D1 - Neuro Exam #2

Front 1

Myofibril

Back 1

one of the longitudinal parallel contractile elements of a muscle cell what are composed of actin and myosin.

Front 2

Myofilaments

Back 2

one of the individual filaments of actin or myosin that make up a myofibril

Front 3

Sarcomere

Back 3

a region between z lines, the smallest unit of muscle contraction

Front 4

Thin filament

Back 4

composed of ~ 350 monomers of the contractile protein actin and 50 molecules of the regulatory proteins troponin and tropomyosin

G-actin – globular actin
F-actin – helical strands

G-actin polymerizes into double helical strands forming F-actin

Front 5

Thick filament

Back 5

Mostly myosin.

Myosin molecule – composed of light meromyosin and heavy meromyosin. The heavy meromyosin sticks out a regular interval along the thick filament. The head of the heavy meromyosin contains binding sites for actin and ATP.

Front 6

Organizational Levels of Muscle

Back 6

Muscle -> fascicle -> fiber -> myofibril -> myofilament

Front 7

Organizational Levels of Muscle Connective Tissue

Back 7

Epimysium – Surrounds entire muscle

Perimysium – surronds groups of fibers

Endomysium – surrounds muscle fiber

Front 8

Titin

Back 8

a very large protein attached to the myosin filament and related to the passive properties of muscle.

Front 9

Nebulin

Back 9

is associated with actin and may act as a template for actin filaments.

Front 10

M-line proteins

Back 10

are located in the central portion of the sarcomere and help keep the myosin filaments in their horizontal orientation.

Front 11

C-proteins

Back 11

are found in the thick filaments and keep the myosin tails in orientation.

Front 12

Dystrophin

Back 12

A very large protein which anchors the contractile apparatus to the surface of the membrane. The precise function of dystrophins are not well understood but defects or the absence of dystrophin leads to muscle weakness and degeneration.

Front 13

The A band

Back 13

is an anisotropic (i.e. dark) region which corresponds to the length of the mysin filaments.

Front 14

The area in the A band where there is no overlap of actin and myosin filaments

Back 14

the H zone

Front 15

The I band

Back 15

is an isotropic (i.e. light) region corresponds to the portion of the actin filaments which do not overlap with myosin.

Front 16

M line

Back 16

composed of proteins which keep the sarcomere is proper orientation as it shortens and lengthens

Front 17

Z disk

Back 17

ends of the sarcomere

Front 18

Length of a single saromere

Back 18

2-2.5 microns

Front 19

Sliding Filament Model postulates that:

Back 19

1) thick and thin filaments slide past each other

2) muscle force is related to number of cross bridges

Front 20

Change of I band and A band during muscle contraction

Back 20

I band – shortens, because the I band is the region where the actin filaments do not overlap with myosin

A band – does not shorten, A band corresponds to the myosin filaments

Front 21

The myosin molecule can be split into two major fragments:

Back 21

1. The globular head or S1 fragment, contains the ATPase activity and is the portion that can combine with actin.

2. The S2 portion includes the flexible region of the molecule and a tail. The tail binds with other myosin molecules to form the thick filament. Myosin contains 6 polypeptide chains, two heavy chains and one light chain. The two heavy chains are wound around each other to form a helical structure. At one end both chains are wound around each other to form the two heads.

Front 22

The binding of Ca++ to troponin causes...

Back 22

a conformational change in troponin leading to movement of the tropomysin complex. The movement of the tropmyosin complex exposes the myosin binding sites. Thus calcium bindning to troponin is essential for muscle contraction.

Front 23

steps in excitation-contraction coupling

Back 23

1. action potentials from neuromuscular junction travel along sarcolemma and invade T-tubules

2. T-tubules signal sarcoplasmic reticulum to release Ca++ into cytosol

3. Ca++ saturates tropinin

4. tropomyosin undergoes conformational change which exposes actin binding site

5. myosin head attaches to active site on actin filament (forms cross-bridge)

6. myosin head moves actin-myosin complex forward and releases ADP and Pi

7. ATP binds with myosin head, which releases actin, and returns to original position

8. after action potential invasion, Ca++ is pumped back into sarcoplasmic reticulum


entire cycle (approx. 50 ms)

single cross bridge produces 3-4 pN force and shortens 10nm

Front 24

The transverse tubules are...

