood vessels) Pia mater + The Spinal Meninges § Are continuous with the cranial meninges § Extend beyond the spinal cord to the second sacral vertebra (S2) § a lumbar puncture (spinal tap) involves the insertion of a needle into the subarachnoid space beyond L3 § this procedure: Ø does not damage the spinal cord Ø is used to withdraw CSF fluid for diagnostic testing (e.g. meningitis) or reducing intracranial pressure L4 Ø is used to administer medications L5 S1 + § Outer dura mater is separated from the vertebral column by an epidural space - site of anaesthetic administration Epidural space denticulate ligaments à extension of the pia mater that prevent lateral movements of the spinal cord +Objective 2: Describe the internal anatomy of the spinal cord and the functions of gray and white matter. Internal Anatomy of the Spinal Cord The neural tissue (neurons & neuroglia) of the spinal cord: § is divided into a left and right side by two grooves § anterior (ventral) median fissure § posterior (dorsal) median sulcus posterior median sulcus anterior median fissure © Monash University  +§ is organised into areas of gray matter & white matter § identical arrangement of gray & white matter, and the structures within them, on each side of the spinal cord Posterior (dorsal) White matter Gray matter Anterior (ventral) Flashback to Brain Outer region of gray matter Inner region of white matter © Monash University + Gray Matter § Composed of neuron cell bodies (mainly), unmyelinated axons & neuroglia § Varies in size and shape down the length of Cervical the spinal cord § Encloses a central canal à filled with cerebrospinal fluid Thoracic Lumbar Sacral © Monash University +§ Gray commissure à site where axons cross from one side of the CNS to the other Gray commissure (site of cross over) Central canal © Monash University + § Subdivided into gray horns Posterior gray horns Lateral Lateral gray gray horn horn Thoracic Lumbar Anterior gray horns © Monash University + § Gray horns contain sensory or motor nuclei Posterior gray horns - sensory function Sensory nuclei Sensory nuclei Autonomic motor nuclei Autonomic motor nuclei Somatic motor nuclei Somatic motor nuclei Anterior & lateral gray horns - motor function © Monash University + Sensory Nuclei of the Posterior Gray Horns § Contain the cell bodies of spinal cord interneurons Dorsal root Dorsal root ganglion Axons of sensory neuron Cell bodies of interneurons receive & process incoming sensory input Spinal nerve © Monash University  + Somatic Motor Nuclei of the Anterior Gray Horns § Contain the cell bodies of lower motor neurons Cell bodies of lower motor neurons à receive outgoing somatic motor output Spinal nerve Ventral root Flashback to Nervous System Axon of lower motor neuron Lower motor neurons are the motor neurons of the somatic nervous system. © Monash University  + Autonomic Motor Nuclei of the Lateral Gray Horns § Contain the cell bodies of preganglionic neurons Cell bodies of preganglionic neurons à receive outgoing autonomic motor output Spinal nerve Ventral root Flashback to Nervous System Axon of preganglionic neuron Preganglionic & postganglionic neurons are the motor neurons of the ANS © Monash University + Spinal Reflexes Gray matter is the site of integration for spinal reflexes. Stimulus Skin Reflex integration centres: receive & interpret Receptor incoming sensory input Sensory neuron decide on & generate the motor output that Integration centre causes the reflex Motor neuron response Effector muscle or gland These reflexes rapidly and involuntarily stimulate: § skeletal muscle contractions = somatic reflex (e.g. patellar reflex) § smooth muscle contractions of visceral organs (e.g. bladder) or gland secretions = autonomic reflex © Monash University + White Matter ”conduction highway” § Superficial to gray matter § Composed of myelinated (mainly) & unmyelinated axons § Anterior white commissure à site where axons cross from one side of the CNS to the other § Subdivided into white columns © Monash University + Posterior white columns Lateral Lateral white column white column Anterior white commissure Anterior white columns © Monash University  + § White columns contain ascending & descending spinal cord tracts = bundles of axons white matter of the spinal cord Ascending tracts Descending tracts http://dailytimes.com.pk/ © Monash University  + Spinal Cord Tracts of the White Matter § Conduct sensory or motor information between the spinal cord & brain § ascending tracts à conduct sensory input to the brain § descending tracts à conduct motor output away from the brain § Tract name often reveals the Sensory Motor input output origin, destination & white matter location e.g. lateral spinothalamic tract § origin = spinal cord § destination = thalamus Lateral Lateral § tract location = lateral white column white white column column © Monash University +Ascending Spinal Cord Tracts Name of Ascending Tract White Column Sensory Information Location Conducted Fasciculus gracilis Posterior white Fine touch columns Vibration Fasciculus cuneatus Light pressure Proprioception Lateral spinothalamic Lateral white Pain & temperature columns Anterior spinocerebellar Lateral white Proprioception Posterior spinocerebellar columns Anterior spinothalamic Anterior white Crude touch columns Deep pressure © Monash University + Posterior Fasciculus gracilis tract white column Fasciculus cuneatus tract Lateral white Spinocerebellar column tracts Lateral spinothalamic tract Anterior (ventral) Anterior spinothalamic tract white column © Monash University + Descending Spinal Cord Tracts Name of Descending Tract White Column Motor Output Conducted Location Lateral corticospinal Lateral white Somatic motor output that controls tracts columns the skeletal muscles of the limbs “L” for lateral =“L” for limbs Anterior Anterior white Somatic motor output that controls corticospinal tracts columns the skeletal muscles of the trunk (axial skeleton) “A” for anterior = “A” for axial muscles © Monash University + Posterior white column Lateral corticospinal tract Lateral white column Anterior white Anterior (ventral) corticospinal tract column © Monash University + Review 1. Internal Anatomy The neural tissue of the spinal cord is organised into regions of gray & white matter. White matter Gray matter © Monash University + Gray Matter § Spatially organised into gray horns à contain sensory & motor nuclei § sensory nuclei receive & process sensory input § motor nuclei receive somatic or autonomic motor output Posterior gray horn Sensory nuclei Lateral Motor nuclei gray horn Anterior gray horn § contains reflex integration centres © Monash University + White Matter § Spatially organised into white columns à contain spinal cord tracts § ascending tracts conduct sensory input to the brain § descending tracts conduct motor output from the brain Posterior white column Lateral white column Ascending Descending Anterior white column sensory tracts motor tracts © Monash University  +Spinal Cord Injuries Posterior gray horns § Result in sensory and/or motor losses at or below the level of the injury § damage to the posterior gray horns or ascending spinal cord tracts = loss of sensation Anterior gray horns § damage to the anterior gray horns or corticospinal tracts = muscle weakness or paralysis Ascending sensory tracts Descending motor tracts © Monash University +Neural Pathways Spinal cord tracts belong to sensory pathways that connect receptors to the brain, and motor pathways that connect the brain to skeletal muscles. These pathways: BRAIN § conduct sensory input from receptors to the brain § conduct motor output from the brain Motor output Sensory input to skeletal muscles § consist of a chain of 2-3 neurons § usually cross over (decussate) within the CNS Receptor Skeletal Muscles © Monash University + Somatosensory Pathways Brain § Conduct general sensory input from receptors to the brain Third-order neuron § Involve a relay of neurons called: Ø first-order neuron Ø second-order neuron second-order neuron Ø third-order neuron First-order neuron Receptor © Monash University  +Objective 3: Map the main somatosensory pathways (include neurons, ascending spinal cord tracts and sensory information conducted in your answer). Three main somatosensory pathways: 1. Spinothalamic pathway 2. Posterior column pathway (a.k.a. dorsal column-medial lemniscal pathway) 3. Spinocerebellar pathway https://www.linkedin.com © Monash University + Spinothalamic Pathway Conducts sensations of crude touch, deep pressure, pain & temperature. § First-order neurons: § conduct sensory input from receptors into a posterior gray horn § synapse with second-order neurons within a sensory nucleus Dorsal root sensory nucleus of a First-order neuron posterior gray horn Thermoreceptor Second-order neuron © Monash University  + PSC § Second-order neurons: Third-order neuron § conduct sensory input to the Thalamus thalamus § ascend spinal cord in a/an: Ø anterior spinothalamic tract (crude touch & deep pressure) Ø lateral spinothalamic tract (pain & temperature) § synapse with third-order Second-order neuron neurons in the thalamus § Third-order neurons: Nociceptor § conduct sensory input First-order neuron to the primary somatosensory cortex (PSC) Thermoreceptor © Monash University + PSC Third-order neuron PSC Third-order