sensory neuroscience Flashcards
why does the spinal cord need protecting
because it is soft tissue
what protect the spinal cord
vertebral column and the meninges (outer dura, then arachnoid then pia mater)
what is the space between 2 spaces filled with
CSF
what carries the blood vessels that go over the surface of the cord and supply it
pia mater
what does the epidural space contain and what is it between
contains oily fat and is between the dura mater and bone
what ligament is either side of the cord and what is its function
dentate ligament. holds together the pia mater and arachnoid mater, prevents spinal cord moving backward and forward
what is the dura mater continuous with?
epineurium of spinal nerve
where does the spinal cord terminate
L1-2
where can other nerve roots continue down to
L2-5
What is the lumbar cistern
space below the tip of the spinal cord which contains spinal roots and is part of the subarachnoid space
what is the cauda equina
nerve roots travelling through the lumbar cistern
how many spinal cord segments
31
what fissure contains the anterior spinal artery
midline fissure
what is grey matter divided into
dorsal and ventral horn
what is the white matter divided into
3 tracts- dorsal white column, lateral white column, anterior white column
what is the white matter on either side connected by
white commissure
what is the dorsal white column divided into
fasciculus gracilis (more medial) and fasciculus cuneatus
is the dorsal horn motor or sensory
sensory
what nuclei run in the dorsal horn of the grey matter
nucleus proprius and substantia gelatinosa
what is the ventral horn
motor
what are the 2 groups of motor neurones in the ventral horn
medial (in every segment) and lateral (only where the segments give rise to nerves forming the limb plexuses)
what do the descending tracts synapse with in the white matter
with lower motor neurones
does white matter decrease or increase as descends?
decreases as go down the descending tract some axons leave
what are the ascending tracts
sensory
as they ascend what happens to the white matter
increases as gather more axons
what is in the middle of the grey matter
central canal which is a remnant of the ventricular system (contains CSF)
how does the dorsal horn change?
depends on how large/sensitive the area supplying it is eg small dorsal horn in thoracic region
how does the ventral horn change?
depends on how many motor neurones has to accommodate. at level of the limbs the lateral group push ventral horn into an oval shape
what can lead to sciatica and parasympathetic disturbances (cauda equine lesions)
the lumbar spine is flexible and lumbosacral nerve roots can be stretched, compressed or irritated
what is sciatica characterised by
pain, muscle wating, exaggerated tendon reflexes, urinary retention
a common cause of sciatica
slipped disc
C1-4
breathing
C2
head and neck movements
c4-6
HR
c5
shoulder movement
c7-t1
head and finger movements
t1-t12
sympathetic tone
t2-t12
trunk stability
t11-L2
Ejaculation
L2
hip motion
L3
knee extension
L4-S1
foot motion
L5
knee flexion
s2-s4
penile erection
s2-s3
bowel and bladder
where is the site of termination of afferents conveying senses of pain, temperature and touch?
substantia gelatinosa
what do the neurones of the nucleus proprius give rise to?
spinothalamic tracts
whats between the dorsal and ventral horns?
groups of interneurones
are the substantia gelatinosa and nucleus proprius in every segment?
yes
what is the lateral horn responsible for
preganglionic sympathetic outflow (only in thoracic and upper lumbar)
what do motor neurones in the medial group innervate?
muscles close to the midline (axial muscles)
what do motor neurones in the lateral group innervate?
limb muscles
where does the lateral division extend from to?
T1-L2/3
where is sacral parasympathetic outflow?
