anatomy & physiology lecture exam 2

isotonic contraction

"same tension" -the muscle length changes, so movement occurs (i.e., it's a dynamic contraction) -shortens or lengthens the muscle (muscle changes length)

oligodendrocytes

#2 = oligodendrocyte #3 = microglia #1 = astrocyte

F-actin

(filamentous actin) made up of globular G-actin subunits; has active sites (= myosin-binding sites)

sensory (afferent ) neurons

(unipolar neurons) carry information from sensory receptors to the CNS - The main sensory receptor types: interoceptors, exteroceptors, proprioceptors

indirect effects via intracellular enzymes

- E.g. lipid-soluble gases like nitric oxide (NO) and carbon monoxide (CO) - There is no receptor; these NTs are small and lipid-soluble, and thus easily diffuse into the cell and bind to intracellular enzymes, producing secondary messengers, which may: • Open ion channels - AND/OR - • Change the metabolism of the cell

Length-tension relationship of smooth muscles

- If you stretch smooth muscle, it adapts to its new length, and it can then contract again - The range of lengths over which smooth muscle contraction can occur is 4X that of skeletal muscle (this property is called plasticity)

Functions of muscle tone

- Stabilize bones and joints - Maintain body position (posture) - Allow more rapid activation of a whole muscle (i.e., accelerate recruitment) - ↑ Energy usage when muscles are at rest (i.e., ↑ resting metabolic rate) - Lookin' good!

directs effects (of neurotransmitters)

- The receptor is an ion channel - The binding of the NT directly opens or closes the ion channel

indirect effects via G proteins

- The receptor is not an ion channel - Mechanism of action: 1. NT binds to the receptor 2. A G protein is activated 3. The activated G protein may activate a second messenger (e.g. cAMP), which may: - Open ion channels - AND/OR - - Activate intracellular enzymes, which change the metabolism of the cell

The nervous system includes all of the neural tissue of the body, which has two main types of cells

- The supporting cells of the nervous system are called NEUROGLIA (or glial cells) - The basic functional cells of the nervous system are NEURONS

Muscle contraction requires lots of ATP energy (don't memorize the numbers, just make sure you got the gist of the concept)

- There are ~ 15 billion thick filaments per muscle fiber - When a muscle fiber is actively contracting, each thick filament breaks down ~ 2,500 ATP molecules per second - 15 billion X 2,500 = 37.5 X 1012 = 37,500,000,000,000 ATPs are needed per muscle fiber per second! • There's only enough ATP stored in muscle fibers for about 2 seconds of maximal (tetanic) contraction

3 types of axons

- Type A fibers: • Largest • Myelinated • Speed = up to 120 m/sec (268 mph!) carry sensory info on fast pain, body position,balance, and delicate touch, as well as somatic motor commands - Type B fibers: • Medium sized • Myelinated • Speed = about 18 m/sec (40 mph) - Type C fibers: • Smallest • Unmyelinated • Speed = about 1 m/sec (2 mph) • Type B and C fibers carry sensory info on temperature, slowpain, general touch, as well as visceral (autonomic) motor commands

• Moderately active skeletal muscle: (part of aerobic metabolism)

- Uses larger quantities of mostly pyruvate (from glycolysis) and free fatty acids (from the bloodstream) as substrates

• Resting skeletal muscle: (part of aerobic metabolism)

- Uses small quantities of mostly free fatty acids (from the bloodstream) as substrates

• Spinal nerves (31 pairs) exit at specific segments of the spinal cord, and contain two roots each:

- Ventral root - contains motor axons - Dorsal root - contains sensory axons • I.e., spinal nerves are mixed nerves • Dorsal root ganglion - contains sensory neuron cell bodies

Passive (leak) channels

- are always open - These channels are important for establishing the resting potential

lactate (lactic acid) removal and recycling

- at rest, lactate can be converted back to pyruvate (both by muscle fibers, and, via the Cori cycle, the liver - clears extra lactic acid from bloodstream); the pyruvate can then be burned aerobically and/or used to synthesize glucose and replenish glycogen reserves

motor (efferent) neurons

- carry information away from the CNS to effectors (muscles, glands, and adipose tissue)...multipolar neurons

multipolar neurons

- have more than two processes - They are the most common type of neuron - E.g. motor neurons and interneurons

unipolar neurons

- have one process (that connects to a continuous axonal fiber) - E.g. sensory neurons

bipolar neurons

- have two distinct processes • They are relatively rare • They are special sensory and found in the eye, ear, and nose

anaerobic endurance

- maximum or near maximum effort, shorter duration (up to 2 minutes) - Improvements are due mainly to hypertrophy, which is an increase in the size (diameter) of muscle fibers (sprinters = more muscular/bulky) - It's limited by: • ATP/CP availability • Glycogen/glucose availability • Tolerance for acidosis (due to lactate production) - anaerobic threshold

Active (gated) channels

- may be open (activated) or closed - Note that "active" does not refer to ATP use in this case

Interoceptors

- monitor (detect changes in the conditions of) internal organ systems - E.g. sensing heart rate, blood pressure, deep pressure/pain (period cramps), etc.

mental/motivational fatigue:

- ↓ pH harms neurons in the brain (causing ↑ pain/weariness, ↓ desire)....runner's high counteracts this

microglia

-"little glue" -remove cell debris, wastes and pathogens by phagocytosis (eats the bad stuff)

ATP generation in moderately active skeletal muscle

-"moderate" = sub-maximal intensity -demand for ATP increases -there is still enough oxygen for the mitochondria to meet that demand, but no excess ATP is produced -the muscle fiber now relies primarily on the aerobic metabolism of glucose from stored glycogen to generate ATP -if the glycogen reserves are low, the muscle fiber can also break down other substrates, such as fatty acids -all of the ATP now produced is used to power muscle contraction (36 ATPs per glucose) -not touching creatine phosphate yet...

what is the typical threshold that needs to be reached in order for an action potential to happen

-60 mV

excitatory neurotransmitter

-GO!GO!GO! (action potential) -depolarization -promotes generation of action potentials

inhibitory neurotransmitter

-NO!NO!NO! (action potential) -hyperpolarization -suppresses generation of action potentials

oligodendrocyte

-a cell with a few branches -myelinate CNS axons -provide structural framework

summary of action potentials

-always depolarize -depol. to threshold must occur before action potential begins -all-or-none; all stimuli that exceed threshold produce identical action potentials -action potential at one site depolarizes adjacent sites to threshold -propagated along entire membrane surface w/out decreasing in strength -refractory period occurs

ATP generation in resting skeletal muscle (see page 19 first slide, in chapter 10 slides for picture)

