Exam 3 - Muscular/Nervous System Flashcards
Components of the Central Nervous System
Brain and Spinal Cord
Components of the Peripheral Nervous System
Cranial nerves, spinal nerves, ganglia, and plexuses
Gray Matter
Areas in the CNS that contain neuron cell bodies, dendrites, and unmyelinated axons; they have a dusky gray color
White Matter
Regions in the CNS that are dominated by myelinated axons.
Divisions of the Peripheral Nervous System
Somatic and Autonomic
Somatic Nervous System
Controls skeletal and muscle contractions
Autonomic Nervous System
Automatically regulates smooth muscle, cardiac muscle, glandular secretions and adipose tissue at the subconscious level
Neuron
Basic functional unit of the nervous system; perform all the communication, information processing, and control functions of the nervous system.
Neuroglia
Supporting cell of the neuron; have functions essential to the survival and functionality of neurons and to preserving the physical and biochemical structure of the neural tissue.
Cell Body
Contains a large, round nucleus with a prominent nucleolus
Perikaryon
The cytoplasm surrounding the nucleus in the cell body
Dendrites
A variable number of slender, sensitive processes which extend out from the cell body.
Play key roles in intercellular communication
Axon
Long cytoplasmic process capable of propagating an electrical impulse known as an action potential
Axoplasm
The cytoplasm of the axon
Axolemma
A specialized portion of the plasma membrane that surrounds the axoplasm.
Classification of Neurons by Structure
Anaxonal, Bipolar, Unipolar, Multipolar
Classification of Neurons by Function
Sensory, Motor, Interneurons
Anaxonal Neurons
Small and have numerous dendrites, but no axon.
Located in the brain and in special sense organs.
Bipolar Neurons
Have two distinct processes - one dendrite that branches extensively into dendritic branches at its distal tip, and one axon-with the cell body between the two.
Rare; they occur in special sense organs, where they relay information about sign, smell, or hearing from receptor cells to other neurons.
Unipolar Neurons
The dendrites and axon are continuous-basically fused- and the cell body lies off to one side.
The initial segment lies where the dendrites converge. The rest of the process, which carries action potentials, is usually considered an axon.
Most sensory neurons of the peripheral nervous system are unipolar.
Multipolar Neurons
Have two or more dendrites and a single axon.
They are the most common neurons in the CNS. All the motor neurons that control skeletal muscles are multipolar neuron.
Sensory Neurons
Afferent; Deliver information from sensory receptors to the CNS
Types of Sensory Neurons
Interoceptors, Exteroceptors, Proprioceptors
Interoceptors
Monitor the digestive, respiratory, cardiovascular, urinary, and reproductive system and provide sensations of distention (stretch), deep pressure, and pain.
Exteroceptors
Provide information about the external environment in the form of touch, temperature, or pressure sensations and the more complex senses of taste, smell, sight, equilibrium (balance), and hearing.
Proprioceptors
Monitor the position and movement of skeletal muscles and joints.
Motor Neurons
Carry instructions from the CNS to the peripheral effectors in a peripheral tissue, organ, or organ system.
Interneurons
Located between sensory and motor neurons; distribute sensory information and coordinate motor activity.
The more complex the response to a given stimulus, the more interneurons involved.
Four Types of Neuroglia in the CNS
- Ependymal Cells
- Astrocytes
- Oligodendrocytes
- Microglia
Ependymal Cells
Line the central canal and ventricles of the CNS, where they form a simple cuboidal to columnar epithelium (known as ependyma)
Astrocytes
Largest and most numerous neuroglia in the CNS
Functions:
- Maintaining the blood-brain barrier
- Repairing damaged neural tissue
- Guiding neuron development
- Controlling the Interstitial Environment
Oligodendrocytes
Have slender cytoplasmic extensions but the cell bodies are smaller with fewer processes than astrocytes
Processes generally are in contact with the exposed surfaces of neurons.
