CNS Lecture 4 Flashcards
How is sensory input used to control body movement?
- Higher centres of the brain generate motor commands and transmit them through the brainstem to the spinal cord
- sensory signals from sensory afferent neurons mediate spinal reflexes and ascend to the brainstem, cerebellum and cerebral cortex where they provide feedback of the evolving movement
Signals from the sensorimotor cortex descend to the ____ and to the ______ _______ ______ which innervate muscle fibres
Signals from the sensorimotor cortex descend to the brainstem and to the spinal cord motor neurons which innervate muscle fibres
Information from sensory receptors travels to the spinal cord via _______ axons. Sensory pathways ascend to the _____, the _____ and the _______ which transmits sensory information to the _________ cortex where sensory input is combined with input from other parts of the brain (integrated) to form output commands to the _____, ________ and the ______
Information from sensory receptors travels to the spinal cord via afferent axons. Sensory pathways ascend to the brainstem, the cerebellum and the thalamus which transmits sensory information to the sensorimotor cortex where sensory input is combined with input from other parts of the brain (integrated) to form output commands to the brainstem, basal ganglia (basal nuclei) and the cerebellum
The basal ganglia and the cerebellum send their outputs to the ______ and the ______
The basal ganglia and the cerebellum send their outputs to the thalamus and the brainstem
What are the supraspinal centres involved in controlling motion?
Supraspinal = above spinal cord
Include:
- sensorimotor cortex
- brainstem
- cerebellum
- cerebral cortex
- thalamus
- basal ganglia
the sensorimotor cortex, the cerebellum and the basal ganglia issue motor commands via the _____ and ______
Describe feedback control of the image:
- the motor command is a desired limb position
- spinal cord transmits the command to the muscles via ______ _____ ____ ______ where it stimulates ______ ______
- receptors in the _____, ______ and _____ signal the position of the limb to the _______ via _______
- What happens in the spinal cord?
- What happens if a load is added?
the sensorimotor cortex, the cerebellum and the basal ganglia issue motor commands via the brainstem and spinal cord
Describe feedback control of the image:
- the motor command is a desired limb position
- spinal cord transmits the command to the muscles via alpha motor neuronal axons where it stimulates muscle contraction
- receptors in the muscles, joints and skin signal the position of the limb to the spinal cord via afferent axons
- What happens in the spinal cord?
- the actual position is subtracted from the desired position and the difference causes motor neurons to contract in order to minimize the difference
- limb moves from actual position to desired position
- greater the difference = stronger the muscle activation
- What happens if a load is added?
- Limb is moved away from desired position
- this movement is detected by receptors
- operation of feedback loop acts to minimize difference corrected for external load
What is necessary for feedback control?
Sensory information and a mechanism for comparing desired to actual state
What two types of muscle receptors provide the most relevant information to the control of muscle?
- Muscle spindle - respond to changes in muscle length
- Golgi Tendon Organs (tendon organs - signal changes in muscle force
Muscle spindles respond to changes in _________
Muscle spindles respond to changes in muscle length
Muscle spindles are located in parallel with the ________ so their sensory endings, which give rise to group ____ and ____ sensory afferents respond to changes in muscle length.
Muscle spindles are located in parallel with the force-producing muscle fibres so their sensory endings, which give rise to group Ia and Group II sensory afferents, respond to changes in muscle length.
Tendon organs are in the ______ ______ at the ends of the muscle fibres.
Their muscle endings (Group ___) respond to muscle _____
Tendon organs are in the tendinous fascicles at the ends of the muscle fibres.
Their muscle endings (Group Ib) respond to muscle Force
In addition to responding to muscle stretch, muscle spindle group Ia afferents also respond to _________
What is the clinical significance of this?
In addition to responding to muscle stretch, muscle spindle group Ia afferents also respond to Muscle or tendon vibration
- Prolonged vibration used in physiotherapy to alleviate spasticity (overactive stretch reflexes) - possibly because Ia afferents activate interneurons that inhibit transmission in the stretch reflex pathway
The sensory endings of muscle spindles are spiralled around specialized muscle fibers called ________
The sensory endings of muscle spindles are spiralled around specialized muscle fibers called intrafusal muscle fibres (which are inside the muscle spindle)
What are the components making up the muscle spindle?
- Connective tissue capsule
- intrafusal muscle fibres
- stretch receptors
What does the term spasticity refer to?
Overactive stretch reflexes
______ (within muscle spindles) generate only tiny amounts of force
intrafusal muscle fibres (within muscle spindles) generate only tiny amounts of force
The main muscle fibres found outside the muscle spindle that produce all of the measurable force are called:
Extrafusal muscle fibres
What are the two types of motor neurons innervating a muscle?
