WEEK 6: The spinal cord & motor control

Question 1

What is the neural pathway that controls a reflex called?

Answer 1

a reflex arc

Question 2

What are the 5 components of the reflex arc?

Answer 2

1. Receptor
2. Sensory neuron - transmit info to CNS via afferent pathways
3. Integration centre - CNS where
4. Motor neuron- transmit info to effector via efferent pathways
5. Effector - muscle fibre/glandular cell that produces response

Question 3

What are the different classifications of reflex arcs?

Answer 3

Spinal - integration happens in the spinal cord
Cranial - integration happens in the brainstem
Visceral - involves smooth muscle, cardiac muscle, glands
Somatic- involves skeletal muscle contraction (patellar reflex)

Question 4

What does superficial stimulation refer to?

Answer 4

stimulation of sensory afferents in the skin

Question 5

What does deep tendon stimulation refer to?

Answer 5

stimulation of sensory afferents within muscle, such as tendons

Question 6

What happens in the deep tendon patellar reflex?

Answer 6

it is a monosynaptic reflex arc that helps maintain posture and muscle tone

Question 7

explain what happens during the patellar reflex

Answer 7

1. a reflex hammer strikes the tendon below the kneecap
2. there is a passive stretch of muscle spindle fibres in the thigh (quadriceps)
3. intrafusal muscle spindle fibres detect this lengthened stretch
4. a sensory signal is sent via afferent tracts to the spinal cord
5. the sensory neuron directly synapses (monosynaptic) with an alpha motor neuron
6. in response, a motor neuron sends a signal via efferent tracts back to the quadriceps muscle, causing it to contract
7. knee jerking action
8. simulatenously, inhibitory interneurons participate in reciprocal inhibition to prevent the antagonist muscle (hamstrings) from contracting
   * important to note that while this reflex arc only occurs in the spinal cord, some input will ascend to the brain

Question 8

What are the two different classifications based on number of synapses?

Answer 8

monosynaptic - one synapse in the CNS between a single sensory neuron and a single motor neuron
polysynaptic - 2+ synapses in the CNS between sensory, motor and interneurons

Question 9

what does the grading system range from?

Answer 9

0 Absent
+ Present (reduced)
++ Normal
+++ Increased , possibly normal
++++ Greatly increased (clonus)

Question 10

What can the spinal cord be described as, in simple terms?

Answer 10

a column of nervous tissue

Question 11

What two things does the spinal cord connect?

Answer 11

the brain to the peripheral NS

Question 12

What is the spinal cord enclosed within (protected by)?

Answer 12

The vertebral canal

Question 13

What type of communication occurs in the spinal cord?

Answer 13

2 way communication?

Question 14

What are the two tracts of communication?

Answer 14

ascending tract (afferent pathway)
descending tract (efferent pathway)

Question 15

What are some inner components of the spinal cord?

Answer 15

White matter (myelinated axons)
grey matter (cell bodies, glia)
central canal (CSF flows through)

Question 16

What are the two roots that carry nerves coming in and out of the spinal cord?

Answer 16

dorsal and ventral roots

Question 17

What information does the dorsal root carry, and what type of tract is it?

Answer 17

sensory input, afferent tracts

Question 18

What information does the ventral root carry, and what type of tract is it?

Answer 18

motor output, efferent tracts

Question 19

somatic motor/sensory neurons carry signals to the?

Answer 19

skeletal muscles

Question 20

visceral motor/sensory neurons are part of the?

Answer 20

autonomic nervous system

Question 21

visceral motor/sensory neurons carry signals to the?

Answer 21

cardiac muscle, smooth muscle and glands

Question 22

Briefly explain what would occur if an individual were to hold their finger close to the stimulus of a candle light

Answer 22

1. thermoreceptors will detect the change in heat, and the information will be sent through afferent tracts in the spinal cord via the sensory nerves.
2. the sensory information will travel through sturctures known as the dorsal root ganglion
3. the dorsal root ganglion will then split off into dorsal roots
4. sensory information will be carried through dorsal roots to the back of the spine, where information will be processed by interneurons
5. interneurons will synapse with motor/efferent neurons which will carry this information out via the motor nerves, into the channels known as ventral roots.
6. motor information is sent to muscles in finger to flinch away from the flame

Question 23

what are interneurons

Answer 23

they process sensory information and transform it into motor information

Question 24

what is a dorsal root ganglion?

Answer 24

a cluster/collection of nerve cell bodies

Question 25

What is the spinal nerve

Answer 25

a structure that both dorsal and ventral roots meet at the middle of, that serve as a tunnel that holds a shared space for two way communication, and then structurally splits out to the ventral and dorsal roots

Question 26

What are the 3 horns involved in spinal cord organisation?