Back 24

envaginations of the sarcolemma deep into the muscle fiber

Front 25

Calcium stored in the SR is released through ________ receptors and then binds to troponin on the thin filaments.

Back 25

ryanodine

Front 26

DHP receptors

Back 26

Structures in the T tubule membrane that bind dihydropyridines (DHPs) and act as calcium channel blockers

Front 27

Release of Ca++ from the sarcoplasmic reticulum is in response to...

Back 27

depolarization of the T tubule.

Front 28

Events of muscle contraction

Back 28

1) Action potential propagates along sarcolemma.

2) Depolarization of T-tubular membranes

3) release of Ca++ from sarcoplasmic reticulum

4) Ca++ in myoplasm binds to tropinin and initiates cross-bridge cycling

5) muscle contraction occurs

6) 60 ms from AP to peak muscle force

Front 29

Isotonic contraction

Back 29

a muscle contraction where the muscle contracts and shortens and the muscle shortens against a constant load. Load does not change.

Front 30

Isometric contraction

Back 30

a muscle contraction where the muscle contracts tension increases but the muscle does not shorten. Length does not change.

Front 31

Concentric contraction

Back 31

a muscle contraction in which the muscle shortens

Front 32

Eccentric contraction

Back 32

an eccentric muscle contraction is a muscle contraction where the muscle contracts and lengthens. This type of contraction typically occurs in walking down stairs.

Front 33

Relationship between cross bridge formation and muscle force in a single muscle fiber.

Back 33

maximum muscle tension is developed when the number of cross bridges is highest.

Front 34

Sarcomeres arranged in series produce the most ______ but the least ______

Sarcomeres arranged in parallel generate less _____, and more _____

Back 34

excursion; force

Front 35

Passive tension

Back 35

proteins within the saromere such as titin contribute substantially to the force generated when a muscle is passively stretched.

Front 36

most muscles are of what architecture type?

Back 36

multipinnate

Front 37

Pinnation decreases the force a muscle exerts, but why is it beneficial?

Back 37

pinnation increases number of fibers that can attach to tendon

Front 38

the greater the physiological cross section, the _____ the amount of muscle force that can be produced

Back 38

larger

Front 39

The total tension generated by the ______ muscle drops as the muscle is lengthened beyond the resting length.

In contract to this, the total tension produced by a ______ muscle increases as the muscle is lengthened beyond its resting length

Back 39

parallel; pinnate

Front 40

As the speed of concentric contraction increases, the amount of muscle force decreases.

As the velocity of eccentric muscle contraction increases, the amount of force increases.

Why is this?

Back 40

This is because the muscle is stretched so rapidly that the individual cross bridges cannot detatch rapidly enough and are thought to be ruptured.

Front 41

How is force produced smoothly by muscles?

Back 41

Asynchronous Activity in Different Portions of a Muscle

Front 42

A motor unit consists of:

Back 42

1. a motoneuron axon
3. its terminal branches and
3. the muscle fibers which it innervates.

Front 43

Motor Unit Territory

Back 43

the region of a muscle that the muscle fibers of an individual motor unit occupy.

- fibers comprising a motor unit are in close proximity to each other and in limb muscles usually spread over 10-30% of the muscle and overlap considerably with other motor units. In masticatory muscles motor unit territories are much smaller and more discrete.

Front 44

The smaller the motor unit muscle, the greater the amount of...

Back 44

fine motor control.

Front 45

motor unit size

Back 45

In general, motor units are largest in those muscles which act on the largest body masses.

