Spinal cord, spinal nerves

spastic paralysis

Damage to only the descending pathways in the white matter of the spinal cord leaves the spinal cord motor neurons and spinal reflexes intact. In this case, muscles remain healthy but their movements no longer under voluntary control because brain connection is lost.

nerve fibers of the PNS are ensheathed in _____ which form a neurilemma and often a ______ around the axon.

Schwann cells, myelin sheath

median n.

a main nerve of the brachial plexus mixed from lateral and medial cords; sensory: skin of lateral 2/3 of hand; tips of digits I-IV; hand joints

ulnar n.

a main nerve of the brachial plexus mixed from medial cord; sensory: skin of palmar and medial hand and digits III-V; elbow and hand joints

radial n.

a main nerve of the brachial plexus mixed from posterior cord. sensory: skin of the posterior arm; posterior and lateral forearm and wrist; joints of elbow, wrist and hand

musculocutaneous n.

a main nerve of the brachial plexus that is mixed from the lateral cord. Sensory: Skin of anterior and lateral forearm and elbow joint

axillary n.

a main nerve of the brachial plexus that is mixed from the posterior cord; sensory: skin of lateral shoulder and arm; shoulder joint

supraclavicular nerve

a somatosensory nerve in cervical plexus; innervates the anterior and lateral neck; shoulder, and anterior chest; from C 3-4.

the _____ gives off a pair of communicating rami which connect with a string of sympathetic chain ganglia alongside the vertebral column

anterior ramus

the cord is divided into

cervical (8), thoracic (12), lumbar (5), sacral (5), and coccygeal (1) regions.

when the nerves to the upper and lower limbs arise, the spinal cord shows obvious enlargments called

cervical and lumbar enlargements

the white matter of the spinal cord is composed of axon bundles that are arranged into 3 columns or funiculi called____, ____, and ____.

posterior (dorsal), lateral, and anterior (ventral) columns

in ascending tracts, sensory signals generally travel across 3 neurons from origin in receptors to destination in the brain sensory areas. These neurons are called

1.) 1st order neuron- detects a stimulus and transmits the signal into the spinal cord or brain stem, 2.) 2nd order neuron- the 1st order neuron synapses with this in the CNS and it continues from here to a "gateway" called the thalamus in the upper end of the brain stem, 3.) 3rd order neuron- goes from here to the sensory region of the cerebral cortex

4 main functions of spinal cord

1.) conduction-bundles of nerves conduct info up and down cord, connecting different levels of trunk with the brain. Allows sensory info to reach the brain and motor commands to reach effectors 2.) neural integration- pads of spinal nerves recieve input from multiple sources, integrate this info, and execute an appropriate output 3.) locomotion- most neurons in the brain initiate walking and all its aspects, but the simple, repetitive muscle contractions of putting one foot in front of another are coordinated by central pattern generators. 4.) reflexes- cord is a motor center for involuntary, stereotyped responses to stimuli and involve brain, spinal cord, and peripheral nerves.

functions of meninges

1.) cover and protect CNS, 2.) enclose/protect blood vessels that supply CNS, 3.) contain the CSF

from superficial to deep, the meninges are

1.) dura mater- tough collagenous membrane/ space between this sheath and vetebrae bones is called epidural space which is occupied by blood vessels, fat tissue, loose connective tissue. 2.) arachnoid mater- consists of simple squamous epithelium adhering to inside of dura and loose mesh of collagenous and elastic fibers filling the gap (subarachnoid space which is filled with CSF) between the arachnoid and the pia. Space between dura and arachnoid is subdural space (can fill with fluid/blood as result of disease/trauma) 3.) pia mater- tranparent/follows closely to spinal cord. At S-2 fuses with the dura and forms coccygeal ligament (anchors cord and meninges to vertebral column) and extensions of the pia called denticulate ligaments extend through arachnoid to dura to anchor cord further

main nerves of the brachial plexus

1.) musculocutaneous n., 2.) axillary n., 3.) radial n., 4.) median n., 5.) ulnar n.