Microglia
The least numerous and smallest neuroglia in the CNS are phagocytic cells
Their slender processes have many fine branches; these cells can migrate through neural tissue
Migrate into the CNS as the nervous system forms. There they remain, acting a wandering janitorial service and police force by engulfing cellular debris, waste products, and pathogens.
Schwann Cells
Either form a thick, myelin sheath or indented folds of plasma membrane around peripheral axons
Satellite Cells
Surround neuron cell bodies in ganglia
They regulate the environment around the neurons.
Types of Membrane Potentials
Resting membrane potential, graded potential, action potential, synaptic activity, information porocessing
Factors Contributing to Membrane Potentials
- Extracellular Fluid (ECF) and Intracellular Fluid (Cytosol) differ greatly in ionic composition - The ECF contains high concentrations of Sodium and Chlorine ions whereas the cytosol contains high concentration of potasium ions and negatively charged proteins.
- Cells have selectively permeable membrane - Ions cannot freely cross the lipid portions of the plasma membrane, they can entor or leave the cell only through the membrane channels.
Electrochemical Gradient
For a specific ion, the sum of the chemical and electrical forces acting on that ion across the plasma membrane
The Na/K Pump
Maintains the concentration of sodium and potassium ions across the plasma membrane.
Leak Channels
Always open; Their permeability can vary from moment to moment as the protein that make up the channel change shape in response to local conditions.
Gated Channels
Open or close in response to specific stimuli. Each gated channel can be in one of three states:
- Closed but capable of opening
- Open
- Closed and incapable of opening
Types of Gated Channels
- Chemically Gated Channels
- Voltage-gated Channels
- Mechanically Gated Channels
Chemically Gated Channels
Open or close when they bind specific chemicals.
Voltage-gated Channels
Open or close in response to changes in the membrane potential. They are characteristic of areas of excitable membranes, which are capable of generating and propagating an action potential.
Mechanically Gated Channels
Open or close in response to physical distortion of the membrane surface.
Graded Potentials
Changes in the membrane potential that cannot spread far from the site of stimulation.
Any stimulus that opens a gated channel produces a graded potential.
What happens during a graded potential?
Resting State - Resting membrane with closed chemically gated sodium ion channels
Stimulation- Membrane exposed to chemical that opens the sodium ion channels
Graded Potential - Spread of sodium ions inside plasma membrane produces a local current that depolarizes adjacent portions of the plasma membrane.
Resting Membrane Potential
The membrane potential of an unstimulated, resting cell.
All neural activities begin with a change in the resting membrane potential of a neuron.
Depolarization
Any shift from the resting membrane potential towards a more positive potential
Repolarization
The process of restoring the normal resting membrane potential after depolarization
Hyperpolarization
An increase in the negativity of the resting membrane potential
Maintenance of the Resting Membrane Potential
- Na/K Pump
- Leak Channels
- Large negative ions that cannot cross the membrane
Action Potential
Propagated changes in the membrane potential that, once initiated, affect an entire excitable membrane.
Action Potential Mechanism
- Stimulus causes sodium channels to open allowing the sodium ions that were outside the membrane to rush into the cell. This causes the cell’s electrical potential to become more positive.
- If the signal is strong enough and the voltage reaches a threshold, it triggers the action potential. More gated ion channels open, allowing more sodium ions inside the cell, and the cell depolarizes so that the charges across the membrane completely reverse. The inside of the cell becomes positively charged and the outside becomes negative.
- The peak voltage of the action potential causes the gated sodium channels to close and potassium channels to open. Potassium ions move outside the membrane and sodium ions stay inside the membrane repolarizing the cell. The result is a polarization that’s opposite of the initial polarization that had Na+ ions on the outside and K+ ions on the inside.
- The neuron becomes hyperpolarized when more potassium ions are on the outside than sodium ions are on the inside. When the potassium ion gates finally close, the neuron has slightly more potassium ions on the outside than it has sodium ions on the inside. The causes the cell’s potential to drop slightly lower than the resting potential.
- The neuron enters refractory period, which returns potassium to the inside of the cell and sodium to the outside of the cell. The sodium potassium pump goes back to work, moving sodium ions to the outside of the cell and potassium ions to the inside, returning the neuron to its normal polarized state.
