Topic 9: Sensorimotor System Flashcards
What are sensory receptors?
transducers
What is transduction?
the conversion of a physical energy (such as light or pressure) into neural activity (such as a receptor (graded) potential) or action potential
What does the vision system respond to?
light energy
What does the auditory system respond to?
air pressure
What does the somatosensory system respond to?
skin pressure
What does the taste & olfaction system respond to?
chemical molecules
What is the frequency at gentle pressure?
low frequency of action potentials per receptor
What is the frequency at more pressure?
high frequency of action potentials per receptor
What happens during dark responses (5)?
- rhodopsin inactive
- Na+ channels open
- rod depolarized
- glutamate released
- bipolar cell either depolarized or hyperpolarized, depending on glutamate receptors
What happens during light responses (5)
- rhodopsin active
- Na+ channels closed
- rod hyperpolarized
- no glutamate released
- bipolar cell either hyperpolarized or depolarized, depending on glutamate receptors
What happens when near vision?
- ciliary muscles contract pulling border of choroid toward lens
- suspensory ligaments relax
- lens becomes thicker and rounder, focusing on nearby objects
What happens when distance vision?
- ciliary muscle relax and border of choroid moves away from lens
- suspensory ligaments pull against lens
- lens becomes flatter focusing on distant objects
How are skeletal muscles formed?
formed by fusion (a syncytium) early in development and are multinucleate when mature
What are the two specialized proteins in sarcomeres?
myosin and actin, arranged thick and thin filaments respectively
What is the I band?
- isotropic: same
- thin filaments only (actin)
What is the H band?
- helles: clear
- thick filaments only (myosin)
What is the M line?
- mittel: middle
- proteins in the middle of sarcomeres where thick filaments attach
What is the Z disk?
- zwischen: in between
- proteins at the ends of sarcomeres where thin filaments attach. two z-disks per sarcomere (each shared with adjoining sarcomere)
What is the structure of each thick filament?
‘surrounded’ by six thin filaments in the A-band overlap zone
What is the structure of each thin filament?
‘sees’ three thick filaments
What happens during contraction?
- thick and thin filaments move (‘slide’) past each other (but do not change length)
- myosin “heads” walk along actin filaments pulling them to the center of the sarcomere
How do myosin-binding sites uncover?
when calcium ions (Ca2+) bind to the troponin complex and expose the myosin-binding sites
What is the concentrations of Ca2+ during contraction?
when the concentration of Ca2+ is high
What is the concentration of Ca2+ during relaxation?
muscle fiber contraction stops when the concentration of Ca2+ is low
How do myosin-binding sites cover?
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
What are the three layers of the triad?
- sarcoplasmic reticulum cistema
- transverse tubule
- sarcoplasmic reticulum cistema
What are transverse tubules (T tubules)?
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
What are the steps of control muscle contraction?
- 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
- 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
- interactions between T tubules and the sarcoplasmic reticulum (SR) triggers release of Ca2+
- the Ca2+ binds to the troponin complex on the thin filaments
- the binding exposes myosin-binding sites and allows the cross bridge cycle to proceed
- transport proteins in the SR pump Ca2+ out of the cytosol
- tropomyosin slides back to cover the myosin-binding sites
When does it mean when contraction is graded?
the extent and strength of its contraction can be voluntarily altered
What are the two basic mechanisms by which the nervous system produces graded concentrations?
- varying the number of fibers that contract
- varying the rate at which fibers are stimulated
What happens when you vary the number of fibers that contract?
each motor protein may synapse with multiple muscle fibers, although each fiber is controlled by one one motor neuron
What does a motor unit consist of?
a single motor neuron and all the muscle fibers it controls
What causes stronger contractons?
recruitment of multiple motor neurons
What is tetanus?
a state of smooth and sustained contraction produced when motor neurons deliver a volley of action potentials
What is proprioception?
the collection of information about body movements and positions
What are muscle spindles?
a capsule buried in other muscle fibers that contains intrafusal fibers
What are intrafusal fibers?
respond to stretch
What happens to the muscle spindles when a muscle is stretched?
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
What are Golgi tendon organs?
organs sensitive to muscle tension
What is the function of Golgi tendon organs?
- to monitor the force of muscle contractions
- detect overloads on muscles and cause a reflexive relaxing of the muscle, preventing damage
What is Golgi tendon organ mediated reflex?
- causes muscle to relax in response to being contracted
- although the tendon reflex is sensitive than the stretch reflex, it can override the stretch reflex when tension is great
