Physiology Exam 2

Autonomic Nervous System

Works with endocrine system to maintain homeostasis

Cerebral cortex

Creates emotions that influence autonomic output

Spinal autonomic reflexes

don’t require input from the brain

Sympathetic Branch

Dominates function in stressful situations (ex: increases heart rate)

Parasympathetic Branch

Dominates rest and digest functions (ex: decreases heart rate)

Sweat glands and smooth muscle of blood vessels

controlled only by the sympathetic branch

preganglionic neuron

originates in the CNS and projects to an autonomic ganglion

autonomic ganglion

outside of the CNS

postganglionic neuron

projects to the target tissue

Divergence

neurons can synapse with up to 32 neurons

Sympathetic AND Parasympathetic

utilize acetylcholine

Preganglionic neurons of both divisions

release acetylcholine onto nicotinic cholinergic receptors

Most postganglionic sympathetic neurons

secrete norepinephrine onto adrenergic receptors on the target cell

Most postganglionic parasympathetic neurons

secrete acetylcholine onto muscarinic cholinergic receptors

Neuroeffector junction

synapse between a post-ganglionic autonomic neuron and its target cell

Autonomic postganglionic axons end with

varicosities filled with neurotransmitters

Neurotransmitter release in autonomic nervous system

released into the interstitial fluid and diffuse to targets

less direct

Adrenal cortex

true endocrine gland that secretes cortisol

Adrenal medulla

modified sympathetic ganglion that is a neurosecretory structure that releases epinephrine directly into the blood

Postganglionic neurons of the Adrenal medulla

chromaffin cells

Cocaine

blocks reuptake of norepinephrine into adrenergic nerve terminals

causes vasoconstriction and possible heart attack

Cholinesterase inhibitors

block ACh degredation

leads to excessive stimulation of autonomic and somatic motor target tissues

Beta blockers

commonly used blood pressure medication

Neuromuscular junction

synapse of motor neuron on a muscle fiber

contains extensions of schwann cells

Active zone

nicotinic ACh receptors when activated

allows for Na+ to enter and depolarize muscle fibers

Motor unit

a group of muscle fibers that function together, and the somatic motor neuron that controls them

Each muscle fiber is innervated by

only a single neuron

Fine motor actions

one motor unit has 3-5 muscle fibers

small response

Gross motor actions

each motor unit contains 100’s to 1000’s of muscle fibers

All muscle fibers in a single motor unit are

the same fiber type

Motor units contract in a

all or nothing fashion

Force of contraction is increased by

recruiting additional motor units

Excitability

respond to stimulation from nervous system via neurotransmitters

conductivity

electrical charge traveling along plasma membrane in response to neurotransmitter

Elasticity

muscle returns to its original length when relaxed

Extensibility

muscle tissue can stretch or extend

Contractility

Allows muscle tissue to pull on its attachment points and shorten with force

Three types of muscle tissue

skeletal, cardiac, smooth

skeletal tissue

multi-nucleated structure

cardiac tissue

fibers with one or two nuclei physically and electrically connected so the entire heart contracts as one unit

smooth muscle tissue

non-striated muscle in the walls of hollow organs

skeletal muscle bundles

fascicles

skeletal muscle functions

protection, sites for blood vessel and nerve distribution, and means of attachment to skeleton or other structures

where in the muscle fiber is Ca2+ stored?

sarcoplasm reticulum

Sarcolemma

cell membrane of muscle fiber

sarcoplasm

cytoplasm of muscle fiber

myofibrils

highly organized bundles of contractile and elastic proteins that carry out contraction

Sarcoplasmic Reticulum

a modified ER that wraps around each myofibril

contains terminal cisternae

allows contraction to happen all at the same time

T-tubules

extensions of the sarcolemma that associates with the terminal cisternae of the SR

continuous with thick and thin filaments

allow action potentials to move from surface to interior of fiber

Thick filaments are composed of

myosin

Thin filaments are composed of

actin

Z disk

zig-zag protein structures that serve as attachment site for thin filaments

within the I-band

I-bands

regions of thin filaments only

lightest region of the sarcomere bands

A-band

entire length of thick filament

Darkest of the sarcomere bands

H-zone

central region of A-band that is thick filaments only

M-line

proteins that form the attachment site for thick filaments

divides A-band in half

Titin

spans from one Z-disk to M-line

stabilizes the position of the contractile filaments and is elastic

Nebulin

inelastic large protein that lies along thin filaments, attaches to Z-disk

Excitation-contraction coupling

muscle action potentials are translated into calcium signals which initiate a contraction-relaxation cycle

