Ascending Tracts

Question 1

What are the different types of sensory neurones? What are they best for?

Answer 1

Free nerve endings - pain and thermal stimuli

Encapsulated nerve ending - touch, vibration (Pacinian)

Nerve ending with specialised cell - taste

Question 2

What are stimulus modalities?

Answer 2

The types of stimuli detected eg light, touch, temperature, chemical changes (taste)

Question 3

What are qualities of modality?

Answer 3

Eg for taste - sweet, sour, salty etc.

Question 4

Give an example of when a receptor is not modality specific

Answer 4

If it is hit hard enough with a different modality eg when hit in the eye, see lights

Question 5

What and where are proprioceptors?

Answer 5

Found in joints and muscles

Tell position of limbs etc.

Question 6

List the types of proprioceptors and what they do

Answer 6

Muscle spindles - length of the muscle

Golgi tendon organs - power the muscle is exerting

Question 7

How is a sensation detected and sent to the CNS?

Answer 7

Stimulus evokes change in permeability to ions of the receptor membrane
Creates a receptor potential - depolarisation
If depolarisation/generator potential is large enough, triggers an action potential which is propagated to the CNS

Question 8

How is the strength of a stimulus detected?

Answer 8

The rate/frequency of action potentials produced

A stronger stimulus can activate adjacent cells

Question 9

What is the difference between slowly adapting (tonic) receptors and rapidly adapting (phasic) receptors?

Answer 9

Tonic - keep firing as long as the stimulus lasts eg joint and pain receptors

Phasic - respond maximally and briefly to a stimulus eg touch receptors. Initially die action potentials and then stop. Some can fire when stimulus is taken away

Question 10

What is acuity?

Answer 10

The precision by which a stimulus can be located

Question 11

What is acuity determined by?

Answer 11

Lateral inhibition of the CNS - increases the ability to locate a stimulus. As a potential passes from a first order to second order neurone, get inhibition of lateral second order neurones

Question 12

What is two-point discrimination?

Answer 12

The minimal interstimulus distance required to perceive two simultaneously applied skin indentations

Question 13

What is two point discrimination determined by?

Answer 13

The density of sensory receptors (higher density, greater discrimination)

Size of neuronal receptive fields (the smaller they are, the better the discrimination)

Psychological factors such as stress and tiredness can reduce it

Question 14

How does synaptic convergence and divergence affect acuity?

Answer 14

Convergence decreases acuity

Divergence amplifies the signal, making it harder to locate

Question 15

Where is convergence seen?

Answer 15

When visceral pain fibres merge with somatic pain fibres

Question 16

What happens at the thalamic level in the somatosensory system?

Answer 16

There is localisation and discrimination of stimuli

Gives highly organised projections to to cortex

Question 17

Where in the cortex is the somatosensory cortex?

Answer 17

In the post-dental gyrus

Question 18

What is the structure of the somatosensory cortex?

Answer 18

Cortical columns of information dedicated to precise areas, modalities and qualities

Question 19

What can lead to loss of two-point discrimination?

Answer 19

A lesion to the sensory cortex eg in repeated epileptic events

Question 20

What is astereognosis?

Answer 20

Inability to identify an object by active touch of the hands

Question 21

What makes up the dorsal column of the spinal cord?

Answer 21

Fasciculi gracilis - contains fibres from the lower limbs and located medially

Fasciculi cuneatus - found only from C1-T6 - fibres from the upper limb

Question 22

What information do the dorsal columns carry?

Answer 22

Fine touch

Conscious proprioception

Question 23

Where are the cell bodies of sensory neurones located?

Answer 23

In the dorsal root ganglion

Question 24

On which side do neurones in the dorsal column travel on?

Answer 24

The ipsilateral side

Question 25

In the dorsal tract, where does each neurone synapse?

Answer 25

First and second - nucleus gracilis or cuneatus in the medulla on the ipsilateral side

Question 26

In the dorsal tract, when do neurones decussate?

Answer 26

Second order neurones decussate at the medulla

Question 27

In the dorsal tract, where do the second order neurones go?

Answer 27

They decussate Run in the medial lemniscus Ascends through the pons and midbrain Synapse with third order neurones in the synapse

Question 28

What does damage to the dorsal tract result in?

Answer 28

Loss of fine touch and proprioception in the ipsilateral side below the level of the spinal cord lesion

Question 29

Symptoms of damage to the dorsal column?

