Motor Control Flashcards
Control of complex movements involve what brain areas?
- Cerebral cortex
- Basal Ganglia
- Cerebellum
- Thalamus
- Brain stem
- Spinal cord
What type of arrangement does the primary motor cortex have? What happens when it is stimulated?
- Somatotopic arrangement
- Excitation stimulates movements instead of contracting a single muscle
What Broadman area is the primary motor cortex involved with?
Broadman area 4 (precentral gyrus)
This area is anterior to the lateral portions of the primary motor cortex below the supplemental area and projects to the primary motor cortex and basal ganglia.
Premotor area
This area is superior to the premotor area lying mainly in the longitudinal fissure and functions in concert with the premotor area to provide attitudinal and fixation movements, positional movements of the head and eyes, and background for finer motor control of arms/hands.
Supplemental motor area
Where does the corticospinal tract originate?
- 30% from the primary motor cortex
- 30% from the premotor and supplemental areas
- 40% from the somatic sensory areas
This tract descends via the posterior limb of the internal capsule and forms the pyramids of the medulla
Corticospinal tract
- Most fibers cross midline and form the lateral corticospinal tract
- Some fibers stay ipsilateral and form the ventral corticospinal tract
This transection involves all tracts being cut and the cord being completely isolated from the brain.
Spinal preparation
This is a transection at the mid collicular level.
Decerebrate preparation
This transection involves the destruction of the cerebral cortex.
Decorticate preparation
What does a spinal preparation result in?
Flaccidity (flaccid or floppy paralysis)
What does a decerebrate preparation result in?
Extensors are tonically hyperactive resulting in “decerebrate rigidity”
What does a decorticate preparation result in?
This creates a different type of rigidity, clinically known as “decorticate spasticity” due to tonic excitation from upper areas of the reticular formation no longer under inhibitory cortical influence (release phenomenon).
This is an experimental procedure that is useful for the study of reflexes. A transection of the midbrain is often at the intercollicular level and motor control is profoundly altered (flexion suppressed/extension is exaggerated).
Decerebration (leads to decerebrate rigidity)
Spinal shock is characterized by what?
- Dramatic fall in arterial blood pressure
- All skeletal muscle reflexes integrated in the cord are blocked
- Sacral reflexes for control of bladder and colon evacuation are suppressed
These reticular nuclei:
- transmit excitatory signals via the pontine reticulospinal tract
- stimulate the axial trunk and extensor muscles that support the body against gravity
- receive stimulation from vestibular nuclei and deep nuclei of the cerebellum,
- have a high degree of natural excitability.
Pontine reticular nuclei
These reticular nuclei:
- transmit inhibitory signals to antigravity muscles via the medullary (lateral) reticulospinal tract
- receive strong input from the cortex, red nucleus, and other motor pathways
- counterbalance excitatory signals from the pontine reticular nuclei
- allows tone to be increased or decreased depending on function needing to be performed.
Medullary reticular nuclei
What are the five important tracts that descend form the brain to the spinal cord?
- Ventral/lateral corticospinal
- Reticulospinal
- Vestibulospinal
- Rubrospinal
- Tectospinal
Out of the five descending pathways to the spinal cord, which are ipsilateral and which are contralateral?
Ipsilateral:
- Ventral corticospinal tract
- Reticulospinal
- Vestibulospinal
Contralateral:
- Lateral corticospinal tract
- Rubrospinal
- Tectospinal
Out of the five descending pathways to the spinal cord, which are part of the lateral motor system of the cord and control more distal muscles of limbs.
- Lateral corticospinal tracts
- Rubrospinal tracts
Out of the five descending pathways to the spinal cord, which are part of the medial motor system of the cord and control mainly the axial and girdle muscles.
- Reticulopsinal
- Vestibulospinal
- Tectospinal
- Anterior corticospinal
What type of arrangement does the primary motor cortex have?