S2-S4
What is a nerve
made up of several roots
what are required for connecting of intersegments
fasciculus proprius; interneurons in gray matter running up and down; corticospinal fibres (from cortex); dorsolateral tract of Lissauer.
what is the fasciculus proprius
sheet of axons between the white and gray matter
what is the dorsolateral tract of lissauer
incoming afferent fibres come in and branch up and down by 1 or 2 segments
what is the dorsal column pathway for?
proprioception, discriminative touch and vibration
how does the primary neurone ascend in the DCP? (dorsal column pathway)
ipsilaterally
where does the primary neurone synapse in DCP?
at the medulla
where are the secondary neurone cell bodies in DCP?
in medullary nucleus gracilis and cuneatus
where is sensory decussation in DCP
after synapsing in the nucleus gracilis or cuneatus
where is the tertiary neurone cell body in DCP?
in the thalamus, travels to the primary cortex
after sensory decussation where does the pathway gather? (DCP)
in the medial lemniscus
where does it terminate in the thalamus (DCP)
ventral posterolateral nucleus of the thalamus
where does the pathway travel through (DCP)
internal capsule
where does the fasciculus gracilis carry information from
lower half of the body (below T6)
where does the fasciculus cuneatus carry information from
upper half of the body
where do the cell bodies of a sensory neurone lie
in the dorsal root ganglia
what channel type is present on dendrite like extension of the axon
stimulus gated channel
are stimulus gated channels all or nothing
no, graded response
if the generator potential is sufficiently large what happens
depolarise the adjacent membrane- open Na+ channels leading to an action potential
what do exteroceptors detect
information from outside environment- eg touch and temp, found mainly on the skin
what do proprioceptors detect
properties of the organism eg muscle and tendon reflexes
what are the slowest types of fibres (speed of conduction)
C fibres
what are the order from fastest to slowest of A fibres
A(alpha), A(beta), A(delta)
which fibres are well myelinated
A(alpha) and A(beta)
what do C fibres and A(delta) detect
C- pain, temp, itch; A(delta)- pain and temp
what do A(alpha) and A(beta) detect
A(alpha)- muscle proprioceptors; A(beta)- skin mechanoceptors
what do naked endings detect
pain, temp, touch
what are the encapsulated endings and what do they detect
Pacinian (vibration), Ruffini’s (shear stress), Merkels (pressure), Meissners (touch)
which receptors are rapidly adapting
Pacinian corpuscle (Merkels- slow)
what is a consequence of nerves being compressed or damaged
conduction velocity falls
what is the dorsal horn of the spinal cord divided into
laminae
what do the laminae 1 and 2 make up?
substantia gelatinosa
where do A (beta) terminate (laminae)
laminae 2-5
where do A (alpha) terminate (laminae)
extend into the ventral horn to synapse with lower motor neurones
what tract is involved in posture and balance
spinocerebellar tract
what is an incomplete lesion
hemicord lesion (brown-sequard lesion)
what pathway is involved in posterior cord syndrome and what are the symptoms
dorsal column pathway. clumsiness, impaired proprioception, good muscle strength
what happens to limbs in their development
grow outwards and rotate
how do upper limbs rotate
laterally. thumb at end of pre axial border
how do lower limbs rotate
medially. big toe at end of post axial border
what roots supply biceps
C5-6
what roots supply triceps
C7-8
what motor supplies gluteal
L5-S1
motor supply to calf muscles
S1-2
what motor supply to pelvic floor, bladder etc
S3-5
what roots involved in finger flexion reflex
C7-8
what roots are involved in the knee reflex
L3-4
what roots are involved in ankle reflex
S1
what are the superficial reflex of epigastric
T7-9
superficial reflex of lower abdominal
T11-L2
superficial reflex of cremasteric reflex
L1-2
what is the superficial anal reflex
S4-5
what is a theory of referred pain
several nociceptors from several locations converge on a single ascending tract in the cord. pain signals from skin more common
where does the afferent input get confused in referred pain
dorsal horn
where does the pancreas refer pain to
back
where does liver and gallbladder refer pain to
tip of scapula
diaphragm, lung and spleen refer where
left shoulder
what information does the mandibular nerve also carry
proprioception
what does all info coming from the head pass via
trigeminal ganglion
after passing through the trigeminal ganglion where do the neurones go
1 of 3 ganglia (GSA trigeminal nuclei)
what tracts are associated with the trigeminal
trigeminothalamic tract
where does the trigeminothalamic tract run to and how
