Bio 365- Midterm 2 (UVIC)

Properties of Pacinian corpuscle

- mechanoreceptor
- low spatial resolution (>10mm)
- most sensitive
- rapid adapting
- responds to high frequency vibrations (5-1000 Hz)
- gives info about vibrations through an object (ex: writing with a pen)

Properties of ruffini corpuscle

- mechanoreceptor
- low spatial resolution (>7mm)
-slow adapting
- gives information about finger position and hand conformation

Ia sensory afferents

wrap around intrafusal muscle fibers and inform CNS about limb movement

II sensory afferents

wrap around intrafusal muscle fibers and inform CNS about static limb position

Properties of Golgi tendon organs

- proprioceptor
- distributed among collagen fibers and tendons
- consists of group Ib afferents
- gives info about muscle tension

Dermatome

territory from a single dorsal root ganglion and it's spinal nerve

What are the 4 dermatomes?

Cervical, Thoracic, Lumbar, Sacral

Properties of Merkel cells

- mechanoreceptor
- highest spatial resolution (0.5mm)
- slow adapting
- in fingertips, sensitive to points, edges, form, texture

properties of Meissner's corpuscles

- mechanoreceptor
- high spatial resolution (3mm)
- rapid adapting
- responds to low frequency vibrations (1-300hz)
- gives info about texture gliding across skin and grip

Properties of muscle spindles

- proprioceptor
- gives info about muscle length
- made up of type Ia and II sensory afferents around intrafusal muscle fibers

primary somatosensory cortex

- mechanosensitive and proprioceptive info arising from the ventral posterior complex of the thalamus project to layer 4 of the primary somatosensory cortex
- comprised of Brodmann's areas 3a, 3b, 1, 2

First pain

initial sharp sensations at the moment of a painful stimulus
- mediated by fast pain pathway A-delta fibers (myelinated)

second pain

more delayed, diffuse, and longer-lasting sensation
- mediated by slow pain pathway C-fibers (unmyelinated)

Nociceptors

free nerve endings that initiate the sensation of pain
- slowly adapting

A-delta fiber group

- myelinated
- fast pain pathway
- responds to intense mechanical or heat stimuli

C fiber group

- unmyelinated
- slow pain pathway
- responds to intense mechanical, warm or cool, and chemical stimuli

TRPs

transient receptor potential channels (cation channels)

TRP for noxious thermal stimulus

TRPV1

TRP for mechanical pain

TRPV4 and TACAN

TRP for chemical pain

TRPA1

TRP for innocuous temperatures

warm- TRPV3 and TRPV4
cold - TRPM8

branches of autonomic nervous system

Sympathetic: fight or flight
Parasympathetic: rest and digest
Enteric: digestion

What are the 3 mechanisms that regulate autonomic function

- Dual innervation: most organs receive input from both systems
- Antagonistic action: one system stimulates while the other inhibits
- Basal tone: under resting conditions, autonomic neurons carry AP's

What is tetanus?

a smooth, sustained contraction of maximal strength

Where does the lost lateral corticospinal tract terminate?

Onto interneurons in lateral portions of ventral horn and intermediate grey matter
- some axons (including Betz cell) synapse directly onto ventral alpha motor neurons

steps of stretch reflex

1. tendon stretches which stretches muscle spindles in leg
2. Sensory neuron synapses with and excites motor neuron in spinal cord. It also excited the spinal interneuron- this inhibits motor neuron to flexor muscles
3. Motor neuron conducts AP to synapses on extensor muscle fibers- this causes contraction. The flexor muscle relaxes because inhibition of motor neurons
4. Leg extends

Parkinson's disease

a neurodegenerative movement disorder involving the progressive loss of dopaminergic neurons in Substantia Nigra (symptoms manifest after loss of 60% of dopaminergic neurons)
- symptoms include bradykinesia, resting tremor, and muscular rigidity

Huntington's disease

A genetic disease characterized by cognitive deterioration, psychiatric impairment, chorea, and dystonia. Due to a dominant mutation in the HTT gene. It causes a massive loss of medium spiny neurons in the caudate putamen (dorsal striatum)

What is the structure of microtubules?

GTP activates alpha tubulin and beta tubulin which then dimerize- these dimers then assemble end to end to form a protofilament. 13 protofilaments line up side by side to form a sheet, which then rolls to form a hollow tube.
- there is a minus end (MTOC anchored near the nucleus, and plus end anchored to integral proteins in the plasma membrane

What are factors affecting microtubule growth and shrinkage

- High tubulin concentration promotes growth
- GTP hydrolyses on beta-tubulin which causes instability
- Low temperature causes disassembly
- Chemicals disrupt dynamics

what are MAPs (microtubule associated proteins) and give some examples

bind at regular intervals along a microtubule wall, allowing for interaction with other cellular structures and filaments
- Tau: associated with axons and causes tight MT binding
- MAP2: associated with dendrites and causes loose MT binding

How does kinesin move?

