Burke, Motor Functions Of The Spinal Cord

Front 1

What is the basic unit of integrated neural activity?

Back 1

Reflex arc

Front 2

What does the reflex arc consist of?

Back 2

Consists of a sense organ, an afferent neuron, one or more synapses in a central integrating station or sympathetic ganglion, an efferent neuron or an effector.

Front 3

What is The connection between the afferent and efferent somatic neurons

Back 3

The connection between the afferent and efferent somatic neurons is generally in the bran or spinal cord.

Front 4

Afferent neurons enter where?

Back 4

The afferent neurons enter via the dorsal roots or cranial nerves – have cell bodies in the dorsal root ganglion

Front 5

Efferent fibers exit where?

Back 5

The efferent fibers exit via the ventral roots or corresponding motor cranial nerves.

Front 6

What is the Bell-Magendie law?

Back 6

the principle that in the spinal cord the dorsal roots are sensory and the ventral roots are motor.

Front 7

A sensory receptor generates action potentials where?

Back 7

A sensory receptor, with a receptor potential, whose magnitude is proportionate to the strength of the stimulus, generates all or none action potentials in the afferent nerve

Front 8

The number of action potentials being proportionate to ?

Back 8

the size of the generation potential

Front 9

In the CNS, how are responses graded?

Back 9

In the CNS, the responses are, moreover, graded in terms of EPSP’s and IPSP’s at the synaptic junction.

Front 10

Describe how "all or none" responses occur and from where?

Back 10

All or none responses are generated in the efferent nerve.
When these reach the effector, they again set up a graded response.
When the effector is a smooth muscle, the responses summate to produce action potentials in the smooth muscle.
When the effector is skeletal muscle, the graded response is always adequate to produce action potentials that bring about muscle contraction

Front 11

Where are the connections between the afferent and efferent neurons and how are they affected?

Back 11

It should be remembered that the connections between the afferent and efferent neurons is usually in the CNS and consequently activity in the reflex arc is subject to modification by the multiple inputs converging on the efferent neurons.

Front 12

Simplest reflex arc?
What is it?

Back 12

is one with a single synapse between the afferent and efferent neurons.

These are monosynaptic reflex arcs and reflexes occurring in them are monosynaptic reflexes.

Front 13

What are polysynaptic neurons?

Back 13

Reflex arcs in which one or more interneurons are interposed between the afferent and efferent neurons are termed polysynaptic.
The number of synapses in the arcs may vary from two to hundreds.

Front 14

What are mono and poly synaptic reflex arc activity modified by?

Back 14

spatial and temporal facilitation occlusion, subliminal fringe effects, etc.

Front 15

what is the stretch reflex?

Back 15

When a skeletal muscle with an intact nerve supply is stretched, it contracts. This is the stretch reflex.
The stimulus that initiates the reflex is the stretch of the muscle.
The response is contraction of the muscle being stretched.
The sense organ is the muscle spindle.
The impulses originating in the spindle are conducted in the CNS, by fast sensory fibers that pass directly to the motor neurons, which supply the same muscle.
Neurotransmitter at the central synapse is glutamate.

Front 16

Give an example of a stretch reflex.

Back 16

Tapping the patellar tendon elicits the knee jerk
Tapping on the tendon of the triceps brachii causes an extensor response at the elbow.

Front 17

In polysynaptic reflexes, the branch is a complex pattern. Describe.

Back 17

Branch in a complex pattern
Number of branches in each pathway is variable.
Because of the synaptic delay incurred at each synapse, activity in the branches with fewer synapses reaches the motor neurons first, followed by activity in the longer pathways.

This causes a prolonged bombardment of the motor neurons from a single stimulus and consequently prolonged responses.
Moreover, some of the branch pathways turn back on themselves thus permitting activity to reverberate until it becomes unable to cause a propagated transynaptic response and dies out.

Front 18

What is the withdrawal reflex?

Back 18

A typical polysynaptic reflex is the withdrawal reflex.
Withdrawal reflex – occurs in response to a noxious (usually painful stimulation of the skin or subcutaneous tissues and muscle.

The response is flexor muscle contraction and inhibition of extensor muscle.
The part being stimulated is flexed and withdrawn from the stimulus.

Front 19

Describe the crossed extensor response.

Back 19

When a strong stimulus is applied to a limb the response includes not only flexion and withdrawal of that limb but also extension of the opposite limb.

Easy to view in a spinal animal
Modulating effects of impulses from the brain abolished by section of the spinal cord
When hind limb of spinal cord is pinched, the stimulated limb is withdrawn, the opposite hind limb extended, the ipsilateral forelimb extended and the contralateral forelimb flexed.

Front 20

What is the irradiation of the stimulus.

Back 20

The speed of excitatory impulses up and down the spinal cord to more and more motor neurons

Front 21

What is recruitment of motor units.

Back 21

The increase in the number of active motor units

Front 22

How are flexor responses be produced?

Back 22

Flexor responses can be produced by innocuous stimulation of the skin, or by stretch of the muscle.

Front 23

How are Strong flexor responses with withdrawal initiated?

Back 23

Strong flexor responses with withdrawal are initiated only by painful noxious stimuli, potentially harmful to the organism.

Front 24

Withdrawal response has what kind of value to the organism?

Back 24

Withdrawal response has survival value to the organism.
Flexion of the stimulated limb gets it away from the source of irritation and extension of the other limb supports the body.

Front 25

What are Characteristics of polysynaptic reflexes?

Back 25

Weak noxious stimulus to one foot evokes a minimal flexion response.
Stronger stimuli produce greater and greater flexion as the stimulus irradiates to more and more of the motor neurons.

Stronger stimuli also elicit a more prolonged response
Prolonged response due to prolonged and repeated firing of the motor neurons
Is called after-discharge and is due to continual bombardment of motor neurons by impulses arriving by complicated and circuitous polysynaptic paths.

Front 26

As noxious stimuli increases, what happens?

Back 26

As the noxious stimulus is increased in strength the reaction time of the organism is shortened.
Spatial and temporal facilitation occurs at synapses in the polysynaptic pathway.
Stronger stimuli produce more action potentials per second in the active branches and cause more branches to become active.
Summation of the EPSP’s to the firing level therefore occurs more rapidly.