Answer 29

Loss of tactile sense, proprioception and an inability to identify objects placed in the hand

Question 30

What information does the lateral spinothalamic tract carry?

Answer 30

Pain and temperature sensations

Question 31

When does the lateral spinothalamic tract fibres decussate?

Answer 31

At the level they enter the spinal cord | Via the ventral white commissure

Question 32

Where do first order neurones of the lateral spinothalamic tract synapse with second order neurones?

Answer 32

In the dorsal horn of the spinal cord

Question 33

In which side do neurones in the lateral spinothalamic tract ascend?

Answer 33

The contralateral side

Question 34

What is the order (from medial to lateral) that the fibres of the lateral spinothalamic tract ascend in?

Answer 34

Cervical Thoracic Lumbar Sacral (outside)

Question 35

Where do axons of the lateral spinothalamic tract synapse with the third order neurones?

Answer 35

In the thalamus

Question 36

Symptoms of damage to the lateral spinothalamic tract?

Answer 36

Loss of pain and temperature sensation on the contralateral side of the body - at and below damage

Question 37

Why does loss of pain sensation happen a few levels below the location of damage to the lateral spinothalamic tract?

Answer 37

The first order afferent fibres in the zone of Lissauer ascend/descend one or two levels before making their synaptic link with the second order neurone

Question 38

Why does sacral sparing occur?

Answer 38

Sacral and lumbar fibres are located more laterally in the lateral spinothalamic tract than cervical and thoracic fibres Any expanding tumour/lesion in the grey matter will affect the thoracic and cervical fibres first, while lumbar and sacral fibres will still have intact pain and temperature fibres (initially)

Question 39

What information does the anterior spinothalamic tract carry?

Answer 39

Crude touch and pressure

Question 40

What is the course of the anterior spinothalamic tract?

Answer 40

Same as the lateral spinothalamic tracts | Known collectively as the anterolateral ascending tracts

Question 41

What information do the anterior and posterior spinocerebellar tracts carry?

Answer 41

Unconscious proprioception -muscle spindle fibres and Golgi spindle organs Convey information about whole limb movements and postural adjustments to the cerebellum

Question 42

Where do the anterior and posterior spinocerebellar tract first order neurones synapse with second order neurones?

Answer 42

In the dorsal horn

Question 43

Where do fibres of the anterior spinocerebellar tracts decussate?

Answer 43

At the level they enter in the tract | Again in the pons

Question 44

Where do the second order neurones synapse with third order neurones in the anterior and posterior spinocerebellar tract?

Answer 44

They don't | Second order neurones terminate in the cerebellum

Question 45

What does damage to the anterior spinocerebellar tract result in?

Answer 45

Loss of proprioception and co-ordination to the contra-lateral lower limb

Question 46

What does damage to the posterior spinocerebellar tract result in?

Answer 46

Loss of proprioception and co-ordinated movement on the ipsilateral side

Question 47

Where do fibres of the posterior spinocerebellar tract decussate?

Answer 47

They don't

Question 48

What information does the cuneocerebellar tract transmit?

Answer 48

Proprioception

Question 49

What is the course of fibres in the cuneocerebellar tract?

Answer 49

Ascend on the ipsilateral side Synapse in the brain stem Second order neurones terminate in the cerebellum

Question 50

Where are the cell bodies of first order neurones located?

Answer 50

In the trigeminal ganglion

Question 51

Where do first order neurones of the trigeminal nerve synapse

Answer 51

In the trigeminal nucleus of the brain stem

Question 52

Where do second order neurones and third order neurones of the trigeminal nerve travel?

Answer 52

Second order from the trigeminal nucleus of the brain stem to the thalamus Third order travel to the cerebral cortex

Question 53

What is tabes dorsalis caused by?

Answer 53

Syphilis

Question 54

What happens in tabes dorsalis?

Answer 54

Central processes of the dorsal root ganglion degenerate - therefore affects the dorsal columns (fasciculus gracilis and cuneatus)

Question 55

Signs and symptoms of tabes dorsalis

Answer 55

Dorsal columns affected - loss of fine touch - loss of two-point discrimination - loss of conscious proprioception - ataxia

Question 56

What is sensation?

Answer 56

The conscious/sub-conscious awareness of an external or internal stimulus

Question 57

What happens in shingles to cause pain?

Answer 57

VZV is reactivated in the dorsal root ganglia, increasing its sensitivity Causes burning and tingling sensations which are painful and the skin of the affected dermatome becomes red and blisters