*Spinal cord and nerves - Google Docs PDF

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Spinal cord ● Long structure comprised of nervous tissue (neurons and associated glial cells)  ● Part of the CNS  ● Located in the vertebral canal   ● Functions of the spinal cord:   Vertebrae- bone structures that surround the spinal cord  ● Stacked on each other to create the vertebral column.  ● Smooth side of the vertebrae = anterior side  ● Spinous processes side =posterior side  ● Function: provide protection for the tissues of the spinal cord   Vertebral foramen- a hole within the spinous processes region that faces superior inferior ● When vertebrae are stacked on top of each other, the successive holes create a canal known as the vertebral canal.  ● The vertebral column is divided into regions based on it's curves (superior -> inferior)  ○ Cervical region  ■ Cervical vertebrae ■ Cervical nerves  ○ Thoracic region  ○ Lumbar region  ○ Sacral and Coccygeal regions ● The name of the regions dictate the names of the vertebrae and the spinal nerves (the spinal nerves that exit) in that region.   Intervertebral foramina- spaces between the vertebrae  ● Where the spinal nerves exit the vertebral canal. 

● Spinal cord starts at the foramen magnum (Circular shaped hole in the base of the skull) and ends by the time it reaches the top of vertebrae L2 (second lumbar vertebrae) ○ Vertebral canal is longer than the spinal cord due to difference of speed of growth during development    ● The spinal cord is kept in place in the middle of the spinal column by the meninges (connective tissue layers)   ● Spinal cord in not quite round, it is flattened on one side ● Diameter of the spinal cord is not uniform along it's length.  ○ There are two enlargements :  1. Cervical enlargement  ● Occurs between vertebra C4 & T1  2. Lumbosacral enlargement  ● Occurs between vertebrae T9 & T12 ○ The enlargements are for extra nervous tissues that are required to supply additional structures of the upper and lower limbs, as they require more neurons   Conus medullaris- The inferior end of the spinal cord.  ● Spinal cord tapers into a cone shape   ● Nerves supplying the lower limbs exit the lumbosacral enlargement and course down through the vertebral canal to exit via the foramina.   Coda equina- the hair like nature of the nerves coming out of the bottom of the spinal cord via the foramina 

Filum Terminale- extension of the Pia mater connective tissue around the spinal cord. Anchors the spinal cord in the inferior part of the vertebral column. Stops any movement of the spinal cord in the superior direction   

Meninges  ● The spinal cord is surrounded by meninges to provide some level of protection.  ● Continuous of the meninges of the brain.   ● Layers of the meninges (superficial – deep): ○ Dura Mater  ● Made up of irregular connective tissue  ● Thickest and strongest layer  ● There is space, Epidural space, between the dura mater and the periosteum (connective tissue on the bone) ● Space is filled with fat, blood vessels, areolar connective tissue  ● Continuus with the brain  ● Prevents the spinal canal from moving  ○ Arachnoid Mater  ● Thin, avascular (no blood supply to the layer) layer ● Contains simple squamous epithelial cells, and delicate network of collagen and elastic fibres.  Subdural space: space between the dura and arachnoid mater. Contains small amount of serous fluid.  ○ Pia Mater  ● Contains blood vessels that supply the spinal cord  ● Tightly adheres to the spinal cord  ● Maintains the spinal cord in the vertebral canal  ● Has small extensions of itself called the denticulate ligaments, that connect it to the dura mater. 

● Denticulate ligaments also help anchor the spinal cord laterally to prevent side to side movement.  Subarachnoid space- space between the pia mater and the arachnoid mater. Contains CSF. Continuus with the subarachnoid space of the brain   ● The cerebral spinal fluid (CSF) helps cushion the spinal cord, delivers nutrients and removes waste products.  

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Internal anatomy ○ The spinal cord has two major portions:  ○ Outer white matter portion  ○ Inner grey matter portion 

 Posterior median sulcus- small groove on the posterior side of the spinal cord Anterior median fissure- large groove on the anterior side of the spinal cord  ● The sulcus and the fissure divide the spinal cord into two halves.  

White matter  ● Contain myelinated axons which run the length of the spinal cord  ● Can be ascending or descending creating nerve tract.   ● Nerve tracts with similar functions are grouped in an organized way and become known as columns.  ● These allow for information to be transmitted in an organized fashion throughout the spinal cord.  ● There are 3 columns in the white matter:  ○ Dorsal (Posterior) column  ○ Ventral (Anterior) column  ○ Lateral column  White commissure- Connects the right and left side of the spinal cord. There are two of them, an anterior and posterior one.  ● Allows signals to one side of the body to another.   