3 forms of muscle paralysis are

1.) paraplegia (paralysis of both lower limbs resulting from spinal lesions at T-11- L-1. 2.) quadriplegia (paralysis of all 4 limbs resulting from lesions above C-5 3.) hemiplegia- paralysis of one side of the body; usually results not from spinal cord injury but from a stroke or other brain lesion

4 important properties of a reflex are

1.) requires stimulation, 2.) are quick, 3.) are involuntary, 4.) are stereotyped

a somatic reflex employs a reflex arc in which signals travel along the following pathways

1.) somatic receptors in skin, muscles, and tendons, 2.) afferent nerve fibers, 3.) an integrating center, 4.)efferent nerve fibers, 5.) effectors

4 zones of spinal gray matter

1.) somatic sensory (SS), 2.) visceral sensory (VS), 3.) visceral motor (VM), 4.) somatic motor (SM)

There are ___ paris of spinal nerves

31

there are ___ pairs of spinal nerves. The first pair of spinal nerves pass between the ____ and ____ and the rest pass through ______.

31 pairs. Pass between the skull and vertrbra C-1, the rest pass through intervertebral foramina

There are ___ cervical, ___ thoracic, ____ lumbar, ____ sacral, and ____ coccygeal spinal nerves

8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal spinal nerve

phrenic n.

Most important nerve of the cervical plexus. It innervates the diaphragm, pleura, and the pericardium. It originates from anterior rami of C 3-5 and is a mixed nerve

Any ONE fiber in the nerve conducts signals in _____ direction(s) only

ONE

dermatomes overlap their edges so to anesthetize a specific dermatome, you have to anesthetize 3 successive spinal nerves called

T-4- nipple line, T-6- xiphoid tip, and T-10- umbilicus

immediately after leaving the intervertebral foramen, the nerve divides into ______, ______, and _______.

an anterior ramus, a posterior ramus, and a small meningeal branch

the cord has longitudinal grooves on the anterior and posterior sides called

anterior (ventral) median fissure and posterior (dorsal) median fissure

In each segment of the spinal cord, nerve rootlets emerge from the anterior surface and converge to form the ______ of the spinal nerve

anterior (ventral) root

cuneate fasciculus (dorsal column pathway)

ascending tract. Joins the gracile at T6 and occupies the lateral portion of the posterior column. It's fibers end in the cuneate nucleus on the ipsilateral side of the medulla. In the medulla, 2nd order fibers of gracile and cuneate decussate and for the medial lemiscus- a tract of nerve fibers that leads to the thalamus. 3rd order fibers go from the thalamus to the cerebral cortex. Because of the decussation, the gracile and cuneate signals go to the contralateral hemisphere.

gracile fasciculus (dorsal column pathway)

ascending tract. carries signals from the midthoracic and middle part of the body. At T-6 it is joined by the cuneate fasciculus. Has 1st order nerve fibers that travel up ipsilateral side of the cord and terminate at the gracile nucleus in the medulla oblongata of the brain stem. Carry signals for vibration, deep/discriminative touch, etc.

spinoreticular tract

ascending tract. this also travels up the anterolateral system. It carries pain signals resulting from tissue injury. 1st order sensory neurons enter posterior horn and immediately synapse with the 2nd order neurons. These decussate to the opposite anterolateral system, forming the spinoreticular tract, ascend up the spinal cord, and end in the reticular formation in the medulla and pons. 3rd order neurons go from pons to the thalamus. 4th order neurons go from here to the cerebral cortex.

spinothalamic tract

ascending tract. this forms the anterolateral system which passes up the anterior (ventral) and lateral columns of the spinal cord. These tracts carry signals for pain, temperature, pressure, tickle, itch, and light or crude touch. 1st order neurons end in posterior horn of the spinal cord. Here they synapse with 2nd order neurons which decussate and form the contralateral ascending spinothalamic tract. 2nd order neurons ascend to the thalamus to synapse with 3rd order neurons. 3rd order neurons go from the thalamus to the cerebral cortex. because of the decussation, sensory signals in this tract arrive in the contralateral cerebral hemisphere from their point of origin.

carry sensory info up the cord to the brain

ascending tracts

posterior (dorsal) and anterior (ventral) spinocerebellar tracts

ascending tracts. travel through the lateral column and carry proprioceptive signals from the limbs and trunk to the cerebellum and rear of the brain. 1st order neurons originate in muscles and tendons and end up in the posterior horn of the spinal cord where they synapse with 2nd order neurons. 2nd order neurons send their fibers up the spinocerebellar tract and end in the cerebellum. Posterior tract fibers travel up ipsilateral side of the spinal cord. Anterior tract crosses over and travels up the spinocerebellar tract on the contralateral side, but then crosses back in the brain stem to enter the ipsilateral side of the cerebellum. Both tracts provide feedback to the cerebellum needed to coordinate muscle action.

