Locomotion and gait

Question 1

How does locomotion happen?

Answer 1

• Animals move by exerting forces on their environment generated by muscles
• Environment can be fluid or solid
• Force is transmitted to bones/joints
• Force is applied to the environment creating movement

Multiple forces: propulsion friction, gravity, buoyancy, density…
• Quadrupedal terrestrial locomotion → focus

Question 2

Components of animal locomotion

Answer 2

• Nervous system
• Pattern generation • Motor control
• Muscles
• Generates forces
• Transforms chemical energy into movement
• Skeleton and joints • Support and lever

Question 3

Gait

Answer 3

• Cyclic pattern of movement of limbs. Speed, energy cost, efficiency, manoeuvrability
• Gaits: Walk, trot, gallop

Question 4

Motor control and pattern generation

Answer 4

• Locomotion requires pattern of co-ordinated movement activity
• Interaction of spinal pattern generators, sensory feedback and descending supraspinal control generates movement!

Question 5

Central pattern generation

Answer 5

• Series of mechanism that allow animals to do movement related activities such as scratching, micturition, ejaculation, breathing, motion
• Involuntary activities that require a cyclic type of movement
• The information does not reach the brain

Question 6

CEREBELUM

Answer 6

Pattern memory and detailed control

We covered physiology of posture and locomotion (lower motor neuron) and the pyramidal and extrapyramidal systems (upper motor neuron)
• The cerebellum is the main third upper motor neuron that regulates lower motor neuron responses
• 10% of the brain volume…. But 50% of the neurons!!!!!!
• The cerebellum does NOT do movement as such. Refines movement

Question 7

FOREBRAIN

Answer 7

Higher level, voluntary control

Question 8

BRAINSTEM

Answer 8

Start and stop

Question 9

SPINAL CORD

Answer 9

Generate stepping patterns and reflex arc

Question 10

Somatic sensory nerves

Answer 10

The primary function of the somatic nervous system is to connect the central nervous system to the body’s muscles to control voluntary movements and reflex arcs. Information taken in by sensory systems is transmitted to the central nervous system.

Question 11

• Visceral sensory nerve

Answer 11

The general visceral afferent (GVA) fibers conduct sensory impulses (usually pain or reflex sensations) from the internal organs, glands, and blood vessels to the central nervous system.

Question 12

Visceral motor nerve

Answer 12

The visceral (or autonomic) motor system controls involuntary functions mediated by the activity of smooth muscle fibers, cardiac muscle fibers, and glands.

Question 13

Somatic motor nerve

Answer 13

the somatic motor system, which innervates and commands skeletal muscles through motor neurons in the ventral horn of the spinal cord

Question 14

simple movement…

Answer 14

1. Generated by the spinal cord with no forebrain involvement
2. Acted by the motor nerves, descending tracts in the spinal cord
3. Initiated and regulated by sensor organs

Question 15

Sensory nerves

Answer 15

Receive information from the external environment. i.e. hot / cold towards CNS

Question 16

Motor nerves

Answer 16

They carry impulses away from the CNS to the skeletal muscle and somatic tissues, which creates a voluntary movement

Question 17

Spinal nerves

Answer 17

• Each spinal nerve has a dorsal root that brings the information from the organs to the spinal cord (sensory fibres) AFFERENT
• Cell bodies of these neurons are in the dorsal ganglion, very close to
the spinal cord
• Once in the spinal cord, they may communicate directly with the
ventral root or through an intercalated neuron
• The ventral root carries motor fibres, leaves the spinal cord towards
the organs to execute the action EFFERENT

Question 18

AFFERENT

Answer 18

Access

Question 19

EFFERENT

Answer 19

Exit

Question 20

Grey matter

Answer 20

Mainly composed of neuronal cell bodies and unmyelinated

Question 21

White matter

Answer 21

Mainly composed of long range myelinated axons (that transmit signals to the grey matter) and very few neuronal cell bodies

Question 22

Spinal cord white matter: columns (funiculi)

Answer 22

1. Dorsal 2. Lateral 3. Ventral

Rubrospinal tract
Ventral spinocerebellar tract
Medullary recticulospinal tract
Pontine recticulospinal tract
Lateral vestibulospinal tract

Question 23

Nerves within the tracts

Ascending

Answer 23

• Transmit sensory information from the sensory receptors to higher levels of the CNS (tactile, movement sense and conscious proprioception)

Question 24

Nerves within the tracts

Decending

Answer 24

• From cortex and brainstem (midbrain, pons and medulla) nuclei
• They carry information related with maintenance of motor activities such as posture, balance, muscle tone, and visceral and somatic reflex activity

Question 25

Spinal cord grey matter: columns

Answer 25

1. Somatic afferent column
2. Visceral afferent column
3. Visceral efferent column
4. Somatic efferent column
   5 and 6 Dorsal and ventral roots
5. Fourth ventricle

Question 26

Spinal cord grey matter: nuclei (laminae)

Answer 26

1. Lateral motor nuclei
2. Medial motor nuclei
3. Motor nucleus of the accessory nerve(from C1 to C7)
4. Thoracic nucleus or Stilling-Clark nucleus(from T1 to L3-L4)
5. Lateral cervical nucleus(C1 and C2)
6. Marginal nucleus(also called dorsomarginal nucleus)
7. Substantia gelatinosa
8. Nucleus proprius
9. Intermediolateral nucleus
10. Intermediomedialnucleus
11. Sacral parasympathetic nucleus

Question 27

How does the NS receive information for movement??

