Spinal Cord, Reflexes And Descending Pathways

Front 1

what is the highest centre of control for motor system

Back 1

cerebral cortex

Front 2

what is the cerebral cortex

Back 2

Front 3

what is the cerebral cortex responsible for

Back 3

spontaneous,novel and adaptive behaviour

Front 4

what structures play a rolein the control of motor pathways

Back 4

cerebral cortex

basal ganglia

cerebellum

simple reflex arc

LMN

CPG

Front 5

Inembryological development the brain and spinal cord are derived from what?

Back 5

hollow fluid filled neural tube

Front 6

the developing spinal cord isdivided into two regions. what are these two, and how are they divided

Back 6

divided into ananterior (ventral) region

a posterior (dorsal) region

the dividingline being the sulcus limitans

Front 7

which part of the spinal cord has motor neurones

Back 7

Theanterior part (to sulcus limitans) is called the basal plate and contains themotor neurones

Front 8

which part of the spinal cord has sensory functions

Back 8

theposterior part (to sulcus limitans) is the alar plate and has sensory function.

Front 9

where are the cell bodies of sensory neurones

Back 9

in the dorsal root ganglia

Front 10

where are the cell bodies of motor neurones

Back 10

in the basal plate

Front 11

how do mixed spinal roots form

Back 11

Motor axons grow out of the anterior partof the spinal cord to form the ventral (motor) spinal nerve roots.

Sensoryneurones grow into the posterior aspect of the cord forming the dorsal(sensory) spinal nerve roots.

Front 12

how is the adult spinal cord structured

(dorsal horns/ventral horns)

Back 12

Spinal cordgrey matter in cross section forms an “H” shape which conists of nerve cells(bodies) which are surrounded by a thick layer of white matter which iscomposed of myelinated axons.

Spinal cordgrey matter divided into left and right dorsal horns which belong to the alarplate and therefore sensory in function.

The ventralhorns derive from the basal plate and contain motor neurones (anterior horncells)

Front 13

what are the laminae of rexed

Back 13

comprise a system of ten layers of grey matter, to label portions of the grey columns of the spinal cord

Front 14

what do lamina 1-6 of the lamina of rexed consist of

Back 14

make up thedorsal horn, laminae VII and X are mid-region of the cord including the areaaround the fluid-filled central canal.

Front 15

what do the lamina 8-9 of the laminae of rexed consist of

Back 15

correspond tothe anterior horn.

Front 16

how are LMN in the spinal cord arranged

(what is the medial-lateral gradient)

Back 16

thoseinnervating proximal (axial and limb girdle) muscles are found close to themidline

motor neurones supplying the distal limb muscles are placedlaterally

Front 17

what is the ventral-dorsalpattern arrangement in the spinal cord

Back 17

Neuronessupplying flexor groups are nearer the back of the cord

extensors aremore towards the front

Front 18

Somegroups of motor neurones in the spinal cord grey matter have discretefunctional roles and are given specific names.

what is the role of the phrenic nucleus

from which vertebrae are its spinal roots

Back 18

(C3, C4, C5)

which supplies the diaphragm via the phrenic nerve and involved in breathing

'C345 keep the diaphragm alive'

Front 19

Some groups of motor neurones in the spinal cord grey matter have discrete functional roles and are given specific names.

what is the role of the Spinal accessory nucleus

from which vertebrae are its spinal roots

Back 19

(C5, C6)

Supplies trapezius and sternocleidomastoid

Front 20

Some groups of motor neurones in the spinal cord grey matter have discrete functional roles and are given specific names.

What is the role of the Onuf’snucleus

from which vertebrae are its spinal roots

Back 20

S2, S3, S4

Importantfor continence as it supplies the external urethral and anal sphincters

Front 21

white matter of the spinal cord are divided bythe lines of attachment of the dorsal and ventral nerve roots into threelongitudinal columns

what are these columns called

Back 21

posterior

lateral (clear line)

anterior columns (arbitrary)

Front 22

white matter of the spinal cord are divided by the lines of attachment of the dorsal and ventral nerve roots into three longitudinal columns

what is the purpose of these columns

Back 22

containdescending pathways from the brain (e.g. those carrying instructions related tomovements)

contain numerous ascending pathways (e.g. tracts mediating sensationssuch as touch, vibration, pain and temperature).

