Lecture 7 Study Guide

Sensory information travels to the brain through ascending tracts of the spinal cord. a.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 (or another way to think of this, where do the second order neurons synapse with the third order neurons?)?

a. three neurons b. first order neurons have their cell bodies in the dorsal root ganglia c. third order neurons have their cell bodies in the thalamus

Somatic motor information leaves the brain by way of descending fiber tracts. Somatic motor commands go to skeletal muscle while autonomic commands go to visceral muscle/organs. 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 two cell bodies and axons of the upper motor neuron cell bodies are found in the primary motor cortex of the pre central gyrus of the frontal lobe lower motor neurons have their cell bodies in the ventral horn of the spinal cord grey matter

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

because that is a tract with all information running through there to farther down points of synapse. if you damage at one place everything below that tract has its signal transmission interrupted as a result.

Where must sensory information reach to be consciously perceived?

cerebral cortex, only the spinothalamic pathway and the posterior column medial lemniscus transfer this info

dorsal gray horns

consist entirely of interneurons.

4. This question addresses the descending pathways that carry somatic motor information. a. Corticospinal pathway (if you can draw this, you have answered the questions i-iv): i. Where are the cell bodies of the upper motor neuron? ii. Where do their axons travel (through which major tracts in the cerebrum, mesencephalon, and medulla)? iii. Where do the fibers cross? Do they all cross in one place? iv. Where is the cell body of the lower motor neuron located? v. What is the effector of the lower motor neuron? vi. What is the difference between the anterior and lateral corticospinal tract?

corticospinal pathway: 1. upper cell bodies are in the cerebral cortes, the primary motor cortex in the pre central gyrus of the frontal lobe. 2. the axons travel through the pyramidal tracts 3. the fibers of the lateral corticospinal cross in the medulla the fibers of the ventral cross in the spinal cord. not all crossing in one place 4. cell bodies of the lower neurons are in the ventral grey horn 5. the effector of the lower neuron is a skeletal muscle 6. anterior control the trunk, lateral control the limbs

descending pathways

deliver efferent impulses from the brain to the spinal cord Direct pathways (pyramidal tract)-- upper, pyramidal cells of the motor cortex Indirect pathways (all others)--lower, ventral horn motor neurons that directly innervate the skeletal muscles motor pathways require two neurons , upper and lower. The

three ascending pathways

dorsal column-medial lemniscal - crosses (decussates in the medulla) spinothalamic -- crosses (decussates) in the spinal cord both transmit impulses via the thalamus to the sensory cortex for conscious perception of discriminative touch and proprioception. spinocerebellar pathway -- terminates in the cerebellum, no perception.

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

dorsal root ganglia = sensory. if you have damage to several you would lose feeling or have reduced feeling in a large area where those nerves are going.

ascending pathways

first order neurons-- cell bodies reside in a ganglion (dorsal or cranial). these conduct impulses from the cutaneous receptors of the skin and from proprioceptors to the spinal cord or brain stem where they synapse with the second order neurons. second order-- neurons reside in the dorsal horn of the spinal cord or in the medullary nuclei. they transmit impulses to the thalamus or to the cerebellum where they synapse. third order neurons-- cell bodies are in the thalamus and they relay impulses to the somatosensory cortex of the cerebrum

indirect pathways

include brain stem motor nuclei and all other motor pathways.

spinothalamic pathways

input from many kinds of sensory receptors and synapse many times in the brain stem. these pathways consist of the lateral and ventral spinothalamic tracts. Fibers cross in the spinal cord. The transmit pain and temperature information

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

left side of the body, no crossover until the medulla

funiculi

long ropes that the white matter can be broken up into. Dorsal, lateral, ventral. There are several white matter tracts in each that are made up of axons with similar destinations and functions.

dorsal column-medial lemniscal pathway

mediate precise sensory inputs of discriminative touch and vibrations. These are found in the dorsal white column of the spinal cord: fasciculus cuneatus fasciculus gracilis medial lemniscus (in the medulla to the thalamus)

lateral gray horns

mostly cell bodies of autonomic (sympathetic) motor neurons that serve the visceral organs and travel with the ventral root as well.

What is a pathway?

neurons in a series that carry information

direct (pyramidal) pathways

originate mostly with pyramidal cells in the pre central gyri. these axons descend without synapsing until the spinal cord where they meet interneurons or the ventral horn. this pathway regulates fast and skilled movements like writing.

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

same as above, the tract carrying that sensory information up has a break point where the damage is so everything below that pathway is interrupted.

