Locomotion and gait Flashcards
How does locomotion happen?
- 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
Components of animal locomotion
- Nervous system
- Pattern generation • Motor control
- Muscles
- Generates forces
- Transforms chemical energy into movement
- Skeleton and joints • Support and lever
Gait
- Cyclic pattern of movement of limbs. Speed, energy cost, efficiency, manoeuvrability
- Gaits: Walk, trot, gallop
Motor control and pattern generation
- Locomotion requires pattern of co-ordinated movement activity
- Interaction of spinal pattern generators, sensory feedback and descending supraspinal control generates movement!
Central pattern generation
- 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
CEREBELUM
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
FOREBRAIN
Higher level, voluntary control
BRAINSTEM
Start and stop
SPINAL CORD
Generate stepping patterns and reflex arc
Somatic sensory nerves
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.
• Visceral sensory nerve
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.
Visceral motor nerve
The visceral (or autonomic) motor system controls involuntary functions mediated by the activity of smooth muscle fibers, cardiac muscle fibers, and glands.
Somatic motor nerve
the somatic motor system, which innervates and commands skeletal muscles through motor neurons in the ventral horn of the spinal cord
simple movement…
- Generated by the spinal cord with no forebrain involvement
- Acted by the motor nerves, descending tracts in the spinal cord
- Initiated and regulated by sensor organs
Sensory nerves
Receive information from the external environment. i.e. hot / cold towards CNS
Motor nerves
They carry impulses away from the CNS to the skeletal muscle and somatic tissues, which creates a voluntary movement
Spinal nerves
• 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
AFFERENT
Access
EFFERENT
Exit
Grey matter
Mainly composed of neuronal cell bodies and unmyelinated
White matter
Mainly composed of long range myelinated axons (that transmit signals to the grey matter) and very few neuronal cell bodies
Spinal cord white matter: columns (funiculi)
- Dorsal 2. Lateral 3. Ventral
Rubrospinal tract Ventral spinocerebellar tract Medullary recticulospinal tract Pontine recticulospinal tract Lateral vestibulospinal tract
Nerves within the tracts
Ascending
• Transmit sensory information from the sensory receptors to higher levels of the CNS (tactile, movement sense and conscious proprioception)
Nerves within the tracts
Decending
- 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
Spinal cord grey matter: columns
- Somatic afferent column
- Visceral afferent column
- Visceral efferent column
- Somatic efferent column
5 and 6 Dorsal and ventral roots - Fourth ventricle
Spinal cord grey matter: nuclei (laminae)
- Lateral motor nuclei
- Medial motor nuclei
- Motor nucleus of the accessory nerve(from C1 to C7)
- Thoracic nucleus or Stilling-Clark nucleus(from T1 to L3-L4)
- Lateral cervical nucleus(C1 and C2)
- Marginal nucleus(also called dorsomarginal nucleus)
- Substantia gelatinosa
- Nucleus proprius
- Intermediolateral nucleus
- Intermediomedialnucleus
- Sacral parasympathetic nucleus
How does the NS receive information for movement??
- Muscle spindle receptor organ
2. Golgi tendon organ
Muscle spindle receptor organ
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
Golgi tendon organ
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
Other receptors
- Receptors are located in the vestibule and semicircular canals in inner ear
- Other sensory receptors in skin, joints and muscles
- Essential for equilibrium/propioception
Spinal segment reflex arc (reflex arc)
• 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
Reflex arc
- 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
reflexes commonly assessed
- Propioception (distal limb, digits posture) • Pedal
- Panniculus
- Palpebral
- Pupillary light reflex
- Patellar
- Perineal
- Thoracolaryngeal (horses)
Monosynaptic reflexes
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
Polysynaptic reflexes
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
Summary of locomotion and gait
- 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
Two main types of movement:
- 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
How is movement regulated?
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
Extrapyramidal system
Vestibulospinal-reticulospinal and tectospinal tracts
- 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
Extrapyramidal system
Rubrospinal tract
- 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
Pyramidal system
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
basal ganglia
- Group of nuclei deep in the brain linked to extrapyramidal system and not well understood in domestic animals
- Includes: caudate nucleus, putamen, globus pallidus, substantia nigra and subthalamus
- Possible role of planning of movement initiated by the pyramidal and extrapyramidal systems
- Possible role in coordinating rhythmic movements
Vestibule
• 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)
Vestibular system
- 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)
Vestibular apparatus/system
- 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
Cerebellum
Three main sections:
• 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
Integration of neuromuscular activities:
summary
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)
