The Spinal Cord And Spinal Nerves

Front 1

What is the spinal cord?

Back 1

The part of the central nervous system that extends from the brain. The spinal cord and associated nerves contain neural circuits that control some of you most rapid reactions to environmental changes - spinal reflexes.

Front 2

What is a spinal reflex and give an example

Back 2

If you pick up something hot the grasping muscles relax and you drop the object before you are consciously aware of the heat and pain. This is an example of a spinal reflex which is a quick, automatic response to certain kinds of stimulus that involves neurons only in the spinal nerves and spinal cord.

Front 3

Besides processing reflexes what else does the spinal cord do?

Back 3

Gray matter of the spinal cord is the site for integration (summing) of excitatory postsynaptic potentials (EPSP) and inhibitory postsynaptic potentials (IPSP). The white matter contains dozens of major sensory & motor tracts, which function as highways along which sensory input travels to the brain and motor output travels from the brain to skeletal muscles & other effectors

Front 4

The nervous system tissues are very delicate and do not respond well to damage or injury. What are the protective structures?

Back 4

First layer of protection is the hard bony skull (encases the brain) and vertebral column (encases the spinal cord). Second protective layer is the meninges, three membranes that lie between the bony encasement and the nervous tissue between both the brain and the spinal cord. Third layer of protection a space between 2 of the meningeal membranes contains cerebrospinal fluid that suspends the central nervous tissues and provides shock absorbing and cushioning

Front 5

What are the meninges?

Back 5

Three protective, connective tissue coverings that encircle the spinal cord and brain. From superficial to deep they are:

1. Dura mater

2. Arachnoid mater

3. Pia Mater

Front 6

Meninges

Back 6

1. Spinal meninges (surround spinal cord)

2. Cranial meninges (encircle the brain)

3. Epidural meninges (space between the dura mater and the wall of the vertebral canal)

Front 7

What is dura mater?

Back 7

Most superficial of the 3 spinal meninges. Thick and strong layer composed of dense, irregular connective tissue. Dura mater forms a sac from the level of the foramen magnum in the occipital bone, where it is continuous with the meningeal dura mater of the brain, to the second saran vertebra. Also continuous with the epineurium, the outer covering of the spinal & cranial nerves

Front 8

What is arachnoid mater?

Back 8

The middle layer. Thin, avascular covering comprised of cells and thin, loosely arranged collagen and elastic fibers. Looks like a spiders web arrangement of fibers. Deep in the dura mater and continuous through the foreman magnum with the arachnoid mater of the brain.

Front 9

What is Pia mater?

Back 9

The innermost layer, thin, transparent connective tissue layer that adheres to the surgace of the spinal cord and brain. Consists of thin squamous to cuboidal cells within interlacing bundles of collagen biers and some fine elastic fibers. Within the pia mater are many blood vessels that supply oxygen and nutrients to the spinal cord.

Front 10

What is the gross anatomy of the spinal cord?

Back 10

Cervical enlargement - Thickening in width of the spinal cord located in inferior cervical region & where branches for the upper limbs originate, C4-T1. Superior enlargement. Lumbar enlargement - thickening in width of the spinal cord found in the lumbosacral region where branches for the upper limbs originate, T9-T12. Inferior enlargement. Conus Medullaris - tapered cone shaped end of the spinal cord located around L2. Inferior to Lumbar Enlargement. Cauda Equine - bundle of nerve roots that occupy the vertebral canal below L2. Filum terminale - anchors the spinal cord to the coccyx and extends inferiorly from the conus medullaris to the coccyx.

Front 11

What are spinal nerves?

Back 11

The paths of communication between the spinal cord and specific regions of the body. The spinal cord appears to be segmented because 31 pairs of spinal nerves emerge at regular intervals from intervertebral foramina.

Front 12

How an paris of cervical nerves are there?

Back 12

8 pairs (C1-C8)

Front 13

How many pairs from thoracic nerves are there?

Back 13

12 pairs (T1-T12)

Front 14

How many pairs of lumbar nerves are there?

Back 14

5 pairs (L1-L5)

Front 15

How many pairs of sacral nerves are there?

Back 15

5 pairs (S1-S5)

Front 16

What are two bundles of axons called?

Back 16

roots which connect each spinal nerve to a segment of the cord by an even smaller bundle of axons called rootlets. Posterior (dorsal) root contain only sensory axons. Anterior (ventral) root contain axons of motor neuron.

Front 17

What are the functional groups that clusters of neuronal cell bodies form in the gray matter of the spinal cord and the brain?

Back 17

Nuclei. Sensory nuclei receive input from receptors via sensory neurons, motor nuclei provide output for effector tissues via motor neurons. Somatic motor nuclei provide nerve impulses for contraction of skeletal muscles. Autonomic motor nuclei regulate the activity of cardiac muscle, smooth muscle and glands

Front 18

The gray matter on each side of the sinal cord are subdivided intp regions called what?

