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Head and Neck Physiology > Motor Functions of the Cerebral Cortex > Flashcards

Motor Functions of the Cerebral Cortex Flashcards

1
Q

How does the brain influence the activity of the spinal cord to command voluntary movements?

A

The central motor system is arranged as a hierarchy of three control levels:
1. The forebrain (association areas of neocortex and basal ganglia): strategy i.e. the goal of the movement and the movement strategy that best achieves the goal.
2. Motor cortex and cerebellum: tactics i.e. the sequences of muscle contractions, arranged in space and time, required to smoothly and accurately achieve the strategic goal
3. Brain stem and spinal cord: execution i.e. activation of the motor neuron and interneuron pools that generate the goal-directed movement and make any necessary adjustments of posture

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2
Q

Describe the layers of the cerebrum?

A
  1. Gray matter
    - Outer layer
    - Composed mostly of neuron cell bodies
  2. White matter
    - Fiber tracts inside the gray matter
    E.g. corpus callosum connects hemispheres
    > The surface is made of ridges (gyri) and grooves (sulci)
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3
Q

What are primary motor areas of the cortex?

A

The primary areas have direct connections with specific muscles or specific sensory receptors for causing discrete muscle movements or experiencing a sensation

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4
Q

What are secondary motor areas of the cortex?

A

The secondary areas make sense out of the functions of the primary areas

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5
Q

Name the cerebral motor areas?

A
  1. primary motor cortex
  2. supplementary motor area
  3. premotor area
  4. the frontal eye field
  5. Broca’s area
    > 30% of upper motor neurons are located in the primary cortex
    > 30% in the premotor area
    > and the rest in the primary somatic sensory cortex
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6
Q

Lesions in which area causes the most marked motor deficits?

A

lesions in the primary motor cortex

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7
Q

What does the primary motor cortex mainly do?

A

controlling the muscles of the hands and muscles of speech (lips, tongue, larynx)
> many efferent neurons are committed to each muscle involved in finely graded or highly skilled movements
Note: the neurons in the primary motor cortex determine the amount of force to be exerted and direction of the movement

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8
Q

The sensory inputs to the primary motor cortex can be grouped as follows?

A
  1. From the periphery via the thalamus
  2. From the cerebellum via the thalamus
  3. From the basal ganglia via the thalamus
  4. From homotopic areas of the sensory cortex
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9
Q

Describe the function of the supplementary motor area?

A

Stimulation of the supplementary motor cortex causes bilateral complex postural responses, suggesting that this area is concerned with extrapyramidal control of motor neurons
E.g. grasping movements of both hands simultaneously

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10
Q

Consequences of removal of the supplementary motor area?

A

Ablation/removal of this area does not cause paralysis but increased muscle tone and difficult in performing tasks which are complex or require bimanual coordination

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11
Q

Describe the function of the premotor cortex (area 6)?

A
  1. Deals with motor activities that are complex and sequential
  2. Generates nerve impulses that cause specific groups of muscles to contract sequentially
    E.g. writing
  3. It may be concerned with setting posture at the start of a planned movement and with getting the individual ready to perform
    E.g. if a person decides to take a step, the neurons in the premotor area determine which muscles must contract, in what order, and to what degree
  4. Also serves as a memory bank for the complex and sequential movements
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12
Q

Name the 3 special motor areas?

A
  1. frontal eye field
  2. Brocas area
  3. Wernickes area
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13
Q

Describe the function of the frontal eye field?

A
  • Stimulation of the frontal eye field causes conjugate deviation of both eyes towards the contralateral direction
  • Controls voluntary scanning movements of the eyes
    e.g. when reading
  • This is accompanied by: blinking, lacrimation, and pupillary changes
  • Also controls eyelid movements
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14
Q

Consequences to damage to the frontal eye field?

A

Ablation causes the eye to be fixed in the direction of the lesion such that it can not be voluntarily moved to the opposite direction

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15
Q

Where is the Brocas area located?

A

Below the frontal eye field at the posterior end of the inferior frontal gyrus is the Broca’s area (left hemisphere)

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16
Q

What is the function of the Brocas area?

A

Controls word formation and the appropriate respiratory changes associated with speech

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17
Q

Consequences to damage of the Brocas area?

A

When damaged, a person cannot speak whole words but uncoordinated utterances or a simple word e.g. “yes” or “no”. (non-fluent aphasia)

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18
Q

What is the function of Wernickes area?

A
  • understanding oral/written words
  • Active when words are translated to thoughts
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19
Q

Name the sensory areas found in the parietal, occipital and temporal lobes?

