Gait and limp - Physiology

Question 1

Describe the components of the somatic motor (simple) reflex arc

Answer 1

1. Stimulation of receptors e.g., externoreceptors (sight, sound, vision, taste, smell, pain, touch, thermal) or proprioreceptors (muscle and joint position)
2. A sensory (afferent) neurone carries information to the CNS from recepors
3. A motor efferent neuron transmits information from the CNS or spinal cord via single motor nerve myelinated and fast conducting to the periphery e.g., neurmsucular junction to skeletal muscle

Question 2

List 3 functions of the motor control system

Answer 2

1. Posture and balance
2. Goal-directed movements
3. Communication

Question 3

Describe the 3 classes of movemement

Answer 3

1. Voluntary

• Complex actions
• Purposeful goal directed
• Learned

2. Involuntary/reflexes
   * Rapid, stereotypes (knee jerk, eye blink0
3. Rythmic motor patterns

• Combines voluntary and reflexive acts (chewing, walkng, running)
• Initiation and termination voluntary but once initiated it is repetitive and reflexive

Question 4

Describe the organisation of the spinal cord in reference to motor control

Answer 4

1. Primary sensory afferent neurons enter spinal cord via dorsal root (and terminate within laminae I to IV)
2. This meets with interneurones within the dorsal and ventral region in anterior horn and synapse in the α-motoneurons
3. α-motoneurons’ cell bodies lie in clumps within ventral horn of the spinal cord (lower motor neurone)
4. Each motor neuron in ventral activates a motor unit (an α motor neuron and all of the skeletal muscle fibers that its axon supplies)
5. Motor neruons project their axons into the periphery to innervate skeletal and smooth muscles that mediate voluntary and involuntary reflexes.
6. Some axon branch back into cord and synapse with interneurons called Renshaw cells (recurrent or feedback inhibition)

Question 5

a) Some axon branch back into cord and synapse with interneurons called Renshaw cells (recurrent or feedback inhibition). Describe the role of renshaw cells
b) Describe the role of renshaw cells in strychine poisoning

Answer 5

a) Suppress weakly firing motor neurons and dampening strong firing ones - modulate firing rate/muscle activity - produces econmical movemement
b) Strychnine poisoniig disables renshaw cell inhibiton which leads to convulsion

Question 6

a) List the sensory fiber types from largest diameter to smallest diameter
b) What is the relationship between the diameter and conduction of speed.
c) What is the fast and the slowest sensory neurone?

Answer 6

a) Largest diameter to smallest: Aα, Aβ, Aδ, C
b) As the fiber diameter decreases the conduction velocity decreases
c) Aα fastest and C slowest

Question 7

Fill in the empty boxes

Answer 7

Question 8

a) List the motor fiber types from largest diameter to smallest diameter
b) What is the relationhsip between the diameter and conduction of speed.
c) What is the fast and the slowest motor neurone?

Answer 8

a) From largest diameter to smallest diameter: Aα, Aγ
b) As the diameter decreases the conduction velocity decreases
c) Fastest is Aα and slowest is Aγ

Question 9

Fill in the boxes

Answer 9

Question 10

List the sensory and motor neurone fibers

Answer 10

Sensory: Aα, Aβ, Aδ, C

Motor: Aα, Aγ

Question 11

Label the structures of the muscle fiber

Answer 11

Question 12

Describe how muscle spindles detect and respond to changes in muscle length.

Answer 12

Muscle spindles respond to changes in muscle length because they lie in parallel with the extrafusal fibers and therefore will also be stretched or shortened along with the extrafusal fibers.

Because intrafusal fibers (like all muscle fibers), display spring-like properties, a change in their length will change the tension that they are under, and this change is sensed by mechanoreceptors of the Ia and II spindle afferents.

Question 13

Myotatic (knee jerk) reflex is an example of a monosynaptic reflex. Describe how this occurs

Answer 13

1. Tap of patella tendon stretches quadriceps muscle
2. This stimulates dynamic nuclear bag receptors of muscle spindle
3. Increase in rate of firing of group of Iα afferent leads to contraction of quadriceps muscle
4. Iα fibers also stimulate inhibitory interneurons which inhibit antagonist (flexor) muscle of knee joint

Question 14

How is the myotatic (knee jerk) reflex lost?

