Reflexes Flashcards
Reflexes
instantaneous, automatic, and involuntary motor responses within the nervous system
they start from stimuli occurring inside or outside of the body. Reflexes come in a variety of forms
Reflex examples
- Subconscious reflexes occur within the body, such as the regulation of blood sugar by the hormones
- shivering in response to body temperature dropping
- you touch a very hot object and involuntarily withdraw your hand
Reflex Arc
refers to the neural pathway that a nerve impulse travels
dorsal root
how sensory information travels into the spinal cord
contains the axons of sensory neurons
ventral root
how Motor information travels out of spinal cord
gray matter
part of spinal cord contains the cell bodies of neurons
its also where neurons synapse with other neurons (such as interneurons)
white matter
part of spinal cord contains the axons of neurons
*spinal cord located centrally, with white matter surrounding the gray matter
interneurons
located only within the central nervous system to connect neurons to each other
dorsal root ganglion (DRG)
contains the cell bodies of sensory neurons
Reflex arc
1) Sensory neurons synapse on cells within the posterior horn of the spinal cord in the gray matter
2) Sensory neurons synapse on interneurons within the gray matter of the spinal cord.
3) Interneurons then synapse on motor neurons.
* Motor neuron cell bodies are located within the anterior horn of the gray matter*
4) Motor neurons (axons) leave the spinal cord via the ventral root
Spinal reflexes
faster than a conscious decision to move coming from the brain
faster not only because they involve fewer neurons, but also because the electrical signal does not have to travel to the brain and back
faster not only because they involve fewer neurons, but also because the electrical signal does not have to travel to the brain and back
Spinal reflex arc
1) The receptor at the end of a sensory neuron reacts to a stimulus.
2) The sensory (afferent) neuron conducts nerve impulses along an afferent pathway towards the central nervous system (CNS).
3) The integration center consists of one or more synapses in the CNS.
4) A motor (efferent) neuron conducts a nerve impulse along an efferent pathway from the integration center to an effector.
5) An effector responds to the efferent impulses by contracting (a muscle) or secreting a product (a gland).
Stretch reflexes
special type of muscle reflex that protect the muscle against increases in length that may tear or damage muscle fibers
important in maintaining upright posture
Muscle spindles
specialized muscle cells that are constantly monitoring the amount of stretch in a muscle
patellar reflex (stretch reflect)
The patellar reflex is also called the knee-jerk reflex used in physicians’ offices
ests the stretch reflex of the quadriceps femoris muscle in the thigh
patellar tendon
attaches the quadriceps muscle to the tibia bone of the lower leg
Patellar reflex arc
1) When the muscle spindle detects the stretch, a signal is sent along the afferent neuron, through the dorsal root ganglion (DRG) to the spinal cord via the dorsal root.
2) The afferent (sensory) neuron synapses in the gray matter of the spinal cord directly onto an efferent (motor) neuron in the anterior horn of the gray matter.
3) The efferent neuron travels out the ventral root and through the nerve to synapse on the same muscle.
* The effect of the motor signal is to contract the quadriceps muscle to prevent it from overstretching
flexor withdrawal reflex arc
1) From the cell body, the impulses travel along the axon of the sensory nerve and synapse on many interneurons within the gray matter of the spinal cord.
2) Excitatory interneurons send excitatory signals to motor neurons, causing muscular contraction.
3) Inhibitory interneurons send inhibitory signals that prevent muscular contraction
* Contraction of the biceps causes elbow flexion, withdrawing the hand from the hot object. The triceps receive an inhibitory signal to prevent contraction, so a co-contraction of the triceps and biceps does not occur.
Additional flexor withdraw reflex
If the biceps and triceps contracted simultaneously, the elbow would remain extended, leaving the hand fixed over the hot object causing increased damage
