Motor Control

Question 1

What is motor control?

Answer 1

Motor control involves a dynamically changing mix of conscious and unconscious regulation of muscle force, informed by continuous and complex sensory feedback, operating in a framework sculpted by evolutionary pressures.

Question 2

What are the types of motor control?

Answer 2

Voluntary: running, walking, talking playing guitar etc.,…….
Involuntary: eye movements, facial expressions, jaw, tongue, postural muscles throughout trunk, hand and fingers, diaphragm, cardiac, intercostals (around lungs), digestive tract……

Question 3

What are the key concepts of motor control?

Answer 3

Motor control governed by lower and upper motor neurons.

•The lower motor neuron begins (has its cell body) in brainstem or spinal cord and projects to the muscle

•The upper motor neurons originate in higher centres and project down to meet the lower motor neurons

Question 4

How do basal ganglia and cerebellum differ?

Answer 4

In the sensorimotor system

Basal ganglia - what to do
Cerebellum - how to do it

Question 5

What is the overview of the sensorimotor system?

Answer 5

A descending controls system but with lots of ascending feedback

Association cortex -> motor cortex -> brainstem circuits -> spinal circuits -> motor unit -> effect on world -> sensory systems

Question 6

How do muscle fibres act?

Answer 6

Individual muscle fibres act in an ‘all-or-none’ manner, and so control of muscle force depends on the way in which lower motor neurons activate different types of muscle fibre.

Question 7

What are muscles like?

Answer 7

Make up about 40% of body weight
•Three types: cardiac, smooth, skeletal

•Smallest is the stapedius, found in the inner ear
•Largest is the gluteus maximus, found in the hip/buttock
•Strongest (based on weight) is the masseter, found in the jaw
•Hardest working?
•Heart (3 billion beats over average lifetime [no rest!])
•Eye muscles (10,000 precisely controlled movements in 1 hour of reading)
•Neck (keeps your 5Kg head in position)

Question 8

How do muscles act?

Answer 8

Muscles can only contract or relax (i.e. stop contracting)
•The activation of muscle fibres is all or none
•So how do we achieve such a range of movements and forces ??
•Antagonistic arrangement – combined co-ordinated action
•Recruitment of muscle fibres – fast/slow twitch, small and large motor units (see later)

Question 9

What are muscle fibres like across individuals?

Answer 9

The number of muscle fibres varies across individuals, but changes little with either time or training – appears to be genetically determined

Question 10

How do muscles contract?

Answer 10

A skeletal muscle is attached to the bone by the tendon
•A skeletal muscle comprises several muscle fasciculi (group of muscle fibres)
•A muscle fasciculus comprises several muscle fibres (= muscle cells)
•A muscle fibre is constituted of several myofibrils
•Myofibrils contain protein filaments: Actin and Myosin myofilaments
•When the muscle fibre is depolarised actin and myosin slide against each other which produce muscle contraction

Question 11

What is the myosin cross-bridge cycle?

Answer 11

Release of the neurotransmitter acetylcholine (ACh) triggers a biochemical cascade in muscle cells.

calcium ions, magnesium ions and ATP (energy)

Actin involved

Question 12

What is the rigor mortis?

Question 13

How does the myosin cross-bridge cycle occur?

Answer 13

The release of acetylcholine causes a cascade of events resulting in the release of packets of calcium from inside the muscle cell (fibre)

This causes the myosin head to change shape, enabling it to bind with the actin filament

ATP (provides energy for cells) is required to break the bond between the myosin head and the actin filament

ATP is produced by oxidative metabolism, which stops upon death

So the muscle become contracted and remain that way until enzymes begin to disrupt the actin/myosin

Question 14

What is a motor unit?

Answer 14

Motor unit = single alpha () motor neuron + all the muscle fibres it innervates – Different motor neurones innervate different numbers of muscle fibres – fewer fibres means greater movement resolution - those innervating finger tips and tongue

Question 15

What are motor units like?

Answer 15

The motor unit is the final common pathway for motor control
• Activation of an alpha motor neuron depolarises and causes contraction of all muscle fibres in that unit (all or none)
• Muscle fibres innervated by each unit are the same type of fibre and often distributed through the muscle to provide evenly distributed force (and may help reduce effect of damage)
•More motor units fire – more fibres contract – more power

Question 16

What is the control of muscle force like?