-demand for ATP is low, more than enough oxygen available for mitochondria to meet demand -absorb fatty acids, which are broken down in the mitochondria creating a surplus of ATP -some mitochondrial ATP is used to convert absorbed glucose to glycogen -mitochondrial ATP is also used to convert creatine to creatine phosphate (CP) -this results in the buildup of energy reserves (glycogen and CP) in the muscle

summary of graded potentials

-depolarize or hyperpolarize -no threshold value -amt. of depol. or hyperpol. depends on intesity of stimulus -passive spread from site of stimulation -effect on membrane potential decreases with distance from stimulation site -no refractory period

hormones and muscle metabolism

-growth hormone+testosterone = stimulate synthesis of contractile proteins and enlargement of skeletal muscles -thyroid hormone = elevate rate of energy consumption in resting and active skeletal muscles -epinephrine (adrenaline) - during sudden crisis, stimulate muscle metabolism and increase both the duration of stimulation and force of contraction

smooth muscles functions in diff. systems

-integ.: around blood vessels regulate flow of blood to superficial dermis, of arrector pili elevate hair -cardiovasc.: control distrib. of blood and help reg. blood pressure -respiratory: alters diameters of resp. passageways and changes the resistance to airflow -digestive: move materials along tract, in gallbladder contract to eject bile into dig. tract -urinary:alter rate of filtration in kidneys, transport urine to bladder, force urine out -repro: move sperm, ejection of glandular secretions, move oocytes, expels fetus at delivery

isometric contraction

-iso = same; metric = meter/length -"same length" -no movement occurs (it's a static contraction) -tension is produced, but it isn't strong enough to overcome the load and cause shortening/movement, so the length of the muscle remains the same -ex: maintaining posture against gravity - yoga pose, wall sit, plank

ependymal cells

-line ventricles (brain) and central canal (spinal cord); assist in producing, circulating and monitoring cerebrospinal fluid

intensity and duration of activity are inversely proportional

-lower intensity for marathon, but longer duration -higher intensity for sprint, but shorter duration

astrocytes

-maintain blood-brain barrier -provide structural support -regulate ion, nutrient, and dissolved gas concentrations -absorb and recycle neurotransmitters -form scar tissue after injury

the nervous system

-one of the two organ systems that function to control or adjust the activities of many other systems simultaneously -provides swift and brief responses to stimuli *Compare this to the endocrine system (the body's other major controlling organ system), which adjusts metabolic operations and directs slower and more long-term changes

overview of neuron membrane physiology

-resting potential (in cell body) -graded potential (near exit to axon in cell body) -action potential (in axon) -synaptic activity (telodendria/synaptic knobs/synapse) -information processing (in postsynaptic cell)

satellite cell

-similar to astrocyte in CNS -surround neuron cell bodies in ganglia -regulate oxygen, carbon dioxide, nutrient and neurotransmitter levels around neurons in ganglia

Schwann cells

-similar to oligodendrocytes in the CNS -surround all axons in the PNS -responsible for myelination of peripheral axons -participate in repair process after injury

levels of organizations in a muscle from largest (macroscopic) to smallest unit (microscopic)

-skeletal muscle -muscle fascicle -muscle fiber -myofibril -sacromere (a measure of flesh)

types of muscle fibers

-slow fibers (dark meat): fatter, richer fibers; aerobic, gets better blood supply, marathon runners have more of these fibers in their body -intermediate fibers -fast fibers (white meat): anaerobic, doesn't need as much blood supply, protein rich, sprinters have more of these fibers in their body

muscle fiber conversions

-some fast twitch convert to intermediate -some intermediate convert to slow twitch -never goes backwards...slow cannot become intermediate and intermediate cannot become fast

entire action potential takes about

1 msec to happen

6 functions of skeletal muscle

1. Produce skeletal movement 2. Maintain posture and body position 3. Support soft tissues (e.g. the floor of pelvic cavity) 4. Guard entrances and exits (e.g. the external anal sphincter) 5. Produce heat to help maintain body temperature 6. Store nutrient (protein) reserves

steps of the contraction cycle and cross bridge formation

1. contraction cycle begins 2. active-site exposure 3. cross-bridge formation 4. myosin head pivoting 5. cross-bridge detachment 6. myosin reactivation

4 steps involved in generation of action potentials

1. depolarization to threshold 2. activation of sodium channels and rapid depolarization (membrane potential changes from -60 mV to a positive value) 3. inactivation of sodium channels and activation of potassium channels (when membrane potential reaches +30 mV...repolarization begins) 4. return to normal permeability (closing of potassium channels = brief hyperpolarization, and then membrane potential returns to normal)

3 effects of neurotransmitters

1. direct effect 2. indirect effect via G proteins 3. indirect effect via intracellular enzymes IMPORTANT: the mechanism of action (and effect—either excitatory or inhibitory) of a specific neurotransmitter (NT) ultimately depends upon the receptor type, not necessarily what the specific NT is - I.e., the same NT may be excitatory at one synapse while it is inhibitory at a different synapse, depending upon whether the NT binding to a receptor at the synapse causes the opening of, for example, a Na+ channel (causing depolarization toward threshold) or a K+ channel (causing hyperpolarization away from threshold), respectively

2 types of synapses

1. electrical synapses 2. chemical synapses

4 classes of opiods

1. endorphins 2. enkephalins 3. endomorphins 4. dynomorphins

4 neuroglia in CNS

1. ependymal cells 2. astrocytes 3. oligodendrocytes 4. microglia

2 main types of neurotransmitters

1. excitatory: GO! GO! GO! 2. inhibitory: NO! NO! NO! (to action potentials)

advantages of reflexes

1. fast 2. predictable

what are the 2 sources of calcium in smooth muscle contraction?

1. from sarcoplasmic reticulum (SR) 2. from extracellular fluid (ECF)

3 receptors

1. interoceptors 2. exteroceptors 3. proprioceptors

2 types of contractions

1. isotonic (2 subtypes) 2. isometric (no subtypes)

overview of skeletal muscle contraction

1. neural control 2. excitation 3. release of calcium ions 4. contraction cycle begins 5. sacromeres shortening 6. generation of smooth muscle tension

simple reflex arc

1. receptor 2. sensory neuron 3. info processing in CNS via interneurons 4. motor neurons 5. response by peripheral nerves

3 types of membrane potentials

1. resting potential 2. graded (local) potentials 3. action potentials (nerve impulses)

2 neuroglia in PNS

1. satellite cells (similar to astrocytes in the CNS) 2. Schwann cells (similar to oligodendrocytes in the CNS)

3 neuron classifications by function

1. sensory (afferent) neurons 2. motor (efferent) neurons 3. interneurons (association neurons)

muscle contraction: events at the neuromuscular junction (NMJ)

