PHYS: Motor Systems + Skeletal Muscle Flashcards

1
Q

function of the posterior parietal cortex

A
  • integrates sensory info and relays it to premotor and prefrontal cortices
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2
Q

function of prefrontal cortex

A
  • receives info from posterior parietal cortex
  • makes decision to execute an action and communicates this to premotor cortex
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3
Q

function of premotor cortex

A
  • receives info from prefrontal cortex and plans the motor sequence
  • communicates this to primary motor cortex
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4
Q

primary motor cortex

A
  • receives motor sequence from premotor cortex
  • executes movement via UMNs, LMNs (alpha or gamma) > skeletal muscles
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5
Q

2 main descending spinal tracts

A
  • corticospinal: supplies body muscles
  • corticobulbar: supplies face, head and neck muscles
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6
Q

2 divisions of the corticospinal tract

A
  • lateral (most fibres): supplies limb muscles
  • anterior: supplies trunk muscles
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7
Q

where are upper and lower motor neurons located?

A
  • upper: originate in cerebral cortex or brainstem and synapse w/ LMN in motor nuclei of cranial nerves (brain stem) or ventral horn of spinal cord
  • lower: nuclei of cranial nerves or ventral horn, terminate @ NMJ
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8
Q

symptoms of an upper vs lower motor neuron lesion

A
  • upper: hypertonia - spasticity (pyramidal), rigidity (extrapyramidal), hyperreflexia (inc. positive babinski reflex), clonus
  • lower: hypotonia, hyporeflexia, muscle atrophy
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9
Q

structure of the basal ganglia

A
  • group of interconnected nuclei below the cerebral cortex:
  • striatum (caudate and putamen)
  • globus pallidus (internal and external) - suppresses movement
  • subthalamic nucleus
  • substantia nigra (pars reticulata and pars compacta)
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10
Q

function of basal ganglia

A
  • learn, plan and initiate voluntary movements
  • evaluate rewards using previous experience
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11
Q

direct and indirect pathways of basal ganglia

A
  • direct: facilitates movement, inhibits global pallidus (normally suppresses movement) which allows thalamus to excite the motor cortex
  • indirect: inhibits movement via longer pathway
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12
Q

2 main types of symptoms re: damage to basal ganglia

A
  • hyperkinetic: involuntary movement - reduced activity of the indirect (inhibitory) pathway e.g. Huntington’s chorea
  • hypokinetic: increased activity of the indirect/inhibitory pathway e.g. Parkinson’s disease
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13
Q

structure of cerebellum

A
  • 2 lobes separated by vermis
  • each lobe controls ipsilateral side of the body > damage causes ipsilateral loss of function
  • grey matter on surface forms cerebellar cortex
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14
Q

functions of cerebellum

A
  • gait coordination
  • maintenance of balance and posture
  • muscle tone control and voluntary muscle activity
  • REFINEMENT of motor commands to match sensory input (not initiation)
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15
Q

motor unit vs motor pool

A
  • unit: one alpha motor neuron + any muscle fibres that it innervates
  • pool: one muscle + its associated nerves (consists of small and large motor units)
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16
Q

alpha motor neurons:
- size
- myelination
- cell body location
- where are the cell bodies located for neurons that innervate more proximal muscles

A
  • type of lower motor neuron
  • larger
  • more myelinated
  • cell bodies in ventral horn
  • a-motor neurons that innervate more proximal muscles have cell bodies more medially
17
Q

gamma motor neurons
- size
- myelination
- cell body location
- function

A
  • type of lower motor neuron
  • smaller
  • less myelinated
  • cell bodies in ventral horn
  • involved in muscle spindles (proprioception)
18
Q

which motor units are more fatigue resistant?

