Chapter 10: Controlling Posture and Locomotion

Question 1

What is a reflex?

Answer 1

an involuntary, stereotyped response to a specific stimulus.

Question 2

T/F all reflexes are innate

Answer 2

false. reflexes can be learned too

Question 3

What triggers the pupillary light reflec

Answer 3

bright light

Question 4

The pupillary light reflex circuitry passes through the ___ and ___ structures

Answer 4

midbrain and pretectum.

Question 5

pupillary dilation is driven by part of the _____ NS.

Answer 5

sympathetic nervous system, which is why our pupil dilate in stressful conditions.

Question 6

explain the pathway of the pupillary constriction reflex.

Answer 6

in response to light, the optic nerve fires APs to the OLIVARY PRETECTAL NUCLEUS, which projects to the EDINGER WESTPHAL NUCLEUS, which relays the info through the OCULOMOTOR nerve (PARASYMPATHETIC ganglion) to trigger CONSTRICTION of CILIARY MUSCLES

Question 7

explain the pathway of the pupillary dilation reflex

Answer 7

stimulus activates the PARAVENTRICULAR NUCLEUS in the HYPOTHALAMUS, which relays the signal through the INTERMEDIOLATERAL column in the spinal cord, and conveys a signal through sympathetic ganglion to PUPILLARY DILATION MUSCLE.

Question 8

the eye blink reflex involves ___ neurons and ___ synapses

Answer 8

3 neurons and 2 synapses; very fast reflex in response to loud sound, air puff, etc.

Question 9

Explain the pathway of the eye blink reflex.

Answer 9

1) noxious stimuli (air puff) excites the SPINAL TRIGEMINAL NUCLEUS 2) STN sends their axon to FACIAL MOTOR NUCLEUS 3) FMN projects to ORBICULARIS OCULI MUSCLE: closes the eye lid when it contracts.

Question 10

the leg withdrawal reflex relies on ____ ___

Answer 10

RECIPROCAL INNERVATION of leg flexors and extensors. Efficient withdrawal of the foot requires hamstring contraction to be acompanied by quad relaxation.

Question 11

How does reciprocal innervation allow for leg withdrawal reflex

Answer 11

the sensory axon branches into TWO COLLATERALS in the DORSAL ROOT: - one synapses onto excitatory interneuron, which excites motor neuron of hamstring -one synapses onto inhibitory interneuron, which inhibits motor neuron of QUAD. Therefore, hamstring contracts, quad relaxes, and leg moves off of the noxious thing it stepped on.

Question 12

as the stimulus strength increases, the number of muscles involved in the withdrawal reflex ____. What is this called?

Answer 12

INCREASES. Called Irradiation: sensory info coming from spinal cord is thought to involve progressively more spinal neurons as stimulus strength increases.

Question 13

the spinal trigeminal nerve, which picks up noxious stimuli around the head, is a long column of cells in the ___

Answer 13

medulla.

Question 14

Explain the process of top down reflex inhibition

Answer 14

Typically, a source of pain excites a sensory receptor, which relays info to dorsal root in spinal cord and excites an EXCITATORY INTERNEURON, which excites a motor neuron, causing a muscular contraction If you need to mitigate this reflex, an axon from neuron in the BRAIN also synapses with the motor neuron, and INHIBITS the motor neuron, preventing a muscular contraction thus the motor neuron receives input both from cerebrum and the reflex arcs.

Question 15

explain the knee jerk/quas stretch relfex

Answer 15

tapping on the knee causes the MUSCLE SPINDLE IN QUAD i to activate and send signals through the dorsal root of the spinal cord. It synapses directly to alpha motor neuron, which moves through the ventral horn and innervates the quad muscle, contracting the quad and facilitating a LEG EXTENSION.

Question 16

_____ reflexes counteract gravity and stabilize the limbs against varying loads.

Answer 16

Stretch reflexes counteract gravity and stabilize the limbs against varying loads.

Question 17

_____ and ____-___ reflexes uses VISUAL and VESTIBULAR signals to generate ___ ____ commands that minimize retinal slip when the head moves relative to the world.

Answer 17

OPTOKINETIC and VESTIBULO-ocular reflexes use visual and vestibular signals, respectively, to generate eye movement commands that minimize retinal image slip when the head moves relative to the world.

