A&p Chapter 13 Spinal Cord, Spinal Nerves, Somatic Reflexes

Front 1

What functions are assigned to the precentral and postcentral gyri ofthe cerebral cortex?

Back 1

Pre-central = motor cortex

Post-central = somatosensory

*see homunculus picture

Front 2

Where does the spinal cord begin and end?

Back 2

It extends through thevertebral canal from

foramen magnum (opening at the base of the skull) to thelevel of the second lumbar vertebra (L2). In infants, it fills the entire vertebral column.

Front 3

What are some characteristics of the spinal cord?

Back 3

It carries information between the brain and the body. Each pair of spinal nerves receives sensory information and sends motor signals to muscles and glands. It is a part of the CNS.

Front 4

What are central pattern generators?

Back 4

They are pools of neurons in the spinal cord thatprovide alternating movements of flexors and extensors—for example while you are

walking.

Front 5

What is the cauda equine?

Back 5

The cauda equinae is from L2 to S5 and it

containsnerve roots—resembles a horses tail.

Front 6

What are the primary functions of the spinal cord?

Back 6

1. Conduction

2. Locomotion

3. Reflexes

Front 7

What is conduction in regards to the spinal cord?

Back 7

Conduction—bundles of fibers passing

information upand down the spinal cord

allowing sensory information to reach the brain and motor commands to reach effectors.

Front 8

What is locomotion?

Back 8

Repetitive, coordinated actions of several musclegroups. Motor neurons in the braininitiate walking and determine speed, distance, and direction. Central pattern generators are pools ofneurons in the spinal cord providing alternating movements of flexors andextensors—for example while walking.

Front 9

Explain how reflexes function in the spinal cord.

Back 9

Reflexes are involuntary, stereotyped responses tostimuli—like removing your hand from a hot stove. Reflexes involve the brain, spinal cord, and peripheral nerves.

Front 10

Describe the characteristics of the meninges and their anatomicalrelationship to each other?

Back 10

They are three fibrous layers enclosing the spinal cord and brain.

*Dura mater: dural sheath & outer layer

*Arachnoid mater: middle layer

*Pia mater: delicate innerlayer

Front 11

What is the dura mater?

Back 11

The dura mater (tough mother) is a tough collagenousmembrane surrounded by epidural space filled with fat and bloodvessels—epidural anesthesia is utilized here in childbirth.

Front 12

What is the arachnoid mater?

Back 12

Arachnoid mater (resembles a spider web) is a layer ofsimple squamous epithelium lining the dura mater and loose mesh of fibersfilled with CSF to create the subarachnoid space.

Front 13

What is the pia mater?

Back 13

Pia mater is the delicate membrane adherent to spinalcord.

Front 14

What is spina bifida?

Back 14

Spinal bifida is a congential neural tube defect. It is the failure of thevertebral arch to close and cover the spinal cord.

Front 15

How can a female decrease the risk of this occurring to the developing embryo?

Back 15

Folic acid as a part of a healthy diet for women of childbearing age reduces the risk—deficiency increases the risk. Some anti-seizure medications can cause neural tube defects if high doses of folic acid are not used during early pregnancy.

Front 16

What is the relationship between the white

matter and grey matter in thespinal cord?

Back 16

The central area of gray matter is shaped like abutterfly and is surrounded by white matter in three columns.

Front 17

What is the functional significance of the white and gray matter?

Back 17

Gray matter has neuron cell bodies with littlemyelin. White matter has myelinatedaxons & the white columns of bundles of myelinated axons carry signals up anddown to and from the brainstem. Thereare three pairs of columns or funiculi (dorsal, lateral, and anterior columns). Each column is filled with tracts orfasciculi (fibers with a similar origin, destination and function).

Front 18

What is the difference in function between the anterior horn andposterior horn of the spinal cord?

Back 18

The pair of dorsal or posterior horns are at thedorsal root of the spinal nerve and contains all sensory fibers. The pair of ventral or anterior horns at theventral root of the spinal nerve contains all of the motor fibers. They are connected by gray commissure.

Front 19

Review the terms decussation, ipsilateral, contralateral and use them todescribe neuroanatomical relationships.

Back 19

Decussation: fibers cross sides

Contralateral: the origin anddestination are on opposite sides

Ipsilateral means on the same side.

Front 20

How many neurons are in a typical ascending sensory pathway?

Back 20

There are typically three neurons. Ascending tracts carry sensory signals up thespinal cord. Sensory signals typicallytravel across three neurons from their origin in the receptors to theirdestination in the sensory areas of the brain.

Front 21

What type of sensations travel in the dorsal

columns? Anterolateral/spinothalamic?

Back 21

The postcentral gyrus is the primary sensory cortex,it is organized somatotopically with sensory homunculus and it has two majorsensory pathways.

Dorsal: touch, vibration, proprioception

Anterolateral: crude touch, pain, temp, tickle, itch, pressure

Front 22

Where do dorsal columns and anterolateral

columns decussate in each system?

Back 22

Dorsalcolumns: decussates in the medulla (crosses)

Anterolateral/spino-thalamic: decussates in the spinal cord.