Gray matter  ● Gray matter is make up of  ○ Neuron cell bodies ○ Dendrites  ○ Axon terminals  ○ Interneurons- shorter neurons that connect various parts of the spinal cord   ● Composed of three horns: 

○ Dorsal (Posterior) horn  ○ Lateral horn  ○ Ventral (anterior) horn ● The horns are highly organized based of nerve functions.  ○ Lateral horns  ● small and found in the thoracic and lumbar region of the spinal cord  ● Associated with the neurons of the autonomic nervous system  ○ Posterior horns  ● where are sensory neurons enter the spinal cord  ● They can wither synapse here with the inter neurons or combine with the white matter and then ascend or descend with the spinal cord.  ○ Anterior horn  ●

largest 

● Ak.a the motor horn  ● Contains cell bodies for the somatic motor neurons that go to skeletal muscles   ● In the grey matter region, the left and right side of the spinal cord are connected by the grey commisures.  ● The central canal is located in the middle of the grey commisures.   Rootlets- at each spinal level, they either leave or enter the spinal cord. Part of the PNS   Ventral root- on the anterior side, where all the motor neurons are going to exit the spinal cord  Dorsal root- on the posterior side, where all the sensory neurons are going to enter the spinal cord. Contains dorsal root ganglion.  ● If there is a bundle on the ventral root, that’s the dorsal root.   Spinal nerve- when the dorsal and ventral root merge together 

● Therefore, all spinal nerves have mixed functions (sensory and motor)  ● Contain sensory and motor axons  ● Exit the vertebral via the intervertebral foramina  

Sensory and Motor Processing Sensory 1. Sensory receptors are activated due to stimuli.  2. Sensory information is going to be brought to the sensory neurons to the dorsal roots of the spinal cord.  3. Then it goes to the posterior grey horn of the spinal cord  4. Then it can either go into the cell bodies of the interneurons or it can go into the white matter go into sensory ascending tract or it can cross over through the grey commissure and enter the sensory ascending tract on the opposite side of the spinal cord   Motor 1. Motor information comes from the brain (cerebrum) from descending tract into the white matter area  2. Then information enters into the anterior grey horn and synapse with the somatic motor neuron  3. The somatic motor neuron goes into the ventral root of the spinal nerve  4. Then is travels all the way to the target skeletal muscle   Motor processing for autonomic nervous system  1. The motor neurons exit from the lateral grey horn into the ventral root of the spinal nerve.  2. They then synapse at the autonomic ganglion 3. They then go to the target tissue (cardiac muscle, smooth muscles, or glands)  

Fasciculi- regions where there are bundles of ascending or descending nerve tracts ● Damage to any region of the spinal cord will result in loss of sensation or motor control.   ● Diseases associated with the anterior horn of the spinal cord which are caused by the degeneration of the grey matter  ○ Polio  ● Caused by the polio virus which attacks the cell bodies of the moto neurons in the anterior horn.  ● Results in motor loss and eventually paralysis  ○ ALS  ● Also affects the motor neurons descending the spinal cord  ● People eventually lose their ability to speak, swallow, or breathing.  

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Spinal nerves ● Part of the PNS ● ●

31 pairs of spinal nerves Named and number from the region of the vertebral column where the exit the vertebral canal

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The 1st pair exit the vertebral column between the skull and the first cervical vertebrae ○ Superior to the initial vertebrae in the vertebral column ○ Referred to as C1 ○ They are named after the vertebrae inferior them ● C1 nerve would be superior to C1 vertebrae ● C2 nerve would be superior to C2 vertebrae ○ C1 – C8 ; Only 7 cervical vertebrae but 8 cervical nerves ● C8 nerve exits below C7 vertebrae

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From the on, the spinal nerves are named after the vertebrae Superior to them T1 nerve is inferior to T1 vertebrae

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There are 4 pair of spinal nerves the exit via the sacral foramina (holes within the sacrum) Rest of the spinal nerves exit through the intervertebral foramina ○ 8 pair of cervical, 12 pairs of thoracic, 5 pair of lumbar, 5 pair of sacral, 1 pair of coccygeal

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For a person with a spinal cord injury, the level of injury is important for determining the function that person will The injury is also determined by whether the person has a complete spinal cord injury (the cord is cut entirely) or partial spinal cord injury ( on part of the cord has been damaged). This is why the symptoms of a spinal cord injury vary for much.

Structure of the Peripheral nerves ● Axons in the nerves are bundles in parallel are grouped together by either motor or sensory function ●

Protective layers of axon (deep -> superficial ○ Schwann cells surround each axon ○ Endoneurium- connective tissue layer. Seperate axons from each ○ Perineurium- connective tissue layer that hold together bundle of endoneurium called fascicles.

Fasciculus- bundles of myelinated axons ○ Epineurium- dense connective tissue layer that is continuous with the dura matter.

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As axons leave the spinal cord, they form smaller bundles called rootlets, that are on the dorsal and ventral surfaces of the spinal cord 6-8 rootlets merge together to form the dorsal or ventral roots. These roots pass through the sub-arachnoid space, pierce the arachnoid and join to form a spinal nerve, which contains both sensory and motor neurons.

Branches of the spinal nerve ● Rootlets exit the anterior and posterior sides, ● Rootles merge to form ventral and dorsal root of spinal nerve ● Dorsal and ventral root merge to form spinal nerve ●

Spinal nerves split into 2 main branches: ○ The Dorsal rami of the spinal nerve is innervating the dorsal truck muscles of the deep muscles of the back responsible for movements of the vertebral column ○ The ventral rami. Their destination is dependent on where you are in the vertebral column ● Thoracic regions (T2-T12): form intercostal nerves (innervate the intercostal muscles which are involved in breathing) ● Remining spinal nerve ventral rami become the roots of the plexuses, which is a intermingling of nerves: five plexuses: ● Ventral rami of C1-C4= cervical plexuses ● Ventral rami of C5-T1= Brachial plexuses ● Ventral rami of L1-L4= lumbar plexuses ● Ventral rami of L4-S4= sacral plexuses ● Ventral rami of S5- coccygeal nerve =coccygeal plexuses...