Chapter 9 & Ch 11 - Muscles and Muscle Tissues & Nervous Tissue and Muscles

KNR 181 - Micheal Torry's Session M, W, F Overview

What are the three types of muscle tissues and how are they different in structure?

What are the three types of muscle tissues and how are they different in structure?

Skeletal muscle -

• attaches to bone, skin, or fascia

• Striations; light & dark bands visible with scope

• Voluntary control of contraction & relaxation

  • Considered voluntary because it is the only under our conscious control. Skeletal muscle is often activated by reflexes.

  • Contracts rapidly but tires easily and must rest after short period (compared to your heart which doesn’t get tired).

  • Can exert tremendous power and is adaptable force needed to pick up a paperclip vs. a heavy dumbbell

Cardiac muscle -

• Occurs only in the heart

• Striated tissue

• Involuntary contraction

  • Makes up the walls of the chambers

  • Contracts without stimulation from the nervous system (intrinsic rhythm set by SA node)

  • But can be manipulated and controlled by the nervous system (sympathetic response) in times where we need heart to speed up

Smooth muscle -

• Found in the walls of hollow visceral organs

  • Smooth, urinary bladder, respiratory passages

  • Functions to force substances through body passages

• Elongated, non-striated tissue

• Slow, sustained, involuntary contraction

  • Action/Myosin present but not myofibrils composing sarcomeres

define excitability

ability to receive and respond to stimulus (muscles respond to neurotransmitter presence/signals contraction)

define contractibility

ability to shorten forcibly upon stimulation (sets muscles apart from other tissue types)

define extensibility

ability to be stretched/lengthened can stretch beyond their resting length when relaxed

define elasticity

ability to return to a resting length after elongation (recoil, resume resting length)

What are the four main functions of muscle?

1) Produce movement - locomotion and manipulating environment

2) Maintain posture - rarely aware of muscles contracting now to maintain our body posture (upright) Function continuously

3) Joint stabilization - most important stabilizing factor is muscles/tendons that cross the joint

4) Produce heat - through contraction which plays a role in maintaining body temperature

Describe the nerve and blood supply for muscle?

One nerve, one artery and one or more veins serve each muscle. These structures all enter or exit near the central part of the muscle and branch profusely through its connective tissue sheaths.

• Each skeletal muscle fiber is generally innervated by one nerve ending.

Skeletal muscle = an organ

• Muscle tissue

• Nervous tissue

• Connective tissue

Richly supplied with blood vessels

• Muscle capillaries

• Oxygen supply; waste removal

Blood - contracting muscles need energy and require continuous delivery of oxygen and nutrients. Muscle cell produces wastes (CO2 and lactate) which must be removed through veins or else contraction could be compromised.

• Capillaries of muscles are long, and winding allow muscle to change lengths and straighten when muscles are stretched.

What are the three components of connective tissue of the muscle and what muscle structures do they protect/surround?

• Supports and reinforces the muscle organ

  • Epimysium: “outside the muscle”

    • Overcoat surrounding the entire muscle of dense irregular connective tissue

    • Sometimes it blends with the deep fascia that lies between neighboring muscles or the superficial fascia deep to the skin

  • Perimysium: “fascicles” “resembles bundle of sticks”

    • Surrounds fascicles (bundles of muscle fibers)

    • around the muscle

    • Each fascicle is a layer of dense irregular connective tissue

  • Endomysium: “within the muscle”

    • Surrounds individual muscle fibers

      • Is a wispy sheath of connective tissue

    • It consists of fine areolar connective tissue

    • Holds things together so that muscles don’t burst out during strong contractions

Define origin and insertion of muscle?

