Somatosensory pathways

Question 1

what are the different types of somatosensation and their names

Answer 1

thermoreception= temperature
mechanoreception= pressure
nociception= pain
proprioception= position in space

Question 2

at what spinal levels is the fasciculus gracilis present alone

Answer 2

The fasciculus gracilis carries sensory input from vertebral level T6 and below and ascends into the gracile nucleus to form the gracile tubercle. The fasciculus cuneatus carries information from T6 and above and ascends into the cuneate nucleus to form the cuneate tubercle. (so above T6 both the fasciculus gracilis + fasciculus cuneatus is present which is why at the cervical level the horns of the grey matter are thinner)

n.b. The gracile nucleus (nucleus gracilis) receives somatosensory information from the lower half of the body and the legs, and the cuneate nucleus (nucleus cuneatus) receives somatosensory information from the upper half of the body and arms

Question 3

what is the point in the human brain at which the fourth ventricle narrows to become the central canal of the spinal cord?

Answer 3

the OBEX (latin for barrier) is the point in the human brain at which the fourth ventricle narrows to become the central canal of the spinal cord The obex occurs in the caudal medulla (it’s the lower margin of the medulla)

Question 4

what are the following large diameter sensory nerve fibres responsible for
* 1a, 1b (Ia,Ib) or A alpha
* II or A beta

Answer 4

• 1a, 1b (Ia,Ib) or A alpha= proprioception
• II or A beta= touch, vibration

Question 5

• fibres of the dorsal columns originate from first order neurons in the _______
• medial lemniscus fibres originate from second order neurons in the cuneate or gracile nuclei in the ______ _____
• The thalamo-cortical fibres in the internal capsule originate from third order neurons in the ________

Answer 5

• fibres of the dorsal columns originate from first order neurons in the DORSAL ROOT GANGLIA
• medial lemniscus fibres originate from second order neurons in the cuneate or gracile nuclei in the LOWER MEDULLA
• The thalamo-cortical fibres in the internal capsule originate from third order neurons in the VPL (Ventero-posterolateral thalamus)

Question 6

what is the difference between PERCEPTION + SENSATION

Question 7

Which tracts carry unconscious proprioceptive information?

Answer 7

spinocerebellar tract

Question 8

Complete the sentence: The third order neurones of the DCML ascend from the ___________ and synapse in the sensory cortex

Answer 8

The third order neurones of the DCML ascend from the THALAMUS and synapse in the sensory cortex

Question 9

where in the brain is the primary somatosensory cortex

Answer 9

the primary somatosensory cortex is located in the postcentral gyrus (anterior part of the parietal lobe)

Question 10

What is spasticity?

Answer 10

Spasticity is abnormal muscle tightness due to prolonged muscle contraction. It is a symptom associated with damage to the brain, spinal cord or motor nerves, and is seen in individuals with neurological conditions, such as: Cerebral palsy (CP) Multiple sclerosis (MS)== its painful for patient

Question 11

what is hyper-reflexia

Answer 11

Hyperreflexia= is the presence of hyperactive stretch reflexes of the muscles.
Hyperreflexia refers to hyperactive or repeating (clonic) reflexes. These usually indicate an interruption of corticospinal and other descending pathways that influence the reflex arc due to a suprasegmental lesion, that is, a lesion above the level of the spinal reflex pathways.

Question 12

what is paresis

Answer 12

Paresis= general term referring to a mild to moderate degree of muscular weakness(can’t contract), occasionally used as a synonym for PARALYSIS (severe or complete loss of motor function). In the older literature, paresis often referred specifically to paretic neurosyphilis

Question 13

spinal tracts are bundles of axons in CNS, these bundles are organised into specific groups with specific functions forming the tracts
ASCENDING TRACTS conduct _____________________
DESCENDING TRACTS= ____________________

Answer 13

spinal tracts are bundles of axons in CNS, these bundles are organised into specific groups with specific functions forming the tracts
ASCENDING TRACTS= conduct sensory info up to brain
DESCENDING TRACTS= motor instructions down the cord

Question 14

Which of these tissues is NOT used in any tissue as a proprioceptor:
* Ruffini ending
* Golgi tendon organs
* Free nerve endings
* Merkel’s disks
* Muscle spindles

Answer 14

free nerve endings are NOT used in any tissue as a proprioceptor

Question 15

Which type of nerve fibres transmit the sense of proprioception?

