Muscle Tissue Types and Properties

Muscle Tissue Types

• Skeletal, cardiac, and smooth muscles are the three types of muscle tissue.
• Voluntary muscle tissue is skeletal.
• Cardiac and smooth muscles are involuntary.
• Multinucleated muscle tissue is skeletal.
• Striated muscle tissues are skeletal and cardiac.
• Smooth and cardiac muscles have one or two nuclei.
• Cardiac muscle has intercalated discs.
• Muscle tissue types differ in nervous control, thin and thick filament arrangement, binding locations, and locations.

Properties of Muscles

• Muscles possess four special properties: excitability/irritability, contractility, extensibility, and elasticity.
• Excitability/irritability refers to a muscles ability to receive and respond to stimuli.
• Contractility refers to a muscles ability to shorten forcibly upon stimulation.
• Extensibility is the property of a muscle that allows it to stretch without damage.
• Elasticity is a muscle's ability to recoil to its resting length after stretching.

Muscle Tissue Functions

• Movement, posture maintenance, movement of body structures, stabilizing joints, and generating heat are major functions of muscle tissue.
• Skeletal muscles facilitate all locomotion and manipulation.
• Muscular system maintains posture through continuous contraction of skeletal muscles via spinal reflexes.
• Smooth muscle in blood vessel walls and digestive, urinary, and reproductive tracts facilitates movement of body structures.
• Muscles stabilize joints by strengthening them.
• Heat is generated when skeletal muscles contract, raising body temperature.

Connective Tissue Layers

• Epimysium, perimysium, and endomysium are the three connective tissue layers surrounding skeletal muscle.
• Epimysium surrounds entire skeletal muscle.
• Perimysium surrounds a fascicle.
• Muscle fascicles consist of bundles of muscle fibers running parallel in skeletal muscle.
• Endomysium surrounds individual muscle fibers.

Sarcomere

• Sarcomere is the structural and functional unit of skeletal muscle.
• H zone, A band, Z disc (line), and I band are the major regions of the sarcomere.
• The H zone contains only actin fibers and disappears during muscle contraction.
• The A band is a region with both myosin and actin filaments; appears darker than the I band and runs length of myosin.
• The Z disc (line) borders the sarcomere, separating neighboring sarcomeres.
• The I band contains the Z disc (line) in the center and only actin filaments, making it lighter than A bands.

Sarcolemma and Related Structures

• Sarcolemma is the plasma membrane of the sarcomere that contains Na+ and K+ gates, which allow action potentials to travel down it.
• Sarcoplasmic reticulum is an organelle storing Ca+ ions until released into sarcoplasm for cross-bridge coupling.
• Myofibrils are thread-like contractile organelles in skeletal muscle fibers.
• T (transverse) tubules are extensions of sarcolemma that extend inward to the muscle next to the terminal cisternae of the sarcoplasmic reticulum.
• Sarcoplasm is the cytoplasm of muscle cells that receives Ca+ ions from the sarcoplasmic reticulum.
• Triad is a T (transverse) tubule with two terminal cisterns for sarcoplasmic reticulum.
• Myoglobin is an oxygen-binding molecule found in muscle.
• Glycosomes are organelles within skeletal muscle that contain glycogen.

Sliding Filament Model

• Thin filaments slide past thick filaments during the sliding filament model of contraction.
• Actin forms thin filaments.
• Myosin forms thick filaments.
• Myosin filaments appear thicker and darker compared to actin.
• Actin filaments appear thinner and lighter.

Neuromuscular Junction

• Neuromuscular junction refers to the axon terminal associated with skeletal muscle.
• Somatic motor fibers are the nerves that go to skeletal muscle.
• The motor end plate is the region of the sarcolemma that has acetylcholine (ACh) receptors.
• ACh is released into the synaptic cleft and binds to ACh receptors for a muscle to contract.
• Na+ channels open when ACh binds to its receptors to allow Na+ influx and initiate an action potential on the sarcolemma.

Excitation-Contraction Coupling & Motor Units

• The sarcolemma is excited by an action potential during excitation-contraction coupling.
• Depolarization and repolarization are the steps in an action potential.
• Na+ moves from the ECF into the ICF through a Na+ protein channel during depolarization.
• K+ moves from the ICF into the ECF through a K+ protein channel during repolarization.
• The action potential travels down the sarcolemma into the T (transverse) tubules.
• The action potential leads to the release of Ca2+ ions from the terminal cisternae of the sarcoplasmic reticulum, resulting in contraction.
• A motor unit consists of a somatic motor neuron and all the skeletal muscle fibers it stimulates.
• Motor units vary; finely controlled motor units have one motor neuron and few skeletal muscle fibers, and coarsely controlled muscles have one motor neuron and many muscle fibers.