Origin

• Typically, the “less” moveable bone

• Usually proximal

Insertion

• Moveable bone

• Usually distal to the origin

• Usually done through (indirect attachments)

What is the organization structure of muscle (from whole muscle to myofilament)

Muscle (organ) - a muscle consists of hundreds to thousands of muscle cells, plus connective tissue wrappings, blood vessels, and nerve fibers

• Connective Tissue Wrappings - covered externally by the epimysium

Fascicle (a portion of the muscle) - a fascicle is a discrete bundle of muscle cells, segregated from the rest of the muscle by a connective sheath

• Surrounded by perimysium

Muscle fiber (cell) - a muscle fiber is an elongated multinucleate cell; it has a bonded (striated) appearance; surrounded by endomysium

Myofibril (complex organelle composed of bundles of myofilaments)

• appears banded

• Rodlike contractile elements that occupy most of the muscle cell volume. Composed of sarcomeres arranged end-to-end

Sarcomere (a segment of myofibril)

• A sarcomere is a contractile unit, composed of myofilaments made up of contractile proteins.

• Thin (actin) filament

• Thick (myosin) filament

Myofilaments (extended macromolecular structure)

• Thick filaments contain bundled myosin molecules; thin filaments contain actin molecules (plus other proteins). The sliding of the thin filaments past the thick filaments produces muscle shortening.

Describe the regions of the striations in skeletal muscle. What makes up each region of the bands of striated muscles?

Sarcomere - The smallest contractile and functional unit of a muscle fiber.

• It extends in the region between two successive Z-discs.

• Sarcomeres are aligned end-to-end to form a myofibril.

• Alternates light and dark bands.

Thin filament (actin) - Extend across the entire length of the ‘I band’ and partially into the ‘A band’

• Anchored by the ‘Z discs’

• Remember z disc to Z disc is one sarcomere

• Thin filaments are made of actin, troponin, & tropomyosin

• The myosin-binding site on each actin molecule is covered by tropomyosin in relaxed muscle

Thick filament (myosin) - Extend across the entire length of ‘A band’

• Each molecule resembles two gold clubs twisted together

• Each thick filament is surrounded by 6 thin filaments

• Myosin heads will [later] form cross bridges with the thin filaments

• Myofilaments = even small structures

A band - Dark band; overlapping thick & thin, filaments

I band - Light band; only contains thin (blue) filaments

H zone - The midsection of an A band; contains an M-line

Z disc (line) - The “ends” of the sarcomere

• Midsection of the I band

M line- formed by protein myosin, place where myosin thick filament tails are connected

What comprises the A and I bands specifically?

Striations- are the overlapping arrangement of myofilaments and the repeating series of dark and light bands, which are evident along the length of each myofibril.

• The intact muscle fiber, the dark ‘A’ bands, and light ‘I’ bands are nearly perfectly aligned, giving the cell its straited appearance.

What are thick and thin filaments? What do troponin and tropomyosin do?

Two main types of myofilaments:

Thick filaments

• Contain and are called myosin.

• They extend across the entire length of ‘A band’

• Each molecule resembles two gold clubs twisted together

• Each thick filament is surrounded by 6 thin filaments

• Myosin heads will [later] form cross bridges with the thin filaments

Thin filaments

• Contain and are called actin

• Extend across the entire length of ‘I band’ and partially into ‘A band’

• Anchored by the ‘Z discs’

  • Remember z disc to Z disc is one sarcomere

  • Thin filaments are made of actin, troponin, & tropomyosin

  • The myosin-binding site on each actin molecule is covered by tropomyosin in relaxed muscle

Both troponin and tropomyosin help control the myosin-actin interactions involved in contraction.

Describe the molecular composition of thick and thin filaments.

Thick filaments

• During contraction, they both form cross bridges and swivel around their point of attachment, acting as motors to generate force. Myosin itself splits ATP (acts as an ATPase) and uses the released energy to drive movement.

• Contains about 300 myosin molecules bundled together, with their tails forming the central part of the thick filament and their heads facing outward at the end of each molecule

Thin filaments

• Actin has kidney-shaped polypeptide subunits, called globular actin or G actin. Each G actin has a myosin-binding site (or active site) to which the myosin heads attach during contraction.