Front 23

Where do the 1st, 2nd, and 3rd orderneurons of the dorsal column ascending pathway travel, decussate, and synapse?

Back 23

*1st order neuron travels up theipsilateral SC terminating in the medulla oblongata

*2nd order neuron hasdecussation in the medulla—it forms the medial lemniscus, a tract that heads upto the thalamus

*3rdorder neuron in the thalamus carries signals to the cerebral cortex.

Front 24

What carries signals from the legs and arms?

Back 24

Fasciculus gracilis and cuneatus carry signals from the leg and arm.

Front 25

Where do the 1st, 2nd, and 3rd orderneurons of the spinothalamic ascending pathway travel, decussate, and synapse?

Back 25

*1st order neuron ends near its point ofentry (the dorsal horn)

*2ndorder neuron decussation occurs in the spinal cord

*3rd order neuron arises in thethalamus and continues into the cerebral cortex.

Front 26

If the entire right side of the spinal cord were injured, where wouldthere be sensory deficits?

Back 26

Injury to the spinal cord will cause loss of pain andtemperature sense on the contralateral side below the lesion. An injury like this will cause ipsilateralloss of fine, discriminative touch, proprioception and vibration below thelesion.

Front 27

In the spinocerebellar pathway, are the

cerebellar region and bodyregion it receives

signals from ipsilateral or contralateral?

Back 27

Ipsilateral. The spinocerebellar pathway hasproprioceptive signals from limbs and trunk travelling up to thecerebellum. Tracts and side ofcerebellum responsible for body is ipsilateral. The spinoreticular tract receives pain signals from tissue injury—the 2ndorder neurons decussate in the spinal cord and ascend with spinothalamicfibers—ends in reticular formation in the medulla and pons—the 3rdand 4th order neurons continue to the thalamus and cerebral cortex.

Front 28

What is the difference between lower motor neurons and upper motorneurons? Where are the cell bodies of each neuron?

Back 28

Descending tracts carry motor signals down the brainstem & spinalcord. It involves two neurons. (1) Upper motor neurons originate in thecerebral cortex or the brainstem and terminate on a lower motor neuron. (2) Lower motor neurons are in the brainstemor spinal cord. Axons of lower motorneurons lead the rest of the way to the muscle or other target organ.

Front 29

In the lateral corticospinal pathway, is the body region controlledipsilateral or contralateral to its primary motor cortex?

Back 29

The body region is controlled contralateral to

its primary motor cortex.

Front 30

How many motor neurons (in sequence) are in the lateral corticospinalpathway? Where do they decussate and where do the neurons synapse?

Back 30

There are two neuron pathways. The upper motor neuron in the cerebral cortexdescends to cord and synapses in the ventral horn with the lower motorneuron. The lower motor neuron cell bodyis in the ventral horn of the spinal cord. They both have decussation in the medulla (pyramids) for lateralcorticospinal tract.

Front 31

Where would deficits be found if the upper

motor neurons were injured onthe right side above the level of the pyramidal decussation in the medulla?What if the injury was below the medulla?

Back 31

Injury of corticospinal system (pyramidal tract) anywhere above thepyramidal decussation (Medulla) causes contralateral paralysis of thelimbs. Injury below the pyramidaldecussation will cause ipsilateral paralysis below the lesion.

Front 32

Where do lower motor neurons reside?

Back 32

In the anterior horn of the spinal cord

Front 33

What do lower motor neurons innervate and what do they form?

Back 33

Lower motor neuron axons innervate the skeletal muscle and form the motor portions of peripheral nerves. They are called the “final common pathway”because they receive input from higher brain areas such as the cerebral cortex.

Front 34

Where are upper motor neurons and what do their axons do?

Back 34

Upper motor neurons are in higher centers such as the motor cortex. Their axons excite or inhibit lower motor neurons.

Front 35

Understand spinal cord trauma.

Back 35

Spinal cord trauma: 55% occur in traffic accidents, it poses risk of respiratory failure ifsegments innervating the diaphragm or above are damaged, early symptoms arecalled spinal shock flaccid paralysis (few days to weeks, loss of sensation,below the lesion and absence of reflexes), hypereflexia occurs in both somaticand autonomic, tissue damage at time of injury is followed by post traumaticinfarction, complete transection of the spinal cord causes immediate loss ofmotor control at and below the level of injury.

Front 36

What are some treatments for spinal cord

trauma?

Back 36

Treatment is to stabilize the spine to prevent further injury, Medrol dose pack (steroid) given early after injury dramatically improves recovery by reducing injury to cell membranes, inhibiting inflammation, and apoptosis, prevents the spread of damage to several spinal cord adjacent segments, surgery to stabilize fractures, and physical therapy for rehab and adaptive equipment.

Front 37

Understand poliomyelitis.

Back 37

Causes destruction of motorneurons and skeletal muscle atrophy. Poliomyelitis is caused by poliovirus spread by fecal contaminatedwater—it destroys motor neurons in the brainstem and ventral horn of the spinalcord—muscle pain, weakness progresses to paralysis and potentially respiratoryarrest.

Front 38

Understand ALS.