1. the cytoplasm of the axon terminal contains vesicles filled with molecules of acetylcholine, or ACh. ACh is a neurotransmitter, a chemical released by a neuron to change the permeability or other properties of another cell's plasma membrane. the synaptic cleft and the motor end plate contain molecules of the enzyme acetylcholinesterase (AChE), which breaks down ACh 2. the stimulus for ACh release is the arrival of an electric impulse, or action potential, at the axon terminal. an action potential is a sudden change in the membrane potential that travels along the length of the axon

more on graded (local) potentials

= local changes in the membrane potential that decrease in intensity with distance from the site of stimulation • caused by ions entering or exiting the dendrites and/or cell body through open (activated) chemically gated or mechanically gated membrane ion channels • Results in local depolarization or hyperpolarization - Whether depolarization or hyperpolarization occurs depends on which specific ion channels are opened - stronger stimulus = greater change in membrane potential and larger area affected -occur on cell bodies and dendrites b/c no voltage gated channels there

more on action potentials (nerve impulses)

= sudden, major changes in the membrane potential that propagate (travel) down the membrane of an axon (could be long distances) • Occur when the local currents from graded potentials cause the membrane at the initial segment of the axon to reach a specific membrane potential called threshold (= between -60 mV and -55 mV for a typical axon) • Exhibit the all-or-none principle: - Either an AP happens all the way at full intensity if threshold is reached, or it doesn't happen at all if threshold isn't reached • Do not decrease in intensity over long distances (unlike graded potentials)

epimysium

A whole skeletal muscle is surrounded by epimysium and contains fascicles

main proteins in thin filaments

F-actin (filamentous actin) Tropomyosin Troponin

perimysium

Fascicles are surrounded by perimysium and contain muscle fibers

information flow

Information in the form of an action potential (nerve impulse) travels along the axon of a neuron

axon classification

Is based on diameter, myelination, and AP propagation speed

hyperpolarization

When gated K+ channels open in a resting membrane, more K+ leaves the cell, and the inside of the membrane becomes more negative

repolarization

When gated Na+ channels close after depolarization, Na+ is pumped back out, returning the membrane to the resting potential - More rapid repolarization occurs when gated K+ channels open immediately after depolarization, such as during an action potential

depolarization

When gated Na+ channels open, more Na+ enters the cell, and the inside of the membrane becomes more positive

The total amount of CP stored in a muscle is enough for

a burst of MAXIMUM-intensity contraction for ABOUT 15 SECONDS (ex: 100 m dash, sprint, etc.)

neurotransmitter

a chemical substance that is released at the end of a nerve fiber by the arrival of a nerve impulse and, by diffusing across the synapse or junction, causes the transfer of the impulse to another nerve fiber, a muscle fiber, or some other structure.

blood-brain barrier

a filtering mechanism of the capillaries that carry blood to the brain and spinal cord tissue, blocking the passage of certain substances.

synapse

a junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter.

resistance of membrane

a measure of how much the membrane restricts ion movement

excitable membrane

a membrane capable of generating and conducting an action potential

myelin

a mixture of proteins and phospholipids forming a whitish insulating sheath around many nerve fibers, increasing the speed at which impulses (action potentials) are conducted.

intersegmental reflex arc

a more complex type of reflex arc that involves multiple spinal cord segments

current

a movement of charges to eliminate a potential difference

facilitated

a neuron whose transmembrane potential shifts closer to threshold

reflex

a rapid, automatic/subconscious response to a stimulus; they can be classified by development (innate - genetically determined or acquired - learned); response (somatic - control skeletal muscle contractions, includes superficial and stretch or visceral (autonomic) - controls actions of smooth and cardiac muscles, glands and adipose tissue); complexity of circuits (monosynaptic, polysynaptic); processing site (spinal cord or brain)

temporal summation

a single synapse is stimulated repeatedly and rapidly

neural control

a skeletal muscle fiber contracts when stimulated by a motor neuron at a neuromuscular junction. the stimulus arrives in the form of an action potential at the axon terminal

dermatome

a specific region of skin that is innervated by a single pair of spinal nerves (amount of overlap b/t individuals varies)

how many ATPs does aerobic metabolism produce?

It is very efficient: 17 ATPs are generated from each pyruvate (so 34 ATPs are generated from each glucose)

myelinated peripheral axon

Schwann cell dedicated itself to myelinating 1 axon

unmyelinated peripheral axon

Schwann cell myelinated many axons at once

PNS repair of axons involves

Schwann cells

the dendrites and cell body are capable of generating graded (local) potentials, but NOT...

action potentials (nerve impulses)

axon terminals

aka synaptic terminals/synaptic knobs. the swollen ends of the telodendria which: - Store chemicals called neurotransmitters (NTs) in synaptic vesicles, and... - Release NTs in response to electrical activity (such as the arrival of an incoming action potential)

what causes smooth muscle to be so plastic? (have such good plasticity?)

all those actins and myosins next to each other

G proteins

an enzyme complex coupled to a membrane receptor

treppe definition

an increase in peak tension with each successive stimulus delivered shortly after the completion of the relaxation phase of the preceding twitch

coccygeal ligament

anchors the conus meduallaris to the coccyx (spinal cord to bone ligament)

how does mitochondria get to the synaptic knob?

anterograde flow (axoplasmic transport)

chemical synapses

are a bit slower; the membranes do not touch each other; neurotransmitter is used to "bridge the gap" - This is by far most abundant type of synapse - E.g. cholinergic synapses - Each individual incoming AP releases one "dose" of neurotransmitter, which may or may not be sufficient to cause a new AP in a postsynaptic neuron

electrical synapses

are fast; the pre and postsynaptic membranes are fused, with gap junctions connecting the two - This type of synapse is extremely rare in the nervous system; it's only found in certain brain regions - Each individual incoming action potential is always propagated to the postsynaptic cell

pre/postsynaptic cells

are often neurons, but may also be muscle fibers, secretory [gland] cells, or adipocytes

neuromodulators

are other chemicals released by axon terminals that can change 1) the rate of NT release by the presynaptic neuron, and/or 2) the postsynaptic cell's response the NT

sacromeres shortening

as the thick and thin filaments interact, the sacromeres shorten, pulling the ends of the muscle fiber closer together

axon potential in

axon

Wallerian degeneration

axon distal to injury site degenerates, and macrophages migrate into the area to phagocytize the debris. the schwann cells do not degenerate; instead they proliferate and form a solid cellular cord that follows the path of the original axon

interations b/t Excitatory PostSynaptic Potentials and Inhibitory PostSynaptic Potentials

basically when ESPS happens alone, doesn't reach threshold, nothing happens, same with IPSP, same when they happen at the same time, b/c they cancel each other out

relative refractory period

begins when the sodium channels regain their normal resting condition and continues until the transmembrane potential stabilizes at resting levels

thick filaments

bundles of myosin proteins, each with an elastic titin protein core that extends to and connects to the Z lines • The myosin heads can break down ATP and pivot • The myosin heads form crossbridges (connections/ interactions) with actin during muscle contraction

ganglia

cell bodies of neurons in the PNS are clustered in masses called ganglia

resting potential is in

cell body

a neuron typically consists of

cell body, dendrites, axon, telodendria

pathways

centers and tracts that connect the brain with other organs and systems in the body

diffusion of ions through the membrane can cause

changes in the resting membrane potential

cell body

contains the nucleus and other organelles

epineuriurm

covers entire nerve

Tropomyosin

covers the active sites on G-actin in resting muscle

where does glycolysis occur

cytoplasm of cells

is glycolysis aerobic or anearobic?

