Lecture 8 Flashcards
Muscle?
Tissue with the ability to contract and relax
Tendon?
Tough band of fibrous connective tissue that connects muscle to bone
Ligament?
Attaches bone to bone
How many skeletal muscles are there in the human body?
Approximately 650
How many surface (anatomical) muscles are there in the human body?
Over 150
Are muscles attached to 2 different bones of the skeleton?
Yes, one attachment is fixed and called the origin and the other called the insertion is drawn towards the origin
Muscles tend to work in groups or sets, so how are they arranged in antagonistic pairs?
- Flexor closes a joint
- Extensor opens a joint
Epimysium?
A loose connective tissue sheath that is bound to each muscle
Muscle composition?
- Each muscle is composed of bundles of fascicles
- Each fascicle is composed of many muscle fibers
- Each fiber is composed of smaller fibers called myofibers
- The myofibers contain the contractile apparatus – the sarcomere
What are three muscle types?
Skeletal muscle:
- Attached to bones
Cardiac muscle:
- Walls of the myocardium
Smooth muscle:
- Organs
Striated Muscle?
- Voluntary muscle i.e. under direct nervous control
- Low endurance muscle
What is the structure of the muscle fibres in striated muscles?
- Hexagonal
- Nuclei on outside (peripheral)
- Fibres generally have the same size
- Polynucleated
How are muscle biopsies done?
Wide-bore Needle inserted into muscle, and a small ‘tube’ of muscle removed
Cardiac muscle?
- Only in the heart
- A type of striated muscle but related to smooth muscle
- Involuntary muscle
- High endurance muscle
What is the structure of the muscle fibres in cardiac muscles?
- Intercalated discs (gap junctions)
- 1- 2 nuclei per cell
- Centrally placed nuclei
- Innervated by the pace maker
Smooth Muscle?
- Lines the digestive tract, bronchus and blood vessels
- Involuntary muscle i.e. not under direct nervous control
- High endurance muscle
What is the structure of the muscle fibres in smooth muscles?
- 1 centrally placed nucleus per cell
- No striations
- Sustained contraction
What is a motor unit?
The functional unit of skeletal muscle is the motor unit (MU)
What is a motor unit composed of?
- A single motor neuron
- The group of muscle fibres innervated by it
Why must some motor neurons innervate more than one fibre?
Bc there are considerably more muscle fibres than there are motor neurons
What does the number of muscle fibres per motor unit vary according to?
- The fineness of the control required
- Fewer muscle fibres per motor unit leads to increased dexterity and vice versa
Neuromuscular Junction (NMJ)?
- Also known as the motor endplate
- The connection between the muscle fibre and its motor neuron
- The membranes of the nerve and muscle cells come into close contact
- One NMJ per fibre
What happens when muscle fibre is stimulated at the NMJ?
It contracts; this is an “all-or-nothing” response
When is there maximal contraction?
When all MUs are firing tog
What are the two ways that muscles contract?
- Isometric contraction
‘same length’ - Isotonic contraction
‘same tension’
Isometric contraction?
- The length of the muscle does not change
- The tension on the muscle increases
- Muscle contracts but doesn’t shorten
Isotonic Contraction?
- The muscle length changes
- The tension remains constant
Two types of Isotonic contraction?
Concentric – Muscle shortens
Eccentric – Muscle lengthens
Concentric Isotonic Contraction?
- Force generated by the muscle is greater than the load to be lifted
- Muscle shortens in length
Eccentric Isotonic Contraction?
- Force generated by the muscle is less than the load applied to it
- Muscle lengthens as it contracts
When/why do Eccentric Isotonic Contractions happen?
- Also occur to slow joint movement
- Muscles undergoing heavy eccentric loading suffer greater damage when overloaded leading to greater muscle necrosis
- Principle behind body building
- Muscles are approximately 10% stronger during eccentric contractions than during concentric contractions
Three phases to muscle contraction?
- Latent period (0.005 sec) between the stimulus and first visible reaction
- Contraction period (0.04 sec) when the muscle shortens
- Relaxation period (0.05 sec) the muscle returns to its original length
- After initial stimulation there is a short period during which muscle will not respond to further stimulus called the Refractory period (0.002 sec)
How does summation happen (general)?
- Muscle can respond to a second stimulation while still contracting
- Stimulation at frequency shorter than the twitch time results in the second stimulus being superimposed on the first
- This results in a greater shortening of the muscle (summation)
What are two different ways in which summation can occur?
- By increasing the number of motor units involved - called multiple motor unit summation (recruitment)
- By increasing the rate of contraction of individual motor units - called wave summation
- In practice both these occur together during contraction helped by the asynchronous firing of the motor units
Tetanization?
- As the impulse frequency increases the twitches become superimposed upon one another in wave summation (10 pulses/sec)
- Eventually increasing stimulus causes the successive contractions to fuse together in a state of maximal contraction called tetanus (>40 pulses/sec)
- Upon tetanization further increased stimulation will only result in very slight shortening
Is the action equal at both the insertion and the origin?
Yes
What is one thing that muscles don’t do?
Push, they can only contract
What does the muscle or its nerve respond with when it is stimulated by a single electric shock?
A quick twitch
