PNS

Question 1

What does the muscle spindle consist of and what do each of them do?

Answer 1

2 intrafusal fibres – Nuclear bag and nuclear chain.
Nuclear bag - muscle length and velocity (dynamic)
Nuclear chain - muscle length (tonic)

Question 2

What does the gamma and alpha motor neuron do in the muscle spindle

Answer 2

Gamma – activates the muscle spindle (contractile ends of spindle fiber); making it shorter or longer changes the spindles sensitivity
Alpha – innovates extrafusal fibres and activates the muscle contraction via regular skeletal muscle fibres

Question 3

What are the 4 types of info conveyed by sensory system?

Answer 3

Modality
Location
intensity
Timing

Question 4

Define modality

Answer 4

The type of info. Eg touch, pressure, pain, temp etc

Question 5

What is labelled line theory?

Answer 5

Modality is nerve specific not receptor specific
The brain knows pain vs touch because it has a map of what receptor is at the end of each nerve fibre, not because it can tell what receptor is at the end

Question 6

Describe tonic vs phasic adaption and provide an example of each.

Answer 6

Tonic receptors turn on, and slowly adapt downwards. They fire the whole time the stimulus is on - eg pain

Phase receptors rapidly adapt, then have a smaller peak when stimulus turns off - eg putting on a tshirt.

Question 7

Explain how lateral inhibition increases accuracy using an example.

Answer 7

If skin is poked by a pencil, multiple receptors are targeted, those closer to the point moreso than those further away.
Lateral inhibition means that the receptors further from the point are turned off, so only transmission from where the strongest stimulus is continues - i.e. where the point of the pencil is.

Question 8

Explain how the patellar reflex assists with standing

Answer 8

The reflex stimulates the extensor muscle, and the spinal cord then inhibits the flexor muscle.
I.e. if the hamstrings aren’t inhibited, we wouldn’t be able to stand up.

Question 9

What is the golgi organs function?

Answer 9

Measures the degree of tension on the tendon to prevent overstretching via the alpha motor neuron inhibiting the muscle if the stretch on the tendon is too strong

Question 10

What is the clinical significance of the pupillary light reflex?

Answer 10

• allows testing for whether the occulomotor nerve, optic tract is is damaged
• Eg if right eye moves but left eye doesnt, then the occulomotor nerve on the left is where the issue is. Optic nerve is fine if message still gets to brain stem

Question 11

What is the vestibulo-occular reflex?

Answer 11

• Keeps the eyes locked on a target whilst head rotates

- eye movement in comatose patient indicates brain stem still functioning

Question 12

What is special about the fovea?

Answer 12

Any light that hits here gets fused into one image from both eyes and is area with higher visual accuity.
It has only cones.

Question 13

Why do we have a blind spot?

Answer 13

From the spot where the optic nerve exits the eye

Question 14

What is presbyopia?

Answer 14

When the cells in the lens that are further away from the fluid start to die off over a lifetime - requires glasses.

Question 15

What is glaucoma?

Answer 15

When the canal of schlemm gets blocked with aqueous humor and pressure builds up.

Question 16

Describe what happens in the eye for long-distance viewing.

Answer 16

• light doesnt have to bend as much
• sympathetic stimulation
• ciliary muscle is relaxed
• suspensory ligaments are taut
• lens is weak and flat

Question 17

Describe what happens in the eye for short-distance viewing.

Answer 17

• parasympathetic stimulation
• light has to bend further
• ciliary muscle is contracted
• suspensory ligaments are slack
• lens is strong and round

Question 18

What is accommodation referring to?

Answer 18

The change in the strength and shape of the lens

Question 19

What is function of cones and rods?

Answer 19

Cones - colour vision. Have less discs so are less sensitive to light.
Rods - black and white vision. Have more discs so are more sensitive to light.

Question 20

What is the macula lutea?

Answer 20

Area immediately around fovea.

Has fairly high accuity.

Question 21

Describe path of sound from outer ear through to inner ear.

Answer 21

• sound wave enters outer ear
• tympanic membrane (ear drum) vibrates
• 3 bones in middle ear vibrate
• oval window vibrates
• wave enters cochlear
• low notes/long frequency will continue through cochlear for longer before hitting organ of corti
• high notes/short frequency will distort the endolymph earlier in the organ of corti
• round window vibrates

Question 22

What is the role of the inner ear hair cells?

Answer 22

• hairs on basilar membrane are bent when the basilar membrane is deflected in relation to the stationary tectorial membrane
• bending of hair opens mechanically gated channels via TP links
• leads to ion movements and receptor potential

Question 23

What is the role of the outer ear hair cells?

Answer 23

• receive efferent input
• move to amplify wave
• tunes and enhances response of inner hair cells

Question 24

Describe the AP process in receptor hair cells (inner ear):

Answer 24

• TP links stretch and open channels
• stereocilia bend towards tallest member
• K+ enters (note: K is higher on outside for these cells as opposed to the usual of K+ higher inside)
• hair cell depolarises
• voltage gated Ca2+ channels open
• Ca enters and more neurotransmitter exits
• more AP in post-synaptic cell

Question 25

Where is the issue for conductive vs sensorineural hearing loss and what are likely causes for each?

Answer 25

Conductive: outer and middle - before vibration hits oval window. Foreign material or middle ear infection.

Sensorineural: in cochlear. Noise damage or prebycusis (age related).

Question 26

Describe rinne hearing test

Answer 26

• tuning fork on mastoid bone behind ear
• tests AC and BC
• normal: AC > BC
• conductive loss: BC> AC
• sensorineural: AC>BC, but both are equally down

Question 27

Describe weber hearing test

Answer 27

• tuning fork sits on top of skull in the middle
• patient with unilateral conductive hearing loss would hear the tuning fork loudest in the affected ear.
• conduction problem masks the ambient noise of the room
• inner ear still fine, so picks up sound via bones of the skull

Question 28

Describe the three types of nociceptors

Answer 28

• mechanical damage
• thermal/temp extremes
• polymodal -> respond equally to all kinds of damaging stimuli

Question 29

Describe fast pain characteristics

Answer 29

• mechanical and thermal noiceptors
• myelinated a-delta fibres
• sharp and prickling
• localised
• initial response

Question 30

Describe slow pain

Answer 30

• polymodal
• unmyelinated C fibres
• dull ache/burning sensation
• poorly localised
• persists for longer and more unpleasant

Question 31

What are the two pain neurotransmitters?

Answer 31

• Substance P. Activates ascending pathways for further processing.
• Glutamate. Major excitatory neurotransmitter.