Maintaining balance and posture Flashcards
Posture =
Relative position of various parts of the body with respect to one another
2 types of postural equilibrium =
Static
Dynamic
Postural system afferents come from:
- Somatosensory receptors on skin
- Proprioceptions on muscles and joints
- Visual system
- Vestibular system
Where do the efferents for the postural system converge?
Brain stem
2 dorsolateral pathways:
Corticospinal
Rubrospinal
4 ventromedial pathways:
Tectospinal
Vestibulospinal (lateral and medial)
Pontine reticulospinal
Medullary reticulospinal
Another name for pontine and medullary reticulospinal tracts
medial and lateral reticulospinal tracts
Which ventromedial tract decussates?
Tectospinal
Brainstem areas which go to the ventral horn of spinal cord to coordinate postural responses:
Vesticular nuclei (medulla) Superior colliculus (midbrain) Pontine and medullary reticular formation
Superior colliculus is located in the
Midbrain
Vestibular nuceli is located in the
Medulla
What does the medial vestibulospinal and tectospinal tract have in common?
Act on head and neck muscles
2 pathways of vestibulospinal tract and their broad functions
Lateral - axial extensor muscles
Medial - head and neck extensors
Extensor muscles also known as
Antigravity muscles
What type of postural reflex is the vestibulospinal tract most involved in
Compensatory
Input to tectospinal tract from:
Optic nerves
Retina
Auditory
Where does the tectospinal tract decussate?
Midbrain - very early
Function of tectospinal tract:
Movements of head in relation to visual stimuli
Function of pontine reticulospinal tract:
Enhances antigravity reflex. Extensors of lower limbs. Increases tone.
Function of medullary reticulospinal tract:
Liberates antigravity muscles (flexors). Reduces muscle tone)
Transection studies allow us to
Remove components of brain (e.g. cerebrum) to study function of one part (e.g. brainstem)
If you transected the cerebrum away from the brainstem what would happen and why?
Decerebrate posturing/decerebrate rigidity: massive increase in tone of extensors as there is no tonic inhibition of the efferents from the cerebrum and cerebellum
Cause of decerebrate posturing:
Brainstem damage
Cause of decorticate posturing:
Cerebral damage
Which type of posturing is more ‘severe’
Decerebrate
Function of vestibular system:
- Sense of balance and motion detection
- Info about head orientation, movements in 3D space
2 otolith organs:
urticle
saccule
Urticle and saccule detect what using what
Linear movement using macule
Urticle detects =
Horizontal acceleration
Saccule detects =
Verticle acceleration
Structures in the vestibular system:
- Otolith organs
- Semicircular canals
- Ampulla
Semicircular canals detect
Head roation, angular acceleration
What does both the macule and ampulla contain?
Hair cells
Describe the structure of the macule in otolith organs:
Hair cells connected to sensory nerve fibers
Gelatinous cap over the top
Otoliths covering cap which move
Otoliths are
Calcium carbonate crystals
Depolarisation of hair cells occurs when
Stereocillia move toward kinocillum
Hyperpolarisation of hair cells occurs when:
Stereocilla move away from kinocillum
3 semicircular canals:
- Anterior
- Posterior
- Lateral/horizontal
Semiciruclar canals are filled with
Endolymph
Main sensory structure of semicircular canals =
Ampulla
What is found in the ampulla of semicircular canals:
Hair cells
Cupula
Where do sensory nerve fibers of CN VIII project to:
- cerebellum
- down through spinal cord to limbs, neck
- extraocular muscles
Function of vestibulo-ocular reflex:
Compensatory mechanism of eyes, eyes move in opposite direction to head rotation (to maintain a steady image on back of retina)
What would happen in head turns left (VOR reflex)
- Endolymph of left horizontal canal moves right and is excited (left is inhibited).
- Signal to vestibular nuclei which synapses with abducens (opposite side) and oculor motor (same side)
- Right abducens flexes right lateral rectus
- Left oculormotor flexes left medial rectus
- Eye moves right
Name of test for VOR in unconscious patient:
Caloric testing
Calortic testing can be done with:
Cold water
Hot water
Brainstem in tact with caloric testing:
eyes move away (cold)
towards (hot) - in fast nystagmus
Nystagumus =
Involuntary movement of eye
2 phases of physiologic nystagumus:
Slow - slow movement to opposite
Fast - quick movement to same
If in caloric testing only one eye moved what might this suggest.
Bilateral MLF lesion (medial longitudinal fasiculus) lesion
Low brainstem lesion caloric testing:
No movement
What can be used to test the vestibular system
Posture platform studies
What do you do to patient to test vestibular balance system
Blindfold
Reticular formation is important in which kind of postural control:
Anticipatory
Name 3 disorders of the vestibular system:
Menieres syndrome
BPPV - benign paroxysmal postural vertigo
MAV - migraine associated vertigo
Cause of menieres syndrome =
Excess endolymph - distended ducts - damage to membranes
Symptoms of menieres syndrome =
Tinnitus
Sensorineural hearing loss
Vertigo
Treatment of menieres syndrome -
Symptomatic.
Prochlorperazine - nausea and vomiting
Antihistamines - nausea, vomiting, vertigo
Treat hearing
Prochlorperazine moa
Dopamine antagonist (anti-psychotic)
Symptoms of BPPV
Suddenly feeling dizzy on moving head or rolling in bed, nausea, vomiting
Cause of BPPV
CaCO3 crystals from otolith organs dislodge and disrupt flow of endolymph in semicircular canals
Which semicircular canal is involved when turning head left to right
Horizontal