What is the sarcolemma?

the plasma membrane of a muscle cell

What are T-tubules and sarcoplasmic reticulum?

T-tubules -

• channels that go into muscle cells and glue electrical impulses, release Ca2+, trigger muscle contraction

Sarcoplasmic Reticulum -

• A system of tubular sacs similar to smooth ER in non-muscle cells that surround each myofibril (like the sleeve of a shirt) and stores Ca²⁺ in a relaxed muscle and later releases Ca²⁺ triggering muscle contraction

What is a sarcomere?

• The smallest contractile unit of a muscle fiber (the functional unit)

• The region between two successive Z-discs

• Sarcomeres are aligned end-to-end to form a myofibril

What is the sliding filament theory and what are the six molecules essential for sarcomere contraction?

• Thick and thin don’t change length, and the theory suggests that striated muscles contract through the overlapping of actin & myosin filaments, resulting in a shortening of the muscle fiber length.

The six molecules are:

Actin, Myosin, Trophonin, Tropomyosin, Calcium ions (Ca2+), and ATP

What is and what are the steps in excitation coupling (see page 293)?

series of events that link the action potential of the muscle cell membrane to muscular contraction

Step 1: The action potential (AP) propagates along the sarcolemma and down the T-tubules

Step 2: Calcium ions are released. Transmission of the AP along the T-tubules of triads causes the voltage-sensitive tubule proteins to change space. This shape change opens the Ca2+ release channels in the terminal cisterns of the sarcoplasmic reticulum (SR), allowing Ca2+ to flow into the cytosol.

Step 3: Calcium binds to troponin and removes the blocking action of tropomyosin. When Ca2+ binds, troponin changes shape, exposing myosin-binding sites on the thin filaments

Step 4: Contraction begins: Myosin binding to actin forms cross bridges and contraction (cross bridge cycling) begins, at this point, E-C coupling is over.

What is cross bridges?

form and break several times during a contraction, acting like tiny ratchets to generate tension and propel the thin filaments toward the center of the sarcomere

• Formed between actin and myosin filaments

How does the sliding filament theory work - Describe the key events that lead to a cross bridge being formed?

Myosin binding sites attach to myosin binding sites on actin filaments which form cross bridges

• thin filaments are pulled to the M-line

• I bands shorten on the inside

• contract together when you flex

• z discs come toward each other

What is the neuromuscular junction and define ACh role in it?. Link the stages listed in Fig 9.7 to the pictures on page 290.

Neuromuscular junction - is the region where the motor neuron contacts the skeletal neuron. It consists of multiple axon terminals and the underlying junctional folds of the sarcolemma

ACh - (acetylcholine) - when a nerve impulse reaches a neuromuscular junction, it releases ACh. Upon binding to sarcolemma permeability leads to membrane potential.

What is a motor unit?

one somatic motor neuron & all the skeletal muscle cells (fibers) it stimulates

How are motor units recruited?

based on the motor unit size with smaller units recruited first

• Motor units must be smaller (less fibers/nerve)

• Easily excitable motor units – smallest muscle fibers (get activated first)

What is temporal summation?

two identical stimuli (electrical shocks or nerve impulses) are delivered to a muscle in rapid succession, the second twitch will be stronger than the first. On a myogram, the second twitch will appear to ride on the shoulders of the first

• 2nd contraction occurs before the 1st contraction is completely relaxed (Refractory period is only 5-10ms) muscle is already partially contracted, more calcium is being released (because another AP been generated) muscle tension produced during the second contraction is greater than the first. Essentially the contractions are summed or added together.

Define unfused/incomplete tetanus?

• Stimulus is applied at an increasingly faster rate; relaxation time between twitches become shorter & shorter; increased Ca2+ presence in muscle

• Results in a sustained but quivering contraction

  • Higher stimulation frequency results unfused tetanus

Define fused/complete tetanus?

• Stimulus application to increase, maximal muscle tension is reached.

