Physiology - Gait and Limp Flashcards
Functions of motor control system
Posture and balance
Goal-directed movements
Communications
What is the motor control system guided by
Sensory systems - detect changes in environments
Classes of movements
Voluntary
Reflexes
Rythmicx motor patterns
Classes of movements - voluntary
Complex actions (reading, writing)
Purposeful goal directed
Learned
Classes of movements - reflexes
Involuntary, rapid, stereotypes (knee jerk, eye blink)
Classes of movements - rhythmic motor patterns
Combines voluntary & reflexive acts (chewing, walking, running)
Initiation & termination is voluntary
Once initiated, repetitive & reflexive
Where are alpha-motor neurons cell bodies found
In clumps within ventral form of spinal cord (lower motor neuron)
What does each motor neuron activate
A motor unit (6-1500 skeletal muscle fibres)
Function of muscle spindles
Identify stretch in muscle and try to prevent over stretching
Examples of monosynaptic reflex arcs
Biceps brachii, triceps brachii and brachioradialis
Most are stretching reflexes
Examples of polysynaptic reflex arcs
Plantar and anal reflexes
Where are sensory neurons (afferent) located
In spinal ganglion
Where do afferent neurons conduct to
The ventral horn where the motor neuron (efferent) is found
Spinal reflex examples
Stretch reflex
Golgi tendon reflex
Withdrawal reflex
Crossed extensor reflex
Steps in spinal reflex
Receptor Sensory fibre (interneuron) Alpha motor neuron Muscle
Stretch reflex
A muscle contraction in response to stretching within the muscle
What type of synaptic reflex is a stretch reflex
Monosynaptic reflexes that provides automatic regulation of skeletal muscle length, with a very short latency period
What happens when a muscle is stretched
The muscle spindle is stretched as a result and increases firing of alpha motor neurons
The muscle fibres then contract synergistically and resist the stretching. Another set of inhibitory interneurons causes the opposing muscle to relax
Myotatic (knee jerk) reflex
Example of monosynaptic stretch reflex
Tap of patellar tendons stretches quads (extensors) and stimulates receptors of muscle spindle
Inc in rate of firing of Ia afferent –> contraction of quads and knee flexors inhibited
When is the knee jerk reflex lost
If lower lumber dorsal roots of spinal cord are damaged
Golgi tendon organ
Detect and respond to changes in muscle tension (force)
What is the Golgi tendon organ activated by
A passive stretch or muscular contraction e.g. standing for too long
Innervation of Golgi tendon organ
Ib afferents – wrapped around bundles of collagen fibres in the tendon
Golgi tendon reflex as a feedback mechanism
Controls muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn – helps maintain posture
Golgi tendon reflex
Tension/ force in tendons will decline and so will activity of afferent Ib fibres
Normal inhibition of motor neurones will be removed so flexor muscles contract more strongly —-> increasing tension in tendon
Inverse myotatic reflex
Force in patellar tendons will decline, this activity in afferent Ib fibres will decline
Normal inhibition of motor neurons supplying quads (extensors) will be removed
Muscle will contract more strongly (flexors), so increasing force in patellar tendon
Sensitivity of Golgi tendon reflex
Less sensitive than the stretch reflex but can override the stretch reflex when tension is great, which explains why we drop heavy things
Withdrawal reflex
Polysynaptic reflex which is intended to protect the body from damaging stimuli
Typically motor neurons send inhibitory impulses to the extensors, so flexion is not inhibited (reciprocal innervation)
When do we not exhibit the withdrawal reflex
In those trained to override it and unconscious people (incl those drugged or drunk)
When does the withdrawal reflex occur
When the flexors in the withdrawing limb contract and the extensors relax but the opposite occurs in the contralateral limb
Why is the crossed extensor reflex described as contralateral
Reflex occurs on the opposite side of the body from the stimulus
The interneurons excite or inhibit alpha motor neurons to the muscles of the contralateral limb
What is the main function of the crossed extensor reflex
Maintain posture and balance, which explains why the opposite leg takes the weight of the whole body
Stance phase of step cycle
Foot touching ground, flexion of knee and ankle
Finishes with extension about all joints for forward movement
Swing phase of step cycle
Bending (flexion) of hip, knee and ankle followed by knee and ankle straightening (flexion)
Where is the central pattern generator for locomotion found
Spinal cord
Central Pattern Generators
2 half centres which activate flexors and extensors respectively and which mutually inhibit each other
Can be modelled using inhibitory 1a interneuron and Renshaw cells
What does the cerebellum contribute to
Coordination, precision and timing of voluntary movement and motor learning
What does the basal ganglia comprise of
Neostriatum – caudate nucleus, putamen
Globus pallidus
Subthalamic nucleus
Substantia nigra
Function of cerebellum
Entirely motor and operates at an unconscious level
Controls the maintenance of equilibrium (balance), influences posture and muscle tone and coordinates movement.
Afferent fibres of A-alpha sensory fibres
Ia
Ib
How much of the gait cycle do we spend in double support
20%
Motor pathway lesions in muscle
E.g. myositis or muscular dystrophy
Normal reflexes
Weakness/ wasting
Motor pathway lesions in neuromuscular junction
E.g. myasthenia gravis
Fatiguable weakness
Normal reflexes
Normal muscle bulk
Causes of motor pathway lesions in UMN
Cerebral vascular accident
Spinal cord trauma
Causes of motor pathway lesions in LMN
Motor neurone disease
Neuropathy
Motor pathway lesions in cerebellum
E.g. MS
Normal reflexes
Strength
Slight decrease in tone
Motor pathway lesions in basal ganglia
E.g. Huntington’s, Parkinson’s
Changes in movement
