5.5.14 Mammalian Muscle Structure Flashcards
What are the different types of muscle?
There are three types of muscle found within mammals
Skeletal muscle (also called striated or voluntary muscle)
Smooth muscle (also called involuntary muscle)
Cardiac muscle
Skeletal muscles are responsible for moving the rigid skeleton of mammals
These muscles have a complicated, unique structure
What is skeletal muscle?
Striated muscle makes up the muscles in the body that are attached to the skeleton
Striated muscle is made up of muscle fibres
A muscle fibre is a highly specialised cell-like unit:
Each muscle fibre contains an organised arrangement of contractile proteins in the cytoplasm
Each muscle fibre is surrounded by a cell surface membrane
Each muscle fibre contains many nuclei – this is why muscle fibres are not usually referred to as cells
The different parts of a muscle fibre have different names to the equivalent parts of a normal cell:
Cell surface membrane = sarcolemma
Cytoplasm = sarcoplasm
Endoplasmic reticulum = sarcoplasmic reticulum (SR)
The sarcolemma has many deep tube-like projections that fold in from its outer surface:
These are known as transverse system tubules or T-tubules
These run close to the SR
The sarcoplasm contains mitochondria and myofibrils
The mitochondria carry out aerobic respiration to generate the ATP required for muscle contraction
Myofibrils are bundles of actin and myosin filaments, which slide past each other during muscle contraction
The membranes of the SR contain protein pumps that transport calcium ions into the lumen of the SR
What are myofibrils?
Myofibrils are located in the sarcoplasm
Each myofibril is made up of two types of protein filament:
Thick filaments made of myosin
Thin filaments made of actin
These two types of filament are arranged in a particular order, creating different types of bands and lines
Components:
H band- Only thick myosin filaments present
I band- only thin actin filament present
A band- contains areas where only myosin filaments are present and areas where myosin and actin filaments overlap
M line- attachment for myosin filaments
Z line- Attachment to actin filaments
Sarcomere- the section of myofibril between two Z lines
What is smooth (involuntary) muscle?
Smooth muscle is vital for the unconscious control of many body parts
Similar to skeletal muscle it contains both actin and myosin filaments however it does not have any banding or striation
Several internal organs (e.g. the gut) contain smooth muscle within their walls
For example, the walls of blood vessels have a layer of smooth muscle that allows for the narrowing of arteries to control blood flow
The structure of smooth muscle is relatively simple
It consists of small elongated cells/spindle-shaped fibres that contain one nucleus
What is cardiac muscle?
Cardiac muscle is only present within the heart
It is a type of specialised striated muscle with the following properties:
It is myogenic, meaning that it can contract without external stimulation via nerves or hormones. This allows the heart to beat at its own regular intervals (the length of the intervals can be regulated by the nervous system and endocrine system)
It does not tire or fatigue so it can contract (beat) continuously throughout an individuals life
The cardiac muscle fibres form a network that spreads through the walls of the atria and ventricles
Cardiac muscle fibres are connected to each other via specialised connections called intercalated discs
There is a large number of mitochondria present in the muscle fibres. These are needed to provide the large quantity of ATP needed for continual contraction
