Week 4: Intro To The Nervous System + Retina

Question 1

What is the nervous system split into (2)?

Answer 1

• The central nervous system: consists of the brain, spinal cord. Main function is perception, cognition and action. ‘Manager of behaviour’.
• The peripheral nervous system: consists of everything else- nerves and receptors. Main functions is sensation, action and body regulation.

Question 2

What is the enteric nervous system?

Answer 2

To do with gastrointestinal tract and enteric motor neurones, always involuntary and becuase you’re not consciously aware that peristalsis taking place of small and large intestines unless in pain.

Question 3

What does the somatic nervous system consist of?

Answer 3

consists of sensory receptors that take information from muscles and skin to the brain and motor neurones take information from the brain to the skeletal muscle.
The function is sensory input and motor output, sensory input to the brain and motor output from the brain and its not just the brain but the spinal cord too.

Question 4

What does Automatic nervous system consist of?

Answer 4

consists of sensory receptors that take information from smooth muscle, heart muscle, gland, fatty tissues, other tissues to the brain and motor neurones take information from the brain to other organs.
Function is to regulate things like temperature, heart rate, blood gas content, digestion and store of glycogen in liver

> Autonomic nervous system has two parts; Sympathetic Nervous system (increase HR, fight-or-flight) and Parasympathetic branch (decrease HR, ‘Rest+Digest’)

Question 5

What are the cells of the nervous system?

Answer 5

• neurones: to receive, process and transmit electrochemical messages. Use electricity to transmit info between each other, and can communicate chemically too/have chemical release at their ends
• neuroglia: to help neurones- they make up 1/2 cell volume in the CNS. Need them to insulate axons (Schwann cells insulate)

Question 6

Structure of a neurone?

Answer 6

• cell body in the middle
• dendrites branching off cell body (input)
• axon which is long and cylindrical (output) and at end of axon also branches out and has little terminals with synaptic end bulb, axon insulated by myelin sheath made up of neuroglia made up of Schwann cells

Question 7

what is the membrane potential at different points? IDKKKKKKK

Answer 7

Cell is very negative compared to the outside circulating cerebral spinal fluid of that cell and when a stimulus arrives, at that level the membrane is at -70mV and get an excitation stimulus, moves the membrane to get less negative as soon as it hits the threshold at -55mV you get an action potential that is triggered regardless of the strength of that stimulus as long as -55mV is reached
> The rising potential from 0mV to +30mV, as it reaches a point as soon as it reaches +30mV, it then has to regenerate itself by going down (red) is called ‘Repolarising phase’ then gets back to -55mV and up to -70mV called the ‘After hyperpolarisation phase so hyper-polarisation is when the inside of the cell becomes more negative than -70mV and repolarising is when it’s coming down to +30mV to get down to that after hyper-polarising phase and depolarising means the outside of the cell is much more positive whereas the inside is negative so it’s a polarised cell. (Nernst equation)

Question 8

Types of neurones

Answer 8

—Typical neurone = multipolar, has several dendrites and one axon

• Bipolar neurone has one main dendrite and one axon (in retina)
• Unipolar neurone = has one process that branches out (one end is dendrites and other end is axon terminal)
• Interneurones are functional type of neurone. They make up 90% of the neuronal population, many varieties: purkinje, renshaw, pyramidal

Question 9

What is special about bipolar neurones?

Answer 9

They have one main dendrite that branches off and one main axon terminal that branches
-retina, olfactory system and inner ear

Question 10

What is special about multipolar neurones?

Answer 10

Have several dendrites and only one axon

-brain and spinal cord

Question 11

What is special about unipolar neurones?

Answer 11

Contain one process which extends from the body and divides into a central branch that functions as an axon and dendritic root.
-usually found in cerebellum

Question 12

What are sensory/afferent neurones?

Answer 12

Convey action potentials into the CNS through cranial or spinal nerves
-they are perceiving the environment

Question 13

What are motor/efferent neurones?

Answer 13

Convey action potentials away from the CNS to effectors (muscles and glands) in the periphery though cranial or spinal nerves. (Most are multipolar)
-acting on the perceived info from sensory neurones and do an action (e.g. moving hand if put in a flame)

Question 14

What are Interneurones/association neurones?