Question 18

a muscle stretch reflex involves a minimum of ___ neurons, while a withdrawal reflex involves a minimum of ___ neurons

Answer 18

a muscle stretch reflex involves a minimum of 4 neurons: (stretch reflexes are monosynaptic) - 1 sensory -1 inhibitory interneuron for antagonistic muscle -2 motor neurons withdrawal reflex involves a minimum of 5 neurons -1 sensory - 2 interneurons (one excitatory for agonist muscle, one inhibitory for antagonist muscle) -2 motor neurons

Question 19

As you are looking out a window in the car, your eyes focus on a spot in the outside world and track it as it moves. When the eyes have moved as far as they can, they rapidly move in the opposite direction and focus on another spot. This reflex is called ____ ___. Purpose?

Answer 19

OPTOKINETIC REFLEX. Minimize retinal slip; without it, you’d see a blur and couldn’t focus on anything

Question 20

Outline the optokinetic reflex circuitry.

Answer 20

Retinal ganglion cells send its axons through the NUCLEUS OF THE OPTIC TRACT, which relays projection to the VESTIBULAR COMPLEX in the MEDULLA. The vestibular complex has two branches: -some projections go through the OCULOMOTOR nucleus. The oculomotor nucleus innervates the MEDIAL RECTUS in one eye ON THE SAME SIDE (IPISILATERAL), which moves the EYE TOWARDS THE NOSE WHEN IT IS CONTRACTED. -other projections go through the ABDUCENS nucleus, which innervates the LATERAL RECTUS muscle and moves the eye AWAY FROM THE NOSE on the OPPOSITE SIDE of the vestibular complex.

Question 21

The lateral rectus muscle moves eyes ___ relative to the nose

Answer 21

moves away from the nose

Question 22

the medial rectus moves eye ____ the nose

Answer 22

TOWARDS the nose.

Question 23

the ____ nucleus innervates the medial rectus in the optokinetic reflex

Answer 23

oculomotor nucleus

Question 24

the ____ nucleus innervates the lateral rectus in the optokinetic reflex

Answer 24

abducens nucleus

Question 25

both the oculomotor nucleus (ipsilateral) and abducen nucleus (contralateral) stem from the ____ complex

Answer 25

vestibular

Question 26

contraction of the lateral rectus should be accompanied by ___ of the medial rectus attached to the same eye. How is this achieved?

Answer 26

RELAXATION. This occurs by inhibitory projections from the vestibular complex to the ipsilateral abducens nucleus and by excitatory projections from the abducens to the contralateral oculomotor nucleus.

Question 27

your eyes remaining stable when you’re looking at yourself in the mirror while moving your head is due to the _____ ___ reflex

Answer 27

vestibulo-ocular reflex

Question 28

head movement causes fluid movement, which stimulates hair cells in the left ____ ____ ___, which activates ____ neurons that project to the oculomotor and abducens nuclei, which then trigger contraction of the LEFT ____ rectus and the RIGHT ___ rectus.

Answer 28

head movement causes fluid movement, which stimulates hair cells in the LEFT HORIZONTAL SEMICIRCULAR CANALS, which activates VESTIBULAR neurons that project to the oculomotor and abducens nuclei, which then trigger contraction of the LEFT MEDIAL rectus and the RIGHT LATERAL rectus.

Question 29

the _____ reflex stabilizes the head in space

Answer 29

OPTOCOLLIC REFELX

Question 30

the ___ reflex stabilizes the head as the BODY turns

Answer 30

VESTIBULOCOLLIC refelx

Question 31

T/F; the optocollic refelx relies on retinal slip. what about the vestibulocollic reflex?

Answer 31

True. the optocollic reflex relies on visual input and retinal slip and will not happen in the dark. the vestibulocollic stabilizes the head as the body TURNS and relies on movement; not visual input. this reflex will still occur in the dark.

Question 32

the __ ___ reflex stabilizes the body when one leg is suddenly withdrawn (ex during leg withdrawal reflex). How does it work?

