Chapter 17: Pathways and Integrative Functions

Question 1

Define ganglion.

Answer 1

Cluster of neuron cell bodies within the PNS

Question 2

Define center.

Answer 2

Groups of CNS neuron cell bodies with a common function

Question 3

Define nucleus.

Answer 3

Center that displays discrete anatomic boundaries

Question 4

Define nerve.

Answer 4

Axon bundle extending through the PNS

Question 5

Define nerve plexus.

Answer 5

Network of nerves

Question 6

Define tracts.

Answer 6

CNS axon bundle in which the axons have a similar function and share a common origin and destination

Question 7

Define funiculus.

Answer 7

Group of tracts in a specific area of the spinal cord

Question 8

Define pathway.

Answer 8

Centers and tracts that connect the CNS with the body organs and systems

Question 9

Define decussation.

Answer 9

Cross over from one side of the body to the other so the left side of the brain is processing info from the right side of the body and vise versa

Question 10

List the components of a typical nerve pathway.

Answer 10

• Pathways conduct either sensory or motor info
• Processing and integration occur continuously along the pathway
• Travel though white matter of brainstem and spinal cord and connect CNS regions with cranial and spinal nerves
• Consist of a nucleus and a tract
• All pathways are composed of paired tracts
• Ascending (afferent) and descending (efferent) pathways
• Some decussate
• Most exhibit a precise correspondence between a specific area of the body and a specific area of the CNS

Question 11

List the primary sensory pathways. Describe their general function, general structure, and location.

Answer 11

Sensory pathways conduct info about limb position and sensations of touch, temp, pressure, and pain.

2 Types

• 1. Somatosensory Pathways (stimuli from skin, muscles, joints))
• 2. Viscerosensory Pathways (stimuli from viscera)

Receptors detect stimuli and conduct impulse to CNS where the sensory pathway centers within the spinal cord or brainstem process and filter the incoming info to determine if it should be transmitted to the cerebrum or terminated (more than 99% do not reach the cerebral cortex and conscious awareness)

Sensory pathways use 2 or 3 neurons to transmit info from body periphery to brain.

1. Primary Neuron (1st order)
   - Dendrites are part of receptor that detects stimulus
   - Cell bodies in posterior root ganglion (spinal nerves) or sensory glial (cranial nerves)
2. Secondary Neuron (2nd order)
   - Interneuron
   - Cell body in posterior horn of spinal cord or brainstem nucleus
   - Axon goes to the thalamus and synapses with tertiary neuron
3. Tertiary Neuron (3rd order)
   - Interneuron also
   - Cell body in thalamus

Question 12

List the 3 types of somatosensory pathways and what makes them unique.

Answer 12

1. Posterior funiculus-medial lemniscal pathway
   - Sensory info: proprioception, discriminative touch, pressure, and vibration
2. Anterolateral pathway
   - Decussation in anterior white commissure
   - Conduct stimuli related to crude touch and pressure, pain and temp
3. Spinocerebellar pathway
   - *No tertiary neuron and does NOT go to thalamus
   - Proprioceptive info to cerebellum for processing tp coordinate body movement

Question 13

List the primary motor pathways. Describe their general function, general structure, and location.

Answer 13

• Descending pathways in brain and spinal cord control and regulate skeletal muscles
• Formed from cerebral nuclei, cerebrum, descending tracts, and motor neurons

2 motor neurons in somatic motor pathway:

• 1. Upper Motor Neuron (CNS)
• 2. Lower Motor Neuron (PNS)

Question 14

Discuss differences between upper and lower motor neurons (location and function).

Answer 14

Upper Motor Neurons (CNS)

• Cell body within cerebral cortex or brainstem
• Excites or inhibits activity of lower motor neuron

Lower Motor Neurons (PNS)

• Cell body within anterior horn or spinal cord or brainstem cranial nerve nucleus
• Always excitatory b/c axons connect directly to skeletal muscles

Question 15

List and briefly describe the 2 types of motor pathways.

Answer 15

Direct Tracts

• Provide conscious control of skeletal muscle activity
• Originate in the primary motor cortex (3)
  1. Corticobullbar (Cranial Muscles: eye movement, tongue, face, neck muscles) originates from facial region of motor homunculus
  2. Lateral Corticospinal (Limb Muscles)
  3. Anterior Corticospinal (Axial Muscles)

Indirect Tracts

• Provide unconscious control of skeletal muscle activity
• Multisynaptic; high degree of complexity
• Originate in brainstem (4)
  1. Rubrospinal (Flexor muscle tone)
  2. Reticulospinal (Unskilled posture/balance)
  3. Tectospinal (Positional change in response to visual and auditory stimuli)
  4. Vestibulospinal (Balance during activity)

Question 16

Discuss the role of cerebral nuclei in motor function.

Answer 16

• Receives impulses from the entire cerebral cortex (motor, sensory, association cortical areas, limbic system)
• Provide patterned background movements needed for conscious motor activities by adjusting the motor commands issued in other nuclei
  ie. walking
• do not directly control lower motor neurons

Question 17

Discuss the role of cerebellum in motor function.

Answer 17

• Continuously receives input from various sensory and motor pathways
• Generates an error correcting signal when it detects disparity between intended movement and actual movement
  ie. You throw a ball and it goes more to the right than what you intended. When you try it again, your cerebellum has made adjustments.
  My cerebellum was terrible at this during that frisbee game on cowboy day. =)

Question 18

Discuss higher order mental functions.

Answer 18

Cerebral cortex
- Control highly variable/complex voluntary motor patterns

• Higher-order mental functions:
• ** - Consciousness (sleep wake cycle), learning, memory, emotion, and reasoning ***
  • Involve multiple brain regions connected by complicated networks or axons
  • Language: Wernicke’s area
  • Cognition: Association areas

Question 19

Discuss cerebral lateralization and give specific examples.

Answer 19

• Each hemisphere tends to be specialized for certain tasks (different but complimentary functions)

Left Hemisphere:

• Categorization and symbolization
• Wernicke’s area, Broca’s area
• Science and Math (analytical reasoning)
• Speech-dominant hemisphere

Right Hemisphere:

• Representational hemisphere
• “Artistic side” - music, art skill, spatial relationships

Question 20

Discuss the higher order processing of language.

Answer 20

• Reading, writing, speaking, understanding words
• Wernicke’s area: allows us to recognize written and spoken language
• Angular gyrus: processes words we read into a form that we can speak

Question 21

Discuss the higher order processing of cognition.

Answer 21

• Awareness, knowledge, memory, perception, problem solving, decision making, info processing, and thinking
• Association areas of the cerebrum are responsible for cognition

Question 22

Discuss the higher order processing of memory.

Including the 4 types

Answer 22

• Different lengths of time and different storage capacities available
• Storing and retrieving info depends on complex interactions between brain regions
• Limbic system, insula, frontal cortex

4 Types:

1. Sensory memory
   - lasts for fractions of a second; won’t remember
2. Short term memory
   - limited capacity, brief duration
3. Working memory
   - temporarily storing and manipulating info
4. Long term memory
   - may exist for limitless periods of time

Question 23

Discuss the higher order processing of consciousness (reticular formation).

Answer 23

• Has motor and sensory components
• Midbrain, pons, medulla

Motor component

• regulates muscle tone
• assists autonomic motor functions like respiration and heart rate

Sensory component

• reticular activating system (RAS) alerts cerebrum to incoming sensory info
• maintains your state of awareness by processing visual auditory, and touch stimuli
• ranging level of alert from high alert to sleep
• sleep is temp. absence of conscience but you can be woken