Answer 16

Average number of muscle fibres innervated by single motor neuron (a motor unit) varies according to two functional requirements for that muscle:
1. Level of control
2. Strength
Typically a range of motor units in a muscle, some with few, some with many fibres.

Question 17

What is the size principle for control of muscle force?

Answer 17

Size Principle
Control of Muscle Force
Units are recruited in order of size (smallest first)
Fine control typically required at lower forces
Try playing the violin with weights attached to your arms!!

Question 18

What are the speed of muscle fibres?

Answer 18

Slow
Fast fatigue resistant
Fast fatigable

Question 19

What is the difference between between fast and slow muscle fibres?

Question 20

What are lower (alpha) motor neurons?

Answer 20

Originating in the grey matter of the spinal cord, or in the brainstem, an alpha motor neuron and the muscle fibres it connects to represent the ‘unit of control’ of muscle force.

Question 21

What is the motor pool?

Answer 21

All the lower motor neurons that innervate single muscle

•The motor pool contains both the alpha and gamma motor neurons (see later)

•Motor pools are often arranged in a rod like shape within the ventral horn of the spinal column

Question 22

Where do alpha motor neurones originate from?

Answer 22

Alpha Motor Neurons originate in the Spinal Cord

Question 23

What are the arrangements for alpha motor neurons?

Question 24

What are alpha motor neurone origination like?

Answer 24

Cell bodies in the ventral horn: activated by:
•Sensory information from muscle
•Descending information from brain

Note the closeness and prominence of sensory input to the dorsal horn indicated in this diagram

Question 25

What is sensing in muscles?

Answer 25

Muscles can be contracted or relaxed to provide movement, but a good control system (the CNS) needs to know two things: (1)how much tension is on the muscle; (2)what is the length (stretch) of the muscle Key part in proprioception Golgi tendon organs sense tension Muscle spindles sense stretch

Question 26

What are Golgi tendon organs like in muscle tension (force)?

Answer 26

The GTO is within the tendon (where the muscle joins to bone) •Mostly, it sends ascending sensory information to the brain via the spinal cord about how much force there is in the muscle •Critical for proprioception Under conditions of extreme tension, it is possible that GTOs act to inhibit muscle fibres (via a circuit in the spinal cord) to prevent damage

Question 27

What are muscle spindles like In muscle length (stretch)?

Answer 27

Muscle spindles sense the length of muscles, i.e. the amount of stretch •This information forms a key part of reflex circuits…….

Question 28

What are the reflex circuits?

Answer 28

C5 – Biceps C6 – Biceps, Brachioradialis C7 – Triceps L4 – Patellar (knee jerk) S1 – Achilles (ankle jerk)

Question 29

What are reflexes like?

Answer 29

Reflexes can be quite simple or quite complex. They can operate without engaging with the brain, and are critical for the avoidance of injury and effective motor control

Question 30

What is the reflex circuit?

Answer 30

Most simple reflex – MONOSYNAPTIC – e.g. the patellar tendon reflex Extradural and intramural muscle fibres etc

Question 31

What is the reflex circuit?

Answer 31

Most simple reflex – MONOSYNAPTIC – e.g. the patellar tendon reflex Extradural and intramural muscle fibres etc

Question 32

What system detects stretch?

Answer 32

We need a system to detect stretch regardless the current muscle length If intrafusal muscle fibre is controlled by same motor neurons as extrafusals, when muscle is slack (or taught), the system won’t be sensitive to slight changes So, intrafusal fibres are innervated separately, by gamma () motor neurons They keep the intrafusal fibres set at a length that optimises muscle stretch detection

Question 33

What is the imp of muscle spindle feedback?

Answer 33

An efficient motor control system needs to know how much each muscle is stretching – information provided by muscle spindles

Question 34

What occurs in muscle spindle feedback?

Answer 34

Embedded within most muscles Composed of intrafusal fibers Detect stretch regardless of the current muscle length Sensory fibres are coiled around the intrafusal fibers Intrafusal fibers are innervated separately, by gamma () motor neurons They keep the intrafusal fibers set at a length that optimizes muscle stretch detection Muscle sensory receptors = muscle spindles

Question 35

What is the simplest reflex?

Answer 35

Stretch reflex

Question 36

What occurs in the quadruped reflexes?

Answer 36

In quadrupeds, sequence and precise control of limb movements appears complex and is substantially altered by speed changes (e.g. walk, trot, gallop) Under control of higher brain centre…? NO! Quadrupeds will walk on treadmill if weight supported if spinal cord damaged at thoracic level Will change to appropriate patterns of limb movement as treadmill speed is altered Complex reflex system responding to nothing more than stretch of muscle spindles!!

