Lec 20: Motor Skills Flashcards
3 Levels of Motor Skills
- Precommand level (highest)
- Projection level (middle)
- Segmental level (lowest)
Precommand Level
2 systems of neurons in the cerebellum and
basal nuclei that:
* start/stop movements
* coordinate movements with posture
* block unwanted movements
* monitor muscle tone
happens BEFORE actual
motor responses
Cerebellum
no access to spinal cord –
communicates with projection areas of brain stem and motor cortex via the thalamus
Basal Nuclei
Receive inputs from all cortical
areas and sent output primarily to premotor and prefrontal cortical areas via the thalamus
* seem to be involved in more complex
management compared to the cerebellum
Projection Level
neurons using direct and indirect motor
pathways (descending projection fibers)
* upper motor neurons of motor cortex
initiate direct (pyramidal pathways) to
muscles
* brain stem motor nuclei oversee the
indirect pathways; help to control reflex
and CPG-controlled motor actions
* in addition to descending pathways,
also send internal feedback to higher
command levels, continually informing
them of what should be happening
- Primary Motor cortex
- Brain stem nuclei
Segmental Level
reflexes and spinal cord circuits that control
automatic movements
* ventral horn neurons are activated and they stimulate certain muscles
* locomotion and other repeated patterns are called central pattern generators (CPGs): networks of oscillating inhibitory and excitatory neurons that set rhythms
- Spinal Cord
Descending Motor Pathway
- efferent impulses from brain to spinal cord
- divided into 2 groups:
- Direct Pathways = pyramidal tracts
- Indirect Pathways = rubrospinal, vestibulospinal, reticulospinal and tectospinal tracts
90% of these neurons in lateral corticospinal
pathway; 10% in the smaller anterior pathway
Motor pathways involve 2 neurons
- upper motor neuron begins in motor cortex
- lower motor neuron is a spinal motor neuron or a cranial nerve motor neuron
Direct Pathways
What is the movement of the direct pathway?
Cortex - putamen - globus pallidus - thalamus - cortex
Direct Pathways
What is the job of the direct pathway?
-To influence the cortex
-Regulate fast and fine (or skilled) movements –
e.g. typing, playing a musical instrument
Spinal Cord Injury and Paralysis
transecting spinal cord at any level results in
total motor and sensory loss in regions
inferior to the cut
Spinal Cord Injury and Paralysis
- Paralysis
- Paraplegia
- Quadriplegia
- Hemiplegia
- paralysis = loss of motor function
- paraplegia: transection between T1 and L1
- quadriplegia: transection in cervical region
- hemiplegia: usually due to a brain injury
rather than the spinal cord
Flaccid paralysis
damage to ventral roots or anterior horns means that impulses do not reach muscles and there is no voluntary or involuntary control of muscles
Spastic paralysis
damage to only upper motor neurons of primary motor cortex;
spinal neurons remain intact meaning that there is loss of voluntary control of
muscles but muscles can still be stimulated irregularly via spinal reflexes
Indirect Pathways
- include brain stem, motor nuclei and all motor
pathways not part of the pyramidal system
Indericet Pathways Tracts
includes rubrospinal, vestibulospinal,
reticulospinal and tectospinal tracts
Indericet Pathways Regulations
- axial muscles for balance and posture
- muscles controlling coarse limb
movements - head, neck and eye movement to follow
objects in visual field
Direct Pathways (pic)
Indirect Pathways (pic)
Putting it all together
- Premotor cortex says “I want to do this”
- Precommand areas (basal nuclei and
cerebellum) provide timing and patterns to
execute the desired movements - Basal nuclei are required to start
movements (release motor centers from
inhibition) - Cerebellum calculates best way to perform
and sends blueprint to motor cortex while
constantly monitoring proprioceptive
feedback - Primary motor cortex sends signals down
direct motor pathways - Indirect pathways (from brain stem nuclei)
assist with balance, eye movements,
muscle tone - Lower motor neurons receive signals from
both pathways - Sum total of all inhibitory and excitatory
signals determines final response of the
lower motor neuron & the skeletal muscles
Reflex Arcs
Reflex arcs permit rapid and predictable responses
2 types: inborn (intrinsic) and learned (acquired)
Inborn
unlearned, unpremeditated and involuntary – help us maintain posture, avoid
pain and control visceral activities without having to think about it
* e.g. drop pot of boiling water when some splashes on your arm
Learned
- results often from practice or repetition (e.g. experienced driver of a car)
- can modify an inborn reflex by learning and conscious effort – e.g. what if your 3-
year-old daughter were standing beside you when the boiling water splashed?