A

Primary somatosensory cortex
Somatosensory association cortex
Visual areas
Auditory areas
Olfactory cortex
Gustatory cortex
Vestibular cortex

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20
Q

Name the lobes of the skull?

A

Named after skull bones
1. The temporal lobe
2. The frontal lobe
3. The parietal lobe
4. The occipital lobe
> The deep central sulcus marks the posterior border of the frontal lobe, caudal to which lies the parietal lobe

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21
Q

Describe the frontal lobe and its function?

A
  • The largest lobes in the human brain and they are also the most common region of injury in traumatic brain injury
  • Important for voluntary movement, expressive language and for managing higher level executive functions
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22
Q

Describe the functional areas of the frontal lobe?

A
  1. primary motor cortex
    > voluntary muscle movement
  2. premotor cortex
    > planning/coordination of movement
  3. frontal eye field
    > voluntary rapid eye movement
  4. prefrontal cortex
    > executive functions, behaviour, personality
  5. Brocas area
    > muscles of speech
    > production of speech
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23
Q

Describe the function of the parietal lobe?

A

• Important for processing and interpreting somatosensory input
• Integrate sensory input and construct a spatial coordinate system to represent the world around us

24
Q

Describe the functional areas of the parietal lobe?

A
  1. Primary Somatosensory Cortex
    > Awareness of Somatic Sensations
    > Touch, Pain, Temperature
  2. The gustatory cortex
    > is involved in taste and is in the parietal lobe just deep to the temporal lobe
  3. The vestibular cortex
    > is involved in balance and equilibrium and is in the posterior insula
25
Q

Describe the function of the occipital lobe?

A

Its primary function is the processing, integration, interpretation, etc. of VISION and visual stimuli

26
Q

Describe the cortical regions of the occipital lobe?

A
  1. Primary Visual Cortex
    > This is the primary area of the brain responsible for sight -recognition of size, color, light, motion, dimensions, etc.
    > Receives visual information
  2. Visual Association Area
    > Interprets information acquired through the primary visual cortex.
    > Relates present and past visual experiences, enables one to recognize objects
27
Q

Describe the function of the temporal lobe?

A

Plays an integral role in:
1. Hearing
> Organization/comprehension of language
2. Information retrieval (memory and memory formation

28
Q

Describe the function of the cortical regions of the temporal lobe?

A
  1. Primary Auditory Cortex
    > Responsible for hearing, receives information for sound. perception
  2. Primary Olfactory Cortex
    > Interprets the sense of smell once it reaches the cortex via the olfactory bulbs. (Not visible on the superficial cortex)
    > involved in memory and emotion
29
Q

Describe association areas and their functions?

A

Allow for analysis of sensory input.
Multiple inputs and outputs.
•Prefrontal cortex
• Language areas
• General interpretation area
• Visceral association area

30
Q

Describe the function of the prefrontal cortex?

A

Involved in analysis, cognition, thinking, personality, conscience, & much more
- in anterior frontal lobes

31
Q

What is the general interpretation area?

A

General area integrates multiple stimuli into a single cogent “understanding of the situation.”
- Found on only one hemisphere - typically left.
- Encompasses 3 lobes: temporal, occipital, and parietal.

32
Q

What is the visceral association area?

A

• Visceral association area is involved in perception of visceral sensations (such as disgust).
• Located in insular cortex

33
Q

What is brain lateralization?

A

The fact that 2 hemispheres are asymmetric

34
Q

How is the brain lateralized?

A

• In about 95% of all people, the left hemisphere is the dominant one.
• Has a more control over language, math, and logic.
• Language production has been found to be lateralized in the left hemisphere for 95% of right-handed people and about 75% of left-handers.
The motor areas for controlling hands are dominant in the left side of the brain in about 9 of 10 persons
• In about 95% of all people, the left temporal lobe and angular gyrus become dominant, and in the remaining 5 %, either both sides develop simultaneously to have dual function, or, more rarely, the right side alone becomes highly developed, with full dominance
Even at birth, the area of the cortex that will eventually become
Wernicke’s area is as much as 50% larger in the left hemisphere than in the right in more than one half of neonates
The right hemisphere is geared towards musical, artistic and other creative endeavors

35
Q

How does the brain communicate with the motor neurons of the spinal cord?

A

Descending spinal tracts

36
Q

Axons from the brain descend through the spinal cord along which two major groups of pathways?

A
  1. Lateral column of the spinal cord
    - The lateral pathways are involved in voluntary movement of the distal musculature and are under direct cortical control
  2. Venteromedial column of spinal cord
    - The ventromedial pathways are involved in the control of posture and locomotion and are under brain stem control
37
Q

Name the lateral pathways?