Medial gastrocnemius - 1000 fibers/unit;
extraocular muscles less than 100 fibers/unit

Innervation Ratio:
Gastrocnemus muscle - 1/1500
Extraocular muscles - 1/3

Front 46

S: Physiological Properties of Type S Motor Units

Back 46

1. slow twitch contraction (50-100ms)
2. twitch force - range (1-5g)
3. repeated contraction does not fatigue the motor unit

Front 47

F: Physiological Properties of Type F Motor Units

Back 47

1. fast twitch contraction (10-50ms)

2. twitch force - range (6-20g)
3. repeated contraction leads to fatigue (i.e. reduced force)

Front 48

Type 1: Biochemical and Morphological Properties of Type I (Slow oxidative) Motor Units

Back 48

1. Small diameter muscle fibers.
2. High levels of succinic dehydrogenase and NADH-dehydrogenase which are enzymes involved in major pathways for oxidative metabolism in the mitochondria.
3. Rich vascularization.
4. These muscle fibers predominately utilize oxidative metabolism.
5. Correlate with physiological type S.

Front 49

Type 2: Biochemical and Morphological Properties of Type II (Fast glycolytic) Motor Units

Back 49

1. Medium to large diameter fibers.
2. High levels of glycolytic enzymes and ATPase related to anaerobic metabolism.
3. Poorly vascularized.
4. These muscle fibers predominately utilize anaerobic metabolism.
5. Correlate with physiological type F.

Front 50

How is muscle force increased?

Back 50

1. - rate modulation - increase in firing frequency of motor units that are already active

2. - recruitment of additional motor units

Front 51

Size principle (muscles)

Back 51

small, slow twitch motor units are activated first and participate in long-lasting but relatively weak contractions.

Fast twitch motor units are activated later, generate more force and fatigue. (some may only be activated in intense movements such as jumping).

Front 52

Muscle Fatigue

Back 52

slowing of conduction velocity

lengthening of relaxation phase of muscle action potential

decrease in motor unit firing rate

Front 53

Gillian-Barré syndrome

Back 53

demyelinating peripheral neuropathy

Front 54

Functions of Muscle Sensory Receptors

Back 54

Proprioception

Kinesthesia

Motor Learning

Compensation for unexpected disturbances

Calibration of movements

Postural control

Front 55

Proprioception

Back 55

sensing the position and movements of the limbs, head, jaws and back. This sensation is generated by receptors that are stimulated by the organism itself, considered to be an unconscious sensation

Front 56

Kinesthesia

Back 56

position sense, or sense of movement this term includes external feedback and influences (such as your feet making contact with the floor). This is considered a conscious sensation.

Front 57

intrafusal fibers

Back 57

small muscle fibers within the spindle receptor (gamma innervation)

force produced by contraction of the intrafusal fibers is negligible.

Front 58

extrafusal muscle fibers

Back 58

skeletal muscle fibers adjacent to the muscle spindle


These are the fibers with which alpha motoneurons synapse to form the neuromuscular junction.

These fibers are the source of contractile force produced by skeletal muscle

Front 59

Passive Stretching of the Muscle Spindle

Back 59

When a muscle is stretched, the muscle spindle receptor is also lengthened activating stretch activated channels in the muscle spindle receptor terminal and generating afferent activity.

Front 60

The Two Types of Muscle Spindle
Sensory Afferent Ending

Back 60

Primary (Ia) afferent ending:
have the largest diameter axons and the fastest conduction velocity (up to 120m/s). generates the most action potentials during muscle stretching. codes Velocity of muscle movement

Secondary (II) afferent ending:
increases its activity in relation to the length of the muscle. codes muscle Length

Front 61

the effects of contraction of homonymous extrafusal skeletal muscle fibers on the afferent discharge of a homonymous muscle spindle receptor.

Back 61

Muscle spindles form monosynaptic excitatory synapses with alpha motoneurons synapsing with extrafusal fibers of the same muscle in which the muscle spindle is located (i.e. homonymous motoneuron). Thus a two-neuron arc is formed.