• Results in a smooth, sustained contraction plateau

• Infrequent in the real word; ‘superhuman strength’, situations

  • At even higher stimulus frequencies there is no relaxation at all between stimuli. This is fused (compete tetanus)

How is muscle force graded using the size principle of recruitment – see figures 9.13 and 9.14?

Muscle contractions can be graded in several ways:

1) Changing the frequency of the stimulus

2) Changing the strength of the stimulus

3) Motor unit size & recruitment

4) Fiber type

Regardless of what option is selected, the overriding principle that our body will select is based on the conservation of energy

Describe the difference between isometric, concentric, eccentric contractions.

Concentric contraction = a muscle shortens to produce force and movement

Eccentric contractions = a muscle lengthens while maintaining force and movement

Isometric contraction = (same measure) no movement occurs

• Tension is generated without muscle shortening

• Maintain posture & support objects in a fixed position

What is the role of ATP in muscle contraction?

The role of ATP is that it supplies energy to move and detach cross bridges, operate the calcium pump in the SR, and operate the Na+, -K+ pump in the plasma membrane.

• Because ATP is the only energy source used directly for contractile activities, it must be regenerated as fast as it is broken down if contraction is to continue.

Describe major steps in direct phosphorylation, anaerobic pathway, aerobic pathway – figures 9.16 and 9.17.

Direct Phosphorylation

Coupled reaction of creatine phosphate (CP) and ADP

Energy source: CP

Oxygen use: NONE

Products: 1 ATP per CP, creatine

Duration of energy: 15 seconds

• A unique high-energy molecule stored in muscles is topped to regenerate ATP while other metabolic pathways adjust to the sudden high demand for ATP

• The fastest pathway

Anaerobic Pathway

Glycolysis and lactic acid formation

Energy source: glucose

Oxygen use: NONE

Products: 2 ATP per glucose, lactic acid

Duration of energy: 30-40 seconds

Aerobic Pathway

Energy source: glucose; pyruvic acid; free fatty acids from adipose tissue; amino acids from protein catabolism

Oxygen: Required

Products: 32 ATP per glucose CO2, and H2O

Duration: Hours

• The slowest pathway

Describe length tension relationship of sarcomeres in skeletal muscle – figure 9.19.

• Depends on the number of myosin cross bridges that are attached to actin

  • Number of muscle fibers recruited

    • More motor units, more force

  • Size of muscle fibers

    • Greater the cross-sectional area the more force it can produce

    • Hypertrophy - Regular resistance exercise increases muscle force by causing muscle cells to increase in size.

  • Frequency of stimulation

    • The higher the frequency, the more force (wave summation)

  • Degree of muscle stretch

    • Provides for optimal overlap of actin/myosin

    • 80-120% of resting length

      • Increases & decreases reduce the ability to generate tension

What are slow fibers and fast fibers?

Slow twitch (slow oxidative) - which moves more slowly but helps to keep you moving longer

• Red in color (lots of mitochondria, myoglobin, & blood vessels)

• Resist fatigue, and sustained contractions to maintain posture

  • Endurance specialists relying on aerobic metabolism

Fast twitch (fast oxidative) - which helps move faster, but for shorter periods

• Pink in color (lots of mitochondria, myoglobin, & blood vessels)

  • Spilt ATP at a very fast rate; contract quickly

What are oxidative fibers and glycolytic fibers?

Oxidative fibers -cells that rely mostly on the oxygen-using aerobic pathways for ATP generation

Glycolytic fibers - these fibers primarily create ATP through anaerobic glycolysis resulting in less ATP per cycle. As a result, they fatigue more rapidly. (Quick, but tire out faster)

Understand how skeletal muscles differ from smooth and cardiac about the presence of myofibrils, t-tubules, regulation of contraction, site of calcium regulation, speed of contraction, and metabolism.

