Muscle Tissue Types and Functions

Muscle Tissue Types

• The three muscle tissue types are skeletal, cardiac, and smooth
• Skeletal muscle is voluntary and multinucleated
• Cardiac and smooth muscle are involuntary with one or two nuclei
• Skeletal and cardiac muscle are striated
• Cardiac muscle contains intercalated discs
• Muscle tissues differ in nervous control, filament arrangement, and locations

Special Properties of Muscles

• Excitability/irritability: Ability to receive and respond to stimuli
• Contractility: Ability to shorten forcibly when stimulated
• Extensibility: Ability to stretch without damage
• Elasticity: Ability to recoil to resting length after stretching

Major Functions of Muscle Tissue

• Movement
• Posture maintenance
• Body structure movement
• Joint stabilization
• Generating heat
• Skeletal muscles facilitate locomotion and manipulation
• Muscular system maintains posture through continuous spinal reflex contractions
• Smooth muscle maintains blood pressure and contracts digestive, urinary, & reproductive organs
• Muscles stabilize joints, and skeletal muscle contraction generates heat

Connective Tissue Layers of Skeletal Muscle

• Epimysium surrounds the entire skeletal muscle
• Perimysium surrounds a fascicle
• A muscle fascicle is a bundle of parallel muscle fibers
• Endomysium surrounds individual muscle fibers

Sarcomere Regions

• Sarcomere is the structural and functional unit
• Major regions include the H zone, A band, Z disc (line), and I band
• The H zone has only actin fibers and disappears during contraction
• The A band contains both myosin and actin filaments and runs the length of myosin filaments, appearing darker
• The Z disc (line) is the sarcomere border, separating neighboring sarcomeres
• The I band has the Z disc (line) in the center and contains only actin filaments appearing lighter

Sarcolemma & Sarcoplasmic Reticulum

• Sarcolemma is the plasma membrane containing Na+ and K+ gates
• Sarcoplasmic reticulum stores Ca+ ions for cross-bridge coupling
• Myofibrils are thread-like contractile organelles inside skeletal muscle fibers
• T (transverse) tubules are sarcolemma extensions carrying impulses
• Sarcoplasm receives Ca+ ions from sarcoplasmic reticulum
• A triad includes a T tubule and two terminal cisterns
• Myoglobin is an oxygen-binding molecule
• Glycosomes are glycogen-containing organelles within skeletal muscle

Sliding Filament Model

• Thin filaments slide past thick filaments during contraction
• Thin filaments consist of actin
• Thick filaments consist of myosin
• Myosin appears thicker and darker
• Actin appears thinner and lighter

Neuromuscular Junction

• Neuromuscular junction where an axon terminal meets a skeletal muscle
• Somatic motor fibers innervate skeletal muscles
• The motor end plate is where the sarcolemma has ACh receptors
• ACh release into the synaptic cleft happens at the neuromuscular junction and binds to ACh receptors
• Binding of ACh causes Na+ channels to open, initiating an action potential on the sarcolemma

Excitation-Contraction Coupling & Action Potential

• The action potential excites the sarcolemma
• Action potential steps include depolarization and repolarization
• Na+ enters the ICF from the ECF through Na+ protein channels during depolarization
• K+ exits the ICF into the ECF through K+ protein channels during repolarization
• The action potential travels down the sarcolemma into the T (transverse) tubules leading to Ca2+ ion release

Motor Units & Muscle Contraction

• A motor unit includes a somatic motor neuron and all stimulated skeletal muscle fibers
• Finely controlled motor units consist of one motor neuron and few muscle fibers (e.g., orbicularis oculi)
• Coarsely controlled muscles consist of one motor neuron and many muscle fibers (e.g., gluteus maximus)
• Ca+ and ATP are required for skeletal muscle contraction
• Ca+ interacts with troponin, which makes the myosin binding site on actin available
• ATP interacts with myosin, breaking it down (via ATPase) to form a cross-bridge with actin
• Troponin and tropomyosin regulate and block the myosin binding site on actin
• The cross-bridge cycle involves myosin forming cross-bridges with actin
• Myosin heads (ATPases) are energized by ATP and bind to myosin binding sites on actin.
• Two ATPs are required per cross-bridge cycle