Answer 26

- dorsal (houses somatic & visceral sensory nuclei) -ventral (houses somatic motor nuclei) -lateral (houses visceral motor nuclei)

Question 27

grey matter can be divided into what 3 sections?

Answer 27

dorsal horn (sensory) lateral horn (autonomic) ventral horn (motor)

Question 28

white matter can be divided into what 3 columns?

Answer 28

dorsal column (sensory only) lateral column (sensory & motor) ventral column (sensory & motor)

Question 29

What regions of the brain can be involved in visceral motor activity?

Answer 29

brain, basal ganglia, cerebellum (indirect modulation)

Question 30

What are the two motor neurons?

Answer 30

Upper motor neurons (UMN) Lower motor neurons (LMN)

Question 31

What is the location of UMNS?

Answer 31

start in the motor cortex (motor/pre motor areas of the brain), and axons extend to either the brainstem or continue to various regions of the spinal cord

Question 32

What is the function of UMNS?

Answer 32

send signals from the brain to LMNS initiate/coordinate voluntary movement regulate reflexes and muscle tone

Question 33

Where are LMNs located?

Answer 33

they sit at the level of the brainstem/various parts of the spinal cord

Question 34

What is the function of LMNS?

Answer 34

they carry information from UMNS to muscles, by sticking their axons out in descending tracts and innervating muscles, causing contractions

Question 35

Where can the lower motor neurons be found in abundance?

Answer 35

- the cervical spinal cord (LMNs innervate upper limbs) - the lumbar spinal cord (LMNs head out to innervate lower limbs)

Question 36

What are the two types of lower motor neurons? (LMNs)

Answer 36

alpha motor neuron and gamma motor neuron

Question 37

what do alpha motor neurons supply?

Answer 37

extrafusal muscle fibres or main muscle mass

Question 38

What are the 3 different inputs an alpha motor neuron can receive

Answer 38

input from spinal interneurons, sensory input from muscle spindles ad input from UMNs

Question 39

What do gamma motor neurons supply?

Answer 39

intrafusal muscle fibres (muscle spindles)

Question 40

what is an intrafusal muscle fibre?

Answer 40

a specialised sensory receptor involved in helping body sense stretch in muscles, maintaining muscle tone and posture

Question 41

What is a word for the types of sensory inputs we get to the motor unit?

Answer 41

proprioceptive

Question 42

What are the two kinds of proprioceptive information?

Answer 42

Muscle spindles Golgi Tendon organs

Question 43

What do muscle spindles do?

Answer 43

- they encode muscle length and synapse on alpha motor neurons

Question 44

what do golgi tendon organs do?

Answer 44

- they encode muscle tension (hence more haphazard fibres) - they synapse on inhibitory interneurons

Question 45

What can interneurons receive input from?

Answer 45

- sensory axons - other interneurons - descending UMNs and LMNs

Question 46

T or F: interneurons can be both excitatory or inhibitory

Answer 46

T

Question 47

What does an interneuron eliciting both an excitatory and inhibitory effect require?

Answer 47

reciprocal inhibition eg. agonist and antagonist muscles like the stretch reflex

Question 48

What is the motor homunculus?

Answer 48

a visual representation of how the motor cortex controls different parts of the body

Question 49

Where is the primary motor cortex (M1)- BA4 found?

Answer 49

in the pre-central gyrus

Question 50

The pre-motor areas and supplementary motor areas are found in?

Answer 50

BA 6

Question 51

Other contributions to the motor areas of the cerebral cortex include?

Answer 51

posterior parietal cortex (spatial awareness) & prefrontal cortex (making decisions)

Question 52

What is the other name for the pyramidal motor system?

Answer 52

the corticospinal tract

Question 53

What is the primary function of the corticospinal tract?

Answer 53

motor planning and initiation

Question 54

Through what pathway do axons travel through in the corticospinal tract?

Answer 54

cell bodies -> corona radiata -> internal capsule -> brainstem (pyramidal decussation) -> spinal cord to synapse onto LMNs

Question 55

what is pyramidal decussation?

Answer 55

when the axon travels from being on the left side of the brain and switches to the right (at the lower medulla of the brainstem)

Question 56

What parts of the brain are involved in the fine tuning of movement?

Answer 56

basal ganglia and cerebellum

Question 57

what does the basal ganglia do in relation to the fine-tuning of movement?

Answer 57

- it modulates movement - it selects and initiates willed movements

Question 58

what does the cerebellum do in relation to the fine-tuning of movement?

Answer 58

- generates appropriate movement sequences on demand (coordination)