Spinal Reflex

Question 1

What are the properties of Reflexs?

Answer 1

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

Question 2

What are the main properties of a reflex?

Answer 2

• stimulus required to initiate a response to sensory input
• rapid response requiring few neurons
• pre-programmed and involuntary response

Question 3

What is reflec arch?

Answer 3

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

Question 4

What are components of relfex arc?

Answer 4

1. Receptor-site of stimulus action
2. Sensory neuron-transmits afferent impulses to the CNS
3. Integration center-either monosynaptic or polysynaptic
   region within the CNS
4. Motor neuron-conducts efferent impulses from the integration center to an effector organ
5. Effector-muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting

Question 5

What are the types of reflex?

Answer 5

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

Question 6

What are the five steps involved in activation of a reflex?

Answer 6

1. Stimulus activates a receptor.
2. Nerve signal travels through to the CNS.
3. Information from the signal is processes by interneurons.
4. Motor neuron transmits a nerve signal to an effector.
5. Effector responds to nerve signal.

Question 7

What is strecth reflex?

Answer 7

• Monosynaptic reflex
• Regulates skeletal muscle length
• Reflexive muscle contraction after stretching of a muscle

Question 8

What is biceps reflex?

Answer 8

• 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

Question 9

What is golgi tendon reflex?

Answer 9

• 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

Question 10

What is golgi tendon reflex path?

Answer 10

• 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

Question 11

What is Reciprocal activation?

golgi tendon reflex

Answer 11

• 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

Question 12

What is withdraw reflex?

Answer 12

• 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

Question 13

What is crossed extensor reflex?

Answer 13

• 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

Question 14

What are the four common spinal reflexes?

Answer 14

Stretch reflex
Golgi tendon reflex
Withdrawal reflex
Crossed-extensor reflex

Question 15

What are reflex varitations?

Answer 15

• 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

Question 16

What is Hyperactive reflex ?

Answer 16

• abnormally strong response
• may indicate damage in brain or spinal cord
• clonus, rhythmic oscillations between flexion and extension
• may especially indicate damage