A
  • smaller are more fatigue resistant
  • therefore can be activated for longer periods of time compared to large motor units
19
Q

classes of muscle fibres
- speed (+ fatigue resistance)
- force
- function

A
  • type I: slow, low force, postural muscles
  • type IIa: fast and fatigue resistant, moderate force, non-postural
  • type IIb: fast and fatiguable, high force, non-postural muscles
20
Q

3 layers of skeletal muscle connective tissue

A
  • epimysium: strong connective tissue around the entire muscle
  • perimysium: bundles muscle fibres into fascicles (contains blood vessels and nerves)
  • endomysium: surrounds individual muscle cells
21
Q

myofibril

A
  • muscle fibres contain cylindrical myofibrils which contain actin and myosin microfilaments
22
Q

sarcoplasm
sarcolemma

A
  • cytoplasm of a muscle fibre
  • plasma membrane of a muscle fibre
23
Q

sarcomere
sarcoplasmic reticulum

A
  • smallest contractile subunit which extends from one Z-line to the next
  • specialised smooth ER of a muscle fibre - stores calcium
24
Q

2 major striations in skeletal muscle

A
  • A bands (anisotropic): dark, where actin (thin) and myosin (thick) bands overlap
  • I bands (isotropic): light, contain actin (thin) filaments but no myosin
25
Q

H band
M line

A
  • H band: area where there is myosin only, between 2 A bands, shortens during contraction
  • M line is in the middle of H band
26
Q

structure of actin

A
  • globular G actin polymerises to form an F actin chain
  • 2x F actin chains interweave to form helix-like actin filament
  • each G actin monomer has cross-bridge binding sites for myosin - these are blocked by tropomyosin when the muscle isn’t contracting
27
Q

structure of troponin

A
  • 3 binding sites: tnI, tnT, tnC
  • tnI (inhibitory): binds to actin, keeping tropomyosin in place which blocks myosin from binding, to stop muscle contraction
  • tnT: binds to tropomyosin
  • tnC: binds to calcium, causing tropomyosin to unblock actin binding sites, allowing myosin to bind for muscle contraction
28
Q

structure of myosin

A
  • 2 heads w/ 2 binding sites each (1 for ATP, one for actin)
  • neck made of myosin light chains: provides flexibility to move heads
  • tail: gives rigidity + support
29
Q

structure of titin

A
  • elastic filament attached to Z lines
  • runs thru myosin for support + rigidity
30
Q

T (transverse) tubule

A
  • located @ A-I junction
  • invagination of sarcolemma (plasma membrane) with membrane on each side called terminal cisternae (forms triad)
  • allows for electrical impulses to pass through deep into muscle cell for rapid contractions
  • allows Ca2+ to be spread from NMJ for uniform contraction of the entire muscle cell @ once
31
Q

what happens in rigor mortis re: muscle tightness?

A
  • after death, ATP stops being produced = cross bridges can’t detach
  • actin and myosin stay bound > muscle stays tight and contracted
32
Q

3 phases of a muscle contraction

A
  • delay: time taken for AP to arrive @ NMJ including refractory period
  • contraction
  • relaxation
33
Q

2 ways to increase muscle contraction force

A
  • recruitment of more motor units from small to large
  • rate-coding: firing another AP before the first twitch is completed > another twitch with increased force (summation > rough/unfused tetanus > smooth/fused tetanus)
34
Q

fused vs unfused tetanus re: rate-coding

A
  • unfused tetanus: when we increase the rate of AP firing, resulting in lots of little contractions (but still greater force)
  • fused tetanus: if we keep increasing the rate of AP firing, it results in one sustained contraction b/c Ca hasn’t had time to go back into sarcoplasmic reticulum > actin and myosin cross bridges stay > muscle stays contracted
35
Q

is the AP or muscle twitch longer in duration?

A

muscle twitch

36
Q

isotonic and isometric movements

A
  • isotonic: tone stays same, muscle length changes
    > concentric: contraction during shortening
    > eccentric: contraction during lengthening
  • isometric: length stays same, tone changes
37
Q

excitation-contraction coupling

A
  • ACh reaches NMJ > depol
  • AP travels along sarcolemma and T tubules
  • DHP receptor on T tubule membrane activates ryanodine receptor (RyR) on sarcoplasmic reticulum, causing Ca2+ release
  • Ca2+ binds to troponin → displaces tropomyosin → exposes binding sites → actin and myosin can bind and sarcomere shortens
38
Q

crossbridge cycling mechanism

A
  • Ca2+ binds to troponin-C, displacing tropomyosin from actin binding sites
  • myosin heads are in a high energy state since ATP is hydrolysed into ADP + Pi
  • when myosin binds to actin, Pi is released, triggering power stroke (myosin pulls actin towards M line and shortens the sarcomere)
  • a new ATP binds to myosin > detaches crossbridge, Ca2+ actively pumped back to sarcoplasmic reticulum
  • tropomyosin moves back to block binding sites > muscle relaxation