Body of Location (Smooth) - unitary muscle in walls of hollow visceral organs (other than the heart); multi-unit muscle in intrinsic eye muscles, airways, and large arteries

_____

Prescence of myofibrils

Cardiac - Yes, but myofibrils are of irregular thickness

Smooth - No, but actin and myosin filaments are present throughout; dense bodies anchor actin filaments

________

Presence of T-tubules

Cardiac - Yes; one per sarcomere at Z disc; larger diameter than those of skeletal muscle

Smooth - No; only caveolae

________

Regulation of contraction

Cardiac - Involuntary; contraction initiated by intrinsic pacemaker cells; regulated by autonomic nervous system, hormones, and stretch

Smooth - Involuntary; initiated by intrinsic pacemaker cells (in unitary muscle) or autonomic nerves (in multi-unit muscle) regulated by local chemicals, hormones, and stretch

---

Site of calcium regulation

Cardiac - Troponin on actin-containing thin filaments

Smooth - calmodulin in the cytosol

_____________________________________________________

Speed of Contraction

Cardiac - Slow

Smooth - Very Slow

___________________________________________________

Metabolism

Cardiac - Aerobic

Smooth - Mainly aerobic

Define muscular dystrophy

Refers to a group of genetic diseases that cause progressive weakness and degeneration of skeletal muscles.

• trouble using arms

• trouble walking

• frequent falls

How does muscular system help: integumentary system, endocrine system, digestive system.

Integumentary System

• Muscular exercise enhances circulation to skin and improves skin health

• Skin protects the muscles by external enclosure; helps dissipate heat generated by the muscles

Endocrine System

• Growth hormone and androgens influence skeletal muscle strength and mass; other hormones help regulate cardiac and smooth muscle activity

Digestive System

• Physical activity increases gastrointestinal motility; skeletal muscle forms the voluntary sphincter of the anus

• Digestive system provides nutrients needed for muscle health; liver metabolizes lactic acid

CH 11

Understand the biology of addiction

the dopamine you get from the drug makes you want to keep doing it, once you don’t have it you keep it doing it the same way so addiction

Define sensory input, integration, motor output of the nervous system

Controls and integrates all body activities that maintain life

Three “overlapping” functions:

• Sensory input - Sensory receptors monitor internal/external changes

• Integration - Process and interpret the input information

• Motor output- Responds to the change

What is the major organization and what are the major divisions of the CNS and PNS – Figure 11.3

Central Nervous System (CNS) – occupies the dorsal body cavity. Interprets sensory input and dictates motor output based on reflexes, current conditions, and experience

• Brain

• Spinal Cord

Peripheral Nervous System (PNS) – outside of CNS, consists of nerves that extend from the brain and spinal cord and ganglia

• Spinal nerves – carry impulses to and from the spinal cord

• Cranial nerves - carry impulses to and from the brain

• Ganglia – collections of neuron cell bodies

Functional divisions of the Peripheral Nervous System (PNS) include:

• Sensory (afferent)

  • Transmits signals/input towards the CNS

• Motor (efferent)

  • Transmits signals away from the CNS

• Two motor divisions:

  • Somatic nervous system – skeletal muscles, voluntary

  • Autonomic Nervous System (ANS) – involuntary, cardiac muscle, smooth muscle, and glands

  • The ANS itself has two branches:

    • Sympathetic Nervous System: Prepares the body for “fight or flight” responses.

    • Parasympathetic Nervous System: Promotes relaxation and conserves energy.

What are the functions of the neuroglia in the CNS; astrocytes, microglial cells, ependymal cells, oligiodendrocytes

Astrocytes

• Functions:

  • Star-shaped

  • Most abundant

  • Hold neurons in place

  • Link neuron with capillary

  • ‘Mop up’ leaked potassium ions and recapture and recycle neurotransmitters

Microglia

• Thorny processes

• Monitor the health of neuron(s)

• Phagocytize microorganisms or neural debris after injury

  • Protective role is important because the immune system has limited access to the CNS

Ependymal cells

• “Wrapping garment”

