IB Sports, exercise and health science B.1.3.1 Muscle Tissue, Neuromuscular Activation, and Motor Unit Recruitment Notes

Muscular contractions and their role in movement

1. Muscles play a crucial role in movement, posture, and stability.
2. They generate force through contraction, enabling locomotion, joint stabilisation, and force production required for activities ranging from simple daily tasks to complex athletic movements.

Types of Muscle Tissue

There are three main types of muscle tissue, each with specific characteristics and functions:

Properties of Muscle Tissue

1. Muscle tissue possesses five key properties that allow it to generate force, produce movement, and adapt to physical demands.
2. These properties are excitability, contractility, extensibility, elasticity, and plasticity.

1. Excitability (Irritability)

1. The ability of muscle tissue to respond to stimuli, usually from a motor neuron.
2. Muscles receive electrical signals called action potentials, which trigger contraction.

2. Contractility

1. The ability of muscles to shorten and generate force.
2. This is the primary function of muscles, enabling movement, strength, and force application.
3. Contractility occurs when the actin and myosin filaments within muscle fibres slide past each other, shortening the muscle.

3. Extensibility

1. The ability of a muscle to stretch without being damaged.
2. Essential for flexibility and joint mobility.
3. Muscles work in antagonistic pairs, when one contracts, the other stretches (e.g., biceps contract while triceps extend).

4. Elasticity

1. The ability of muscle tissue to return to its original length after being stretched.
2. This prevents overstretching and muscle damage.

5. Plasticity

1. The ability of muscle tissue to change in response to repeated loading, including increases in size or efficiency over time.
2. Muscles can undergo hypertrophy (increase in size) with strength training or atrophy (shrinkage) due to inactivity or injury.

The Neuromuscular Junction (NMJ)

1. The neuromuscular junction is the point where electrical signals from the nervous system are converted into chemical signals, triggering muscle contraction.
2. The NMJ consists of the following key components:
   1. Motor neuron ending (synaptic terminal): Releases neurotransmitters to stimulate the muscle.
   2. Synaptic cleft: A small gap between the motor neuron and muscle fibre where neurotransmitters travel.
   3. Motor end plate: A specialized region of the muscle fibre that contains acetylcholine (ACh) receptors to receive the signal.
   4. Neurotransmitter (Acetylcholine, ACh): A chemical messenger that binds to receptors on the muscle, initiating contraction.

Structure of a Neuron

1. A neuron is a specialized nerve cell responsible for transmitting electrical and chemical signals throughout the body.
2. In the context of muscular movement, motor neurons specifically transmit signals from the CNS (brain and spinal cord) to muscle fibres.

Motor neuron components

1. Dendrites

1. Dendrites are short, branched extensions that receive electrical signals from other neurons or sensory receptors.
2. They transmit these signals to the soma (cell body) for processing.

2. Soma (Cell Body)

1. The cell body of the neuron contains the nucleus and organelles necessary for its function.
2. The soma integrates information from the dendrites and determines if an impulse should be sent.

3. Axon

1. A long, thin extension that carries electrical impulses away from the soma.
2. Axons can be short or long (e.g., the sciatic nerve extends from the spinal cord to the foot).

4. Myelin Sheath

1. A fatty layer that insulates the axon.
2. Increases the speed of nerve impulse transmission by preventing signal loss.

5. Node of Ranvier

1. Small gaps in the myelin sheath.
2. Allow for faster conduction of impulses via saltatory conduction.