Answer 27

1. Muscle spindle receptor organ

2. Golgi tendon organ

Question 28

Muscle spindle receptor organ

Answer 28

Muscle spindle receptor organ
Spindle neuron→peripheral nerve (sensory)→dorsal root to spinal cord→ventral root→peripheral nerve (motor)→some to intrafusal gamma (spindle fibres) and a separate lot for the extrafusal alpha (the belly muscles) but through the same root!
When the “right” length is achieved : negative feedback loop. Process stops!

he patellar reflex is a good example of how the muscle spindle receptor organ works and the stretch reflex. Biceps tendon or common calcaneus tendon reflexes are also good examples of this
• The muscle spindle organ and stretch reflex allow the CNS to adjust muscle length according to body position
• This is used to assess integrity of the sensory and motor pathways
• When antagonist muscle has to be relaxed and this involves activation of inhibitory neurons

Question 29

Golgi tendon organ

Answer 29

At the muscle – tendon junction and it is extrafusal
Golgi tendon organ→peripheral nerve (sensory)→dorsal root to spinal cord
Golgi tendon organ has no motor innervation

Question 30

Other receptors

Answer 30

• Receptors are located in the vestibule and semicircular canals in inner ear
• Other sensory receptors in skin, joints and muscles
• Essential for equilibrium/propioception

Question 31

Spinal segment reflex arc (reflex arc)

Answer 31

• Involuntary automatic response to a certain stimuli e.g. treading on something sharp
• Simple, rapid, automatic, fixed, involuntary responses to certain stimuli
• Used to test the function of the spinal cord
• Withdrawal of the limb indicates the reflex arc is working
• Withdrawal of the limb and a conscious response (e.g. biting) indicates the animal can feel and respond to the stimulus (conscious deep pain)
It does not involve the brain

Question 32

Reflex arc

Answer 32

• Two types:
• Monosynaptic or simple
• involve 1 synapse in the pathway
• Polysynaptic or complex
• Involving at least 1 intercalated neuron and synapses in the pathway

Question 33

reflexes commonly assessed

Answer 33

• Propioception (distal limb, digits posture) • Pedal
• Panniculus
• Palpebral
• Pupillary light reflex
• Patellar
• Perineal
• Thoracolaryngeal (horses)

Question 34

Monosynaptic reflexes

Answer 34

Patellar reflex
• When the tendon is lightly stretched, the muscle fibres stretch
• A response is initiated in the muscle spindles and a nerve impulse passes
along the sensory nerve to the spinal cord
• Sensory nerve synapses with the motor nerve and an impulse passes along the muscle fibres causing contraction
• This kicks the leg out completing the reflex arc
• Very rapid due to chemical transmission – cross only one synapse

Question 35

Polysynaptic reflexes

Answer 35

Pedal reflex
• Involves one or more intercalated neurons and several synapses in the pathway
• Produce far more complicated responses because interneurons can control several muscle groups

Question 36

Summary of locomotion and gait

Answer 36

• Muscle tone is maintained thanks to muscle spindle and Golgi receptor organs, whose information travels through sensory peripheral (somatic) afferent nerves
• Changes in movement rely ultimately in changes in muscle contraction
• Sensory information enters the spinal cord through dorsal root (afferent neuron) and exits (+/-interneuron) through ventral root (efferent neuron) to motor nerves to carry a desired action
• There are other receptors contributing to capture information related posture such as vestibular receptors
• Examples of basic reflexes important in clinics are nociceptive (pedal), proprioceptive, panniculus/cutaneous tronci, patellar, perineal and PLR
• Reflex arcs do not involve the brain and are the simplest type of involuntary movement
• The CNS controls posture through the extrapyramidal system (brainstem and three tracts)
• Information for axial musculature (involuntary, dominated by extensor muscle activity) travels through medial tracts in the spinal cord
• The pyramidal system initiates voluntary discrete learnt movements and there is cross over of information

Question 37

Two main types of movement:

Answer 37

• Learnt, conscious, voluntary (dominated by flexor muscle activation)
• Discrete contraction away from the spinal cord – lateral alpha motor neurons
• Postural, antigravity, involuntary (dominated by extensor muscle activity)
• Long term contraction muscles close to spinal cord – medial alpha motor neurons

Question 38

How is movement regulated?