does not require oxygen, anearobic

generation of smooth muscle tension

during the contraction, the entire skeletal muscle shortens and produces a pull, or tension, on the tendons at either end

action potential

electrical signal

connective tissues in skeletal muscles

epimysium, perimysium, endomysium, tendons

sodiums entering cell

excitatory graded potential (becoming more positive)

EPSP

excitatory postsynaptic potential -graded depol.

graded potential is in

exit of cell body towards the axon

substrates used for ATP generation during contraction (metabolism) of fast, slow, intermediate fibers

fast = carbohydrates (anaerobic) slow = lipids, carbs, amino acids (aerobic) intermediate = primarily carbs (anaerobic)

contraction speed of fast, slow, intermediate fibers

fast = fast slow = slow intermediate = fast

mitochondria of fast, slow, intermediate fibers

fast = few (anaerobic) slow = many (aerobic) intermediate = intermediate

glycolytic enzyme concentration in sarcoplasm of fast, slow, intermediate fibers

fast = high slow = low intermediate = high

cross sectional diameter of fast, slow, intermediate fibers

fast = large slow = small intermediate = intermediate

fatigue resistance of fast, slow, intermediate fibers

fast = low slow = high intermediate = intermediate

myoglobin content of fast, slow, intermediate fibers

fast = low slow = high intermediate = low

time to peak tension of fast, slow, intermediate fibers

fast = rapid slow = prolonged intermediate = medium

capillary/blood supply of fast, slow, intermediate fibers

fast = scarce slow = dense intermediate = intermediate

alternative names of fast, slow, intermediate fibers

fast = type II-B, FF (fast fatigue), white, fast-twitch glycolytic slow = type I, S (slow), red, SO (slow oxidative), slow-twitch oxidative intermediate = type II-A, FR (fast resistant), fast-twitch oxidative

color of fast, slow, intermediate fibers

fast = white slow = red intermediate = pink

electrochemical gradient

for a specific ion is the sum of the chemical and electrical forces acting on that ion across the plasma membrane

absolute refractory period

from the moment the voltage-gated sodium channels open at threshold until sodium channel inactivation ends, the membrane cannot respond to further stimulation, b/c all voltage-gated sodium channels either are already open of are inactivated

refractory period

from the time an action potential begins until the normal resting potential has stabilized, the membrane will not respond normally to additional depol. stimuli

neuronal pools

functional groups of interconnected interneurons in the CNS

the percentage of fast vs. slow fibers in each muscle is

genetically determined

glia

glue

Troponin

has a Ca2+-binding site

what kind of activity uses glycolysis?

high intensity activites (sprints, that kind of stuff)

neural circuits

how neuronal pools are organized into patterns (divergence, convergence, serial processing, parallel processing, reverberation)

peripheral nervous system contains

in gray matter: -ganglia = collections of neuron cell bodies in the PNS in white matter -nerves = bundles of axons in the PNS

central nervous system contains

in gray matter: -neural cortex = gray matter on the surface of the brain -centers = collections of neuron cell bodies in the CNS; each center has specific processing functions -nuclei = collections of neurons cells bodies in the CNS -higher centers = the most complex centers in the brain (on the surface of the brain, where higher thinking happens) in white matter: -tracts = bundles of CNS axons that share a common origin and destination -columns = several tracts that form an anatomically distinct mass (bigger than tracts)

where are neurotransmitters stored?

in the axon terminals/knobs

where are neurotransmitters made?

in the cell body

potassiums leaving cell

inhibitory graded potential (becoming less positive)

IPSP

inhibitory postsynaptic potential -graded hyperpolarization

Transverse (T) tubules

internal extensions of the sarcolemma, which carry action potentials (APs) deep into the muscle fiber

neuron classification by structure

is based on the number and type of processes attached to the cell body

initial segment of the axon

is where action potentials (APs) are generated

anaxonic neurons

lack an axon • They are found in the brain and some special sensory organs • Their functions are poorly understood

Myofibrils

long, parallel, cylindrical structures that are surrounded and separated by SR - They contain contractile protein filaments called myofilaments: • Thin filaments are mostly made of the protein actin • Thick filaments are mostly made of the protein myosin

example of aerobic metabolism

marathon run

presynaptic inhibition and facilitation

may occur at axoaxonic synapses

where does aerobic metabolism occur?

mitochondria of cells

Sarcoplasmic reticulum (SR) + function

modified smooth endoplasmic reticulum (SER) - Function: store/concentrate (with the help of a protein called calsequestrin - sequesters away calcium) and release Ca2+ ions (the blue stuff in the picture)

calmodulin

modulates muscle contractions in smooth muscles google definition: a protein that binds calcium and is involved in regulating a variety of activities in cells.

• Exteroceptors -

monitor the external environment - E.g. sensing ambient temperature, light, touch, sound, etc.

• Proprioceptors -

monitor the position and movement of muscles and joints (i.e., body position)...body's awareness of where it is in space

interneurons (association neurons)

most carry information within the CNS (sensory neuron -> interneuron -> motor neuron)

descending pathway

motor

local current

movement of positive charges parallel to inner and outer surfaces of a membrane

spatial summation

multiple synapses are stimulated at the same time

my/myo

muscle

what is each cell in a muscle called?

muscle fiber

where are there no slow fibers?

