What are the 3 types of muscle tissue?
Skeletal, cardiac, smooth
Attaches to bone, skin, or fascia (connective tissue); striated with light and dark bands that are visible under a microscope; voluntary control of contraction and relaxation
Forms most of the heart; striated appearance, branched, and contains intercalated discs; involuntary control regulated by autonomic nervous system and hormones from endocrine glands
Attached to hair follicles in skin and found in walls of hollow internal structures, such as blood vessels, airways, and gastrointestinal tract; not striated; involuntary control
List the special characteristics of muscle tissue
1) electrical excitability (ability to respond to stimuli by generating electrical signals)
2) conductivity (ability to propagate electrical signals over membrane)
3) contractility (ability to shorten and generate force when stimulated by an action potential)
4) extensibility (ability to be stretched without damaging the tissue)
5) elasticity (ability to return to original shape after being stretched)
List the general functions of muscle tissue
1) produce body movements
2) stabilize body positions
3) store and move substances within body
4) generate heat (thermogenesis)
Name the two contractile proteins
1) actin (in thin filament; has myosin-binding sites)
2) myosin (in thick filaments; binds to actin, undergoes power stroke, and pulls on actin to generate force)
Name the two regulatory proteins
forms complex and holds tropomyosin in place blocking myosin binding sites on actin; when Ca binds to it, it changes shape and moves tropomyosin away to expose binding sites
covers myosin-binding sites on actin when muscle is relaxed; uncovers binding sites when Ca binds to troponin, which triggers muscle contraction
Name the 4 structural proteins
1) titin (anchors thick filament to the M line and the Z disc)
2) M line (connects to titin and thick filaments to hold thick filaments in place)
3) dystrophin (links thin filaments to the sarcolemma and transmits tension to the tendon)
4) nebulin (an inelastic protein that helps align the thin filaments)
What is the basic functional unit of a muscle myofibril?
What neurotransmitter is released at a neuromuscular joint (NMJ) to initiate a muscle contraction?
What is the resting membrane potential (in mV) of muscle cells?
What is the threshold potential (in mV) required to generate and action potential?
Describe Phase 1 of the events that lead to muscle fiber contraction
Phase 1: Motor Neuron Stimulates Muscle Fiber
- Action potential arrives at axon terminal at neuromuscular junction ->
- ACh released; binds to receptors on sarcolemma ->
- Ion permeability of sarcolemma changes ->
- Local change in membrane voltage (depolarization) occurs ->
- Local depolarization (end plate potential) ignites AP in sarcolemma
Describe Phase 2 of the events that lead to muscle fiber contraction
Phase 2: Excitation-Contraction Coupling Occurs
- AP travels across the entire sarcolemma ->
- AP travels along T tubules ->
- SR releases Ca (2+); Ca (2+) binds to troponin; myosin-binding sites (active sites) on actin exposed ->
- Myosin heads bind to actin; contraction begins
Summarize the steps in crossbridge (contraction) cycle
1) Crossbridge formation: myosin heads attach to actin to form crossbridges
2) Power (working) stroke: ADP and Pi are released and myosin heads pivot and pull thin filaments toward M line
3) Crossbridge detachment: myosin detaches from actin when another ATP binds to head
4) Cocking of myosin head: ATP is hydrolyzed to ADP and Pi to energize myosin head and return it to its prestroke high-energy "cocked" position
Summarize the events that restore relaxation
1) ACh effects are terminated by its breakdown in the syphatic cleft by acetylcholinesterase and diffusion away from the junction
2) Repolarization: restoring the sarcolemma to its initial polarized state (negative inside, positive outside)
3) The Aftermath
Elaborate on repolarization of restoring relaxation.
Repolarization occurs as Na+ channels close and voltage-gated K+ channels open. Because K+ concentration is substantially higher inside the cell than in the extracellular fluid, K+ diffuses rapidly out of the muscle fiber.
Elaborate on the aftermath of restoring relaxation.
When the muscle AP ceases, the voltage-sensitive tubule proteins return to their original shape, closing the Ca (2+) release channels of the SR. Ca (2+) levels in the sarcoplasm fall as Ca (2+) is continually pumped back into the SR by active transport. Without Ca (2+), the blocking action of tropomysin is restored, myosin-actin interaction is inhibited, and relaxation occurs.
Describe rigor mortis and what causes it.
Most muscles begin to stiffen 3-4 hours after death. Peak rigidity occurs at 12 hours and then gradually dissipates over the next 48-60 hours. Shortly after breathing stops, ATP synthesis ceases, but ATP continues to be consumed and cross bridge detachment is impossible. Actin and myosin become irreversibly cross-linked, producing the stiffness of rigor mortis, which gradually disappears as muscle proteins break down after death.