arising from the medullary cone is a bundle of nerve roots called _____ that occupy the vertebral canal from L-2 to S-2 and innervates the pelvic organs and lower limbs.

cauda equine (shaped like a horsetail)

except in the thoracic region, the anterior rami branch and merge to form 5 nerve divisions called

cervical plexus (small one in the neck), brachial plexus (near the shoulder), lumbar plexus (in the lower back), sacral plexus (very often lumped with lumbar to be called the lumbosacral plexus), and coccygeal plexus (very small)

severe damage to the ventral horn or to the ventral motor roots destroys the somatic motor neurons in the region of the injury and results in ________.

complete or flaccid paralysis of the skeletal muscles

spina bifida

congenital defect in which one or more vertebrae fail to form a complete vertebral arch to enclose the spinal cord. Most common in lumbosacral region.

crossed extension reflex

contraction of extensor muscles in the limb opposite from the one that is withdrawn

because of ______ the left side of the brain recieves sensory info from the right side of the body and sends motor commands to that side (right) while the right side of the brain senses and controls left side of the body

decussation (meaning that tracts cross over from one side to the other as they pass up and down the spinal cord)

tectospinal tract

descending tract. Begins in the midbrain area (superior colliculus) called the tectum and crosses to contralateral side of the midbrain. It descends in the ventral column to upper neck and stops. Involved in reflex turning of the head.

corticospinal tract

descending tract. carries motor signals from the cerebral cortex for precise, finely coordinated voluntary limb movements. Fibers of this system form ridges called pyramids on the anterior surface of the medulla. Most corticospinal fibers decussate in the lower medulla (pyramids) and form the lateral corticospinal tract on the contralateral side of the spinal cord. A few fibers remain uncrossed and form the anterior (ventral) corticospinal tract on the ipsilateral side. Fibers of the anterior tract decussate lower in the spinal cord, so even they control contralateral muscles.

conduct motor impulses down the cord to effectors of the body

descending tracts

lateral and medial vestibulospinal tracts

descending tracts. begin in the brainstem (vestibular nuclei in the medulla) and recieve impulses for balance from the inner ear. The lateral tract facilitates neurons that control the extensor muscles of the limbs. The medial tract plays a role in the control of the head position.

lateral and medial reticulospinal tracts

descending tracts. originate in the reticular formation of the brainstem (nuclear group of the pons and medulla) and travel down in the ventral and lateral columns. They control muscles of upper and lower limbs as well as many visceral motor functions

All other anterior rami outside thoracic region form the ______

different nerve plexuses

External to the neurilemma, each fiber is surrounded by a basal lamina and then a thin sleeve of loose connective tissue called the _____

endoneurium

_____ consists of dense irregular connective tissue an protects the nerve from stretching and injury

epineurium

cerebral spinal fluid (CSF)

fluid that fills subarachnoid space and central hollow cavities of the brain. Provides liquid cushion/ gives buoyancy to CNS

an ample dietary intake of ____ reduces risk of spina bifida in a child

folic acid (Vit. B)

sacral plexus

formed from anterior rami of nerves L 4-5 and S1-4. Has 6 roots and anterior and posterior divisions. Nerves include: superior gluteal, inferior gluteal, tibial, fibular, and pudental. All are mixed and the sensory nerve is posterior cutaneous.

lumbar plexus

formed from the anterior rami of L1-4 and some fibers from T-12. It has 5 roots and 2 divisions. Nerves include the iliohypogastric, ilioinguinal, genitofemoral, and obturator all being mixed nerves. The lateral femoral cutaneous is a somatosensory nerve.

shingles

if the virus herpes zoster remains in your system and the immune system gets compromised, this disease can take place. This disease travels along sensory nerve fibers and causes extreme pain. Antiviral drugs can shorten the course of it but only if started in the first 2-3 days of outbreak.

the cord arises from the brain stem and extends down the vertebral column to the inferior border of ___ in adults. In medicine we say cord runs to ___ in adults. In children, it runs to ____.

inferior border of L-1, in medicine runs to L-2, in children L-3.

medullary cone

inferior to the lumbar cord enlargement, the cord tapers into this point

meningitis

inflammation of the meninges caused by bacteria or virus. Diagnosed by doing an LP for CSF an examining for microbes.

spinal cord

information highway that connects the brain with the lower body

anterior ramus in the thoracic region forms an ______.

intercostal nerve

when a tract does not decussate we say it is

ipsilateral

the _____ innervates the anterior and lateral skin and muscles of the trunk and gives rise to nerves of the limbs.

