Skeletal and Cardiac Muscle Flashcards
Describe some of the characteristics of skeletal muscle
- Multinuclear
- Many mitochondria
- Special structures called transverse tubules
- Has myofibrils and sarcomeres
What is a sarcolemma?
Plasma membrane of a skeletal muscle fibre
What is a sarcoplasm?
Cytoplasm of a skeletal muscle fibre
What is a sarcoplasmic reticulum?
Smooth ER of skeletal muscle fibre
What are myofibrils?
They are the structures that give skeletal and cardiac muscle fibres their striated appearance.
How do striations occur?
From the orderly arrangement of thin and thick myofibrils
Describe some of the characteristics of cardiac muscle
- Cells have one/two nuclei which are central
- Use sliding filament mechanism to contract
- Branching cells with intercalated discs with desmosomes and gap junctions
Give a feature of nodal cells
They have the ability to generate their own action potentials. This is called automaticity or auto-rhythmicity
What are intercalated discs?
Mechanical and electrical connections between cardiac cells
What protein subunits make up gap junctions?
Connexins
What is the central diameter of gap junctions
1.5nm
Where do neurons from the primary motor cortex synapse?
On the motor neuron located in the grey matter in the ventral horn of the spinal chord.
What is a motor unit composed of?
Axon and muscle fibre.
What is an Alpha Motoneuron
It is a motor neurons, the names mean the same thing.
What is a motor unit defined as?
The motor neuron (which can innervate many fibres) and the skeletal muscle fibres it innervates.
What do fine motor movements like (typing) rely on?
Motor units with relatively few fibres
What allows for motor neurons to propagate action potentials at high velocities?
They are myelinated and are the largest-diameter axons in the body.
What is the motor end plate?
The region of the muscle fibre plasma membrane that lies directly under the terminal portion of the axon.
Within Neurovascular junctions what is the neurotransmitter released and how is it degraded
Acetylcholine and it is degraded enzymatically by acetylcholinesterases
On the muscle fibre sarcolemma, where are the ACh receptors and voltage activated Na channels located?
ACh receptors are at the top of the junctional folds. Na channels are located at the bottoms of junctional folds
How do Nicotinic Acetylcholine/cholinergic receptors work
Two ACh molecules bind to the receptor causing the opening of the nonspecific monovalent cation channel
Describe the events that occur at the motor end plate
- Action potentials cause calcium channels to open at the axon terminal allowing for inward diffusion of Ca into the axon.
- There is a fusion of vesicles containing ACh with the presynaptic membrane
- ACh then diffuses across the synaptic cleft where they can bind to nicotinic ACh receptors on the sarcolemma.
- There is then a net entry of Na into the end plate region causing depolarisation (epp - end plate potential)
- Action potential is triggered
What is Myasthenia Gravis
It is an auto immune disease characterised by muscle weakness that increases during periods of activity but improves after rest. It is mostly likely to effect eye and eyelid movement, facial expression, chewing, talking and swallowing. However can also cause paralysis of respiratory muscles
What causes Myasthenia gravis
The production of auto-antibodies. This most commonly targets nicotinic acetylcholine receptors but some impair the ability of ACh to bind to receptors and some lead to the destruction of receptor.
Name some muscle myopathies and what they cause/their explination
Myositis - inflammation
Muscular dystrophy - Inherited disorder that with progressive weakness
Myasthaenia - weakness that gets worse with exercise
Myotonia - Sustained contraction with slow relaxation
Channelopathy - Ion channel disorder
Metabolic Myopathies - Metabolic/enzyme defects
