3Muscular System 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.
4Types of Muscles Skeletal muscle Voluntary. 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.
5Types of Muscles Cont. Smooth muscle. Involuntary. 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.
6Types of Muscle Cont. Cardiac muscle. Found only in the heart. Striated and branched.Involuntary.Cells are fused- when one contracts, they all contract.
9Characteristics of Muscles When a muscle becomes shorter, thicker & causes movement, it is said to have?CONTRACTIBILITY
10Excitability (irritability)- the ability to respond to certain stimuli by producing impulses.
11Extensibility- the ability to be stretched. Elasticity- ability of muscle to return to its original length when relaxing.
12Movement 1.Muscles move bones by pulling on them. 2. Groups of muscles usually contract to produce a single movement.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.
13Movement Cont. Motor unit- a motor neuron plus all the muscle fibers it stimulates.
14Muscle FatigueMuscle fatigue- caused by the accumulation of lactic acid in the muscles.
15Neuromuscular Junction Neuromuscular junction- the junction between the motor neuron’s fiber which transmits the impulse-and the muscle cell membrane.
16Acetylcholine Is a chemical neurotransmitter, diffuses across the synaptic cleft (carriesimpulse acrosssynaptic cleft).
17If a muscle cell is stimulated repeatedly without rest it losses its ability to contract! This is called?