5. What is the importance of sensory information to motor control? a. How are the basal ganglia, cerebellum, and brainstem involved in motor control? What generally is the extrapyramidal motor system? How does this system influence motor control? Do we have consciousness of this system?

sensory information is very important to motor control. it lets the muscles know the position already happening. a. basal ganglia regulate and terminate muscle tone through inhibition cerebellum refines and smooths the movements, it corrects the plans the brainstem is also involved, they all don't communicate directly with the motor neurons that effect muscles but send input up and down to other systems not conscious, this is the extrapyramidal system

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

sensory propriceptive information is crucial for motor control, because it sends information we are not always conscious of to our brain letting us know where our muscles are / how stretched they are, allowing our body to make adjustments to keep us upright in our position. Unconscious commands reach our skeletal muscles using extra-pyramidal (indirect) pathways. These include: rubrospinal tactospinal reticulospinal and vestibulospinal all of these tracts begin in the brainstem

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?

sharp pain from your left would use the spinothalamic pathway. This would be a first order neuron synapsing in the posterior gray horn with another neuron that would cross the body there in the spinal cord. This second order neuron would carry information up to the thalamus before synapsing with a third order neuron to bring info to the cerebrum. in terms of sites of processing, both pains would be consciously perceived so they would reach the cerebral cortex, however the pain would reach different parts of the somatosensory region. left side would have synapses in the posterior grey horn, stomach pain would have synapses in the lateral grey horn.

further classification of the grey horn based on what it is serving

somatic sensory (dorsal top) visceral sensory visceral motor somatic motor (anterior bottom)

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

somatic sensory information

ventral gray horns

some interneurons but mostly house the cell bodies of somatic motor neurons. these send their axons out to skeletal muscles using the ventral roots

d.--Spinocerebellar Tracts (you do not need to be able to draw this one): i. What types of sensory information travel in the spinocerebellar tracts of the spinal cord? ii. Where does this information go (where does the pathway end)? iii. Are we are consciously aware of this information? Why or why not?

spinocerebellar tract: 1. information about unconscious position travels here (muscle or tendon stretch) 2. information goes to the cerebellum 3. no, not in the cortex

How does sensory information reach the cerebral cortex?

stimuli triggers sensory receptors which carry information to the CNS using action potentials to send info to the spinal cord. The info then goes up to the CNS where it reaches the thalamus, the relay center for sensory information. Then another neuron carries the information to the cerebral cortex for conscious perception. conscious pathways are the posterior column-medial lemniscus pathway and the spinal thalamic pathway in the lateral column

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?

the spinothalamic tract was damaged and it crosses over in the spinal cord so it effects the other side of her body.

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

this would be the spinocerebellar tract that doesn't cross over, it is ipsalateral. this tract conveys information about unconscious muscle position, and T2 is a part of your brachial plexus, so upper limb. so this means the right arm would not have unconscious motor control so there would be difficulty in controlling this limb.

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?

to put a key in a lock the body relies on sensory information first to get a sense of the bodies position. From there, it uses the lateral corticospinal pathway to send motor controls from the cerebral cortex across the medulla oblongata to the spinal cord where it will synapse in the anterior grey horn and out to control the motor action. Unconscious motor actions likely are involved as well.

Spinocerebellar pathways

ventral and dorsal spinocerebellar tracts. they convey info about muscle or tendon stretch to the cerebellum to coordinate muscle activity. not conscious. They either don't decussate or cross over twice so it is "undone"

What do the pathway maps tell you?

we can map both the white matter and gray matter of the spinal column just as we did the brain, so we know exactly what kind of information is being carried there and where it is going to (hands, upper limbs, ect.)

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2--.This question addresses the ascending pathways that carry sensory information. B.--Posterior column-Medial lemniscus pathway (if you can draw this, you have answered the questions i-vi): i. What types of sensory information travel in the posterior columns of the spinal cord? ii. Which order neuron axons make up the posterior columns? iii. Where do the axons of the posterior column synapse with the second order neurons? iv. Where does crossover occur? v. Where do the second order neurons synapse with the third order neurons? vi. Where does this pathway end? vii. Are we are aware of this information?

Posterior column medial lemniscus = 1. touch and vibration sensory information 2. first order neurons make up the columns of the spinal cord 3. axons of the posterior column synapse in the grey matter of the medulla 4. cross over occurs in the medulla 5. second order neurons synapse in the thalamus 6. this pathway ends in the cerebral cortex, the primary somatosensory region in the post central gyrus of the parietal lobe 7. yes, aware

c.--Spinothalamic Tracts (if you can draw this, you have answered the questions i-vi) i. What types of sensory information travel in the spinothalamic tracts of the spinal cord? ii. Where do the first order neurons synapse with the second order? iii. Where does crossover occur? iv. Which order neuron axons make up the spinal cord component of the spinothalamic tracts? v. Where do the second order neurons synapse with the third order neurons? vi. Where does this pathway end? vii. Are we are aware of this information?

Spinothalamic tract: 1. temperature and pain or pressure travel here 2. first order neurons synapse with second order in the grey matter of the spinal cord, in the posterior grey horn 3. cross over occurs in the spinal cord 4. second order neurons make up the spinal cord component of the tract. 5. these 2nd order synapse in the thalamus with the third 6. ends in the cerebral cortex, post central gyrus in the primary somatosensory cortex. 7. aware