Back 38

Amyotrophiclateral sclerosis (Lou Gehrig disease) is degeneration of motor neurons andatrophy of muscles—sclerosis of lateral regions of spinal cord—astrocytefailure to reabsorb glutamate neurotransmitter—becomes neurotoxic—paralysis andmuscle atrophy.

Front 39

How does Guillian-Barre syndrome affect nerve conduction? Does it affectCNS axons or PNS

axons? What signs orsymptoms would be present in a patient suffering from this disorder?

Back 39

It is also known as acute inflammatory

demyelinatingpolyradiculoneuropathy. It is one of themost common life threatening diseases of the PNS.

Front 40

How do local anesthetics work?

Back 40

Local anesthetics, like lidocaine, act by blocking thecytoplasmic side of the voltage gated Na+ channel. The hydrophobicity of the anestheticdetermines how efficiently it diffuses across lipid membranes and how it bindsto the Na+ channel, and therefore its potency.

Front 41

Where are local anesthetics applied?

Back 41

Local anesthetics are injected or applied outside ofthe peripheral nerve epineurium—meaning it must cross the epineurium to reachthe perineurium, which is the most difficult layer to penetrate due to tightjunctions.

Front 42

Anesthetics can pass through what?

Back 42

Anesthetics can pass through the endoneurium whichinvests the myelinated and unmyelinated fibers, Schwann cell andcapillaries. Only anesthetics that havepassed through these 3 sheaths can reach the neuronal membranes where thevoltage gated sodium channels that affect nerve conduction reside.

Front 43

What is a peripheral nerve ganglion?

Back 43

The spinal cord communicates with the rest of the bodyby way of the spinal nerves—peripheral nerves.

Front 44

Where do the sensory axons enter the spinal cord and where are the cell bodiesof the

neurons?

Back 44

The dorsal root of the spinal cord/input to the spinalcord has the sensory axons.

Front 45

Where do the motor axons leave the spinal cord before entering a spinalnerve?

Back 45

The ventral root of the spinal cord/output of thespinal cord has the motor axons.

Front 46

What is a dermatome?

Back 46

Each spinal nerve receives sensory input from aspecific area of skin called a dermatome. It overlaps at the edges. A totalloss of sensation requires anesthesia of 3 successive spinal nerves.

Front 47

Discuss the pathology of shingles.

Back 47

Shingles are skineruptions along the path of sensory nerves. Varicella-zoster virus remains for life in dorsal rootganglia. It occurs after the age of 50if immune system is compromised. It travelsback down the sensory nerves by fast axonal transport causing skindiscoloration and fluid filled vesicles along the cutaneous region of thenerve. Antiviral drugs, acyclovir, canshorten the course of an episode if taken within the first 2 to 3days of outbreak. Post herpeticneuralgia can cause intense pain along the course of the nerve for months oreven years and is difficult to treat.

Front 48

Discuss the pathology of radiculopathies.

Back 48

Radiculopathiesare sensory or motor dysfunction caused by injury to a nerve root. Injuries to posterior (dorsal) roots causesensory disturbances. Injuries toanterior (ventral) roots cause motor disturbances. It is commonly due to vertebral discherniation. Often has burning pain ortingling radiates in affected dermatome. Motor deficits may result in muscle paresis (weakness), atrophy, andfasciculation. Muscles are not normallyparalyzed if only one root is affected—for example, if the C6 anterior root isinjured, the biceps are weak, not paralyzed.

Front 49

Discuss the pathology of neuropathies.

Back 49

Neuropathies aresensory or motor dysfunction caused by pathology affecting a nerve. It can result from metabolic disorders suchas diabetes mellitus—diabetic neuropathy (can use gloves and stockings). Can manifest as burning pain or tinglingradiates in affected nerve distribution. Sensory deficits involve portions of adjacent dermatomes. Motor neuropathies cause muscle paralysis,atrophy, and fasciculation.

Front 50

Describe the patella tendon reflex arc.

Back 50

Muscle spindles detect muscle length and stretch. When a muscle is stretched by tapping itstendon with a reflex hammer, that information is carried to the spinal cord bya 1A afferent axon. The 1A fiber is aproprioceptive afferent—meaning it carries information about deep somaticstructures. The 1A fibers synapse directly on alpha motor neurons thatinnervate the muscle (monosynaptic)—the alpha motor neurons fire and the musclecontracts. Alpha motor neuronsinnervating the antagonist muscle are inhibited.

Front 51

Describe the reflexes which occur if you

unexpectedly step on a piece of glass.

Back 51

Flexor withdrawal reflexes occur during withdrawal offoot from pain. Polysynaptic reflex arcis involved. Neural circuitry in spinalcord controls sequence and duration of muscle contractions. Crossed extensor reflexesmaintain balance by extending the other leg. Inter-segmental reflex extends up and down the spinal cord. Contralateral reflex arcs explained by pain atone foot causes muscle contraction in the other leg. The Golgi tendon reflex has proprioceptors ina tendon near its junction with a muscle—is about 1mm long and is anencapsulated nerve bundle—excessive tension on tendon inhibits motor neuronmeaning muscle contraction decreases—it also functions when the musclecontracts unevenly.