Topic 9: Sensorimotor System

Question 1

What are sensory receptors?

Answer 1

transducers

Question 2

What is transduction?

Answer 2

the conversion of a physical energy (such as light or pressure) into neural activity (such as a receptor (graded) potential) or action potential

Question 3

What does the vision system respond to?

Answer 3

light energy

Question 4

What does the auditory system respond to?

Answer 4

air pressure

Question 5

What does the somatosensory system respond to?

Answer 5

skin pressure

Question 6

What does the taste & olfaction system respond to?

Answer 6

chemical molecules

Question 7

What is the frequency at gentle pressure?

Answer 7

low frequency of action potentials per receptor

Question 8

What is the frequency at more pressure?

Answer 8

high frequency of action potentials per receptor

Question 9

What happens during dark responses (5)?

Answer 9

1. rhodopsin inactive
2. Na+ channels open
3. rod depolarized
4. glutamate released
5. bipolar cell either depolarized or hyperpolarized, depending on glutamate receptors

Question 10

What happens during light responses (5)

Answer 10

1. rhodopsin active
2. Na+ channels closed
3. rod hyperpolarized
4. no glutamate released
5. bipolar cell either hyperpolarized or depolarized, depending on glutamate receptors

Question 11

What happens when near vision?

Answer 11

1. ciliary muscles contract pulling border of choroid toward lens
2. suspensory ligaments relax
3. lens becomes thicker and rounder, focusing on nearby objects

Question 12

What happens when distance vision?

Answer 12

1. ciliary muscle relax and border of choroid moves away from lens
2. suspensory ligaments pull against lens
3. lens becomes flatter focusing on distant objects

Question 13

How are skeletal muscles formed?

Answer 13

formed by fusion (a syncytium) early in development and are multinucleate when mature

Question 14

What are the two specialized proteins in sarcomeres?

Answer 14

myosin and actin, arranged thick and thin filaments respectively

Question 15

What is the I band?

Answer 15

1. isotropic: same
2. thin filaments only (actin)

Question 16

What is the H band?

Answer 16

1. helles: clear
2. thick filaments only (myosin)

Question 17

What is the M line?

Answer 17

1. mittel: middle
2. proteins in the middle of sarcomeres where thick filaments attach

Question 18

What is the Z disk?

Answer 18

1. zwischen: in between
2. proteins at the ends of sarcomeres where thin filaments attach. two z-disks per sarcomere (each shared with adjoining sarcomere)

Question 19

What is the structure of each thick filament?

Answer 19

‘surrounded’ by six thin filaments in the A-band overlap zone

Question 20

What is the structure of each thin filament?

Answer 20

‘sees’ three thick filaments

Question 21

What happens during contraction?

Answer 21

1. thick and thin filaments move (‘slide’) past each other (but do not change length)
2. myosin “heads” walk along actin filaments pulling them to the center of the sarcomere

Question 22

How do myosin-binding sites uncover?

Answer 22

when calcium ions (Ca2+) bind to the troponin complex and expose the myosin-binding sites

Question 23

What is the concentrations of Ca2+ during contraction?

Answer 23

when the concentration of Ca2+ is high

Question 24

What is the concentration of Ca2+ during relaxation?

Answer 24

muscle fiber contraction stops when the concentration of Ca2+ is low

Question 25

How do myosin-binding sites cover?

Answer 25

the regulatory protein tropomyosin held in place by the troponin complex covers the myosin binding site on actin when muscle is at rest; this prevents actin and myosin from interacting

Question 26

What are the three layers of the triad?

Answer 26

1. sarcoplasmic reticulum cistema 2. transverse tubule 3. sarcoplasmic reticulum cistema

Question 27

What are transverse tubules (T tubules)?

Answer 27

extensions of the plasma membrane, penetrating the muscle cell at two points in each sarcomere: the junctions of the A and I bands. brings the extracellular space closer to the myofibrils deep inside the sarcomere

Question 28

What are the steps of control muscle contraction?

Answer 28

1. the stimulus leading to contraction of a muscle fiber is an action potential in a motor neuron that makes a synapse with the muscle fiber. the synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine 2. acetylcholine depolarizes the muscle, leading to the generation of an action potential. Action potentials travel to the interior of the muscle fiber along transverse (T) tubules 3. interactions between T tubules and the sarcoplasmic reticulum (SR) triggers release of Ca2+ 4. the Ca2+ binds to the troponin complex on the thin filaments 5. the binding exposes myosin-binding sites and allows the cross bridge cycle to proceed 6. transport proteins in the SR pump Ca2+ out of the cytosol 7. tropomyosin slides back to cover the myosin-binding sites

Question 29

When does it mean when contraction is graded?

Answer 29

the extent and strength of its contraction can be voluntarily altered

Question 30

What are the two basic mechanisms by which the nervous system produces graded concentrations?

Answer 30

1. varying the number of fibers that contract 2. varying the rate at which fibers are stimulated

Question 31

What happens when you vary the number of fibers that contract?

Answer 31

each motor protein may synapse with multiple muscle fibers, although each fiber is controlled by one one motor neuron

Question 32

What does a motor unit consist of?

Answer 32

a single motor neuron and all the muscle fibers it controls

Question 33

What causes stronger contractons?

Answer 33

recruitment of multiple motor neurons

Question 34

What is tetanus?

Answer 34

a state of smooth and sustained contraction produced when motor neurons deliver a volley of action potentials

Question 35

What is proprioception?

Answer 35

the collection of information about body movements and positions

Question 36

What are muscle spindles?

Answer 36

a capsule buried in other muscle fibers that contains intrafusal fibers

Question 37

What are intrafusal fibers?

Answer 37

respond to stretch

Question 38

What happens to the muscle spindles when a muscle is stretched?

Answer 38

the muscle spindle stretches and triggers action potentials in afferent sensory nerves; the spinal cord and brain are informed about the extent and rate stretch, and the load

Question 39

What are Golgi tendon organs?

Answer 39

organs sensitive to muscle tension

Question 40

What is the function of Golgi tendon organs?

Answer 40

1. to monitor the force of muscle contractions 2. detect overloads on muscles and cause a reflexive relaxing of the muscle, preventing damage

Question 41

What is Golgi tendon organ mediated reflex?

Answer 41

1. causes muscle to relax in response to being contracted 2. although the tendon reflex is sensitive than the stretch reflex, it can override the stretch reflex when tension is great