Lesson 31 - Proprioception

What is an ipsilateral spinal column ascending tract?

tract travels up the spinal cord on the same side as where the afferent signal arrived to the spinal cord

What is an contralateral spinal column ascending tract?

tract travels up the spinal cord on the opposite side of where the afferent signal arrived to the spinal cord

What is ataxia?

lack of coordination of voluntary muscle movements

What are the causes of ataxia?

dysfunction of proprioceptive system, cerebellum, vestibular system

What is the dorsal column pathway?

ascending pathway in the dorsal funiculus that carries the sense of conscious proprioception

What are the golgi tendon organs?

proprioceptors located in tendons that detect change in muscle tension

What is the function of the golgi tendon organs?

prevent muscle damage by inhibiting excessive force

What are joint receptors?

proprioceptors located in the capsules and ligaments of joints that detect changes in joint position and movement

Where is the cell body of lower motor neurons located?

ventral gray horn of the spinal cord

Where are the axons of lower motor neurons?

travel from spinal cord and transmits signals to skeletal muscles

What is muscle tone?

continuous and passive partial contractions of muscles, or the muscle's resistance to passive stretch while at rest

What is the function of muscle tone?

helps maintain posture and ensures muscles are ready for action

What are muscle spindles?

proprioceptors found within muscles that detect changes in muscle length and stretch

What changes do proprioceptors detect?

stretch, tension, and pressure

Where does conscious proprioception afferent signals travel to?

cerebral cortex

Where does unconscious proprioception afferent signals travel to?

cerebellum

What is a reaction?

voluntary, conscious, and deliberate response to a stimulus

What is a reflex?

involuntary, unconscious, and rapid response to a stimulus

Where are the spinocerebellar tracts?

lateral funiculi

What is the function of the spinocerebellar tracts?

unconscious proprioceptive information to the cerebellum

Where is the upper motor neuron cell body located?

brain

Where is the axons of the upper motor neuron located?

descends down the spinal cord where it synapses with lower motor neurons in the ventral gray horns

What is the vestibular system?

sensory system located in the inner ear that provides information about the orientation of the head in space

How many neurons are typically involved in the ascending pathway?

3

Where does the first order neuron action potential start?

sensory receptors via a peripheral/spinal nerve

Where does the action potential of a first order neuron end at?

dorsal gray horn of the respective spinal cord segment

Where does the action potential of a second order neuron start at?

dorsal gray horn

Where do the action potentials of a second order neuron travel to?

spinal tracts to the ascending reticular activating system (ARAS)

Where do the action potentials of a third order neuron start at?

ARAS

Where do the action potentials of a third order neuron end at?

cortex

What is the first motor neuron that an efferent signal travels down?

upper motor neuron

What is the second motor neuron that an efferent signal travels down?

lower motor neuron

Where do the upper and lower motor neuron synapse?

ventral gray horns

Where do the lower motor neurons contact the skeletal muscle?

motor end plates

What are the different types of movement in proprioception?

automated movements and skilled, detailed movements

What are the automated movements?

gross motoric/gait

What are the skilled, detailed movements?

fine motoric

What are the characteristics of gross motoric?

coordination of large muscle groups, mostly subconscious

What are the characteristics of fine motoric?

conscious movements of small and large muscle groups

what happens with loss of proprioception?

loss of coordination/sensory ataxia

What monitors muscle stretch?

muscle spindles

What monitors pull on tendons during muscle contraction?

golgi tendon organs

What monitors changes in joint angulation and rotation?

joint receptors

What are the sensory receptors of first order neurons like?

mechanoreceptors

What is the stimulation process for the sensory receptors of first order neurons?

stretching of membrane pulls the gate open causing ion influx and depolariztion

What reduces the amount of action potentials in the sensory nerves?

relaxation/compression of the membrane channels

What makes up the muscle spindles?

