Cellular Physiology of Muscle Fiber

Cellular Physiology of the Muscle Fiber

• Muscle fiber contraction is triggered by electrical potential changes in the extracellular fluid surrounding the muscle fibers.
• This change is caused by ion influx and efflux across numerous muscle fibers.
• The exchange of ions occurs in a wave-like motion, producing an action potential.
• The action potential triggers the release of calcium from the sarcoplasmic reticulum into the intracellular environment.
• Calcium binds to troponin, leading to actin-myosin cross-bridging and muscle fiber contraction.

Motor Unit Potential (MUAP)

• The MUAP is the theoretical waveform of an action potential measured using a surface electrode.
• The action potential from the innervation zone (IZ) propagates bilaterally along the muscle fibers.
• The waveform direction reverses depending on the electrode's location relative to the IZ.
• A normal MUAP is triphasic with larger first and second-phase peaks and a smaller third-phase peak.

EMG Signal

• The theoretical EMG signal represents action potentials propagated along muscle fibers.
• Action potentials are attenuated based on the distance between muscle fibers and surface electrodes.
• These attenuated action potentials are superimposed in surface EMG.

Electrocardiogram (ECG) Basics

• The heart is a four-chambered pump for the circulatory system.
• Ventricles are responsible for the heart's pumping function.
• Atria store blood during ventricle pumping.
• Diastole is the heart's filling/resting phase.
• Systole is the heart's pumping phase.
• A coordinated series of electrical activities within the heart facilitates rhythmic contraction of atria and ventricles.
• These electrical activities are initiated by a synchronized series of events within the specialized conduction system of the heart.
• Non-ideal factors in EEG measurements include thermal noise, flicker noise, power line interference, and electrode offset voltage.

EEG Acquisition System

• The EEG acquisition system consists of electrodes, amplifiers, and filters.

EEG Application

• EEG can be used for brain disease detection, such as brain edema and Parkinson's disease.

EMG Application

• EMG applications include myoelectric prostheses, pattern recognition-based prosthetic control, and neuro control prosthesis.
• Neuro control prosthesis techniques include targeted muscle reinnervation (TMR), brain computer interface (BCI), and peripheral nerve interface (PNI).

Muscle Simulators

• Muscle simulators utilize similar principles to myoelectric sensors but with larger electrodes, a stimulating analog circuit, and higher power delivery requirements.

Temporal Resolution in Medical Imaging

• Temporal resolution refers to the time taken to acquire an image or the time between images.
• Image capture is not instantaneous, and the signal takes time to travel from the body to the detector.

Radiometric/Color/Contrast Resolution in Medical Imaging

• This resolution represents the level of variability encoded by each pixel or voxel.
• It defines the range of intensity values possible, often expressed in bits.

Image Acquisition Systems

• Common image acquisition systems include X-ray, CT, PET, and microscopy.

X-rays

• X-rays are electromagnetic radiation with wavelengths between 10 pm-10 nm.
• They can be used to image the body because different tissues absorb different amounts of radiation.
• The amount of radiation that passes through the body is detected by a detector.

Examples of X-ray Imaging

• High density objects (bone) block more X-rays than lower density objects (soft tissue).
• Objects of differing thicknesses absorb different amounts of X-rays.