Answer 32

crossed extensor reflex. in addition to the 5 neurons needed to withdraw the foot facing a noxious stimulus, a 6th COMMISSURAL INTERNEURON connects to 2 INTERNEURONS (one excitatory and one inhibitory) on the OPPOSITE SIDE of the spinal cord, which innervates the OPPOSITE LEG so it can bear weight.

Question 33

What is the reflex chain hypothesis?

Answer 33

locomotor activity is caused by a chain of sensorimotor reflexes. The movement of one muscle stimulates sensors that reflexively activate another muscle, whose contraction then triggers another reflex and so on.

Question 34

Central pattern generator hypothesis

Answer 34

locomotor rhythyms are created within the central nervous system, independently of sensory inputs.

Question 35

What is the current hypothesis of locomotion?

Answer 35

central pattern generator hypothesis. Favored over reflex chain hypothesis.

Question 36

reciprocal inhibition between two sets of neurons can lead to rhythmic output. The two inhibitor neurons in this network form a ___ ___ ___ . Explain this type of rhythmic output

Answer 36

half center oscillator. When one of these neurons is slightly more active than the other, it INHIBITS the less active neuron. After a while, if the neuron gets fatigued, the inhibited gets more excited (due to disinhibition), and inhibits the neuron that was once inhibiting it. This continues to cycle.

Question 37

Fishes swim by ___ ____, in which muscles on one side of a body segment contract while the muscles on the other side relax.

Answer 37

lateral undulation.

Question 38

T/F: lateral undulation is sensroimotor reflex chain

Answer 38

false. It is a CPG. Lateral undulation is present in fictive swimming when there are no muscles attached to the spinal root. Side to side alternation arises because of a burst of activity on one side of the spinal cord inhibits inhibitory neurons on the other side until that burst has exhausted itself, which then lets the other side enter its own burst phase (half center oscillator)

Question 39

What would happen if you cut the commissural swimming neurons in a lamprey?

Answer 39

Reciprocal inhibition is a critical element in the CPG for swimming in lampreys. If the commissural connections are cut, the oscillation mechanism is no longer functioning properly, and then each side continues to fire rhtymically but the two sides no longer alternate activity.

Question 40

In animals that walk on all fours, the ____ ____ contain a central pattern generator for walking

Answer 40

SPINAL CORD. Even if an animal is decebrate (no connection between brain and spinal cord), they can still be induced to walk on a treadmill as long as their bodies are supported in a sling.

Question 41

T/F: CPGs can be modulated by external inputs

Answer 41

true. CPG can be modulated by DESCENDING input from the midbrain locomotor area. When this brain region is stimulated electrically, the walking CPG becomes active, and with increasing stimulation intensity, its rhythym accelerates.

Question 42

T/F CPG needs to be initially started, but then it can continue on by itself.

Answer 42

true. You just need to add either NMDA, 5Ht, or physical stimulus at the level of the spinal cord (move the treadmill), and the remaining motor neurons are able to fire alternately.

Question 43

T/F: In CPGs, the rhythym is produced entirely by neuronal circuits in the spinal cord

Answer 43

true. the brain is not required for a locomotor central pattern generator to function, descending pathways can influence activity though

Question 44

the most posterior portion of the motor cortex is ____> The anterior portion of the motor cortex is ___. THe most medial portion of the motor cortex is

Answer 44

the most posterior portion of the motor cortex is PRIMARY MOTOR CORTEX. The anterior portion of the motor cortex is PREMOTOR CORTEX. THe most medial portion of the motor cortex is SUPPLEMENTARY MOTOR AREA.

Question 45

corticospinal neurons that project from the motor cortex down into the spinal cord mostly project onto spinal cord ____. Exceptions to this?

Answer 45

INTERNEURONS. some axons may terminate directly onto motor neurons if responsible for finger movements.

Question 46

corticospinal neurons can either project from the motor cortex to the ___ ___ or the ____.

Answer 46

Spinal cord or the medulla.

Question 47

corticospinal neurons that project from the motor cortex to the medulla are known as ___ ____ projections. What do they help modulate?

