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HYMS Block 5 > CNS and Motory Pathways > Flashcards

CNS and Motory Pathways Flashcards

1
Q
  1. what does the brainstem consist of?
  2. what is found either side of the median sulcus of the medulla?
  3. which cranial nerves come off the brainstem?
  4. which cranial nerve comes off the dorsal surface?
  5. where does the third cranial nerve emerge?
  6. on the dorsal surface, what does the tectum of the midbrain split into?
A
  1. midbrain, pons, medulla
  2. medullary pyramids
  3. III-XII
  4. IV
  5. ventral surface, from the interventricular fossa
  6. inferior and superior coliculi (looks like 6 pack(
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2
Q
  1. what are the 2 main parts (and further divisions) of the midbrain?
  2. what is the pons?
  3. what are the two major components of the Pons?
  4. what is the function of:
    a) the medulla (2)
    b) the pons (1)
    c) midbrain (2)
A
  1. tectum (which is further divided into the colliculi) and cerebral peduncles (which are further divided into crus cerebra and tegementum
    2 a group of nerves that acts as a connection between cerebrum and cerebellum
  2. pontine nuclei and tegementum

4a) carrys ascending and descending tracts; pyramids are site of decussation
contains nuclei that control vital function
4b) connects different parts of the brain
4c) colliculi serve as reflex centres for certain visual and auditory activities
contains substantia nigra and red nuclei therefore has roles in co-ordination of movement

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3
Q
  1. what is brainstem death? (UK definition)
  2. what is the general criteria for brainstem death?
  3. what is the more definitive criteria for brainstem death (affects on cranial nerves) - 8
A
  2. unconscious. Heartbeat and breathing maintained by a ventilator. evidence of serious incurable brain damage. no doubt that the condition is irriversible
  3. fixed pupils that do not respond to light
    no corneal reflex
    absent oculouvestibular reflex (cold water in ear)
    no response to supraorbital pressure
    no gagging response to pharyngeal stimulation
    absent motor response to somatic stimulation
    no observed respiratory effort when ventilator is disconnected
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4
Q
  1. what is the difference between upper and lower motor neurons?
  2. using the functional division of motor tracts, how do pyramidal and extrapyramidal tracts differ?
  3. how are motor tracts divided anatomically?
A
  1. upper motor neurons are contained within the CNS. Cortex > spinal cord. Cell bodies are found in the spinal cord and they project to muscles
  2. pyramidal tracts are responsible for voluntary control of musculature. Extrapyramidal tracts are responsible for involuntary control of musculature
  3. Dorsolateral - innervate distal muscles and control fine movements
    Ventromedial - innervate proximal muscles and control righting movements and posture
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5
Q
  1. Name the 2 dorsolateral tracts

