Lecture 8 (Spinal Cord, Reflexes, Spinal Nerves, PNS)

Question 1

Where is the spinal cord found? How long is it? What is it protected by?

Answer 1

Location: Found within spinal cavity

Length: 45 cm (adult)

Protected by bone, meninges, CSF and adipose tissue

Question 2

Define the term Nerve

Answer 2

• A bundle of hundreds to thousands of axons and associated tissue
• Found outside the central nervous system (CNS)
• Each nerve follows a defined path and serves a specific region of body

Question 3

Define the term Ganglion

Answer 3

• Group of neuronal cell bodies
• Also found outside central nervous system (CNS)

Question 4

What are the 2 Nerve fibers that stems out of the spinal cord?

Answer 4

1) Dorsal Nerve Root (Posterior Root)
Carries information from receptors into the CNS and the cell bodies are found in the ganglions

2) Ventral Nerve Root (Anterior Root)
Carries motor information out of the spinal cord and the cell bodies are found in the grey mater of the spinal cord

Question 5

Describe the anatomy of a spinal cord disk

Answer 5

1) Spinal Nerves: both sensory and motor neurons
2) Posterior root ganglion: cell bodies of sensory neurons
3) Posterior root: sensory neurons
4) Anterior root: motor neurons
5) Anterior horns of grey mater: contains the cell bodies of motor neurons
6) Posterior horns of grey mater: cell bodies and axons of interneurons

Question 6

What are the 2 main functions of the spinal cord?

Answer 6

1) White mater of the spinal cord acts as a communication highway
- sensory impulses travel toward the brain
-motor impulses travel from the brain towards skeletal muscle and other effector tissues

2) Grey mater of the spinal cord receives and integrates incoming and outgoing information
-acts as the site for integration of reflexes

Question 7

Define the term Reflex

Answer 7

A reflex is a fast, involuntary sequence of actions that occur in response to a particular stimulus

Question 8

What’s a reflex arc?

Answer 8

The pathway followed by nerve impulses from neuron to neuron that produces a reflex

Question 9

What are the 5 main components of a reflex arc?

Answer 9

1) Sensory receptor
2) Sensory neuron
3) Integrating center
4) Motor neuron
5) Effector

Question 10

Explain Knee jerk (aka Patellar Reflex)

Answer 10

Extension of the lower leg in response to tapping the patellar tendon.
Tendon and muscles are stretched, stimulating muscle spindles and initiating conduction over a 2-neuron reflex arc.

Question 11

Explain Angle jerk (aka Achilles reflex)

Answer 11

Extension of the foot in response to tapping the achilles tendon; tendon reflex and deep reflex mediated by 2-neuron spinal arcs; center lie in first and second sacral segments of the cord