Answer 47

corticobulbar projections. they help control respiration, urination, and other VEGETATIVE funtions. Some involved with tongue movements and vocal chords (basic human speech functions)

Question 48

Corticospinal projections from motor cortex to spinal cord are mainly _____< whereas corticobulbar projections from motor cortex to ____ are more ___

Answer 48

Corticospinal projections from motor cortex to spinal cord are mainly CONTRALATERAL whereas corticobulbar projections from motor cortex to MEDULLA are more BILATERAL. Therefore, extensive unilateral damage of the motor cortex severely weakens the arm and legs muscles on the opposite side. But unilateral damage leave corticobulbar targets (respiration, urination etc) with only minor impairments, since these functions can still receive input from the opposite, undamaged side.

Question 49

the primary motor cortex projects mainly to the ___ spinal cord through the corticospinal tract. its axons terminate mainly in the spinal cord’s ___ ___ onto interneurons in the ___ zone.

Answer 49

the primary motor cortex projects mainly to the CONTRALATERAL spinal cord through the corticospinal tract. its axons terminate mainly in the spinal cord’s VENTRAL HORN onto interneurons in the INTERMEDIATE zone.

Question 50

according to penfield’s MOTOR homunculus, the movements of the ___ and ___ are overrepresented in the M1

Answer 50

face and hands. Goes to show those areas have high dexterity and are more sensitive.

Question 51

T/F: microstimulation in a small patch of the motor cortex generally activates a single muscle.

Answer 51

FALSE. it activates a number of functionally related muscles. Therefore, the motor cortex does NOT map MUSCLES. it maps MOVEMENTs.

Question 52

how does electrical stimulation of the motor cortex elicit goal-directed movements?

Answer 52

the motor homunculus maps MOVEMENTS. Stimulation activates a number of functionally realted msucle. It also can trigger the reaching/movement TOWARDS a specific location. Therefore, Different sites on the MOTOR CORTEX are associated with MOVEMENTS towards different LOCATIONS (goal-directed)

Question 53

movements (ex/ of a hand) are encoded by large populations of neurons working together, rather than being encoded by single neurons. In order words, the instructions for performing a movement are encoded in a ____ ____

Answer 53

POPULATION CODE, where a code in which information is represented in the pattern of activity across a population of neurons.

Question 54

___ ___ ___ neurons fire during learned sequential tasks, but not when the buttons are illuminated to indicate which button to press next. What does this mean?

Answer 54

SUPPLEMENtARY MOTOR AREA fire during LEARNED sequential tasks Ex/ knowing how to a put a paper in the envelope. But it does not fire during single actions (ex/ fold paper in half. Pick up paper. Put paper in envelope. Lick envelope. Seal envelope.

Question 55

Appraxia is the inability to execute sequences of movements. What part of the brain is damaged?

Answer 55

the supplementary motor area of the motor cortex.

Question 56

Which tracts make up the LATERAL GROUP DESCENDING tract?

Answer 56

1) the corticospinal tract (motor cortex to spinal cord) 2) corticobulbar ( motor to medulla) 3) rubrospinal tract (primarily facilitates flexion in the upper extremities)

Question 57

which cortical spinal tract connects the distal limbs with the spinal cord and motor cortex?

Answer 57

the LATERAL cortical spinal tract connects primarily with distal limbs, but not many connections in the trunk.

Question 58

A person has a stroke and cannot move their limbs, but is capable of sitting straight. Why has this happened?

Answer 58

the stroke most likely damaged the Lateral corticospinal tract, which connects primarily with limbs. They can sit upright because trunk innervation is not affected by the lateral corticospinal tract.

Question 59

The VENTROMEDIAL Group involves which tracts?

Answer 59

1) vestibulospinal tract (vestibular system is to maintain head and eye coordination, upright posture and balance, and conscious realization of spatial orientation and motion) 2) tectospinal tract (mediate reflex postural movements of the head in response to visual and auditory stimuli) 3) reticulospinal tract (controls the muscles responsible for postural movements. 4) VENTRAL corticospinal tract

Question 60

the corticospinal tract is a group that originates in the motor cortex and terminates inthe ____ gray matter of the spinal cord

Answer 60

ventral

Question 61

the pyramidal tract is a portion of the ____ tract on the ventral border of the -__

Answer 61

corticospinal tract on the ventral border of the medulla.

Question 62

the lateral corticospinal tract is a system of axons that originates in the ___ ___ and terminates on the ____ and ___ gray matter of the spinal cord. What is its function?