Front 23

what information do the dorsal columns bring to the brain

Back 23

vibration,proprioception and discriminative touch

Front 24

what infomation does the spinothalamic tract bring to the brain

Back 24

bringing painand temperature info to the brain.

Front 25

what information does the spinocerebellar tract bring to the brain

Back 25

conveys information to the cerebellum about length and tension of muscle fibers (i.e., unconscious proprioceptive sensatio

Front 26

what is the role of the cerebellum

Back 26

gathers a vast amount of sensory andother information and uses this to “advise” the motor areas of the frontallobe, helping to ensure that actions are performed in a smooth, precise andcoordinated manner

For this reason, cerebellar damage or disease often leadsto clumsiness and poor coordination (termed cerebellar ataxia).

Front 27

what is cerebellar ataxia

Back 27

is a disorder that occurs when the cerebellum becomes inflamed or damaged.

The cerebellum is the area of the brain responsible for controlling gait and muscle coordination

Front 28

what is the corticospinal tract (where do its neurones originate and synapse)

Back 28

a descending tract of the spinal cord which contains bundles of axons which originate in the cerebral cortex and descend to synapse within the brainstem or spinal cord.

Front 29

where is the lateral and anterior column if the cerebrospinal tract

Back 29

The lateralcorticospinal tract occupies the lateral column of the cord

the anteriorcorticospinal tract and occupies the anterior column of the cord.

Front 30

what is the lateral corticospinal tract

Back 30

Lateralcorticospinal tract deals with distal flexors mainly.

Lateralcorticospinal tract contains about 90% of the fibres and these are the onesthat crossed over at the level of the foramen magnum.

Front 31

what is the anterior corticospinal tract

Back 31

Ant spinaltract deals with proximal extensors

Anterior spinaltract is the direct continuation of the pyramids of the medulla. This is why itis situated either side of the midline at the front and doesn’t cross

Front 32

how does the amount of white matter change as you descend the verebral column

Back 32

Cross sectionsat different cord levels show that the cervical region contains the most whitematter because of all the descending and ascending pathways present at thislevel.

Whereas in thelowermost part of the spinal cord most of the descending pathways are no longerpresent and most of the ascending pathways have yet to join the cord.

Front 33

how does the amount of grey matter change as you descend the vertebral column

Back 33

grey matterwhich varies in proportion to the amount of muscle tissue at each level; forthis reason the cervical and lumbosacral regions have the largest amount ofgrey matter (to supply the limbs) whilst the thoracic cord has the least.

Front 34

how can movement be categorised

(4 main types)

Back 34

reflexive

postural

rhythmic

voluntary

Front 35

how do the different types of movement vary

Back 35

vary incomplexity and the degree to which they can be considered voluntary vsautomatic

Front 36

what is voluntary movement

(where do these movements originate etc)

Back 36

leastautomatic action goal orientatedvoluntary acts that require participation of the cerebral cortex.

originatefrom the frontal lobe

Involve directconnections from cortex to spinal cord, the lateral corticospinal tract.

Front 37

what is rhythmic movement

(where do these movements originate/ how are they coordinated)

Back 37

semi-automaticmovements that are mainly rhythmic patterns of activity

initiatedand maintained by subcortical structures such as brain stem and spinal cord

coordinated bynetworks of neurones called central pattern generators.

littleor no contribution from the cerebral hemispheres or cortex

Front 38

what is reflexive movement

(how are they triggered, what types of nerve do they involve)

Back 38

Reflexesare rapid and automatic responses to particular sensory stimuli and as such arestereotyped varying only in speed, magnitude or duration

mostbasic form consists of only two nerve cells (one sensory, one motor) plus anintervening synapse eg the stretch reflex

They aretriggered by proprioceptors. These are reflex arcs.

