Pre Lab Quiz #2

Lab 2 + 3 background info

What are specialized receptors?

Receptors in the muscle that respond to the stretching of the tendon attached to the muscle and then send signals to motor neurons through a single synapse.

What happens to the muscles in response?

They depolarize and twitch (contract) in response to the incoming impulse from the motor neuron.

What do the skeletal muscle receptors convey?

Information about muscle length, tension, and pressure to the central nervous system.

What are sensory receptors responsible for?

Providing information about the length or the rate of change of the length.

What muscles do sensory receptors convey information of?

Muscle spindles

How are muscle spindles arranged?

In parallel with muscle fibers.

How are the muscles spindled stretched?

Stretched when the muscle is stretched by an external force.

What is the purpose of muscle spindles?

Develops antigravity reflexes and maintains muscle tone.

What do muscle spindles contain?

Contain a small bundle of intrafusal fibers and extrafusal fibers

Do intrafusal fibers contribute to the overall tension of the muscle?

No

What do intrafusal fibers contribute to?

They regulate the excitability of the sensory afferent spindle nerves

How do intrafusal fibers regulate the excitability of afferent spindle fibers?

They mechanically deform the receptors

What are intrafusal fibers innervated by?

Gamma motor neurons.

What do most muscles consist of?

Extrafusal fibers

What are extrafusal fibers innervated by?

Alpha motor neurons

What are extrafusal fibers responsible for?

Developing muscle tension

What happens when a muscles is stretched?

The excitation of its muscle spindles cause a reflex contraction of the muscle

What is this reflex called?

Stretch (myotactic) reflex

What causes minimal delay between the muscle stretching and the reflex contraction?

The monosynaptic pathway.

What happens during the monosynaptic pathway?

Afferent nerves from the spindles synapse directly with motor neurons

Are there interneurons in this monosynaptic pathway?

There are no interneurons

What does this monosynaptic pathway constitute to?

The shortest possible reflex arc.

Why do we have this reflex arc?

Its the main reason why we keep our balance and do not fall when changing certain body positions.

Which muscle groups are involved in plantar flexion of the ankle?

Gastrocnemius and soleus

Which muscle groups are involved in dorsiflexion of the ankle?

The anterior compartment of the lower leg (so the tibia’s, extensor digitorum and hallucis longus, and the peroneus tertius.

Besides excitatory inputs from stretch receptors, what synaptic inputs might influence the activity of spinal motor neurons?

• Descending motor commands

• Inhibitory spinal interneurons

• Sensory afferent neurons

• Modulatory inputs

How many muscles does the human eye have?

6 muscles

What surface are these muscles attached to?

The exterior surface

How many groups are the muscles in

3 antagonistic pairs

How are these muscles grouped?

1. Horizontal

2. Vertical

3. Torsional

movement and position of the eye

What muscles move around the vertical axis?

• Medial rectus and lateral rectus muscle

How do these muscles move around the vertical axis?

• Medial rectus: Turns eye towards nose (ADDUCTS)

• Lateral rectus: Turns eye away from nose (ABDUCTS)

What muscles move around the horizontal axis?

• Superior and inferior rectus muscles

How do these muscles move around the horizontal axis?

• Superior rectus: Turns eye up w slight rotation to nose (ELEVATES + INTORTS)

• Inferior rectus: Turns eye down w slight rotation away from nose (DEPRESSES + EXTORTS)

What muscles move around the torsional axis?

• Superior and inferior oblique muscles

How do these muscles move around the torsional axis?

• Superior oblique: Rotates top of eye to nose w slight depression (INTORTS)

• Inferior oblique: Rotates top of eye away from nose w slight elevation (EXTORTS)

How are these muscles innervated?

Innervated by motor neurons that have electrical activity w a tonic and phasic component

What does the tonic component control?

The position of the eye

What does the phasic component control?

The velocity of the eye

How are the eye velocity commands sent?

Along direct path from specialized brain formations or fields to the motor neurons

What are the eye position commands a product of?

The integration of eye velocity commands sent along an indirect path to a network of neurons functioning as neural integrators.

What is the output oof the integrator?

Provides eye position commands to the motor neurons

What do the integration of signals control?

5 types of eye movement each w a unique function and distinctive property

What are the five types of eye movement?

1. Saccades

2. Pursuit

3. Vestibular ocular reflex (VOR)

4. Vergence

5. Optokinetic reflex

What is the recording of the electrical activity of the eye known as?

Electrooculogram (EOG)

What is the fovea centralis (focal point)

The region of the retina that sees in detail.

What do the saccadic eye movements do?

Rotate both eyes of that the image of interest falls on the fovea.

How fast are saccadic eye movements?

They’re quick w a velocity as high as 800 degrees in a second

Are the saccades accurate?

Yes

How are the saccades accurate?

The system uses an internal estimate of eye position from its neural integrator to guide and stop the saccades.

What does the pursuit eye movement do?

Keeps the fovea pointed at a moving target like a bouncing ball

What happens during pursuit movement?

There is an initial delay because the signal from the eye indicates that the object is moving, which has to be conducted through many synapses to the brainstem.

How does the saccade help with pursuit movement?

Helps the fovea catch up to the object until the pursuit movement begins to track the object.

What does the VOR movement do?

Keeps the image of the outside world stationary on the entire retina when the head moves.

Is VOR tonic or phasic?

Its a phasic response that is faster than pursuit

Why is VOR faster than pursuit?

Because it’s a simple central reflex arc that involves only three neurons.

Where does the signal that indicated the velocity of head movement originate from?

In the semicircular canals of the ear which goes through an afferent nerve and an interneuron on its way to the motor neuron of the oculomotor muscles.

What happens during VOR movement?

The muscles rotate the eyes at a velocity that matches the velocity of the head, keeping the image stationary on the retina.

Are the eyes held on the image going through a tonic or phasic response?

Tonic response

Where is the tonic response happening?

The tonic response is along an indirect path through a reverberating neural circuit between the afferent nerve and motor neurons

What would happen without this neural circuit (short-term memory device)

The eyes would drift back to the centre and off the image while the head was still rotated.

What is the vergence movement?

Points the fovea of each eye onto an object when you look from a target that is distant to the one that is closer (vice versa)

What happens during vergence?

The eyes rotate in opposite directions

What happens to the eye when looking from far to near?

Convergence

What happens to the eye when looking from near to far?

Divergence

Why is vergence important?

Prevents double vision

When is the optokinetic reflex activated?

When the full field of vision has moved across a large portion of the retina

How fast is the optokinetic reflex?

It is slower than the VOR, hence complementing this movement

Why do we have the optokinetic reflex?

Better suited for working on slow and prolonged movements

What device is used to test the optokinetic reflex?

An optokinetic drum

What does the optokinetic drum do?

Projects a series of rotating images on the wall of a small circular room while the subject is seated in the centre of the room/