Chapter 11 - Motor Functioning Flashcards
main components of motor system
- forebrain: responsible for initiating movement
- brainstem: responsible for species-typical movement
- spinal cord: responsible for executing movement
brain regions assisting the motor system
- basal ganglia: in the forebrain, helps produce the appropriate amount of force
- cerebellum: in the brainstem, regulates timing and accuracy
prefrontal cortex (PFC)
responsible for planning our behavior and setting our goals (e.g. deciding to return a book to the library)
- does not specify the precise movements to be made, just sets the goal
- sends instructions to the premotor cortex
premotor cortex
responsible for organizing movement sequences and ensuring that the required body parts are coordinated (e.g. gripping the bike handlebar while pedalling)
- elicits whole body movements
primary motor cortex (M1)
produces specific movements and executes the action
brainstem
responsible for species-typical movements
- also important for standing upright, coordinating movements of the limbs, walking, swimming, etc.
- damage to the brainstem leads to locked-in syndrome and also cerebral palsy (CP)
locked-in syndrome
the patient is conscious and awake but cannot move and communicate verbally because all voluntary muscles are paralyzed (except the eyes)
spinal cord
the connection between the brain and the body
- contains complex motor programs based on reflexes: scratch reflex, knee-bending reflex, and walking reflex
- when the connection between the brain and the spinal cord is severed, spontaneous movements are still possible, but they are no longer guided and timed by the brain
cut to cervical region of the spinal cord
causes paralysis and loss of sensation in the arms and legs
- called quadriplegia
cut below the cervical region in the spinal cord
causes paralysis and loss of sensation in the legs and lower body
- called paraplegia
movements spatially coded in a somatotropic arrangement
different parts of the motor cotex (M1) are responsible for the specific movements of different body parts (based on 2 principles)
- the relative sizes of body parts are disproportionate
- body parts are discontinuous
disproportionate sizes of body parts
the M1 areas responsible for movement in the hands, fingers, lips, and tongues, are larger compared to M1 areas responsible for movement in other body parts
- the larger areas allow for more precise movement regulation
Penfield’s homunculus
discontinuous body parts
the areas in M1 (and S1) are arranged differently from those of our body (e.g. the “hand” area in M1 lies above the “face” area)
constraint-induced therapy
uses neural plasticity to treat stroke-induced paralysis
motility is efferent
information goes from the brain (cortex) to the body (muscles)
corticospinal tracts
the most important motor pathways (one on each side)
- originates in layer V of the motor cortex, continues to the ventral/anterior surface of the brainstem where it forms bumps or “pyramids” on both sides, and ends in the anterior horn of the spinal cord
- in the brainstem, some axons of the corticospinal tract cross to the contralateral side, while others remain on the same side
neuromuscular junction
the efferent connection between motor neurons and muscle fibers
- main neurotransmitter is acetylcholine (released by motor neurons and attaches to specialized areas on muscles called end plates)
basal ganglia
a collection of nuclei just beneath the cortex
- modulates the activity of cortical motor systems
- includes the caudate nucleus, putamen, globus pallidus, nucleus accumbens, subthalamic nucleus, and substantia nigra
- dopamine is the main neurotransmitter
globus pallidus
- if it is excited, it inhibits the thalamus and blocks movement
- if it is inhibited, motor cortex circuits that include the thalamus can produce movement
2 types of symptoms from damage to the basal ganglia
- hypokinetic symptoms
- hyperkinetic symptoms
hypokinetic symptoms
(too little force)
- paucity of movement (rigidity) is involved in Parkinson’s disease, which is caused by a deficiency of dopamine in the substantia nigra, which makes it difficult to initiate movements
hyperkinetic symptoms
(too much force)
- excessive involuntary movements are involved in Huntington’s disease
- here cells of the putamen and caudate nucleus are damaged, causing sudden and exaggerated movements
- tourette syndrome, which involves excessive involuntary movements, is another disorder that is linked to damage to the putamen and caudate nucleus
cerebellum
allows us to get to know movements and remember how to perform them
- can be divided into 3 areas (the base, medial part, and lateral parts)
- contributes to the timing and accurate execution of movements
- if the cerebellum is damaged, the ability to correct errors by comparing the intended and actual movement is reduced
the base of the cerebellum (flocculus)
controls eye movements and balance, in cooperation with the vestibular system in the middle ear
medial part of the cerebellum
support movements in the face and trunk
lateral parts of the cerebellum
support movements of the limbs, hands, feet, and digits
somatosensory system
ensures that we feel everything, from pain to movement of the joints
2 types of skin
- hairy skin (e.g. arms, legs, back)
- glabrous skin (e.g. tongue, lips, hand palms); most sensitive
somato sensory receptors
classified into 3 groups
- nociception (irritation)
- hapsis (pressure)
- proprioception (body awareness)
nociception
the perception of pain, temperature, and itch
- when the nerve endings are irritated or damaged, a chemical is released, causing an action potential
hapsis
the ability to distinguish objects by touch
- this is the perception of light touch or pressure
proprioception
the perception of body location and movement
- the nerve endings are sensitive to muscle extension and the movement of joints
rapidly adapting receptors
activate neurons when stimulation starts and when it ends
slowly adapting receptors
activate neurons if a sensory event is present, they detect if an event is still ongoing
projection from the somatosensory system to the cortex
takes place via the thalamus
- when the axons of somatosensory neurons enter the CNS, they split, forming 2 pathways
posterior spinothalamic tract
formed by haptic and proprioceptive axons which lie in the posterior part of the spinal cord
- carries fine touch and pressure fibres
anterior/ventral spinothalamic tract
formed by the nociceptive axons transmitting their information to the neurons in the grey matter on the dorsal side of the spine, from where the axons of these neurons cross to the contralateral ventral side of the spinal cord
monosynaptic reflex
is a reflex caused by a direct connection between a sensory and motor neuron (knee-jerk reflex)
- cortex is not involved
- fast reflex (approximately 30 ms)
- function is mainly protective
pain gating theory
tries to find an explanation for the phenomenon that you can reduce acute pain by rubbing the sore spot
- haptic and proprioceptive fibres and nociceptive fibres synapse with the same interneuron having opposite effects (stimulation vs inhibition)
referred pain
occurs when pain that arises from an internal organ (e.g. the heart) is felt on the body surface (e.g. the left shoulder)
- happens because internal organs and body surface receptors share the same pathway to the cortex
organ of balance
in the inner ear, near the cochlea
- consists of 2 groups of receptors: semi-circular canals and otolith organs
semi-circular canals
- one for each direction
- each canal is filled with fluid (endolymph) and contains hair cells
- movement of the head makes the cilia on the hair cells move, which leads to action potentials
otolith organs
- consist of utricle and saccule
- these receptors detect gravity (tilt) and linear acceleration
- utricle and saccule also contain hair cells, but in a jelly-like substance (otoconia), which bends when the head moves up or down, which in turn causes action potentials
2 main areas of the somatosensory cortex
- primary somatosensory cortex
- secondary somatosensory cortex
primary somatosensory cortex
receives sensory information from the body through the thalamus (sensory relay station)
secondary somatosensory cortex
receives sensory information from the primary somatosensory cortex and from the visual and auditory cortexes