- alpha motor neurons
- gamma motor neurons
What do alpha motorneurons (often just called ‘motor neurons’) activate?
What is their conduction velocity?
Motor neurons activate the main (extrafusal) muscle fibres to contract
- conduction velocities similar to those of muscle spindle 1A afferents and tendon organ 1B afferents
What muscle fibres are activated by Gamma motor neurons?
What is their conduction velocity?
Gamma motor neurons activate intrafusal muscle fibres at each end of the muscle spindle (middle is non-contractile)
- conduction velocity between 25-40 m/s
Muscle spindle afferents (1A and 2) signal changes in ______
muscle length
What happens when the intrafusal muscle fibres are activated?
stretches the elastic non-contractile middle part where the sensory endings are located =
- causes sensory afferents to fire more rapidly and become more sensitive to changes in length of muscle as a whole
What afferents signal muscle force?
What group do these afferents belong to?
Golgi tendon organ afferents (group 1B) signal muscle force
What is alpha-gamma coactivation?
What does this theory suggest about the simultaneous activation of intrafusal muscle fibres and alpha motorneurons
Theory that suggested gamma motor neurons are coactivated with alpha motorneurons to keep the muscle spindle afferents firing during muscle shortening
- if intrafusal muscle fibres are activated at the same time as alpha motorneurons, this will keep the muscle spindle taut as the muscle shortens
- the elastic non-contractile region remains approx the same length instead of going slack
- intrafusal contraction compensates for extrafusal muscle shortening, tightening the spindle so the afferents maintain (or increase) their firing
According to the theory of alpha-gamma coactivation, what is the main role of gamma motor neurons?
Alter the sensitivity of muscle spindles to changes in muscle length
Describe what is happening in each of the figures
a, b) no gamma activity: spindle afferent firing increases with muscle stretch and decreases with shortening
c) descending signals from the brain coactivate alpha and gamma MN’s.
- alpha MN’s activate extrafusal muscle fibres = cause muscle shortening
- gamma MN’s activate intrafusal muscle fibres
- intrafusal contraction compensates for extrafusal muscle shortening, tightening the spindle so the afferents maintain their firing
In the spinal cord reflex, what happens at the muscle spindle fibre when a stretch reflex is activated via muscle stretch?
- tap of patellar tendon - small but rapid increase in the length of the muscle or stretch of the muscle - activates muscle spindle afferents
- AP’s in the afferents travel to the spinal cord
- synaptically activate quadriceps motoneurons
- muscle shortens
- Reflex acts to counteract the stretch
- Stretch reflex connection btwn muscle spindle afferent and alpha motor neurons automatically performs the subtraction between actual state and desired state
- afferent excitation of inhibitory interneurons causes inhibition of motoneurons innervating antagonist muscles (hamstrings)
What effect does the tap of the patellar tendon have on the golgi tendon organs?
- Tap on patellar tendon activates golgi tendon organ
- Signals from golgi tendon organ travel to the spinal cord and have the reverse reflex action to that of the muscle spindle afferents
- Golgi tendon afferent from the extensor muscle activates an interneuron which activates the antagonist flexor motor neuron
How does flexor withdrawal reflex work?
Afferent signals from nociceptors in the foot cause a reflex activation of the flexor motor neurons and a reflex inhibition of the extensor motor neurons resulting in lifting of the leg away from the stimulus
The primary motor cortex is also called the:
Sensorimotor cortex
What are 5 areas of the cerebral cortex that control movements of the extremities?
- Pre-motor cortex
- supplementary motor cortex
- primary motor cortex (sensorimotor)
- somatosensory cortex (primary sensory)
- parietal lobe association areas
What is the other name for the coricospinal tract?
Pyramidal tract: because it passes through the brainstem “pyramids”
What forms the corticospinal tract?
Axons from neurons in the sensorimotor cortex
What happens in the corticospinal tract at the level of the brainstem?
Crosses to the contralateral side of the NS
Corticospinal tract neurons make ________ connections with spinal _______ whose axons in turn activate muscle
- How many synapses separates CST neurons from muscles
Corticospinal tract neurons make monosynaptic connections with spinal alpha motoneurons whose axons in turn activate muscle
- CST neurons are only one neuronal synapse away from muscles
What are the two main speech areas in the brain?
- Broca’s area
- Wernicke’s are
What is wernicke’s area responsible for?
- Comprehension of language
- association of visual, auditory and tactile input with words
