NEURO: Quiz 4 Flashcards
Golgi tendon organ reflex (unloaded muscle)
- Steps
- Components
- Purpose
Basic reflex:
(1) Muscle contracts
(2) Depolarize 1b afferent fiber
- - Carries signal into gray matter of spinal cord
(3) Synapse on 1b inhibitory interneuron
(4) Ib inhibitory interneuron synapses on alpha motor neuron
- - Inhibits efferent signal to muscle
(5) Muscle relaxes
Purpose:
- Response to very fine changes in muscle force (e.g., soft hands)
- Big response of big muscles in arm
- Gentle response of muscles in hands
NOTE: Ib inhibitory interneuron excited/inhibited by various inputs;
- Ib afferent
- Other interneurons from:
- Muscle spindle
- Cutaneous receptors
- Cortical paths
- Inputs excite/inhibit IB inhibitory interneuron activity
- In turn decreasing/increasing alpha MN activity
- If it fires, it inhibits alpha MN
- If it doesn’t, it excites alpha MN
Monosynaptic stretch reflex
- Steps
- Components
- Grading
- Clinical and functional roles
- Latency
(1) Muscle stretched (e.g., tendon tap)
- - Muscle spindle stretched
(2) 1a afferent fiber depolarized by stretch
- - Annulospiral endings wrap intrafusal fibers (static and dynamic)
- - Detects change in muscle length
- - Impulse travels via DRG to spinal cord gray matter
(3) Ia synapses with alpha and gamma motor neurons (anterior horn)
- - Alpha MN sends signal to extrafusal fibers to contract
- - Gamma MN sends signal to ends of intrafusal fibers to contract
(4) Muscle contracts
- - Contractile ends of intrafusal pulls center taut
- - Muscle spindle remains sensitive to further stretch
Grading: 0 = no response 1 = decreased relative to other side 2 = normal 3 = exaggerated relative to other side 4 = hyperreflexive (clonus in extreme case)
Clinical role
– Test integrity of spinal cord circuity
Functional role
– Regulate muscle stiffness
– Correct/prevent small movement errors
Latency = Time to cross single synapse (~30 s)
Reciprocal inhibition
Autogenic inhibition
State dependent reflex reversal
Reciprocal inhibition
– In order for agonist to contract, antagonist must relax:
– Stretch muscle and depolarize 1a
– 1a synapses in SC gray matter:
– Alpha MN = excitatory signal to agonist
– Inhibitory interneuron – alpha MN = inhibitory signal to antagonist
– Result:
– Agonist contract
– Antagonist relax
NOTE: Occurs concurrent with gamma MN signal to muscle spindle intrafusal fibers (alpha-gamma coactivation)
Autogenic inhibition:
- Unloaded muscle experiences sudden strenuous contraction
- GTO Ib afferent synapses on Ib inhibitory interneuron
- Ib inhibitory interneuron synapses on alpha motor neuron
- Hyperpolarizes alpha motor neuron (inhibits its activity)
- Muscle relaxes
State dependent reflex reversal:
– Loaded muscle (e.g., bearing weight) experiences sudden strenuous contraction
– GTO Ib inhibitory interneuron is INHIBITED
– Depolarizes alpha motor neuron (excites its activity)
– Muscle contracts
NOTE: SDRR also helped by:
– Sudden load also causes slight stretch of muscle (eccentric contraction)
– Muscle spindle facilitates contraction (increase alpha MN firing)
– Descending (motor) pathways also facilitate muscle contraction to prevent a fall
Muscle spindle
- Definition
- Location
- Components
Definition:
- Sensory receptor that detects change in muscle length (proprioceptive)
- Conveys length info to the CNS via sensory neurons
- Info processed by the brain to determine the position of body parts
- Info activates MNs via the stretch reflex to resist muscle stretch
Location:
- In parallel with muscle fibers (muscle cells) within muscle belly
- Embedded in extrafusal muscle fibers
Components:
(1) Intrafusal fibers (3 types) (3-12 fibers per spindle)
– Dynamic nuclear bag
= Sensitive to small, rapid change in length
– Static:
= Sensitive to steady-state muscle length
– Static nuclear bag
– Nuclear chain
(2) Afferent fibers
– Type Ia afferent (annulospiral endings)
– Detect onset of stretch
– Carry impulse from dynamic and static fibers
