Lecture 7 - Locomotion Flashcards
Where are Lower Motor Neurons located
In the spinal cord and brainstem. They project out of CNS and innervate muscles
What is the Final Common Pathway
All movement is initiated through activation of LMNs. Motorneuron activity (action potential) elicits muscle contraction
What is the size principle
Small motor neurons are recruited first followed by large ones
Small motor neurons innervate
Slow motor units (Type 1 fibers)
Higher threshold motor neurons innervate
Fast motor units (Type 2a, b fibres)
Pathology of LMNs is associated with
Paresis (weakness) as muscles innervated by these LMNs are compromised
Tick Paralysis LMN Disease
Ticks release neurotoxin that affect LMN neuromuscular function where Ach & nicotinic receptors are
Myasthenia Gravis - disease where
Ach not present, but nicotinic receptors blocked
Can EMG be used as a diagnostic aid
Yes
EMG stands for
Electromyography
Normal EMG is generally
Quiet at rest
EMG Denervation potential can occur following
LMN disease/injury
Denervation potentials result in
Spontaneous action potentials known as fibrillation potentials, which do not depend on voluntary muscle activity of patient
Denervation/spontaneous action potentials (fibrillation potentials) may be due to
Ach receptors proliferation and increased responsivity to circulating levels of Ach following muscle denervation
How do fibrillation potentials contrast with fasciculations?
Fasciculations are often benign, can be visually observed, underlying causes are not clear
Fasciculations can be caused by
Stress
Low magnesium & some diseases
Examples of Normal EMGs
Insertional EMGs - caused by needle insertion, normal reaction
Resting EMGs - normal EMGs is quiet at rest
Motor unit action potential
Abnormal EMGs
Fibrillation potentials
Positive sharp waves
Fasciculations
Polysynpatic motor unit action potentials
Abnormal EMG - Fibrilation potentials
Spontaneous contraction of single motor unit
Abnormal EMGs- positive sharp waves
Associated with damage to muscle fibre membrane
Abnormal EMGs - fasciulations
Contractions are visually apparent - more than a single fibre
Abnormal EMGs - Polysynaptic motor unit action potentials
Seen during sub maximal activation-diffuse loss of MUs
Upper Motor Neuron (UMN) is confined to
The central nervous system (CNS)
The UMN system is divided into
Pyramidal and extrapyramidal system
Pyrimidal system (UMN) consists of
Neurons whose cell bodies are located in the motor cortex and project directly to the spinal cord
Pyramidal system is more important in
Primates and humans compared to domestic production animals, cats, and dogs
The pyramidal system provides
Fine control of movement
The extrapyramidal system consists of
Neurons in the brain that project directly or indirectly to the brain stem and onto the LMNs though final common pathway.
The Extrapyramidal system includes structures such as
The basal nuclei, red nucleus, thalamus, reticular formation, and much more
The extrapyramidal system is very important in which animals
Domestic animals, dogs, cats
The pyridimal system resides in the motor cortex, then goes to
Gather into a tract system then into descending fibres. Then, ipsilaterally bifurcates. Also has contralateral control still. Travels to LMN and ends there.
Point of ipsilateral and contralateral control
Plasticity after injury - can control/compensate from other side
Reticulospinal tract pathway
From medulla to interneurons and LMNs of the spinal cord
function of reticulospinal tract
Posture, initiation of walking
Rubrospinal tract pathway
From red nucleus (midbrain) to LMN
Rubrospinal cord function
Voluntary movement especially to large muscles. Promotes flexión, inhibits extension
Corticospinal (pyramidal system) tract pathway
From primary motor cortex to LMNs in spinal cord
Corticospinal (pyramidal system) tract function
Voluntary movements especially fine control. Participates in postural control.
Vestibulospinal tract pathway
From vestibular nuclei to interneurons and LMNs
Vestibulospinal tract function
Posture and balance control
Corticobulbar tract pathway
From motor cortex to pons and medulla in brainstem
Corticobulbar tract function
Multiple roles, jaw, facial muscles, swallowing, tongue
Can interneurons be excitatory and inhibitory?