-8 nm/step
- moves in anterograde fashion (toward +end)
- ATP causes tight binding to beta tubulin on leading head
- ATP hydrolyses on lagging head, allowing loosening
- power stroke causes conformational change- lagging head becomes leading head
- ADP replaced with ATP on leading head allowing tight binding

How are cilia and flagella formed?

Nine pairs of microtubules around a central pair
Asymmetric activation of dynein causes movement

How are microfilaments formed?

G-actin monomers nucleate to form F-actin. 2 F-actin strands then form a helix.

Tropomodulin

prevents assembly and disassembly at minus end of microfilament

Cap Z

caps + end of actin, prevents polymerization

Cofilin

binds ADP-actin filaments, accelerates disassembly

Profilin

binds G-actin and speeds elongation

ARP

Promotes nucleation of F-actin branches (acts as a base plate for attachment)

Filamin

An actin-binding protein that cross-links actin filaments into networks. Promotes cortical 'gel' formation

fimbrin and alpha-actinin

Cause bundling of actin filaments.... actin filament bundles can be found in microvilli (which are immobile)

Fimbrin in microvilli

Alpha-nectin in stress fibers

both in filopodia

Dystrophin

links the thin filaments to the integral proteins of the sarcolemma

What are the steps in actin-based cell crawling?

1- Protrusion extension: ARP2/3 mediates G-actin nucleation. Branched F-actin extends.
2- Substrate attachment: Integrins anchored in actin and ECM allow for focal adhesions
3- Tension generation- At rear of cell, myosin II walks along tubulin like a treadmill

What are the steps in the sliding filament model?

1- Myosin is bound to actin
2- ATP binds, causing myosin to detach
3- Myosin head extends, attaches to adjacent actin (closer to +end)
4- Phosphate is released, causing a power stroke (actin moves toward - end)
5- ADP is released

Myocytes

Muscle cells- contractile cell unique to animals

thick filaments

composed of myosin

thin filaments

composed of alpha- actin
ends capped by tropomodulin and CapZ to stabilize
Troponin and tropomyosin on surface

What are the two main types of muscle cells

Striated (appears striped): composes skeletal and cardiac muscle- actin and myosin arranged in parallel
Smooth (not striped): composes vessel walls..etc.- actin and myosin not arranged in any particular way

How is the sarcomere organized?

the repeating unit of a myofibril in a muscle cell, composed of an array of overlapping thick and thin filaments between two adjacent Z discs.

Z disc

anchors the thin filaments and connects myofibrils to one another

A-band

middle area in the sarcomere where thick filaments are found

I band

area of sarcomere where thin filaments are found (either side of Z-disc)

M line

Middle of A band where opposing myosin II filaments join

Nebulin

Along the length of thing filaments- helps hold F-actin strands together

Titin

are strands of protein
reach from tips of thick filaments to the Z line
stabilize the thick filaments

What is the role of troponin and tropomyosin?

At rest, myosin binding sites on actin are blocked by tropomyosin
When stimulated, Calcium binds to troponin (TnC) which causes a conformational change- tropomyosin shifts out of the myosin binding site, allowing cross-bridges to form

What are the 3 different kinds of troponin and what are their roles

- TnI: binds actin
- TnC: binds calcium
- TnT: binds other troponins

What is the steps in the muscle contraction cycle?

1- Myosin-ADP-Pi: high energy conformation, myosin head is bound to actin
2- Pi release: causes conformational change- thin filament slides past thick filaments which generates tension
3- ADP-ATP: myosin has a conformational change and the cross-bridge dissociates
4- ATP hydrolysis: ADP and Pi are bound which sends it into the cocked state- myosin head rebinds thin filament

How does calcium regulate muscle contraction?

Calcium channels elevate cytosolic calcium levels. (L-type channel in cell membrane, ryanodine receptor in SR membrane)
Transporters remove calcium from cytoplasm. (CaATPase and Na/Ca exchanger in cell membrane, CaATPase (SERCA) in SR membrane)

Parvalbumin

Cytosolic Ca2+ binding protein buffers Ca2+

How are skeletal and cardiac muscles different in initial cause of depolarization?

Heart is myogenic (begins in muscle) and is spontaneous due to pacemaker cells (depolarize spontaneously and rythmically)
Skeletal muscles are neurogenic (begins in nerve): excited by neurotransmitters (Ach activates nicotinic Ach receptors)

How are skeletal and cardiac muscles different in their action potentials?

Cardiac: longer in activation of Na+ channels, longer to activate K+ channels, does not allow summation (smaller SR)
Skeletal: Allows summation (larger SR)

How are skeletal and cardiac muscles different in excitation-contraction coupling?

Cardiac: Ca2+ induced Ca2+ release. Calcium fluxes through L-type calcium channels- activates ryanodine receptors
Skeletal: Depolarization induced Ca2+ release. There is a physical interaction between L-type calcium channels and ryanodine receptors.