– Type II afferent (flower spray endings)
– Sensitive to sustained stretch
– Carry impulse from static fibers
(3) Efferent fibers
– Cause ends of intrafusal fibers to contract when muscle contracts
– Center of fibers remain taut and sensitive to stretch
– Dynamic gamma motor neurons
– Signal to dynamic fibers
– Static gamma motor neurons
– Signal to static fibers
Golgi tendon organ (GTO)
- Definition
- Purpose
- Location
- Components
Definition:
– Sensory receptor sensitive to TENSION
– Sensitive to small changes in force
– Constantly active
Purpose:
– Coordinates large and small force production at various muscles to complete a task
– Provides CNS with time info about muscle force changes
Location:
– In SERIES with muscle fiber
– Within musculotendinous junction
Components:
– Type Ib afferent fibers
– Endings intertwined with collagen fibers of tendon
– Collagen pinches nerve endings when muscle contracts
Alpha and gamma MN coactivation
- Muscle stretch
- Proprioceptive information
- Muscle contraction
- Muscle steady-state length
Muscle stretch:
- Extrafusal muscle fibers stretch
- Muscle spindle stretched in middle
- Ia afferent depolarizes (increases firing rate to CNS)
- Proprioceptive information to CNS:
- Change in muscle length
- Change in position of limb
- Speed of change
Muscle contraction:
- Ia afferent synapses on:
- Alpha MN – Extrafusal fibers contract
- Gamma MN – Intrafusal fiber ends contract (stretch middle)
- Muscle spindle remains taut and sensitive to stretch
- Sends info to CNS about limb position change
Muscle steady-state length:
– Type IIa fibers increase firing rate
– Equal to firing rate of type Ia
– Provide constant background noise to CNS
– Type I then resets itself so it is able to respond to sudden change in length
NOTE: Occurs during very short period between stretch and contraction
Propriospinal tracts
- Definition
- Purpose (e.g., role in reflexes)
= Intrinsic circuits of the spinal cord
- Intersegmental spinal tracts along edge of gray matter
- Connect all segments of the spinal cord
Purpose:
- Coordinate and synchronize reflex activity on both sides of body
- Make polysynaptic reflexes possible, including movements between:
- Proximal and distal segments of one limb
- Upper and lower limbs
- Lower limbs on each side of body
- Carry proprioceptive info (e.g., Lissauers Tract)
Flexor withdrawal - Crossed extension reflex
- Polysynaptic
- Multi-level
- Bilateral
Polysynaptic = > 1 level involves interneuronal pathway
- Multilevel = Mass flexion ipsilateral to stimuli (flexor withdrawal)
- Bilateral = Mass flexion ipsilaterally and extension contralaterally (crossed extension)
Pathway:
S1: Painful stimulus – Free nerve ending
– A-Delta fiber stimulated (sharp, fast pain)
– Connects to Lissauers tract – ASCEND
L5: Collateral fiber – SYNAPSE
– Excitatory interneuron (ipsilateral) – SYNAPSE
– Alpha motor neuron to knee flexors (hamstrings)
– Ipsilateral knee FLEXION
– Signal continues along Lissauers Tract – ASCEND
L4: Collateral fiber – SYNAPSE
– Excitatory interneuron (contralateral) – SYNAPSE
– Alpha motor neuron to hip extensors
– Contralateral hip EXTENSION
– Signal continues along Lissauers Tract – ASCENDS
L2: Collateral fiber – SYNAPSE
– Excitatory interneuron (ipsilateral) – SYNAPSE
– Alpha motor neuron to hip flexors
– Ipsilateral hip FLEXION
NOTE: Contralateral extension occurs to keep us from falling when leg flexes
Central pattern generator
= Neural network that produces rhythmic output without sensory feedback
– Exists for all rhythmic movements in animals (e.g., walking, breathing, swimming)
In humans:
- Flexor withdrawal/crossed extension reflex forms basis for walking CPG
- Spinal cord produces stepping gait w/o cortical input (e.g., below spinal cord lesion)
- Can replicate normal walking ability using reflexes
UMN syndrome disorders
- Hyperreflexia
- Spastic paralysis
LMN syndrome disorders
- Hyporeflexia
- Flaccid paralysis
UMN syndrome:
