PNS pt 2 Flashcards
Reflexes
Inborn intrinsic reflex: rapid, involuntary predictable motor response to stimulus
Ex: splashing hot water from pot on your arm
Learned (acquired) reflexes from practice/repition
Ex: driving skills
- Receptor
- Sensory neuron
- Integration center
- Motor neuron
- Effector
Reflex arc
Components of reflex arc
1. Receptor: site of stimulus action
2. Sensory neuron: transmits afferent impulses to the CNS
3. Integration center: monosynaptic/polysynaptic region within the CNS
4. Motor neuron: conducts efferent impulses from the integration center to an effector organ
5. Effector: muscle fiber/gland cell that responds to efferent impulses by contracting/secreting
Spinal reflexes
Integration center is in spinal cord
Effectors are skeletal msucle
Stretch, flexor, crossed-extensor
Stretch reflexes
How stretch reflex works:
- stretch activates muscle spindle (receptor)
- sensory neurons synapse directly w/ alpha motor neurons in spinal cord
- alpha motor neurons cause stretched muscle to contract
- all stretch reflexes are monosynaptic and ipsilateral
Patellar knee jerk reflex
- Tapping patellar ligament excites muscle spindles in quads
- Afferent impulses travel to spinal cord, synpases occur w/ motor neurons
- motor neruons senc activating impulses to quads, contractions, extending knee
Abnormal stretch reflex
Flexor + crossed-extensor reflexes
Flexor withdrawal reflex
- initiated via painful stimulus
- automatic withdrawal of threatened body part
= ipsilateral + polysynaptic
- descending signals from brain can override flexor reflexes
Crossed extensor reflex
- flexor reflexes in weight-bearing limbs to maintain balance
- ipsilateral flexor reflex + contralateral extensor reflex
- stimulated side withdrawn (flexed)
- contralateral side is extended
Superficial reflexes
Plantar reflex (babinski reflex)
- stimulus: stroking lateral of sole of foot
- normal response: downward flexion of toes
- tests fuction of corticospinal tracts