2. name the 3 ventromedial tracts

A
  1. rubrospinal and corticospinal

2. reticulospinal, tectospinal and vestibulospinal

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6
Q
  1. where do reticulospinal tracts originate and project to?
  2. do they decussate?
  3. what muscles do they act upon?
  4. what is their affect on
    a) extensors
    b) flexors
  5. what is their overall role?
  6. where do tectospinal tracts originate and project to?
  7. do they decussate
  8. what muscles do they innervate?
  9. what peripheral input do they receive?
  10. what is their role?
  11. where do vestibulospinal tracts originate and project to?
  12. do they decussate?
  13. what do medial tracts innervate?
  14. what do lateral tracts innervate?
  15. what is their role?
A
  1. reticular formation > spinal cord
  2. NO
  3. trunk and proximal limb
    4a) excite . 4b) inhibit
  4. involved in automatic posture and gait related movements
  5. superior colliculi > spinal cord
  6. yes
  7. muscles of proximal shoulder girdle and neck
  8. peripheral visual input
  9. mediates head turning in response to visual stimuli
  10. vestibular nuclei > spinal cord
  11. no
  12. cervical and upper thoracic spinal cord
  13. all spinal cord segments
  14. involved in positioning head and neck, and maintaining balance
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7
Q
  1. where do rubrospinal tracts originate and project to?
  2. where do they decussate?
  3. what do they innervate?
  4. what is the effect of innervation on flexors?
  5. what is their role?
  6. where do the corticospinal tracts originate and project to?
  7. where do they decussate?
  8. where do anterior tracts terminate? Where do lateral tracts terminate?
  9. what is their role?
A
  1. from red nucleus to cervical spinal cord
  2. mesencephalon
  3. pectoral girdle
  4. excite
  5. control and co-ordination of movement
  6. cortex > spinal cord
  7. lateral tracts decussate in the medullary pyramids; anterior tracts decussate at the spinal cord
  8. anterior tracts terminate in the cervical and upper thoracic segments; lateral tracts terminate at all spinal levels
  9. voluntary, skilled motor activity.
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8
Q
  1. what are the effects of injury on ventromedial tracts?
  2. why do effects only usually arise from bilateral lesions?
  3. what are the effects of injury on dorsolateral tracts?
A
  1. loss of righting reactions, navigational control. Axial immobility and forward slump. Can’t reach out for objects. Can flex elbow and individual digits
  2. because they project onto interneurons with bilateral spread
  3. normal walking and navigation, righting movements and axial posture
    arms hang limply. reach by shoulder circumduction. elbow inactive and fingers flex together.
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9
Q
  1. Name the three types of movement
  2. describe the somatotopic arrangement of the spinal cord
  3. describe the basic heirarchy of the motor system
  4. describe the path of upper motor neurons
  5. describe the path of lower motor neurons
A
  1. reflex, rhythmic, voluntary
  2. cell bodies supplying axial muscles are found medially. cell bodies supplying distal muscles are found laterally
  3. command from brain/brainstem (upper) > spinal cord alpha neurons (lower) > skeletal muscle > movement
  4. cell bodies in cerebral cortex and brainstem. Axons remain in CNS. Synapse on lower motor neurons either directly or indirectly
  5. cell bodies found in brainstem or spinal cord. Axons leave CNS and synapse onto muscles
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10
Q
  1. what is a reflex?
  2. what is a reflex arc?
  3. what type of synapses to interneurons in a reflex arc make?
  4. name 2 reasons why we have reflexes
A
  1. involuntary movement that occurs as a result of sensory stimulation. Involves impulses travelling through a reflex arc
  2. circuit composed of sensory neurons, interneurons and a motor neuron
  3. multisynaptic (1 sensory signal can affect multiple motor targets)
  4. protect body against damage. co-ordination of musclew activity
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11
Q
  1. describe the structure of a muscle spindle
  2. what is the difference between extrafusal and intrafusal muscles
  3. which type of motor neurons are involved in the stretch reflex mediated by muscle spindles?
  4. what type of reflex arc is the stretch reflex mediated by?
  5. name an example of this type of reflex
  6. what also occurs reciprocally in a stretch reflex?
A
  1. intrafusal muscle which runs parallel to extrafusal muscle. 1a afferents wrap themselves around the intrafusal muscle. They detect the amount and rate of change of muscle length
  2. extrafusal muscles contract when they recieve a motor signal, whilst intafusal muscle make up the muscle spindle and detect change in muscle length
  3. alpha motor neurons innervate the extrafusal muscle
    gamma motor neurons innervate the intrafusal muscle, to maintain tautness, which adjusts the sensitivity of the muscle spindle to detect small changes in the extrafusal muscle. Both alpha and gamma motor neurons are co-stimulated by the interneuron
  4. monosynaptic - no interneuron
  5. knee jerk reflex
  6. inhibition of opposing muscles
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12
Q
  1. which proprioceptors mediate inverse stretch reflexes?
  2. which type of afferents are these sensory organs innervated by?
  3. how do these receptors work?
  4. describe the rest of the reflex arc
  5. what is the purpose of this reflex?
A
  1. golgi tendon organs
  2. Ib afferents
  3. force generated by muscle contraction acts directly on the tendon to increase tension. This compresses the intertwined sensory fibres, to increase activity in Ib afferent
  4. synapse with inhibitory internneurons which act to decrease activity of alpha motor neurons
  5. protection from muscle and tendon damage if lifting something too heavy
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13
Q
  1. describe the flexor withdrawal reflex
  2. in terms of synapses, what type of reflex is this?
  3. what also occurs reciprocally in this reflex?
  4. how does spinal cord circuitry produce complex rhythmic movements outside of higher control?
A
  1. stepping on a tac activates nociceptive cutaneous receptors
    signal travels through afferent neurons to spinal cord interneurons
    interneurons synapse with alpha motor neurons
    one alpha neuron flexes the hamstring to bend the knee. another alpha neuron relaxes the quadriceps to extend the opposite leg
  2. polysynaptic
  3. reciprocal inhibition of opposing muscles
  4. central pattern generators that produce oscillatory pattern outputs without sensory feedback
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14
Q
  1. what is a useful landmark for distinguishing between upper and lower motor neuron lesions?
  2. what type of lesions occur above this landmark?
  3. what type of lesions occur below this landmark?
  4. how do upper and lower motor neuron lesions differ (2)
  5. how does diffuse atrophy differ from muscle atrophy?
A
  1. anterior horn
  2. upper
  3. lower
  4. upper - increased muscle tone and exaggerated reflexes. diffuse atrophy
    lower - decreased muscle tone and diminished/absent reflexes. muscle atrophy
  5. diffuse - occurs when muscle is no longer active as usual
    muscle - damage to anterior horn cells causes a cease i n production of trophic factors that promote muscle growth/regeneration, leading to atrophy
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15
Q
  1. describe 8 characteristics of cerebellar lesions
  2. describe 4 characteristics of basal ganglia lesions
  3. name 4 causes of UMN lesions
  4. name 3 causes of LMN lesions
A 
1. dysdiadochokinesia
ataxia
nystagmus
intention tremor
slurred speech
hypotonia
past pointing
resting tremor
  1. dystonia
    akathesia
    parkinsonism
    dyskinesia
3. stroke
MS
traumatic brain injury
cerebral palsy
4. bells palsy
guillian barre syndrome (autoimmune disease against LMNs)
motor neuron disease
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16
Q