- Hyperreflexive = Increased or exaggerated reflexes
- Spastic = Increase in resistance to passive stretch (excess tone)
- Velocity dependent
- Most often in anti-gravity muscles (UE flexors and LE extensors)
- Disorders affect UMN (CNS) control of reflexes
- Stroke
- Multiple sclerosis
- Cerebral palsy
- Spinal cord injury
- Traumatic brain injury
UMN syndrome:
- Hyporeflexive = Diminished or absent reflexes
- Flaccid = Decrease in resistance to passive stretch (no tone)
- Disorders affect peripheral part of reflex loop:
- Afferent: Sensory neuropathy (e.g., diabetes)
- Efferent:
- Poliomyelitis (anterior horn cells)
- AIDP (acute inflammatory demyelinating polyneuropathy or Guillan Barre)
- ALS
- Botulism
- Efferent:
NOTE: Paralysis = inability to move; paresis = weakness
Descending motor pathways
= UMN tracts descending from brain or brainstem to spinal cord
– Regulate (inhibit) spinal reflexes to prevent interference with movement
Lateral corticospinal = from primary motor cortex
Rubrospinal = from red nucleus
Vestibulospinal = from pons and medulla
Reticulospinal = from reticular system
Anterior corticospinal = from primary motor cortex
Visual deficits
- Single eye blindness
- Bitemporal hemianopsia
- Nasal hemianopsia (R/L)
- Homonymous hemianopsia (R/L)
- Homonymous inferior quadratic hemianopsia (R/L)
- Homonymous superior quadratic hemianopsia (R/L)
- Homonymous hemianopsia with macular preservation (R/L)
Causes:
– Single eye blindness = Optic neuritis, trauma
– Bitemporal hemianopsia = Damage to optic chiasm (e.g., pituitary tumor)
– Nasal hemianopsia (R/L) = Pressure from aneurysm of ICA (most lateral fibers)
– Homonymous hemianopsia (R/L):
– Anterior choroidal artery dysfunction
– Tumor or abscess of temporal lobe
– Homonymous inferior quadratic hemianopsia (R/L) = Superior opposite side visual cortex
– Occipital or parietal lobe tumor
– Homonymous superior quadratic hemianopsia (R/L) = Inferior opposite side visual cortex
– Occipital or temporal lobe dysfunction
– Homonymous hemianopsia w/ macular preservation (R/L)
= Visual cortex except most posterior pole
– Posterior cerebral artery dysfunction, trauma, tumor
Named for deficits in visual field:
- Right, left or bilateral
- Temporal or nasal
- Homonymous = both eyes affected on same side
- Hemianopsia = half visual field is blind
- Anopsia = blindness
- Quadratic = one quadrant affected only
- Superior or inferior
- Macular preservation = central field unaffected
Cochlear hair cells
- Location
- Gelatinous material
- Stimulus
Vestibular hair cells
- Locations (2)
- Gelatinous material
- Stimulus
Cochlear:
- Location = Organ of Corti (in basilar membrane)
- Gelatinous = Tectoral membrane (overlays Organ of Corti)
- Stimulus = Sound
Vestibular: Semi-circular canals -- -- Location = Christae (inside ampullae) -- Gelatinous = Cupula (inside ampullae) -- Stimulus = Angular acceleration (head rotation)
Saccule and utricle (otolithic organs)–
- Location = Macula (within otolithic organs)
- Gelatinous = Otolithic membrane (with CaCO3 otoconia)
- Stimulus = Linear acceleration (up/down, ant/post, lateral)
Vestibulocochlear hair cells
- Anatomy
- Locations
- Depolarization/Hyperpolarization
= Common sensory transducers for auditory and vestibular systems
Anatomy:
– Cell body with cilia in gelatinous material
– Stereocilia = 1000s per cell (short)
– Kinocilium = 1 per cell (long)
– Tip links = connect cilia
– CN VIII at base (cochlear or vestibular branch)
Locations:
– Cochlea – Organ of Corti
– Vestibular apparatus
– Semicircular canals – Christae (within ampullae)
– Saccule and utricle – Macula (within otolithic organs)
Depolarization/Hyperpolarization:
– Movement of perilymph at a given frequency
– Kinocilium bends away from stereocillia (EXPANSION)
= Stereocilia bend TOWARD kinocilium – DEPOLARIZE
= Impulse sent via CN VIII to brain
– Kinocilium bends towards stereocillia (COMPRESSION)
= Stereocillia bends AWAY from kinocillium – HYPERPOLARIZE
= No impulse sent