larger anterior ramus

brain is connected to the body periphery by ______ located in the white matter of the CNS.

multineuron pathways (composed of interconnected fiber tracts)

sciatic nerve injury

often occurs when a herniated lumbar disc presses on the sacral dorsal roots within the vertebral canal. When tibial nerve is injured, muscles in calf can't plantar flex and results in shuffling gait. When common fibular nerve is damaged, dorsiflexion is lost and "footdrop" happens.

any damage to the spinal cord or spinal roots leads to some functional loss, either _____ or _____.

paralysis (loss of motor function) or paresthesia (abnormal or lost sensation)

spinal cord trauma

paralysis from this type of trauma is usually a result of vertebral fractures. The highest incidence is in males age 16-30 because of high risk behavior and the invincible mentality. Most injuries come from motorcycle and auto accidents.

in most nerves, the fibers are gathered in bundles called fascicles, each wrapped in a sheath called the _____

perineurium

A set of rootlets emerge from the posterior surface of the spinal cord and converge to form the ______

posterior (dorsal) root

The posterior root swells to form the _____ which contains neurosomas of sensory neurons

posterior (dorsal) root ganglion

the _____ innervates the muscles and joints in that region of the spine and skin of the back.

posterior ramus

near its attachment to the spinal cord, a spinal nerve branches into _____ and an ______.

posterior/dorsal root (carries sensory nerve fibers which enter the posterior horn of the cord) and an anterior/ventral root (contain large somas of the somatic motor neurons. axons from these neurons exist via the anterior root of the spinal nerve and lead to skeletal muscles and glands)

flexor reflex (withdrawal)

quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus

cervical plexus

recieves fibers from anterior rami of C 1-5.

tendon reflex

response to excessive tension on a tendon. It inhibits alpha motor neurons to the muscle so the muscle does not contract as strongly. This serves to moderate muscle contraction before it tears a tendon or pulls it loose from the muscle or bone.

partial quadriplegia

spinal cord lesions from C 5-7 can produce this which is total lower limb paralysis and partial paralysis of the upper limbs

Distal to the posterior (dorsal) root ganglion the 2 roots merge to form the ______

spinal nerve proper

lateral, posterior, and medial cords

the 6 divisions of the brachial plexus merge to form these 3 large fiber bundles

meninges

the spinal cord and brain are enclosed in 3 fibrous connective tissue membranes called _____. These separate the tissue of the CNS from the bones of the vertebrae and brain.

brachial plexus injuries

these injuries typically result from stretching the plexus as can pccur when a tackler yanks the arm of a ball carrier or when a blow depresses the shoulder and laterally flexes the head away from the shoulder during football

brachial plexus

this is formed from anterior rami of C 5-T1. It innervates the upper limb and some of the muscles of the neck and shoulder. Subdivisions are called roots, then trunks, then divisions, (anterior and posterior) and finally cords.

median nerve injury

this nerve is often severed during wrist slashing suicide attempts. Destruction of this nerve makes it difficult to oppose the thumb towards the little finger

radial nerve injuries

trauma to this nerve results in wrist-drop, which is an inability to extend the hand at the wrist.

gray matter

type of nervous tissue that contains little myelin and does contain somas, dendrites, and proximal parts of axons of neurons. It is the site of synaptic contact between neurons and thus the site of all neuronal integration in the spinal cord. Has abundance of glial cells.

white matter

type of nervous tissue with an abundance of myelin. Composed of bundles of axons called tracts that carry signals from one part of CNS to another. Has abundance of glial cells.

post herpetic neuralgia (PHN)

unfortunate aftermath of singles is this severe pain. Sympathetic blocks are strongly advised to try and prevent this. Zostavax is a new vaccine for adults that is strongly recommended over age 60 to prevent this.

somatic reflexes

unlearned skeletal muscle reflexes that are mediated by the brainstem and spinal cord.

a descending tract typically involves 2 neurons called ____ and ____

upper and lower motor neurons. The upper motor neuron begins with a soma in the cerebral cortex or brain stem and has an axon that terminates on a lower motor neuron in the brain stem or spinal cord. The axon of the lower motor neuron then leads the rest of the way to the muscle or other target organ.

stretch reflex

when a muscle is suddenly stretched, it fights back--it contracts, increases tone, and feels stiffer than an unstretched muscle.

dermatome

with the exception of C-1, each spinal nerve recieves sensory input from a specific area called this.