Answer 14

• mainly found in CNS between sensory and motor neurones.
• interneurones integrate incoming sensory info from sensory neurones, then elicit a motor response by activating appropriate motor neurones.
• most interneurones are multipolar

Question 15

What are the two types of neural circuits ?

Answer 15

• Converging circuit: where you have many inputs into one neurone and then its output
• Diverging circuit: one neurone is sending its input to more than one neurone, which will send it to more than one neurone and so on..
• Reverberating circuit: input that goes down to output neurone and every time its ending, a feedback loop to the intermediate interneuones which is also sending input to the next level up and the next level up.
• Parallel after-discharge circuit: main neurone sending info directly to output but many others which are sending input to output neurone simultaneously and in parallel

Question 16

How do neuroglia support neurones?

Answer 16

• by forming the blood brain barrier (BBB)
• by forming the myelin sheath (nerve insulation) around neuronal axons
• making the CSF (cerebral spinal fluid) that circulates around the brain and spinal cord
• participating in phagocytosis

Question 17

What are the types of neuroglia? (6)

Answer 17

• Astrocytes: maintain the right chemical environment for neurone to function, form scar tissue, maintain BBB, provide structural support
• Microglia: clean up (cell debris, waste, pathogens by phagocytes) and defend nervous system from disease
• Ependymal cells: make CSF (cerebral spinal fluid), line ventricles (brain) and central canal (spinal cord)
• Satellite cells: support neurones in the PNS (peripheral nervous system) by surrounding cell bodies in ganglia (groups of neurones) + regulate O2+CO2+neurotransmitters
• Schwann cells: make myelin sheath that provides an insulating cover for axons in the PNS. The nuerolemma in the myelin aids nerve regeneration. Repair after injury.
• Oligodendrocytes: structural support + make myelin sheath in the CNS, this has no nueorlemma (like in Schwann cells for myelin in PNS) therefore no regeneration of oligodendrocytes in the CNS - multiple sclerosis (movement jerky + blindness caused by optic nerve stripped of oligodendrocytes)

Question 18

Pain is an example of myelinated or unmyelinated axons?

Answer 18

In PNS, unmyelinated axons, Schwann cells supporting the but not insulating them and important because they give us pain which is slow, takes time to build up and in chronic sin such as rheumatoid arthritis these unmyelinatd axons are hypersensitive and carry pain up to brain.

Question 19

What is Myelin?

Answer 19

• fatty substance that provides electrical insulation for axons. It acts to prevent short-circuiting of axon all signals and sped up nerve impulse propagation (of AP). Some axons are unmyelinated however are slow conducting.
• types of cell that make myelin:oligodendrocytes in CNS and Schwann cells in PNS. Myelin layered like onions.
• Impulses propagated at breaks in myelin sheath called “Nodes of Ranvier”- speed propagation

Question 20

What is grey and white matter?

Answer 20

Myelin covered parts of brain and spinal cord look white and those not covered look grey.

• grey matter is on inside of spinal cord and on the outside in brain
• white matter is on outside of spinal cord and inside brain (are myelin covered axons)

Question 21

What is Multiple Sclerosis?

Answer 21

De-myelinating disease which results in compromising of speed of nerve impulses

Question 22

What is the process of forming a myelin sheath which insulted and increases nerve impulse speed?

Answer 22

Myelination

Question 23

What is myelin formed by?

Answer 23

Myelin formed by oligodendrocytes in the CNS and Schwann cells in PNS

Question 24

What is White matter?

Answer 24

White matter of the brain and spinal cord is formed from aggregations of myelinated axons from many neurones.
-the lipid part of myelin makes the appearance white

Question 25

What is grey matter?

Answer 25

Grey because it lacks myelin, of the brain and spinal cord, is formed from neuronal cell bodies and dendrites.

Question 26

Where is grey/white matter in spinal cord and in brain?

Answer 26

Horizontal section of spinal cord shows grey matter in inside and white matter on outside so cell bodies sitting inside butterfly, but white matter on outside so axons on outside.
-Frontal picture of brain showing white matter on inside and grey matter (v small) on outside

Question 27

What are nodes of ranvier?

Answer 27

Gaps in myelin sheath.

-each Schwann cell wraps one axon segment between two nodes of ranvier. (Cell,gap,cell,gap)

Question 28

Where does nerve tissue NOT regenerate?

