Reflex Arcs (Neurophysiology III)

Question 1

Explain the higher centers of control in the CNS.

Answer 1

• cerebral cortex (conscious + voluntary movement)

Question 2

Explain the middle level of control in the CNS.

Answer 2

• sensorimotor cortex
• cerebellum –> monitors execution
• basal ganglia –> semi-voluntary movements (helps cerebral cortex develop voluntary movements)

Question 3

Explain the lower level of control in the CNS.

Answer 3

• spinal cord from which motor neurons exit
• site of somatic reflex arcs

Question 4

What is proprioception?

Answer 4

• tensions in muscles, tendons + angles of joints send back sensory information to the CNS
• tells position of the body

Question 5

What components are involved in planning + programming of movements?

Answer 5

• cerebral cortex
• basal ganglia
• thalamus
• cerebellum

Question 6

What components are responsible for the execution of movements?

Answer 6

• cerebral cortex
• cerebellum
• brain stem
• spinal cord

Question 7

What does the somatic reflex arc involve?

Answer 7

involves local integration in the spinal cord

Question 8

What are the 5 fundamental components of a reflex arc?

Answer 8

• sensory cells/receptors (detect stimulus)
• sensory nerve fibers
• coordinating center (CNS) –> integration center decides if AP should be fired
• motor nerve fibers
• effectors (muscle or gland cells) –> execute reflex

Question 9

What are the functions of receptors in the reflex arc?

Answer 9

• detect signals
• transduce the environmental energy –> skin, muscle (spindle) + tension (golgi)
• convert energy into AP
• frequency of AP is proportional to the intensity of energy transduced (enables CNS to detect intensity)

Question 10

What are the functions of the sensory (afferent) nerves in reflex arcs?

Answer 10

• conduct AP from receptor
• cell body in ganglion outside of spinal cord
• enter spinal cord via dorsal roots

Question 11

What are the functions of the coordinating center (CNS synapses) in reflex arcs?

Answer 11

• monosynpatic (muscle spindle reflex):
  sensory neuron –> dorsal root ganglion –> dorsal horn –> synapse directly on motor neuron
• multisynaptic (elaborate reflex) –> reflex response at spinal cord requires response from many muscles

Question 12

What are the functions of the motor (efferent) nerve in reflex arcs?

Answer 12

• carries AP from CNS to target (effector) organs via ventral roots
• cell body within the CNS

Question 13

What detects changes in muscle length in stretch + tendon reflex?

Answer 13

• muscle spindles

Question 14

Explain what happens when the spindle fibers detect change in muscle length.

Answer 14

• middle segment acts as stretch receptor by pinching the bare end of the sensory neuron (receptor) –> sensory afferent nerve –> spinal cord
• sensory nerves makes excitatory synaptic contact with motor neurons serving the same muscle (extrafusal alpha fibers) –> muscle shortens

Question 15

What detects changes in tendon length?

Answer 15

golgi organ

Question 16

Explain what happens when the golgi detects changes in tendon length.

Answer 16

• muscle contracts –> pulls tendon –> squeezes bare end of neuron (receptor) –> sensory nerve contacts with inhibitory interneuron in spinal cord –> inhibits motor neurons serving same muscle

Question 17

What kind of group are skeletal muscles organized in?

Answer 17

antagonistic muscle groups
- reflex targets both agonist + antagonist muscle