Activation of the homonymous muscle spindle generates excitatory synaptic input to the motoneurons which contract the extrafusal fibers returning the muscle to the original length.

Front 62

reciprocal inhibition

Back 62

muscle spindle axons form an excitatory synapse with a spinal cord interneuron. This interneuron forms an inhibitory synapse with motoneurons of the heteronymous (or antagonist) muscle

Front 63

fusimotor drive

Back 63

Activation of gamma motoneurons

Front 64

Gamma motoneurons

Back 64

small motoneurons within the ventral horn of the spinal cord (trigeminal motor nucleus for masticatory muscles).

These motoneurons have smaller diameter axons than alpha motoneurons and thus conduct more slowly.

Gamma motoneurons synapse onto the intrafusal muscle fibers within a muscle spindle.

Activation of gamma motoneurons is usually referred to as fusimotor drive.

Activation of gamma motoneurons allows muscle spindle receptors to maintain sensory feedback during muscle shortening and more importantly fusimotor drive from gamma motoneurons alters the sensitivity of the muscle spindle.

Front 65

Dynamic fusimotor effects

Back 65

particularly enhance the output of the primary afferent ending and thus make the spindle more sensitive to changes in muscle length (i.e. velocity and acceleration).


. In learning a new motor task or in behaviors where unexpected movements may be encountered, fusimotor activity is increased. In sedentary behaviors, fusimotor activity is low.

Front 66

Golgi Tendon Organ

Back 66

it is in series with the extrafusal muscle fibers.


The tendon organ receptor endings are intermingled amongst the collagen fibers of the muscle tendon. When the tendon is stretched, the collagen fibers stretch the sensory terminals generating a receptor potential and activation of the tendon organ.


there is no motor innervation to the tendon organ (in contrast to the muscle spindle) thus the tendon organ cannot be adjusted to different behavioral circumstances.

tendon organs monitor the tension produced by a very small number of motor units and thus are involved in small adjustments in muscle tension.

The tendon organ is said to ‘code’ muscle force

Front 67

Activation of Tendon Organ Compared to Muscle Spindle
When the muscle is passively stretched

Back 67

both are activated.

Front 68

Response of Muscle Spindle Afferent and Tendon Organ
When muscle is actively contracted

Back 68

The muscle spindle afferent becomes silent during the muscle contraction. This is because the spindle length is reduced and there is no stretch of the sensory terminals.

In contrast to this, the tendon organ is strongly activated by the muscle contraction. Thus the tendon organ readily senses muscle contraction or active muscle force.

Front 69

Ib inhibition

Back 69

The tendon organ afferent neuron (termed Ib) has an inhibitory synapse onto the homonymous motoneuron.

Front 70

Group III and IV muscle afferents end as...

Back 70

free nerve endings

Front 71

Sensory Fibers from Muscle

Back 71

Ia - Primary spindle ending: muscle velocity, acceleration

Ib - Golgi Tendon Organ: muscle force

II - Secondary spindle endings: muscle length

II - Non-spindle endings: deep pressure

III - Free nerve endings: pain

IV - Free nerve endings: pain, chemical stimuli, temp.

Front 72

Is Tendon organ feedback + or - ?

Back 72

Negative, since the more active the tendon organ, the more it inhibits alpha motoneurons

Front 73

Muscle Tone

Back 73

amount of tension in muscle

Front 74

Hypertonus

Back 74

abnormally high muscle tone

Front 75

Spasticity

Back 75

an involuntary increase in muscle tone during muscle stretching (spastic muscle at rest is flaccid)

Front 76

Clasp-knife reflex

Back 76

abrupt decline in muscle force during movement of a spastic limb (via group III)

Front 77

Tonic Vibration Reflex

Back 77

if a limb muscle is vibrated at 50-150 Hz, a slowly developing reflex contraction occurs. This reflex invovles both monosynaptic and polysynaptic muscle spindle reflexes (via Ia).