  • Line cavities of the brain and spinal cord

  • Cilia-movement of cerebrospinal fluid in cavities

    • Can be squamous or columnar, and many are ciliated

    • Line the central cavities of the brain and spinal cord

    • Cilia help circulate CSF

Oligodendrocytes

• Wrap CNS nerve fibers

  • Wrap their processes around CNS neurons

  • Produce covering called myelin sheath

What are the functions of the neuroglia in the PNS; satellite cells, schwann cells

Satellite cells – named for their moon-like appearance

• Function similar to astrocytes of the CNS

• Supporting/bracing/communication between neurons and nearby capillaries

Schwann cells

• Similar to oligodendrocytes of the CNS

  • Surround and form myelin sheaths around peripheral nerve fibers

What are neurons and what are their major structural components – Figure 11.3

Neurons (nerve cells) = structural units in the nervous system

• Receive/transmit messages in the form of nerve impulses

• Three characteristics of neurons

  • Extreme longevity

  • Amitotic - lost their ability to divide

  • High metabolic rate - need abundant supplies of O2 and glucose

• Axon - Transmits signals away from the cell body

• Cell body- Spherical nucleus: biosynthetic center (control center) houses normal organelle located in cell cytoplasm to make proteins and other chemicals

• Dendrites- Receive signals entering the cell body

• Lots of Rough ER (called Chromatophilic substance)

  • Most cell bodies are located in the CNS where they are protected by the bones of the skull and vertebral column

    • Clusters of cell bodies in the CNS = nuclei

    • Clusters of cell bodies in the PNS = ganglia

What is myelination of the PNS, how does it form and why is it important?

Myelination - is a crucial process in the nervous system PNS

• Refers to the formation of a myelin sheath around neuronal axons

• Myelin sheaths are composed of lipids & proteins and has a whitish appearance

• It consists of many concentric layers of plasma membrane, creating a protective covering around the axons

  • Schwann cells play a crucial role

  • They wrap around large-caliber axons forming the myelin sheath

  • Schwann cells insulate axons, allowing for rapid conduction of nerve impulses

    • The smallest-diameter axon are nonmyelinated.

    • These nonmyelinated axons are covered by the long extensions of adjacent glial cells

What is myelination of the CNS called, why is it important?

can greatly increase the speed of signals transmitted between neurons

Oligodendrocytes – from myelin sheaths

White matter:

• Regions in brain/spinal cord containing dense collections of myelinated fibers

Gray matter:

• Regions of CNS containing mostly cell bodies and unmyelinated fibers

Multiple Sclerosis (MS)

• An acquired inflammatory demyelinating disorder affecting the CNS

What are the functions of the sensory afferent neurons?

• transmit impulses from sensory receptors in the skin or internal organs toward or into the CNS

• bringing sensory information from the outside world into the brain

• detecting and responding to external signals

• virtually all sensory neurons are unipolar, and their cell bodies are located in sensory ganglia outside the CNS

What are the functions of the motor efferent neurons?

• carry impulses away from the CNS to the effector organs (muscles & glands) of the body

• Motor neurons are multipolar

• Expect for some neurons of the autonomic nervous system, their cell bodies are located in the CNS

What are ion channels; what are ligand gated channels, voltage gated channels, mechanically gated channels?

Ion channels - which allows ions to pass through channel pore including sodium, potassium, calcium, and chloride ions to pass through the impermeant lipid cell membrane

Ligand-gated channels - (chemically gated channels) - open when the appropriate chemical (in this case a neurotransmitter) binds

Voltage-gated channels - open & close in response to changes in the membrane potential

Mechanically gated channels - open in response to physical deformation of the receptor (as in sensory receptors for touch and pressure)

What is the sodium potassium pump and what does it do – pg 400

• is a transmembrane protein pump that transports sodium & potassium ions across the cell membrane

• The pump uses ATP to move 3 sodium ions out of the cell and two potassium ions into the cell

• this creates a concentration gradient of sodium & potassium ions which helps, establish the resting membrane potential of cells, especially neurons

What is a neuron membrane potential – Figure 11.8; how does it change in depolarization, hyperpolarization and what is the physiology of this potential?

the potential difference between an electrode inside a neuron and the ground electrode in the extracellular fluid is approximately -70mV (inside negative)

• Depolarization - is a decrease in the membrane potential. The inside of the membrane becomes less negative (moves closer to zero) than the resting potential.

