Chapter 12: Control of Body Movement

Question 1

lower motor neurons

Answer 1

somatic motor neurons have their cell bodies in the lower parts of the CNS (in either the brain stem or spinal cord)

Question 2

Q: Where do LMNs from the brain stem send their axons?

Answer 2

Through cranial nerves to innervate skeletal muscles of the face and head

Question 3

Where do LMNs from the spinal cord send their axons?

Answer 3

axons of lower motor neurons extend through spinal nerves to innervate skeletal muscles of limbs + trunk

Question 4

Final common pathway

Answer 4

All signals controlling movement - voluntary and involuntary must pass through the LMN to reach muscles

Question 5

What are local circuit neurons?

Answer 5

Neurons near LMN cell bodies in the brain stem and spinal cord that coordinate somatic reflexes and help with locomotion (walking, running)

Question 6

What are upper motor neurons (UMNs) and what are their functions?

Answer 6

• UMNs are neurons with cell bodies in motor centers of the upper CNS. They give input to LMNs and local circuit neurons
• are essential for planning and executing voluntary movements and also help regulate posture, balance, muscle tone, and reflexive movements of the head and trunk

Question 7

What is the role of basal nuclei in movement control?

Answer 7

They assist UMNs by initiating movements, suppressing unwanted ones, and establishing normal muscle tone

Question 8

What is the role of the cerebellum in motor control?

Answer 8

It compares intended and actual movements, issues corrective commands, coordinates body movements, and helps maintain posture and balance

Question 9

What are somatic reflexes?

Answer 9

Fast, involuntary responses that allow skeletal muscle to contract quickly in response to stimuli such as pain, overstretching, or excessive tension, via a somatic reflex arc

Question 10

What are the components of a somatic reflex arc? (5)

Answer 10

1. Sensory receptor
2. Sensory neuron
3. Integrating center
4. Motor neuron
5. Effector (skeletal muscle)

Question 11

role of the sensory receptor in a somatic reflex arc

Answer 11

It’s the distal end of a sensory neuron that produces a receptor potential. Examples include nociceptors, muscle spindles, and tendon organs

Question 12

the integrating center in a somatic reflex arc

Answer 12

A region of gray matter in the brainstem or spinal cord that processes sensory input.

Spinal reflex → Integration in spinal cord

Cranial reflex → Integration in brainstem

Question 13

What’s the difference between a monosynaptic and polysynaptic reflex arc?

Answer 13

Monosynaptic: Only one synapse in the CNS (e.g., stretch reflex)

Polysynaptic: Involves multiple types of neurons and multiple CNS synapses

Question 14

role of the motor neuron in a somatic reflex arc?

Answer 14

It carries the action potential from the integrating center to the effector (skeletal muscle)

Question 15

the effector in a somatic reflex arc

Answer 15

Skeletal muscle, which responds by contracting

Question 16

What is the stretch reflex and how does it work?

Answer 16

A reflex that causes contraction of a skeletal muscle in response to being stretched. It operates via a monosynaptic reflex arc

Question 17

Describe the steps of the stretch reflex

Answer 17

Stimulus: Muscle is stretched

Receptor: Muscle spindles detect stretch

Afferent neuron: Sends AP to spinal cord

Integration: Sensory neuron synapses with motor neuron

Efferent response: Motor neuron sends AP to same muscle

Muscle contracts to resist stretch (releases acetylcholine)

Question 18

patellar (knee-jerk) reflex

Answer 18

extension of the leg at the knee joint by contraction of the quadriceps femoris muscle of the thigh in response to tapping the patellar ligament

Question 19

ipsilateral reflex

Answer 19

A reflex where sensory input and motor output occur on the same side of the spinal cord. All monosynaptic reflexes are ipsilateral

Question 20

What is muscle tone

Answer 20

A slight, continuous contraction of muscles at rest that helps maintain posture and keeps muscles firm and ready to respond

Question 21

reciprocal innervation

Answer 21

A neural circuit arrangement where contraction of one muscle is accompanied by relaxation of its antagonist

Question 22

The Tendon Reflex

Answer 22

Operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might torn
- Less sensitive

Question 23

Tendon organs:

Answer 23

sensory receptors for this reflex and lie within a tendon near its junction with a muscle
- Detect and respond to changes in muscle tension that are caused by passive stretch or muscular contraction

Question 24

Tendon reflex operates as:

Answer 24

1. Too much tension is applied to a tendon.
2. A tendon organ (a sensor in the tendon) gets activated.
3. It sends a signal to the spinal cord through a sensory nerve.
4. In the spinal cord, the signal activates an inhibitory interneuron.
5. This interneuron tells the motor neuron to slow down.
6. As a result, the muscle relaxes, which reduces the tension on the tendon.

Question 25

Flexor (withdrawal) reflex:

Answer 25

Causes flexion of a limb to withdraw the limb from a painful stimulus

Question 26

flexors

Answer 26

muscles that can flex a limb

Question 27

The flexor reflex, like the stretch reflex, is ipsilateral

Answer 27

the incoming and outgoing action potentials propagate into and out of the same side of the spinal cord

Question 28

intersegmental reflex arc

Answer 28

A reflex arc where sensory input activates motor neurons in multiple spinal cord segments, producing a more complex and coordinated response

Question 29

crossed extensor reflex

Answer 29

- causes extension of the opposite limb to help maintain balance - synchronizes the extension of the contralateral limb with the withdrawal (flexion) of the stimulated limb

Question 30

the crossed extensor reflex operates as follows:

Answer 30

You step on a tack with your right foot… 1. Pain detected Your right foot has pain sensors that send a signal to your spinal cord. 2. Signal enters the spinal cord A nerve carries that pain signal into the spinal cord. 3. Signal spreads Inside the spinal cord, the signal gets passed to many interneurons, which then: Send the message to other spinal cord levels (not just one). Cross over to the left side of the spinal cord. 4. Muscles on the left leg are activated Those interneurons activate motor neurons that go to the left leg’s extensor muscles. 5. Left leg extends to support your body Your left thigh muscles contract, straightening the leg. This helps shift your weight onto the left leg since your right leg is hurt and lifting up.

