Mod5-Obj6+7: Somatic motor pathways

Question 1

Somatic motor pathways

Answer 1

Conveys motor output from the primary motor cortex to skeletal muscles via a chain of two successive neurones

1. ) Upper motor neuron (pyramidal neuron)
2. ) Lower motor neuron

Question 2

Upper motor neurons (interneurons)

Answer 2

Conduct motor output from the primary motor cortex to the spinal cord

• Cell body located in primary motor cortex
• Axon descends in the spinal cord in a corticospinal tract to a motor nucleus within the anterior gray horn and synapses with a lower motor neuron

Question 3

Lower motor neurons

Answer 3

Conduct motor output from the spinal cord to skeletal muscles

• Cell body is located in a motor nucleus of an anterior gray horn
• Axon exits the spinal cord via the ventral root and travel to skeletal muscles

Question 4

Two main somatic motor pathways are:

Answer 4

1. ) Lateral corticospinal pathway

2. ) Anterior corticospinal pathway

Question 5

Lateral corticospinal pathway

Answer 5

Begins in the primary motor cortex

• Ends at the skeletal muscles of the limbs
• Axons or upper motor neurons travel in a lateral corticospinal tract
• Relays motor output that controls voluntary skeletal muscle contractions

Question 6

Anterior corticospinal pathway

Answer 6

Begins in the primary motor cortex

• Ends at the skeletal muscles of the axial skeleton, pectoral and pelvic girdles
• Axons of upper motor neurons travel in an anterior corticospinal tract
• Relays motor output that controls voluntary skeletal muscle contractions

Question 7

Neural pathway: Posterior column pathway

Answer 7

Spinal tract: 
Fasciculus gracilis tracts Fasciculus cuneatus tracts
Information relayed:
-Fine touch
-Vibration
-Pressure
-Proprioception

Question 8

Neural pathway: Spinothalamic (anterolateral) pathway

Answer 8

Spinal tract:
Lateral spinothalamic tracts
Information relayed:
-Pain 
-Temperature

Question 9

Neural pathway: Spinothalamic (anterolateral) pathway

Answer 9

Spinal tract:
Anterior spinothalamic tracts
Information relayed: 
-Crude touch
-Pressure
-Tickle and itch

Question 10

Neural pathway: Spinocerebellar pathway

Answer 10

Spinal tract:
Spinocerebellar tracts (anterior & posterior)
Information relayed:
Proprioception

Question 11

Neural pathway: Lateral corticospinal pathway

Answer 11

Spinal tract:
Lateral corticospinal tracts
Information relayed:
Motor commands to skeletal muscles (limbs)

Question 12

Neural pathway: Anterior corticospinal pathway

Answer 12

Spinal tract:
Anterior corticospinal tracts
Information relayed:
Motor commands to skeletal muscles (trunk, neck, pectoral & pelvic girdles)

Question 13

Somatic reflex pathways

Answer 13

Rapid, involuntary activation of skeletal muscles in response to a stimulus

• Spinal cord processes incoming sensory information, decides on and generates a motor response (acts as an integration centre)
• Lower motor neurons relay the motor output to the effector skeletal muscle

Question 14

Somatic reflexes

Answer 14

Can be facilitated or inhibited by motor output issued by the primary motor cortex and relayed down the spinal cord via the corticospinal tracts

Question 15

Somatic reflexes can be used to assess the condition of:

Answer 15

• Lower motor neurons
• Spinal cord
• Primary motor cortex
• Corticospinal tracts

Question 16

Somatic reflexes

Answer 16

• Patellar reflex
• Biceps reflex
• Triceps reflex
• Abdominal reflex
• Plantar reflex

Question 17

Patellar reflex

Answer 17

Stimulus 
-Tap to patellar tendon
Normal response 
-Extension at the knees (kick)
Spinal segment assessed 
-L2-L4

Question 18

Biceps reflex

Answer 18

Stimulus
-Tap to biceps brachii tendon
Normal response
-Flexion at elbow
Spinal segment assessed 
-C5,C6