Muscle Contraction

• Calcium and ATP are required for skeletal muscle contraction.
• Calcium interacts with troponin, which makes the myosin binding site on actin available.
• ATP interacts with myosin, which breaks down ATP (myosin acts as an ATPase) and forms a cross-bridge with actin.
• Troponin and tropomyosin are the two regulatory molecules that block the myosin binding site on actin.
• In the cross-bridge cycle, myosin forms cross-bridges with actin.
• Myosin heads (ATPases) are energized by ATP and physically move to bind to myosin binding sites on actin.
• Two ATPs are required per cycle.
• Myosin pulls actin toward the sarcomere's center during the power stroke, allowing myofilaments to slide over one another.
• Another ATP is required for myosin (ATPase) to detach from the myosin binding site on actin after the power stroke.
• Calcium returns to storage in the terminal cisternae of the sarcoplasmic reticulum, and ACh is deactivated, causing muscle relaxation.
• Rigor mortis occurs when there is no ATP available to break cross-bridges.

Muscle Twitch Periods

• Latent, contraction, and relaxation are the periods of a muscle twitch and are measured on a myogram.
• The latent period occurs after the excitation-contraction coupling period, when Ca2+ begins to exit the sarcoplasmic reticulum into the sarcoplasm (cytosol of sarcomere).
• Cross-bridges are active, and the myogram tracing rises to a peak during the contraction period.
• Calcium is pumped back into the sarcoplasmic reticulum during the period of relaxation.

Muscle Metabolism

• The three types of muscle metabolism include direct phosphorylation, anaerobic respiration, and aerobic respiration.
• Muscle metabolism produces ATP
• Enzymes and heat can increase the rate of metabolism.
• Direct phosphorylation involves the transfer of a phosphate group from creatine phosphate to ADP to make ATP, lasting about 15 seconds.
• Anaerobic respiration involves breaking down glycogen into glucose and then glycolysis which occurs where pyruvic acid (product from glycolysis) is converted to lactic acid due to a lack of oxygen (2 ATP per glucose molecule; lasts about 60 seconds).
• Aerobic respiration involves breaking down glycogen into glucose and then glycolysis, which occurs with oxygen so pyruvic acid (product from glycolysis) results in cellular metabolism and more ATP (36 ATP per glucose molecule).
• Complete glucose breakdown produces CO2, H2O, and 36 ATP, called cellular respiration.
• Around 40% of the ATP is converted to mechanical energy to form cross-bridges (myosin).
• Around 60% of ATP is converted into heat by skeletal muscle shivering.
• Blood moves to superficial layers via blood moving through capillaries and sweating.
• Energy from aerobic respiration lasts hours and is the most efficient, while anaerobic respiration provides the most strength.
• When ATP production cannot keep up with the demands of the body, ionic imbalances, lactic acid production, and lack of muscle contraction occur.
• Oxygen debt is the amount of oxygen needed to restore the muscle to its resting state.

Muscle Contraction and Response

• A muscle twitch refers to the brief contraction of all muscle fibers in a motor unit in response to a single action potential.
• Threshold stimulus is the lowest strength of stimulus required to get a muscle contraction.
• Graded muscle responses depend on the number of action potentials affecting the muscle and vary based on the level of motor unit recruitment.
• The treppe stage of muscle contraction occurs when muscle contractions become more efficient, and wave summation starts to occur.
• Characteristics of the treppe stage graded response is that contractions are complete, the first contraction is the weakest, and subsequent contractions get stronger and heat increases.
• Incomplete tetanus is an abnormal muscle contraction with unfused wave summation.
• Complete/fused tetanus refers to the loss of muscle relaxation; a period of sustained skeletal muscle contraction in which individual twitches fuse into one contraction, which is normal muscle contraction due to fused wave summation.
• Temporal wave summation occurs when a second stimuli happens before the muscle has a chance to relax completely, which leads to fused muscle summation.