Answer 28

Nerve tissue regeneration occurs only in PNS and not CNS (Astrocytes form scar tissues)

• The cell bodies of neurones lose their mitotic features at birth @ birth and can only be repaired though regeneration after an injury (never replaced by daughter cells like in epithelial tissues) ONLY IN PNS
• The outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath, is the neurolemma (sheath of schwann), when axon is injured the nuerolemma aids regneration by forming a regeneration tube that guides and stimulates regrow the of the axon.
• For any regeneration to occur, neurone must be in PNS and have intact cell body, and be myelinated by functional schwann cells having nuerolemma

Question 29

What is demyelination?

Answer 29

• Refer to the loss or destruction of myelin sheathes around axons. May result from disease, or from medical treatments such as radiation therapy and chemotherapy.
• Any single episode of demyelination may cause deterioration of affected nerves

Question 30

What happens in Amyotrophic Lateral Sclerosis? (Like motor neurone disease)

Answer 30

The upper motor neurone in the brain cuts away from all information going down spinal cord going down the spinal cord from the muscle and eventually inability to move and Px will have reduced myelination but not much, eventually Px will die because breathing apparatus which is innovated by respiratory neurones stop working.

Question 31

What happens in Guillain-Barre Syndrome?

Answer 31

• Disease of the Peripheral nervous system- autonomic nervous system branch- phagocytosis of myelin by macrophages when nerve is infiltrated by lymphoid cells
• ascending muscle weakness and paralysis , respite ray failure possible but most recover
• remyelination over a period of 3-4 months

Question 32

What is optic neuritis?

Answer 32

Inflammation of the optic nerve

Acute vision loss

Question 33

What are Clark’s?

Answer 33

Oligodendrocytes that are stripped of their myelin
Build up and show up as white spots on MRI scans (demyelination)
-multiple sclerosis

Question 34

What happens in glaucoma?

Answer 34

• glaucoma: you loose cell bodies of the retinal ganglion cells that you get in the periphery
• leads to tunnel vision (central vision preserved however if remains untreated can lose vision).
• glaucomatous cupping shown on fundus camera where you’ve lost some perfusion blood vessels around that optic nerve head. (Looks like white spot)

Question 35

What is macular degeneration?

Answer 35

• optical coherence tomography OCT tells you what’s happening in the centre of the retina, in the phovia
• you’re losing photoreceptors not the other neurones but the photoreceptors convert the light energy and where those receptors are lost you lose bits of central vision and you get what is called a Scatoma (big black spot).

Question 36

What are the layers of the eye?

Answer 36

• sclera (white stuff)
• Choroid (lots of blood vessels)
• Basement membrane (BM) and surrounding photoreceptors (rods and cones)

Question 37

How does vision work (3)?

Answer 37

1. Eyes and ocular motor system: form clear, centred, optical images on the retina (i.e. position, focus, light control and optical quality)
2. The retina; Transduction: convert light into electrical potential. Encoding: converts electrical potentials into action potential sequences for retinal output
3. The brain: interprets retinal output into a meaningful visual scene

Question 38

What is the ora seratta?

Answer 38

-Where the retina begins and goes right around the back of the eye

Question 39

What does an Optus camera show?

Answer 39

Wide field view of the retina

-what’s happening in periphery

Question 40

How does light convert to biological energy?

Answer 40

Light travels through the cornea, aqueous humour, through pupil and lens then the vitreous humour, and hits the retina through the nerve cell layer, through the ganglion cell layer, bipolar cell layer, rods and cones and then light is transformed into biological energy then sent back up again anteriorly through bipolar cells and retinal ganglion cells and though optic nerve axons

Question 41

Which is bigger, rods or cones?

Answer 41

Cones are bigger then rods and respond to different wavelengths of light

Question 42

Which only responds to monochromatic light wavelengths (black and white) rods or cones?

Answer 42

Rods

Question 43

What is the direction of nerve impulses through the retina?

Answer 43

nerve impulses go from pigmented epithelium, rods and cones (photoreceptor cell layer), outer synaptic layer, to bipolar cell layer (horizontal cells, bipolar cells, amacrine cells), ganglion cell layer (ganglion cells) to optic nerve (2) and propagate along optic nerve towards optic disc.

(Light going opposite way from ganglion cell layer to pigmented cell layer)

Question 44

What are the types of photoreceptors?