Power Stroke

• Myosin pulls actin for the power stroke to allow myofilaments to slide
• Another ATP is required for the myosin (ATPase) to detach from the actin binding site
• Skeletal muscle relaxation is enabled with Ca+ returning to storage in the terminal cisternae and ACh deactivation

Rigor Mortis

• Rigor mortis occurs due to lack of ATP to break cross bridges after death

Muscle Twitch Periods & Measurement

• Periods include latent, contraction, and relaxation phases
• Events are measured on a myogram
• The latent period occurs after excitation-contraction coupling as Ca2+ exits the reticulum
• The contraction period occurs as cross-bridges become active
• Relaxation occurs as Ca2+ is pumped back into the sarcoplasmic reticulum

Muscle Metabolism

• Three types are direct phosphorylation, anaerobic respiration, and aerobic respiration
• Muscle metabolism produces ATP
• Enzymes and heat increase the rate of metabolism

Direct Phosphorylation

• Direct phosphorylation involves transferring a phosphate group from creatine phosphate to ADP to make ATP
• Energy lasts for 15 seconds

Anaerobic Respiration

• Glycogen is broken down into glucose, entering glycolysis
• In the absence of oxygen, pyruvic acid gets converted to lactic acid
• Two ATP are produced per glucose molecule
• Energy lasts for 60 seconds

Aerobic Respiration

• Glycogen is broken down into glucose, entering glycolysis in the presence of oxygen
• Pyruvic acid is produced, and cellular metabolism continues
• 36 ATP are produced per glucose molecule
• CO2, H2O, and 36 ATP are produced from complete glucose breakdown
• 40% of ATP is converted to mechanical energy
• 60% of ATP is converted into heat via shivering
• Blood moves heat to the surface via capillaries and sweating
• Energy lasts for hours

Strength of Respiration

• Anaerobic respiration provides the most strength
• With ATP production failing to meet demand, ionic imbalances, lactic acid production, and lack of muscle contraction occurs
• Oxygen debt is the amount of oxygen needed to restore the muscle to its resting state

Muscle Twitch

• A muscle twitch involves brief contraction of all muscle fibers in a motor unit
• Threshold stimulus is the lowest strength to cause a muscle contraction
• Graded muscle responses depend on the number of action potentials affecting muscle

Treppe Stage of Muscle Contraction

• Treppe is a condition where muscle contractions become more efficient, and wave summation starts to occur
• Contractions are complete
• The first contraction is weakest, and subsequent contractions get stronger with increased heat

Abnormal Muscle Contraction

• Incomplete tetanus is an abnormal muscle contraction with unfused wave summation
• Complete or fused tetanus involves the loss of muscle relaxation; a period of constant skeletal muscle contraction in which twitches fuse

Temporal Wave Summation

• Temporal wave summation is achieved when a second stimuli occurs before the muscle has a chance to relax

Muscle Contractions

• Isometric contractions involve no change in length or sarcomere shortening; cross-bridges form with no power stroke
• Isotonic contractions involve myofilaments sliding over one another as myosin forms cross-bridges, pulling actin towards the H zone

Types of Isotonic Contraction

• Isotonic concentric contractions involve muscle shortening
• Isotonic eccentric contractions involve muscle lengthening

Muscle Tone

• Muscle tone is a slightly contracted state maintained by spinal reflexes through motor unit stimulation
• Factors influencing muscle contraction include the degree of stretch, frequency of stimulation, and the number of muscle fibers

Muscle Fiber Types

• Slow oxidative fibers have high oxygen, are fatigue-resistant, use slow ATPases (myosin), and use aerobic metabolism (36 ATP per glucose)
• Fast glycolytic fibers have low oxygen, high glycogen, fatigue quickly, use fast ATPases (myosin), and anaerobic metabolism (two ATP per glucose)
• Fast glycolytic fibers have more strength but less endurance
• Muscles cannot contract after prolonged tetanus until stores are replenished
• Fast oxidative fibers are both aerobic and anaerobic

Muscle Adaptations

• Hypertrophy is excessive muscle development
• Atrophy is the degeneration of muscle cells due to lack of use
• Hyperplasia is an increase in the amount of muscle cells