Types of Muscle Contractions

• Isometric and isotonic (concentric and eccentric) are the two types of muscle contractions.
• Isometric contractions occur when there is no change in length, thus no sarcomere shortening; cross-bridges form, but there is no power stroke occurring to cause sliding of filaments.
• Isotonic contractions occur when myofilaments slide over one another due to myosin forming cross-bridges and pulling the actin filaments towards the H zone.
• Isotonic concentric contractions occur when muscle shortening happens
• Isotonic eccentric contractions occur when muscle lengthening happens.
• Muscle tone is a slightly contracted state from alteration of motor unit stimulation by spinal reflexes.
• Degree of muscle stretch, frequency of stimulation, and the number of muscle fibers influence the force of a muscle contraction.

Skeletal Muscle Fibers

• Slow oxidative fibers have a high oxygen environment, fatigue resistance, slow ATPases (myosin), and aerobic metabolism producing 36 ATP per glucose.
• Fast glycolytic fibers have a low oxygen environment, high glycogen levels, are quick to fatigue, contain fast ATPases (myosin), and use anaerobic metabolism for two ATP per glucose.
• Fast glycolytic fibers have more strength but less speed due to not having long-term ATP
• Muscles cannot contract after prolonged tetanus until stores are replenished when fatigue occurs.
• Fast oxidative fibers are both aerobic and anaerobic.
• Hypertrophy is the excessive development of a muscle.
• Atrophy is muscle wasting away or degeneration from lack of use for an extended period.
• Hyperplasia refers to the increase in the amount of muscle cells.

Smooth Muscle

• Maintaining blood pressure in the cardiovascular system, propelling food in the gastrointestinal (GI) tract, and shunting blood between organs in the cardiovascular system are functions of smooth muscle.
• The layers of smooth muscle surrounding blood vessels or parts of the GI tract are circular and longitudinal, with the circular layer directly surrounding the lumen.
• Variations between smooth and skeletal muscle tissue include Calcium’s affinity for calmodulin (smooth) instead of troponin (skeletal), varicosities allowing neurotransmitter binding (smooth) instead of neuromuscular junctions (skeletal), the ability of smooth muscle to adapt to stretch, caveolae (smooth) instead of T-tubules (skeletal), and slower contractions.
• Smooth muscle cells are arranged in sheets of muscle tissue around hollow organs (like blood vessels or the GI tract).
• Smooth muscles contract in unison.
• Peristalsis involves alternating smooth muscle contraction and relaxation that moves food along the GI tract.
• Acetylcholine causes smooth muscle contraction.
• Norepinephrine relaxes bronchioles and constricts blood vessels.

Skeletal Muscle Organization

• Skeletal muscles are organized into functional groups separated by connective tissue.
• Agonist, antagonist synergist, and fixator are all within a functional group.
• Agonist is responsible for producing specific movement.
• Antagonist opposes the agonist.
• Synergist helps the agonist by reducing undesirable movement.
• Fixator acts as a synergist and stabilizes the origin of the agonist.
• Muscles are named based on location, shape, size, fiber/fascicle direction, the number of origins, location of attachments, and muscle action.
• A triangular fascicle arrangement spreads over a broad area and converges at a single tendon.
• Rectus, transversus, and oblique are types of directional muscle fibers.
• Oblique indicates a diagonal arrangement.
• A circular fascicle arrangement surrounds an opening, forming a sphincter (orbicularis oris).
• Multipennate fascicle arrangements involve a muscle inserting that tapers into multiple tendons (deltoid).
• Convergent fascicle arrangements involve widespread expansion with fascicles converging to a common point (pectoralis major).
• Fusiform fascicle arrangements are spindle-shaped with a wide center and narrow ends (biceps brachii).
• Parallel fascicle arrangements include fibers running parallel to the muscle’s longitudinal axis (sartorius).
• Bipennate fascicle arrangements include fibers converging on both sides of a central tendon (rectus femoris).
• Unipennate fascicle arrangements include fibers converging on one side of a tendon (extensor digitorum longus).
• Maximus, medius, and minimus describe the relative size of muscles.