to the thalamus, bilaterally
what is the nucleus destination of the trigeminothalamic tract
ventral posteromedial nucleus of the thalamus
after the ventral posteromedial nucleus of the thalamus where does the information go
through internal capsule to the primary sensory cortex
what fibres are found in the anterior and posterior limbs of the internal capsule
thalamocortical fibres
what fibres are found in the post limb of the internal capsule
corticospinal and corticonuclear
what supplies the internal capsule (blood)
MCA
what supplies the anterior limb of the internal capsule
lateral and middle striate branches
what supplies the posterior limb of the internal capsule
anterior choroidal artery
what is the brodmanns area for primary motor cortex
4
what is the brodmanns areas for primary sensory cortex
1,2,3
how does the motor homunculus represent info
contralateral and inverted
where are the inferior parts of the body represented on the sensory homunculus
on medial surface (as move laterally and downward, move upwards on the body)
what information goes to area 3a (central sulcus)
muscle spindles
what info goes to area 1
from joints
where is all info transferred to from area 3
area 2
how does info relay from visual cortex to wernickes area
via angular gyrus
what connects wernickes and brocas areas
arcuate fasciculus
what is nociception
signals derived from tissue damage
what is pain
unpleasant sensation associated with nociception
what fibres are responsible for the first sharp localised pain
A delta
what fibres are involved in the long prolonged dull pain following the initial pain
C fibres (poorly localised)
what speed do C fibres carry
0.5-3m/s
what speed do A delta carry
5-30 m/s
what do all primary sensory neurones have as their excitatory neurotransmitter
glutamate
what is further released for pain to perceived as moderate- intense pain
substance P
what does substance P stimulate
histamine release leading to vasodilation and an inflammatory response
what other peptide is released by primary sensory neurone which aids in vasodilation
CGRP
what do mast cells release to activate nociceptors
5HT
what happens in primary hyperalgesia
histamine with prostaglandins and bradykinin increase the sensitivity of nociceptive sensory endings
what happens in chronic stimulation of nociceptors
build up of peptides in dorsal horn; increase in activity of neuronal responsiveness (wind up)
what is the wind up in activity of neuronal responsiveness due to
change in responsiveness of NMDA glutamate receptors, so NDMA antagonists are used in pain relief; also increase size of nociceptive receptive fields (inhibition of inhibitory neurones by substance P)
what is secondary hyperalgesia
central increase in pain sensitivity due to wind up in the activity of neuronal responsiveness
what is allodynia
touch sensitive sensory neurones (low threshold) start to generate sensation of pain
what is the gate theory of pain
some spinothalamic neurones receive inputs from both touch sensitive sensory neurones and nociceptors (which stimulate strongly). activation of the low threshold touch sensitive neurones blocks the nociceptors
what are some endogenous analegesics
endorphins, enkephalins
What neurotransmitter (monoamine) can inhibit the passage of nociceptive info?
5HT
What is somatic pain
within the body eg muscle, body
what happens in peripheral neuropathic pain
cut axons sprout but if blocked forms a neuroma which is hypersensitive
how do endorphins and enkephalins work?
prevent info transfer from nociceptors to sensory interneurons in the dorsal horn
what is a neuroma
tangled mass of neurones
what can neuromas be hypersensitive to
pressure and temperature
what can neuromas do to increase pain
change their phenotype to express alpha-adrenergic receptors, so if sympathetic axons release NA then pain arises
what does the spinothalamic pathway convey
pain, simple touch and temperature
what happens in the dorsolateral tract of Lissaeur (spino)
birfurcates, travels up/down by 1 or 2 segments
in the substantia gelatinosa, the branches make contact with secondary neurones from where? (spino)
nucleus proprius
where do the axons decussate in spinothalamic pathway
axons of nucleus proprius cross over
ascends in spinothalamic tract to synapse where
ventral posterolateral nucleus of thalamus
what tract brings proprioceptive info to the cerebellar cortex
spinocerebellar tract. from muscle spindle, tendon organs and joint capsules
what is the spinocerebellar tract important in
motor function, balance and posture, info on position of limbs
what is significant in the spinothalamic pathway
1 or 2 segments up or down from where the primary afferents entered