Vertical columnar arrangement which functions as an integrative processing system
Within the primary motor cortex pyramidal cells have what two types of output signals?
Dynamic (initiates contraction) and static (maintain contraction)
What is the pathway in the planning and program phase of voluntary movement?
Signals for movement originate in the sensory association cortex and output to premotor cortex directly and indirectly via the basal ganglia and cerebrocerebellum
What is the pathway in the execution phase of voluntary movement?
- Premotor cortex–>primary motor cortex (PMC)–>spinal cord (corticospinal projections)
- PMC—>spinocerebellum
- Feedback from periphery–>spinocerebellum–>PMC
These maintain the body in an up-right balanced position and provide constant adjustments necessary to maintain stable postural background for voluntary movement.
Postural reflexes
Adjustments to posture include what two types of reflexes?
- Static reflexes (sustained contraction
- Dynamic short term phasic reflexes (transient movements)
Postural reflexes are caused by changes in excitability of ____ neurons and changes in rate of discharge in the ____ neurons to muscle spindles.
Motor; gamma efferent
What are the three types of postural reflexes?
- Vestibular reflexes
- Tonic neck reflexes
- Righting reflexes
This is the organ that detects sensations of equilibrium, provides information about position and movement of head in space, and helps maintain body balance and helps coordinate movements.
Vestibular apparatus
The vestibular apparatus consists of what structures? Where is is located?
- It consists of the semicircular canals, utricle, and saccule
- It is embedded in the petrous portion of the temporal bone
This is the sensory area of the utricle and saccule and is covered with a gelatinous layer in which many small CaCO3 crystals are embedded.
Macula
What does the macula of the utricle and saccule detect?
- Orientation of the head with respect to gravity
- Linear acceleration
Which plane does the macula of the utricle lie? What is its role?
- It lies mainly in the horizontal plane
- It plays an important role in determining orientation of the head when a person is upright
Which plane does the saccule lie? What is its role?
- It lies mainly in the verticle plane
- It plays an important role in determining orientation of the head when a person is lying down
This is the sensory organ of rotation located in the semicircular canals of the inner ear.
Crista ampullaris
This is the loose gelatinous tissue mass on top of the crista ampullaris,
Cupula
There are three pairs of semicircular canals at 90 degrees to one another. What planes are they located in?
Anterior, horizontal, and posterior
- Right anterior with left posterior
- Right and left horizontal
- Left anterior with right posterior
What fluid are the semicircular canals with?
Endolymph
What do the semicircular canals detect?
Rotational acceleration and deceleration
What occurrences is stimulation of the semicircular canals associated with?
Increased extensor tone and nystagmus
What are the two components of nystagmus?
- Slow component (tracking): can be initiated by semicircular canals
- Fast component (jump ahead to a new focal spot): initiated by the brain stem nuclei
What brain structure do the semicircular canals work closely with?
Cerebellum, especially the flocculonodular lobe
This condition is characterized by a sudden sensation of spinning, usually when moving the head.
Vertigo
This procedure relocates free floating particles in the semicircular canals back to the utricle, where they can no longer stimulate the cupula. It is used to relieve patients of vertigo.
Epley’s maneuver
One’s sense of uprightness is generally a combination of cues that include what types of information?
Visual and vestibular information
This term is used to describe overall position of the body and limbs relative to one another and their orientation in space.
Posture
What types of reflexes are evoked by changes in the position of the head?
Vestibular reflexes
What types of reflexes are evoked by the tilting or turning of the neck?
Neck reflexes
To support the head and body against gravity, maintain a center of gravity, and stabilize supporting parts of the body while others are being moved are all functions of what?
Postural adjustments
What are the main mechanisms of postural adjustments?
- Anticipatory (feed forward): predict disturbances and modified by experience
- Compensatory (feedback): evoked by sensory events following the loss of balance
Where do postural mechanisms receive sensory input from?