Movable attachment of a muscle
Attachment of a muscle that remains relatively fixed during muscular contraction
The front or under part of a vertebrae body from the breastbone to the pelvis, containing the abdominal viscera
Plasma membrane of muscle cell
Cytoplasm of muscle cells
Oxygen-binding pigment in muscle.
Contractile elements of muscle cells.
Basic functional units of a muscle myofibril.
Define sarcoplasmic reticulum.
System of tubular sacs that encircle each myofibril; similar to smooth ER in nonmuscle cells; stores Ca (2+) in relaxed muscle; release of Ca (2+) triggers muscle contraction
Define neuromuscular junction.
Region where a motor neuron comes into close contact with a skeletal muscle cell
Define muscle tension.
The force exerted by a contracting muscle on some object
The opposing force exerted on the muscle by the weight of the object to be moved
Define motor unit.
Consists of a somatic motor neuron and all skeletal muscle fibers (cells) it stimulates
Define isometric contractions.
Tension may build to peak capacity but muscle neither shortens nor lengthens
Define concentric isotonic contractions.
Muscle shortens and does work.
Define eccentric isotonic concentrations.
Muscle generates force as it lengthens
Wasting away of muscles due to progressive loss of myofibrils; disuse atrophy and denervation atrophy.
Increase in the diameter of muscle fibers.
Define muscular dystrophy.
A group of inherited muscle-destroying diseases.
Muscle pain resulting from any muscle disorder.
Any disease of muscle.
A sudden, involuntary twitch in smooth or skeletal muscle ranging from merely irritating to very painful.
Excessive stretching and possible tearing of a muscle due to muscle overuse or abuse.
What is muscle tone and how is it achieved?
- Sustained by weak, involuntary contractions of a small number of motor units that alternate between active and inactive in a constantly shifting pattern
- Keeps muscles firm but does not produce movement
- Important for maintaining posture and blood pressure
- If motor nerves supplying a muscle are damaged or cut, muscle becomes limp due to muscle tone loss
What are the 3 sources of ATP production within muscle?
1) Creatine phosphate
2) Anaerobic cellular respiration
3) Aerobic cellular respiration
Briefly describe slow oxidative (slow-twitch) fibers.
- Smallest in diameter and least powerful
- Red fibers
- Generate ATP mainly by aerobic respiration and hydrolyze ATP slowly
- Used for activities that require prolonged, sustained contractions, such as maintaing posture
Briefly describe fast oxidative-glycolytic (fast-twitch A) fibers.
- Intermediate diameter
- Red fibers
- Generate ATP mainly by aerobic respiration and hydrolyze ATP rapidly
- Moderately high resistance to fatigue
- Used for activities such as walking and sprinting
Briefly describe fast glycolytic (fast-twitch B) fibers.
- Largest in diameter and most powerful
- White fibers
- Large amounts of glycogen
- Generate ATP mainly by glycolysis (anaerobic) and hydrolyze ATP rapidly
- Fatigue quickly
- Used for intense anaerobic movements of short duration, such as weight lifting and ball-throwing
Describe the characteristics of cardiac muscle.
1) Striated, branching fibers
2) Ends of cells connected by intercalated discs
3) Same arrangement of thick and thin filaments into sarcomeres as skeletal muscle
4) Under involuntary control
5) Cardiac muscle has built-in pacemaker: autorhymithic fibers that are self-stimulating and set rhythm for contraction of other contractile fibers.
Describe the characteristics of smooth muscle.
1) Small muscle cells that taper at ends
2) Little sarcoplasmic reticulum so limited Ca (2+) storage
3) No T tubules
4) Thick and thin myofilaments are not orderly arranged so no sarcomeres
5) Since no regular pattern of overlap between filaments, no striations
6) Muscle fiber twists into a helix as it contracts and untwists as it relaxes
7) Under involuntary control
What is the most common and serious form of muscular dystrophy?
Define the actions of the prime mover (agonist).
Contracts to produce an action.
Define the actions of the antagonist.
Stretches and yields to effects of prime mover.
Define the actions of the synergists.
Contract to stabilize intermediate joints.
Define the actions of the fixators.
Stabilize origin of the prime mover.
Name the 5 types of fascicle arrangements.
Describe a parallel fascicle arrangement.
- Fascicles parallel to longitudinal axis of muscle
- Ends terminate in flat tendons
- Example: Stylohyoid muscle
Describe a fusiform fascicle arrangement.
- Fascicles almost parallel to longitudinal axis of muscle
- Ends terminate in flat tendons
- Example: Digastric muscle
Describe a circular fascicle arrangement.
