SPINAL CORD AND REFLEXES- JONES

What does Ipsilateral mean?

What does Contralateral mean?

• Ipsi= same side

• Contra= opposite side

What does “tract” mean?

bundle of nerves

What does decussation mean?

crossing/where nerves cross

What’s the difference between cranial and caudal?

cranial- head

caudal- away from head

What’s the difference between distal and proximal?

distal- away from torso

proximal- close to torso

What’s the difference between medial and lateral?

medial- close to midline

lateral- away from midline

What’s the difference between anterior and posterior?

anterior- front

posterior- back

What’s the difference between ventral and dorsal?

ventral- front

dorsal- back

What are the functions of the spinal cord?

1. conduction (action potentials)

2. neural integration (respond to stimuli)

3. locomotion (what signals allow us to move)

4. reflexes

What are the anatomical regions of the spinal cord?

(jones- “know general progression”)

1. cervical

2. thoracic

3. lumbar

4. sacral

The grey matter of spinal cord is made up of the dorsal and ventral horn.

What’s their function? What do they send/receive?

• dorsal- RECEIVES sensory input (from dorsal root ganglion)

• ventral- CARRYS motor signals

PRACTICE:

Damage to the dorsal root would cause what deficit?

sensory loss (in that region where the ganglion was damaged)

Describe the white matter of the spinal cord:

axons carrying information to and from the brain

The spinal cord carries sensory information from the body to the brain via _______________________.

a. ascending tracts

b. descending tracts

a.

The corticospinal tract is the major pathway for voluntary motor control, carrying signals from the brain to muscles or via _______________________.

a. ascending tracts

b. descending tracts

b.

There are 2 major ascending spinal tracts involved with sensory perception.

The dorsal column-medial lemniscal carries what sensory information?

The spinothalamic system carries what sensory information?

• dorsal column-medial lemniscal: touch, pressure, movement

• spinothalamic system: pain, heat/cold

Where do each of the following cross to the opposite site or decussate?

• dorsal column-medial lemniscal

• spinothalamic system

• dorsal column-medial lemniscal- medulla

• spinothalamic system- spinal cord

In general how many neurons does it take to reach the brain for the dorsal column-medial lemniscal and spinothalamic system?

a. 1

b. 2

c. 3

d. 4

c.

For each of the following does the signal travel Ipsilateral or contralateral on the spinal cord?

• dorsal column-medial lemniscal

• spinothalamic system

• dorsal column-medial lemniscal- Ipsilateral (same side)

  • ex: Right foot touch → travels up right dorsal column → crosses in medulla → left somatosensory cortex.

• spinothalamic system- Contralateral (opposite side)

  • ex: Left hand pain → crosses in spinal cord → ascends right spinothalamic tract → right thalamus → right somatosensory cortex.

Where does the corticospinal tract cross/ decussate?

medulla

What is a “ganglion”?

cluster of cell bodies outside the CNS ganglion

What are the components to a basic/normal reflex?

1. stimulus

2. —-

3. —-

4. —-

5. change in skeletal muscle contraction

(not that imp test wise—> good for understanding)

1. stimulus—> receptor (ion channels to change mV)

2. sensory neurons have AP’s

3. SC synapses

4. motor neurons ±

5. change in skeletal muscle contraction

What do muscle spindles detect, and what reflex do they trigger?

• detect mechanical stretch

• trigger stretch reflex

The muscle spindle is made up of modified fibers called what?

nuclear chain + nuclear bag also known as INTRAFUSAL muscle fibers

Explain how the stretch reflex works:

1. muscle spindle (receptor) detects mechanical stretch

2. what afferent neurons are then activated?

3. where is information processed? synapse?

4. what is then activated?

5. final result?

1. muscle spindle (receptor) detects mechanical stretch

2. 1a sensory neurons activated

3. integration/ in spinal cord synapses with motor neuron

4. activate ALPHA motor neuron to the same muscle where receptor was

5. contraction of the muscle

What is the role of gamma motor neurons in the stretch reflex/ muscle spindle reflex?

active when a muscle is contracting and allows the INTRAFUSAL muscle to sense stretch

What is the stimulus for the inverse stretch reflex or golgi tendon reflex?

muscle contraction

Explain how the inverse stretch reflex or golgi tendon reflex works:

1. stimulus—> muscle contraction

2. receptor senses ___________

3. what afferent neurons are then activated?

4. where is information processed? synapse?

5. what is then inhibited?

6. final result?

1. stimulus—> muscle contraction

2. receptor (mechanical) senses pulling in tendon

3. 1b sensory neurons activated

4. integration/ in spinal cord synapses with motor neuron

5. inhibits ALPHA motor neuron to the same muscle where receptor was

6. relaxation of the muscle

Compare and contrast the Golgi tendon reflex with the muscle spindle reflex:

	Stretch Reflex (muscle spindle)	Inverse Stretch Reflex (Golgi tendon)
receptor
stimulus
afferent neuron
what happens in SC?
result?

	Stretch Reflex (muscle spindle)	Inverse Stretch Reflex (Golgi tendon)
receptor	muscle spindle (intrafusal fibers)	golgi tendon organ
stimulus	muscle STRETCH	muscle CONTRACTION
afferent neuron	group 1a	group 1b
what happens in SC?	activates a-motor neurons	inhibits a-motor neurons
result?	muscle contraction	muscle relaxation