2. Spinal cord Flashcards
structure of spinal cord
- segmental
- spinal cord ends at L1

spinal cord: functions
- processing sensory information
- movement
- regulating visceral functions
review anatomical planes:
- coronal (frontal)
- sagittal (median)
- axial (transverse, horizontal)

what is found in WHITE MATTER?
axon bundles; ascending and descending

what is found in GRAY MATTER?
neuronal cell bodies

white matter territories and if motor/sensory
- VENTRAL (anterior) funiculus : mostly MOTOR
- LATERAL funiculus: (BOTH) mostly mostly, some sensory
-
DORSAL (posterior) funiculus: ONLY SENSORY
- Fasiculus gracilis: found at all cord levels
- Fasiculus cuneatus: present from C1-T6

gray matter territories
- dorsal/posterior horn
- ventral/anterior horn
- medial motor neurons (M)
- lateral motor neurons (L)

does amount of white/gray matter change at different spinal levels?
why or why not?
yes, because there are spinal enlargements for upper limbs and lower limbs. *The cervical and lumbar enlargements of the spinal cord result from enlargement of the gray matter that contains the neural machinery necessary to operate the limbs
- cervical enlargement (C5-T1)
- lumbosacral enlargement (L2-S2)

describe the blood supply of the spinal cord?
- posterior spinal arteries
- anterior spinal artery

each spinal segment has:
dorsal and ventral roots –> come together to form spinal nerves

dorsal root ganglion: define
swelling on the dorsal roots; contains the cell bodies of sensory neurons

how does information flow from periphery to spinal cord?
- From periphery:
- sensory axons from skin, muscle spindles, etc
- sensory axons from visceral organs
- Cell bodies of sensory neurons are found in dorsal root ganglion

where are cell bodies of sensory neurons found?
dorsal root ganglion
pathways for sensory axons
- central processes enter the spinal cord gray matter
- **can synapse on cells in dorsal horn (more often), OR
- ascend to other levels

pathway of MOTOR INFORMATION from the spinal cord
Exits the gray matter of the spinal cord:
- motor neurons from ventral horn send axons out to innervate skeletal muscles (aka lower motor neurons, or alpha motor neurons)
- motor neurons from the lateral gray matter send axons to innervate neurons that control viscera (cardiac muscle, glands, etc)

dorsal root ganglion neurons give rise to:
- central processes which enters the spinal cord to bring information to various parts of the CNS
- peripheral process which innervates a dermatome

dermatomes: define
area of skin innervated by single spinal nerve;
can divide the vody into segments accordingly

myotomes
motor equivalent of a dermatome
muscles innervated by a single spinal nerve

descending motor pathways:
function, and location
- these descending tracts of fibers control movement
- location:
- lateral funiculus descending tracts –> synapse in lateral ventral horn (extremities)
- medial funiciulus descending tracts –> synapse in medial ventral horn (trunk and axial musculature)

reflex: define
- action performed as response to stimulus w/o conscious though
- thought of as protective measures
- local circuits in spinal cord are important parts of many reflexes
basic components of a reflex

what are the receptors for the stretch reflex?
muscle spindles
what are the main muscle contractors in stretch reflex?
extrafusal fibers;
innervated by alpha motor neurons
describe stretch reflex (mechanism)
- sensory receptors in muscles (muscle spindles, composed of intrafusal fibers) detect:
- muscle length
- changes in muscle length
- extrafusal fibers are main muscle contractors –> generate movement

what motor neurons innervate extrafusal fibers?
alpha motor neurons
what motor neurons innervate muscle spindles/ intrafusal fibers
gamma motor neurons
locate:
- intrafusal fibers
- extrafusal fibers


myotatic stretch reflex: describe the steps
- relax muscles acting at the knee
- tap the patellar ligament to activate muscle spindle (vibrations will activate)
- sensory (alpha motor) neuron sends AP to CNS
- activation of motor neuron stimulates contraction of quadriceps muscle, producing knee jerk
- at same time, branch of sensory neuron stimulates inhibitory interneuons that inhibits the motor neuron responsible for contraction of the hamstring muscle

withdrawal reflex w/ crossed support
a painful stimulus causes flexion of the knee, meaning:
- flexors need to be stimulated
- extensors need to be inhibited
& on the opposite side of the body:
- extensors need to be activated
- flexors need to be inhibited

details of withdrawal reflex w/ crossed support
- step on a tack, causing pain receptors to fire
- sensory neuron sends AP to CNS, where it synapses on neurons that excite other neurons
- motor neurons are stimulated to excite the flexor on the affected side; and the extensor on the opposite side
- at the same time, inhibitory interneurons inhibit the motor neuron responsible for the extension of the affected side, and contraction of the opposite side
