Neural + voluntary control of movement

Question 1

when do babies usually learn to walk; explain where these behaviours develop

Answer 1

roughly 12 months. Guideline is between 10 and 18 months old

1) Pons - 1-5 months
* Bridge from brainstem to cerebellum
* Crawling on stomach - attention and motivation
* Hands out integrating grasp reflex
* Vital tactile info received
* Head and eye movements
2) Midbrain - 4-13 months
* Crawling on hands/knees
* Hands open and close
* Connects vestibular, proprioception and visual systems
3) Cortex - 8 - 96 months
* Upright walk and cross pattern
* Cortical opposition of both hands working together but independently
4) Prefrontal cortex - up to 25 yrs
* Refined skills for performance
Executive functions (planning, organisation)

Question 2

you have an itch on ur forehead. Explain how the brain processes this

Answer 2

1. Have itch on forehead
   * Sensory receptors send info up spinal cord to cerebellum (unconscious proprioception) and into sensory cortex (conscious proprioception)
2. Thought of having to scratch itch forms in prefrontal cortex
3. Signals to appropriate cortex to begin composing motor plans
   * Prefrontal cortex and motor association areas
4. From cortex to basal ganglia nuclei - perfects motor plan
   * Also sends to thalamus (relay system)
5. Back to cerebral cortex before execution of action impulse in PNS down via corticospinal tract - activating LMNs at right level/amount to cause muscle contraction corresponding from motor plan
6. Sensory receptors signal if plan worked and if not then repeat if yes then is okay
   Cerebral cortex to cerebellum - motor plan + proprioception info

Question 3

what do we mean by the term somatotopically organised

Answer 3

Somatotopy is the point-for-point correspondence of an area of the body to a specific point on the central nervous system. Typically, the area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus)

e.g. homunucli v specific

Question 4

where are lower motor neurons located, what are some of the symptoms of damage to LMNs + what causes damage to LMNs

Answer 4

LOWER MOTOR NEURONS (LMNs)
Located in
* Anterior/ventral horn of spinal cord - axon leaves via ventral root to get to target muscle
* Cranial nerve in nuclei in brainstem
* All voluntary movements rely on direct innervation from a motor neuron
* Very metabolically active - producing ACh
Damage to LMN=
* Flaccid paralysis (weakness)
* Hypotonia (low tone muscles floppy)
* Fasciculations (twitches)
* Absent deep tendon reflexes (aka areflexia)
* Muscle atrophy (muscle requires contractions to maintain the maintenance of actin and myosin so it will atrophy aka waste away)
Some causes of this damage=
* Poliomyelitis (aka POLIO we still have in some lower economic countries)
* Motor neuron disease
Spinal cord injury

Question 5

what 3 functionally distinct motor pathways do upper motor neurons (UpMNs) contribute to

Answer 5

• In layer 5 of motor cortex
• Do not innervate muscle directly
• Carry voluntary motor commands to the LMNs
• UpMNs synapse directly/indirectly onto LMNs via corticospinal/corticobulbar tract
• Corticobulbar for cranial nerves
• UpMN cell bodies mostly in primary motor cortex (precentral gyrus)
• Some in associative areas and premotor cortex
  UpMN contribute to 3 functionally distinct motor pathways :
• Corticospinal tract (and corticobulbar) (direct) - precise movements
• **Rubrospinal tract **(indirect)
  -Gross movements (large muscles)
  -Facilitates flexor movement
• Vestibulospinal and reticulospinal tracts
  -Posture and balance
  -Muscle tone
  -Position of head and limbs

Question 6

*Lateral corticospinal tract controls ______ musculature

Ventral (anterior) corticospinal tract controls _____ musculature

Answer 6

Lateral corticospinal tract controls **distal musculature **

Ventral (anterior) corticospinal tract controls **axial musculature **

Question 7

where does corticospinal tract decussate

Answer 7

corticospinal tract decussates at the spinomedullary junction

left side of brain controls motor movement of right arm and vice versa

Question 8

what are the function of the cerebellum ‘aka little brain’ and what happens if its damaged

Answer 8

the cerebellum
* Coordinates complicated multi joint movements
* Acts as compactor/predictor of movement
* Receives direct input from muscles and compares it with indented signal for movement
* UNCONSCIOUS Proprioception is transmitted to the cerebellum via spinocerebellar tracts. This information is used by the cerebellum to regulate muscle tone, posture, locomotion, and equilibrium.
! Damage results in un-coordinated movements

Question 9

what are the functions of the vestibulocerebellum

Answer 9

Vestibulocerebellum :
* Balance and posture
* Coordinates eye and head movements
* Damage - impairs ability to stand up, maintain posture
Cerebellar nystagmus

Question 10

what are the functions of the spinocerebellum

Answer 10

Spinocerebellum :
* Locomotion
* Voluntary movements of arms and legs
* Damage - overshoot and intention tremor, impair gait
Intention tremor - involuntary tremor during an intentional movement

Question 11

what are the functions of the cerebrocerebellum

Answer 11

Cerebrocerebellum :
* Skilled motor tasks
* Speech, hand-eye coordination and cognitive eye movements
Damage - ataxia failure of smooth progression

Question 12

in the basal ganglia their are 5 nuclei responsible for initiation and maintenance of motor actions - decision making about what we are going to do next
* Unlike cerebellum, they don’t directly regulate execution of movements
* In conjunction with motor association cortex, they scale the strength of the response and organise correct sequence of activity