T tubules

Also called transverse tubules, these are deep invaginations of the plasma membrane found in skeletal and cardiac muscle cells. These invaginations allow depolarization of the membrane to quickly penetrate to the interior of the cell.

sarcoplasmic reticulum (SR)

specialized smooth endoplasmic reticulum, which stores, releases, and retrieves Ca2+

terminal cisternae of SR

Expanded ends of the sarcoplasmic reticulum found on either side of a t-tubule. Important in calcium storage used in muscle contraction

How is smooth muscle different to striated muscle?

-no sarcomeres
- no t tubules, minimal SR
- connected by gap junctions
-contract in all dimensions
- controlled by hormones, nerve, stretch
- lacks troponin
- Ca2+ binds calmodulin, binds caldesmon, caldesmon moves tropomyosin free of myosin binding sites

slow twitch fibers (type I)

red muscle fibers that are fatigue-resistant but have a slow contraction speed and a lower capacity for tension

fast twitch fibers (type IIa)

Red muscle fibers that are somewhat fatigue resistant and generates contractions with greater power and velocity

fast twitch fibers (type IIb)

White muscle fibers that are fast fatigable and generates contractions with the greatest power and velocity

annelid circulatory system

tube worms- open
earthworms- closed

mollusc circulatory system

some closed, some open
all have hearts, some have blood vessels

continuous capillaries

have a wall where the endothelial cells fit very tightly together.

fenestrated capillaries

have pores in vessel wall; found in kidneys, intestines, and endocrine glands

sinusoidal capillaries

leaky capillaries; found only in the liver, bone marrow, lymphoid tissues and some endocrine glands; allow large molecules to pass between blood and surrounding tissues

arthropod circulatory system

open, small sinuses like vessels
insects: multiple "hearts" along dorsal vessel- use tracheal system for most gas transport

water-breathing fish circulatory system

closed, single circuit, lower metabolic rate and O2 consumption

how many circuits to mammals have

2
right- circulatory
left- systemic
higher metabolic rate and o2 consumption

Circulatory system of amphibians/reptiles

two atria and 1 ventricle- blood from both atria go into the ventricle, oxygenated and deoxygenated blood mix

Decapod crustaceans heart and cardiac cycle

pumps hemolymph via arteries, returns via ostia during diastole
heart suspended with ligaments
neurons in cardiac ganglion undergo spontaneous depolarization, cardiomyocytes contract, heart volume decreases, ostia valves close, hemolymph pumped out via arteries, ligaments pull on heart walls, heart volume increases, ostia open, hemolymph enters

Fish heart structure

2 chambers (1 atria, 1 ventricle), blood in sinus venosus (weakest contraction), blood enters atrium (contracts), blood enters ventricle (strongest contraction), blood leaves via bulbous arteriosus (does not contract)

Pericardium

Double-layered membrane surrounding the heart.

epicardium (visceral pericardium)

the inner layer of the pericardium that covers the surface of the heart

Myocardium

muscular, middle layer of the heart

endocardium

inner lining of the heart

amphibian heart structure

3 chambers (2 atria and 1 ventricle)
blood enters via sinus venosus (right atriur) and pulmonary vein (left atrium), enters ventricle, exits via systemic and pulmocutaneous arteries (spiral fold redirects oxygenated and deoxygenated blood)

Non-Crocodilian Reptile Heart structure

5 chambers (2 atria, 3 ventricles)
deoxygenated blood enters into cavum atriosum, goes to cavum pulmonale, exits to lungs
oxygenated blood enters via pulmonary vein, enters cavum venosum and exits via arteries

bird and mammal heart

four chambers (two atria, thin-walled), two ventricles (thick-walled), ventricles separated by intraventricular septum
deoxygenated blood enters via superior vena cava, enters right atrium, enters right ventricle, exits via pulmonary artery
oxygenated blood enters via pulmonary vein, enters left atrium, enters left ventricle, and exits via aorta

atroventricular valves

between atria and ventricles
right AV is tricuspid valve; left AV is mitral valve

semilunar valves

pulmonary and aortic valves located between the right ventricle and the pulmonary artery and between the left ventricle and the aorta

pacemaker cells

heart cells that regularly produce spontaneous electrical impulses located in right atrium

pacemaker potential

spontaneous gradual depolarization to threshold of some neurons and muscle cells' plasma membrane

left to right shunt

allows quicker oxygenation of myocardium in reptile hearts- oxygenated blood reenters pulmonary side

right to left shunt

-Bypasses pulmonary circulation
-during breath holding

How many chambers do bird and mammal hearts have

4
Two atria
Two ventricles

intraventricular septum

Separates the two ventricles of bird and mammal hearts

What are the atrioventricular valves?

tricuspid (right) and bicuspid/mitral (left) valves found between atria and ventricles

What are the semilunar valves?

pulmonary (between right ventricle and pulmonary artery) and aortic (between left ventricle and aorta)

Systole

contraction phase of the heart

Diastole

Relaxation of the heart