Answer 62

the lateral corticospinal tract is a system of axons that originates in the MOTOR CORTEX and terminates on the CONTRALATERAL and VENTRAL gray matter of the spinal cord. CONTROLS MOVEMENTS OF THE DISTAL LIMBS.

Question 63

The VENTRAL corticospinal tract is a system of axons that originate in the ___ ___ and terminates in the ___ and __ gray matter of the spinal cord. What does it control?

Answer 63

The VENTRAL corticospinal tract is a system of axons that originate in the MOTOR COTEX and terminates in the IPSILATERAL and VENTRAL gray matter of the spinal cord. Controls movement of UPPER LEGS and TRUNk

Question 64

the corticobulbar tracts projects from the ___ ___ to the __ __ __ ___ and __ Cranial nerves through the medulla to control the movements of the ___, ___, ___< and parts of the extraocular eye muscles.

Answer 64

the corticobulbar tracts projects from theMOTOR CORTEX to the 5th, 7th, 9th, 11th and 12th Cranial nerves through the medulla to control the movements of the FACE, NECK, TONGUE and parts of the extraocular eye muscles.

Question 65

The corticorubral tract travels from the motor cortex to the ___ ___. of the _____ tract. Axons travel from the ___ ___ to the spinal cord. Whats its function?

Answer 65

The corticorubral tract travels from the motor cortex to the RED NUCLEUS. of the RUBROSPINAL tract. Axons travel from the RED NUCLEUS to the spinal cord. CONTROLS INDEPENDENT LIMB MOVEMENTS OF PROXIMAL muscles. Not distal limb control. distal limb control is dealt with by the lateral corticospinal tract.

Question 66

T/F: the vestibulospinal tract is non cortical.

Answer 66

True. it travels from the vestibular nuclei to the gray matter of the spinal cord. Controls postural movements in response to info from the vestibular system, not the cortex.

Question 67

T/F: the tectospinal tract is non cortical

Answer 67

true. it travels from the tectum (midbrain) to the spinal cord and coordinates head and trunk movements with eye movements. it does not involve the neocortex

Question 68

T/F: the reticulospinal tract is non cortical

Answer 68

true. It travels from the reticular formation in the brainstem/pons/medulla to the gray matter of the spinal cord in order to control the muscles responsible for postural movement. it does not involve the neocortex.

Question 69

Mirror neurons fire furing both performed actions and observed actions, but only when:

Answer 69

the observed action matches the motor pattern that the neuron encodes. Ex/ watching someone move their hands will not activate mirror neurons associated with leg movement.

Question 70

it has been suggested that a dysfunctional ___ ___ ___ is responsible for the poorly developed “theory of mind” in autistic infividuals.

Answer 70

Dysfunctionally mirror neuron system. Mirror neurons may be responsible for our capacity to imitate the actions of others More broadly they may be responsible for our capacity to understand the actions, goals and motives of others. these are deficits seen in individuals with autism

Question 71

The cerebellum uses ___-___-___ learning to modulate circuits that control movement. Lesions of the cerebellum remove its adaptive ______ control function, creating tremors and instability.

Answer 71

The cerebellum uses trial-and-error learning to modulate circuits that control movement. Lesions of the cerebellum remove its adaptive FEEDFORWARD control function, creating tremors and instability.

Question 72

largest principle cerebellar neuron

Answer 72

purkinje cell

Question 73

2 major inputs to purkinje cells of the cerebellum

Answer 73

1) paralllel fibers from the granule cell layer underneath the purkinje cell layer 2) climbing fibers that stem from the inferior olive in the medulla.

Question 74

Whenever an inferior olive neuron fires an action potential, the purkinje cell also fires a long, large AP called a ___ spike. in contrast, purkinje cells respond to granule/parallel fiber cell activity only when thousands of those cells fire simultaneously, eliciting a ____ spike. Why is this the case?

Answer 74

Whenever an inferior olive neuron fires an action potential, the purkinje cell also fires a long, large AP called a COMPLEX spike. in contrast, purkinje cells respond to granule/parallel fiber cell activity only when thousands of those cells fire simultaneously, eliciting a SIMPLE spike. This occurs because the purkinje cell has WAY MORE synapses with inferior olive/climbing fibers than they do with granule/parallel fibers. Therefore, they respond wayyy more dramatically to INFERIOR OLIVE INPUT.