Muscle Attachments and Lever Systems

• Quadriceps femoris has four origins.
• Biceps brachii has two origins.
• Triceps brachii has three origins.
• Sternocleidomastoid is named for its attachments.
• Flexor carpi ulnaris is named for its action.
• Muscles attach to bones via a cord-like tendon extension from the epimysium, while a sheet-like attachment refers to an aponeurosis.
• The two muscle attachments include the origin and insertion.
• The origin attaches to the stationary bone.
• The insertion attaches to the moveable bone.
• The three lever systems are 1st, 2nd, and 3rd degree.
• Effort, load, and fulcrum are the three parts of lever systems.
• Effort refers to the contracting muscle's force to move the load.
• Load refers to the bone and surrounding tissues providing resistance.
• For motion to occur, the effort must exceed the load.

Muscle Functions - Head and Neck

• The buccinator cheek muscle is a powerful sucking muscle participating in mastication and used for whistling.
• The frontalis forehead muscle raises the eyebrows.
• The masseter jaw muscle elevates the mandible and participates in mastication.
• The occipitalis back of head muscle pulls the skin posteriorly.
• The orbicularis oculi eye muscle closes the eye, as in blinking and squinting.
• The orbicularis oris mouth muscle purses and protrudes the lips, as in kissing.
• The platysma neck muscle depresses the mandible.
• The temporalis jaw muscle closes the jaw and elevates and retracts the mandible.
• The zygomaticus cheek muscle elevates the lateral corners of the mouth upward to smile and participates in mastication.
• The sternocleidomastoid neck muscle flexes and laterally rotates the head.
• The trapezius shoulder muscle stabilizes, raises, retracts, and rotates the scapula.

Muscle Functions - Shoulder and Arm

• The deltoid shoulder muscle abducts the arm.
• The latissimus dorsi back muscle extends the arm, adducts the arm, and rotates the arm medially at the shoulder.
• The levator scapula elevates the scapula.
• The rotator cuff muscles include the supraspinatus, infraspinatus, teres minor, and subscapularis.
• Supraspinatus initiates arm abduction and stabilizes the shoulder joint.
• Infraspinatus stabilizes the shoulder joint (rotates the humerus laterally).
• Teres minor stabilizes the shoulder joint (rotates the humerus laterally).
• Subscapularis rotates humerus medially.
• Teres major extends, medially rotates, and abducts the humerus, and stabilizes the scapula.
• Biceps brachii flexes the elbow.
• Brachialis flexes the forearm.
• Triceps brachii extends the elbow.
• Brachioradialis flexes the forearm.
• Flexor carpi radialis flexes and abducts the hand at the wrist joint.
• Flexor carpi ulnaris flexes and adducts the hand at the wrist joint.
• Extensor carpi radialis extends and abducts the hand at the wrist joint.
• Extensor carpi ulnaris extends and adducts the hand at the wrist joint.
• Extensor digitorum extends the fingers.
• Pronator teres pronates the forearm.
• Palmaris longus flexes the wrist.

Muscle Functions - Thorax, Abdomen and Leg

• Diaphragm facilitates normal breathing.
• External intercostals move the ribs upward and outward for inspiration.
• Internal intercostals move the ribs downward and inward for expiration.
• Pectoralis major flexes the arm (rotates arm medially and adducts and flexes the arm).
• Pectoralis minor draws the scapula forward and downward when the ribs are fixed.
• Serratus anterior rotates the scapula, resulting in the movement of its inferior angle laterally and upward.
• External obliques (most superficial) flex the vertebral column and compress the abdominal wall.
• Internal obliques flex the vertebral column and compress the abdominal wall.
• Rectus abdominus flexes and rotates the lumbar region of the vertebral column.
• Transversus abdominis compresses abdominal contents.
• Gluteus maximus extends the thigh.
• Gluteus medius abducts and medially rotates the thigh.
• Adductor longus adducts, flexes, and medially rotates the thigh.
• Adductor magnus adducts and medially rotates thigh.
• Gracilis adducts the thigh and flexes and rotates the leg medially.
• The hamstring muscles include the biceps femoris, semitendinosus, and semimembranosus:
  • Biceps femoris extends the thigh and flexes the knee.
  • Semitendinosus extends the thigh and flexes the knee.
  • Semimembranosus extends the thigh and flexes the knee.
• The quadriceps muscles include the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius:
  • Rectus femoris extends the knee and flexes the thigh at the hip.
  • Vastus lateralis extends and stabilizes the knee.
  • Vastus medialis extends the knee.
  • Vastus intermedius extends the knee.
• The sartorius flexes, abducts, and laterally rotates the thigh as well as flexes the knee.
• The tensor fascia lata steadies the knee and trunk.
• The gastrocnemius plantar flexes.
• The fibularis (peroneus) longus plantar flexes.
• The soleus plantar flexes.
• The tibialis anterior dorsiflexes.
• The extensor digitorum longus extends the toes.