MRC scale. What do the scores 5-0 mean?

A
  1. full power
  2. reduced power against resistance
  3. active movement against gravity. resistance eliminated
  4. no movement against gravity
  5. flicker of movement
  6. no movement
17
Q
  1. what are single muscle fibres surrounded by?
  2. what are muscle fibres bundled into and what by?
  3. what are whole muscles contained within?
  4. what are the connective tissue layers in muscle continuous with?
A
  1. endomysium
  2. into fasicles by perimysium
  3. epimysium
  4. tendons
18
Q
  1. what happens during development to myoblasts?
  2. what does this mean for growth of muscles?
  3. what is the sarcolemma?
  4. what are T tubules?
  5. what does the sarcoplasmic reticulum store?
  6. what are myofibrils and where are they found?
A
  1. many fuse to form muscle fibres
  2. they loose the ability to divide therefore growth occurs by hypertrophy
  3. plasma membrane of muscle fibre
  4. invaginations of sarcolemma that project into the centre of the muscle fibre. They propagate the action potential into the centre of the cell
  5. calcium ions
  6. contractile unit of skeletal muscle, made up of myofillaments
19
Q
  1. describe the composition of myosin
  2. what fillaments make up thin fillaments?
  3. describe the structure of the thin fillament components
A
  1. 6 polypeptide chains - 2 heavy and 4 light
    heavy chains form tail. Ends of heavy chains are folded bilaterally into a globular peptide structure forming the head. the light chains help control the function of the head.
  2. actin, tropomyosin and troponin
  3. actin - doubble f actin helix. Myosin binding sites
    tropomyosin - wraps around actin, and in resting state cover the myosin binding sites
    troponin - heterotrimer consisting of TnT, TnC and TnI
    TnT binds to tropomyosin, TnC binds Ca and TnI binds actin. Ca binding induces a conformational change which moves tropomyosin to uncover the myosin binding site.
20
Q