Question 37

What occurs in the withdrawal reflex?

Answer 37

Reciprocal Innervation Principle described by Sherrington (also called Sherrington’s Law of reciprocal innervation) Reciprocal innervation of antagonistic muscles explains why the contraction of one muscle induces the relaxation of the other Permits the execution of smooth movements

Question 38

What is the buttered cat paradox?

Question 39

Why do cats always land on their feet?

Answer 39

More complex reflexes (4)! The righting reflex, or vestibular righting reflex Vestibular system detects that the body is not upright (orientation), as well as any acceleration due to gravity (i.e. falling) Information from the vestibular system is combined with visual, somatosensory and proprioceptive sensory input in order to specify a pattern of motor activity that will restore ‘uprightness’ and a safe landing The cerebellum, which compares the intended motor plan with the actual situation is critical for computing the desired motor activity (see next in lecture)

Question 40

What is variable muscle force provided by?

Answer 40

Variable muscle force is provided by gradual recruitment of motor units

Question 41

why is it so hard to build robots that can walk, run, track moving objects with robotic eye etc….?

Answer 41

Control of gross movement patterns (which can be quite complex) can be devolved to simple spinal circuitry, but constant modulation based on sensory feedback is required to account for the unexpected. •Higher CNS centres constantly adjust ongoing activity to resolve conflicting demands on the motor system and direct it towards goals.

Question 42

What are the brainstem structures like?

Answer 42

Pathways and nuclei within the brainstem (and midbrain) connect sensory input to motor output in quite direct ways, providing an evolutionarily ancient but still very important control system.

Question 43

What is the ancient brainstem motor control?

Answer 43

without cortical involvement e.g. balance and postural control …also orienting, gross limb movement/positioning Vestibular organ - effects on oculomotor control - head movement - vertical positioning of eyes e.g. branches of vagus nerve project to larynx to control speech – this circuit richly interconnected with cerebellum and other brainstem sensorimotor systems Also control of respiration!!

Question 44

What is a combination of ancient and modern cooperation?

Answer 44

Speech : primitive sounds sculpted by cortex In many motor activities, ancient and modern (cortical) control systems work co-operatively…

Question 45

What is the primary motor cortex like?

Answer 45

Primary motor cortex exerts quite direct, top down control over muscular activity, with as few as one synapse (in the spine) between a cortical neuron and innervation of muscle cells

Question 46

What are descending projections from cortical motor areas?

Answer 46

Motor command originates in motor cortex pyramidal cells (in layer 5-6, grey matter). •These are the upper motor neurons. •Pyramidal cell axons project directly or indirectly (e.g. via brainstem) to spinal cord, where they synapse with lower motor neurons. •The axons of these upper motor (pyramidal) neurons form the pyramidal tract •Most cortical projections innervate contralateral motor units

Question 47

What is the hommunculus?

Answer 47

Homunculus is a reasonable representation, but an oversimplification: damage to a single finger area doesn’t mean loss of voluntary control of that finger. •Representations are more complex and overlapping •After all, few motor commands require isolated activation of a single motor unit Involved In motor control

Question 48

What is an overview of motor control?

Answer 48

But the Basal Ganglia and Cerebellum are doing quite different things, not just opposing one another (simplified schematics have their limits!)

Question 49

What are the Descending Projections from Motor Cortex?

Question 50

How are the dorsolateral and ventromedial tracts similar?

Answer 50

Both contain a direct corticospinal route Both contain an indirect route via brainstem nuclei

Question 51

What occurs in the dorsolateral tract?

Answer 51

Via red nucleus Innervate contralateral side of one segment of spinal cord Sometimes project directly to alpha motor neuron Project to distal muscles, e.g. fingers

Question 52

What occurs in the ventromedial tract?

Answer 52

Via tectum, vestibular nuclei, reticular formation & cranial nerve nuclei Diffuse innervation projecting to both sides and multiple segments of spinal cord Project to proximal muscles of trunk and limbs

Question 53

How movement modulated by basal ganglia and cerebellum?

Question 54

What is the basal ganglia?

Answer 54

A group of structures beneath the cortex that act as a ‘gate-keeper’ for control of the motor system (muscles)

Question 55

What is the basal ganglia like?

