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Download Skeletal Muscle
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Muscular System There are three different types of muscle: Skeletal Muscle o Well-organized body tissue, composed in a complex array of smaller and smaller structures o Attaches to and covers the bony skeleton, moves skeleton o Composed of many units called muscle fascicles fascicles are bound together by a type of connective tissue called fascia Smaller strands called myofibrils organize muscle fibers Move as skeletal muscle contracts. It is the interaction of the myofibrils as they slide and pull along side each other that gives skeletal muscle its functional ability to do work and move things. o Myofibrils compose muscle fibers, muscle fibers make-up muscle fascicles, and muscle fascicles are bound together by fascia to compose skeletal muscle. Smooth Muscle o Found in the walls of the body organs o Involuntary (functions without conscious control) o Muscle fibers are much smaller than Skeletal muscle fibers The muscle fibers are gathered into dense sheets or bands Densely and irregularly packed together, most often so that the narrower portion of one fiber lies against the wider portion of its neighbor Fibers have connections The plasma membranes of two neighboring fibers form gap junctions that act as low resistance pathway for the rapid spread of electrical signals throughout the tissue. The multi-unit smooth muscle fibers have no interconnecting bridges: they are mingled with connective tissue fibers. Cardiac Muscle o Found only in the heart, making up most of the heart wall o Contains specialized conduction system that controls our heartbeat o Involuntary muscle highly branched with cells connected by overlapping projections of the sarcolemma called intercalated discs. These discs contain desmosomes and gap junctions cardiac muscle is autorhythmic, generating its own action potential, which spreads rapidly throughout muscle tissue by electrical synapses across the gap junctions. o Throughout our life, it contracts some 70 times per minute pumping about 5 liters of blood each minute. How do muscles contract 2 http://docs.google.com/leaf?id=0B29v4HMlhbfmOWFlY2VlYTgtOGM1NC00ODhlLTkzYTQ tY2EwYjA3ZjQwMTMz&hl=en The cell membrane of a muscle cell is called the sarcolemma, and this membrane, like that of neurons, maintains a membrane potential. So, impulses travel along muscle cell membranes just as they do along nerve cell membranes. Acetylcholine: One of the most common neurotransmitters of the vertebrate nervous system; a chemical (CH3COOCH2CH2N+(CH3)3) that transmits impulses between the ends of two adjacent nerves or neuromuscular junctions. Neuromuscular Junctions: The specialized junction between a nerve ending and a muscle, which is a type of synapse. http://docs.google.com/leaf?id=0B29v4HMlhbfmOWFlY2VlYTgtOGM1NC00ODhlLTkzYTQt Y2EwYjA3ZjQwMTMz&hl=en What is a reflex? A reflex is a response to a perturbing stimulus that acts to return the body to homeostasis. This may be subconscious as in the regulation of blood sugar by the pancreatic hormones, may be somewhat noticeable as in shivering in response to a drop in body temperature; or may be quite obvious as in stepping on a nail and immediately withdrawing your foot. Examples of reflexes that protect the body Blinking Sneezing Coughing DTR; stands for deep tendon reflex A reflex arc refers to the neural pathway that a nerve impulse follows. The receptor at the end of a sensory neuron reacts to a stimulus. The sensory (afferent) neuron conducts nerve impulses along an afferent pathway towards the central nervous system (CNS). The integration center consists of one or more synapses in the CNS. A motor (efferent) neuron conducts a nerve impulse along an efferent pathway from the integration center to an effector. An effector responds to the efferent impulses by contracting (if the effector is a muscle fiber) or secreting a product (if the effector is a gland). Sensory neuron (input) and a motor neuron (output)The sensory neuron (such as a pain receptor in the skin) detects the stimuli and sends a signal towards the CNS. This type of reflex is the "withdrawal" reflex and is monosynaptic, meaning only one synapse has to be crossed between the sensory neuron and the motor neuron. It is the simplest reflex arc and the integration center is the synapse itself. Polysynaptic reflexes are more complex and more common. They involve interneurons which are found in the CNS. More complex reflexes may have their integration center in the spinal cord, in the brainstem, or in the cerebrum where conscious thoughts are initiated On average, humans have a reaction time of 0.25 seconds to a visual stimulus, 0.17 for an audio stimulus, and 0.15 seconds for a touch stimulus (2). Stretch reflexes are a special type of muscle reflex which protect the muscle against increases in length which may tear or damage muscle fibers. Visceral reflexes (also known as autonomic reflexes) refer to reflexes such as those which affect the gland secretion or smooth muscle of the cardiac system to contract. The main purpose of the visceral reflexes is to ensure that the involuntary process of the body are in full operating condition and can be tailored to react to a given situation. Heart rate, respiratory rate, blood flow, and digestion are just examples of the types of visceral reflexes that require constant monitoring by the internal body systems. Reflexes like coughing, swallowing, sneezing, or vomiting are considered to autonomic, however, these reflexes require at least some participation of the skeletal muscles. Somatic reflexes refer to those that include some participation of the skeletal muscles. Somatic reflexes are segregated into three different types, each named after the response that they produce. For instance, the stretch reflex requires only the participation of two neurons and one synapse in the reflexive pathway. Thus, this is referred to as a monosynaptic reflex arc. Neuromuscular spindles initiate a minor stretching within their receptors. A sensory neuron along the spinal column picks up this stretching, and a synapse occurs within the gray column (anterior) with a motor neuron. The motor unit that corresponds with all this stretching is then activated, and specified muscle fibers automatically contract to cause stretching. The receptors and the effector organs that are involved in this action are situated along the same side of the spinal column, and thus this particular reflex receives the term ipsilateral arc. An additional example of an ipsilateral arc is the knee-jerk reflex. withdrawal reflex, also known as a flexor reflex, is a polysynaptic reflex arc. Sensory and motor neurons are part of this reflex, as are association neurons. Pain is the most obvious stimuli that initiates the flexor reflex, as painful stimuli sets the whole reflex into action How does the nervous system and muscular system interact? o Receptors in muscles provide brain with info about body position and movement o Brain controls contraction of skeletal muscles o nervous system regulates speed at which food moves through digest track