- Fascicles in concentric circular arrangements
- Form sphincter muscles that enclose an orfice (opening)
- Example: Orbicularis oculi muscle
Describe a triangular fascicle arrangement.
- Fascicles spread over broad area and converge at thick central tendon
- Makes muscle appear triangular
- Example: Pectoralis major muscle
Describe a pennate fascicle arrangement.
A) Unipennate: Fascicles arranged only on one side of tendon
- Example: Extensor digitorum longus muscle
B) Bipennate: Fascicles arranged on both sides of centrally arranged tendons
- Example: Rectus femoris muscle
C) Multipennate: Fascicles attach obliquely from many directions to several tendons
- Example: Deltoid muscle
Describe functions/characteristics of a lever.
- Rigid structure that can produce movement around a fixed point
- Bone acts as lever
Describe functions/characteristics of a fulcrum.
- The fixed point in a lever system
- Joint serves as the fulcrum
Name 2 forces that act on lever at different points.
1) Effort: causes movement; effort is force exerted by muscle contraction
2) Load (resistance): opposes movement; load is weight of body part and/or object that is moved
True or false, motion occurs when load exceeds effort?
List characteristics of a mechanical advantage.
Load is closer to the fulcrum than effort is.
- Has leverage, so smaller effort can move heavier load
- Produces more force; heavy load can be moved but not very far or fast
- Trade-off: less speed and range of motion, but smaller effort exerted over relatively large distance moves larger load slowly for a short distance
- Example: Mandible (lever) is moved by contraction of jaw muscles (effort) at temporomandibular joint (fulcrum), which produces powerful mechanical advantage that pulls jaw upward and crushes food (load)
List characteristics of a mechanical disadvantage.
Effort is closer to the fulcrum than load is.
- Larger effort needed to move a lighter load
- Trade-off: can only move light load and requires larger effort, but can move load faster and farther
- Has greater range of motion and produces faster speed, only light load can be moved, but it can be moved faster and farther
Describe a first-class lever system (scissors and seesaws).
Fulcrum is between effort and load.
- Can produce mechanical advantage or disadvantage depending on whether effort or load is closer to fulcrum
- Few in body
- Example: head resting on vertebral column
- lever: head
- load: weight of anterior part of skull
- fulcrum: atlanto-occipital joint
- effort: contraction of posterior neck muscles
Describe a second-class lever system (wheelbarrow).
Load is between fulcrum and effort.
- Always produces mechanical advantage
- Debatable whether they exist in human body
- Example: raising on toes
- lever: foot
- load: weight of body
- fulcrum: metarsophalangeal joint (ball of foot)
- effort: contraction of calf muscles
Describe a third-class lever system (forceps).
Effort is between fulcrum and load.
- Always produces a mechanical disadvantage
- Favors speed and range of motion over effort
- Example: elbow joint, forearm bones, and biceps brachii muscle
- lever: forearm bones
- load: weight of forearm
- fulcrum: elbow joint
- effort: contraction of biceps brachii
What is cell is the functional unit of the nervous system?
List the 3 basic functions of nervous tissue.
1) Sensory input: sensing internal and external changes with sensory receptors
2) Integration: processing, interpreting, and remembering those changes
3) Motor output: responding to those changes with effectors (muscular contractions and glandular secretions)
List the 2 primary divisions of the nervous system.
1) Central nervous system: contains the brain and spinal cord
2) Peripheral nervous system: consists of cranial and spinal nerves that contain both sensory and motor fibers
List the 3 divisions of the peripheral nervous system.
1) Somatic (voluntary) nervous system
2) Autonomic (involuntary) nervous system
3) Enteric nervous system.
Describe the somatic (voluntary) nervous system.
- Sensory neurons from skin and special sensory receptors to the CNS
- Motor neurons to skeletal muscle
Describe the autonomic (involuntary) nervous system.
- Sensory neurons from visceral organs to CNS
- Motor neurons to cardiac muscle, smooth muscle, and glands
- Two divisions:
- Sympathetic division: "fight or flight" response
- Parasympathetic division: homeostasis
Describe the enteric nervous system.
- Involuntary sensory and motor neurons that control gastrointestinal tract
- Neurons function independently of ANS and CNS
List the 6 types of neuroglia.
1) Astrocytes (CNS)
2) Oligodendrocytes (CNS)
3) Microglia (CNS)
4) Ependymal cells (CNS)
5) Satellite cells (PNS)
6) Schwann cells (PNS)
- Form blood-brain barrier by covering blood capillaries
- Metabolize neurotransmitters
- Regulate K+ balance
- Provide structural support
- Processes form myelin sheath (lipid and protein covering) around more than one axon in CNS
- Enables rapid conduction of nerves impulses down axon of neuron
- Analogous to Schwann cells of PNS
- Small cells found near blood vessels
- Phagocytic function
1) Remove dead cells
2) Derived from same cells that give rise to macrophages and monocytes
Describe ependymal cells.