Front 78

Dorsal Rhizotomy

Back 78

Muscle spasticity is a common problem in cases of cerebral palsy. If the spasticity cannot be controlled pharmacologically and as a last resort a surgical procedure called a dorsal rhizotomy can be performed. The neurosurgeon examines which dorsal roots contribute to the spasticity and severs those dorsal roots. You know that sensory feedback travels in these dorsal roots so the surgeon is essentially reducing the sensory input to the spinal cord.

Front 79

Convergent pathways to motoneuron pools:

Back 79

1. Segmental reflexes

2. Reticular formation

3. Vestibular formation

4. Red nucleus

5. Cerebral Cortex
a. Basal ganglia
b. cerebellum

Front 80

final common pathway of the motor system

Back 80

Cell bodies of the motoneuron, because all behaviors involving muscle pass through the motoneuron.

Front 81

Segmental neural circuits

Back 81

refers to neural circuits that are primarily restricted to a single segment of the spinal cord.

An example of this would be the monosynaptic stretch reflex. In the reflex the primary afferent neuron is located in the dorsal root ganglion. A central process from this neuron projects to the same spinal cord segment and synapses with a motoneuron within the same spinal segment.

Note that segmental circuits can be within a single spinal segment or can cross multiple segments

Front 82

Descending Motor Pathways

Back 82

1. Corticospinal - major descending motor pathway from the motor cortex to the spinal cord, involved in discrete movements such as fractionated finger movements

2. Rubrospinal - descends from the red nucleus to the spinal cord, important for distal forelimb movement.

3. Reticulospinal - function more generally in posture and balance

4. Vestibulospinal - function more generally in posture and balance

Front 83

Corticospinal Tract

Back 83

Facilitates fine, fractionated
distal movements.

Pathway: most of the corticospinal tract crosses the midline at the pyramidal descussation. Thus lesions of the right motor cortical areas largely affect left motor function

Front 84

Rubrospinal Tract

Back 84

less focused than the corticospinal tract. The rubrospinal tract facilitates distal limb movements. Descending fibers of the rubrospinal tract synapse mostly onto segmental interneurons.

Pathway: originates in the red nucleus, crosses the midline and synapses mainly onto segmental interneurons

Front 85

Reticulospinal tract

Back 85

postural, midline muscles

Pathway: originates in the reticular formation of the brainstem. This tract synapses in medial parts of the spinal cord where it influences local circuit neurons that coordinate axial and postural muscles.

Front 86

Vestibulospinal

Back 86

coordination between semicircular canals and neck and postural movements

Pathway: There is a medial and a lateral vestibulospinal tract. The medial originates from the medial vestibular nucleus while the lateral originates from the lateral vestibular nucleus. The medial vestibular tract terminates bilaterally in the cervical spinal cord where it regulates head position. The lateral vestibulospinal tract terminates in medial parts of the spinal cord and is involved in the control of proximal muscles.

Front 87

Tectospinal

Back 87

orientation and coordination of head movement and visual field

Pathway: originates from the tectum of the brainstem. This tract projects to axial muscles of the neck and is involved in orienting the head in relationship to visual stimuli.

Front 88

list of the generic components of a reflex:

Back 88

1. Receptor – The receptor activates a nerve impulse in a sensory neuron in response to a stimulus.

2. Sensory Neuron – Neuron which conducts the nerve action potential from the receptor to its synaptic terminal in the CNS.

3. Interneurons – Area of integration

4. Motoneuron – integrates and transmits action potential to organ.

5. Effector – The organ of the body which responds to the impulse from the motoneuron.

Front 89

Stretch reflex

Back 89

two neuron reflex arc

the stretch reflex resists changes in muscle length.

initiated by primary and secondary muscle spindle afferent sensory receptors.

excitatory to the same muscle in which the muscle spindle is located.

The muscle spindle afferent cell body is located in the dorsal root ganglion for limb muscles (trigeminal nucleus for jaw muscles).

Impulses are transmitted along the primary afferent fiber into the ventral horn of the spinal cord, where the afferent neuron makes an excitatory synapse with a homonymous motoneuron


If the motoneuron is activated, it sends an action potential to extrafusal muscle fibers of the same muscle that the muscle spindle receptor is located in.

