Neuromuscular Control

Question 1

Resting Membrane Potential

Answer 1

-70 mV

Potassium (+) is concentrated intracellularly
Sodium (+) & Chloride (-) are extracellularly

Na channels are resting & K channels are closed

Question 2

Action Potential

Answer 2

“all or none” response

10-15 mV stimulus causes DEPOLARIZATION reaching threshold (-70 to +30 in ~1ms)

• -> this causes voltage gated Na channels to open &rapid influx of Na into cell
• -> REFRACTORY period (absolute) is when the Na channels are inactivating and the K channels are open which hyperpolarizes the cell
• -> Relative Refractory period - the K channels stay open making it hard for stimulus to generate AP

Question 3

Graded Potentials

Answer 3

localized disturbances in the post-synaptic membrane
- arise from VARIOUS ion channels (not dependent on K & Na)

• summation can occur spatially or temporally (summed across space or over time)
• graded amplitude is proportional to strength of stimulus
• no refractory period
• can occur anywhere in the membrane region that receives sensory stimuli

Question 4

Excitatory Post-Synaptic Potential

Answer 4

(EPSP)

increases Na permeability; slightly depolarizes the cell but not enough to reach threshold and cause AP

Question 5

Inhibitory Post-Synaptic Potential

Answer 5

IPSP

decreases Na and increases Cl permeability; slighly hyperpolarizes the cell making it harder for stimulus to bring it to threshold (inhibiting AP)

Question 6

Velocity of Action Potentials are determined by?

Answer 6

1. Fiber diameter
   - larger diameter = lower resistance = faster conduction
2. Presence of myelin sheath
   - allows for saltatory conduction (“skip” from node to node)
   - produced by Schwann cells (PNS) & oligodendricytes (CNS)

Question 7

Motor Unit

Answer 7

the motor neuron and all the muscle fibers it innervates - the functional unit of skeletal muscle

• fine motor activity: less fibers per motor neuron for precison, accuracy and coordination
• large motor activity: lots of fibers/ motor neuron

Question 8

Neuromuscular Junction

Answer 8

includes the axon terminal & motor end plate

1. AP (depolarization) of axon terminal opens voltage gated Ca channels
2. Vesicles fuse to pre-synaptic membrane (containing Ach)
3. Ach is released into synaptic cleft via exocytosis
4. Post-synaptic Na & K channels open, depolarizing the motor end plate
5. End plate potential (EPP) depolarizes sarcolemma, propagating AP to each myocyte
6. Ach is resorbed into terminal axon or degraded
7. Ion channels close & resting membrane potential is restored

Question 9

Thalamus - control of movement

Answer 9

contributes to motor generation & self-monitoring
(fine tuning)

relay pathways from basal ganglia, cerebellum & superior colliculus to motor cortex

Just know its main function is to RELAY INFORMATION

Question 10

Hypothalamus - control of movement

Answer 10

maintains homeostasis by regulating internal environment

Question 11

Cerebellum - control of movement

Answer 11

coordinates the timing and sequence of muscle activity; perform smooth movement

Question 12

Brain stem - control of movement

Answer 12

contains autonomic regulatory centers for respiratory & CV system

Reticular System - activated when you are upright
- responsible for keeping you awake, alert, coordinates muscle function, maintains muscle tone & pain control

Question 13

Sensory vs. Motor Control of Movement

-pyramidal vs. extrapyramidal

Answer 13

Sensory - transmits info to somatosensory areas

Motor -
contains pyramidal & extrapyramidal systems

Pyramidal: corticospinal & corticobulbar tracts

• innervate motor neuron in brainstem & spinal cord
• involved in VOLUNTARY movement

Extrapyramidal: located in reticular system

• modulated by cortex, cerebellum & basal ganglia
• involved in reflexes, postural control & coordination of movement

Question 14

Exercise in Stroke Pateints

Answer 14

VO2 40% less than that of age-matched peers (~15-18 mL/kg/min)

Exercise Goals include..

• improving or maintaining CV function, functional capacity and ROM
• prevent contractures
• reduce risk of falls

AEROBIC: 3-5x/week, 20-60min, low to mod intensity (40-70% VO2 or HRR)
RESISTANCE: 2-3x/week, low to moderate intensity
- emphasize functional movements & activities

Question 15

Exercise in patients w/ Parkinson’s

Answer 15

be consistent w/ training schedule, progress slowly (every 4-5 weeks), monitor pain

Goals…

• improve or maintain aerobic, resistance & flexibility
• reduce risk of respiratory compromise from kyphotic posture

AEROBIC: 3+ days/week, up to 60 minutes, low to mod intensity (40-80% peak HR)
- walking is ideal - 20-30 min/day, 4-6 sessions, self-selected pace

RESISTANCE: 3+ days/week, low intensity (1 set of 8-12 reps)
- emphasis on core & extensor muscles

FLEXIBILITY: 1-3 sessions/week, gentle static stretching

Question 16

Exercising in patients w/ MS

Answer 16

morning is optimal time for exercise, hydration is crucial!
- perform aerobic & resistance training on opposite days since fatigue is an issue

AEROBIC: 3+ days/week, 30 min, low to mod intensity (50-70% VO2 or 60-85% MHR)

FLEXIBILITY: 5-7 days/week