Chapter 16 - Pathways and Higher-Order Functions

Where is the continuous flow of information or constant feedback between in the N.S.?

Between the brain, spinal cord, and peripheral nerves

What do nerve pathways (that axons form) or tracts do?

Connect the CNS and PNS

What are the two types of pathways called?

Ascending (sensory) pathways or descending (motor) pathways

What indicates origin and destination for tracts?

The tract name 

What does bubar mean?

The brainstem

What are the three sensory pathways?

1. Posterior column pathway

2. Spinothalamic pathway

3. Spinocerebellar pathway

What does dorsal mean again?

Sensory

Where does the spinothalamic pathway originate and its destination?

Spine —> thalamus 

Where does the spinocerebellar pathway originate and its destination?

Spine → cerebellum

What is special about the spinocerebellar pathway?

There is only 2 neurons when sensory pathways usually contain 3

What are the sensory pathways?

Ascending, afferent, and sensory

What are the three neurons that sensory pathways usually contain?

1. First-order neuron - to the CNS

2. Second-order neuron - an interneuron located in either the spinal cord or the brain stem

3. Third-order neuron - carries info from the thalamus to the cerebral cortex

What are the two sections of the posterior column pathway?

Fasciculus gracilis

Fasciculus cuneatus

What does the fasciculus gracilis do?

Senses information from below the diaphragm

What does the fasciculus cuneatus do?

Senses information from above the diaphragm

What are the two sections of the spinocerebellar tract?

Posterior and anterior spinocerebellar tract

What are the two sections of the spinothalamic pathway

Lateral and anterior spinothalamic tract

When you look into a sensory or motor homunculus does it look like you?

No it does not - whatever you have more innervation for the bigger it is (hands for touch and tongue in sensory)

What does the sensory homunculus tell us about injuries?

It tells us where we are having issues based on parts of the cerebrum

From the longitudinal fissure how does the sensory homunculus go?

Feet → trunk → arms → face

Where does the posterior column pathway decussate?

In myelencephalon

Where is sensory information being relayed to?

The post-central gyrus

What does the posterior column pathway feel?

Fine-touch, vibration, pressure, and proprioception (it crosses over remember)

Where does decussation occur in the anterior spinothalamic pathway?

Lower level of S.C.

What does the anterior spinothalamic tract feel?

Rough touch, crude touch and pressure sensations from right side of the body

What does the lateral spinothalamic tract feel?

Pain and temperature sensations → survival

What receptors do we have more of, cold or hot?

Cold for survival

What does the spinocerebellar pathway do and does it cross over?

No, it does not cross over because there are not three neurons, and it is the proprioceptive input from golgi tendon organs, muscle spindles, and joint capsules 

Is the spinocerebellar pathway conscious?

No, it only goes up to the cerebellum so it is below the point of consciousness

Info does not come up unilaterally and it is bilateral to the pons

Where is the third order of the fasciculus gracilis and fasciculus cuneatus?

Ventral posterolateral nucleus of thalamus

Where is the third order of the lateral and anterior spinothalamic tracts

Ventral posterolateral nucleus of thalamus 

Where is the third order neuron for the posterior and anterior spinocerebellar tracts?

jokes - it does not have one

What are the motor pathways

1. The corticospinal pathway

   1. Corticobulbar tracts

   2. Corticospinal tracts

2. The medial and lateral pathways

What are motor pathways?

Descending and efferent

Are we born with the corticospinal pathway?

No, this is why it is the most critical and why we have the lewinsky reflex in babies on their feet -→ it takes time for axons to grow

Where does the corticobulbar tract go?

From the cortex → brainstem

Where does the corticospinal tract go?

Cortex → spine

Where do the medial and lateral pathways cross over?

Medullary pyramid

What are the two neurons that the somatic nervous system has in their motor pathways?

1. Upper motor neuron

2. Lower motor neuron

Where is the upper motor neuron found in the somatic nervous system pathways?

Within the CNS (remember that the CNS ends at L1/L2

Where are the lower motor neurons in the somatic nervous system motor pathways?

From CNS (L1/L2) to effector 

What paralysis is impacted with the upper motor neuron?

Spastic paralysis

What paralysis is impacted with the lower motor neuron?

Flacid paralysis

What two neurons are associated with the autonomic nervous system?

1. Preganglionic neuron (cholinergic)

2. Ganglionic neuron

Where are the upper motor neurons going in the brain?

To the precentral gyrus

If you were to put a lesion above the decussation of the corticospinal pathway where would the problem be?

On the same side

Where does the corticospinal pathway go?

From feet-face

Broca’s aphasia

Cannot speak/swallow but can understand in motor area of the brain

Where does the tectospinal tract go?

Form corpora quadrigemina → spine 

Location of upper motor nueron of the corticobulbar tract, lateral corticospinal tract, and anterior corticospinal tract

Primary motor cortex

Action of the corticobulbar tract, lateral corticospinal tract, anterior corticospinal tract

Conscious motor control of skeletal muscles

If a tract is dealing with the cortex is it conscious or unconscious?