Smooth Muscle Functions

• Smooth muscle maintains blood pressure in cardiovascular system, propels food in the GI tract, and shunts blood
• Layers include the circular and longitudinal layer
• Key differences between smooth and skeletal muscles are Ca2+ binding to calmodulin, neurotransmitter binding at varicosities, stretch adaptation, and caveolae, with slower smooth muscle contraction

Smooth Muscle Characteristics

• Muscle cells are arranged in sheets around hollow organs
• Smooth muscles contract in unison to facilitate peristalsis
• Peristalsis involves alternating contraction and relaxation in the GI tract moving food

Muscle Contraction Effects

• Acetylcholine causes smooth muscle contraction
• Norepinephrine relaxes bronchioles and contracts blood vessels

Organization of Skeletal Muscles

• Skeletal muscles are organized into functional groups
• Connective tissue binds separate muscles into functional groups
• Muscles name is derived from muscle location, muscle shape, muscle size, direction of muscle fibers or fascicles, number of origins, location of attachments, and muscle action.
• These groups include prime movers (agonists), antagonists, synergists, and fixators

Roles of the Functional Group

• Prime mover (agonist) produces specific movement
• Antagonist opposes the prime mover
• Synergist helps prime mover, reducing unnecessary movement
• Fixator acts as a synergist, stabilizing the agonist's origin

Muscle Organization

• Triangular fascicle arrangement is spread over a broad area and converges at a single tendon
• Examples of muscle fiber direction are rectus, transversus, and oblique
• Oblique indicates a diagonal muscle arrangement
• Circular fascicle arrangement surrounds an opening creating a sphincter, like the orbicularis oris
• Multipennate fascicle arrangement inserts into multiple tendons, tapering towards a common tendon (e.g., deltoid)

Muscle Examples

• Convergent fascicle arrangement has a widespread expansion, with fascicles converging to a common attachment point (e.g., pectoralis major)
• Fusiform fascicle arrangement is spindle-shaped with wide center and narrow ends (e.g., biceps brachii)
• Parallel fascicle arrangement has fibers running parallel along the muscle's longitudinal axis (e.g., sartorius)
• Rectus femoris has a bipennate fascicle arrangement: Fibers converge on both sides of a central tendon
• Extensor digitorum longus has a unipennate fascicle arrangement: Fibers converge to one side of a tendon

Muscle Size & Origins

• Maximus, medius, and minimus are examples of muscles' relative size
• The quadriceps femoris muscle has four origins
• The biceps brachii muscle has two origins
• The triceps brachii muscle has three origins

Attachment & Lever Systems

• Sternocleidomastoid is named for its attachments
• Flexor carpi radialis is named for its action
• Muscles attach via tendons made of dense connective tissue
• An aponeurosis is a sheet-like attachment from muscle to bone
• Every muscle has an origin and insertion

Origin & Insertion

• Origin refers to the point of attachment to less movable bone
• Insertion refers to the point of attachment to movable bone
• Lever systems work with effort, load, and fulcrum
• Effort is the force needed to contract the muscle and move the load
• Load represents the bone and surrounding tissues resisting movement
• Motion occurs, if effort exceeds the load

Buccinator

• The buccinator participates in mastication, powerful sucking muscle, used for whistling and compresses the cheek

Frontalis

• The frontalis produces horizontal wrinkles in the forehead and raises eyebrows

Masseter

• The masseter participates in mastication and elevates the mandible

Occipitalis

• Occipitalis pulls skin posteriorly

Orbicularis Oculi

• The orbicularis oculi closes the eye, responsible for blinking and squinting

Orbicularis Oris

• The orbicularis oris is the kissing muscle, closes, purses, and protrudes lips

Platysma

• The platysma depresses the mandible

Temporalis

• The temporalis closes the jaw, elevates, and retracts the mandible

Zygomaticus

• Zygomaticus participates in mastication, smiling and raises lateral corners of mouth upward

Sternocleidomastoid

• The sternocleidomastoid flexes and laterally rotates the head

Trapezius

• The trapezius stabilizes, raises, retracts, and rotates scapula

Deltoid

• Deltoid is the prime mover of arm abduction

Latissimus Dorsi

• Latissimus dorsi is the prime mover of arm extension, a powerful arm adductor, and medially rotates arm at the shoulder

