The Spinal Cord and Periphery

Question 1

What are tracts?

Answer 1

Tracts – bundle of myelinated axons – each bundle is carrying one modality – e.g. touch goes through one tract

These tracts have set pathways

Cross from one side to another at different levels

Question 2

Where are sensory and motor fibres found?

Answer 2

The axons of sensory fibres enter through the dorsal root into the dorsal horn of grey matter

Motor neurons have their cell bodies in the ventral horn

Question 3

How is white matter arranged?

Answer 3

The white matter is arranged in 3 columns – posterior, lateral & anterior

Each column has various bundles (tracts) of axons

Ascending pathways are sensory, descending pathways are motor

Question 4

What is the Corticospinal/pyramidal tract?

Answer 4

carries motor impulses from motor cortex to skeletal muscles

Question 5

What is the Posterior/dorsal column?

Answer 5

carries touch, tactile localisation, vibration sense, proprioception

Question 6

What is the Lateral spinothalamic tract?

Answer 6

carries pain and temperature

Question 7

What are 3 importnt tracts?

Answer 7

Corticospinal/pyramidal tract

Posterior/dorsal column

Lateral spinothalamic tract

Question 8

What does the corticospinal/pyramidal tract do?

Answer 8

Control of voluntary skilled movements (i.e. motor pathway)

Question 9

What is the pathway of the corticospinal/pyramidal tract?

Answer 9

Pathway starts from the motor cortex (Area 4)

Posterior limb of Internal Capsule (blood supply middle cerebral artery)

Corticobulbar fibres go to contralateral cranial n nucleii

Corticospinal fibres mostly cross in decussation of pyramids (Lateral corticospinal tract)

Question 10

Where do corticospinal/pyramidal fibres cross over (decussation)?

Answer 10

in the lower part of the medulla

Question 11

How many neurons are there in the corticospinal/pyramidal pathway?

Answer 11

2

they are called upper and lower neurons

Question 12

What horn are the lower motor neurons of corticospinal/pyramidal neurons in

Answer 12

ventral horn

Question 13

What is the difference between ascending spinal tracts/sensory pathways and motor pathways

Answer 13

There are 3 neurons between peripheral receptor and cortex

goes to area 3, 1, 2 of the brain

the crossing over occurs in the second neuron this time

Question 14

What does the posterior/dorsal column carry?

Answer 14

Carries sensations of fine touch, tactile localisation, vibration sense, proprioception

Question 15

What is the course of the posterior/dorsal column

Answer 15

1st order neuron ends by synapsing with the cell body of the 2nd neuron. This is situated in the lower part of the medulla

2nd order neuron crosses over (decussates) in the medulla

The tract now is called medial lemniscus and passes through the medulla, pons and midbrain to reach the thalamus

The third order neuron starts from the thalamus and axons pass through the IC and radiate to the post-central gyrus (Area 2,1,3)

Question 16

What is the tract called when the second neuron crosses in the medulla?

Answer 16

medial lemniscus

Question 17

What does the lateral spinothalamic tract carry?

Answer 17

pain and temperautre

Question 18

What is the course of the lateral spinothalamic tract?

Answer 18

First order neuron enters into the grey matter and ends at the same level

2nd order neurons cross over to reach the lateral column and is now called lateral spinothalamic tract

2nd order neuron ends in thalamus and 3rd order passes through IC, radiation to reach post-central gyrus

Question 19

Where does decussation occur in the lateral spinothalamic tract?

Answer 19

decussation is occurring at the level of entry!!

Question 20

Name what each picture is showing from left to right?

Answer 20

corticospinal/pyramidal tract

posterior/dorsal column

lateral spinothalmic tract

Question 21

Does all sensory information need ot be sent to the brian for decisions to be made?

Answer 21

no

in certain instances where an immediate response in needed, the spinal cord or other lower centres themselves can take these decisions

these make up some of our reflexes

Question 22

What are reflexes?