Continuous Propagation
Occurs in unmyelinated axons
Step by step depolarization and repolarization of each adjacent segment of axolemma
Saltatory Propagation
Occurs in myelinated axons
More rapid; Voltage gated channels present primarily at nodes of Ranvier
Action potential appears to leap from node to node
Less overall movement of sodium and potassium ions during propagation so less ATP energy used by sodium potassium pumps maintaining membrane potential
Refractory Period
Period when the plasma membrane does not respond normally to additional depolarizing stimuli from the time an action potential begins until the normal resting membrane potential has been stabilized
Absolute Refractory Period
This is the time during another stimulus given to the neuron (no matter how strong) will not lead to a second action potential
Relative Refractory Period
A period when a greater than normal stimulus can stimulate a second response
Type A fibers
Largest, myelinated axons, with diameters ranging from 4 to 20 picometers.
These fibers carry action potentials at speeds of up to 120 meters per second, or 268 mph.
Carry sensory information about position, balance, and delicate touch and pressure sensations from the skin surface to the CNS. The motor neurons that control skeletal muscles also send their commands over large, myelinated Type A axons.
Type B fibers
Smaller, myelinated axons, with diameters ranging from 2-4 picometers.
Their propagation speeds average around 18 meters per second or roughly 40 mph.
Type B fibers and carry information to and from the CNS. They deliver temperature, pain, and general touch and pressure sensations. They also carry instructions to smooth muscle, cardiac muscle, glands, and other peripheral effectors.
Type C fibers
Unmyelinated and less than 2 picometers in diameter.
These axon propagate action potentials at the leisurely pace of 1 meter per second, or a mere 2 mph.
Type C fibers carry information to and from the CNS. They deliver temperature, pain, and general touch and pressure sensations. They also carry instructions to smooth muscle, cardiac muscle, glands, and other peripheral effectors.
Afferent
Coming to CNS
Efferent
Going away from CNS
Neurilemma
The outer surface of a Schwann cell that encircles an axon in the PNS
Neurofibrils
Microfibrils in the cytoplasm of a neuron
Ganglion
A collection of neuron cell bodies in the PNS
Myelin
An insulating sheath around an axon; consists of multiple layers of neuroglial membrane; significanly increases the nerve impulse propagation rate along the axon
The All or None Principle
A stimulus of threshold intensity that could elicit maximum contraction
Twitch
Single, isolated skeletal muscle contraction
Stages of Twitch
- Latent Period - Period from when stimulus arrives at the muscle until the actual shortening of the ends or until contraction begins (Impulse going in, calcium going out of the sarcoplasmic reticulum)
- Contraction - The cross bridge cycle is taking place, the myosin is pulling over itself. The myosin and actin are interacting together. The fibers are going back to the initial length.
- Resolution - The muscle is returning to its initial length because the calcium is coming back in.
- Refractory Period - Period of time after the stimulus during which the muscle cannot respond to another stimulus
Tetanus
Fused twitches - Continually twitches without relaxation
Incomplete Tetanus
There is some relaxation between the twitches
Complete Tetanus
Tetanus in which stimuli to a particular muscle are repeated so rapidly that decrease of tension between stimuli cannot be detected.
Tone
State of partial contraction of the entire muscle
Does not defy the all or none law
Not all cells are working at the same time in the muscle
Factors that Determine Tension of Skeletal Muscle
Metabolic Conditions Initial Length of Fiber Frequency of Stimulus Strength of Stimulus Temperature
Mechanism of Tone
- Some motor neurons are firing, some are not.
