2. Spinal cord

Question 1

structure of spinal cord

Answer 1

• segmental
• spinal cord ends at L1

Question 2

spinal cord: functions

Answer 2

• processing sensory information
• movement
• regulating visceral functions

Question 3

review anatomical planes:

1. coronal (frontal)
2. sagittal (median)
3. axial (transverse, horizontal)

Answer 3

Question 4

what is found in WHITE MATTER?

Answer 4

axon bundles; ascending and descending

Question 5

what is found in GRAY MATTER?

Answer 5

neuronal cell bodies

Question 6

white matter territories and if motor/sensory

Answer 6

1. VENTRAL (anterior) funiculus : mostly MOTOR
2. LATERAL funiculus: (BOTH) mostly mostly, some sensory
3. DORSAL (posterior) funiculus: ONLY SENSORY
   
   • Fasiculus gracilis: found at all cord levels
   • Fasiculus cuneatus: present from C1-T6

Question 7

gray matter territories

Answer 7

• dorsal/posterior horn
• ventral/anterior horn
  
  • medial motor neurons (M)
  • lateral motor neurons (L)

Question 8

does amount of white/gray matter change at different spinal levels?

why or why not?

Answer 8

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)

Question 9

describe the blood supply of the spinal cord?

Answer 9

1. posterior spinal arteries
2. anterior spinal artery

Question 10

each spinal segment has:

Answer 10

dorsal and ventral roots –> come together to form spinal nerves

Question 11

dorsal root ganglion: define

Answer 11

swelling on the dorsal roots; contains the cell bodies of sensory neurons

Question 12

how does information flow from periphery to spinal cord?

Answer 12

• 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

Question 13

where are cell bodies of sensory neurons found?

Answer 13

dorsal root ganglion

Question 14

pathways for sensory axons

Answer 14

• central processes enter the spinal cord gray matter
  
  • **can synapse on cells in dorsal horn (more often), OR
  • ascend to other levels

Question 15

pathway of MOTOR INFORMATION from the spinal cord

Answer 15

Exits the gray matter of the spinal cord:

1. motor neurons from ventral horn send axons out to innervate skeletal muscles (aka lower motor neurons, or alpha motor neurons)
2. motor neurons from the lateral gray matter send axons to innervate neurons that control viscera (cardiac muscle, glands, etc)

Question 16

dorsal root ganglion neurons give rise to:

Answer 16

1. central processes which enters the spinal cord to bring information to various parts of the CNS
2. peripheral process which innervates a dermatome

Question 17

dermatomes: define

Answer 17

area of skin innervated by single spinal nerve;

can divide the vody into segments accordingly

Question 18

myotomes

Answer 18

motor equivalent of a dermatome

muscles innervated by a single spinal nerve

Question 19

descending motor pathways:

function, and location

Answer 19

• 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)

Question 20

reflex: define

Answer 20

• 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

Question 21

basic components of a reflex

Answer 21

Question 22

what are the receptors for the stretch reflex?

Answer 22

muscle spindles

Question 23

what are the main muscle contractors in stretch reflex?

Answer 23

extrafusal fibers;

innervated by alpha motor neurons

Question 24

describe stretch reflex (mechanism)

Answer 24

• 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

Question 25

what motor neurons innervate **extrafusal fibers?**

Answer 25

**alpha motor neurons**

Question 26

what motor neurons innervate **muscle spindles/ intrafusal fibers**

Answer 26

gamma motor neurons

Question 27

locate: 1. intrafusal fibers 2. extrafusal fibers

Answer 27

Question 28

myotatic stretch reflex: describe the steps

Answer 28

1. relax muscles acting at the knee 2. tap the patellar ligament to activate muscle spindle (vibrations will activate) 3. **sensory** (alpha motor) **neuron** sends AP to CNS 4. activation of **motor neuron** stimulates contraction of quadriceps muscle, producing knee jerk 5. at same time, branch of **sensory neuron** stimulates **inhibitory interneuons** that inhibits the **motor neuron** responsible for contraction of the hamstring muscle

Question 29

**withdrawal reflex w/ crossed support**

Answer 29

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

Question 30

details of withdrawal reflex w/ crossed support

Answer 30

1. step on a tack, causing pain receptors to fire 2. **sensory neuron** sends AP to CNS, where it synapses on neurons that excite other neurons 3. **motor neurons** are stimulated to excite the flexor on the affected side; and the extensor on the opposite side 4. at the same time, **inhibitory interneurons** inhibit the **motor neuron** responsible for the extension of the affected side, and contraction of the opposite side