Answer 38

Several degrees of cranial CNS involvement→complexity and voluntary movement
A) Spinal cord only (segmental reflex arc)
b)Spinal cord and brainstem (extrapyramidal system)
a) Involuntary, posture (medial tracts, all but rubrospinal tracts)
b) Voluntary skilled HL movement (lateral, distal skilled movement)
C)Frontal lobe involvement (pyramidal system)

More complex→+ brainstem • Spinal cord and brainstem
• Axial and proximal musculature
• Rubrospinal, reticulospinal, tectospinal and vestibulospinal tracts
• Extrapyramidal (descending) motor system or descending brainstem motor pathways

Question 39

Extrapyramidal system

Vestibulospinal-reticulospinal and tectospinal tracts

Answer 39

• Involuntary maintenance of postural control and locomotion. Keeping body upright and muscle tone
• Axial/proximal muscles (extensor muscles – medial descending tracts)
• Neurons from reticular formation (brainstem)
• Tectospinal - cervical spinal cord (VI–VIII) and is involved in neck and head motor contro

Question 40

Extrapyramidal system

Rubrospinal tract

Answer 40

• Voluntary skilled
• Flexor muscles lateral descending tracts

Inhibition to lower motor neurons which maintain posture, is removed when separating forebrain
• Increase of basal muscle tone -> rigid animal

Question 41

Pyramidal system

Answer 41

c. Even more complex→involving cerebral cortex
• From the motor cortex (frontal lobe): primary motor cortex, supplementary motor cortex and premotor cortex
• To corticospinal tract
• 80% Crossover of neuron (pyramidal decussation) means affecting opposite side of the body
• Most dexterous movement

• Motor cortex better studied in humans
• Sensory cortex likely to help adjusting the movement
• Influence on contralateral limb lower motor neuron (pyramidal decussation) → lesion in pyramidal system cause contralateral weakness and loss of proprioception

Question 42

basal ganglia

Answer 42

1. Group of nuclei deep in the brain linked to extrapyramidal system and not well understood in domestic animals
2. Includes: caudate nucleus, putamen, globus pallidus, substantia nigra and subthalamus
3. Possible role of planning of movement initiated by the pyramidal and extrapyramidal systems
4. Possible role in coordinating rhythmic movements

Question 43

Vestibule

Answer 43

• Between the cochlea and semicircular canals
• Composed of utricle and saccule
• Hair cells covered by
a gelatinous matrix (endolymph)that contains crystals of calcium carbonate (otoliths)

Question 44

Vestibular system

Answer 44

• Position and motion of the head in space
• Bilateral (one per ear)
• Close to structures infected (otitis) so seen in clinics often: head tilt, circling-rolling, nystagmus
• It is located in the same place with the ear receptors – multiple sections to be discussed in ear lesson.
• Hair cells – otoliths→change in angle and acceleration
• The vestibular system is also sensory for other reflexes (including pyramidal and extrapyramidal systems)

Question 45

Vestibular apparatus/system

Answer 45

• Somatic sensory nerves (vestibulochoclear VIII) sensory information about position of the head (informs balance)→brainstem
• Vestibular nuclei receive information from the vestibule (and cerebellum)→vestibulospinal tract activating antigravity muscles of trunk and limbs in response to acceleration or head tilt
• Vestibular nuclei is able to influence rotatory movements of the eye (nystagmus), it is in close communication with the cerebellum and it sends information to the cerebral cortex
• The vestibular system, receptors all over the body and the cerebellum are responsible for our proprioception, which means they make sense of our movement and where we have and place our limbs

Question 46

Cerebellum

Three main sections:

Answer 46

• Vestibulocerebellum (flocculonodular lobe): • Afferent: Vestibular system and eye
• Efferent: vestibular nuclei
• Balance and eye movements
• Spinocerebellum:
• Afferent: sensory from muscles and skin + ear + eye and
vestibular system
• Efferent: cerebellar nuceli→extrapyramidal and pyramidal systems
• Control of movement of limbs and tone (coordination of execution)

Three main sections:
• Cerebrocerebellum:
• Afferent: not the body but the cortex
• Efferent: motor and premotor cortex (see previous lesson on voluntary complex movement)
• Preparation and planning of complex motor actions

• Motor learning is affected by the cerebellum • This is the principle of clinical skill practice!!
The cerebellum compares the intended movement with the actual movement. Signs of cerebellar disease:
- Ataxia
- Wide base gait
- Dysmetria
- Intention tremor

Question 47

Integration of neuromuscular activities:

summary

Answer 47

The need for a movement arises (Golgi receptors/muscle spindle/proprioceptors in skin/vestibule). This information reaches the CNS and depending on the complexity it stays in spinal cord (segmental movement, reflex arc) or goes cranially (up to frontal lobe). In reflex arc, stimulation of muscle leads to movement of a limb. Depends which part needs to be moved a set of muscles or their antagonists will be activated. This is the basis of locomotion. Apart from MSK system, spinal cord, brainstem, efferent and afferent nerves, vestibular system and cerebellum play important roles.
For voluntary actions, the CNS activates motor neurons in a coordinated manner to move the adequate muscles.
All of these paths when they are activated they are coordinated by the cerebellum and the information is also stored in a way that can be recalled later (learnt movement)