Answer 15

Ia + Ib (large diameter fibres originating from muscles, tendons + joints)

Question 16

Which type of nerve fibres conveys the sense of touch?

Answer 16

II (Aβ)

Question 17

In which spinal cord 2 laminae touch + conscious proprioceptive fibres synapse?

Answer 17

Lamina III
Lamina IV

Question 18

The ascending fibres that leave the dorsal column nuclei are called ____ _____ fibres

Answer 18

The ascending fibres that leave the dorsal column nuclei are called INTERNAL ARCUATE fibres

Question 19

The fibre tract that ascends contralaterally towards the thalamus is called the _____ _______

Answer 19

The fibre tract that ascends contralaterally towards the thalamus is called the medial lemniscus

Question 19

The thalamic nucleus where the information from the DCML pathway is relayed is the __________ nucleus

Answer 19

The thalamic nucleus where the information from the DCML pathway is relayed is the ventroposterolateral (VPL) nucleus

Question 19

The _____ ____ is the tract that conveys sensory information from the sensory thalamus to the primary somatosensory cortex

The primary somatosensory cortex is located in the _______ gyrus

Answer 19

The internal capsule is the tract that conveys sensory information from the sensory thalamus to the primary somatosensory cortex

The primary somatosensory cortex is located in the postcentral gyrus

Question 20

The trigeminal nucleus is the medullar relay of the pathway (2nd order neuron), but where are the cell bodies of the 1st order neuron

Answer 20

the cell bodies of the trigeminal nerve are found in the trigeminal (Gasserian) ganglion which is the equivalent of a dorsal root ganglion

Question 21

What is the cortical proximity principle

Answer 21

cortical proximity principle: if a limb was amputated, it was believed that the area devoted to that limb shrunk and the area devoted to surrounding parts of the body would expand

in amputation or congenital malformation of an arm: neighbouring areas in the somatosensory cortex would overtake the deprived hand region
= this is considered maladaptive, causing the emergence of phantom limb pain, a percept of pain ascribed to the missing hand

Question 22

what regions of the body have the highest density of touch receptors

Answer 22

hands, lips and tongue have the highest density of touch receptors

as a general rule areas of skin w highest density of touch + proprioceptive receptors occuoy largest areas of the cortical map (HOMUNCULI)

Question 23

what do we mean by homunculi (or homunculus) of brain

Answer 23

The sensory homunculus is a map along the cerebral cortex of where each part of the body is processed. The sensations occur all along the body. The impulses from the body will be sent into the spinal cord and eventually back to the brain to be processed. While the trigeminal nerve carries the face's sensations.

Question 24

what is stereognosis

Answer 24

the tactile ability to perceive the form of solid objects

Question 25

which kind of accessory is used to test the sense of touch

Answer 25

a piece of cotton wool

Question 26

Which sensory pathways convey the senses below? * joint position sense + vibration * temperature (warmth) * discriminative touch * temperature (cold) * crude touch * pricking pain

Answer 26

* joint position sense + vibration = Dorsal column medial lemniscus pathway * temperature (warmth)= anterior spinothalamic tract * discriminative touch= dorsal column medial lemniscus pathway * temperature (cold)= lateral spinothalamic tract * crude touch= anterior spinothalamic touch * pricking pain= lateral spinothalamic touch