Front 90

Tendon Reflex

Back 90

Ib inhibition

provide exquisitely fine negative feedback of muscle force

disynaptic reflex pathway initiated from a tendon organ receptor

Stretching the tendon activates this receptor


the nerve impulse is then transmitted via a primary afferent neuron in the dorsal root ganglion

this sensory neuron synapses with a segmental interneuron

the segmental interneuron forms an inhibitory synapse with a motoneuron

Thus this reflex inhibits the activity of the motoneuron

Front 91

Flexor Reflex (withdrawal reflex)

Back 91

Initiated via free nerve endings

Primary nociceptive afferent synapses with segmental interneurons (reflex is polysynaptic)

Produces limb withdrawal by activating flexor motoneurons and inhibiting extensor motoneurons.

Front 92

Corneal Reflex

Back 92

Nociceptive Reflex

trigeminal primary afferent neurons, whose receptors are located in the cornea, relay noxious activation to brainstem interneurons

These brainstem interneurons then project to the facial motor nucleus and activated facial motoneurons which contact the orbicularis oculi muscle

this is a bilateral reflex

Front 93

Gag Reflex

Back 93

A protective reflex of the alimentary tract

The primary sensory information for this reflex comes from receptors located in the tonsillar pillars, palate and base of the tongue.

Sensory feedback is conveyed from these receptors via the glossopharyngeal and vagal nerves to the nucleus tractus solitarius.

Projections from the nucleus tractus solitarius to the nucleus ambiguus complete the reflex arc.

the nucleus ambiguus sends efferent fibers to the pharynx causing constriction and elevation of the pharynx

Front 94

Cough Reflex

Back 94

A protective reflex of the upper respiratory tract that involves the active, explusion of air from the airways

Mechanism – there is an initial inspiration and then closing of the glottis, followed by rapid glotic opening and expusion of air with the active participation of the expiratory muscles.

Adequate stimulus – usually resulting from irritation of the mucosa of the larynx, trachea or large brochi, but other vagal nerve fibers are sometimes involved.

CNS connections – afferent impulses reach the solitary tract nucleus by way of the vagus nerve. From there connections are made with the respiratory center to bring about forced expiration, and the nucleus ambiguus to affect changes in the larynx and pharynx.

Front 95

Rotational Movement of the head

Back 95

Yaw – rotation about the z-axis

Pitch – y axis

Roll – x axis

Front 96

respond to linear acceleration of the head

Back 96

two otolith organs (hair cells contained in utricle, saccule)


hair cells divided into populations with different response directions

Front 97

respond to rotational accelerations of the head

Back 97

three semicircular canals (hair cells located in ampullae)


hair cells polarized in one direction

Front 98

Vestibular Hair Cells:
Movement of the stereocilia toward the
_______ opens mechanically gated transduction channels depolarizing the hair cell and causing transmitter release onto the vestibular nerve fibers.

Back 98

kinocilium

Front 99

The sensory epithelium in the otolith organs are called the...

Back 99

macula

Front 100

macula

Back 100

sensory epithelium in the otolith organs

Front 101

Otolith Organs

Back 101

transduce linear acceleration of the head.

The sensory epithelium in the otolith organs are called the macula. This epithelium consists of hair cells and supporting cells.

Overlying the hair cells is a gelatinous layer.

Above this layer is a fibrous structure called the otolith membrane.

Embedded in this membrane are calcium carbonate crystals termed otoconia.

The functional significance of the otoconia is that they make the otolith membrane heavier than the surrounding structures.

Because of this, when the head tilts gravity causes the membrane to shift relative to the sensory epithelium and hair cells are displaced.

Front 102

The macula in the utricles are oriented _____ while the macula in the saccule is oriented _______.

Back 102

horizontally; vertically

Front 103

What is the functional significance of the resting discharge?