- Cutaneous recpetors from the skin (especially feet)
- Proprioceptors from joints and muscles (short latency 70-100ms)
- Vestibular signals (longer latency, 2x proprioceptor latency)
- Visual signals (longer latency, 2x proprioceptor latency)
When the body is swaying, contraction of muscles to maintain balance occur in what order?
Distal to proximal
When the neck is extended, do extensors or flexors of arms/legs tend to contract?
Extensors of arms/legs
When the neck is flexed, do extensors or flexors of arms/legs tend to contract?
Flexors arms/legs
When rotation or lateral bending of the neck occurs, what happens to the limb muscles?
- Extensors on the ipsilateral side contract
- Flexors on the contralateral side contract
What are the input nuclei of the basal ganglia?
- Caudate
- Putamen
- Nucleus accumbens
What are the output nuclei of the basal ganglia?
- Globus pallidus
- Subthalamic nucleus
- Substantia nigra
- Ventral tegmental area
What are the four principal nuclei of the basal ganglia?
- Striatum (caudate and putamen)
- Globus pallidus (internal and external)
- Substantia nigra
- Subthalamic nucleus
Does the basal ganglia have direct input or output connections with the spinal cord?
No
Motor functions of the basal ganglia are mediated by what?
The motor areas of the cortex
Disorders of the basal ganglia have three characteristic types of motor disturbances. What are they?
- Tremor and other involuntary movements
- Changes in posture and muscle tone
- Poverty and slowness of movement
This major circuit of the basal ganglia plays a major role in cognitive control of motor activity.
Caudate circuit
This major circuit of the basal ganglia deals with subconcious execution of learned patterns of movement.
Putamen circuit
This abnormality of the basal ganglia is due to a lesion of the globus pallidus and is characterized by spontaneous and continuous writhing movements.
Athetosis
This abnormality of the basal ganglia is due to a lesion in the subthalamus and characterized by sudden violent flailing movements of a limb.
Hemiballismus
This abnormality of the basal ganglia is due to multiple lesions in the putamen and characterized by flicking movements in the hands, face, etc.
Chorea
This brain structure contains more than half of all neurons in the brain and plays a crucial indirect role in movement and posture by adjusting the output of the major descending motor systems.
Cerebellum
This division of the cerebellum governs eye movements and body equilibrium.
Vestibulocerebellum (floculonodular lobe)
This division of the cerebellum plays a major role in movement and influences descending motor systems.
Spinocerebellum (vermis and intermediate)
This division of the cerebellum deals with the planning and initiation of movement and extramotor prediction, mental rehearsal of complex motor actions, and conscious assessment of movement errors.
Cerebrocerebellum (lateral zone)
These are the major inhibitory cells in the cerebellar cortex.
Purkinje cells
What two types of output signals do purkinje cells produce?
Complex and Simple action potentials.
Complex action potentials come from what types of fibers?
Climbing fibers from the inferior olivary nucleus (1:1 ratio with purkinje cells)
Simple action potentials come from what types of fibers?
Mossy fibers via granule cells (1 mossy fiber excites 100s-1000s of purkinje cells)
Mossy fiber input is from everywhere except what?
Inferior olivary nucleus
What is the role of the inferior olivary nucleus?
- Compares intention with performance
- Affects the cerebellum via climbing fiber input
Lesions in the cerebellum create what types of findings in the body? Ipsilateral or Contralateral?
Ipsilateral, due to pathway crossing twice or not at all.
What are some functions of the cerebellum?
- Motor learning
- Cognitive processing and emotion
- Loaded by the integrity of joint mechanoreceptors
What are the three pairs of deep nuclei in the cerebellum?
- Fastigial
- Interposed (globose and emboliform)
- Dentate
This peduncle, which connects the cerebellum to the brain stem, contains most efferent projections and ventral spinocerebellar tracts.
Superior peduncle
This peduncle, which connects the cerebellum to the brain stem, contains primary pontocerebellar tracts.