Question 19

Triceps reflex

Answer 19

Stimulus 
-tap to triceps brachii tendon 
Normal response
-Extension at elbow 
Spinal segment assessed 
-C6, C7

Question 20

Abdominal reflex

Answer 20

Stimulus 
-Stroking of abdomen 
Normal response 
-Contraction of abdominal muscles 
Spinal segment assessed 
-T7-T12

Question 21

Plantar reflex

Answer 21

Stimulus 
-Stroking of lateral side of sole of the foot 
Normal response
-Curling of toes (>1yr)
Spinal segment assessed 
-L4-S2

Question 22

Patellar (knee-jerk) reflex

Answer 22

Sensory neuron (first order), Lumbar region, Lower motor neuron 
Normal response: Extension of the knee

Question 23

Patellar (knee-jerk) reflex: Hyporeflexia

Answer 23

Damage to lower motor neurone or spinal cord segment

Reduces or absent intensity of the reflex

Question 24

Patellar (knee-jerk) reflex: Hypereflexia

Answer 24

Damage to brain or corticospinal tract

-Series of kicks, instead of just one=inhibitory

Question 25

Plantar reflex

Answer 25

L4-S2 damage

Question 26

Plantar reflex: Normal response

Answer 26

Flexion of the toes

Question 27

Plantar reflex: Abnormal response: Babinski sign

Answer 27

Fanning of the toes | -Normal response in children (<1yr old) as corticospinal tracts are not fully developed

Question 28

"Spastic" paralysis

Answer 28

Upper motor neuron damage=loss of voluntary movements. Spinal reflex activity intact and stimulates muscles irregularly

Question 29

If compression or a spinal cord segment damages all spinal cord tract, these occur below the level of compression

Answer 29

- A loss of voluntary skeletal muscle activity - A loss of sensation - Abnormal reflex activity

Question 30

The degeneration of lower motor neurons will result in...

Answer 30

- A loss of voluntary skeletal muscle activity | - A loss of reflex activity

Question 31

Lower motor neurone activity will be affected if...

Answer 31

- An anterior grey horn damage | - A ventral nerve root damage

Question 32

"Flaccid" paralysis

Answer 32

Muscles can not move voluntarily and involuntary muscles atrophy

Question 33

Transection of the spinal cord results in...

Answer 33

- A loss of voluntary skeletal muscle activity (below lesion) - Sensory loss below the lesion - Paraplegia if it occurs between T1-L1 - Quadraplegia if it occurs in the cervical region

Question 34

"Spinal shock"

Answer 34

A transient period of complete motor paralysis, sensory loss and loss of all reflexes (somatic and autonomic) below the level of the lesion. Reflex activity gradually returns

Question 35

Nerve structure and classification

Answer 35

The axons (fibres), blood and lymphatic vessels that comprise nerves are enclosed by three connective tissue layers 1. ) Epineurium 2. ) Perineurium 3. ) Endoneurium

Question 36

Epineurium

Answer 36

Tough fibrous outer layer that encloses entire nerve

Question 37

Perineurium

Answer 37

Middle layer that surrounds bundles of axons called fascicles

Question 38

Endoneurium

Answer 38

Innermost layer that surrounds each individual axon

Question 39

Nerves can be classified as: sensory nerves

Answer 39

Contain the axons of sensory neurons

Question 40

Nerves can be classified as: Motor nerves

Answer 40

Contain the axons of motor neurons

Question 41

Nerves can be classified as: Mixed nerves

Answer 41

Contain both sensory and motor axons

Question 42

Nerves can be classified as: Cranial nerves (12 pairs)

Answer 42

Arise from the brain to innervate the head and neck, visceral organs

Question 43

Nerves can be classified as: Spinal nerves (31 pairs)

Answer 43

Arise from the spinal cord and branch into peripheral nerves that innervate all body areas except some head and neck regions