15. The Spinal Cord and Spinal Nerves - Kines 262 PDF

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Human Anatomy, , Martini/Timmons/Tallitsch

The Nervous System – The Spinal Cord and Spinal Nerves I.

Gross Anatomy of the Spinal Cord ● The adult spinal cord measures approximately 45 cm (18 in.) in length and extends from the foramen magnum of the skull to the inferior border of the first lumbar vertebra. ● The entire spinal cord can be divided into 31 segments. 1. A letter and number designation identify each segment. a. The segments are labeled: o Cervical – C1-C8 

The “extra” cervical segment is due to C1 being above cervical vertebrae C1 and exiting between the atlas and the occipital bone.

● In the cervical region the first pair of spinal nerves, exits between the skull and the first cervical vertebra. As discussed earlier 1. For this reason, cervical nerves take their names from the vertebra immediately following them. 2. The transition from this identification method occurs between the last cervical and first thoracic vertebrae. a. This is C8, thus, there are seven cervical vertebrae but eight cervical nerves.  o Thoracic – T1-T12 o Lumbar – L1-L5 o Sacral – S1-S5 o Coccygeal – C0 See Powerpoint now for a comparison of neurological terms 3. Every spinal segment is associated with a pair of dorsal root ganglia (more on this later) that contain the cell bodies of sensory neurons. Psuedounipolar type. a. These sensory ganglia lie between the pedicles of adjacent vertebrae. o On either side of the spinal cord, a dorsal root contains the axons of the sensory neurons in the dorsal root ganglion. 4. Anterior to the dorsal root, a ventral root leaves the spinal cord.

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Human Anatomy, , Martini/Timmons/Tallitsch

The Nervous System – The Spinal Cord and Spinal Nerves a. The ventral root contains the axons of both somatic and visceral motor neurons that control peripheral effectors. 5. The dorsal and ventral roots of each segment enter and leave the vertebral canal between adjacent vertebrae at the intervertebral foramina. 6. Distal to each dorsal root ganglion, the sensory and motor fibers form a single spinal nerve. a. Spinal nerves are classified as mixed nerves because they contain both afferent (sensory) and efferent (motor) fibers. 7. After age 4 the vertebral column continues to grow, but the spinal cord does not. a. This vertebral growth carries the dorsal root ganglia and spinal nerves farther and farther away from their original position relative to the spinal cord. b. As a result, the dorsal and ventral roots gradually elongate. 8. The adult spinal cord extends only to the level of the first or second lumbar vertebra; thus spinal cord segment S2 lies at the level of vertebra L1. ● The filum terminale and the long ventral and dorsal roots that extend caudal to the conus medullaris are called the cauda equina. ●

II.

The filum terminale ("terminal thread"), is a delicate strand of fibrous tissue, about 20 cm in length, proceeding downward from the apex of the conus medullaris. It is one of the modifications of pia mater. It gives longitudinal support to the spinal cord

Spinal Meninges ● The vertebral column and its surrounding ligaments, tendons, and muscles isolate the spinal cord from the external environment. ● The delicate neural tissues also must be protected against damaging contacts with the surrounding bony walls of the vertebral canal. 1. Specialized membranes, collectively known as the spinal meninges, provide protection, physical stability, and shock absorption to the spinal cord and surround the spinal nerve roots. 2. Blood vessels branching within these layers also deliver oxygen and nutrients to the spinal cord.

There are three meningeal layers: Seen below 2of 7

Human Anatomy, , Martini/Timmons/Tallitsch

The Nervous System – The Spinal Cord and Spinal Nerves Acronym for you DAP 

1.

Dura Mater The tough, fibrous dura forms the outermost covering of the spinal cord and brain. It is not bound to the bony walls of the vertebral canal – so it allows the spinal cord to move around in the vertebral canal Localized attachment of the dura mater to the skull, the sacrum, and each vertebra stabilizes the position of the spinal cord within the vertebral canal. b. The spinal dura mater fuses with the periosteum of the cranial cavity at the margins of the foramen magnum.

● 2. Arachnoid Mater the middle meningeal layer, consists of a simple squamous epithelium. The subarachnoid space contains cerebrospinal fluid (CSF) that acts as a shock absorber as well as a diffusion medium for dissolved gases, nutrients, chemical messengers, and waste products. a. The subarachnoid space of the spinal meninges can be accessed easily between L3 and L4 for the clinical examination of cerebrospinal fluid or for the administration of anesthetics. The blood vessels supplying the spinal cord are found in the pia mater • • • •

Spinal Tap Headache _happens due to leakage of CSF - which thus lowers pressure in CFS system – get and causes a headache. They correct this by creating an Epidural Blood Patch which is an insertion of patient’s blood into epidural space and plugging the hole with a clot or scab. In addition the extra volume of blood will raise the pressure in the space. Symptoms disappear usually within 6-24 hours.

● 3. Pia Mater – most deep and delicate of the three. The blood vessels supplying the spinal cord are found in the pia mater. • • •

Meningitis a large-scale inflammation due to immune system response to a pathogen. Bacterial or viral Subarachnoid space is enlarged due to increased intracranial-spinal pressure from the inflammatory process. Pressure causes decreased blood flow to spine and brain and thus cutting off vital circulation to nerves etc….

