Spinal Reflex Flashcards
What are the properties of Reflexs?
Reflex properties
Rapid, pre-programmed, involuntary reactions of muscles or glands
* e.g., touch burner on stove
* automatically remove hand from stimulus
* survival mechanism
* enables quick response without waiting for brain to process
- Stimulus required to initiate response
** Rapid response**
* few neurons involved and minimal synaptic delay
Pre-programmed response
* occurs same way every time
Involuntary response
* requires no conscious intent
* awareness occurring after completion of reflex act
What are the main properties of a reflex?
- stimulus required to initiate a response to sensory input
- rapid response requiring few neurons
- pre-programmed and involuntary response
What is reflec arch?
Reflex arc
- Neural “wiring” of a single reflex
- Begins at a receptor in PNS
- Communicates with CNS
- Ends at a peripheral effector (muscle or gland)
- Varying number of intermediate steps
What are components of relfex arc?
- Receptor-site of stimulus action
- Sensory neuron-transmits afferent impulses to the CNS
- Integration center-either monosynaptic or polysynaptic
region within the CNS - Motor neuron-conducts efferent impulses from the integration center to an effector organ
- Effector-muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting
What are the types of reflex?
Ipsilateral reflex arcs
* both receptor and effector organs on same side of spinal cord
* e.g., remove hand from hot stimulus on same side
Contralateral reflex arcs
* sensory impulses from receptor on opposite sides of spinal cord
* e.g., step on object with left foot
* contract right leg to maintain balance (as withdraw left leg)
**Monosynaptic reflexes **
* simplest of all reflexes
* sensory axons directly synapsing on motor neurons very minor synaptic delay
* e.g., patellarreflex
- tap patellar ligament with a reflex hammer
- muscle spindles in quadriceps stretched
- causes a reflexive contraction, noticeable leg kick
Polysynaptic reflexes
* more complex neural pathways
- more prolonged synaptic delay before response
- e.g., withdrawal reflex initiated by painful
- stimulus sensory input transmitted to spinal cord
- received by interneurons
- stimulate motor neurons to flex muscles in limb
- hand pulled away from painful stimulus
What are the five steps involved in activation of a reflex?
- Stimulus activates a receptor.
- Nerve signal travels through to the CNS.
- Information from the signal is processes by interneurons.
- Motor neuron transmits a nerve signal to an effector.
- Effector responds to nerve signal.
What is strecth reflex?
- Monosynaptic reflex
- Regulates skeletal muscle length
- Reflexive muscle contraction after stretching of a muscle
What is biceps reflex?
- monosynaptic stretch reflex
- muscle spindle in biceps brachii stretched by tap
- sensory neurons synapsing with alpha motor neurons
- transmit signals to extrafusal muscle fibers
- initiate muscle contraction and flex elbow joint
What is golgi tendon reflex?
- Prevents muscles from contracting excessively
- Polysynaptic reflex
- Results in muscle lengthening
- Occurring in response to tension at Golgi tendon organ
- composed of sensory nerve endings within a tendon
- or near muscle-tendon junction
What is golgi tendon reflex path?
- tendon stretched with muscle contraction
- Golgi tendon organ activated
- sensory neuron transmission to interneurons
- inhibit alpha motor neurons in muscle
- associated muscle allowed to relax
- protects muscle and tendon from excessive damage
What is Reciprocal activation?
golgi tendon reflex
- stimulation of alpha motor neurons of antagonistic muscles
- e.g., Golgi tendon organ activated in quadriceps
- relaxation of quadriceps femoris due to Golgi tendon reflex
- hamstrings stimulated to contract via reciprocal activation
- occurs via interneurons in spinal cord
- Golgi tendon reflex and stretch reflex
- stretch reflex may be nullified by Golgi tendon reflex
- under extreme tension
What is withdraw reflex?
- Reflex path
- polysynaptic reflex initiated by painful stimulus
- transmitted by sensory neuron to spinal cord
- received by interneurons
- motor neurons signaled to flex
- e.g., step on sharp object
- signal transmission to spinal cord synapse with interneurons stimulate hamstrings to flex
- quadriceps reciprocally inhibited
What is crossed extensor reflex?
- Often in conjunction with withdrawal reflex
- Reflex path
- sensory transmission to spinal cord
- synapse with interneurons in stretch and crossed-extensor reflex synapse with motor neurons on antagonistic muscle in opposite limb
- e.g., step on sharp object with right lower limb
- cross-extensor reflex stimulating left quadriceps femoris to contract
left limb stays extended
What are the four common spinal reflexes?
Stretch reflex
Golgi tendon reflex
Withdrawal reflex
Crossed-extensor reflex
What are reflex varitations?
- Can be important diagnostic tool
- Used to test specific muscle groups and spinal nerves
- Some variation normal
- Consistently abnormal reflex
- may signal damage to nervous system or muscles