Back 18

Horns.

Posterior (dorsal) gray horns - contain cell bodies and axons of the interneurons as well as axons of incoming sensory neurons.

Anterior (ventral) gray horns - contain somatic moto nuclei.

Lateral gray horn - Between the posterior and anterior horns and present on in the thoracic and upper lumbar segments of the spinal cord.

Front 19

White matter is also divided into regions. The anterior and posterior gray horns divide the white matter on each side of its 3 board areas. What are these areas called?

Back 19

Columns.

1. anterior (ventral) white columns

2. posterior(dorsal) white columns

3. lateral white columns

Front 20

Each column contains distinct bundles of axons called...

Back 20

Tracts.

Sensory (ascending) tracts - consist of axons that conduct nreve impulse toward the brain

Motor (descending) tracts - consist of axons that carry nerve impulses from the brain.

Front 21

Where is the largest amount of gray matter?

Back 21

In the cervical and lumbar segments of the spinal cord because these segments are responsible for sensory and motor innervation of the limbs

Front 22

Where is there less white matter?

Back 22

Less in the cervical and sacral segments of the spinal cord because more sensory and motor tracts are present in the upper segments of the spinal cord than in the lower segments

Front 23

What are the two main reasons that there is variation in the spinal cord white matter?

Back 23

1. AS the spinal cord ascends from the sacral to the cervical segments, more ascending axons are added to the spinal cord and white matter to form more sensory tracts.

2. As the spinal cord descends from the cervical to the sacral segment, the motor tracts decreases in thickness as more descending axons leave the motor tracts to synapse with neurons in gray matter of the spinal cord.

Front 24

What are the connective coverings of spinal nerves?

Back 24

Individual axons within a nerve , whether myelinated or unmyelinated are wrapped in endoneurium, the innermost later which consists of collagen fibers, fibroblast, & macrophages. Groups of Axons with their endoneurium are held together in bundles called fassicles, each of which is wrapped in perineurium which is a thicker layer of connective tissue. The outermost covering over the entire nerve is epineurium which consists of fibroblast and thick collagen fibers.

Front 25

Distribution of spinal nerves: Branches

Back 25

Shortly after passing through its intervertebral foreman the spinal nerve divides into several branches known as rami. The Posterior (dorsal) ramus serves the deep muscles and skin of the posterior surface of the trunk. The anterior (ventral) rams serves the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk. The meningeal branch reenters the vertebral cavity through the intervrtebral foreman and supplies the vertebrae, vertebral ligaments and blood vessels of the spinal cord and meninges.

Front 26

Distribution of spinal nerves: Plexuses

Back 26

The principle plexuses are:

Cervical Plexus

Brachial plexus

Lumbar plexus

sacral plexus

coccyygeal plexus

Front 27

Distribution of spinal nerves: Intercostal nerves

Back 27

The anterior rami and the spinal nerves T2-T12 do not enter into the formation of the plexuses and are known as intercostal or thoracic nerves. These nerves connect directly to the structure that they supply in the intercostal spaces.

Front 28

What is a dermatome?

Back 28

The area of the skin that provides sensory input to the CNS via one pair of spinal nerves or the tirgeminal (V) nerve. Knowing what spinal cord segments supply each dermatome makes it possible to locate damaged regions of the spinal cord.

Front 29

why are all spinal nerves classified as mixed nerves?

Back 29

because their posterior roots contain sensory axons and their anterior roots contain motor axons.

Front 30

What five important nerves arise from the brachial plexus?

Back 30

The axillary, musculocutaneous, radial, median, and ulnar nerves are five important nerves that arise from the brachial plexus.

Front 31

What is the origin of the sacral plexus?

Back 31

The origin of the sacral plexus is the anterior rami of spinal nerves L4-L5 and S1-S4.

Front 32

Which is the only spinal nerve that does not have a corresponding dermatome?

Back 32

The only spinal nerve without a corresponding dermatome is C1.

Front 33

Based on its name, list the origin and destination of the spinothalamic tract. Is this a sensory or motor tract?

Back 33

The spinothalamic tract originates in the spinal cord and ends in the thalamus (a region of the brain). Because "spinal" comes first in the name, you know it contains ascending axons and thus is a sensory tract.

Front 34

The area of the skin that provides sensory input to the CNS via one pair of spinal nerves is called

Back 34

dermatome

Front 35

What are some common characteristics of dermatomes?

Back 35

Can be used clinically to determine area of spinal cord damage, complete anesthesia of a single dermatome often requires blocking three adjacent spinal nerves, dermatomes are designated based on the cranial or spinal nerve that serves that area of the skin, and the dermatome serving the face is supplied by the trigeminal cranial nerve.

Front 36

What are some common characteristics of the spinothalamic tract?

Back 36

Begins in the spinal cord, terminates in the thalamus, found in the white matter of the spinal cord, and is composed of multiple axons carrying information in the spinal cord. Conveys nerve impulses for sensing pain, warmth, coolness, itching, tickling, deep pressure and crude touch.

