l>BIOL 237 course Notes - The Spinal Cord and Spinal Nerves
*
Click on photo or hypertext for a larger view.

You are watching: Muscles of the neck and shoulder are innervated by spinal nerves from the ________ region.

The Nervous system - Spinal Cord and also Peripheral Nerves
*
*
The spinal cord is the connection facility for the reflexes as well asthe afferent (sensory) and efferent (motor) pathways for most of thebody below the head and also neck. The spinal cord starts at thebrainstem and also ends at about the second lumbar vertebra. Thesensory, motor, and interneurons discussed previously are found inspecific components of the spinal cord and nearby structures. Sensoryneurons have their cabinet bodies in the spinal (dorsal root) ganglion.Their axons travel v the dorsal root into the gray matter ofthe cord. In ~ the gray matter room interneurons through which thesensory neurons might connect. Additionally located in the gray matter arethe motor neurons who axons take trip out of the cord v theventral root. The white matter surrounds the gray matter. Itcontains the spinal tracts which ascend and also descend the spinal cord.Surrounding both the spinal cord and the brain are the meninges, athree layered covering of connective tissue. The dura mater is thetough external layer. In ~ the dura is the arachnoid i m sorry is favor aspider net in consistency. The arachnoid has actually abundant an are withinand beneath it (the subarachnoid space) which containscerebrospinal fluid, together does the room beneath the dura mater(subdural space). This cerebrospinal fluid supplies buoyancy forthe spinal cord and brain to help carry out shock absorption. The piamater is a really thin layer i beg your pardon adheres tightly come the surface ar of thebrain and spinal cord. It adheres to all contours and fissures (sulci) ofthe mind and cord.
Terms:ganglion - a arsenal of cabinet bodies located external the main Nervous System. Thespinal ganglia or dorsal source ganglia contain the cabinet bodies of sensory neurons enteringthe cord at that region.nerve - a team of yarn (axons) outside the CNS. The spinal nerves save on computer the fibers ofthe sensory and motor neurons. A nerve does not contain cell bodies. They are located inthe ganglion (sensory) or in the gray matter (motor).tract - a group of yarn inside the CNS. The spinal tracts lug information up or downthe spinal cord, to or indigenous the brain. Tracts within the mind carry information from oneplace to another within the brain. Tracts space always part of white matter.gray matter - an area the naipublishers.comyelinated neurons where cell bodies and also synapses occur. Inthe spinal cord the synapses in between sensory and also motor and also interneurons wake up in thegray matter. The cabinet bodies that the interneurons and also motor neurons also are discovered in thegray matter.white matter - an area of myelinated fiber tracts. Myelination in the CNS different fromthat in nerves.
*
At 31 areas along the spinal cord the dorsal and also ventral roots cometogether to kind spinal nerves. Spinal nerves save both sensoryand motor fibers, as do most nerves. Spinal nerves space givennumbers which indicate the section of the vertebral obelisk in whichthey arise. There are 8 cervical (C1-C8), 12 thoracics (T1-T12), 5lumbar (L1-L5), 5 sacral (S1-S5), and also 1 coccygeal nerve. Nerve C1arises in between the cranium and also atlas (1st cervical vertebra) and C8arises in between the 7th cervical and 1st thoracic vertebra. All theothers arise listed below the respective vertebra or previous vertebra in thecase that the sacrum. Because the actual cord ends at the second lumbarvertebra, the later on roots happen close with each other on the cord and also traveldownward to exit at the appropriate point. This nerve roots arecalled the cauda equina due to the fact that of your resemblance to a horsestail.
The dermatomes room somatic or musculocutaneous locations served by fibers from specificspinal nerves. The map that the dermatomes is shown by number 13.11.This map is useful indiagnosing the beginning of specific somatic pain, numbness, study abroad etc. When thesesymptoms are led to by press or inflammation that the spinal cord or nerve roots.Referred pain is caused when the sensory yarn from an inner organ get in the spinalcord in the same root together fibers indigenous a dermatome. The mind is bad at interpretingvisceral pain and also instead interprets it together pain from the somatic area of the dermatome. Sopain in the heart is often understood as ache in the left eight or shoulder, pain in thediaphragm is understood as follow me the left clavicle and also neck, and the "stitch in your side"you sometimes feel when running is ache in the liver as its vessels vasoconstrict. (SeeFigure 14.8)
Spinal nerves join together in plexuses. (See number 13.5) A plexus is an interconnectionof fibers which type new combinations together the "named" or peripheral nerves. There arefour voluntary plexuses (there room some autonomic plexuses which will certainly be mentionedlater): they are the cervical plexus, the brachial plexus, the lumbar plexus, and also thesacral plexus. Every plexus provides rise to brand-new combinations of fibers as the peripheralnerves. The nerves and plexuses you need to know are:Cervical Plexus (See number 13.7, Table 13.3) - the phrenic nerve travels through thethorax to innervate the diaphragm.Brachial Plexus (See number 13.8, Table 13.4) - Axillary nerve - innervates the deltoid muscle and also shoulder, along with the posterioraspect the the top arm. Musculocutaneous nerve - innervates anterior skin of upper arm and elbow flexors. Radial nerve - innervates dorsal aspect of the arm and also extensors that the elbow, wrist,and fingers, abduction of thumb. Median nerve - innervates the middle elbow, wrist and finger flexors, adducts thethumb. Ulnar nerve - innervates the medial element wrist and finger flexors.Lumbar Plexus (See number 13.9, Table 13.5) genitofemoral - to the external genitalia obturator - to the adductor muscles femoral - innervates the skin and also muscles of upper thigh, including the quadriceps.Sacral Plexus (See figure 13.10, Table 13.6) gluteal nerves (superior and inferior) - remarkable innervates the gluteus medius andminimus, inferior innervates the gluteus maximus. sciatic nerve - the body"s biggest nerve, consists of two major branches, the tibialand common peroneal. With each other they innervate most every one of leg consisting of the flexors ofthe knee, part of adductor magnus, muscles for plantar flexion, dorsiflexion, and othermovements of the foot and toes.
*
Structure the a nerve:A peripheral nerve is arranged much like a muscle in terms of itsconnective tissue. It has actually an external covering which forms a sheatharound the nerve, referred to as the epineurium. Frequently a nerve will certainly runtogether with an artery and vein and also their connective coverings willmerge. Nerve fibers, which room axons, organize into bundles knownas fascicles through each fascicle surrounding by the perineurium.Between separation, personal, instance nerve fibers is one inner class of endoneurium.