Back 103

Resting discharge allows sensitivity in both directions

Front 104

Semicircular Canals

Back 104

The three semicircular canals sense head rotation.

Each semicircular canal has a bulbous expansion called the ampulla.

The ampulla houses the sensory epithelium called the crista which contains the hair cells.

The hair bundles extend out from the crista into a gelatinous mass called the cupula.

The cupula forms a barrier that the endolymph contained within the canal cannot penetrate.

Thus the cupula is distorted by movements of the endolymphatic fluid.

When the head turns in one direction the inertia of the endolymph produces a force across the cupula, distending it away from the direction of head movement and displacing the hair cells.

In contrast to rotational movement, linear accelerations of the head produce equal forces on the two sides of the cupula so the hairs are not displaced.

Front 105

Nystagmus

Back 105

repeated rapid eye movements. In most individuals rotating the head evokes physiological nystagmus. This consists of a slow eye movement counter to the direction of head rotation followed by a rapid movement eye movement (saccadic movement).

Front 106

COWS

Back 106

cold opposite, warm same

If cold water is placed in the ear, convection currents will be set up in the endolymph and direct cooling of the nerve will mimic rotary head movements away from the irrigated ear. In normal individuals this will evoke slow eye movements toward the irrigated ear and a fast movement away from it. The fast movement is most readily detected.

Front 107

Caloric testing used to test brainstem function.

Back 107

. If dysfunction is in cerebral cortex but brainstem is intact, saccadic movements are not made (i.e. lose fast component).

If the dysfunction is in the lower brainstem (i.e. vestibular nuclei, connections from vestibular nuclei to ocular motoneurons or related peripheral nerves), vestibular responses will be altered or abolished.

Front 108

Vestibular feedback is conveyed through the VIII cranial nerve. It arises from bipolar neurons those cell bodies are in the _________ ganglion

Back 108

vestibular (Scarpa’s ganglion).

Front 109

Vestibulo-Ocular Reflex

Back 109

The vestibular-ocular reflex keeps the visual field fixed onto the retina during head movement.

The neural circuit consists of primary afferent input to the vestibular nuclei. Output from the vestibular nuclei then project as excitatory and inhibitory pathways to the motor nuclei of eye muscles

Front 110

Vestibulospinal Tract

Back 110

The LATERAL vestibulospinal tract is an uncrossed tract that originates from the lateral vestibular nucleus and is predominately an otolith signal. Fibers descend in the ventral white column and terminate on alpha and gamma motoneurons at all levels of the spinal cord. This tract is important in regulating muscle tone throughout the body such that balance is maintained.


Fibers from the MEDIAL vestibular nucleus descend in the medial vestibulospinal tract and mediate primarily a canal signal. This tract terminates in the ventral horn throughout the cervical region. This tract is thought to mediate changes in the tone of neck muscles required to support the head in various positions.

Front 111

Thalamo-Cortical Vestibular Pathways

Back 111

In addition to descending pathways, vestibular feedback is projected to the thalamus (ventral posterior nuclei) and then relayed to the cerebral cortex. Two areas of the cortex receive vestibular information.


These areas are thought to be involved in the perception of body orientation in extrapersonal space.

Front 112

Motor unit types

Back 112

PHYSIOLOGICAL:

FF - Fast fatigable - high force, fast contraction speed but fatigue in a few seconds.

FR - Fast fatigue resistant - intermediate force, fatigue resistant - fast contraction speed and resistant to fatigue.

FI - Fast intermediate - intermediate between FF and FR.

S - Slow (oxidative) - low force, slower contraction speed, highly fatigue resistant.

BIOCHEMICAL:
I - Low glycolytic and high oxidative presence. Low(er) myosin ATPase.
IIa - High glycolytic, oxidative and myosin ATPase presence

IIb - High glycolytic and myosin ATPase presence. Low oxidative presence.

IIi - fibers intermediate between IIa and IIb.

Histochemical and Physiological types correspond as follows:
S and Type I
FR and type IIa
FF and type IIb
FI and IIi.