muscle structure

the muscular system consists of how many muscles

600

each muscle is an organ made up of

muscle tissue, nervous tissue, and connective tissue

stapedius

smallest muscle (located in the middle ear)

gluteus maximus

largest muscle

sartorius

longest muscle

Muscle Functions:

1. Movement

2. Maintaining posture and body position

3. Stabilizing joints

4. Generating heat

5. Propels food

6. Form valves to ensure one way passage of food

7. Control pupil size

8. Protect internal organs

9. Express emotions

sarcolemma

cell membrane of a muscle cell

• Transverse tubules – evaginations of the sarcolemma.

sarcoplasm

cytoplasm of a muscle cell

• glycosomes – granules of stored glycogen

• myoglobin – a red pigment which stores oxygen

• myofibrils – hundreds to thousands of rod-like contractile elements made of smaller elements called myofilaments

sarcoplasmic reticulum

specialized smooth endoplasmic reticulum which stores and releases calcium

mitochondria

the 3 types of skeletal muscle have different amounts

myofibrils

• Form the characteristic striations assoc. with skeletal muscle

• Composed of repeating units called the sarcomere

Main Parts of a Sarcomere

1. I bands (light bands) = thin actin filaments attached to z line (alpha-actinin protein)

   
   

2. A bands (dark bands) = composed of a region where thick myosin filaments overlap thin actin filaments.  

   
   

3. H zone = a light region within the A band.  It contains the M line.

   
   

4. Z line = midline interruption in the I band.

neuromuscular junction

a place where a motor neuron and a muscle fiber intersect.

• Muscle cells only contract when given a command by the motor neuron

• The signal to contract comes from a chemical messenger called a neurotransmitter.

• Neurotransmitters are held in sacs (synaptic vesicles) at the end of a motor neuron.

• When the brain commands movement, the synaptic vesicles fuse with the cell membrane and dump the neurotransmitters into the synaptic cleft.  

• Neurotransmitters alter the muscle cell and contraction occurs.

structure of a skeletal muscle

Origin – fixed attachment point for muscle

Insertion – moveable attachment point for muscle

Tendon – attaches muscle to bone

origin:

fixed attachment point for muscle

insertion:

moveable attachment point for muscle

tendon

connects muscle to bone

Skeletal Muscle Tissue

• Voluntary muscles that are under the control of the nervous system

• Typically found in skeletal muscles that create body movement

types of muscle tissue:

Smooth Muscle Tissue

• Typically found in the irises, walls of blood vessels, urinary bladder, stomach, intestines, and uterus

• Some are under the control of hormones others are self-exciting and excite surrounding muscle cells

Cardiac Muscle Tissue

• Found only in the heart

• Involuntary

• Muscle cells are joined end to end creating cross bands called intercalated discs

cardiac muscle cells:

intertwined

skeletal muscle cells”

straight

smooth muscle cells”

smooth