Question 31

contralateral reflex arc

Answer 31

is a reflex where the stimulus affects one side of the body, but the response happens on the opposite side

Question 32

Central Pattern Generators

Answer 32

networks of local circuit neurons in the spinal cord—specifically the lumbar region—that produce rhythmic, alternating movements, like walking or running

Question 33

what 2 areas in cerebral cortex play important roles in motor control?

Answer 33

- primary motor cortex - premotor cortex

Question 34

what is a motor plan

Answer 34

a plan that identifies which muscles should contract how much they need to contract and in which order then: premotor cortex --> plan trasmitted to primary motor cortex for execution

Question 35

primary motor cortex

Answer 35

controls muscles by forming descending pathways that extend to the spinal cord and brainstem - voluntary movements features: - controls opposite side of the body - has a motor map (motor homonculus) - more brain area is devoted to muscles with fine control (hands, face, tongue)

Question 36

motor homunculus

Answer 36

a visual map of how the primary motor cortex controls different parts of the body - which regions of the cortex send signals to specific muscles - located on the pre central gyrus

Question 37

direct motor pathways

Answer 37

also known as pyramidal pathways - consist of axons that descend from pyramidal cells of the primary motor cortex and premotor cortex

Question 38

pyramidal pathways

Answer 38

- carry action potentials for voluntary movements - originate in a pyramidal cells of the primary motor and premotor cortices

Question 39

Corticospinal Tracts

Answer 39

conduct action potentials for for voluntary control of skeletal muscles of the LIMBS and TRUNKS

Question 40

lateral corticospinal tract

Answer 40

- 90% of axons decussate in the medulla. - Control distal limb muscles (e.g., hands, feet). - Enables precise, skilled movements.

Question 41

Ventral (Anterior) Corticospinal Tract:

Answer 41

- 10% of axons do not decussate in medulla, but many cross in the spinal cord. - Control proximal limb and trunk muscles.

Question 42

The Corticobulbar Pathway

Answer 42

conducts action potentials for voluntary control of skeletal muscles in the head

Question 43

corticobulbar tract

Answer 43

axons travel from cortex to brain stem - synapse with lower motor neurons of 9 cranial nerves controls muscles for: - facial expression - chewing - speech - eye, tongue and neck movements

Question 44

4 major motor centers that help regulate body movements

Answer 44

1. vestibular nuclei in the medulla and pons 2. reticular formation location throughout brain stem 3. superior colliculus in the midbrain 4. red nucleus - in the midbrain

Question 45

indirect motor pathways (extrapyramidal pathway)

Answer 45

These pathways involve upper motor neurons from the brain stem and help control involuntary movements like: - posture - balance - muscle tone - reflexive movements of head & trunk

Question 46

postural reflexes

Answer 46

keep the body in an upright and balanced position comes from three sources: 1. the eyes - which provide visual information about the position of the body in space 2. the vestibular apparatus of inner ear - provides info about position of head 3. proprioceptors in muscles and joints

Question 47

tectospinal tract

Answer 47

function: turns the head/trunk reflexively toward sudden sights or sounds - when this input occurs in a sudden, unexpected manner

Question 48

saccades

Answer 48

small, rapid jerking movements of the eyes that occur as a person looks at different points in the visual field - superior colliculus is an integrating centre for it

Question 49

functions of basal nucelei

Answer 49

- initiation of movements - supression of unwanted movements - regulation of muscle tone - regulation of non motor processes

Question 50

1. initiation of movements

Answer 50

- received input from sensory, association and motor areas of the cerebral cortex - from cortex --> basal nuclei --> thalamus --> cortex

Question 51

2. suppression of unwanted movements

Answer 51

- tonically inhibiting the neurons of the thalamus that affect the activity of the upper motor neurons in the motor cortex to perform a movement: inhibition if briefly lifted allowing the movement to proceed

Question 52

3. regulation of muscle tone

Answer 52

neurons of the basal nuclei send action potentials into the reticular formation that reduce muscle tone via the medial and lateral reticulospinal tracts

Question 53

4. regulation of non motor processes

Answer 53

Help control cognitive (e.g., attention, memory, planning), sensory, emotional, and linguistic processes - interact with the limbic system for emotional behavior regulation

Question 54

what neurons do the cerebellum act on

Answer 54

upper motor neurons

Question 55

cerebellar function: 1) monitoring intentions for movement

Answer 55

gets input from: - motor cortex - basal nuclei - info comes from pontine nuclei in the pons - this tells the cerebellum what movement is planned

Question 56

cerebellum function: 2) Monitoring Actual Movement

Answer 56

gets real time feedback from: - proprioceptors in joints and muscles - inner ear (vestibular apparatus) - eyes signals travel via ventral and dorsal spinocerebellar tracts to tell the cerebellum what is actually happening

Question 57

cerebellum function: 3) comparing command signals with sensory information

Answer 57

The cerebellum compares: - Intended movement (from cortex) - Actual movement (from sensory input) This is known as its comparator function.

Question 58

cerebellum function: 4) Sends out corrective feedback

Answer 58

adjusts movements through upper motor neurons to refine performance