Answer 44

• Short-wave, middle-wave and lone-wave cone cells.

- rod cells

Question 45

What are the different parts of the retina?

Answer 45

Pigment epithelium (posterior)
Rods and cones
outer limiting membrane 
Muller cells 
Bipolar cells 
Amacrine cells 
Ganglion cells 
Nerve fibre layer 
Inner limiting membrane

Question 46

What are the 4 cellular layers of the retina?

Answer 46

1. Pigment epithelium
2. rods and cones
3. Outer limiting membrane: muller cells, horizontal cells, bipolar cells, amacrine cells
4. Ganglion cells

Question 47

Which cell are the largest in the retina?

Answer 47

Ganglion cells

-final integration of information

Question 48

What is the optic disc?

Answer 48

• Where the optic nerve transports action potentials to brain
• 1.5mm in diameter
• called blind spot becuase no photoreceptors or RPE so image will have fallen on optic disc then cant see it

Question 49

What is the Fovea? (And parafovea and perifovea)

Answer 49

• Fovea is where there are only cones and you get maximum sense of vision (in middle, white spot in middle of fundus photos or dip in OCT scan) 1mm
• Parafovea space is just around the phovia you have rods and cones and inner and outer nuclear layers 3mm
• In the perifovea you have all retinal layers (periphery) 5mm

Question 50

What is the macula?

Answer 50

• 5.5mm, overlaps the fovea, parafovea and perifovea (centre of retina)
• where most of the photoreceptors are, where clearest (sharpest) vision is so looking straight in front, periphery vision not as clear because not in macula

Question 51

What’s the size difference between the fovea and foveola ?

Answer 51

Fovea: 1-2mm, depression with inner retinal layers pushed aside
Foveola: 0.3mm (optimal acuity) , only long - slender cone outer segments

Question 52

What are colour are long wavelength cones sensitive to?

Answer 52

Red sensitive

Question 53

What colour are medium wavelength cones sensitive to?

Answer 53

Green sensitive

Question 54

What colour are shorter wavelength cones sensitive to?

Answer 54

Blue sensitive (not as many as red and green)

Question 55

What are the functions of the Retinal Pigment Epithelium (RPE)?

Answer 55

1. Light absorption (melanin pigment granules absorb stray light reducing light scatter from behind retina and between photoreceptors = improves resolution)
2. Epithelial transport (blood-retinal barrier, stops retina from being bathed in red blood, active import from the choriocapillaris of glucose,vitamin A for visual cycle, Omega3 fatty acids rebuild photoreceptor membranes, diffusion of H2O, O2, CO2 and CL- and active export of waste products (lactic acid), tight junctions isolate neural retina from circulation
3. Active Potassium Transport: Ion levels must be stable for R+C to function correctly, ions rapidly exchanged during light dependent activity, rapid ion compensation in outer retina by PRE cells + muller cells in inner retina
4. Vitamin A metabolism, retinal is small molecule made by modifying VitA, photons absorbed by transformation of retinal in R+C membranes, retinal transformed in rods restored to active state by enzymes in RPE (visual cycle)
5. Photoreceptor membrane recycling (phagocytosis) R+C continuously shed, Rod outer segments shed in morning (1-2 hours after dawn), cone outer segments shed at night (3-5 hours after dark)
6. Hormone production & secretion for regulation of metabolism/pathology or injury

Question 56

How many rods compared to cones?

Answer 56

110-130 million per retina of rods compared to 5-7million cones per retina

Question 57

Which is wider, rods or cones?

Answer 57

Rods are long slim cells (2 microns) cones are wider cells (6 micron diameter)

Question 58

Is the blind spot (optical disc) closer to the nose or the temple?

Answer 58

Closer to nose

Question 59

What is the role of proteins in photopigments? (Rhodopsin)

Answer 59

11-cis retinal by itself in solution only has 3% efficiency with peak sensitivity for UV light but when rhodopsin added efficiency = 50% and peak efficiency for blue-green wavelength of light.

Question 60

What is the visible light spectrum in nm, and colours?

Answer 60

400nm (violet) to 700nm (red)

Question 61

What is the photo transduction cascade? (IDKKKKKKK)

Answer 61

In the dark, rod and cone cells are excited and become hyper polarised by light so become more negative (double check this idk)