AP Lecture 7 Study Questions

CORTICOSPINAL PATHWAY: Where do the fibers cross? Do they all cross in one place?

The fibers pass through the medulla oblongata and cross over to the contralateral side in the spinal cord.

CORTICOSPINAL PATHWAY: What is the difference between the anterior and lateral corticospinal tract?

The lateral cortico-spinal tract serves the limbs whereas the anterior cortico-spinal tract serves the abdominal and back muscles.

Does damage to the left half of the spinal cord posterior white matter create deficits on the left or right side of the body?

The left half spinal cord posterior matter houses the Posterior medial lemniscus tracts, and cross over does not occur until the medulla oblongata, therefore damage to the left side of the spinal cord in this area would create sensory deficits in the left side of the body.

CORTICOSPINAL PATHWAY: What is the effector of the lower motor neuron?

The motor neuron travels through the ventral root and out to the skeletal muscles (effectors)

How many neurons make up the sensory chain that brings sensory information to the postcentral gyrus? Where are the first order neuron cell bodies? Where are the third order neuron cell bodies?

The posterior column pathway brings sensory information to the post central gyrus of the parietal lobe, which houses the primary somatosensory cortex. The first order neuron cell bodies are out in the sensory receptive regions of the periphery. The 3 rd order neuron cell bodies are housed in the Thalamus.

Why do people become insensitive to stimuli in regions below spinal cord damage?

The receptors for stimuli are still present on the skin, but this information is not able to make it up to the cerebral cortex, and so it is not conscious and the patient with damage becomes insensitive to stimuli.

CORTICOSPINAL PATHWAY: Where do their axons travel (through which major tracts in the cerebrum, mesencephalon, and medulla)?

Their axons travel through the mesencephalon and the medulla oblongata.

SPINOTHALAMIC TRACTS: Where do the second order neurons synapse with the third order neurons?

They synapse in the thalamus.

SPINOTHALAMIC TRACTS: Where does this pathway end?

This pathway ends in the parietal lobe of the cerebral cortex where pain and temperature information are processed.

POSTERIOR COLUMN PATHWAY: What types of sensory information travel in the posterior columns of the spinal cord?

Touch, pressure, vibration, conscious position sense

In terms of sites of processing, what is the difference between feeling a sharp pain on your left side and feeling like your stomach hurts?

While both examples are sensory information, a pain in your left side is a somatosensory signal, where a stomach ache is a visceral-sensory signal. These are mapped differently, where visceral is located closer to the lateral gray horn and somatic is located in the dorsal (or posterior) gray horn. This information travels through the same pathway (the spinothalamic pain pathway) up to the cortex for conscious perception of pain signals.

SPINOTHALAMIC TRACTS: Are we are aware of this information?

Yes

SPINOCEREBELLAR: Where does this information go (where does the pathway end)?

cerebellum

CORTICOSPINAL PATHWAY: Where are the cell bodies of the upper motor neuron?

the primary motor cortex of the pre-central gyrus in the frontal lobe

What happens if the lateral white matter at the level of T2, right side, has a tumor? What can't you feel or do? What map/maps would help you answer this question?

this is below the brachial and cervical plexuses, so nerve supply to the head neck and upper two limbs would be fine. Nerve supply however the the lower trunk and limbs would be disrupted, pertaining to pain and temperature information on the left side of the body and motor information on the right side (limbs only).

SPINOCEREBELLAR: What types of sensory information travel in the spinocerebellar tracts of the spinal cord?

unconscious position information

SPINOTHALAMIC TRACTS: Where do the first order neurons synapse with the second order?

1 st order neurons synapse with second order neurons in the dorsal grey horn of the spinal cord

You suffer damage to your dorsal root ganglia of several spinal cord segments. What problems would you expect? Are largely motor or sensory portions affected?

A loss of sensation in the posterior trunk and muscle weakness would be expected.

What is a pathway?

A pathway is a "line" of neuron tracks that runs to a specific location for higher processing or for action using effector organs.

CORTICOSPINAL PATHWAY: At least how many neurons are involved in the simplest descending somatic motor pathways? Where are the cell bodies and axons of the upper and lower motor neurons in the somatic motor pathways?

