Anatomy and Physiology Flashcards
how many descending white matter tracts are there in the spinal cord?
6
what are the two main classifications of descending motor tracts in the spinal cord?
lateral (pyramidal) and ventromedial (extrapyramidal)
which motor tracts are lateral/pyramidal tracts?
- lateral corticospinal tract
- rubrospinal tract
which motor tracts are ventromedial/extrapyramidal?
- tectospinal tract
- vestibulospinal tract
- medullary reticulospinal tract
- pontine reticulospinal tract
what is the function of the tectospinal tract?
it stabilises eyes during movement
what is the function of the vestibulospinal tract?
it steadies the head and neck
what is the function of the lateral pyramidal tracts?
voluntary control of fine movement
what is the function of the reticulospinal tracts?
control of axial muscles for body positioning and posture
what is the decussation of the pyramids?
the point in the medullary pyramids where the corticospinal tract fibres cross over to the opposite side
where does the rubrospinal tract begin?
in the red nucleus in the midbrain
what structure in the brain is the 3rd ventricle associated with?
diencephalon
what structure in the brain is the cerebral acqueduct associated with?
midbrain
what structure in the brain is the 4th ventricle associated with?
posteriorly - cerebellum
anteriorly - pons and medulla
which two motor tracts complement eachother?
corticospinal tract and rubrospinal tract
where do the pyramidal tracts originate from?
cerebral cortex
where do the extrapyramidal tracts originate from?
brainstem
what are the two simultaneous actions of corticospinal tract neurons?
1 - monosynaptic excitation of agonist motor neurons
2- inhibition of antagonist motor neurons (through interneurones)
which motor neurons are activated by lateral corticospinal tracts? what action do they carry out?
distal limb muscles - voluntary movement
what is the somatotopic distribution of lower motor neurons in the spinal cord?
axial and proximal muscles medially
distal muscles laterally
are the actions of the ventromedial motor pathways voluntary or reflexes?
reflexes
are the actions of the lateral motor pathways voluntary or reflexes?
voluntary
what area of the brain (name and Brodmann area number) is responsible for planning movements?
premotor cortex - Brodmann area 6
what do PMA and SMA stand for, and what muscles do they each innervate?
PMA = premotor area - innervates proximal motor units SMA = supplementary motor area - innervates distal motor units
what kind of neurons are found in the corpus striatum?
medium spiny neurones
what is the corpus striatum composed of?
caudate nucleus and putamen
what actions does firing of the caudate nucleus predict?
eye movements
what actions does the firing of the putamen predict?
body/limb movements
what are the main steps of the basal ganglia direct pathway? what kind of neurotransmitter signal does each step send?
- cortex to corpus striatum - excitatory (glutamate)
- corpus striatum to globus pallidus (internal) - inhibitory (GABA)
- globus pallidus to thalamus (VLo) - reduced inhibition
- thalamus (VLo) to Area 6 (SMA) - excitatory (glutamate)
which area of the thalamus is involved in the basal ganglia pathway?
VLo - ventral lateral nucleus in dorsal thalamus
what is the resting state of the thalamus?
inhibited by action of globus pallidus
what is the function of the indirect basal ganglia pathway?
to stop antagonistic movements from being activated by the thalamus
what is the corticopontocerebellar tract, and what is its function?
a large projection tract from the somatosensory cortex to the pons and cerebellum, involved in motor control
which area of the cortex is activated as a result of the direct basal ganglia pathway?
supplementary motor area (SMA)
how does cerebellar information get fed back to the SMA for motor control?
cerebellum –> superior cerebellar peduncles –> ventrolateral thalamus –> back to motor cortex
which two types of neurons are involved in motor pathways?
upper and lower motor neurons
how many different neurons are involved in a sensory pathway?
three - first, second and third order neurons
what sensations does the spinothalamic tract carry?
pain and temperature
what sensation does the dorsal column tract carry?
proprioception, vibration and light touch
what are the three common characteristics of first, second and third order sensory neurons involved in ascending pathways?
- first order neuron always pseudounipolar with a dorsal root ganglion
- second order neuron always the one to cross to contralateral side
- third order neuron always starts in contralateral medulla
what is the crossover point of ascending fibers from the dorsal column?
gracile and cuneate nuclei in medulla
what is the crossover point of ascending fibers from the spinothalamic tract?
spinal cord
at which level of any ascending pathway does the third order neuron get activated?
at the contralateral thalamus
what is the dorsal column tract called after crossover at the cuneate and gracile nuclei?
medial lemniscus
which nerve fibres carry pain sensation?
A delta
C fibres
name some characteristics of A beta fibers and what sensations they carry
large diameter
myelinated
mechanoception
name some characteristics of A delta fibers and what sensations they carry
medium diameter myelinated mechanoception fast pain (nociception) pressure
name some characteristics of C fibres and what sensations they carry
small
unmyelinated
carry slow pain
temperature (hot)
which lamina of Rexed receive pain input?
mainly 2 and 5
which system is involved in modulating descending pain pathways?
PAG (periacqueductal grey) pathway
what is the gate control theory with regards to pain sensation?
firing of A-beta fibres and PAG fibres may activate inhibitory interneurons, which block the firing of C fibres
how does the PAG mechanism modulate pain?
through action at 5HT, NA and opioid receptors
what is the difference between pain and nociception?
pain - subjective experience
nociception - physiological stimulus to tissue damage
which type of pain (acute or chronic) is physiological?
acute pain
define the three types of peripheral sensitisation to pain
allodynia - reduced threshold for nociception
hyperalgesia - increased neuronal firing for non-painful stimulus
spontaneous pain - independent firing of neurons with no physiological cause
define the three types of central sensitisation
wind up: only affects affected synapses, increased firing when stimulus increases, firing stops when stimulus stops
classical: new synapses triggered in response to painful stimulus, firing outlasts stimulus
long-term potentiation: adaptation of affected synapses as result of repeated stimulus to that area
list the three types of central pain sensitisation
wind up sensitisation
classical sensitisation
long-term potentiation
list the three types of peripheral pain sensitisation
allodynia
hyperalgesia
spontaneous firing
what is normally the cause of neuropathy?
nerve damage
at which stages of the pain pathway can drugs modulate it?
transduction (peripheral afferents)
transmission (to thalamus)
response (descending pathway)
which two systems are involved in modulating pain, according to the gate control theory?
- A-beta fibre firing
- PAG (periacqueductal grey) and NRM (nucleus raphe magnum) firing
which molecules are used to inhibit pain sensation in the gate control theory?
opioid peptides (endorphins)
explain the mechanism of action of NSAIDS
they block cyclo-oxygenase, which converts arachidonic acid to prostaglandins
explain the mechanism of action of local anesthetics
they block sodium channels, stopping depolarisation of afferent neurons
explain the mechanism of action of opiates
desensitise nociceptors
trigger inhibitory interneurons in dorsal horn
trigger PAG/NRM descending pathway
list some chemical triggers found in injured tissue which can activate the pain pathway
low pH temperature bradykinin histamine prostaglandins
what are the three areas of the brain that are essential for forming, accessing and storing memories?
forming - hippocampus
accessing - thalamus
storing - cortex
name the four types of memory
- immediate
- short term memory
- intermediate term memory
- long term memory
name the four structures involved in the Papez circuit
- hippocampus
- mammillary bodies
- thalamus
- cingulate cortex