muscles of eye and hand (b/c swift/brief contractions are only present there...there are no slow contractions in eye and hand movements)

opiods

neuromodulators. have effects similar to those of drugs, opium and morphine, b/c they bind to same group of postsynap. receptors

neuron vs. nerve

neuron = microscopic cell, 1 axon nerve = mascroscopic, bundle of axons

reflex arc

neuronal pattern

synaptic delay

occurs b/t arrival of ap at synapt. knob and effect on the postsyn. membrane

incomplete tetanus definition

occurs if the stimulus frequency increases further. tension production rises to a peak, and the periods of relaxation are very brief

wave summation definition

occurs when successive stimuli arrive before the relaxation phase has been completed

motor unit

one motor neuron and all of the muscle fibers that it innervates - The size of a motor unit is inversely related to the precision of its control (e.g. eye muscles vs. leg muscles)

skeletal muscles are

organs that are made up mainly of skeletal muscle tissue, but also connective tissues (CTs), nerves, and blood vessels

neurilemma

outer surface of Schwann cell

The membrane at rest is

polarized; i.e., the inside is slightly negative (about -70 mV) compared to the outside

depolarized

positively charged ions flowing inside the cell (like sodium ions coming in)

information processing in

postsynaptic cell

passive electrical gradients

potassium ions leave the cytosol more rapidly than sodium ions enter b/c the plasma membrane is much more permeable to potassium than to sodium. as a result, there are more positive charges outside the plasma membrane. negatively charged protein molecules within the cytosol cannot cross the plasma membrane, so there are more negative charges on the cytosol side of the plasma membrane. this results in an electrical gradient across the plasma membrane

percentage of fast, intermediate and slow fibers in a skeletal muscle can be quite variable

proportion can change with physical conditioning

"Fast stream" axoplasmic transport

proteins called kinesin and dynein actively (via ATP) move materials along the axon

dendrites

receive information (often from other neurons) and carry it toward the cell body

how is tension produced by whole muscles?

recruitment

perikaryon

region surrounding the nucleus

Sarcomeres

regular, repeating, functional sections/units of myofilaments within myofibrils - Each myofibril may contain up to 10,000 sarcomeres end to end! • the smallest functional units of muscle contraction • Each sarcomere extends from Z line to Z line • The A bands (darker) and I bands (lighter) cause skeletal muscle tissue to have a striated (banded) appearance microscopically

adrenergic synapses

release norepinephrine

what is the source of calcium in skeletal muscle contraction?

sarcoplasmic reticulum (SR)

autonomic =

self governing

action potentials (nerve impulses)

self-regenerating changes in the membrane potential that occur when the initial segment of the axon reaches a specific membrane potential value called threshold (due to stimulation by a graded potential) - Spread over long distances (their intensity does not decrease as they travel down the axon) -all or nothing

ascending pathways

sensory

Muscle fatigue

skeletal muscle can no longer perform at the desired level of activity, due to... - ↓ Energy reserves, so there's ↓ substrate availability - ↓ pH: excessive hydrogen ions (H+) ↓ enzyme activity and displace Ca2+ from troponin (forming less cross bridges) - Sarcolemma and SR damage

what kind of fibers are back and calf muscles?

slow

telodendria

small branches at the end of an axon

active sodium/potassium pumps

sodium-potassium exchange pumps maintain the concentration of sodium and potassium ions across the plasma membrane

nodes

spaces b/t myelin on an axon

myosatellite cells

stem cells, help with repair

patellar reflex is an example of

stretch reflex

what kind of activity uses aerobic metabolism?

submaximal intensity (marathon, that kind of stuff)

neuroglia general function

support and protect neurons

muscle fiber: surrounded by + contains?

surrounded by endomysium contains myofibrils

skeletal muscle: surrounded by + contains?

surrounded by epimysium contains muscle fascicles

muscle fascicle: surrounded by + contains?

surrounded by perimysium contains muscle fibers

myofibril: surrounded by + contains?

surrounded by sarcoplasmic reticulum consists of sacromeres (z line to z line)

peri

surrounding

perineurium

surrounds fascicles (bundles of axons)

aerobic endurance

sustained sub-maximal effort, longer duration (from a few minutes to a few hours) - Improvements are due mainly to muscle fiber type alterations, ↑ cardiovascular and respiratory function, and ↑ capillary density in muscles - It's (mainly) limited by: • Aerobic substrate (glycogen/glucose, fatty acids, and/or amino acids) availability

synaptic fatigue

synapse weakens until ACh replenished

synaptic activity in

telodendria (in synaptic knobs + synapse)

graded (local) potentials

temporary, local changes in the membrane potential that occur when the cell body and dendrites are stimulated - Do not self-regenerate or spread over long distances (their intensity decreases with distance from the stimulus site)

muscle tone is

tension production by whole muscles

excitation

the action potential causes the release of ACh (acetylcholine) into the synaptic cleft, which leads to excitation - the production of an action potential in the sarcolemma

excess postexercise oxygen consumption (EPOC)

the amount of O2 required to restore normal resting conditions -breathing VERY hard after exercise

Sarcolemma

the cell membrane of a muscle fiber; it can conduct an electrical impulse (action potential) (sarco = flesh, lemma = husk)

contraction cycle begins

the contraction cycle begins when the calcium ions (Ca2+) bind to troponin, resulting in the exposure of the active sites on the thin filaments. this allows cross bridge formation and will continue as long as ATP is available.

threshold

the critical level to which a membrane potential must be depolarized to initiate an action potential. Threshold potentials are necessary to regulate and propagate signaling in both the central nervous system (CNS) and the peripheral nervous system (PNS)

Sarcoplasm

the cytoplasm of a muscle fiber (the filler where nothing else is)

hyperplasia

the enlargement of an organ or tissue caused by an increase in the reproduction rate of its cells (steroids do this to your muscle...this is not natural...except when it concerns cancer cells)

hypertrophy

the enlargement of an organ or tissue from the increase in size of its cells.

fast vs. slow muscle fibers

the fast ones are the lighter ones, the slow are darker

muscle contraction: the contraction cycle and cross-bridge formation

the first half = resting the second half = contracted

passive chemical gradients

the intracellular concentrations of potassium ions is relatively high, so these ions tend to move out of the cell thru potassium leak channels. similarly, the extracellular concentration of sodium ions is relatively high, so sodium ions move into the cell thru sodium leak channels. both of these movements are driven by a concentration gradient (chemical gradient)

muscle tone definition

the low level of resting tension that is present in skeletal muscle at all times (it is NOT enough tension to produce movement, however) - Some motor units are active at any given point in time - Which motor units are active varies constantly

Retrograde flow

the movement of certain chemicals TOWARD the cell body (performed by dynein)

Anterograde flow

the movement of neurotransmitters and organelles AWAY from the cell body (performed by kinesin)

if cell body dies

the neuron dies

postsynaptic cells

the neurons that communicate after synapses

presynaptic cells

the neurons that communicate before synapses

resting sacromere length picture

the peak is optimal resting sacromere length

Recovery

the return of conditions (pH, oxygen consumption, temperature, etc.) to normal, resting levels after exercise; mechanisms include... - Lactate (lactic acid) removal and recycling - Repaying oxygen debt (a.k.a. excess postexercise oxygen consumption, or EPOC) - Heat loss (e.g. via dermal vasodilation and/or sweating)