can be a lot more complex involvingnumerous nerve cells and synapses extending over several spinal cord segmentsor brain stem levels and in some cases both sides of the body (e.g. limbwithdrawal reflex).eas(0��z�

Front 39

what is the stretch (myotatic) reflex

Back 39

muscle spindles are stretch detectors, and found scattered throughout skeletal muscles

Each spindlecontains a few striated fibres described as “intrafusal”. Musclespindles are in parallel with the extrafusal fibres so whenever the msucle belly is put under tension causing the muscle spindles to respond.

spindles are excited triggering reflex contraction of the homonymous (same) muscle group, resisting change inmuscle length.

achieved by asimple spinal cord reflex with a sensory limb, a motor limb and a single synapse,this is the stretch reflex.

Antagonistmuscles are inhibited at the same time (reciprocal inhibition) by inhibitoryinterneurones, activated by collaterals of the afferent.

Front 40

how does an UPN lesion affect the stretch reflex

Back 40

The stretchreflex is normally dampened down by descending influences from the brain stemto ensure that muscle tone is not excessive. Thismoderating influence tends to be lost in patients with upper motor neuronelesions

With the normaldampening down influence lost, the stretch reflex becomes abnormally strong(hyperreflexia) so excessive muscle tone(hypertonia) which manifests as firm resistance to manipulation of joints. Boththe agonist and antagonist muscles start having a tug-of-war trying to contractmaking the muscle stiff, this is spasticity.

Front 41

what are the effects of a LMN lesion

Back 41

theperipheral nerve supply to the muscle is interrupted

Loss of motornerve supply to the muscle results in flaccid (floppy) paralysis of theaffected muscles accompanied by a complete absence of normal tone (atonia) andloss of deep tendon reflexes (areflexia).

so we get gradual wasting(atrophy) of the muscle due to lack of use (disuse atrophy)

Front 42

why may we get twitching in a LMN lesion

(fasiculations)

Back 42

caused by increased receptor concentration on muscles to compensate for lack of innervation

Front 43

what are the main protective reflexes

Back 43

flexor/withdrawalreflex

crossed extensor reflex.

Front 44

how do the protective reflexes coordinate eg when you step on a pin

Back 44

If you’rewalking along and step on a pin you immediately pull your foot away and you maythink you did this voluntarily but actually it was an automatic reflex.At the sametime you straighten your other leg so you support your body and don’t fallover.

The pulling theleg away is the withdrawal reflex, the straightening of the leg is the crossedextensor reflex. These two reflexes coordinate automatic limb withdrawal from anoxious stimulus

Front 45

where does the withdrawal reflex start and what is it triggered by

Back 45

The withdrawalreflex is polysynaptic and triggered by nociceptors and is a cutaneous reflex(starts in skin).

Front 46

what is the central pattern generator CPG

Back 46

networks of neurones within the spinal grey matter or brain stem involved in coordinating rhythmic motor sequences such as walking, chewing, breathing .

Front 47

how are CPG coordinated

Back 47

canbe selected and recruited by descending projections from the brain (‘commandneurons’

operaterelatively independently and autonomously

Front 48

where is the CPG located

Back 48

in the spinal cord.

command neurones send signals up into the brain

Front 49

what are the basal ganglia loops

Back 49

The connections between the motorcortex and the basal ganglia are arranged as a set of “loops” which each arise ina particular region of the frontal lobe and pass through the basal ganglia beforeprojecting back to the cortical region of origin (via a relay in the thalamus)

Front 50

what do the basal ganglia loops do

Back 50

involved in

(i) the initiation ofvoluntary actions

(ii) selection of a particular action among a range ofpossible or potential actions

(iii) the learning and performance of variousrepetitive, semi-automatic behaviours (or ‘habits’)

Front 51

what Neurotransmitter is involved in the basal ganglia loops

Back 51

dopamine

Front 52

disease and damage to the basal ganglia is associated with what?

Back 52

associatedwith a movement disorder, the best example of which is Parkinson’s disease

Thebasal ganglia are also involved in cognition, behaviour and emotion due to thepresence of non-motor loops that arise and terminate in other parts of thecerebral cortex.