Answer 55

The basal ganglia are a group of nuclei lying deep within cerebral hemispheres •Widely studied (including here at Sheffield) •Role in motor control not fully understood •Basal ganglia dysfunction implicated in many disorders

Question 56

What is the basal ganglia involved in?

Answer 56

Receives excitatory input from many areas of cortex (Glutamate) •Output goes back to cortex via the thalamus •Output is mainly inhibitory (GABA) •Complex internal connectivity involving 5 principle nuclei: Substantia Nigra (pars compacta & pars reticulata) Caudate & Putamen (together=striatum) Globus Pallidus (internal and external segments) Subthalamic Nucleus

Question 57

What is the selection problem?

Answer 57

Multiple command systems •Spatially distributed •Processing in parallel •All act through final common motor path •[Cannot do more then one thing (well) at a time] •How do you resolve the competition???

Question 58

How does disinhibitory gating of motor cortex output occur in the basal ganglia?

Answer 58

Excitatory Input from Cortex Dopaminergic Input from Substantia Nigra

Question 59

What are the loops?

Answer 59

Motor Oculomotor Prefrontal Limbic

Question 60

What is the cerebellum?

Answer 60

The cerebellum is a large brain structure that acts as a ‘parallel processor’, enabling smooth, co-ordinated movements. It may also be very important in a range of cognitive tasks.

Question 61

What is the cerebellum like?

Answer 61

Like basal ganglia, no direct projection to the lower motor neurons – instead modulate activity of upper motor neurons Contains approx half total number of CNS neurons •Just 10% of total brain weight •Projects to almost all upper motor neurons

Question 62

What are the inputs and outputs of the cerebellum?

Answer 62

Spinal cord, cerebral cortex and vestibular system -> pons -> cerebellum -> thalamus -> motor cortex Cortical - Mostly from motor cortex (copies of motor commands) - Also somatosensory and visual areas of parietal cortex Spinal - Proprioceptive information about limb position and movement (muscle spindles, other mechanoreceptors) Vestibular - Rotational and acceleratory head movement (semicircular canals / otoliths in inner ear)

Question 63

What is the cerebellar function?

Answer 63

A) It knows what the current motor command is A)It knows about actual body position and movement B)It projects back to motor cortex Computes motor error and adjusts cortical motor commands accordingly 1. Not just motor control, but motor learning too, in collaboration with basal ganglia and cortical circuits. 2.Functional brain imaging studies have demonstrated that the cerebellum is involved in a wide variety of non-motor tasks

Question 64

Could recordings of cortical electrical activity be used to directly control lower motor neurons, thus bypassing (possibly damaged) spinal pathways?

Answer 64

DISCUSS. The direct projection from primary motor cortex to lower motor neurons is very direct. More resent answer yes

Question 65

Where do motor commands originate?

Answer 65

Motor commands originate in upper motor neurons of primary motor cortex and descend along corticospinal tracts to lower motor neurons originating in spinal cord

Question 66

Where does a great deal of motor control and muscle activity, happen?

Answer 66

outside of conscious awareness

Question 67

What is the final common pathway of motor control?

Answer 67

•The motor unit innervated by a single alpha motor neuron, is the final common pathway of motor control

Question 68

What is precise motor control governed by?

Answer 68

Precise motor control is governed by the size principle, different types of muscle fibre, and the antagonistic arrangement of muscles

Question 69

What are motor commands like?

Answer 69

•Motor commands are ‘gated’ by the basal ganglia nuclei, by a system of ‘disinhibition’

Question 70

What does the cerebellum provide?

Answer 70

The cerebellum provides precise control, fine adjustment and co-ordination of motor activity based on continual sensory feedback

Question 71

What is the organisation of the motor pathway - peripheral?

Question 72

How do we move?

Answer 72

We need constantly to process a vast amount of afferent information from muscle spindles

Question 73

What do basal ganglia do?

Answer 73

processing all that afferent information

Question 74

What are peripheral nerves like?

Answer 74

Peripheral nerves are motor and sensory • Some carry autonomic fibers • Pathology could be axonal, demyelination or both (Read) • When impaired features are – Numbness, tingling, burning, freezing pain – Weakness and muscle wasting – Poor balance as a result – Deformities secondary to weakness

Question 75

What are some causes of peripheral nerve damage?

Answer 75

Diabetes Idiopathic (Leprosy) (HIV) Deficiency states e.g. B12 Folate Alcohol/Toxins/Drugs Hereditary Neuropathies Paraneoplastic Syndromes Metabolic abnormalities Porphyria

Question 76

What are the major event in neuromuscular transmission?