Levator Scapula

• Levatator Scapula elevates the scapula

Muscles in the Rotator Cuff Group

• Rotator cuff muscles include supraspinatus, infraspinatus, teres minor, and subscapularis

Supraspinatus

• Supraspinatus initiates arm abduction and stabilizes the shoulder joint

Infraspinatus

• Infraspinatus stabilizes the shoulder joint and rotates the humerus laterally

Teres Minor

• Teres minor stabilizes the shoulder joint and rotates the humerus laterally

Subscapularis

• Subscapularis is the chief medial rotator of arm

Teres Major

• Teres major extends, medially rotates, and adducts the humerus

Biceps Brachii

• Biceps brachii is the prime mover of flexing the elbow

Brachialis

• Brachialis is the forearm flexor

Triceps Brachii

• Triceps brachii extends the elbow

Brachioradialis

• Brachioradialis flexes the forearm

Flexor Carpi Radialis

• Flexor carpi radialis flexes and abducts the hand at the wrist joint

Flexor Carpi Ulnaris

• Flexor carpi ulnaris flexes and adducts the hand at the wrist joint

Extensor Carpi Radialis

• Extensor carpi radialis extends and abducts the hand at the wrist joint

Extensor Carpi Ulnaris

• Extensor carpi ulnaris extends and adducts the hand at the wrist joint

Extensor Digitorum

• Extensor digitorum is the prime mover of finger extension

Pronator Teres

• Pronator teres pronates the forearm

Palmaris Longus

• Palmaris longus flexes the wrist

Diaphragm

• The diaphragm allows normal breathing in and out

External Intercostals

• The external intercostals allows breathing, pulling ribs upward and outward for inspiration

Internal Intercostals

• The internal intercostals allows breathing, pulling ribs downward and inward for expiration

Pectoralis Major

• Pectoralis major is the prime mover of arm flexion, rotates arm medially, adducts and flexes the arm

Pectoralis Minor

• Pectoralis minor draws the scapula forward and downward when the ribs are fixed

Serratus Anterior

• Serratus anterior rotates the scapula so that its inferior angle moves laterally and upward

External Obliques

• External obliques flexes the vertebral column and compresses the abdominal wall

Internal Oblique

• Internal oblique flexes the vertebral column and compresses the abdominal wall

Rectus Abdominus

• Rectus abdominus flexes and rotates the lumbar region of vertebral column

Transversus adbominus

• Transversus Abdominus compresses abdominal contents

Gluteus Maximus

• Gluteus maximus extends the thigh

Gluteus Medius

• Gluteus Medius abducts and medially rotates the thigh

Adductor Longus

• Adductor longus adducts, flexes, and medially rotates the thigh

Adductor Magnus

• Adductor Magnus adducts and medially rotates

Gracilis

• The gracilis is responsible for adduction of the thigh and flexion/medial rotation of the leg

Hamstrings

• Hamstrings include biceps femoris, semitendinosus, and semimembranosus

Biceps Femoris

• Biceps Femoris extends the thigh and flexes the knee

Semitendinosus

• Semitendinosus extends the thigh and flexes the knee

Semimembranosus

• Semimembranosus extends the thigh and flexes the knee

Quadriceps

• Quadriceps include rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius

Rectus Femoris

• Rectus Femoris extends the knee and flexes thigh at the hip

Vastus Lateralis

• Vastus Lateralis extends and stabilizes the knee

Vastus Medialis

• Vastus Medialis extends the knee

Vastus Intermedius

• Vastus intermedius extends the knee

Sartorius

• The sartorius flexes abducts, laterally rotates the thigh, and flexes the knee

Tensor Fascia Lata

• Tensor fascia lata steadies the knee and trunk on thigh by making iliotibial band taut.