Answer 14

Reflex is lost if lower lumbar dorsal root of spinal cord is damaged

Question 15

a) What is the role of the golgi tendon organ
b) Describe how it is activated?
c) Describe how it is innervated

Answer 15

a) Detects the force in tendon
b) Activated by muscle stretch and contraction

• Information on static
• Rate of change in length
• Force generated

c) Sensory innervation - Group Ib afferent - wrapped about bundles of collagen fibers in the tendon of the muscle

Question 16

a) What is the role of the inverse myotatic (golgi tendon) reflex
b) Describe how it wokrs

Answer 16

a) Contributes to maintenance of posture

b)

1. During maintained posture (e.g., standing), quadriceps muscle will start to fatigue
2. Force in patellar tendon will decline, thus activity in afferent Ib fibers will decline
3. Normal inhibiton of motor neurons supplying quadriceps will be removed
4. Muscle will contract more strongly, so increasing force in patellar tendon

Question 17

Descrbe the role of the withdrawal reflex and crossed extensor reflex

Answer 17

• Withdrawal reflex - protective reflex from damaging stimuli
• Crossed extensor reflex - stimulation of withdrawal reflex, frequently elicits extension of the contralateral limb 250ms later - helps maintain posture and balance

Question 18

a) Where is the central pattern generation (CPG) for locomotion
b) What is its role?
c) What is it modulated by?
d) What is it thought to be initiated by?

Answer 18

a) Spinal cord
b) Neural networks in the spinal cord, referred to as “central pattern generators” (CPGs), are capable of producing rhythmic movements, such as swimming, walking, and hopping, even when isolated from the brain and sensory inputs - Therefore capable of autonmous signals.
c) Modulated by proprioception input
d) Thought to be initiated by mesencephalic locomotor region - output through reticular nulei and reticulospinal tracts

Question 19

List the 5 components of the motor cortex

Answer 19

1. Primary motor cortex (M1)
2. Four premotor cortical arears:

• Supplementary motor area (SMA)
• Cingulate gyrus
• Ventral premotor cortex
• Dorsal premotor cortex

Question 20

List the structures of the basal ganglia/nuclei

Answer 20

• Neostriatum: Caudate nucleus and putamen
• Globulus pallidus
• Subthalamic nucleus
• Substantia nigra

Question 21

Label the structures of the basal ganglia/nuclei

Answer 21

Question 22

a) List the 3 pathways of basal ganglia/nuclei
b) Describe the roles of the pathways of basal ganglia/nuclei

Answer 22

a) Hyperdirect pathway, direct pathway and indirect pathway

b)

• The pathways are responsible for initiation and termination of movement/motor programmes
• Gives an inhibitory effect on the globus pallidus. This stops the inhibiton of the thalamus and allows thalamocortical neurons to initiate the movement

Question 23

Describe the role of the cerebellum

Answer 23

Adjusts motor responses by comparing the intended output with sensory signals and to update movement commands if they deviate from the intended trajectory

Question 24

What role does the cerebrocerebellum input from the cerbral cortex have?

Answer 24

Role in movement planning and initiation of movement

Question 25

List the 3 parts of the cerebella and describe their roles

Answer 25

1. Cerebrocerebellum- gets input from cerebreal cortext for movement plannng and initiation of movement
2. Spinoerebellum - gets input from spinal cord about limb position, touch, and pressure
3. Vestibulocerebellum - balance and eye movement

Question 26

3 pednucles connects cerebellum to the brain cortex. List the 3 pedncules and describe their role

Answer 26

Superior pednucles

• Connects cerebellum to midbrain
• Neurons in deep cerebellar nuclei and communication with motor cortex via thalamus

Middle pednucles

• Connects cerebellum to pons
• Input from cerebral cortex

Inferior pednucles

• Connects cerebellum to medulla
• Sensory information from proprioreceptors and vestibular
• Output to upper motor neurons

Question 27

List the main descending tracts involved in voluntary movement and where in the brain they are

Answer 27

Cerebral cortex

• Corticospinal tract

Brain stem and medulla

• Reticulospinal tract
• Vestibulospinal tract
• Rubrospinal tract
• Tecticulospinal tract

Question 28

Do all descending motor pathways originate in the brain stem?

Answer 28

All descending motor pathways except for the corticospinal tract originate in the brain stem

Question 29

Describe the input from musle and tendon proprioreceptor in the control of movememnt

Answer 29

• They have a secondary role in control of postural mechanims - they exert control on a moment-by-moment basis
• They have a third role in maintenance of tone of muscles

Question 30

Provide an example of a disease that occurs in a) cerebellum and b) Basal ganglia and also the effect this will have on the person

Answer 30

Cerebellum - Multiple scelerosis

• Incoordination
• Normal reflexes, strength and slight decrease in tone

Basal ganglia - Parkinsons’s, Huntington’s

• Movement changes

Question 31

There are clinical differences in upper and lower motor neuron lesions. Fill in the boxes

Answer 31