Return to A&P I (updated 10/17/05)
Review for Exams over Muscles, Muscle Physiology & Neurophysiology
The list of assigned muscles includes most of the superficial muscles of the body, plus the diaphragm and muscles of the abdominal wall. There are 14 questions over muscles, 26 over muscle tissue and muscle physiology, and 13 covering general information about the nervous system, types of cells, and neurophysiology.
Muscle Chapter: Questions on the muscles include those referring to the origin and insertion of muscles, the location of muscles, the action of muscles, and two questions about tendons of muscles. One group of almost vestigial muscles on a human are the auricularis muscles, those that wiggle the ears. Know the muscles in the quadriceps and hamstring groups.
Know what a synergistic group is (syn = with; erg = an energy force): in the instance of the effects of alcohol and valium, 1+1=100; either one may have relaxing effects, whereas both together may be deadly!
Muscle and nerve tissue and physiology: Neurons and muscle cells have much in common, in that they both are excitable, conduct electric impulses by allowing sodium ions to enter and potassium ions to exit, and both function by allowing calcium ions to move back and forth across membranes. Most cells contain more potassium and magnesium, while the surrounding tissue fluids contain more sodium and calcium. When at rest, muscle and neuron cell membranes are polarized (more positively charged on the outside, and more negatively charged on the inside due to negative charges on the inner membrane proteins), and are said to have a resting potential, (see material on cell membrane structure and physiology). The brain sends a message (impulse or action potential) to muscles through motor neurons that may innervate from one to nearly 2000 muscle cells, depending on how much the neurons diverge within and outside the brain. Once an impulse reaches the neuromuscular (myoneural) junction, Ca++ ions must enter the synaptic knobs before the neuron can release its neurotransmitter (usually acetylcholine) to stimulate the muscle cell. Know the sequence of events that follows this step, allowing a muscle to contract, then relax. What are synaptic vesicles, and what is their function? Describe a Motor unit. What is acetylcholinesterase (Ach'ase), and what is its role in muscle physiology?
In terms of associated connective tissues, we also see similarities between muscles and nerves. Both are surrounded by connective tissue (epimysium and epineurium, respectively), both are subdivided into groups of cells (called fascicles, or fasciculi) surrounded by connective tissue (perimysium and perineurium), and each cell is surrounded by connective tissue (endomysium and endoneurium). However, a muscle fiber is the same as a muscle cell, while many authors describe a nerve fiber as a neuron and its associated Schwann cell (neurolemma). Neurons consist of three major structural types, unipolar (sensory cells that have one process entering and leaving the cell body), bipolar (sensory cells containing one dendrite leading to the cell body, and one axon leading away from the cell body), and multipolar (cells with many dendrites entering the cell body (soma), and one axon leaving the cell body (that may later subdivide into as many as 2-2000 branches). The larger the diameter of the neuron, the faster it conducts an impulse, especially if it is myelinated.
Study, in detail, the types and characteristics of muscle tissue, its microscopic anatomy, and physiology. What is a triad? What are the similarities and differences in a muscle contraction and a nerve impulse? What is/are: summation (spatial & temporal), facilitation, isotonic and isometric contraction, tetanus, atrophy? What causes muscle fatigue? …nerve fatigue? Distinguish by structure and function the differences in slow- and fast-twitch fibers. What are the energy sources for muscles? What is oxygen debt, what are its causes, and how is it paid off? What is meant by aerobic and anaerobic respiration? What are the roles of ATP in muscle and neurophysiology? What are the roles of myoglobin, hemoglobin, mitochondria, and creatine phosphate (phosphocreatine) in muscle function? What are gap junctions, and what is their role in smooth and cardiac muscle function?
A&P I Muscle Physiology
Compare the connective tissue coverings of the muscles with those of the nerves. The extensions of epimysium, perimysium, and endomysium into tendons are called epitendinium, etc. Nerves also contain fascicles (fasciculi), which are covered by perineurium, and contain neurons.
Additional labels of structures upon and within a muscle.
A muscle fiber and muscle cell are synonymous.
The cell membrane of a muscle fiber is the sarcolemma.
The Z line is often called the Z disk.
At rest, the troponin-tropomyosin complex blocks the active sites of the actin proteins, which prevents attachment of the cross-bridges of the thick (myosin) filaments.
Makeup of the sarcoplasm. Know functions of all structures.
Illustration and transmission electromicrograph of a sarcomere. Be able to identify and know structure of each zone and line.
A motor unit is one neuron and all of the muscle cells innervated. These average 150 muscle cells, but may range from 1 to 2000 cells.
