Physiology of Motor Systems Flashcards
Where is the primary motor cortex located?
located in the precentral gyrus of the frontal lobe of each hemisphere
Describe pyramidal cells
- located in the gyri
- allow us to consciously control the precise or skilled voluntary movements of our skeletal muscles.
What is anterior to the precentral gyrus in the frontal lobe
Premotor cortex
Role of premotor cortex
- helps plan and coordinate movements
- control voluntary actions that depend on sensory feedback
What Lies anterior to the inferior region of the premotor area
Broca’s area
In which area is Broca’s area usually present in
left
What is the role of Broca’s area?
- motor speech area that directs the muscles involved in speech production
What is Located partially in and anterior to the premotor cortex and superior to Broca’s area
Frontal eye field
The descending pathways that deliver efferent impulses from the brain to the spinal cord are divided into two groups:
(1) Direct pathways, which are the pyramidal tracts
(2) Indirect pathways, essentially all others
Motor pathways involve two neurons:
- Upper motor neurons are the pyramidal cells of the motor cortex and the neurons of subcortical motor nuclei
- Lower motor neurons are the ventral horn motor neurons. These directly innervate the skeletal muscles (their effectors)
The direct pathways originate mainly with the pyramidal cells located where
in the precentral gyri
neurons of the direct pathway send impulses through the brain stem via the large …
pyramidal (corticospinal) tracts
What does the pyramidal pathway regulate?
- regulates fast and fine (or skilled) voluntary movements such as texting or playing an instrument
The indirect pathways includes what?
brain stem motor nuclei and all motor pathways except the pyramidal pathways.
The indirect pathway is most involved in regulating…
- Axial muscles that maintain balance and posture
- Muscles controlling coarse limb movements
- Head, neck, and eye movements that follow objects in the visual field
Rubrospinal tracts role
control flexor muscles
Reticulospinal and vestibulospinal tracts role
maintain balance by varying the tone of postural muscles.
Tectospinal tracts and the superior colliculi role
mediate head movements in response to visual stimuli.
the pathways to and from the head are similar to those of the trunk and limbs, with two exceptions:
- The axons of the tracts servicing the head are located in cranial nerves
- The cell bodies are located in the brain stem rather than in the spinal cord.
CN III, IV and VI innervate
extraocular muscles
CN V innervates
muscles of mastication (chewing)
CN VII innervates
muscles of facial expression
CN IX innervate
muscles of the pharynx
CN XI innervate
sternocleidomastoid and trapezius
CN XII innervates
muscles of the tongue
Which part of the brain is part of the precommand area
cerebellum and basal nuclei
What is the role of the cerebellum and basal nuclei
precisely start or stop movements, coordinate movements with posture, block unwanted movements, and monitor muscle tone.
Role of precommand area
- control the outputs of the cortex and brain stem motor centers
- stand at the highest level of the motor hierarchy.
Difference between inborn or learned reflex
- Inborn (intrinsic) reflex is a rapid, predictable motor response to a stimulus. It is unlearned and involuntary.
- Learned (acquired) reflex Results from practice or repetition
All reflex arcs have five essential components:
STEP 1 Receptor: Site of the stimulus action.
STEP 2 Sensory neuron: Transmits afferent impulses to the CNS
STEP 3 Integration center: In simple reflex arcs, the integration center may be a single synapse between a sensory neuron and a motor neuron (monosynaptic reflex). More complex reflex arcs involve multiple synapses with chains of interneurons (polysynaptic reflex).
STEP 4 Motor neuron: Conducts efferent impulses from the integration center to an effector organ
STEP 5 Effector: Muscle fiber or gland cell that responds to the efferent impulses (by contracting or secreting)
Reflexes are classified functionally as:
Somatic reflexes: They activate skeletal muscle
Autonomic (visceral) reflexes: They activate visceral effectors (smooth or
cardiac muscle or glands)
True or false. Many spinal reflexes occur without the direct involvement of higher brain center
True
Muscle spindles measure…
length
Tendon organs measure…
tension
Each muscle spindle consists of:
- Intrafusal muscle fibers
- Extrafusal muscle fibers
- Sensory endings
- Alpha (α) motor neurons to stimulate the extrafusal muscle fibers
- Gamma (γ) efferent to stimulate intrafusal muscle fibers
fibers
Describe the patellar/knee-jerk reflex
As your knees begin to buckle and the quadriceps lengthens, the stretch reflex causes the quadriceps to contract without your having to think about it.
reciprocal activation
motor neurons in spinal cord circuits supplying the contracting muscle are inhibited and antagonist muscles are activated in response to muscle tension
Tendon reflex/tendon organ
- Muscles relax and lengthen in response to tension
- help to prevent muscles and tendons from tearing when they are subjected to potentially damaging stretching force
what initiates the flexor?
a painful stimulus
The Flexor and Crossed-Extensor Reflexes
- a complex spinal reflex consisting of an ipsilateral withdrawal reflex and a contralateral extensor reflex.
- Incoming afferent fibers synapse with interneurons that control the flexor withdrawal response on the same side of the body and with other interneurons that control the extensor muscles on the opposite side.
True or false. Flexor reflexes are contralateral and monosynaptic,
False. Flexor reflexes are ipsilateral and polysynaptic,