Nissl bodies

the ribosomes, Golgi apparatus, rough endoplasmic reticulum and mitochondria of the perikaryon of a typical neuron

recruitment

the stimulation of additional motor units - The more motor units stimulated → the more actively contracting muscle fibers → a stronger total contraction by the whole muscle -depending on load, recruits just enough fibers

contralateral reflex arc

the stimulus and response are on the opposite sides of the body

ipsilateral reflex arc

the stimulus and response are on the same side of the body

complete tetanus definition

the stimulus frequency is so high that the relaxation phase is eliminated; tension plateaus at maximal levels

resting potential

the voltage difference across the cell membrane for an unstimulated ("resting") cell; it's about -70 mV for most neurons

release of calcium ions

this action potential travels along the sarcolemma and down T tubules to the triads. this triggers the release of calcium ions (Ca+) from the terminal cisternae of the sarcoplasmic reticulum

ium

tissue

troponin and tropomyosin combine to form the

troponintropomyosin complex

4 visceral and 1 somatic effector(s)

visceral: 1. smooth muscles 2. glands 3. cardiac muscle 4. adipose tissue somatic: skeletal muscle fibers

key to action potentials

voltage-gated sodium and potassium channels

reciprocal inhibition

when one set of motor neurons is stimulated, and the neurons that control the antagonistic muscles are inhibited

resting membrane potential

whenever positive and negative ions are held apart, a potential difference arises. we measure the size of that potential difference in millivolts (mV). the resting membrane potential for most neurons is about -70 mV. the minus sign shows that the inner surface of the plasma membrane is negatively charged with respect to the exterior

axon hillock

where the axon attaches to the cell body (a thickened region)

flexor reflex is an example of

withdrawal reflex

endoneurium

wraps individual axons

does aerobic metabolism require oxygen?

yes, it's aerobic - So it depends on the ability of the respiratory and cardiovascular systems to deliver enough oxygen to meet the demand for it

3 main subtypes of gated channels

» a. Chemically (ligand-) gated channels » b. Voltage-gated channels » c. Mechanically gated channels

ATP generation in skeletal muscle that is in peak activity

• "Peak" = MAXIMAL or NEAR-MAXIMAL intensity • Most ATP is produced from CP (for about the first 15 seconds) and via anaerobic glycolysis (for a couple of minutes) - the demand for ATP is enormous. oxygen cannot diffuse into the fiber fast enough for the mitochondria to meet the demand. only a third of the cell's ATP needs can be met by the mitochondria -the rest of the ATP comes from glycolysis, and when this produces pyruvate faster than the mitochondria can utilize it, the pyruvate builds up in the cytosol. this process is called anaerobic metabolism b/c no oxygen is used -under these conditions, pyruvate is converted to lactic acid, which dissociates into a lactate ion and a hydrogen ion -the buildup of hydrogen ions increases fiber acidity, which inhibits muscle contractions, leading to rapid fatigue

info processing by individual neurons

• A single postsynaptic cell may receive many inputs • The effect of a presynaptic neuron's NT on a postsynaptic cell's membrane causes a postsynaptic potential (PSP) - These are graded (local) potentials and can be: • Excitatory (EPSP), which is a graded... - Depolarization - a postsynaptic neuron's membrane potential moves closer to threshold ("facilitation") » So a postsynaptic neuron is more likely to produce an action potential » E.g. when postsynaptic gated Na+ channels open • Inhibitory (IPSP), which is a graded... - Hyperpolarization - a postsynaptic neuron's membrane moves further away from threshold ("inhibition") » So a postsynaptic neuron is less likely to produce an action potential » E.g. when postsynaptic gated K+ channels open

single stimulus: twitch

• A twitch = a single stimulus-contraction-relaxation sequence in a muscle fiber - Note: a single twitch is too brief to be part of any useful muscular activity by itself

skeletal muscle fibers are

• A.k.a. muscle cells or myofibers • Formed by the fusion of embryonic myoblasts • Extremely large - up to a foot long and 10X the diameter of a typical cell! • Multinucleate and striated

axon

• Carries information away from the cell body - It may have major side branches called axon collaterals (they go to different targets than the telodendria)

muscle performance

• Consider the tradeoffs of generating maximal force/strength vs. having longer endurance • Muscle performance is mainly dependent upon: 1. Muscle fiber type • Slow fibers ("dark meat") • Intermediate fibers • Fast fibers ("white meat") 2. Physical conditioning/training (maximizing the genetic gift)

Tension (force/strength) production - by individual muscle fibers

• First, keep in mind that all sarcomeres in an individual muscle fiber will contract together maximally when the fiber is stimulated; i.e., a muscle fiber is either "on" (producing tension) or "off" (relaxed) • Ultimately, the amount of tension produced by an individual muscle fiber depends on the number of pivoting cross-bridges formed • Main factors: - 1. Resting sarcomere length - affects the degree to which thin and thick filaments overlap - 2. Frequency of stimulation - affects the amount of Ca2+ in the sarcoplasm - 3. The size (diameter) of the individual muscle fiber - affects the amount of actin and myosin available to interact with each other

glycolysis

• Glucose (either absorbed from your last meal or released from stored glycogen reserves) is broken down to form 2 pyruvate (pyruvic acid) molecules • In anaerobic conditions, glycolysis is used after ATP/CP reserves are depleted during a burst of maximum-intensity contraction

saltatory propagation of an action potential

• If myelin is present: saltatory propagation of an AP occurs -faster than continuous propagation of an AP -saltar = leaping/jumping

continuous propagation of an action potential

• If no myelin is present, continuous propagation of an AP occurs - is slower than saltatory propagation of an AP -each segment depolarizes the next segment

Multiple stimuli: incomplete and complete tetanus

• If the stimulus frequency that produced wave summation continues, incomplete tetanus occurs and sustained tension production is near maximal • If the stimulus frequency is even higher, complete tetanus occurs • Almost all normal whole muscle contractions involve tetanic contractions by individual muscle fibers

Multiple stimuli: treppe and wave summation

• With treppe, a relatively low maximum tension is reached, but with wave summation, one twitch is added to another, so the contraction gets stronger and stronger • Each successive twitch gets stronger because there is increasing [Ca2+] in the sarcoplasm - There's not enough time in between stimuli to pump it all back into the SR

examples of neurotransmitters and neuromodulators (know these!)