The neuromuscular (or myoneural) junction. Know functions of each structure.
Proteins of muscles and crossbridges formed in contraction.
Interaction of thick and thin filaments.
Detail of the sliding filament theory of muscle contraction, showing roles of calcium ions and ATP. (1)
Detail of the sliding filament theory of muscle contraction, showing roles of calcium ions and ATP. (2)
Detail of the sliding filament theory of muscle contraction, showing roles of calcium ions and ATP. (3)
Table detailing processes involved in contraction and relaxation of a muscle.
Detail of the sliding filament theory of muscle contraction, showing roles of calcium ions and ATP. (4)
Role of cellular respiration in providing ATP for muscle contraction. Note the role of circulation, and the production of body heat in cellular respiration.
The time involved in a single muscle twitch of mammalian muscle is approximately 50 msec.
(a) successive twitches; (b) summation, in which three stimuli are applied before relaxation is completed. This involves recruitment of more muscle cells to make the contractions more powerful; (c) incomplete tetanus eventually leading to complete tetanic contraction after 8 stimuli are applied.
Transmission EM illustrating intercalated disk in cardiac muscle.
Neurophysiology:
Resting membrane potential - neurons communicate by electrical signals brought about by movement of ions (primarily sodium [Na+] and potassium [K+], but also calcium [Ca++] and magnesium [Mg++]) across the plasma membrane. The inside of a neuron is more negatively charged than the outside, mainly because of internal proteins and nucleic acids that are negatively charged. Even though K+ is present within the cell, it is less abundant than the negative charges. Note the table and three drawings below.
Function of sodium-potassium pump.
A voltage-gated ion channel.
The resting potential of most neurons is between - 70 and - 90 millivolts (mV).
When a neuron is stimulated, an action potential (or nerve impulse) begins, the sodium channels open and allow Na+ to enter the cell. This is a passive process of diffusion. After the impulse passes a particular point on the neuron, the sodium/potassium pump pumps out three sodium ions for every two potassium ions that are pumped back into the cell. Note the three illustrations below.
During depolarization (rising phase) of an action potential, Na+ ions are entering muscle (through T tubules) and nerve cells (through sodium ion channels) passively, where the electrical charge goes from -70 to -90 mV (resting) up to +30 to +35 mV at the peak of the action potential. Technically, neurons are depolarized when they reach a 0 mV charge. During repolarization (the falling phase), K+ ions leave the neurons. During recovery, Na+ and K+ are pumped back to their proper sites by active transport with the use of ATP. Neurons and muscles must reach a threshold potential before they can send an impulse or contract, respectively.
Action potential (1) - depolarization.
Action potential (2) - repolarization.
Action potential propagation along a neuron.
In myelinated neurons (large somatic neurons {A fibers}, which stimulate skeletal muscles), the impulse appears to jump (Latin - 'saltare') from one node to the next. Conduction is rapid, approximately 110 Meters per second. In small myelinated neurons (autonomic, preganglionic neurons {B fibers}, which connect to unmyelinated, autonomic postganglionic neurons {C fibers}, which stimulate smooth muscles, cardiac muscles, or glands).
Below is shown a synapse with a skeletal muscle cell.
Effect of acetylcholine on the sodium/potassium ion channel.
Acetylcholine (ACh) stimulates skeletal muscle cells, while inhibiting cardiac muscle cells, while Epinephrine (E) and Norepinephrine (NE) stimulate cardiac muscle and some smooth muscle. In the vertebrate CNS, glutamate (glutamic acid, an amino acid) is a major excitatory neurotransmitter, and produces EPSPs (excitatory postsynaptic potentials). On the other hand, Glycine and GABA (gamma- aminobutyric acid) are inhibitory, and produce IPSPs.
Serotonin is involved in the regulation of sleep. Insufficiency of neurons that release serotonin can result in depression. Prozac blocks the reabsorption of serotonin into the neurons, and thus, prolongs serotonin's effects.
The brain and spinal cord compose the Central Nervous System, and nerves constitute the Peripheral Nervous System. Neurons in the PNS are protected by a phospholipid sheath of myelin in Schwann cells (neurolemmocytes). This neurolemma is necessary for a neuron to regenerate if damaged.
Our body is loaded with sensory receptors (sense organs and small structures capable of detecting sensations); muscles and glands are effectors. Neurons and the entire nervous system conduct the messages between these two types of structures, and allow us to respond to stimuli. The nervous system can give a rapid, precise, local response, while the endocrine system usually delivers a slow, long-lasting response.