L7: Sensory-motor integration

Question 1

Describe the pathway to an image being produced

Answer 1

1. Specialised cells in the retina (cones + rods) transduce the physical energy of the light into a depolarisation of retinal ganglion cells
2. this results in trains of action potentials in the optic nerve

Question 2

What is the difference between the two specialised cells in the retina: rods and cones?

Answer 2

Rods:

• good for low light
• no colour vision

Cones:

• 3 cones which are colour sensitive
• chickens are more sensitive to colour gradation (green, oil droplets)

Question 3

What is special about the retinal circuitry?

Answer 3

• rods and cones are hyper-polarised by lights

- also have a resting potential closer to 0mV than most neurons

Question 4

What does the optic nerve project to?

Answer 4

• Lateral geniculate nucleus

- then to the primary visual cortex

Question 5

With forward facing eyes (binocular field of view), do optic nerve fibres form the nasal half of the retina cross the midline/ optic chiasm?

Answer 5

YES

• silce eyes into the half closer to the nose (nasal) or to the outside of the face (temporal)
• nasal half cross midline = project contralaterally (opposite)
• left nasal optic fibre to the right lateral geniculate nucleus

Question 6

With forward facing eyes (binocular field of view), do optic never fibres from the temporal half of the retina cross the midline/ optic chiasm?

Answer 6

NO

• retina projects ipsilaterally
• do not cross at the optic chiasm

Question 7

What are the cosequences to sight if the following area of the retina circuitry was damaged:

1. right optic nerve
2. optic chiasma
3. optic tract on the right side

Answer 7

1. vision from the right side lost
   - plus depth perception
2. loss of periphery vision
3. Loss of vision from the left visual field

Question 8

What sort of information is processed in each of the following pathways following on from the retina:

• dorsal
• central
• Superior Colocolos?

Answer 8

Retina —> Lateral Giniculate Nucleus —> Primary visual cortex =

1. Dorsal = (dome) where (box) —> posterioir parietal cortex
2. Ventral = What (chocolate)—> inferotemporal cortes
3. superioir Colocolos —> pulvina nucleus —> Posterioir parietal cortex

Question 9

The projections from brain stem (acetylcholine, serotonin, noradrenaline) to cortex are important in maintaining what?

Answer 9

• attention

- arousal-like processes

Question 10

What is a saccade and what is it controlled by?

Answer 10

1. saccade = when eyes more from one fixation to another
2. Primary motor cortex = strip at back of the frontal lobe
3. Pertaining that is the supplementary premotor area
   = help control voluntary control of gaze direction

Question 11

What does the basal ganglia include of?

Answer 11

• caudate nucleus
• putamen
• globus pallidus
• substantia nigra

Question 12

Saccades require the disinhibition of what structure and how does this happen?

Answer 12

1. Superioir colliculus
2. by pause of firing of cells within the substantia nigra

• info come from eye, then once dopanergic info has been sent, the info is relsead from the substantia nigra

Question 13

What is the general pathway of the coritco-striato-thalamo-cortical (CSTC) loops?

Answer 13

1. Cortical input
2. Striatum
3. Pallidum
4. Thalamus

Question 14

What are the cortical target of the motor and occulomotor loop?

Answer 14

1. Motor =
   - primary motor
   - premotor
   - supplementary motor cortex
2. Occulomotor loop
   - Frontal eye field
   - supplementary eye field

Question 15

What is the function of the basal ganglia in relation to motor control?

Answer 15

1. Initiation + termination of actions
2. Selection of actions
3. Relating actions to reward or reinforcement value

Question 16

What is Penfield’s motor homonculus?

Answer 16

• mapped by electrical stimulation of the human motor cortex

Question 17

What allows our hand muscle movements to be precise?

Answer 17

• amount of relay (synapses) between the motor cortex + hand muscles are very small

Question 18

What is the neurotransmission pathway for a muscle contraction?

Answer 18

1. Achetylcholine is released at the muscle end plate
   - binds to nicotinic receptors
   - opening sodium channels
2. The muscle membrane becomes depolarised close to the end plate
   - depolarisation is transmitted along the membrane
3. Depolarisation + sodium influx releases stored calcium ions within the muscle fibre

Question 19

What is a motor unit?

Answer 19

• initially thought by Sherrington 1920’s

- consists of the motor neuron + set of muscle fibres which it innervates

Question 20

What are the two different ways muscle contraction can happen?

Answer 20

1. Recruitment
   - of additional motor units
2. Rate coding
   - increasing the degree of contraction of the motor unit by increasing the firing frq of the motor neurons

Question 21

When is the supplemetary motor highly active?

Answer 21

• just before a movement is made

- actual movement is taken care of by the motor cortex

Question 22

What was found when low amplitude transcortical magnetic stimulation (TMS) was delivered to the motor cortical hand region at different points?

Answer 22

• muscles involved in grasps become more sensitive in late stages
• probably additive effect with increased sensitivity of cortical cells to tactile input

Question 23

What receptors do taste buds in the tongue contain?

Answer 23

• salt
• sour = ionotrophic - NA + H
• sweet
• bitter
• umami = metabotrophic

Question 24

What is the pathway of a flavour?

Answer 24

1. substance bind to receptor
2. Information projected to hindbrain
   - nucleus of the solitary tract
   - then thalamus
3. Then to cortical areas
   - including the insula

Question 25

What key structures are included in the ‘reward’ and ‘reinforcement’ system that “brings us back for more”?

Answer 25

• ventral tegmentum

- nucleus accumbens