Lecture 16: NS II

4 main functions of spinal cord

1. conduction
2. neural integration
3. locomotion
4. reflexes

4 main functions of spinal cord - conduction

nerve fibers conduct sensory and motor information up and down the spinal cord

4 main functions of spinal cord - neural integration

ex: it can integrate the stretch sensation from a full bladder with cerebral input concerning the appropriate time and place to urinate and execute control of the bladder accordingly

4 main functions of spinal cord - locomotion

simple repetitive muscle contractions coordinated by groups of neurons (central pattern generators; AKA CPGs)
ex: put 1 foot in front of the other repeatedly while walking

what are CPGs?

CPG are circuits of interneurons present within different spinal cord segments. When activated, they produce the patterns of neural activity that underlie rhythmic motor behaviors such as walking, breathing, flying and swimming

4 main functions of spinal cord - reflexes

involuntary responses to stimuli that are vital to posture, motor coordination and protective responses to pain or injury

cervical enlargement

beginning of the spinal cord; origin for nerves of upper limbs

lumbosacral enlargement

origin for nerves of pelvis and lower limbs

conus medullaris

where the spinal cord ends

cauda equina

bundle of spinal nerves in vertebral canal; innervates pelvis and lower limbs; latin for horse's tail

filum terminale

portion of the pia mater that supports the cauda equina

How many layers of membrane protect the brain and spinal cord?

3

T or F: There is an anterior root ganglion

False; there is no anterior root ganglion (somas of these neurons are in the gray matter of the spinal cord)

Cross-section of spinal cord

Why is white matter white?

because it contains lipids

Gray matter

butterfly or H-shaped neuron cell bodies; regions of gray matter also have farious groups of neuron cell bodies called nuclei; subdivided into regions called horns: posterior gray horn, lateral gray horn, and anterior gray horn.

white matter

composed primarily of myelinated axons (organized in tracts); divided into 3 columns (funiculi): posterior white column, lateral white column, and anterior white column

lateral gray horn

Only through T1-L2. It contains the cell bodies of autonomic motor neurons which innervate cardiac muscle, smooth muscle, and glands - sympathetic NS),

T or F: Sensory information enters the spinal cord via the ventral roots of the spinal nerves

False; sensory information enters through the dorsal roots

Where are the cell bodies of sensory neurons located?

in the ganglion

Where are the cell bodies of motor neurons located?

in the horns of the spinal cord

What kind of information does the ventral root carry?

motor/efferent

What does SS indicate?

Interneurons receiving input from somatic sensory neurons; found in dorsal horn

What does VS indicate?

Interneurons receiving input from visceral sensory neurons; found in dorsal horn

What does VM indicate?

Visceral motor (autonomic) neurons (cell bodies) that innervate smooth muscle, cardiac muscle, and glands; found in lateral horn

What does SM indicate?

Somatic motor neurons (cell bodies) that innervate skeletal muscle; found in ventral horn

Do axons or cell bodies correspond to sensory neurons?

axons

Do axons or cell bodies correspond to interneurons?

cell bodies

dorsal root ganglion

contain the cell bodies of the (1st order) sensory neurons

How do sensory neuron axons enter the spinal cord?

through the posterior roots

How do motor neurons exit the spinal cord?

through the anterior roots

What kind of information uses the ascending tract?

Sensory information

What kind of information uses the descending tract?

Motor information

tract

bundles of CNS axons that share a common origin, destination, and function

what are ascending tracts also known as?

somatosensory pathways or systems

What are the three primary types of ascending pathways on each side of the spinal cord?

1. Spinothalamic (or anterolateral) pathway
2. Spinocerebellar pathway
3. Dorsal column-medial lemniscus pathway

ipsilateral

when the origin and destination of a tract are on the same side of the body

decussation

point at which some tracts cross over from left side of the body to the right or vice versa

contralateral

on opposite sides of the body

neurites

small processes on developing neurons that ultimately grow out into axons or dendrites

How many tracts make up the Spinothalamic (or anterolateral) pathway? What are they?

2 separate tracts; lateral and anterior; these fibers cross over (decussate) within the spinal cord; although the tracts are functionally distinct, these tracts run alongside each other, and they can be considered a single pathway

What order neurons make up the Spinothalamic (or anterolateral) pathway?

1st, 2nd, and 3rd order; 1st order neurons come from periphery (ex: skin), go through dorsal neurons to the interneuron in the vertebra; the info is passed to 2nd order neurons here; moves up the axons to the thalamus where we have 3rd order neurons; these pass info to the cortex

sebstantia gelatinosa

synapse between 1st and 2nd order neurons at the tip of the dorsal horn

What type of information does the lateral tract of the Spinothalamic (or anterolateral) pathway detect?

Temperature and pain

What type of information does the anterior tract of the Spinothalamic (or anterolateral) pathway detect?

crude touch (non-discriminative) and pressure

If information reaches the cortex is it conscious or unconscious?

conscious

Does the spinocerebellar tract deal with conscious or unconscious sensation?

unconscious senesation

How many neurons make up the spinocerebellar tract?

2 neurons; anterior and posterior spinocerebellar tracts

What kind of information does the spinocerebellar tract recieve? Why is this important?