— reflexes activate
skeletal muscle while
— reflexes
activate smooth muscle,
cardiac muscle or glands.
Somatic reflexes activate
skeletal muscle while
autonomic (visceral) reflexes
activate smooth muscle,
cardiac muscle or glands.
Stretch and Tendon Reflexes
- help you smoothly coordinate activity of skeletal muscles
- nervous system needs to know:
- length of the muscle (muscle spindles)
- tension in the muscle plus tendons (tendon organs)
2 types of afferent nerve endings:
- anulospiral endings – from larger
nerve axons and monitor both rate
and degree of stretch - flower spray endings – from smaller
nerve axons and monitor degree of
stretch only
Muscle can be stretched by:
a) external force or contraction of antagonistic muscle
b) activating motor neurons that put stretch on middle of the spindle
All stretch reflexes involving the agonist muscle are
monosynaptic and ipsilateral
The Tendon Reflex (polysynaptic)
- acts in the opposite direction – muscles relax and lengthen in response to tension
- contracting muscle relaxes as its antagonist is activated (reciprocal activation)
Why is Tendon Reflex important?
- protects against tearing when damaging stretching force is applied
- during normal intensity of muscle contraction, help ensure smooth on and off
Superficial Reflexes to Test for Spinal Cord Damag
Abdominal Reflex
- using a tongue depressor, stroke skin that is lateral, superior or inferior to the
umbilicus - should see movement of umbilicus toward site of stimulation due to reflex
contraction of abdominal muscles - Tests integrity of T8 to T12
Superficial Reflexes to Test for Spinal Cord Damag
Plantar Reflex
- draw blunt object from heel to toe along lateral aspect of plantar surface of foot
- should induce plantar flexion (except in infants less than 1 year)
- Babinski’s sign (great toe dorsiflexes and remaining toes fan laterally) is
indicative of damage to the primary motor cortex or L4 to S2 are damaged
Babinski’s sign
Effectors:
- Somatic: skeletal muscle;
- ANS: smooth muscle, cardiac muscle & glands
Effectors
Somatic use — pathway
Acetylcholine
Effectors
ANS (sympathetic) use — pathway
Norepinepherine
Effectors
ANS (parasympathetic) use — pathway
Acetylcholine
Pathways and Gangila
Somatic:
thick, myelinated axon from spinal cord to skeletal muscle; rapid
conduction of impulses (no ganglia)
Pathways and Gangila
ANS:
two-neuron chain: preganglionic neuron: originates in brain or spinal cord;
preganglionic axon synapses with 2nd motor neuron (postganglionic) in
ganglion outside CNS – the postganglionic axon to effector organ
* conduction is slow; preganglionic axons are thin & lightly myelinated; postganglionic
axons are thinner & unmyelinated
The sympathetic system
mobilizes the body during extreme situations
The parasympathetic performs
maintenance activities and conserves energy
Parasympathetic Division:
- « resting & digesting system »
- keeps body’s energy use low while regulating « housekeeping » activities (digestion,
elimination of feces & urine) - “D” system: digestion, defecation, diuresis
Sympathetic Division:
- “ fight or flight” system; also important during exercise: increased heart rate, rapid,
deep breathing, cold sweaty skin, dilated eye pupils - “E” system: exercise, excitement, emergency, embarrassment