NOTE: Each section of basilar membrane is most sensitive to a given frequency of sound b/c of orientation of hair cells attached to membrane (different hair cells depolarize or hyperpolarize at different frequencies)
Ear structures
- Outer ear
- Middle ear
- Inner ear
Outer ear (air filled)
- Auricle = Ear lobe
- External auditory meatus = Ear canal
- Tympanic membrane = Border with middle ear
Middle ear (air filled)
- Ossicles = Bony structures
- Malleus (hammer) = Attached to tympanic membrane
- Incus (anvil)
- Stapes (stirrup) = Attached to oval window
- Eustachian (Pharyngo-Tympanic) tube = Connects ear to throat
- Oval and round window = Border with inner ear (superior and inferior)
Inner ear (fluid filled): Contains membranous labrynthe (cochlea and VA)
– Vestibular apparatus
– Semicircular canals = Angular acceleration
– Anterior, posterior, and horizontal
– Otolithic organs (utricle and saccule) = Linear acceleration
– Cochlea = Auditory structure
– CN VI (Facial) and VIII (Vestibulocochlear)
= Exit via internal auditory meatus
Cochlea structures
– Basilar membrane
= Horizontal division of scala tympani and media
– Contains Organ of Corti
– Organ of Corti = Sensory receptor
– Embedded in basilar membrane
– Contains hair cells
– Overlain by gelatinous tectoral membrane
– Converts mechanical vibration (perilymph movement) to electrical signal)
– Tectoral membrane = Gelatinous material over Organ of Corti
– Creates drag in fluid
– Causes cilia of hair cells to move (depolarize or hyperpolarize)
– Spiral ganglion = Cochlear end of CN VIII
– Receives impulses from depolarized hair cells
– Relays impulse to auditory (i.e., cochlear) nerve (first order neuron)
Spaces (superior to inferior):
- Scala vestibuli = Contains perilymph (surrounds tube)
- Reisnners membrane at base
- Scala media = Contains endolymph (middle of tube)
- Basilar membrane at base
- Scala tympani = Contains perilymph (surrounds tube)
Associated bony structures:
- Bony core = Surrounds membranous cochlea
- Petrous ridge = Petrous portion of temporal bone contains cochlea
- Internal auditory meatus = Passage for CNs VII and VIII
Retina visual pathway
- Light – External to internal (passes through 3 layers)
- Pigment epithelial cells (base of retina) = Sensory receptors
- Rods and cones = First order neurons – DEPOLARIZE
- Rods (100-125 million) = Vision in low intensity light
- Cones (6-7 million) = Color vision and visual acuity
- Bipolar cells = Second order neurons – DEPOLARIZE
- Ganglion cells = Third order neurons – DEPOLARIZE
- Optic nerve (CN II) to visual cortex
- Rods and cones = First order neurons – DEPOLARIZE
NOTE: Light first passing through layers helps filter and diminish light (otherwise would be too bright to interpret)
Visual pathway: Ganglion cells – Visual cortex
Visual field:
- Peripheral vision
- Central field of vision
- Middle field of vision
- Upper vs. lower
- Right vs. left
Ganglion cells = Third order neurons
- Form OPTIC NERVE (at optic disc) – Exit eye
- Optic nerves bifurcate at OPTIC CHIASM
- Fibers transmit to side of brain where light hit retina
- Optic nerves bifurcate at OPTIC CHIASM
- Fibers from both eyes merge in OPTIC TRACT
- Synapse at LATERAL GENICULATE body = Fourth order neurons
- Travel posteriorly via OPTIC RADIATIONS
- End in visual cortex of occipital lobe (upper/lower calcarine cortex)
Visual field – Visual cortex:
- Peripheral vision – Anterior
- Central field vision – Posterior (occipital pole)
- Middle field vision – Middle
- Upper visual field – Lower retina and visual cortex
- Lower visual field – Upper retina and visual cortex
- Right visual field – Left retina and visual cortex
- Left visual field – Right retina and visual cortex
Pupillary light reflex pathways
- Parasympathetic
- Sympathetic
Constriction (parasympathetic)
- Light – Retina
- Optic nerve
- Optic tract
- THROUGH lateral geniculate
- Brachium of superior colliculli
- SYNAPSE tectal nuclei (superior colliculli) on 2 neurons (one per eye)
