Spinal Cord Seminar Slides PDF

Spinal Cord Presentation by Dr Anna Gould Senior lecturer Structure and Function Intended Learning Outcomes To describe the gross anatomy and internal structure of the spinal cord To identify the locations of the ascending and d...

Spinal Cord Presentation by Dr Anna Gould Senior lecturer Structure and Function Intended Learning Outcomes To describe the gross anatomy and internal structure of the spinal cord To identify the locations of the ascending and descending tracts of the spinal cord To distinguish between upper and lower motor neurons To describe the mechanism of spinal reflexes and their significance  Vertebral body Location Extends from the medulla to L1/L2. Within the vertebral canal in the vertebral column Protected by vertebral column, meninges and cerebrospinal fluid In an adult, the spinal cord occupies only the upper two thirds of the vertebral column. Vertebral arch Vertebral foramen Gross anatomy Two swollen regions cervical lumbar Tortora, p240 Gross anatomy Spinal cord ends between L1 and L2 Considerably shorter than the vertebral column WARNING: Look away now if squeamish!  Gross anatomy Conus Medullaris: Tapered end of spinal cord (L1/L2) Filum Terminale: Delicate strand of fibrous tissue preceding downwards from apex of conus medullaris Cauda Equina: Lumbosacral nerve roots surround the filum terminale and form a cluster (resembles the tail of a horse) Meninges of the spinal cord Outer to inner 1.Dura Mater 2.Arachnoid 3.Pia Mater Introduction to the human body, Tortora, p239 Spinal Nerves Attached to spinal cord on each side are a series of spinal nerves Spinal nerves are made up of two bundles of axons, called roots; posterior roots and anterior roots Spinal nerves exit through Introduction to the human body, Tortora, p241 intervertebral foramen. Spinal nerves from several levels of the spinal cord will combine to form a peripheral nerve Spinal Segmentation There are 31 pairs of spinal nerves: 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal Cervical nerves exit above corresponding vertebral body (C8 spinal nerve but no C8 vertebral body) All other spinal nerves exit through the intervertebral foramen below the vertebra of the same name Lumbar and sacral nerves descend some distance before they exit from their respective Dermatome = An area of skin innervated by a single spinal nerve root Myotome = A group of muscles innervated by a single spinal nerve root Internal structure of the spinal cord Central canal of the spinal cord - continuous with the ventricles of the brain (from the fourth ventr icle), Introduction to the human body, Tortora, p241 allowing for the flow of CSF to Grey matter 1.Anterior Horn - Anterior Horn Cell – Motor Neuron 2.Lateral Horn – Lateral Horn Cell – Autonomic Motor Neuron 3.Posterior Horn – Posterior Horn – Sensory Neuron (Skeletal and Autonomic) White matter 1.Anterior Column 2.Lateral Column 3.Posterior Column Neurological Assessment, A Clinician’s Guide, Jones. Neurological Assessment, A Clinician’s Guide, Jones, p114 Types of neurons in the spinal cord Sensory Neuron Upper motor neurons Alpha (skeletomotor) neurons Gamma (fusimotor) neurons Interneuron  Motor neuron Upper motor neuron (is a neuron confined entirely within CNS) Lower motor neuron (cell body lies in CNS but whose axon innervates muscle) Spinal Reflex A reflex is a fast, involuntary sequence of actions that occurs in response to a particular stimulus The pathway that followed by nervous impulses to produce a reflex is called a reflex arc. Classification of Reflexes: 1. Monosynaptic/ polysynaptic 2. Ipsilateral/Contralateral 3. Intra-segmental/Inter-segmental Spinal Reflexes Examples: 1. Stretch reflex 2. Flexor Withdrawal 3. Crossed extensor 4. Plantar Reflex/ Babinski Simple stretch reflex arc 1. Patella hammer strikes the patella tendon, causing the quads muscle to stretch. 2. Stretch is picked up by muscle spindle in the quads. Sensory information travels to the grey matter of the spinal cord via a sensory neuron. 3. The sensory neuron synapses with an alpha motor neuron. 4. The motor neuron carries impulses back to the quadriceps muscle 5. which contracts, and extends the lower leg. Reciprocal Inhibition 1a afferents also synapse with an inhibitory interneuron This inhibits the alpha motor neuron of the antagonist muscle (hamstrings). The antagonist muscle therefore is relaxed. 2. Flexor withdrawal reflex 1. Noxious stimuli applied to skin stimulating free nerve endings 2. Impulses conducted through afferent fibers 3. These fibers make polysynaptic connections with excitatory interneurons 4. Results in ipsilateral flexor muscles contract, ipsilateral antagonist extensor muscles relax 5. The person withdraws the limb Essential Neuroscience, Siegel and Sapru, p171 3. Crossed extension reflex 1. Noxious stimuli activates pain fibers 2. Impulses conducted through afferent fibers 3. Afferents send collaterals through the anterior commissure to alpha motor neurons innervating contralateral flexors and extensor muscles 4. Activations of these polysynaptic pathways results in relaxation of the contralateral flexors muscles, while contralateral extensor muscles are contracted. 5. Permits extension of contralateral limb and withdrawal (flexion) of the ipsilateral limb. 4. Plantar Reflex/Babinski Sign Upper motor neuron normally modulates the response causing toes to adduct and flex down. If there is a lesion within the upper motor neuron, toes will abduct and extend. = Positive Babinski is a sign of upper motor neuron syndrome What does the spinal cord do? 1. Motor control 2. Transmission of Sensory Information 3. Autonomic Regulation 4. Central Pattern Generators Central Pattern Generators Still a lot we don’t know!! Neural circuits that co-ordinate rhymical stepping are found in spinal cord = Central Pattern Generators But humans need upper motor neuron pathways to mediate stepping movements. Intended Learning Outcomes To describe the gross anatomy and internal structure of the spinal cord To identify the locations of of the ascending and descending tracts of the spinal cord To distinguish between upper and lower motor neurons To describe the mechanism of spinal reflexes and their significance