- Form epithelial membrane lining cerebral cavities and central canal
- Produce cerebrospinal fluid (CSF)
Describe satellite cells.
Flat cells surrounding neuronal cell bodies in peripheral ganglia support neurons in PNS ganglia
Describe Schwann cells.
- Cells encircle PNS axons
- Each cell produces part of the myelin sheath surrounding an axon in PNS (enables rapid conduction of nerve impulses down axon of neuron)
- Neurilemma: cytoplasm and nucleus
True or false, neuroglia can conduct nerve impulses?
List the 2 parts of a neuron.
- Conduct impulses toward the cell body (receive input)
- Typically short, highly branched and unmyelinated
- Cell may have one to many
- Surfaces specialized for contact with other neurons
- Contain neurofibrils and Nissl bodies
- Conduct impulses away from cell body (transmit output)
- Long, thin cylindrical process of cell
- Cell only has one axon
- Originates at axon hillock
- Impulses arise from initial segment (trigger zone)
- Side branches (collaterals) end in fine processes called axon terminals
- Synaptic end bulbs (terminal boutons): swollen tips on axon terminals that contain synaptic vesicles filled with neurotransmitters
True or false, neurons can conduct nerve impulses?
Describe myelination in the PNS.
1) Schwann cells myelinate (wrap around) axons in the PNS during fetal development
2) Schwann cell cytoplasm and nucleus forms outermost layer of neurolemma with inner portion being the myelin sheath
3) Tube guides growing axons during repair
Describe myelination in the CNS.
1) Obligodendrocytes myelinate axons in the CNS
2) Broad, flat cell process wrap about axons, but cell bodies do not surround axons
3) No neurilemma is formed
4) Lacks a distinct tube or neurilemma, so little regrowth possible after injury
List the 3 structural classifications of neurons and their characteristics.
1) Multipolar neurons: have several dendrites and one axon
- Most common cell type
2) Bipolar neurons: have one primary dendrite and one axon
- Found in retina, inner ear, and olfactory tissue
3) Unipolar neurons: have only one process that branches into one dendrite and one axon
- Develops from a bipolar cell
- Are always sensory neurons
List the 3 functional classifications of neurons and their functions.
1) Sensory (afferent) neurons: transport sensory information from skin, muscles, joints, sense organs, and viscera to CNS
2) Motor (efferent) neurons: send motor nerve impulses to muscles and glands
3) Interneurons (association) neurons: connect sensory neurons to motor neurons; account for about 90% of neurons in the body
Name the 4 states of an action potential.
1) Resting state
2) Depolarization (depolarizing phase)
3) Repolarization (repolarizing phase)
4) Hyperpolarization (refractory phase)
Describe the resting state of an action potential.
Exists prior to generation of action potential
- all Na+ and K+ channels are closed
- resting membrane potential is -70 mV
Describe the depolarizing phase of an action potential.
- Chemical or mechanical stimulus causes a graded potential to reach at least -55 mV (threshold)
- Voltage-gated Na+ channels open and Na+ rushes into cell
- Membrane potential changes considerably (up to +30 mV)
- Positive feedback process
Describe the repolarizing phase of an action potential.
- When threshold potential of -55 mV is reached, voltage-gated K+ channels also open
- However, K+ channel opening is much slower than Na+ channel opening (that caused depolarization)
- When K+ channels finally open, the Na+ channels have already closed (Na+ inflow stops)
- K+ outflow returns membrane potential to -70 mV
- If enough K+ channels exits cell, it will reach a -90 mV membrane potential and enter the after-hyperpolarizing phase
- K+ channels close and membrane potential returns to resting potential (-70 mV)
Describe the refractory phase of an action potential.
Period of time during which neuron cannot generate another action potential (AP)
- Absolute refractory period
- Even very strong stimulus will not initiate another AP
- Inactivated Na+ channels must return to the resting state before they can be reopened
- Relative refractory period
- A superthreshold stimulus can generate an AP
- K+ channels are still open, but Na+ channels have closed
Name the characteristics of a continuous nerve conduction.
- Slow conduction
- Occurs at unmyelinated fibers
- Step-by-step depolarization of each part along the length of the axolemma
Name the characteristics of a saltatory conduction.
- Occurs at myelinated fibers
- Fast conduction
- Depolarization only at nodes of Ranvier; impulse jumps from node to node