neuron Thalamus Thalamus Axon of second-order neuron in a lateral spinothalamic tract Axon of second-order neuron in an anterior spinothalamic tract Nociceptor Thermoreceptor Tactile receptor © Monash University +osterior Column Pathway P Conducts sensations of fine touch, light pressure, vibration & proprioception. § First-order neurons: medulla oblongata § conduct sensory input Second-order into a posterior gray horn neuron and up to the medulla oblongata Axons of first-order neurons in a § ascend spinal cord fasciculus gracilis Proprioceptor or fasciculus in a fasciculus gracilis cuneatus tract or fasciculus First-order cuneatus tract neuron § synapse with Tactile second-order neurons receptor in the medulla oblongata © Monash University  PSC + Third-order neuron Thalamus § Second-order neurons: § conduct sensory input to the thalamus § synapse with third-order neurons in the thalamus § Third-order neurons: Second-order neuron § conduct the sensory input Medulla Oblongata to the PSC Proprioceptor First-order neuron Tactile receptor © Monash University  + Spinocerebellar Pathway Conducts sensations of proprioception. § First-order neurons: § conduct sensory input from proprioceptors into a posterior gray horn § synapse with second-order neurons within a sensory nucleus Dorsal root sensory nucleus of a posterior gray horn Proprioceptor First-order neuron © Monash University  + § Second-order neurons: § conduct sensory input to the cerebellum § ascend spinal cord in an anterior Cerebellum or posterior spinocerebellar tract Flashback to Brain The cerebellum uses this proprioceptive information to maintain posture, balance, and ensure smooth, coordinated Axon of second-order neuron movements in a spinocerebellar tract Proprioceptor © Monash University First-order neuron + Objective 4: Map the main somatic motor pathways (include neurons, descending spinal cord tracts and the skeletal muscles they innervate In your answer). Somatic Motor Pathways § Conduct somatic motor output from the primary motor cortex (PMC) to skeletal muscles § Involve a relay of two neurons: Ø upper motor neuron Ø lower motor neuron Upper motor neuron § Two main somatic motor pathways: 1. Lateral corticospinal pathway 2. Anterior corticospinal pathway Lower motor neuron https://jnassi.com © Monash University  PMC + Lateral Corticospinal Pathway Conducts the somatic motor output that controls the skeletal muscles of the limbs. § Upper motor neurons: § conduct somatic motor output from the PMC to an anterior gray horn § descend spinal cord in a lateral corticospinal tract Axon of upper motor neuron in a lateral corticospinal Skeletal muscle tract (limbs) § synapse with lower motor neurons in a motor nucleus Lower motor neuron © Monash University + § Lower motor neurons: § conduct somatic motor output to skeletal muscles of the limbs Upper motor neuron Skeletal muscle (limbs) motor nucleus of an anterior gray horn Ventral root Lower motor neuron © Monash University + Anterior Corticospinal Pathway PMC Conducts the somatic motor output that controls the skeletal muscles of the trunk (axial skeleton). § Upper motor neurons: § conduct somatic motor output from the PMC to an anterior gray horn § descend the spinal cord in an anterior corticospinal tract Axon of upper motor neuron in an anterior corticospinal tract Skeletal muscle (trunk) § synapse with lower motor neurons in a motor nucleus Lower motor neuron © Monash University + § Lower motor neurons: § conduct somatic motor output to skeletal muscles of the trunk Upper motor neuron Skeletal muscle (trunk) motor nucleus of an anterior gray horn Ventral root Lower motor neuron © Monash University + Neural Pathway Name of Information Conducted Ascending/Descending Tract Posterior column Fasciculus gracilis tracts Fine touch Pathway Fasciculus cuneatus tracts Vibration Light pressure Proprioception (conscious) Spinothalamic pathway Lateral spinothalamic tracts Pain Temperature Anterior spinothalamic tracts Crude touch Deep pressure Spinocerebellar Spinocerebellar tracts Proprioception pathway (anterior & posterior) (unconscious) Lateral corticospinal Lateral corticospinal Somatic motor output to pathway tracts skeletal muscles (limbs) Anterior corticospinal Anterior corticospinal Somatic motor output to pathway tracts skeletal muscles (trunk) © Monash University +eview 2. Sensory & Motor Pathways R Integration by interneurons in cerebral cortex PSC PMC Third-order neuron Upper motor neuron Thalamus or Cerebellum Second-order neuron Spinal Spinal cord cord or medulla First-order neuron Lower motor neuron Sensory receptor Skeletal muscle (skin, muscles, tendons, joints) © Monash University