Answer 76

Motor neuron depolarization causes action potential to travel down the nerve fiber to the neuromuscular junction (1). • Depolarization of the axon terminal causes an influx of Ca2+ (2) which triggers fusion of the synaptic vesicles (3) and release of neurotransmitter (Acetylcholine; ACh) (4). • ACh diffuses across the synaptic cleft and binds to post- synaptic ACh receptor (AChR) located on the muscle fiber at the motor end-plate (5).

Question 77

What does the binding of ACh to AChRs do?

Answer 77

Binding of ACh to AChRs opens the intrinsic ion channel, resulting in a cation entry locally. This results in a local depolarisation of the sarcolema. • Local sarcolemmal depolarisation results in opening of the sodium channels (VGSC) causing an influx of Na (5), depolarization of the sarcolemma that travels down the t-tubules (6) and ultimately causes the release of Ca2+ from the sarcoplasmic reticulum - CONTRACTION. • Unbound ACh in synaptic cleft defuses away or is hydrolyzed (inactivated) by acetylcholinesterase (AChE) (7).

Question 78

What is skeletal muscle like?

Answer 78

Muscle cell = muscle fiber (a single cell with one nucleus) – Muscle fibers are made of myofibrils (striated) – Myofibrils are made of units called sarcomeres – Sarcomeres are made of thick and thin filaments – Z line is the end of the sarcomere – Thick and thin filaments slide over one another to shorten the muscle during contraction

Question 79

What is the sliding filament theory?

Answer 79

Links the structure of a sarcomere to its function • During contraction thin filaments slide over thick filaments • Thick filaments= myosin and have “heads” • Thin filaments = actin, these slide • Ca and ATP required for sliding and attachment

Question 80

Describe the sliding filament theory

Answer 80

1. ATP binds to myosin head, which is released from an actin filament 2. Hydrolysis of ATP cocks the myosin head 3. The myosin head attaches to an actin binding site with the help of calcium 4. The power stroke slides the actin (thin) filament

Question 81

What is the structure of muscle like?

Answer 81

100-1000‘s muscle fibres make up a muscle Muscle fibres long structure multinucleated bound by sarcolemma

Question 82

What is the structure of myofibril like?

Answer 82

Myofibril The contractile element within the myofibre Myofibril Thin filaments (I) - Actin Thick filaments (A) - Myosin

Question 83

What is needed to coordinate the movement?

Answer 83

Coordinate the movement- extrapyramidal system is needed Coordination is also mediated by cerebellum (read features of cerebellar dysfunction, ataxia) • Sensory input about place of joints in relation to the 3D space (read about joint position sense, dorsal column structure and purpose, sensory ataxia)

Question 84

Why do we have 2 eyes?

Answer 84

Useful to have a spare •Allows us to see in 3D (stereopsis) •Widens our visual field

Question 85

What are the layers of the eye?

Answer 85

Outer layer Sclera and cornea •Middle layer Uvea •Inner layer Retina

Question 86

What is the outer layer for the eye like?

Answer 86

Sclera – tough fibrous outer coat, made up of collagen •Cornea – also made up of collagen! Light transmission – must be transparent Barrier to trauma and infection – must be tough Responsible for ~2/3 refractive power of the eye (43D)

Question 87

What is the outer layer for the eye like?

Answer 87

Sclera – tough fibrous outer coat, made up of collagen •Cornea – also made up of collagen! Light transmission – must be transparent Barrier to trauma and infection – must be tough Responsible for ~2/3 refractive power of the eye (43D)

Question 88

What are the layers of the outer layer of the eye?

Answer 88

5 layered structure 1. Epithelia 2. Bowman’s layer 3. Stroma 4. Descemet’s layer 5. Endothelium

Question 89

What are the layers of the outer layer of the eye?

Answer 89

5 layered structure 1. Epithelia 2. Bowman’s layer 3. Stroma 4. Descemet’s layer 5. Endothelium

Question 90

What is the middle layer of the eye like?

Answer 90

Made up of iris, ciliary body and choroid

Question 91

What is the middle layer of the eye like?

Answer 91

Made up of iris, ciliary body and choroid

Question 92

What is the iris like?

Answer 92

Iris – coloured part at front of the eye contains dilator and sphincter pupillae muscles pupillary reflexes

Question 93

What is the ciliary body like?

