12-2: Spinal Cord - reflexes Flashcards
spinal reflex
quick, involuntary responses to stimuli that allow the body to maintain homeostasis
reflex arc
pathway over which a reflex is transmitted
What are the five steps of a reflex arc?
- receptor
- sensory neuron
- integration (reflex) center
- motor neuron
- effector
receptor
step 1 of reflex arc; specialized dendrite of a sensory neuron that responds to a change in the environment (stimulus) by generating a nerve impulse
sensory neuron
step 2 of reflex arc; sends afferent nerve impulses from the receptor into the CNS
integration (reflex) center
step 3 of reflex arc; area in the CNS where an incoming sensory impulse generates an outgoing motor impulse. IT may contain (an) association neuron(s)
motor neuron
step 4 of reflex arc; sends efferent nerve impulse from the CNS out to an effector
effector
step 5 of reflex arc; the muscle or gland that responds to a motor impulse (the response is called a reflex)
How are spinal nerves connected to the cord?
each pair of spinal nerves is connected at two points: dorsal root and ventral root
dorsal root
contains only sensory neurons, conduct impulses from the periphery out of the body into the spinal cord
ventral root
contains only motor neurons; conduct impulses from the spinal cord out to effectors in the periphery of the body.
Where are the cell bodies of sensory neurons located?
dorsal root ganglion (swelling on the dorsal root)
Where are the cell bodies of motor neurons located?
in the gray matter of the cord
monosynaptic reflex arc
1 synapse, 2 neurons: 1 sensory and 1 motor
What type of reflex arc is a stretch reflex?
monosynaptic
stretch reflex
results in the contraction of a skeletal muscle when it is stretched suddenly (eg. patellar reflex to assess L2 - L4)
muscle spindle
receptors in the muscle that monitor muscle length
What are the steps in the stretch reflex?
> muscle spindle monitors muscle length
> when stretched, nerve impulse is generated and sent through a sensory neuron through the dorsal root of a spinal nerve in the spinal cord
> the sensory neuron synapses with a motor neuron in the anterior horn
> the motor neuron exists the cord through the ventral root and stimulates the stretched muscle to contract
What is the stretch reflex essential for?
posture, muscle tone, and preventing injury due to overstretching of muscle
polysynaptic reflex arc
more than one synapse - association neurons are involved
What is an example of a polysynaptic reflex arc?
flexor (withdrawal) reflex
flexor reflex
aka withdrawal reflex
results in movement of a body part to avoid pain by contracting flexor muscles and inhibiting extensors. Stimulus can be actual or perceived pain.
Touching a hot stove results in a ___ reflex (a type of ___ reflex arc).
flexor; polysynaptic
The patellar reflex is an example of a __ reflex (a type of ___ reflex arc).
stretch; monosynaptic