Yes
What is a reflex
A fast involuntary motor response to peripheral stimulus
Types of reflexes
Tendon-tap stretch reflex (monosynaptic reflex)
Golgi Tendon organ reflex
Withdrawal reflex
Crossed extensor reflex
Reflex Arc components
- Receptor
- Afferent Pathway
- Integration Centre
- Efferent Pathway
- Effector
Muscle stretch pathway - muscle stretch leads to
Impulses being produced by muscle spindle. Impulse travels to the spinal cord through dorsal root, where the alpha motor neuron gets excited. Then, contraction of muscle occurs
Muscle stretch detection by muscle spindles - muscle spindles increase activity when
Stretched passively but decrease activity when muscles contract
What happens to muscle spindles when the muscle is contracted?
Since they lie parallel to the muscle they would be silenced following a contraction- but DOES NOT HAPPEN because the interior of the spindle is kept taut by intrafusal muscle
Gamma motoneurons are
A special class of motoneurons that innervate the intrafusal muscle fibres of muscle spindles. They allow contraction based on the stretch of muscle
Gamma motoneurons innervate
Muscle fibres
Gamma motoneurons allow
Muscle spindles to signal length changes even when muscle is shortening
Stretch reflex can be modified by
Higher centres, which allows reflexes to be optimized to the ongoing behaviour
Do you need the brain for descending control of stretch reflex?
No, but brain can modify or intensify response
Can you clinically assess stretch reflex?
Yes
Functional score of 0 - stretch reflex
Absent, interpret as LMN disease (peripheral nerves/spinal cord)
Functional score of 1 stretch reflex assessment
Assessment: decreased, interpret as LMN disease (peripheral nerves/spinal cord)
Functional score 2 assessment of stretch reflex
Assessment - normal; interpret - normal reflex
Clinical assessment stretch reflex score of 3
Exaggerated, interpret - can occur with spinal cord trauma and other conditions
Clinical assessment of stretch reflex score 4
Clonus (pulsing), interpret - UMN pathology may accompany spasticity
Golgi Tendon Organ (GTO) Reflex
when muscles are contracting afferent traffic from the GTO inhibits ongoing motoneurons activity - thought to be a protective reflex
When an animal is locomotion, the GTO reinforces what
Extensor muscle activity - opposite to GTO reflex function - if anyone understands this pls contact Nicole <3
Gait
Pattern of footfalls or manner of walking, trotting, galloping
Stride
Single coordinated movement of all limbs with a return to the starting position
locomotion
The interaction between muscles and the skeleton to produce movement
Walk
Provides maximum body support when speed is slow. Combination of 3 beat and 2 leg support phases. Characterized as 4 beat gait
Trot
At faster speeds. Characterized by a diagonal alteration of limbs. 2 beat gait
Canter
3 beat gait. 1-2-1 (hindlimb on ground, then diagonal front and hindlimb, then forelimb)
Gallop
Transverse 4 beat. Used for moderate speed
Steps in Step cycle
F
E1
E2
E3
F step of walking
All joints flexing and paw off the ground
E1 step of walking
Extension but paw is still on ground
E2 step of walking
Paw on ground, ankle flexes to absorb weight
E3 step of walking
Thrust phase, all joints extending.
Which stage of locomotion changes most in stepping frequency
E3, or the thrust phase
Locomotion requires
A rhythm & a pattern
Are flexion and extension active at the same time when doing locomotion?
No
What does the locomotor central pattern generator do
Decide pattern / rhythmicity of walking
What is NOT necessary for basic pattern of locomotion
Sensory information from skin and muscle is not necessary
Rhythmic descending input from brain is not essential
The neutral circuitry within spinal cord can produce a
Patterned locomotor pattern in the absence of patterned descending input from brain (called central pattern generator)
2 types of central pattern generators
Pacemaker CPG or circuit driven CPG
Pacemaker CPG
Single cell or collection of cells that are capable of oscillating based purely on intrinsic properties alone
Example- SA node in RA of heart
Circuit-driven CPG
A collection of cells that produce oscillations based on the collective contribution of intrinsic, synaptic, and circuit properties
- no clear structure, distributed throughout spinal cord
