Task 1 - voluntary movements Flashcards
what parts does the central nervous system contain of ?
- brain
-> cerebrum
-> cerebellum
-> brainstem - spinal cord
spinal nerves (are part of the PNS)
= each attaches to the spinal cord via 2 branches
-> dorsal root = afferent nerves (CNS)
-> ventral root = efferent nerves (CNS)
what parts does the peripheral nervous system contain of ?
= all the other parts of the nervous system
- somatic peripheral nervous system
- autonomic nervous system (ANS) / visceral PNS
what is the somatic peripheral nervous system?
= part of the PNS
involves all spinal nerves that innervate skin/ joints and muscles that are under voluntary control
what is the autonomic nervous system / visceral PNS?
= part of the PNS
its neurons excite the internal organs, blood vessels and glands and are under involuntary control
Bears hierarchical structure of the motor system
- highest level = strategy
-> Association Areas
-> Basal ganglia - middle level = tactics
-> Motor Cortex (= Area 4+6)
-> Cerebellum - lowest level = execution
-> Brain stem
-> spinal cord
What is Gazzaniga’s structure of the motor system?
- highest level = (goals), on experience
-> Association Areas
-> Area 6 - middle level = action prep
-> area 4
-> brainstem
-> indirectly from basal ganglia + cerebellum - lowest level = execution
-> spinal cord
-> motor neurons
-> interneurons
-> muscles
What are the descending spinal tracts?
lateral pathways = voluntary movement
-> corticospinal tract (pyramidal)
-> rubrospinal tract
ventromedial pathways = involuntary movement
-> vestibulospinal tract
-> tectospinal tract
-> potine reticulospinal tract
-> meduallary reticuspinal tract
what is the corticospinal tract ?
- lateral pathway
- direct pathway
- contralateral
- pyramidal pathway (passes through pyramids of medulla oblongata)
- involved in voluntary (& fine) movement of DISTAL muscles
-> motor cortex
-> internal capsule
-> base of cerebral peduncle
-> pons
-> base of medulla (🔀 = decussating)
-> dorsolateral region of the ventral horns + intermediate gray matter
what is the rubrospinal tract ?
- lateral pathway
- extrapyramidal
- contralateral
- receives main input from motor cortex
- main aim has been replaced by the corticospinal tract (! can compensate)
-> red nucleus (of the midbrain)
-> pons ( 🔀 = decussating)
-> joins the corticospinal tract in lateral column of the spinal cord
what is the vestibulospinal tract?
- ventromedial pathway
- extrapyramidal
- bilateral & ipsilateral
- keeping the head balanced on the shoulders when body moves and turns in response to a stimuli
- originates in the brain stem
-> vestibular nuclei in the medulla
-> one part projects down to spinal cord = BILATERALLY (controls neck & back muscles)
-> one part projects to the lumbar spinal cord = IPSILATERALLY (helps to maintain balanced posture)
What is the tectospinal tract?
- ventromedial pathway
- extrapyramidal
- contralateral
- originates in the brian stem
- aims to create a visual map of the world
-> receives input from the retina + vosual cortext
-> projects down to the spinal cord
(helping to mediate reflex postural movements of the head in response to a stimuli)
what are the pontine & medullary reticulospinal tracts?
pontine
- from pontine reticular formation in the brainstem
- helps the body resist the effects of gravity
= enhances anti-gravity
medullary
- from reticular formation in the brainstem (medullary reticular formation)
- liberates antigravity muscles from reflexes
= helps avoidance of anti-gravity
=> balance needed for optimal movement & posture
What is the motor cortex?
- consists of 2 areas
-> A4/ M1 (= primary motor cortex)
-> A6 (= secondary motor cortex) - control of all the voluntary motor movement
what is the primary motor cortex?
- anterior to the central sulcus
- essential for volitional movement
- has the lowest threshold for elicitation of movement (by electrical stimulation)
- contains somatotopic organisation
= with cortical magnification - relies heavily on the sensory system
= sensorimotor system - consists of a rostral region
its axons project to
-> spinal interneurals
-> caudal region (has evolved more recently) - which projects to alpha motor neurons
what is the sensory-motor system?
describes the central integration and processing components of sensory and motor information
what is the secondary motor system?
= area 6
- supplementary motor area (SMA)
-> sends axons that innervate distal motor units (planning a sequence of learned actions)
-> in achieving internally guided goals - premotor area (PMA)
-> connects to reticulospinal neurons that innervate proximal motor units
-> coordinates external sensory-guided actions (grabbing a cup of coffee)
what is the posterior parietal cortex?
= highest level of motor hierarchy
= decisions are made about actions and their likely outcome
- association areas
- generate a mental body image
= critical for own representation in space - receives input
-> somatosensory
-> proprioceptive
-> visual
what is the prefrontal cortex?
= highest level of motor hierarchy
= decisions are made about actions and their likely outcome
- important for
-> abstract thought
-> anticipating the consequences of one´s own actions - has direct connections to area 6 (PMA + SMA)
what happens in the neural coding of movement?
- M1 neurons fire immediately and during a voluntary movement
= this encodes two aspects of movement
-> force
-> direction - direction is not ecoded by a single cell´s activity but a collective activity
-> every cell has a preferred drection (= highest firing rate)
-> the higher the preference, the longer the vector
-> population vector = average of all vectors plotted together ~ every neuron has a vote
-> strong correlation between population vector ad actual direction of movement
Evaluation of population vector theory
PRO
- in line with the somatotopic representation of the motor cortex
- provides an explanation for fitness + accuracy in everyday movements
CONTRA
- findings that contradict this understanding
-> many cells don’t exhibit a directional tuning
-> tuning may shift during a movement
Name 3 examples, of when the motor system fails
Apraxia
= inability to perform complex motor acts
= caused by lesions to secondary motor areas
Parkinson´s disease
= inability to produce volitional movement
= results from cell death in the substantia nigra
Ataxia
= impairment of sensory coordination of distal limb movments
= caused by damage to the cerebellum
