Nearly half our weight comes from muscle tissue. There are 650 different muscles in the human body. Muscles give us shape, posture, movement and form. Muscles produce most of our body heat.
Skeletal muscle Attached to bone. Striated (striped) appearance. Voluntary. Multinucleated muscle cell bundles (muscle cells = muscle fibers). Sarcolemma = cell membrane. Contract quickly, fatigue easily, can’t maintain contraction or long period of time.
Smooth muscle. Visceral (organ) muscle. Found in walls of digestive system, uterus and blood vessels. Cells small and spindle- shaped. Involuntary. Controlled by autonomic nervous system. Act slowly, do not tire easily, can remain contracted for long time.
Cardiac muscle. Found only in the heart. Striated and branched. Involuntary. Cells are fused- when one contracts, they all contract.
When a muscle becomes shorter, thicker & causes movement, it is said to have? CONTRACTIBILITY
Excitability (irritability)- the ability to respond to certain stimuli by producing impulses.
Extensibility- the ability to be stretched. Elasticity- ability of muscle to return to its original length when relaxing.
As a muscle contracts, it pulls the insertion bone closer to the origin bone. Movement occurs at the joint between the origin and the insertion. Rule: A muscle’s insertion bone moves toward its origin bone. 1.Muscles move bones by pulling on them. 2. Groups of muscles usually contract to produce a single movement.
Motor unit- a motor neuron plus all the muscle fibers it stimulates.
Muscle fatigue- caused by the accumulation of lactic acid in the muscles.
Neuromuscular junction- the junction between the motor neuron’s fiber which transmits the impulse- and the muscle cell membrane.
Is a chemical neurotransmitter, diffuses across the synaptic cleft (carries impulse across synaptic cleft).