Nervous vs. Endocrine System

• Both the nervous and endocrine systems are controlling systems concerned with maintaining homeostasis.
• The nervous system communicates with other neurons via electrical impulses (graded potentials or action potentials) and neurotransmitters.
• The endocrine system communicates with other organs via released hormones into the blood or ECF.
• The nervous system communicates with another neuron within milliseconds.
• The endocrine system communicates with other organs in seconds, minutes, hours, weeks, or months.

Functions of the Nervous System

• The three main functions of the nervous system include sensory input, integration, and motor output.
• Sensory input monitors changes occurring inside and outside the body (afferent input).
• Integration processes sensory input and decides what to do with it.
• Motor output travels from the control center to activate effector organs (muscles and glands), causing a response (efferent).
• The nervous system communicates using graded or action potentials along nerves.

Divisions of the Nervous System

• The central and peripheral nervous systems are the two main parts of the nervous system.
• The brain and spinal cord make up the central nervous system.
• The cranial nerves, spinal nerves, and ganglia make up the peripheral nervous system.
• Sensory (afferent) and motor (efferent) divisions are the two functional divisions of the peripheral nervous system.
• The PNS has voluntary and involuntary divisions.
• The somatic nervous system is voluntary and controls skeletal muscles.
• The autonomic nervous system is involuntary.
• The autonomic nervous system (ANS) controls cardiac muscle, smooth muscle, and glands.
• Sympathetic and parasympathetic nervous systems are the two divisions within the ANS.
• Somatic sensory fibers and visceral sensory fibers are in the sensory (afferent) division.
• Somatic sensory fibers convey voluntary impulses from the skin, skeletal muscles, and joints toward the CNS.
• Visceral sensory fibers convey impulses from visceral organs.

Nervous System Cells

• Glial cells are supporting cells that do not conduct electrical nerve impulses.
• Astrocytes, microglia, ependymal cells, oligodendrocytes, Schwann cells, and satellite cells are the glial cells.
• Astrocytes, microglia, ependymal cells, and oligodendrocytes are in the CNS.
• Schwann and satellite cells are in the PNS.
• Astrocytes support and brace neurons, anchor them to capillaries, control the chemical environment around them, and remove leaked potassium ions/neurotransmitters.
• Microglia are macrophages that phagocytize microorganisms.
• Ependymal cells line ventricles and central cavities inside the brain and spinal cord, circulate CSF around the CNS.
• Oligodendrocytes produce myelin sheaths that tightly wrap the fibers.
• Myelin is made of lipids.
• Schwann cells surround all axons (nerve fibers) in the PNS, produce myelin sheath around thicker nerve fibers.
• Satellite cells surround neuron cell bodies and help to regulate ion concentration.

Neurons

• Neurons (nerve cells) conduct action potentials and are the structural units of the nervous system.
• Neurons survive for a lifetime and have a high metabolic rate.
• Dendrite, cell body (soma), axon hillock (trigger zone), and axon are the main parts of a neuron.
• Dendrites are short numerous regions that receive information.
• The cell body (soma) contains the nucleus in an integrative region.
• Nissl bodies are ribosomes in the cell body.
• The axon hillock is the initial region of the axon where an action potential is generated.
• There is a high amount of Na+ gates that allow for rapid depolarization.
• The axon is the conducting region that leads away from the cell body (soma).

Neuron Types

• The three different types of neurons are multipolar, bipolar, and unipolar.
• Multipolar neurons have the most dendrites and one axon, and are the most common in the CNS. (interneurons and motor neurons)
• Bipolar neurons have one dendrite and one axon (special senses).
• Unipolar neurons have one process that comprises an axon (sensory neurons).

Resting Membrane Potential

• The resting membrane potential of a plasma membrane is -70 mV; the ICF is more negative compared to the ECF, caused by ion distribution (Na+ and Cl- in the ECF vs. K+ and amino acids in the ICF).
• Sodium channels open and sodium goes from the ECF to the ICF during the depolarization phase to reach the threshold.
• Threshold is -55 mV
• At +30 mV there is a reversal of the action potential, and repolarization occurs.
• Potassium channels open, and potassium exits the cell from the ICF to the ECF during the repolarization phase.
• During hyperpolarization, more K+ exits to make the ICF even more negative.
• The absolute refractory period refers to a period of time during and just after an action potential when the membrane cannot respond.
• The relative refractory period is when most Na+ channels have returned to their resting state and some K+ channels are still open and repolarizing.
• SodiumPotassium channels pump three Na+ out into the ECF and two K+ into the ICF.

