Anatomy and physiology

Slow Oxidative Fibres:

Functional Characteristics:

• Slow speed of contraction
• Low anaerobice capacity
• High resistance to fatigue
• High aerobic capacity
• Low force of contraction

Slow Oxidative Fibres:

Structural characteristics:

• Small fibre size
• Lots of mitochondria
• High number of capillaries
• High myoglobin content
• Low glycogen stores
• Low PC stores

Fast Oxidative Glycolytic Fibres:

Functional characteristics:

• Fast speed of contraction
• High anaerobic capacity
• Low resitance to fatigue
• Low aerobic capacity
• Strong force of contraction

Fast Oxidative Glycolytic Fibres:

Structural Charcteristics:

• Large fibre size
• Moderate amount of mitochodria
• High number of capillaries
• Moderate myoglobin content
• High glycogen stores
• High PC stores

Fast Glycolytic Fibres:

Functional characteristics:

• Fastest speed of contraction
• Highest anaerobic capacity
• Lowest resistance to fatigue
• Lowest aerobic capacity
• Highest force of contraction

Fast Glycolytic Fibres:

Structural Characteristics:

• Large fibre size
• Small number of mitochondria
• Low number of capillaries
• Low myoglobin content
• High glycogen stores
• High PC stores

Mucle Contraction- Key Terms:

Mitochondria- structure responsible for aerobic energy production.

Phosphocreatine- high energy compound stored in muscle cell, used as fuel for high intensity energy production.

Myoglobin- Protein in muscle that carries oxygen.

 Capillaries- thin walled vessels that carry blood over sites for gas exchange

Motor Units:

What is a motor unit?

• A group of muscle fibres and its neurone

What is the role of a motor unit?

• To csrry nerve impulses from the brain and spinal chord to the muscle fibres to intiate muscle contraction.

What is a motor neurone and what does it do?

• Specialist nerve cells that transmit nerve impulses rapidly to a grup of muscle fibres, made up of the cell body (brain/spinal chord) and the extending axon which connects motor end plates to a group of muscle fibres

Motor Units 2:

What is an action potential?

• A positive electrical charge inside the nerve and muscle cells which conduct the nerve impluses down the neurone and into the muscle fibres.

What is a neurotransmitter?

• A chemical that is produced and secreted by a neuron which transmits the nerve impulses across the synaptic cleft to the muscle fibres.

Describe the all or non law?

• When a motor unit receives a stimulus and creates an action potential that reaches a certain threshold then all of the muscle fibres in the muscle unit contract at the same time with maximum force. If thr action potential is below this then no muscle fibres will contract.

Mechanics of breathing- Inspiration:

At rest:

• The external intercostal muscles and the diaphragm contract. Resulting in the diaphragm flattening and the ribs move up and out, this increases thoracic cavity volume and decreases lung air pressure which causes air to be sucked in.

During exercise:

• External intercostal musces and diaphragm contract at a greater force than at rest. Additionally the pectoralis minor and sternocleidomastiod contract to produce a greater force of contraction. The diaphragm flattens with more force with the ribs and sternum being pushed up and out further. This increases thoracic cavity volume further than at rest and decreases lung air pressure further than at rest. As a result more air is forced in to the lungs.

Mechanics of breathing- Expiration:

At rest:

• External intercostal muscles and the diaphragm relax. The diaphragm returns to a dome shape whislt the ribs and sternum go down and in. As a result thoracic cavity volume decreases as lung air pressure increases. This causes air to be pushed out.

During exercise:

• The internal intercostal muscles and rectus abdominus contract to give a larger force. The diaphragm returns to a dome shape with more force and the ribs and sternum are pulled further down and in. Thoracic cavity volume decreases more than at rest whilst lung air pressure increases more than at rest. This causes more air to be forced out.

Control of inspiration at rest:

• The inspiratory centre tells the intercostal nerve to stimulate the external intercostals which causes them to contract and to pull the rib cage up and out.
• The inspiratory centre also tells the phrenic nerve to stimulate the diaphragm which flattens.

With mechanics of breathing:

• This causes the thoracic cavity volume to increase and the lung air pressure to decrease, causing air to be sucked into the lungs.

Control of inspiration during exercise:

• Proprioceptors inform the inspiratory centre (IC) in the respiratory control centre of increased movement.
• Thermoceptors inform the IC of increased blood temperature.
• Chemoreceptors inform the IC of chemical changes in the blood stream i.e. more CO2 less O2

The inspiratory centre responds by:

• Increasing stimulation of the phrenic nerve to the diaphragm and intercostal nerve to the external intercostals.
• Stimulating additional inspiratory muscles, the sternocleidomastoid and the pectoralis minor, which increases the force of contraction and therefore depth of breathing.

Mechanics of breathing:

• This causes thoracic cavity volume to increase more than at rest and lung air pressure to decrease more than at rest.

Control of expiration during exercise:

• Baroreceptors, known as stretch receptors, in the lungs detect an increase in lung inflation and inform and stimulate the expiratory centre (therefore the inspiratory centre is inhibited).
• This is due to a need for active forced expiration
• The expiratory msucles are stimulated to contract to cause forced expiration during exercise.
• These are the internal intercostals and the rectus abdominus.
• This safety mechanism prevents the lungs from overinflating and is known as the Hering-Breuer reflex.

Mechanics of breathing:

This results in thoracic cavity volume decreasing further than at rest and lung air pressure to increase more than at rest. This causes more air to be forced out.