Gastrocnemius

• Gastrocnemius allows plantar flexion

fibularis (peroneus) longus

• allows Plantar flexion

Soleus

• Soleus allows Plantar flexion

Tibialis Anterior

• Tibialis Anterior allows Dorsiflexion

Extensor Digitorum Longus

• Extensor Digitorum Longus extends the toes

Nervous System & Endocrine System

• Both systems are controlling systems concerned with maintaining homeostasis

Communication Methods

• The nervous system communicates with electrical impulses and neurotransmitters
• The endocrine system communicates with hormones in the blood or ECF

Speed of Communication

• The nervous system communicates in milliseconds
• The endocrine system communicates in seconds, minutes, hours, weeks, or months

Three Main Functions Of Nervous System

• Sensory input
• integration
• motor output

Sensory Input

• Monitor changes occurring inside and outside the body
• Gather that information as sensory (afferent) input

Integration

• The nervous system processes sensory input
• Decides what to do with it

Motor output

• Motor (efferent) output travels from the control center
• Activates effector organs (muscles and glands) to cause a response

Neural Communication

• Graded or action potentials along nerves
• The two main parts of the nervous system are the central and peripheral nervous systems

Central & Peripheral Nervous Systems

• The central nervous system parts include the brain and spinal cord
• The peripheral nervous system parts include cranial nerves, spinal nerves, and ganglia
• Functional divisions of the peripheral nervous system are the sensory (afferent) and motor (efferent) divisions
• Voluntary division of the PNS is the somatic nervous systems
• The somatic nervous systems controls skeletal muscles
• The involuntary division is the autonomic nervous system
• The divisions within the autonomic nervous system are sympathetic and parasympathetic systems

Autonomic Nervous System

• Autonomic nervous systems controls cardiac muscle, smooth muscle, and glands

Fibers

• The types of fibers in the sensory (afferent) division are somatic sensory fibers and visceral sensory fibers

Types of Impulses

• Somatic sensory fibers conveys impulses from the skin, skeletal muscles and joints that convey voluntary information toward the CNS
• Visceral sensory fibers conveys impulses from visceral organs

Glial Cells

• They are supporting cells that do not conduct electrical nerve impulses

Glial Cell Types

• Astrocytes
• microglial cells
• ependymal cells
• oligodendrocytes
• Schwann cells
• satellite cells

Neuroglial Cells

• Astrocytes, microglial cells, ependymal cells, oligodendrocytes are in the CNS
• Schwann cells and satellite cells are in the PNS

Astrocytes

• Support and brace neurons and anchor them to capillaries
• Controls chemical environment around neurons
• Remove leaked potassium ions or leaked neurotransmitters

Microglial Cells

• Type of macrophage that phagocytizes microorganisms

Ependymal Cells

• Line ventricles and central cavities of brain and spinal cord

Oligodendrocytes

• Produces myelin sheaths that wrap their processes tightly around the fibers

Lipids

• Myelin is made of lipids

Schwann Cells

• Surround all axons (nerve fibers) in the PNS and produce myelin sheath around thicker nerve fibers

Satellite Cells

• Surround neuron cell bodies and help to regulate ion concentration
• Neurons (nerve cells) are electrical and capable of conducting action potentials

High Metabolic Rate in Neurons

• Neurons can function for a lifetime
• Contain high metabolic rate

Neuron Parts

• Dendrite
• cell body (soma)
• axon hillock (trigger zone)
• axon

Dendrites

• Shorter, and more numerous regions of the neuron that receives information

Cell Body (Soma)

• Integrative region of the neuron that contains the nucleus

Nissl Bodies

• Nissl bodies are the names for ribosomes in the cell body

Axon Hillock (Trigger Zone)

• Initial region of the axon where the action potential is generated
• Is where action potential is generated (highest amount of Na+ gates)

Axon

• Conducting region of the axon that leads away from the cell body (soma).

Three types of neurons

• Multipolar
• bipolar
• unipolar

Multipolar Neurons

• Have the most dendrites, only one axon, and are the most common neurons in the CNS
• Function as interneurons and motor neurons

Bipolar Neurons

• Have one dendrite and one axon
• Function in the special senses

Unipolar Neurons

• Have one process which comprises an axon
• Most unipolar neurons are sensory neurons
• Resting membrane potential of a plasma membrane is -70 mV

ICF vs ECF

• The ICF is more negative compared to the ECF
• Caused by the distribution of ions in the ECF (Na+ and Cl-) vs. ICF (K+ and amino acids)

Depolarization

• Na+ channels open and Na+ goes from the ECF to the ICF and it reaches threshold

Threshold

• Threshold is -55 mV
• Reversal of the action potential and repolarization occur at +30 mV

Repolarization

• K+ channels open and K+ exits the cell from the ICF to the ECF

Hyperpolarization

• More K+ exits the cell to make the ICF even more negative

Absolute Refraction

• Period of a stimulus during and just after an action potential when the membrane can’t respond
• Period of lost excitability because no action potential can occur.

