CNS Lecture 4

Question 1

How is sensory input used to control body movement?

Answer 1

• 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

Question 2

Signals from the sensorimotor cortex descend to the ____ and to the ______ _______ ______ which innervate muscle fibres

Answer 2

Signals from the sensorimotor cortex descend to the brainstem and to the spinal cord motor neurons which innervate muscle fibres

Question 3

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 ______

Answer 3

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

Question 4

The basal ganglia and the cerebellum send their outputs to the ______ and the ______

Answer 4

The basal ganglia and the cerebellum send their outputs to the thalamus and the brainstem

Question 5

What are the supraspinal centres involved in controlling motion?

Answer 5

Supraspinal = above spinal cord

Include:

• sensorimotor cortex
• brainstem
• cerebellum
• cerebral cortex
• thalamus
• basal ganglia

Question 6

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?

Answer 6

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

Question 7

What is necessary for feedback control?

Answer 7

Sensory information and a mechanism for comparing desired to actual state

Question 8

What two types of muscle receptors provide the most relevant information to the control of muscle?

Answer 8

1. Muscle spindle - respond to changes in muscle length
2. Golgi Tendon Organs (tendon organs - signal changes in muscle force

Question 9

Muscle spindles respond to changes in _________

Answer 9

Muscle spindles respond to changes in muscle length

Question 10

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.

Answer 10

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.

Question 11

Tendon organs are in the ______ ______ at the ends of the muscle fibres.

Their muscle endings (Group ___) respond to muscle _____

Answer 11

Tendon organs are in the tendinous fascicles at the ends of the muscle fibres.

Their muscle endings (Group Ib) respond to muscle Force

Question 12

In addition to responding to muscle stretch, muscle spindle group Ia afferents also respond to _________

What is the clinical significance of this?

Answer 12

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

Question 13

The sensory endings of muscle spindles are spiralled around specialized muscle fibers called ________

Answer 13

The sensory endings of muscle spindles are spiralled around specialized muscle fibers called intrafusal muscle fibres (which are inside the muscle spindle)

Question 14

What are the components making up the muscle spindle?

Answer 14

• Connective tissue capsule
• intrafusal muscle fibres
• stretch receptors

Question 15

What does the term spasticity refer to?

Answer 15

Overactive stretch reflexes

Question 16

______ (within muscle spindles) generate only tiny amounts of force

Answer 16

intrafusal muscle fibres (within muscle spindles) generate only tiny amounts of force

Question 17

The main muscle fibres found outside the muscle spindle that produce all of the measurable force are called:

Answer 17

Extrafusal muscle fibres

Question 18

What are the two types of motor neurons innervating a muscle?

Answer 18

1. alpha motor neurons
2. gamma motor neurons

Question 19

What do alpha motorneurons (often just called ‘motor neurons’) activate?

What is their conduction velocity?

Answer 19

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

Question 20

What muscle fibres are activated by Gamma motor neurons?

What is their conduction velocity?

Answer 20

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

Question 21

Muscle spindle afferents (1A and 2) signal changes in ______

Answer 21

muscle length

Question 22

What happens when the intrafusal muscle fibres are activated?

Answer 22

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

Question 23

What afferents signal muscle force?

What group do these afferents belong to?

Answer 23

Golgi tendon organ afferents (group 1B) signal muscle force

Question 24

What is alpha-gamma coactivation?

What does this theory suggest about the simultaneous activation of intrafusal muscle fibres and alpha motorneurons

Answer 24

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

Question 25

According to the theory of alpha-gamma coactivation, what is the main role of gamma motor neurons?

Answer 25

Alter the sensitivity of muscle spindles to changes in muscle length

Question 26

Describe what is happening in each of the figures

Answer 26

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

Question 27

Spindle afferent firing increases during ______ and decreases during ______ (but the changes are less than they would be in the absence of gamma mn activity)

Answer 27

Spindle afferent firing decreases during _shortening_ and increase during _lengthening_ (but the changes are less than they would be in the absence of gamma mn activity)

Question 28

How do golgi tendon organ afferents respond to **passive stretching** of a muscle?

Answer 28

With small increases in their firing rate * stretch of an inactive muscle causes a small increase in the force measured at the tendon

Question 29

How do golgi tendon organs respond when an extrafusal muscle fibre contracts?

Answer 29

Contraction of extrafusal muscle fibres causes the golgi tendon organ to fire much more rapidly * force in the tendon of a contracting muscle is *much higher* than that during passive stretch of a non-contracting muscle

Question 30

Why do golgi tendon organs fire more rapidly in contraction than in passive stretch?

Answer 30

Golgi tendon organs respond to the **force produced by a muscle**, especially force produced during active contractions

Question 31

In the spinal cord reflex, what happens at the muscle spindle fibre when a stretch reflex is activated via muscle stretch?

Answer 31

1. tap of patellar tendon - small but rapid increase in the length of the muscle or stretch of the muscle - activates **muscle spindle afferents** 2. AP's in the afferents travel to the spinal cord 3. synaptically activate quadriceps motoneurons 4. muscle shortens 5. Reflex acts to *counteract* the stretch 6. Stretch reflex connection btwn muscle spindle afferent and alpha motor neurons automatically performs the subtraction between actual state and desired state 7. afferent excitation of inhibitory interneurons causes inhibition of motoneurons innervating antagonist muscles (hamstrings)

Question 32

What effect does the tap of the patellar tendon have on the golgi tendon organs?