Describe the following:

  1. z discs
  2. a band
  3. i band
  4. H zone
  5. M line
  6. sarcomere
A
  1. separate one sarcomere from another.
  2. where thick and thin fillaments overlap
  3. thin fillaments only. Z discs pass through middle of i band
  4. thick fillaments only
  5. region of H zone that contains proteins that hold thick fillaments together
  6. basic functional unit of myofibril. Z disc to Z disc
21
Q
  1. how to muscles contract?

2. describe the events in cross bridge cycling

A
  1. sarcomere shortening
    • ATP binds to myosin head, reducing affinity of ,myosin for actin
      - ATP hydrolysed by intrinsic ATPase activity of myosin. Myosin head becomes cocked
      - cocked head binds on new myosin position
      - release of Pi from myosin induces conformational change, causing power stroke
      - ADP is released
22
Q
  1. what is the forcefulness of muscle contraction dependent on
  2. name 2 exceptions to this
  3. how does a muscle cell restore its calcium concentration following muscle contraction?
A
  1. starting length
  2. upon too much stretching, zone of overlap shortens, thus fewer myosin heads can make contact with thin fillaments
    shortening - the tension that can develop decreases as thick fillaments are crumpled by z discs
  3. SR contains Ca Active transport pumps (SERCA pumps). move Ca back into SR. Inside the SR, calsequesterin binds to Ca and enables even more Ca to be sequestered.
23
Q
  1. How is ATP produced from creatinine phosphate
  2. what is a motor unit?
  3. what is a twitch contraction?
  4. what is motor unit recruitment?
  5. what is wave summation?
  6. what is unfused tetanus?
  7. what is fused tetanus?
A
  1. creatinine kinease catalyses the transfer of phosphate groups from ATP to creatinine, creating creatinine phosphate
    when the ADP level starts to rise, creatinine kinase catalyses the transfer of phosphate group from creatinine phosphate to ATP.
  2. somatic motor neuron and all the skeletal muscle fibres it stimulates
  3. brief contraction of all muscle fibres in a motor unit in response to a single AP
  4. process by which the number of active motor units increase
  5. second contraction is stronger than first when stimulated after a refractory period
  6. when skeletal muscle is stimulated at a rate that enables partial relaxation
  7. when skeletal muscle is stimulated at a rate that does not enable relaxation
24
Q
  1. what is isotonic contraction? What are these contractions used for?
  2. what is isometric contraction? What are these contractions used for?
A
  1. tension developed remains constant. Muscle changes length. Used for body movements
  2. tension develops without change in muscle length. Used to maintain posture and to support objects in a fixed position
25
Q
  1. what is the colour of slow twitch fibres
  2. how many mitochondria to slow twitch fibres have?
  3. why are these fibres said to be slow
  4. what is the colour of fast twitch glycolytic fibres
  5. why are they said to be fast?
  6. what is their fatigue resistance?
  7. what is the colour of fast twitch fatigue resistant fibres?
  8. how many mitochondria do they have?
  9. what is their fatigue resistance?
A
  1. dark red (as they contain large amounts of myoglobin and blood capillaries)
  2. many
  3. ATP in myosin head hydrolyses slowly thus contraction cycle proceeds at a slower pace
  4. dark red
  5. ATPase in myosin heads hydrolyses quickly
  6. relatively resistant to fatigue as they can generate a considerable amount of ATP by aerobic resperation
  7. white
  8. few
  9. fatigue quickly (limited aerobic respiration)

HYMS Block 5 (5 decks)

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