- Acetylcholine - Biogenic amines: • E.g. epinephrine, norepinephrine, dopamine, serotonin, histamine - Amino acids: • E.g. glutamate, aspartate, glycine, GABA - Neuropeptides: • E.g. enkephalins, endorphins, substance P - Purines: • E.g. ATP, adenosine, GTP - Gases: • E.g. nitric oxide (NO), carbon monoxide (CO)

process of smooth muscle contraction

- Ca2+ ions bind to the protein calmodulin - Calmodulin activates the enzyme myosin light chain kinase (adds a phosphate group from ATP to something, like myosin) - Myosin light chain kinase activates myosin, allowing cross-bridges to form - Myosin pulls on actin, and the cell shortens ("bunches up")

review of skeletal muscle contraction

1. ACh released (at nuermuscular junctions and binds to ACh receptor on the sarcolemma) 2. action potential reaches T tubule (an action potential is generated and spreads across the membrane surface of the muscle fiber and along the T tubules) 3. sarcoplasmic reticulum releases (stored) Ca2+ (calcium ions) 4. active site exposure and cross-bridge formation (calcium ions bind to troponin, exposing the active sites on the thin filaments. cross-bridges form when myosin heads bind to those active sites) 5. contraction cycle begins (as repeated cycles of cross-bridge binding, pivoting and detachment occur - all powered by ATP

2 divisions of the peripheral nervous system (PNS)

1. Afferent division: brings sensory information from receptors to the CNS 2. Efferent division: carries motor commands from the CNS to effectors

CNS repair of axons is very limited

1. An injury to the CNS would destroy many axons at once 2. Astrocytes produce scar tissue, which blocks axon regrowth (no more communication from that nerve) 3. Astrocytes release axon growth inhibitors

There are 3 main processes used to generate additional ATP in skeletal muscle for contraction:

1. Breakdown of stored creatine phosphate (CP) 2. Glycolysis (2 ATP per glucose) 3. Aerobic metabolism (34 ATP per glucose) • Which process muscles use depends upon both the INTENSITY and DURATION of their activity

3 types of muscle tissue

1. Cardiac muscle - involuntarily controlled 2. Smooth (visceral) muscle - involuntarily controlled 3. Skeletal muscle - (mostly) voluntarily controlled

2 main nervous systems

1. Central nervous system (CNS) = the brain and spinal cord; it functions to integrate, process, and coordinate sensory data and motor commands; the brain also provides higher functions such as intelligence, memory, learning, and emotion 2. Peripheral nervous system (PNS) = neural tissue (mostly spinal nerves and cranial nerves) that is located outside the CNS

2 types of smooth muscle cells

1. Multiunit smooth muscle cells 2. Visceral (single unit) smooth muscle cells

Tension production by individual muscle fibers: frequency of stimulation

1. Single stimulus: - Twitch 2. Multiple stimuli: - Treppe - Wave summation - Incomplete tetanus - Complete tetanus

2 systems of the efferent division

1. Somatic nervous system (SNS): mostly voluntary control of skeletal muscle 2. Autonomic nervous system (ANS) (a.k.a. the visceral motor system): involuntary control of smooth muscle, cardiac muscle, glands, and adipose tissue

2 divisions of the autonomic nervous system (ANS)

1. Sympathetic division 2. Parasympathetic division

3 parts of a twitch

1. The latent period • The AP is followed by Ca2+ release from the SR 2. The contraction phase • Tension increases to a peak 3. The relaxation phase • Tension decreases • There's no more stimulation, so Ca2+ is pumped back into the SR

Action potential propagation speed is influenced by:

1. The presence of electrical insulation (myelin) • ↑ Electrical insulation (such as in a myelinated axon) → ↑ speed 2. Axon (fiber) diameter • ↑ Fiber diameter → ↑ speed

generation of an action potential

1. a graded depolarization brings an area of excitable membrane to threshold (-60 mV) 2. voltage-gated sodium channels open and sodium ions move into the cell. the membrane potential rises to +30 mV *during absolute refractory period, membrane cannot respond to further stimulation 3. sodium channels close, voltage-gated potassium channels open and pot. ions move out of cell, repolarization begins. 4. pot. channels close, sod. and pot. channels return to norm states *rel. refrac. per. membrane can respond to only a larger than norm stimulus

steps in initiating muscle contraction (1-5)

1. acetylcholine released, binding to receptors 2. action potential reaches T tubules 3. sarcoplasmic reticulum releases calcium ions 4. active site exposure, cross-bridge formation 5. contraction begins

2 types of physical conditioning

1. anaerobic endurance 2. aerobic endurance

4 neuron classifications by structure

1. anaxonic neurons 2. bipolar neurons 3. unipolar neurons 4. multipolar neurons

2 types of flow in axon

1. anterograde flow 2. retrograde flow • So the presence of certain chemicals at the synapse may affect gene activity in the presynaptic neuron's nucleus

2 types of isotonic contractions

1. concentric contraction = the muscle shortens if the tension produced exceeds (even if just barely) the load 2. eccentric contraction = the muscle lengthens in a controlled manner (exerting tension in opposition to an external force such as gravity), if the tension produced is less than the load (lowering a weight)

how many ATP's does glycolysis produce?

2 ATPs generated from each glucose molecule (makes glycolysis seem relatively inefficient)

3 for 2 exchange

3 sodiums out for every 2 potassiums in

muscle contraction: continued events at the neuromuscular junction (NMJ)

3. when the action potential reaches the neuron's axon terminal, permeability changes in its membrane trigger the exocytosis of ACh into the synaptic cleft. exocytosis occurs as vesicles fuse with the neuron's plasma membrane. 4. ACh molecules diffuse across the synaptic cleft and bind to ACh receptors on the surface of the motor end plate. ACh binding alters the membrane's permeability to sodium ions. b/c the extracellular fluid contains a high concentration of sodium ions, and sodium ion concentration inside the cell is very low, sodium ions rush into the cytosol. 5. the sudden inrush of sodium ions results in the generation of an action potential in the sarcolemma. ACh is removed from the synaptic cleft in 2 ways. ACh either diffuses away from the synapse, or it is broken down by AChE into acetic acid and choline. this removal inactivates the ACh receptor sites.

how many spinal nerves are there altogether

31 pairs

steps of relaxation/ending contraction...continued from "review of skeletal muscle contraction"

6. ACh is broken down (by acetylcholinesterase (AChE), ending action potential generation) 7. sarcoplasmic reticulum reabsorbs Ca2+ (as the calcium ions are reabsorbed, their concentration in the cytosol decreases) 8. active sites covered, and cross bridge formation ends (w/out calcium ions, the tropomyosin returns to its normal position and the active sites are covered again) 9. contraction ends 10. muscle relaxation occurs (the muscle returns passively to its resting length due to a combo of other external forces, such as elasticity, gravity, and/or the contraction of opposing (antagonistic) muscles)

steps in muscle relaxation (6-10)

6. acetylcholine broken down by acetylcholinesterase 7. sarcoplasmic reticulum recaptures calcium ions 8. active sites covered, no cross-bridge interaction 9. contraction ends 10. relaxation occurs, passive return to resting length

"Potential"

