Lab 7: Somatic Reflex Arcs (2 questions)単語カード | Quizlet

What does the simplest form of a reflex arc include?

receptor, afferent neuron, integration (usually in CNS), efferent neuron, effector

A spinal reflex allows for

a rapid, automatic response

cognitive analysis occurs after reflex is completed

What are alpha motor neurons

stimulate extrafusal fibers of skeletal muscle

control force

What happens if you inhibit the alpha motor neuron?

hyperpolarizes the neuron and it can't send an action potential to the neurotransmitter junction

in this way, the agonist muscle can contract and the antagonist muscle relaxes

What is a stretch reflex

detects stretch in a skeletal muscle and results in the contraction of the muscle to overcome the stretch

What are extrafusal fibers?

innervated with alpha motor neurons

responsible for development of force by skel. muscles

What are intrafusal fibers?

modified skeletal muscle fibers located in muscle spindles and are used in the detection of muscle stretch

the central region lacks actin and myosin and are wrapped in sensory endings that act as stretch receptors

intrafusal fibers stretch - stretch receptors send info to CNS - synapse with alpha motor neuron - extrafusal fibers of skeletal muscles - force/contraction

gamma motor fibers control the degree of stretch

reciprocal inhibition

allows relaxation of the antagonist so the agonist muscle can better contract and develop force

afferent neuron of agonist stimulates inhibitory interneuron of spinal cord

multisynaptic

Upper motor neurons

located in motor cortex and descending pathways

completely in CNS

When upper motor neurons are damaged, the muscles under their control will

no longer perform movements directed by the cerebral motor cortex

they will maintain tonus (spinal reflex) and can still be stimulated by other spinal reflexes

can't consciously move the muscle

SPASTIC paralysis

Spastic paralysis

muscles can only be stimulated to move reflexively

Lower motor neurons

true motor neurons that exit spinal cord and synapse directly w/muscle fibers and stimulate contraction

When alpha lower motor neurons are damaged,

extrafusal fibers of the motor units under the control of those alpha motor units can no longer be stimulated, will lose tonus, and exhibit flaccid paralysis

Flaccid paralysis

lose tonus, can't move

Babinski sign

not adduction and plantar flexion of toes in response to cutaneous reflex

instead big toe dorsiflexes

normal in babies

not in adults