Conscious

What are the three medial pathways?

1. Vestibulospinal tract

2. Tectospinal tract

3. Reticulospinal tract

Location of upper motor nueron of the vestibulospinal tract?

Vestibular nucleus (border of pons and medulla oblongata)

Location of upper motor neuron of the tectospinal tract?

Tectum (mesencephalon: superior and inferior colliculi)

Location of upper motor neuron for reticulospinal tract

Reticular formation

Action of the vestibulospinal tract

Subconscious regulation of balance and muscle tone

Action of the tectospinal tract

Subconscious regulation of eye, head, neck, and upper limb position in response to visual and auditory stimuli

Action of the reticulospinal tract

Subconscious regulation of reflex activity

Location of upper motor neuron of the rubrospinal tract

red nuclei of mesencephalon

Action of the rubrospinal tract

subconscious regulation of upper limb muscle tone and movement 

What is the lateral pathway

Rubrospinal tract

What do the basal nuclei do for somatic motor control?

Modify voluntary and reflexive motor patterns at the subconscious level

What does the hypothalamus do for somatic motor control?

Controls stereotyped motor patterns related to eating, drinking, and sexual activity; modifies respiratory reflexes (with pons and medulla)

What do the pons and superior medulla oblongata do for somatic motor control?

Control balance, reflexes, and more-complex respiratory reflexes

What do the brain stem and spinal cord do for somatic motor control?

Control simple cranial and spinal reflexes

What does the inferior medulla oblongata do for somatic motor control?

Controls basic respiratory reflexes

What does the cerebellum do for somatic motor control?

Beneath consciousness, it coordinates complex motor patterns

What do the thalamus and mesencephalon do for somatic motor control?

Control reflexes in response to visual and auditory stimuli

What does the cerebral cortex do for somatic motor control?

Plans and initiates voluntary motor activity

What are higher-order functions?

• Performed by the cerebral cortex

• Complex interconnections and communication between areas within the cerebral cortex and between other areas of the brain (unconscious and conscious processing)

• they are not part of the programmed “wiring” of the brain, so the functions are subject to modification and adjustment over time (aka learning)

What does the auditory association area do?

I hear it, what is it, how do I respond

What are the integrative regions of the cerebral cortex?

Cortical areas that act as centers for complex sensory stimuli and motor responses

• General interpretive area

• Speech area

• Prefrontal cortex

General interpretive area (gnostic - knowing)

Receives information from all sensory association areas, only present in mostly the left hemisphere

Do females have a smaller brain?

Yes, they do, but they also have a more efficient brain (more neuroplastic), damage to one side will allow the other to take over

Speech Center (Broca’s area)

Regulates patterns of breathing and vocalization

Motor area of the face

Cannot make sounds to speak or to swallow

Prefrontal cortex

Coordinates information from the secondary and special association areas of the cortex and performs abstract intellectual functions

In a lobotomy, can the prefrontal association cortex get back to normal?

No, when these nerves are damaged it is hard to get back 

Wernicke’s area

“Word salad”, make sounds but no idea what it means

How long do short term memories last?

Seconds to hours

Transfers from STM → LTM other than when neural nets change creating false memories

What are electrical memories?

What you eat for breakfast

Memory

Process of accessing stored bites of information

What parts of the brain are essential to memory consolidation?

Amygdaloid body and the hippocampus

Memory consolidation 

Conversion from a short-term memory to a long-term memory 

Conscious states

1. Delirium

2. Dementia

3. Confusion

4. Normal consciousness

5. Somnolence

6. Chronic vegetative state

Delirium

Disorientation, restlessness, confusion, hallucinations, agitation, alternating with other conscious states; develops quickly

Dementia

Losing cholinergic neurons

Progressive decline in spatial orientation, memory, behavior, and language

Confusion

Slight form of dementia in DSM

Reduced awareness, easily distracted, easily startled by sensory stimuli, alternates between drowsiness and excitability; resembles minor form of delirium state

Normal consciousness

Aware of self and external environment, well-oriented, responsive

Somnolence

Extreme drowsiness, but will respond normally to stimuli

Chronic vegetative state

Conscious state

Conscious but unresponsive, no evidence of cortical function

Unconscious states

** not conscious by standards

Asleep

Stupor

Coma

Asleep

can be aroused by normal stimuli (light touch, sound, etc.)

Stupor

Can be aroused by extreme and/or repeated stimuli

Coma

Cannot be aroused and does not respond to stimuli (coma states can be further subdivided according to the effect on reflex responses to stimuli)

What are common age-related anatomical changes in the nervous system?

• Reduction in brain size and weight (like a sponge)

• Reduction in the number of neurons

• Decrease in blood flow to the brain

• Changes in synaptic organization of the brain

• Intracellular and extracellular changes in CNS neurons