What are these 5 nuclei of the basal ganglia

Answer 12

• caudate
• putamen
• Globus pallidus
• Substantia nigra
  *Subthalamic nuclei

MAKE SURE U CAN LABEL THESE

Question 13

what happens if u have damage to basal ganglia

Answer 13

Brake theory (basal ganglia is responsible for this)
* To keep still you put brakes on all movements except those reflexes that maintain an upright posture
* To move you must apply a brake to some postural reflexes and release brake on voluntary movement

Damage to basal ganglia will result in=
* Tremors
* Involuntary muscle movements
* Abnormal increase in muscle tone
* Difficulty initiating movement
* Abnormal posture
Parkinson’s disease

Question 14

what is muscle tone

Answer 14

Muscle tone
* Tension in muscle due to a partial state of contraction in some fibres
* Muscle tone is dependent on the integrity of the monosynaptic reflex
* Tone is maintained reflexively (by stretch & reflex & gamma motor neurons) and adjusted to needs of posture and movement
Tone is also regulated by descending motor pathways
* Golgi tendon organs detects tension in the tendon
* Spinocerebellar tract and interneuron in the spinal cord
Inhibition of alpha motor neuron causes muscle relaxation relieving tension in muscle

Question 15

what happens to the following things in a) lower motor neuron lesion
b) upper motor neuron lesion

• muscle strength
• muscle tone
• reflex strength
• wasting

Answer 15

LMN lesion:
* muscle strength= weakness/ paralysis
* muscle tone= decreased/ absent muscle tone
* reflex strength= decreased/absent reflex strength
* wasting= rapid muscle wasting

UpMN lesion:
* muscle strength= weakness/ paralysis
* muscle tone= increased muscle tone
* reflex strength= increased reflex strength +babinski sign
* wasting= muscle mass is maintained

Question 16

what mechanism maintains muscle tone?

Answer 16

gamma motor neurons form an important muscle stretch reflex mechanism that acts in conjunction with the alpha motor neurons. This sensitivity to stretch provides fine compensations of muscle length and velocity and helps maintain muscle tone. SO descending pathways regulate this

golgi tendon organs detect tension
Spinocerebellar tract and interneuron in the spinal cord
Inhibition of alpha motor neuron causes muscle relaxation relieving tension in muscle

Question 17

Most of bodyweight is _____ to ventral column

Answer 17

Most of bodyweight is anterior to ventral column

Question 18

• Association motor cortex + basal ganglia is responsible for what?
• Primary motor cortex + cerebellum - tactics is responsible for what?
• Brainstem + spinal cord is responsible for what?

Answer 18

• Association motor cortex + basal ganglia - strategy - planning & selecting motor programmes to produce desired movements
• Primary motor cortex + cerebellum - tactics - sequence of muscle contractions over time to produce smooth accurate movements
• Brainstem + spinal cord - execution of voluntary movement and any necessary postural adjustment

n.b.
* Lesions produce distinct clinical signs
* Voluntary movement is initiated by circuits in forebrain
* Cerebral cortex can use pyramidal/extra-pyramidal tracts for voluntary movement
* Voluntary tracts and reflex tracts simultaneously compete for control of local interneurons
Final common pathway neurons are controlled mainly via interneurons

Question 19

what brain regions involved in the control of voluntary movement?

Answer 19

Primary Motor Cortex (M1): Essential for executing voluntary movements by sending signals to control muscle contractions.

Premotor Cortex: Adjacent to M1, it plays a role in planning movements and selecting specific actions.

Supplementary Motor Area (SMA): Involved in planning and coordinating complex or sequential movements.

Basal Ganglia: A group of subcortical nuclei important for initiating movement, controlling repetitive movements, posture, and muscle tone, as well as playing a role in motor learning.

Cerebellum: Key for motor control, coordinating and timing movements to ensure they are smooth and accurate, and involved in motor learning.

Thalamus: The main relay station for motor information to the cortex, transmitting signals from the basal ganglia and cerebellum to M1.

Brainstem: Includes various nuclei and pathways crucial for automatic functions and integrating motor commands for posture and gaze control.

Frontal Eye Fields: Important for controlling voluntary eye movements.

Question 20

Describe the main descending motor tracts

Answer 20

The main descending motor tracts in the central nervous system are the pathways by which motor signals are sent from the brain to control muscle movements. Here are the key tracts:

Corticospinal Tract: The most significant motor pathway involved in voluntary movement control, it originates in the cerebral cortex. The lateral corticospinal tract crosses over (decussates) at the level of the medulla oblongata and descends in the lateral column of the spinal cord to control the limbs and digits. The anterior corticospinal tract descends ipsilaterally before decussating at the level of the spinal segment it innervates, mainly influencing the trunk muscles.

Corticobulbar Tract: This tract controls movements of the face, head, and neck via cranial nerves. It begins in the cortex and terminates on motor neurons within the brainstem.

Rubrospinal Tract: Originating in the red nucleus of the midbrain, this tract also crosses over and descends in the lateral column of the spinal cord, and is mainly involved in the control of distal limb muscles, complementing the functions of the corticospinal tract.

Vestibulospinal Tract: Arising from the vestibular nuclei in the brainstem, it helps to maintain posture and balance in response to head movements. It has both lateral and medial components, which influence the activity of muscles that control postural adjustments.

Reticulospinal Tract: Emanating from the reticular formation in the brainstem, this tract influences muscles of the trunk and proximal limbs. It has a significant role in maintaining posture and locomotion.

Tectospinal Tract: Originating from the superior colliculus in the midbrain, this tract is involved in reflex postural movements in response to visual stimuli.

These tracts carry motor signals that control muscle tone, posture, and fine movements. They operate by modulating the activity of lower motor neurons, which directly innervate muscles to produce movement.