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Human Anatomy, , Martini/Timmons/Tallitsch

The Nervous System – The Spinal Cord and Spinal Nerves III.

Sectional Anatomy of the Spinal Cord 1. The projections of gray matter toward the outer surface of the spinal cord are called horns.

● Organization of Gray Matter a. The Posterior or (dorsal) gray horns contain somatic and visceral sensory nuclei. b. The Anterior or (ventral) gray horns contain neurons concerned with somatic motor control. c. The Lateral or (intermediate horns), found between segments and contain visceral motor neurons.

● Organization of White Matter 1. The white matter can be divided into regions, or columns. a. Ascending tracts relays sensory information toward the brain. b. Descending tracts relays motor commands into the spinal cord.

IV.

Spinal Nerves ● Peripheral Distribution of Spinal Nerves 1. Each spinal nerve forms through the fusion of dorsal and ventral nerve roots as those roots pass through an intervertebral foramen. 

The distribution of the sensory fibers within the dorsal and ventral rami illustrates the segmental division of labor along the length of the spinal cord

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Roots vs Rami…Roots come out from the spinal cord either front or back and Rami are where a spinal nerve (which is the formation of a spinal nerve) splits again to go to periphery.

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Dermatome. - An area of skin supplied with afferent nerve fibers by a single posterior spinal root

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Human Anatomy, , Martini/Timmons/Tallitsch

The Nervous System – The Spinal Cord and Spinal Nerves ● Nerve Plexuses a. In segments controlling the skeletal musculature of the neck and the upper and lower limbs, the peripheral distribution of the ventral rami does not proceed directly to their peripheral targets. o In these regions the ventral rami of adjacent spinal nerves blend their fibers to produce a series of compound nerve trunks. o Such a complex interwoven network of nerves is called a nerve plexus. o Nerve plexuses exist where ventral rami are converging and branching to form these compound nerves. o The four major nerve plexuses are the: The Cervical Plexus Branches from the cervical plexus innervate the muscles of the neck and extend into the thoracic cavity to control the diaphragm. The Phrenic nerve, the major nerve of this plexus, provides the entire nerve supply to the diaphragm. The Brachial Plexus The brachial plexus is larger and more complex than the cervical plexus. The brachial plexus innervates the pectoral girdle and upper limb, with contributions from the ventral rami of spinal nerves C5–T1. 

The lateral cord forms the musculocutaneous nerve exclusively.

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The lateral cord together with the medial cord, contributes to the meidan nerve.

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The ulnar nerve is the other major nerve of the medial cord.

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The posterior cord gives rise to the axillary nerve and the radial nerve. How to remember the Brachial Plexus

o Robert___________ Taylor________________ Drinks__________________ Cold__________________ Beers_____________________

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Human Anatomy, , Martini/Timmons/Tallitsch

The Nervous System – The Spinal Cord and Spinal Nerves • • • • • • • • • • •

Thoracic Outlet Syndrome – is a compression of a neurovascular bundle between the anterior scalene and middle scalene. It affects the brachial plexus and/or subclavian artery. The compression caused by 2 possible things: Positional (caused by movement of the clavicle (collarbone) and shoulder girdle on arm movement) Static enlargement or spasm of muscles surrounding the neurovascular bundle A first rib fixation and a cervical rib. Pinched Nerve - aka AKA – Radiculopathy (stinger) See mostly in high-contact sports It is a neurovascular entrapment or nerve compression or traction (pulling/tearing) Can also see artery vein (Vascular entrapment) Pain can and does occur with burning down the arm or “dead arm.”

Carpal Tunnel – is a median entrapment neuropathy that causes paresthesia, pain, numbness, and other symptoms in the distribution of the median nerve due to its compression at the wrist in the carpal tunnel. See intermittent numbness of the thumb, index, long and radial half of the ring finger. [The numbness often occurs at night. Causes - repetitive movement and manipulating activities.

2. The Lumbar and Sacral Plexuses The lumbar plexus is formed by the ventral rami of T12–L4. o The major nerves of the lumbar plexus are the: 

Genitofemoral nerve

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Lateral femoral cutaneous nerve

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Femoral nerve

b. The sacral plexus contains the ventral rami from spinal nerves L4–S4 o The major nerves of the sacral plexus are the: 

Sciatic nerve - The sciatic nerve passes posterior to the femur and deep to the long head of the biceps femoris muscle. a. As it approaches the popliteal fossa, the sciatic nerve divides into two branches: the common fibular nerve and the tibial nerve

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Pudendal nerve – is also a earlier branch of the sciatic and it is involved in Excretory and Reproductive functions.

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Human Anatomy, , Martini/Timmons/Tallitsch

The Nervous System – The Spinal Cord and Spinal Nerves  Sciatica aka (sciatic neuritis, sciatic neuralgia or lumbar radiculopathy) radiculopathy is a set of symptoms including pain caused by general compression or irritation of one of five spinal nerve roots of each sciatic nerve—or by compression or irritation of the left or right or both sciatic nerves. Symptoms include lower back pain, buttock pain, and numbness, pain or weakness in various parts of the leg and foot. Other symptoms include a "pins and needles" sensation, or tingling and difficulty moving or controlling the leg. Typically, symptoms only manifest on one side of the body. The pain may radiate above the knee, but does not always.

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