3-10 modified skeletal muscle fibers (intrafusal) embedded in each muscle belly (extrafusal)

What is wrapped tightly around the intrafusal fibers?

sensory nerve endings of first order neurons

What do the golgi tendon organs consist of?

modified collagen fibers in a capsule within each tendon

What happens to action potentials of muscle spindles and golgi tendon organs when the muscle contracts?

muscle spindles action potentials decrease; golgi tendon organs action potentials increase

What happens to action potentials of muscle spindles and golgi tendon organs when the muscle relaxes?

muscle spindles action potentials increase; golgi tendon organs action potentials decrease

Where are the joint receptors located?

joint capsule

What is another name for the spinal stretch reflex?

spinal myototic reflex

What is the mechanism of the spinal stretch reflex?

stretching of muscle spindle causes increased impulse to dorsal horn and impulse travels down lower motor neuron of same nerve and signals are sent to the brain

What is the function of the spinal stretch reflex?

maintain basic muscle tone and posture and protect muscles from injury caused by excessive stretching

What are the clinical tests of the spinal stretch reflex?

palpate muscle tone, observe posture, testing spinal stretch reflexes

What is an example of a clinical test of the spinal stretch reflex?

patellar reflex

How does the patellar reflex work?

tap patellar tendon, stretches quadriceps muscle which leads to knee jerk

What vertebra innervate the quadriceps?

L4-6

What is the grading scale for the patellar reflex?

0 - +4

What is a normal patellar reflex score?

2

What is the reciprocal inhibition reflex?

spinal reflex where contracting one muscle causes the antagonistic muscle to relax

What is the function of the reciprocal inhibition reflex?

prevent muscles from working against each other and ensure smooth movement

What are the afferent signals of the reciprocal inhibition reflex?

muscle spindles sends signal through afferent fibers that bifurcate in the spinal cord

What are the efferent signals of the reciprocal inhibition reflex?

lower motor neuron is stimulated for muscle contraction while inhibitory interneuron is stimulated which will inhibit lower motor neuron of antagonistic muscle

What are the clinical tests for the reciprocal inhibition reflex?

tested indirectly via reflexes and observing gait

What would be the result of lack of reciprocal inhibition?

smooth movement hampered

What is the withdrawal reflex?

in response to a pain stimulus causes entire limb to flex

How is the withdrawal reflex different than the reciprocal inhibition reflex?

withdrawal engages all limb muscles

What is the afferent signal like for the withdrawal reflex?

sensory information ascends via periperal nerve and enters the spinal cord

What are the efferent signals like for the withdrawal reflex?

lower motor neurons of all flexors are stimulated and lower motor neurons of all extensors are inhibited

What are the clinical tests for the withdrawal reflex?

in lateral recumbency a foot is pricked and the smooth flexion of entire limb is observed

What is the crossed extensor reflex?

one leg is lifted while standing so the opposite leg stabilizes the body

What is the mechanism of the crossed extensor reflex?

interneurons from the lifted leg cross the midline and communicate with the contralateral side

What are the clinical tests for the crossed extensor reflex?

with large animals that are standing, put weight on coronary band area and watch the animal withdraw the limb while extending the other one

What muscles are contracting in the crossed extensor reflex?

affected leg flexors and standing leg extensors

What muscles are relaxing in the crossed extensor reflex?

affected leg extensors and standing leg flexors

What are the central pattern generators?

neural network in the spine which synchronize front and hind limb activities

What types of neurons are present in the central pattern generator?

pacemaker neurons as well as excitatory and inhibitory neurons

Which proprioceptive pathway does not cross sides?

subconscious pathway

What clinical test is used for gross motoric?

watch animals' gait for smoothness, rhythm, and coordination

What clinical test is used for fine motoric?

watch how an animal corrects and coordinates its response to a challending posture

What are signs of ataxia?

incoordination, wide-based stance, truncal swaying, delayed protraction

What is not affected with damage to proprioceptive pathways?

muscle strength