Ascending pathways 2

Question 1

what pattern do most conscious sensory tracts follow
what is the exception to this rule

Answer 1

there are three neurons
primary afferent (first order neuron) enter spinal cord- synapse to secondary neuron which projects to the thalamus to third neuron to somatosensory cortex. ALWAYS GO THROUGH THALAMUS
where they synapse is always slightly different
the exception is olfaction which does not go through the thalamus (bypasses it)

Question 2

what does the thalamus do in regards to signals

Answer 2

it relays info, receive feedback and modulates signals
thalamus is linked to all parts of the cortex
can turn signals up or down

Question 3

what do the cells of reticular nucleus in the thalamus do (GABA cells)

Answer 3

it receives excitatory afferents from both cortical and thalamic neurons and sends inhibitory projections
high activity go down collateral fibres to excite inhibitory neurons (turn down response)

Question 4

what are the three principal ascending tract systems in the spinal cord

Answer 4

dorsal column medial lemniscus pathways
spinothalamic pathways
spinocerebellar pathways

Question 5

why is the light touch pathway different

Answer 5

transmitted using two pathways,
therefore if lose this sensation you cant tell which pathway is affected

Question 6

what is the dorsal column medial lemniscal pathway for

Answer 6

FOR MECHANICAL STIMULI
conscious proprioception
discriminative touch
vibration
pressure

Question 7

describe the pathway of the dorsal column medial lemniscal pathway

Answer 7

ascend ipsolaterally up dorsal column (spinal cord)
synapses high up in spinal cord
crosses onto contralateral side at medulla and synapses at thalamus to synapse with third order neuron to somatosensory cortex

Question 8

how do you diagnose where a lesion may be for dorsal column pathway

Answer 8

eg position sense will disappear for joints below the level of the lesion
the modaility will help differentiate the pathway
REMEMBER it is ipsolateral, so same side

Question 9

what is fine tactile and proprioceptive info used for

Answer 9

determine the shape of an object without sight
determine the texture of an object

Question 10

what is asteriognosis

Answer 10

describe inability to discriminate shape and size by touch and the inability to recognize objects by touch.

Question 11

what is amorphosynthesis

Answer 11

it is a lesion of one of the somatosensory association cortex
cant recognise complex objects by feel on the opposite to the lesion
they still appreciate pain and temperature but cant locate with any certainty

Question 12

what do lesions of gracile fasciculus cause

Answer 12

gait ataxia

Question 13

what do lesions in the cervical cord cause

Answer 13

upper extremity ataxia

Question 14

what is the stamp and stick gait

Answer 14

look at floor, stamp foot to reinforce proprioception
usually minimise sensory ataxia as compensating
broad stance

Question 15

describe the spinothalamic pathway

Answer 15

synapse quickly in the dorsal horn and cross immediately, ascending in the lateral or anterior spinothalamic tract
synapse at the thalamus then projects to sensory cortex

Question 16

what kind of fibres are found in the spinothalamic pathways

Answer 16

slow fibres with smaller diameters with no specialised sensory endings
A delta and C fibres

Question 17

what do a delta fibres detect

Answer 17

discrimination sensation
heat
cold
sharp pain

Question 18

what do c fibres detect

Answer 18

non discriminative dull aching pain and itch
thermal and mechanical

Question 19

what is the difference in fibres between the spinothalamic later and anterior routes

Answer 19

lateral is a mixture of A delta and C fibres
anterior is C fibres only

Question 20

how do lesions of the spinothalamic tract present

Answer 20

decreased perception of pain and temperature on the contralateral side of the body ONE or TWO dermatomes below the level of the lesion
cause paraesthesia (nerve ending starts to heal but still leaky membrane, allowing na ions in and action potentials
patients become aware when they experience painless cuts or burns

Question 21

what do cancer patients use when no other methods prevent the pain or other patients

Answer 21

CORDOTOMY
section through asecnding tracts- high level
cut through ascending pain fibres, relieving brain of incoming pain signals
only used for terminal cases and it is not permanent (returns after 1 year) due to plasticity in spinal cord with lateral fibres going to other side of the spinal cord allowing a signal to come through.
pain come back to areas that havent been damaged - rewired incorrectly.

Question 22

what does the anterolateral system look like

Answer 22

high in brain stem there are lateral fibres
come off (spinoreticular tract)as reticular formation, monitors ascending pain info and back to thalamus via interlaminar area
further branches (spinomesencephalic tract) goes into periaqueductal grey and superior colliculus found in mesenphalic part of brain– descends pain modulation
back to mixture that havent branched off
anterolateral system divides into two
1. paleospinothalamic tract (terminates in dorsomedial DM and intra laminar areas)
mainly all c fibres go through thalamus towards LIMBI system (provide emotional context for pain - depression of chronic pain, scared)
2. neo-spinothalamic tract (terminates in the ventral posterior lateral nucleus VPL)
a delta go through thalamus and to primary somatosensory cortex

Question 23

what do lesions in the neo part cause

Answer 23

decreased perception of pain and temperature on contralateral side of the body
1 or 2 dermatomes below the level of the lesion

Question 24

describe the spinocerebellar pathway

Answer 24

unconscious pathway
take info about changes of postural set and goes to cerebellum which is integrated with descending motor info via a lateral pathway so cereblum knows what movement u want to do and where your body it
then can adjust body with fine movements in relation to intended movement so no overshooting
drinking alcohol affects cerebellum (suppressed)

Question 25

what are the two routes for information in spinocerebellar pathway

Answer 25

anterior and posterior

Question 26

anatomy of spinocerebellar pathway

Answer 26

only two neurons (1st and 2nd order) in both anterior and posterior routes
carry info from muscle spindles (muscle length), golgi organs (proprioception) and touch receptors
used by cerebellum for control of posture and co-ordination of movement
cell bodies of 2nd order neurons are in dorsal horn of the spinal cord and terminate in the vermis of the cerebellum
lesions in cerebellum always produce IPSILATERAL effects (anterior might be double crossed and others not, posterior is entirely ipsilateral)

Question 27

where are lesions in cerebellum - ipsi or contra

Answer 27

IPSIilateral

Question 28

testing modalities

Answer 28

jps- for dorsal column testing STABALISE JOINT
pain and temperature- lateral spinothalmic tracts SHARP/ DULL/ COLD TUNING FORK
light touch- localises lesion
vibration sense- good screening for several pathologies 125hz TUNING FORK

Question 29

What happens if there is a lesion on one side

Answer 29

jps and vibration blocked same side
pain and temperature blocked from other side (as they cross)