• Hyperpolarization - is an increase in membrane potential: the inside of the membrane becomes more negative (moves farther) than the resting potential.

  • A resting (non-signaling) neuron has a voltage across its membrane called the resting membrane potential. Is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion.

What is salutatory conduction; why is it important?

• Saltire = ‘to leap’ (30 times faster)

• AP’s generated at gaps in myelin sheath

  • They appear to jump rapidly

  • Myelin prevents almost all charge from leaking from the axon and allows the membrane voltage to change more rapidly

• Saves energy by decreasing the use of sodium-potassium pumps in the use of sodium-potassium pumps in the axonal membrane. It also increases the speed of conduction, allowing the organism to react and think faster.

What are the three axo- synapses – fig 11.16

Axodendritic synapses - are the most common types of synapses

• They occur between the axon terminal of one neuron and the dendrite of another neuron

• Allow for communication & signal transmission between neurons

Axosomatic synapse - occurs between the axon terminal of one neuron and the cell body soma of another neuron

• These synapses can influence the overall excitability of the post-synaptic neuron

• Play a role in regulating neuronal firing and maintaining homeostasis

Axoaxonic synapse - between the axon terminal of one neuron and the axon of another neuron

• These play a regulatory role by modulating neurotransmitter release

• They can enhance or inhibit the release of neurotransmitters from the pre-synaptic neuron

• Axoaxonic synapses are found throughout the CNS, including in the hippocampus, cerebral cortex, and stratum in mammals

How does ACh work across NMJ synapses? Pg 410 and Fig 11.3

ACh crosses the synaptic gap and binds to ACh receptors tightly clustered on the surface of the muscle fiber; this leads to the endplate potential (EPP) which initiates the muscle action potential that results in muscle contraction

• Reabsorbed & recycled ready to transmit another chemical message

What is temporal summation?

A rapidly firing presynaptic neuron causes EPSPs that are close in time.

From Table 11.3, pg 419-420 - What are neurotransmitters and what are the major functions of the following neurotransmitters:

Glutamate

Dopamine

Serotonin

Histamine

Endorphins

Norepinephrine

Epinephrine

ACh

Neurotransmitters - are your body’s chemical messengers. They play a crucial role in transmitting signals from nerve cells to target cells, which can be other nerve cells, muscle cells, or glands cells.

Cell body: Vital for producing neurotransmitters and maintaining nerve cell function

Axon: Carries electrical signals along the nerve cell to the axon terminal

Axon terminal: where the electrical message is converted to a chemical signal using neurotransmitters

Glutamate: generally excitatory; direct action (dedicated to learning & memory)

Dopamine: feel good or motivational drive

Serotonin: mainly inhibitory; stabilizing mood, and plays a role in sleep, appetite, nausea, and migraine headaches

• Drugs that block its uptake relieve anxiety and depression.

Histamine: excitatory or inhibitory depending on receptor type bound; accelerating heart rate, and acting as the brain, spinal cord, and uterus

Endorphins: generally inhibitory; relieve pain, reduce stress

Norepinephrine (NE): excitatory or inhibitory; increasing alertness, arousal, and attention

Epinephrine: or adrenaline is a hormone and a neurotransmitter that boosts your heart rate, blood pressure, and energy in stressful situations

ACh: acts at two classes of receptors: nicotinic and muscarinic

• regulates the levels of other neurotransmitters in the brain

What is a neurotoxin and what is neuropathy?

Neurotoxin - substance that is poisonous or destructive to nervous tissue, eg. botulinum & tetanus toxins

Neuropathy - any disease of nervous tissue, but particularly degenerative diseases of nerves