- 2 SYNAPSES Edinger-Westphal nucleus (of oculomotor nucleus)
- Preganglionic parasympathetic neurons (one per eye)
- 2 SYNAPSES ciliary ganglia (one per eye)
- Ciliary nerves (one per eye)
- Sphincter pupillae muscles – PUPIL CONSTRICTS
Dilation (Sympathetic)
- Hypothalamus – T1-4 – Lateral horn – Ventral root
- White rami communicantes – Sympathetic chain
- Superior cervical ganglia – SYNAPSE
- Postganglionic neurons – Carotid plexus (arteries)
- Dilator pupillae muscles – PUPIL DILATES
NOTE: Dilation can also occur just by decreasing parasympathetic input
Accommodation reflex
- Components
- Pathway
= Process in which clear visual image is maintained as gaze shifts far to near
Components:
- Lens thickens (becomes rounder)
- Pupil constricts
- Eyes converge (ADD)
Pathway:
- Visual (occipital) cortex –
- Superior colliculli (tectal nuclei) – 2 SYNAPSES (one per eye)
- Oculomotor nucleus (2 synapses per eye = 4 total)
- Parasympathetic fibers
- Edinger-Westphal nucleus
- Ciliary ganglion – Ciliary nerves
- Sphincter pupillae (constriction) and ciliary muscles (lens accommodation)
- Parasympathetic fibers
- Somatic fibers
- Somatic nuclei
- Medial rectus muscles (ADD of eyes)
Eye movements
- Muscle(s)
- Test
- Nerve
Elevation
- Superior rectus – CN III (Oculomotor)
- Inferior oblique – CN III (Oculomotor)
- H-Test
Depression
- Inferior rectus – CN III (Oculomotor)
- Superior oblique – CN IV (Trochlear)
- H-Test
Abduction
– Lateral rectus – CN VI (Abducens)
Adduction
– Medial rectus – CN III (Oculomotor)
Extorsion = Rotate eye away from nose
- Inferior oblique – CN III (Oculomotor)
- Tilt head (watch for eye alignment)
Intorsion = Rotate eye toward nose
- Superior oblique – CN IV (Trochlear)
- Tilt head (watch for eye alignment)
Gaze movements:
- Definition
- CNS centers
- Conjugate
- Saccades
- Smooth pursuit
- Vestibulo-ocular reflex
- Optokinetic movements
- Disconjugate
- Vergence
- Fixation
Conjugate = Eyes move same direction
– Saccades
= Rapid, steplike movements used to acquire image on fovea (700-900 deg/s)
– Frontal eye field and superior colliculli
– Smooth pursuit
= Slow tracking of object
– Frontal eye field and superior colliculli
– Vestibulo-ocular reflexes
= Hold image on fovea during head movement (all directions)
– Very short latency
– Oscillopsia = absence of reflex (jerky vision)
– Semicircular canal – CN VIII – Vestibular nuclei
– Optokinetic movements
= Track and re-acquire slow moving objects
– Optokinetic nystagmus = beating eyes tracking fast moving objects
– Vestibular nuclei
Disconjugate = Eyes move opposite
- Vergence = Keep object in focus as it moves near or far
- Convergence = Both eyes ADD as object approaches
- Divergence = Both eyes ABD as object moves away
- Superior colliculli
– Fixation
= Maintenance of focus on object
– Higher cortical centers suppress brainstem activity
Gaze movement pathway
- General pathway
- CNS centers
Pathway:
-- Movement trigger
= Gaze shift -- FEF, SC, VN
= Object moves -- FEF, SC
-- Brainstem centers
-- Pontine reticular formation
-- Medullary reticular formation
-- Medial longitudinal fasciculus
-- CN nuclei: Trochlear, Oculomotor, Abducens, (Accessory)
-- Eye muscles -- Movement execution
-- Cerebellum and basal ganglia -- Movement refinement ("rehearsal")
CNS Centers:
- FEF Frontal eye field = Plans movement
- Superior colliculli = Triggers movement
- Vestibular nuclei = VO reflex and Optokinetic movements
- NOTE: VOR pathway = SCC – CN VIII – VN – Brainstem – MLF – CNs
- Brainstem centers (PRF, MRF) = Program movement
- Cerebellum = Refines timing of movement
- Basal ganglia = Refines amplitude of movement
Vestibular cerebellum
- Structures
- Roles
Structures:
- Nodulus = Anterior center
- Flocculi = Anterior, inferior to cerebral peduncles
- Cerebral peduncles
- Oculomotor vermis = Medial, posterior
Roles:
- Gaze stability
- Postural stability
NOTE: Damage causes “gaze-based ataxia”
– Over and undershooting when tracking object