Front 37

Based on its name, list the origin and destination of the spinothalamic tract. Is this a sensory or motor tract?

Back 37

The spinothalamic tract originates in the spinal cord and ends in the thalamus (a region of the brain). Because "spinal" comes first in the name, you know it contains ascending axons and thus is a sensory tract.

Front 38

Motor output to skeletal muscles travels down the spinal cord in two types of descending pathways

Back 38

Direct and indirect

Front 39

The direct pathways include:

Back 39

lateral corticospinal

anterior coriticospinal

corticobulbar

Front 40

The indirect pathways include:

Back 40

rubrospinal

tectospinal

lateral reticulospinal

medial reticulospinal tracts

Front 41

What is a reflex?

Back 41

A fast, involuntary, unplanned sequence of action that occur in response to a particular stimulus. Some reflexes are inborn such as pulling hand away from a hot surface before you feel its hot. Others are learned and acquired.

Front 42

When integration takes place in teh spinal cord gray matter the reflex is?

Back 42

Spinal reflex

Front 43

if the integration occurs in the brain stem rather than the spinal cord the relex is?

Back 43

cranial reflex

Front 44

You are probably most aware of these reflexes which involve contraction of skeletal muscles

Back 44

somatic reflexes

Front 45

You generally do not consciously perceive these reflexes.

Back 45

autonomic (visceral) reflexes

Front 46

What is the reflex arc?

Back 46

The pathway followed by nerve impulses that produce a reflex

Front 47

The reflex arc includes the following 5 functional components.

Back 47

1. Sensory receptor

2. Sensory neuron

3. Integrating center

4. Motor neuron

5. Effector

Front 48

What does a stretch reflex do?

Back 48

Causes contraction of skeletol muscle (the erector) in response to stretching of the muscle. This type of reflex occurs via monosynaptic reflex arc and ipsilateral. The reflex can occur by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron.

Front 49

What is involved in the tendon reflex?

Back 49

Operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn. Less sensitive than a stretch reflex it can override stretch reflex when the tension is too great. sensory receptors fro the reflex arc are called tendon (Golgi tendon) organs which in the tendon near it junction with a muscle.

Front 50

How does a tendon reflex operate?

Back 50

As the tension applied to a tendon increases, the tendon organ (sensory receptor) is stimulated (depolarized to threshold).

The nerve impulses arise and propagate into the spinal cord along a sensory neurone. Within the spinal cord (integrating centre), the sensory neuron activates an inhibitory interneuron that synapes with a motor neurone. The inhibitory neurotransmitter inhibits (hyperpolarizes) the motor neurone, which then generates fewer nerve impulses. The muscle relaxes and relieves the excess tension

Front 51

What is the flexor (withdrawal) reflex?

Back 51

The flexor reflex causes withdrawal of a part of the body in response to a painful stimulus. This reflex is protective because it moves the body away from the source of a possibly damaging stimulus. they are polysynaptic and ipsilateral.

Front 52

How does the flexor reflex operate?

Back 52

Stepping on a tack stimulated the dendrites (sensory receptors) of a pain sensitive nueron. This sensory neuron then generates nerve impulses which propagate into the spinal cord. Within the spinal cord ( integrating centre), the sensory neuron activates interneurons that extend to several spinal cord segments. The interneurons activate motor neurons in several spinal cord segments. AS a result, the motor neurons generate nerve impulses, which propagate towards the axonterminals. Acetylcholine released by the motor neurons cause te flexor muscles in the thigh (the effectors) to contract, producing a withdrawal of the leg.

Front 53

Why is the flexor reflex classified as an intersegmental reflex arc?

Back 53

The flexor reflex is intersegmental because impulses go out over motor neurons located in several spinal nerves, each arising from a different segment of the spinal cord.

Front 54

What is the crossed extensor reflex?

Back 54

causes contraction of muscles that extend joint in the limb opposite a painful stimulus.

Front 55

Why is the crossed extensor reflex classified as a contralateral reflex arc?

Back 55

The crossed extensor reflex is a contralateral reflex arc because the motor impulses leave the spinal cord on the side opposite the entry of sensory impulses.

Front 56

What makes this an ipsilateral reflex?

Back 56

In an ipsilateral reflex, the sensory and motor neurons are on the same side of the spinal cord.

Front 57

What is reciprocal innervation?

Back 57

Reciprocal innervation is a type of arrangement of a neural circuit involving simultaneous contraction of one muscle and relaxation of its antagonist.

Front 58

Somatic Spinal reflexes include the following reflexes?

Back 58

Stretch reflex: Imporant in maintaining muscle tone

Tendon reflex: prevents damage to muscles and tendons when muscle force becomes too extreme

Flexor (withdrawal) reflex:moves limb away from source of painful stimulus

Crossed extensor reflex: maintains balance as a result of the flexor reflex

all exhibit reciprocal innervation