Answer 32

1. Tap on patellar tendon activates golgi tendon organ 2. Signals from golgi tendon organ travel to the spinal cord and have the **reverse reflex action** to that of the muscle spindle afferents 3. Golgi tendon afferent from the extensor muscle activates an interneuron which activates the antagonist flexor motor neuron

Question 33

How do muscle spindle and golgi tendon organ feedback respond during spinal cord reflexes (such as tap at patellar tendon)

Answer 33

* muscle spindle feedback resists the **increase in length** by reflexly *activating* extensor motor neurons * The golgi tendon organ feedback resists the **increase in force** by reflexly *inhibiting* the extensor motor neurons

Question 34

Why are muscle spindle feedback and golgi tendon organ feedback competing during muscle stretch?

Answer 34

results in muscles resisting stretch in a *spring-like* manner (the stronger the spindle reflex = the stiffer the spring, the stronger the GTO reflex, the more compliant the spring)

Question 35

What is flexor withdrawal reflex?

Answer 35

reflex response that results in withdrawal of a limb from a painful input

Question 36

Where does flexor withdrawal reflex occur?

Answer 36

In the spinal cord

Question 37

How does flexor withdrawal reflex work?

Answer 37

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

Question 38

noxious stimulus evokes flexion of _____ leg and extension of _____ leg

Answer 38

noxious stimulus evokes flexion of _ipsalateral_ leg and extension of _contralateral_ leg

Question 39

The primary motor cortex is also called the:

Answer 39

Sensorimotor cortex

Question 40

What are 5 areas of the cerebral cortex that control movements of the extremities?

Answer 40

1. Pre-motor cortex 2. supplementary motor cortex 3. primary motor cortex (sensorimotor) 4. somatosensory cortex (primary sensory) 5. parietal lobe association areas

Question 41

How was the somatotopic map created?

Answer 41

Using transcranial magnetic stimulation (TMS) to activate neurons in the primary motor cortex and observing ilicited movement

Question 42

What is the other name for the coricospinal tract?

Answer 42

Pyramidal tract: because it passes through the brainstem "pyramids"

Question 43

The corticospinal tract conveys signals from the ________ through the _____ to the \_\_\_\_\_\_

Answer 43

The corticospinal tract conveys signals from the _sensorimotor cortex_ through the _brainstem_ to the _spinal cord_

Question 44

What forms the corticospinal tract?

Answer 44

Axons from neurons in the sensorimotor cortex

Question 45

What happens in the corticospinal tract at the level of the brainstem?

Answer 45

Crosses to the contralateral side of the NS

Question 46

Corticospinal tract neurons make ________ connections with spinal _______ whose axons in turn activate muscle * How many synapses separates CST neurons from muscles

Answer 46

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

Question 47

What are the sensory motor cortex and the corticospinal tract sometimes referred to as?

Answer 47

The final common pathway - because CST neurons are only one neuronal synapse away from muscles

Question 48

What results from a CST (corticospinal tract) lesion? What are clinical terms for CST lesions?

Answer 48

* Spastic hemiplegia: hemiplegia = inability to move the limb on the contralateral side of the body * "stroke", "cerebro-vascular accidant (CVA)", "brain attack"

Question 49

What are five symptoms of a CST lesion (spastic hemiplegia)? What side of the body would they compare in relation to the location of the brain damage?

Answer 49

1. Weakness (paresis) or paralysis of extremities 2. Exaggerated stretch reflexes (hypertonus, spasticity) 3. Spasms 4. Speech deficits (dysarthria) 5. Attentional deficits (aphasia, apraxia, hemi-neglect) * Occur on the opposite side of the body to the brain damage

Question 50

CST lesions are called ________ because of the idea that CST neurons are the final output pathway from the brain and synapse directly onto spinal alpha motoneurons (which are called the "lower" motoneurons)

Answer 50

CST lesions are called _Upper motoneuron lesions_ because of the idea that CST neurons are the final output pathway from the brain and synapse directly onto spinal alpha motoneurons (which are called the "lower" motoneurons)

Question 51

What is hypertonus?

Answer 51

Excessive level of skeletal muscle tension or activity

Question 52

What is spasticity?

Answer 52

State of increased muscular tone with exaggeration of the tendon reflexes

Question 53

What is aphasia?

Answer 53

Inability to understand the meaning of sensory inputs or a defect in language

Question 54

What is apraxia?

Answer 54

Problem using day to day objects

Question 55

What is Hemi-neglect?

Answer 55

Occurs when patients fail to be aware of items to one side of their body

Question 56

In most people, which side of the brain controls speech?

Answer 56

Left

Question 57

What are the two main speech areas in the brain?

Answer 57

1. Broca's area 2. Wernicke's are

Question 58

What aspects of speech are controlled by broca's area?

Answer 58

Motor aspects of speech (movements of tongue/lips)

Question 59

Slurring in speech (motor aphasia) could indicate lesions in which area of the brain?

Answer 59

Broca's area

Question 60

What is wernicke's area responsible for?

Answer 60

1. Comprehension of language 2. association of visual, auditory and tactile input with words

Question 61

Lesions in wernicke's area result in:

Answer 61

1. sensory aphasia - difficulty understanding meaning of sensory inputs 2. dyslexia - difficulty in reading aloud fluently

Question 62

What is an example of sensory aphasia?

Answer 62

* A person is handed a pen and says it's a spoon * but write their name when asked to use the object * problem producing the correct linguistic response, yet appropriate motor response

Question 63

What does sensory aphasia suggest about the relationship between sensory to motor transformation and sensory to linguistic transformation?

Answer 63

indicates that the sensory to motor transformation is separate from the sensory to linguistic transformation