Middle peduncle
This peduncle, which connects the cerebellum to the brain stem, contains dorsal spinocerebellar tracts.
Inferior peduncle
This is the concept whereby body states are regulated toward a steady state.
Homeostasis
This part of the nervous system controls visceral functions and functions to maintain a dynamic internal environment, necessary for proper function of cells, tissues, organs, under a wide variety of conditions and demands.
Autonomic nervous system
What are the three divisions of the autonomic nervous system?
- Sympathetic (fight/flight/fright)
- Parasympathetic (rest/digest)
- Enteric (neuronal network in the walls of the GI tract)
These cells of the sympathetic nervous system are intermediolateral horn cells located from C8-L2/3 and primarily release Ach and some neuropeptides (LHRH).
Pre-ganglionic cells
These cells of the sympathetic nervous system are paravertebral/prevertebral ganglia. Most fibers release norepinephrine and some neuropeptides (NPY).
Post-ganglionic cells
Negative feedback in norepinephrine receptors is attributed to what?
The presence of alpha 2 adrenoceptors in sympathetic nervous system terminals
What does yohimbine (alpha 2 blocker) do to norepinephrine release?
Increase norepinephrine release
This term is used to describe an increased sympathetic activity.
Sympathocotonia
This condition is due to an interruption of SNS supply to the head. It results in partial ptosis (drooping of eyelid), pupillary constriction, anhydosis (inability to sweat), and enophthamos (eyes are withdrawn back).
Horner’s syndrome
Which cranial nerves are parasympathetic?
III, VII, IX, X
What substance do preganglionic cells of the parasympathetic nervous system release? Postganglionic?
Preganglionic: acetylcholine
Postganglionic: acetylcholine
Preganglionic and parasympathetics project to the enteric ganglia of the stomach, colon, and rectum via what nerves?
Vagus and pelvic splanchnic nerves
This division of the enteric nervous system is found between the longitudinal and circular muscle layer and controls gut motility.
Myenteric plexus (Auerbach’s)
What do excitatory and inhibitory motor neurons of the myenteric plexus release?
Excitatory: Ach and substance P
Inhibitory: Dynophin and vasoactive intestinal peptide (VIP)
This division of the enteric nervous system regulates ion/water transport across the intestinal epithelium and glandular secretions. Additionally it communicates with the myenteric plexus and releases neuropeptides.
Submucosal plexus
These fibers accompany visceral motor fibers in autonomic nerves, supply information that originates in sensory receptors in viscera, and are important for homeostatic control and adjustment to external stimuli.
Visceral afferent fibers
Many visceral afferent fibers may release an excitatory neurotransmitter called what?
Glutamate
What are some examples of autonomic reflexes?
- Cardiovascular (baroreceptor, Bainbridge reflex)
- GI autonomic reflexes (smell of food elicits the release of digestive juices, fecal matter elicits strong peristaltic contractions)
Which glands are exclusively innervated by cholinergic sympathetics?
Sweat glands
What is the fate of acetylcholine after being released?
It is rapidly hydrolysed by acetylcholinesterase
What is the fate of norepinephrine after being released?
It is taken up by nerve terminals, degraded by MAO and COMT, and then carried away by the blood
What is the precursor for dopamine, norepinephrine, and epinephrine?
Tyrosine
What is the precursor of acetylcholine?
Choline
What do adrenergic receptors bind?
Epinephrine and norepinephrine
What nicotinic and muscarinic receptors bind?
Acetylcholine
What is the affinity of norepinephrine for alpha and beta receptors?
It has equal affinity for both
What is the affinity of epinephrine for alpha and beta receptors?
It has a greater affinity for beta compared to alpha receptors
What can happen to receptors if there is upregulation?
- The number of receptors can increase
- The sensitivity of receptors can increase
What happens to receptors if there is downregulation?
- The number of receptors can decrease
- The sensitivity of receptors can decrease