Relative Refractory

• Most Na+ channels have returned to their resting state, some K+ channels are still open, and repolarization is occurring
• Since the Na+ and K+ is now out of balance the Na+/K+ channel must pump out three Na+ out into the ECF and two K+ into the ICF

Nuclei

• Collections of cell bodies within the CNS like those in the thalamus and hypothalamus

Ganglia

• Collections of cell bodies in the PNS

Tracts

• Groups of axons in the CNS like the spinocerebellar tracts and corticospinal tracts

Nerves

• Groups of axons in the PNS like the cranial nerves and spinal nerves

Two Types of Matters in the CNS

• White matter and gray matter
• White matter contain myelinated fiber tracts like axons

Grey Matter

• Collections of cell bodies
• Dendrites
• axon terminals
• neuroglia
• nonmyelinated fibers

Potentials

• The white matter contains the fastest transmission of potentials because it has myelinated sheaths

Saltatory Conduction

• Because electrical impulses (action potentials) leap from Node of Ranvier (gap in myelin sheath) to Node of Ranvier because of the diameter of the axon and the degree of myelination

Continuous Conduction

• Slower conduction of impulses in nonmyelinated axons

Compare Graded Potentials

• Potentials that travel short distances on the dendrite or cell body (so short lived)

Characteristics About Graded Potentials

• Referred to as postsynaptic potentials
• Decrease in amplitude
• Open ligand/chemically gated channels

Is EPSP

• Excitatory post synaptic potential

Membrane Potential During An EPSP

• Depolarization of the membrane so it becomes less negative and moves towards threshold (but does not reach threshold so referred to as subthreshold)

Ions

• Pass through membrane proteins
• Na+ enters the cell and K+ exits the cell simultaneously

IPSP

• Inhibitory post synaptic potential

Membrane Potential During An IPSP

• Hyperpolarization of the membrane so the ICF becomes more negative and moves away from threshold

Ions

• K+ exits the cell or Cl- ions enter the cell
• Multiple EPSPs in a row summate to make an action potential

Row Result

• There is no action potential produced

More Characteristics

• Occur on axons and travel all the way down the axons to the axon terminal
• Are all the same (all-or-none rule) so they do not increase or decrease in amplitude and involve voltage-gated channels

Main Steps in Synaptic Transmission

• Chemical synapses
• The Space between the axon terminal and the next neuron or muscle

Action Potential

• Arrives at the axon terminal (also called synaptic bulb or synaptic knob)
• Play a Role with Ca2+ at the Axon Terminal
• Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal

Post Synaptic Membrane

• Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane

Gated Potentials

• binding of the neurotransmitter opens ion channels and creates graded potentials (either an EPSP or IPSP)

The Neurotransmitter

• Terminated (if it is acetylcholine then acetylcholinesterase breaks it into two parts
• be removed from a synaptic cleft by Reuptake by the presynaptic neuron and diffusion

Two Types Of Synapses

• Electrical and chemical
• type of chemical synapses is axodendritic
• axosomatic
• axoaxonic

Purpose Of Channels

• Neurotransmitters bind to ligand or chemical gated channels
• Creates graded potentials (either an EPSP or IPSP)

Purpose For Where Are They Found?

• Charged ions flow through voltage gated channels
• Depolarize or repolarize plasma membranes
• They are involved in action potentials

Neurotransimtters

• Acetylcholine (ACh): EPSP, released by motor neurons that innervate skeletal muscles
• IPSP in cardiac muscle.

NE

• Norepinephrine releases enhanced by amphetamines
• Dopamine is an EPSP or IPSP and deficient in Parkinson’s disease
• Provides reward or pleasure
• Serotonin is IPSP, regulates mood and relieves anxiety and depression
• GABA: Main inhibitor in brain (effects increased by alcohol and antianxiety drugs)
• Glutamate: Learning, memory and released when a stroke occurs
• Endorphin: Inhibits pain
• Substance P is and mediates pain in the PNS

Depolarizes

• An EPSP increases the charge

Hyperpolarizes

• An IPSP decreases the charge