2. When all are firing, it causes fatigue
Isometric vs. Isotonic
Isometric - The tone changes but the length stays the same
Isotonic - The length changes but the tone stays the same
Types of Skeletal Muscle Fibers
Slow Oxidative Type I - Split ATP more slowly
Fast Oxidative Type II A - Split ATP more quickly but still oxidate
Fast Glycolytic Type II B - Split extremely fast
Characteristics of Smooth Muscle
Non-striated, uninucleated, involuntary
Gets some calcium from the outside of the cell
Sarcoplasmic reticulum is not well developed (when action potential comes to the cell, calcium comes out)
Short, spindle-like fibers
No T Tubules
Physiology of Smooth Muscle Contraction
The trigger for smooth muscle contraction is the appearance of free calcium ions in the cytoplasm. This produces an overall rise in calcium ion concentration in the cell.
Once in the sarcoplasm, the calcium ions interact with calmodulin, a calcium-binding protein. Calmodulin then activates the enzyme myosin light chain kinase which in turn enables myosin heads to attach to actin.
Slower onset of contraction
Maintenance of muscle tone
Stretch-relaxation response of smooth muscle
Multiunit Smooth Muscle Cells
Innervated in motor units comparable to those of skeletal muscles, but each smooth muscle cell may be connected to more than one motor neuron.
Visceral Smooth Muscle Cells
Lack direct contact with any motor neuron
Structural Characteristics of Cardiac Muscle Tissue
Relatively small; has a single, centrally placed nucleus; typically branched
The T tubules are short and broad and there are no triads; they encircle the sarcomeres at the Z lines rather than at the zones of overlap.
An action potential makes the sarcolemma more permeable to extracellular calcium ions.
Contain intercalated discs; involuntary; striated
Intercalated Discs in Cardiac Muscle Tissue
At an intercalated disc, the sarcolemmas of two adjacent cardiac muscle cells are extensively intertwined and bound together by gap junctions and desmosomes. These connections help stabilize the position of adjacent cells and maintain the 3-D structure of the tissue.
The gap junction allows ions and small molecules to move from one cell to another. These junctions create a direct electrical connection between two muscle cells.
Functional Characteristics of Cardiac Muscle Tissue
- Nervous stimulus is not required (automaticity). Specialized cardiac muscle cells called pacemaker cells normally determine the timing of the contractions.
- The nervous system can alter the pace or rate set by the pacemaker cells and adjust the amount of tension produced during a contration.
- Cardiac muscle cell contractions last about 10 times as long as they do those of skeletal muscle fibers. They also have longer refractory periods and do not readily fatigue.
- The properties of cardiac muscle sarcolemmas differ from those of skeletal muscle fibers. As a result, individual twitches cannot undergo wave summation, and cardiac muscle tissue cannot produce tetanic contractions. This different is important because a heart in a sustained tetanic contraction could not pump blood.
Physiology of Cardiac Muscle Tissue
- Nervous stimulus not required
- Prolonged contraction period
2a. Plateau in action potential due to voltage gated calcium channels
2b. Longer refractory period prevents tetanus - Dependence upon aerobic metabolism for ATP
- Contracts as unit
Epimysium
Connective tissue covering the entire muscle body
Fascia
Layers of connective tissue that surround muscle and nerves
Fasicle
Bundle of muscle cells
Perimysium
Connective tissue that surrounding a bundle of muscle fibers
Endomysium
Connective tissue that surrounds each individual muscle fiber
Tendon
Cylindrical band that binds muscle to bone
Aponeurosis
Broader sheet type of connective tissue that is connecting muscle to muscle or muscle to bone
Origin
Point of fixed attachment that does not change position when the muscle contracts
Insertion
Point of attachment of a muscle; the end that is easily moveable
Agonist
Primary mover; muscle responsible for a specific movement
Antagonist
Opposes the movement of the agonist
Synergist
Muscle that assists a prime mover in performing its primary action
Fixator
Muscle that acts as a stabilizer of one part of the body during movement of another part
Compartment Muscle Groups
Consist of the muscles in this region along with the nerves and vessels thta come to this region
How Muscles are Named
- Size - Gluteus maximus
- Shape - Deltoid
- Direction of Fibers - Rectus femoris
- Action - Levator scapulae
- Origin and Insertion - Sternocleidomastoid
- Number of Origins - Triceps brachii
- Location - Biceps brachii
Threshold
The membrane potential at which an action potential begins