Question 75

All cerebellar purkinje cells use ___ as their main neurotransmitter

Answer 75

GABA.

Question 76

Target cells of purkinje cells are located in ___ ___ ___. Some purkinje cells also project to ____ ___ rather than their target cells tho.

Answer 76

deep cerebellar nuclei. but some purkinje cells also project to vestibular complex.

Question 77

the cerebellum can be divided into three major divisions: what are they?

Answer 77

1) vestibulocerebellum: most posterior. involved with modulating the vestibulo-ocular reflex. 2) spinocerebellum: midline. Connected primarily to regions that control neck and trunk movements 3) cerebrocerebellum: lateral portions and connected to the frontal lobe

Question 78

the ____ lobe is a region of the ceerebellum involved in control of postural reflexes.

Answer 78

flocculonodular lobe

Question 79

Where is the vermis?

Answer 79

The portion of the cerebellum located at the midline; receives somatosensory information and helps to control the vestibulospinal and reticulospinal tracts through its connections with the fastigial nucleus.

Question 80

the vermis is associated with the ____ nucleus. Function?

Answer 80

fastigial nucleus A deep cerebellar nucleus; involved in the control of movement by the reticulospinal and vestibulospinal tracts.


Question 81

the ____ nucleus in the cerebellum is involved in the control of the rubrospinal system.

Answer 81

INTERPOSED nucleus. Recall: the RUBROSPINAL tract Axons travel from the RED NUCLEUS to the spinal cord. CONTROLS INDEPENDENT LIMB MOVEMENTS OF PROXIMAL muscles.

Question 82

the major function of the cerebellum is :

Answer 82

adaptive feedforward control

Question 83

HOw does the cerebellum modulate sensorimotor circuits?

Answer 83

the cerebellum forms a SIDE LOOP to sensorimotor reflex arcs that pass through precerebellar and deep cerebellar nuclei. Purkinje cells receibve a copy of the sensory input that drives the sensorimotor reflex by the way of GRANULE CELL INPUTS. The purkinje cells modify the sensory signal, and then send an inhibitory output signal to the motor side of the reflex arc by way of the CLIMBING/INFERIOR OLIVE output error signals. the feedforwards control signal coming from purkinje cells is adaptive rather than fixed. it eliminates movement errorss by means of trial and error learning.

Question 84

the vestibulo-ocular reflex that is used to prevent retinal image slipping when your head moves can be MODIFIED by means of the ______ forming a side loop to this reflex circuit.

Answer 84

VESTIBULOCEREBELLUM region. The vestibulocerebellum allows for VOR ADAPTATION: an experience-dependent change in the gain of the vestibulo-ocular reflex (e.g., after wearing magnifying or reducing lenses)

Question 85

the lack of motor coordination due to cerebellar damage

Answer 85

cerebellar ataxia. ex/ VOR adaptation cannot occur if you damage vestibulocerebellum. Sensorimotor reflexes may also be erroneous since the cerebellum has side loop modifications to these pathways.

Question 86

Why can’t you tickle yourself?

Answer 86

because your cerebellum plays a role in discriminating between self-generated and external sensory movement. When you do something to yourself, the motor command sends an EFFERENCE copy to the cerebellum, which allows the cerebellum to essentially FACTOR in a PREDICTIOn of the sensory signals that should result from the self-generated movement. -allows people to determine what should be seen as “sensory” and what shouldn’t be alarming (because you did it to yourself). Your brain essentailly filters out the sensations of your own movements.

Question 87

explain how the cerebellum plays a central role in the eye blink conditioning.

Answer 87

See image. The cerebellum has a “side loop” to the Eye Blink Reflex.

Question 88

vRemoving cortical inputs to the spinal cord causes a period of “____ ___”, after which spinal reflexes come back with a vengeance, causing “____”. Why?

Answer 88

vRemoving cortical inputs to the spinal cord causes a period of “spinal shock”, after which spinal reflexes come back with a vengeance and cause excessive movements in response to sensory limb perturbation, causing “spasticity” because there are no descending inputs from the cortex (or cerebellum side loops) to modulate the reflexes.