At least a first order and a second order neuron are involved in descending somatic motor pathways. The cell body of the upper motor neurons are located in the cerebral cortex (specifically the primary motor cortex of the pre-central gyrus in the frontal lobe), which travel down to the anterior and lateral white areas of the spinal cord.

SPINOTHALAMIC TRACTS: What types of sensory information travel in the spinothalamic tracts of the spinal cord?

Conscious somatosensory information (pain and temperature)

SPINOTHALAMIC TRACTS: Where does crossover occur?

Cross over occurs from the dorsal gray horn to the opposite lateral white matter of the spinal cord.

POSTERIOR COLUMN PATHWAY: Where does crossover occur?

Cross over occurs in the medulla oblongata

POSTERIOR COLUMN PATHWAY: Where does this pathway end?

Ends in the post central gyrus where somatosensory information arrives at the primary somatosensory cortex.

Where must sensory information reach to be consciously perceived?

Information must reach the cerebral cortex for higher processing and conscious perception.

POSTERIOR COLUMN PATHWAY: Are we are aware of this information?

It is in the cerebral cortex, so yes.

SPINOTHALAMIC TRACTS: Which order neuron axons make up the spinal cord component of the spinothalamic tracts?

Mostly second order. (First order synapses here).

Why do people become paralyzed below the region of the spinal cord when damage occurs?

Motor information is not able to get through the pyramids

SPINOCEREBELLAR: Are we aware of this information? Why or Why not?

No, the cerebellum is unconscious and helps us to regulate things like posture and normal mannerisms without having to think about it.

POSTERIOR COLUMN PATHWAY: Where do the axons of the posterior column synapse with the second order neurons?

Nucleus gracillis and nucleus cuneatus of the medulla oblongata.

Why type of information would not reach the brain if the posterior gray horn was damaged?

Pain and temperature information from the right side of the body from that point down.

What do the pathway maps tell you?

Pathway maps allow you to see where information travels, through primary, secondary and third order neurons, where this information is synapsing, and if damage occurs, exactly where that damage is. Without maps of the nervous system, doctors would not be able to identify location of damage from neurological deficits.

POSTERIOR COLUMN PATHWAY: Which order neuron axons make up the posterior columns?

Primary, secondary and third order neurons.

How does your body control your ability to put a key into a lock? What parts of the brain are involved? Which parts can you control?

Putting a key in a lock involves pressure and location information

POSTERIOR COLUMN PATHWAY: Where do the second order neurons synapse with the third order neurons?

Second order neurons synapse with third order neurons in the ventral nuclei in the thalamus.

What is the importance of sensory information to motor control? How do unconscious commands reach skeletal muscle?

Sensory information is processed in the central nervous system (integration), which makes a plan for action using association cortexes, and executes that plan using the primary motor cortex. This is located in the post central gyrus of the parietal lobe. This information is then sent down an efferent pathway called the Cortico-spinal path to either the anterior or lateral white areas, and then out to an effector organ (usually a muscle).

How does sensory information reach the cerebral cortex?

Sensory information travels from sensory receptors in the skin muscles and organs and travels through the dorsal root ganglion where it synapses with a neuron in either the spinothalamic pathway (for pain and temperature information) or the posterior column medium lemiscus pathway (for touch, location, vibration, and pressure information)

Your friend suffers damage to her spinal cord. Below the level of damage she cannot feel temperature or pain stimuli on the opposite side of the body. What reason would account for this?

She must have damaged her spinal cord in a region that the spinothalamic pathway passes through, which would cut of sensory information to the rest of that pathway below that area. Anything above that area would travel along to the cerebrum fine. For this pathway damage could be in either posterior grey Horn (first synapse) or the lateral/anterior white matter (cross over).

CORTICOSPINAL PATHWAY: Where is the cell body of the lower motor neuron located?

The cell bodies of the lower motor neurons are located in the ventral gray horn of the spinal cord

How are the basal ganglia, cerebellum, and brainstem involved in motor control?

The cerebellum unconsciously coordinates/refines skeletal muscle movements and influences posture and balance. The basal ganglia regulate/terminate muscle tone and act through inhibition. The cerebellum and basal ganglia refine motor information by sending signals to the cerebral cortex or by sending signals to the lower motor neurons through brainstem pathways.