See more: Anderson East & Miranda Lambert Pushin Time, A Love Song With Anderson

*
The myelin sheath in peripheral nerves consists of Schwann cellswrapped in countless layers around the axon fibers. Not all yarn in anerve will certainly be myelinated, however most that the voluntary yarn are. TheSchwann cells are portrayed as arranged follow me the axon likesausages on a string. (A much more apt analogy would be like jelly rolls!)Gaps between the Schwann cells are called nodes that Ranvier.These nodes permit an advertise to travel faster due to the fact that it doesn"tneed to depolarize every area of a membrane, just the nodes. Thistype of conduction is dubbed saltatory conduction and method thatimpulses will certainly travel faster in myelinated fibers than in naipublishers.comyelinatedones.The myelin sheath does number of things:1) It offers insulation to assist prevent short circuiting betweenfibers. Illness which ruin the myelin sheath cause inability tocontrol muscles, perceive stimuli etc. One such an illness is multiplesclerosis, one autoimmune disorder in which your very own lymphocytesattack the myelin proteins. .2) The myelin sheath provides for faster conduction.3) The myelin sheath offers for the possibility of fix ofperipheral nerve fibers. Schwann cells help to keep the micro-environments of the axons and also their tunnel (the neurilemma tunnel)permits re-connection through an effector or receptor. (See below)CNS fibers, not having actually the same kind of myelination accumulatescar organization after damage, which prevents regeneration.
Regeneration that a peripheral nerve fiber (See number 13.3) relies upon numerous things.First the damages must be far from the cabinet body. Anterograde degeneration destroys theaxon distal come the suggest of damage. Retrograde degeneration reasons the fiber todegenerate for a distance earlier toward the cabinet body. The amount of axoplasm lostdetermines whether the neuron have the right to survive. Secondly the myelin sheath and itsneurilemma tunnel should be intact. Chemicals such as the myelin proteins have tendency to inhibitregrowth, yet macrophages will go into the damaged area and also phagocytize this proteinsand other debris. Schwann cells will proliferate and also secrete development stimulating factorsand administer the chemical and physical needs essential for growth and re-innervation bythe axon.
*
The Spinal Tracts: (See figure 12.30)The white matter of the spinal cord includes tracts which travel upand down the cord. Countless of these tracts travel to and from thebrain to administer sensory input come the brain, or bring motor stimulifrom the mind to control effectors. Ascending tracts, those whichtravel towards the mind are sensory, descending tracts room motor.Figure 12.30 reflects the location of the significant tracts in the spinalcord. For many the name will show if the is a motor or sensorytract. Many sensory tracts names begin with spino, denote originin the spinal cord, and their name will finish with the part of the brainwhere the street leads. For example the spinothalamic tract travelsfrom the spinal cord to the thalamus. Tracts who names beginwith a part of the brain are motor. For example the corticospinaltract begins with yarn leaving the cerebral cortex and also travels downtoward engine neurons in the cord.
NEXT: The Reflexes