Answer 93

Ciliary body – glandular epithelium produces aqueous humour ciliary (smooth) muscle controls accommodation Choroid – blood supply to outer third of retina heat sink

Question 94

What is the choroid like?

Answer 94

Choroid – blood supply to outer third of retina heat sink

Question 95

What is the inner layer of the eye?

Answer 95

Retina •Specialised organ of phototransduction •Many layers

Question 96

What is the retina made up of?

Answer 96

Macula lutea •Fovea centralis •Cones •Rods

Question 97

What are the layers of the retina?

Answer 97

8 layers?

Question 98

What does the retina contain?

Answer 98

Retinal photorecptors •Bipolar cells •Amacrine & horizontal cells •Mullers glial cells •Retinal ganglion cells

Question 99

What is Phototransduction?

Question 100

What is the anterior segment?

Answer 100

Aqueous humour •Nutrition to lens and cornea •Maintains intraocular pressure

Question 101

What is the lens like?

Answer 101

Biconvex •Responsible ~1/3 refractive power of the eye (~20D) •Accommodation

Question 102

What is the lens like?

Answer 102

Biconvex •Responsible ~1/3 refractive power of the eye (~20D) •Accommodation

Question 103

What is Emmetropia?

Question 104

What is Hypermetropia?

Answer 104

Underpowered to focus near objects on retina •May be due to: - corneal curvature too shallow - lens not flexible enough - axial length of eyeball too short

Question 105

What is myopia?

Answer 105

Overpowered so can’t focus far objects on retina •May be due to: - corneal curvature too steep - axial length of eyeball too long

Question 106

What is in the posterior segment?

Answer 106

Vitreous humour •Avascular viscoestalic gel •Hyaluronic acid (GAG) •Collagen

Question 107

What is adnexae?

Answer 107

Lids •Conjunctiva •Tear film

Question 108

What is the structure of the adnexae?

Answer 108

Levator palpebrae superior is muscle Superior suspensory ligament of the globe Aponeurosis Superior tarsal (mullers muscle) Superior suspensory ligament of the fornix

Question 109

What does teh adnexae include?

Answer 109

Lids – protect the globe •Anterior skin •Eye lashes •Meibomian glands •Orbicularis oculi •Tarsal plate •Tarsal conjunctiva •Levator palpebrae superioris & sympathetic muscle

Question 110

What are …. Of the adnexae?

Answer 110

Conjunctiva palpebral (tarsal) vs. bulbar (ocular) •Conjunctival fornix •Limbal stem cells •Mucous membrane (Goblet cells) •Lymphoid cells (protective)

Question 111

What is the tear film like in the adnexae?

Answer 111

Tear film •3 layers anterior lipid middle aqueous posterior mucous •Protective •Nutrition for cornea

Question 112

What is the tear film like in the adnexae?

Answer 112

Tear film •3 layers anterior lipid middle aqueous posterior mucous •Protective •Nutrition for cornea

Question 113

What is the arterial supply of the eye?

Answer 113

Internal carotid a. → ophthalmic a. •Branches of ophthalmic a. (ocular group) central retinal a. posterior ciliary a. → long and short posterior ciliary a. muscular a. → anterior ciliary a. •Branches of ophthalmic artery (orbital group) lacrimal a.

Question 114

What is the blood supply of the inner retina?

Answer 114

Inner 2/3 retina supplied by central retinal a. •Branches into superior/inferior/temporal/nasal branches •Drained by branch retinal veins → central retinal v. → ophthalmic v. → cavernous sinus → internal jugular v.

Question 115

What is the blood supply of the outer retina?

Answer 115

Outer 1/3 supplied by choroid •Posterior ciliary a. → choroidal a. → choriocapillaris •Blood-retinal barrier at RPE regulates movement of nutrition and solutes from choroid into subretinal space

Question 116

What is the venous drainage for the eye?

Answer 116

Vortex veins drain the choroid •Usually one for each quadrant •Superior drain to SOV, inferior drain to IOV

Question 117

Where do the veins drain into for the eye?

Answer 117

Superior ophthalmic veins drain directly into the cavernous sinus •Inferior ophthalmic veins drain into pterygoid venous plexus •Valveless system – orbital cellulitis/facial infection can precipitate cavernous sinus thrombosis

Question 118

What is the lymphatics for the eye?

Answer 118

No lymphatic drainage from the globe •Conjunctiva and lids do have lymphatic drainage to submandibular and pre-auricular nodes

Question 119

How does light travel through the eye?