Nuclei and Matter

• Nuclei refer to collections of cell bodies within the CNS.
• Ganglia refer to collections of cell bodies in the PNS.
• Tracts refer to the groups of axons that are in the CNS.
• Nerves refer to the groups of axons in the PNS.
• The matter types in the CNS include white and gray.
• White matter contains myelinated fiber tracts (axons).
• Gray matter contains collections of cell bodies, dendrites, axon terminals, neuroglia, and nonmyelinated fibers.
• White matter involves the fastest transmission of potentials due to having myelinated sheaths.
• Saltatory conduction occurs in white matter because electrical impulses (action potentials) leap from one node of ranvier to the next.
• Continuous conduction is slower conduction of impulses in nonmyelinated axons.

Graded vs. Action Potentials

• Graded potentials travel short distances on the dendrite or cell body (short-lived).
• Postsynaptic potentials, decreased amplitude, and open ligand/chemically gated-channels define graded potential.
• An EPSP is an excitatory post-synaptic potential.
• Depolarization of the membrane and a movement towards the threshold define it
• Sodium enters, and Potassium exits during an EPSP
• IPSP is an inhibitory post-synaptic potential.
• Hyperpolarization and the movement away from the threshold are indicative of an IPSP.
• Potassium exits or Chloride enters during an IPSP.
• Multiple EPSPs create an action potential.
• Multiple IPSPs cancel out and prevents the formation of an action potential.
• Action potentials occur on axons, are not decreased but they are all equal (all/nothing), and involve voltage-gated channels.

Synaptic Transmission

• Synaptic transmission occurs in chemical synapses and is the space between the axon terminal and the next neuron/muscle.
• Voltage-gated Calcium 2+ channels within the axon terminal open, causing them to enter the axon terminal.
• Vesicles move to the axon terminal membrane due to the entry of Calcium 2+.
• A neurotransmitter (ex. acetylcholine) is released from the synpatic vesicle by means of exocytosis.
• The neutrotransmitter diffused across synpatic cleft and binds to the receptors on the post-synpatic mambrane.
• This binding opens ion channels and creates graded potentials (EPSP or IPSP).
• If acetylcholine is the neurotransmitter then acetylcholinesterase breaks it into two parts to terminate the actions.
• Reuptake (presynpatic neurone) and diffusion are the other ways to get rid of a neutrotransmitter.

Synapse Types

• Electrical and chemical syncapses are the two types
• Chemical connections are most prevalent.
• Axodendritic, axosomatic, and axoaxonic are chemical synapses.
• The axon is the presynaptic membrance and the dendrite is the postsynaptic membrane (axodendritic).
• The axon is the presynaptic membrance and the cell body is the postsynaptic membrane (axosomatic).
• The axon in the presynpatic and postsynaptic membrane (axoaxonic).
• Ligand or chemical gated and voltage gated are plasma membrane channels.
• To initiate an EPSP or IPSP, neurotransmitters bind channels that are chemical/ ligand gated and in the postsynpatic membrane.
• Charged ions pass the voltage gated channels in order to repolarize/depolarize plasma membranes.

Neurotransmitters

• Acetylcholine (ACh) is an EPSP released by motor neurones for contractions, or IPSP in cardiac muscle.
• EPSP/IPSP of Norepinephrine’s (NE) is augmented by amphetamines.
• Dopamine is an EPSP/IPSP and involved in the enjoyment/reward system (Parkinsons is deficient in dopamine).
• Serotonin is an IPSP; regulates mood, SSRIs’ relieve anxiety and depression.
• GABA, which is an IPSP and the core inhibitor, is enhanced by antidepressants / alcohol.
• EPSP and functions in memory and learning or stroke, is Glutamate.
• Endorphin is an IPSP; inhibits pain serving as a normal painkiller, mimics morphine, heroin, etc.
• Substance P is an EPSP which serves as PNS pain mediator.
• EPSP depolarizes and IPSPs hyperpolarizes the membrane.