Proprioceptive information from golgi tendon organs, muscle spindles and joint capsules; for the control of posture and coordination of movements

Where do the third order neurons have their cell body in the anterolateral system?
A) Cortex
B) Thalamus
C) Medulla
D) Spinal cord

B) Thalamus

The cell bodies found in the posterior gray horns of the substantia gelatinosa belongs to:
A) 1st order sensory neurons
B) 2nd order sensory neurons
C) 3rd order sensory neurons
D) 1st order motor neurons

B) 2nd order sensory neurons because their fibers form the ascending tracts. They carry sensory impulses to the thalamus

Which of the sensory modalities (sensory information) is NOT carried by the spinothalamic system?
A) Pain
B) Pressure
C) Crude touch
D) Proprioception

D) Proprioception because the spinothalamic tract conveys pain, temperature, and crude touch; the spinocerebellar tract carries proprioception.

What sensory modalities does the dorsal column-medial pathway (DCML) carry?

-fine (discriminative) touch
-proprioception (movement and joint position)
*Conscious sensations

medial lemniscus

second order sensory neuron of the DCML; formed in the medulla as fibers from the posterior column nuclei cross the midline

dorsal column

posterior funiculus of spinal cord

How many fasciculi does the DCML contain?

2 fasciculus; fasciculus cuneatus and fasciculus gracilis

What sensations does the fasciculus cutaneous of the DCML detect?

sensations from upper limb and chest; T6 and above

What sensations does the fasciculus gracilis of the DCML detect?

sensations from lower limbs and lower trunk; below T6

nucleus cuneatus

where the 2 fasciculus synapse with other neurons

What are the two major groups of descending motor tracts in the spinal cord?

pyramidal tracts and extrapyramidal tracts (EPTs)

Where do pyramidal tracts originate?

cerebral motor cortex

Where do extrapyramidal tracts originate?

brain stem

What is the cerebral motor cortex responsible for?

voluntary (conscious) control of the musculature

What two tracts does the cerebral motor cortex control?

corticobulbar tract (musculature of the head and neck) and the corticospinal tract (musculature of the limbs and trunk)

How do pyramidal tracts innervate neurons?

They directly innervate neurons in the ventral horn

How do extrapyramidal tracts (EPTs) innervate neurons?

They indirectly innervate interneurons that will either activate or inhibit the lower motor neurons; the cerebral cortex of the brain sends signals to the spinal cord and then this info is carried from the spinal cord to the muscle

What is the importance of the Extrapyramidal tract?

Aids in tone, balance, posture, and locomotion

What is the brainstem responsible for?

the involuntary movement and autonomic control of musculature (unconscious)

extrapyramidal tracts - vestibulospinal tract

helps to maintain balance

extrapyramidal tracts - reticulospinal tract

involved in analgesic pathways (transmission of pain signals)

extrapyramidal tracts - Tectospinal tract

produces head-turning reflex in response to auditory and visual stimuli

extrapyramidal tracts - rubrospinal tract

regulation of muscle tone

medullary pyramids

paired white matter structures of the brainstem's medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts

what does the corticospinal pathway control?

contralateral muscles

how many motor neurons are involved in the corticospinal tract?

2 motor neurons (upper and lower)

where does the upper motor neuron of the corticospinal pathway originate/end?

Starts in the motor cortex and runs down spinal cord

where does the lower motor neuron of the corticospinal pathway originate/end?

neurosoma is in the brainstem/spinal cord and its axon leads to a muscle/target organ

what two tracts make up the corticospinal pathway?

lateral corticospinal tract and anterior corticospinal tract

do fibers of the lateral corticospinal tract stay on one side of the body or cross over? What % of fibers are in the lateral corticospinal tract?

fibers cross over the pyramids to other side of the body; 90% of fibers in corticospinal pathway are lateral.

do fibers of the anterior corticospinal tract stay on one side of the body or cross over? What % of fibers are in the lateral corticospinal tract?

fibers stay on one side; 10% of fibers in the corticospinal pathway are anterior

How do spinal nerves communicate with the brain?

via the spinal cord

how many pairs of spinal nerves are there? Are they mixed? What do they innervate?

31 pairs; yes; trunk and limbs

how many pairs of cranial nerves are there? Are they mixed? What do they innervate?

12 pairs of cranial nerves; some are snesory or motor but most are mixed; they innervate the head and neck and the vagus nerve (internal organs); these originate from the bade of the brain

what are the two major groups of nerves?

spinal and cranial nerves

what two nerve roots fuse together to form a spinal nerve?

dorsal and ventral nerve roots

epinerium

covers the entire peripheral nerve

perineurium

the sheath of connective tissue that covers a bundle of nerve fibers (fascicles)

endoneurium

delicate connective tissue around individual nerve fibers in nerve

what is each fascicle in a nerve composed of?

motor, sensory, and sympathetic fibers

what does a typical nerve consist of

several axon bundles (fascicles)

mixed nerve

spinal nerve; nerve containing both sensory and motor fibers

What kind of axons are in the posterior root?

sensory axons only; cell bodies of sensory neurons are located in posterior root ganglion

What kind of axons are in the anterior root?

motor axons only; multiple anterior rootlets arise from the spinal cord and merge to form a single anterior root

Where are the cervical nerves of the spine?

Top of the spine; C1-C8

Where are the thoracic nerves of the spine?

Under the cervical nerves and above the lumbar nerves; T1-T12

Where are the lumbar nerves of the spine?

Above the sacral nerves and under thoracic nerves; L1-L5

Where are the sacral nerves of the spine?

Bottom of the spine; S1-S5

What is the relationship between each segmental region of the spinal cord and its function?

Each segmental region of the spinal cord innervates a specific region of the skin, muscle, or organ group

What are the effects of damage to the spinal cord?

partial or complete loss of function below the level of injury

dermatome map

diagram of the cutaneous regions innervated by each spinal nerve (areas of sensation)