= an electric voltage difference • The membrane potential is usually reported in millivolts (mV) • At rest, the inside of a cell is more negative than the outside of a cell

Electrochemical gradients

= both the chemical [concentration] and electrical forces acting on each ion - The movement of ions across the membrane, both by active transport (e.g. the Na+-K+ exchange pump) and by diffusion through membrane channels: passive (leak) channels and active (gated) channels - These channels are important for generating graded (local) potentials and action potentials (APs)

muscle contraction: generating tension

Again, when sarcomeres shorten → myofibrils shorten → muscle fibers shorten → the whole muscle shortens...so the muscle produces tension (a pulling force) on thetendons at either end

synaptic activity

At a synapse, the signal passes from a presynaptic neuron to a postsynaptic cell (neuron, muscle fiber, glandular cell, or adipocyte)

neural responses to injuries

IMPORTANT: for repair to occur, the neuron cell body must remain alive!

endomysium

Muscle fibers are surrounded by endomysium and contain myofibrils

epi

above, on top

cholinergic synapses release

acetylcholine

rate of generation of action potentials

• Information (such as the magnitude or intensity of stimulation) is often encoded by the nervous system on the basis of action potential frequency (i.e., APs per second) - E.g. treppe vs. a tetanic contraction in a skeletal muscle fiber - E.g. a few APs/sec along a sensory neuron may be interpreted as light touch, while many APs/sec along the same sensory neuron may be interpreted as painful pressure • Remember, the initial segment of an axon can produce frequent, consecutive APs if it remains above threshold (due to continuous excitatory stimulation): - The next AP is produced when the absolute refractory period of the previous AP is done - AND - - If there is enough excitatory stimulation during the relative refractory period of the previous AP to overcome the brief hyperpolarization that occurs during this period • The highest AP frequencies recorded from axons in the body are 500-1,000 AP/sec

membrane potential in general

• Is CAUSED by a separation of electrical charges (ions) across a cell membrane (e.g. Na+ and K+ ions, among others) • Is INFLUENCED by: Electrochemical gradients

smooth muscle tissue

• Is not striated (because there are no sarcomeres/myofibrils) • Has no T tubules, but it does have sarcoplasmic reticulum (SR) • Has myosin scattered throughout the sarcoplasm, and actin attached to dense bodies... • Dense bodies anchor adjacent cells together, as well as interconnect protein filaments called desmin (hold everything together), providing structural support to the cell

functions of the spinal cord

• It carries sensory information from the spinal nerves to the brain • It carries motor information from the brain to the spinal nerves • It reflexively integrates sensory and motor info

breakdown of stored creatine phosphate (CP)

• It is a fast (it only requires one enzyme!), SHORTTERM method of ATP generation • At rest, excess ATP combines with creatine to form CP, and when needed (e.g. during a brief bout of intense muscular activity), CP "recharges" spent ADP into fresh ATP... - The reversible equation: CP + ADP ↔ creatine + ATP -CP is a similar molecule to ATP

Tension (force/strength) production - by whole muscles

• Main factors: 1. The amount of tension produced by individual muscle fibers 2. Recruitment - affects the # of motor units (and thus fibers) that are stimulated..picking up heavier object, muscle recruits more motor units, lighter object = less motor units recruited 3. The size of the whole muscle - which depends on the # of muscle fibers present (and the diameter of those fibers)

- The problem: in anaerobic conditions, glycolysis ends up with the pyruvate converted to lactate (lactic acid), leading to H+ buildup...

• Muscle fiber intracellular pH ↓ (more acid in muscles..this is when you feel the burn during exercise) • Enzyme function is negatively affected (extreme pH denatures protein) • So muscle fibers can only provide a burst of NEAR-MAXIMUM-intensity contraction for ABOUT 2 MINUTES before fatigue kicks in • Glycolysis also supplies 2 pyruvate molecules as organic substrates for the initial step of aerobic metabolism

chemically (ligand-) gated channels

• Open after binding to a specific chemical (ligand) • Are most abundant on the cell body and dendrites of neurons, and the motor end plate of muscle fibers • Are important for the generation of graded (local) potentials • E.g. ACh receptors - The binding of ACh changes the shape of the receptor, opening the channel, allowing small ions like Na+ and K+ to diffuse through

voltage gated channel

• Open in response to changes in the membrane potential (voltage) • Are important for the generation and propagation (spread) of action potentials (nerve impulses), the release of Ca2+ from the sarcoplasmic reticulum during muscle contraction, and the release of neurotransmitter from axon terminals • E.g. voltage-gated K+, Na+ and Ca2+ channels • Can exist in 3 different states: - Closed, but can be opened - Open (activated) - Closed, and cannot be opened (inactivated)

mechanically gated channels

• Open or close in response to physical distortion of the membrane • E.g. sensory receptors such as touch and pressure receptors

summation

• Postsynaptic potentials are added together to produce a net (overall) postsynaptic membrane potential - If the initial segment of the axon of a postsynaptic neuron reaches threshold, then an action potential is produced, and vice versa Two types of summations: 1. Temporal summation 2. Spatial summation

aerobic metabolism

• Pyruvate (from glycolysis) or other organic substrates (such as fatty acids or amino acids) are broken down in a multienzyme pathway • It provides energy for LONG-TERM exercise (A FEW MINUTES TO A FEW HOURS) of SUBMAXIMAL-intensity muscular contractions

control of smooth muscle contraction

• Remember, smooth muscle is involuntarily (subconsciously/autonomically/automatically) controlled

visceral (single unit) smooth muscle cells

• Respond to local stimuli (chemicals/hormones, stretching, etc.); neural stimulation is not required (things other than the nervous system controls these cells) • May include pacesetter cells that spontaneously trigger contraction of entire muscular sheets • Have gap junctions, so the tissue contracts in a rhythmic wave • E.g. the walls of the digestive tract and urinary bladder

mutliunit smooth muscle cells

• Respond to stimuli from motor neurons • Are precisely controlled (by nervous system) • E.g. the iris, the walls of large arteries, and arrector pili

characteristics of smooth muscle contraction

• Smooth muscle contraction is slower and longer lasting than skeletal muscle contraction • Stimulation of smooth muscle causes Ca2+ release from the SR and Ca2+ entry from the extracellular fluid (ECF).

resting sacromere length

• The resting length of a sarcomere affects the amount of overlap between the thin and thick filaments • There is an optimal resting length for a sarcomere at which force generation is maximal

The sliding filament theory of skeletal muscle contraction

• The sarcomere shortens as the thin and thick filaments slide past one another • Sarcomeres shorten → myofibrils shorten → muscle fibers shorten → the whole muscle shortens!

cholinergic synapses

• Use acetylcholine (ACh) as the neurotransmitter • Are the most common type of chemical synapse