Question 27

what is sensory ataxia

Answer 27

sensory ataxia= inability to balance when visual input is removed

Question 28

what nerve fibres transmit 1) fast pain 2) slow pain

Answer 28

Aδ=fast fibres (sharp pain= short but v unbearable, localised) transmitted by posterior spinothalamic tract C= slow pain (dull pain= long lasting + bearable but burning,itchy, hard to localise) transmitted by anterior spinothalamic (polysynaptic tract) Aδ fibres have smaller + more numerous cutaneous receptive fields than C fibres. Allows accurate location of painful stimulus n.b. pain perception occurs when the sensation is interpreted, as such by the brain and this involves various forebrain regions

Question 29

in dorsal horn Aβ fibres (touch + vibration) terminate in ____ laminae _____ Afferent fibres from Aδ and C fibres terminate in ______ laminae ______ these are specific for pain Aδ fibres also terminate in laminae III + V

Answer 29

in dorsal horn Aβ fibres (touch + vibration) terminate in **deep laminae (III-V)** Afferent fibres from Aδ and C fibres terminate in **superficial laminae (I+ II) **these are specific for pain Aδ fibres also terminate in laminae III + V

Question 30

What are WDR neurons + where are they found

Answer 30

laminae IV + VI contain multireceptive wide dynamic range (WDR) neurons aka convergent neurons, these WDR neurons: * are involved in transmission + processing of nociception (pain) but also in the modulation of incoming info (gate control of pain) * respond to noxious + non-noxious stimuli * posses broad receptive fields

Question 31

Cell in lamina I (projection neurons) + projections arising from lamina II project across the midline (decussate) in spinal cord + ascend in the contralateral anterolateral part of the cord as the __________ or the _________

Answer 31

Cell in lamina I (projection neurons) + projections arising from lamina II project across the midline (decussate) in spinal cord + ascend in the contralateral anterolateral part of the cord as the **lateral spinothalamic tract (Aδ fibres)** or the **anterior spinothalamic tract (C fibres)**

Question 32

What are pyramidal tracts and give an example of one u need to know

Answer 32

**Pyramidal tracts** – These tracts originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem. They are responsible for the voluntary control of the musculature of the body and face. The pyramidal tracts derive their name from the medullary pyramids of the medulla oblongata, which they pass through. * **Corticospinal tract** ( from cortex to spinal cord ) = carries motor signals from the primary motor cortex in the brain, down the spinal cord, to the muscles of the trunk and limbs. Thus, this tract is involved in the voluntary movement of muscles of the body.)

Question 33

unilateral meaning

Answer 33

affecting one side only (e.g. unilateral lesion is a lesion affecting one side only)

Question 34

What do we know about referred pain? Know common examples : cardiac ischemia, inflamed appendix

Answer 34

pain is usually referred to a structure that developed from the same embryonic segment or dermatome as the structure in which the pain originates cardiac ischemia: PAIN FROM T1-T4 dermatomes pain sensation can occur in the upper chest as a restricted feeling, or as an ache in the left shoulder, arm or even hand inflamed appendix: pain felt in T10 dermatome arround umbilicus ruptured spleen indication: upper back pain, especially between your shoulder blades (Kehr's sign) colon/ kidney issues: Lower back pain or flank pain

Question 35

What is the thalamic relay for the anterior spinothalamic tract?

Answer 35

intralaminar (IL) nuclei of the thalamus

Question 36

An anterior cord syndrome results in bilateral loss of what 3 sensations? What 2 sensations are preserved below level of lesion

Answer 36

an anterior cord syndrome results in bilateral loss of motor function, temperature and pain. fine touch/discriminative touch and conscious proprioception is preserved below the level of lesion

Question 37

a complete/transverse cord lesion of the spinal cord results in bilateral loss of _______ and ______ functions

Answer 37

a complete/transverse cord lesion of the spinal cord results in bilateral loss of **motor** and **sensory** functions

Question 38

what kind of ipsilateral and contralateral loss does Brown-Sequard syndrome aka partial cord/hemicord lesion result in

Answer 38

Brown-Sequard: results in ipsilateral loss of motor function, conscious proprioception and fine touch it also results in contralateral loss of pain and temperature