A
  1. corticospinal tract
  2. rubrospinal tract
38
Q

Describ ethe corticospinal tract?

A
  • The most important component of the lateral pathways
  • Two-thirds of the axons in the tract originate in the motor cortex.
  • Most of the remaining axons in the corticospinal tract derive from the somatosensory areas of the parietal lobe and serve to regulate the flow of somatosensory information to the brain
  • After leaving the cortex, it passes through the brain stem to form pyramids of the medulla (When cut, the tract’s cross section is roughly triangular)
    > also called pyramidal pathway
39
Q

The corticospinal tract is involved in?

A
  1. maintaining muscle tone
  2. controlling speed and precision of skilled movements, primarily fine movements involved in dexterity
40
Q

Describe the decussation of the corticospinal tract?

A
  • the pyramidal tract crosses, or decussates, at the pyramidal decussation.
    > This means that the right motor cortex directly commands the movement of the left side of the body, and the left motor cortex controls the muscles on the right side.
  • As the axons cross, they collect in the lateral column of the spinal cord and form the lateral corticospinal tract
  • The remaining 15-25% descends uncrossed in the anterior corticospinal tract (neck and upper limbs)
41
Q

Describe the rubrospinal tract?

A
  • Begins in the red nucleus (boundary between diencephalon and midbrain)
  • Decussates in the midbrain and descends in the lateral column of the spinal cord
42
Q

Rubrospinal tract is involve in?

A

Regulates fine motor control of muscles in distal part of upper limbs
- Damage to the tract impairs forearm and hand movements

43
Q

What are ventromeidial pathways and their functions?

A
  • originate in the brain stem and terminate among the spinal interneurons controlling proximal and axial muscles
  • use sensory information about balance, body position, and the visual environment to reflexively maintain balance and body posture
44
Q

Name the ventromedial pathways?

A
  1. the vestibulospinal tract
  2. the tectospinal tract
  3. the pontine reticulospinal tract
  4. the medullary reticulospinal tract
45
Q

Describe the vestibulospinal tract?

A
  • Originate in the vestibular nuclei of the medulla and synapse with interneurons and lower motor neurons in the spinal cord
  • Vestibular nuclei relay sensory info from the vestibular labyrinth in the inner ear
    Receive major input from the vestibular nerve and the cerebellum
46
Q

Vestibulospinal tract is involved in?

A

Primarily involved in maintenance of posture
1. One component projects bilaterally down the spinal cord and activates the cervical spinal circuits that control neck and back muscles and thus guide head movement
2. Another component projects ipsilaterally as far down as the lumbar spinal cord. It helps us maintain an upright and balanced posture by facilitating extensor motor neurons of the legs

47
Q

Describe the tectospinal tract?

A

Originates in the superior colliculus (the tectum /roof of the midbrain) which receives direct input from the retina.
- Also receives projections from visual cortex, as well as afferent axons carrying somatosensory and auditory information.

48
Q

Tectospinal tract is involved in?

A

Controls reflex movement of the head to bright lights, noises, and rapid movements

49
Q

Describe the reticulospinal tract?

A

Neuron cell bodies are in the reticular formation of the pons and medulla
1. pontine reticulospinal
2. medullary reticulospinal

50
Q

Reticulospinal tract is involved in?

A
  1. The pontine reticulospinal tract enhances the antigravity reflexes of the spinal cord
  2. In contrast, the medullary reticulospinal tract liberates the antigravity muscles from reflex control
51
Q

Clinical consequences of damage to the cortical control of skeletal muscles?

A

the upper motor neuron syndrome
1. weakness without significant muscle wasting
2. spasticity (increased muscle tone with clasp-knife rigidity)
3. clonus
4. hyperreflexia of deep tendon reflexes
5. spinal shock
6. positive Babinski sign

52
Q

Common cause of upper motor neuron syndrome?

A

stroke
A ruptured blood vessel that haemorrhages into the brain or thrombosis of one of the major arteries supplying the brain.
The result is loss of blood supply to the cortex or to the corticospinal tract
> Muscle spasm almost invariably occurs in the afflicted muscle areas on the opposite side of the body

53
Q

Clinical manifestations of lower motor neuron damage?

A

Characterised by muscle atrophy, weakness and hyporeflexia without sensory involvement

54
Q

Lower motor neuron damage is classifed broadly as?

A

classified as hereditary, sporadic or immune-mediated.

55
Q

Name and describe lower motor neuron damage syndromes?

A
  1. Amyotrophic lateral sclerosis (affects both upper and lower motor neurons)
  2. Spinal muscular atrophies (SMAs)
  3. Guillain-Barré syndrome
  4. Poliomyelitis

Head and Neck Physiology (18 decks)

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