Contraction-relaxation cycling

the sliding of filaments back and forth

muscle twitch

Sarcomeres shorten during

contraction

Thick and thin filament length during contraction

NEVER CHANGES!

Power stroke

myosin crossbridges swivel and push actin filaments toward the center of the sarcomere

myosin heads release all at the same time (T/F)

false

Energy from power stroke comes from

ATP

Myosin is considered what type of enzyme?

ATPase

Troponin

calcium binding protein complex

controls positioning of tropomyosin

tropomyosin

wraps around actin filaments and partially covers the myosin binding site of actin (unless moved by troponin activation)

1st step of Muscle Contraction Cycle

ATP binds to myosin and myosin releases actin

2nd step of Muscle contraction cycle

Myosin hydrolyzes ATP

Myosin head rotates to the cocked position and binds weakly to actin

3rd step of Muscle contraction cycle

Calcium signal reaches troponin and power stroke commences

actin filament moves toward M line

4th step of Muscle contraction

Myosin releases ADP at the end of the power stroke

returns to rigor state

Most relaxed muscles remain in

2nd step of muscle contraction

myosin head in cocked position

Which neurotransmitter is responsible for stimulating muscle cells?

acetylcholine

Latent period

delay between the muscle action potential and the beginning of muscle tension development

caused by time required for calcium to be released from SR and bind to troponin

Central fatigue

Arise in CNS

Subjective feelings of tiredness and a desire to stop activity

Psychological failure

comes from physical failure as a protective mechanism (so you don’t kill yourself)

Peripheral fatigue

arises between the neuromuscular junction and the contractile elements

ACh is not synthesized fast enough in the axon terminal

depletion of muscle glycogen stores, ion imbalances, etc

Fast twitch fibers (type II)

develop tension 2-3x faster than slow twitch (type 1)

split ATP more rapidly and go through contractile cycles faster

Duration of contraction

dependent on how fast SR removes Ca2+ from the cytosol

Slow-twitch fibers are useful for

standing, walking, maintaining posture

What primarily relies on oxidative phosphorylation and the electron transport chain for ATP production

oxidative fibers

Fast twitch type IIB

rely primarily on anaerobic glycolysis to produce ATP quickly

more explosive

leads to acidosis and fatigues faster

Oxidative fibers (type 1 slow twitch and type IIA fast twitch)

have more mitochondria and more blood vessels in connective tissue to deliver oxygen. can sustain work for longer

Type IIA fast-twitch

have properties of both oxidative and glycolytic fibers. uses both aerobic and anaerobic metabolisms

A sarcomere at optimal length

will contract with optimal force

How filaments are impacted by optimal length

filaments begin contracting with numerous crossbridges

Force generated by the contraction of a single muscle fiber can be increased by

increasing the rate at which muscle action potentials stimulate the muscle fiber

tetanus

maximal muscle contraction

incomplete tetanus

stimulation rate is not at maximum, fiber relaxes slightly between stimuli

complete tetanus

stimulation rate is fast enough to reach maximum tetanus

ATP will run out and muscles will inevitably go to resting state

During skeletal-muscle contraction, the I band and H zone shorten but the A band stays the same (T/F)

True

Isometric contraction

Muscle tension insufficient to overcome resistance

Contraction of muscle and increased tension

Muscle length the same

Pushing on a wall, holding a weight but your arm doesn’t move

isometric contraction

Isotonic contraction

muscle tension able to overcome resistance

result is movement

tone same but length changes

swinging a tennis racket

isotonic contraction

Concentric contraction

muscle shortens as it contracts

biceps when lifting

concentric contraction

eccentric contraction

muscle lengthens as it contracts

biceps when lowering a load

eccentric contraction