Answer 22

a reflex is an involuntary stereotyped pattern of response brought about by a senssory stimulus

many reflexes are mediated at the level of the spinal cord (spinal reflexes)

anatomically they may be monsynaptic (strech reflex) or polysynaptic (flexor reflex)

Question 23

Describe the strech reflex?

Answer 23

strech reflex is important in contorl of msucle tone and posture. if the tendon is streched the the muscle contracts in order to prevent falling and reserve balance

sensory receptors in muscle carry strech impulses and tells the nerve in the ventral horn to contract the muscleand at the same time also tells the antagonistic muscle to relax

one muscle always contracts and one always relaxes

Question 24

What is the flexor (and crossed externsor) reflex?

Answer 24

flexor reflex helps protect the body from painful stimuli

sensory neuron goes to spinal cord and causes motor neurons to contract the muscle to cause withdrawl from the painful stimulus

at the same time it also causes a crossed extensor response to the other limb to compensate for the loss of support of the other limb

Question 25

Do UMN or LMN mediate reflexes?

Answer 25

LMN

Question 26

If LMN is not affected in a UMN lesion that causes paralysis then what happens to reflexes?

Answer 26

Reflexes are exaggerated - UMN tells your LMN how much of a reflex to give but if it is not working then this cannot happen

Question 27

What controls tone of a muscle?

Answer 27

requires LMN

Question 28

How does a UMN and LMN lesions affect tone?

Answer 28

UMN lesions cause increased tone (spasticity) but if it was a LMN then this would cause flaccidity

Question 29

Corticospinal/pyramidal tract:

what would happen if someone had a left UMN lesion at the internal capsule (top arrow)

Answer 29

right sided paralysis - contralateral

hyper-reflexia

incresed tone - spasticity

Question 30

Corticospinal/pyramidal tract:

what would happen if someone had a left UMN lesion at the upper cervical spinal cord (middle arrow)

Answer 30

left sided paralysis - below the level of decussation so it is ipsilateral paralysis

hyper-reflexia

increased tone - spasticity

Question 31

Corticospinal/pyramidal tract:

what would happen if someone had a left LMN lesion (bottom arrow)

Answer 31

left sided paralysis - ipsilateral

absent reflexes - arreflexia

flaccid

Question 32

What is motor neuron disease (lower motor neuron)

Answer 32

Group of diseases affecting the lower motor neuron in the ventral horn of spinal cord

The neuron dies and as a result muscle supplied by it atrophies

Progressive, incurable disease

Question 33

What is the posterior/dorsal column responsible for?

Answer 33

fine touch

tactile sensation

vibration sensation

proprioception

Question 34

posterior/dorsal column?

what lesion is the top arrow pointing at and what effect would it have?

Answer 34

Lesion above decussation at IC – contralateral (right sided) sensory loss

Question 35

posterior/dorsal column?

what lesion is the bottom arrow pointing at and what effect would it have?

Answer 35

Lesion at L cervical spinal cord (below decussation) – L sided (ipsilateral) sensory loss

Question 36

What does the lateral spinothalamic tract sense?

Answer 36

pain and temperature

Question 37

What would lesions at the areas show by the arrows cause?

Answer 37

Lesion at L IC – R sided (contralateral) pain and temperature loss

Lesion at L cervical spinal cord – R sided (contralateral) sensory loss

Both lesions are above the decussation, so pain and temperature sensation lost on the opposite side

Question 38

Would a lesion above decussation cause signs and symptoms on the same or opposite side and would a lesion below decussation cause signs and symptoms on the same or opposite side?

Answer 38

If lesion is above level of decussation then signs and symptoms are C/L

If lesions is below the level of decussation then signs and symptoms are ipsilateral

Question 39

Is the strech and flexor reflex monosynaptic or polysynaptic?

Answer 39

monosynaptic (strech reflex)

polysynaptic (flexor reflex)