L7: Sensory-motor integration Flashcards
Describe the pathway to an image being produced
- Specialised cells in the retina (cones + rods) transduce the physical energy of the light into a depolarisation of retinal ganglion cells
- this results in trains of action potentials in the optic nerve
What is the difference between the two specialised cells in the retina: rods and cones?
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)
What is special about the retinal circuitry?
- rods and cones are hyper-polarised by lights
- also have a resting potential closer to 0mV than most neurons
What does the optic nerve project to?
- Lateral geniculate nucleus
- then to the primary visual cortex
With forward facing eyes (binocular field of view), do optic nerve fibres form the nasal half of the retina cross the midline/ optic chiasm?
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
With forward facing eyes (binocular field of view), do optic never fibres from the temporal half of the retina cross the midline/ optic chiasm?
NO
- retina projects ipsilaterally
- do not cross at the optic chiasm
What are the cosequences to sight if the following area of the retina circuitry was damaged:
- right optic nerve
- optic chiasma
- optic tract on the right side
- vision from the right side lost
- plus depth perception - loss of periphery vision
- Loss of vision from the left visual field
What sort of information is processed in each of the following pathways following on from the retina:
- dorsal
- central
- Superior Colocolos?
Retina —> Lateral Giniculate Nucleus —> Primary visual cortex =
- Dorsal = (dome) where (box) —> posterioir parietal cortex
- Ventral = What (chocolate)—> inferotemporal cortes
- superioir Colocolos —> pulvina nucleus —> Posterioir parietal cortex
The projections from brain stem (acetylcholine, serotonin, noradrenaline) to cortex are important in maintaining what?
- attention
- arousal-like processes
What is a saccade and what is it controlled by?
- saccade = when eyes more from one fixation to another
- Primary motor cortex = strip at back of the frontal lobe
- Pertaining that is the supplementary premotor area
= help control voluntary control of gaze direction
What does the basal ganglia include of?
- caudate nucleus
- putamen
- globus pallidus
- substantia nigra
Saccades require the disinhibition of what structure and how does this happen?
- Superioir colliculus
- 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
What is the general pathway of the coritco-striato-thalamo-cortical (CSTC) loops?
- Cortical input
- Striatum
- Pallidum
- Thalamus
What are the cortical target of the motor and occulomotor loop?
- Motor =
- primary motor
- premotor
- supplementary motor cortex - Occulomotor loop
- Frontal eye field
- supplementary eye field
What is the function of the basal ganglia in relation to motor control?
- Initiation + termination of actions
- Selection of actions
- Relating actions to reward or reinforcement value
What is Penfield’s motor homonculus?
- mapped by electrical stimulation of the human motor cortex
What allows our hand muscle movements to be precise?
- amount of relay (synapses) between the motor cortex + hand muscles are very small
What is the neurotransmission pathway for a muscle contraction?
- Achetylcholine is released at the muscle end plate
- binds to nicotinic receptors
- opening sodium channels - The muscle membrane becomes depolarised close to the end plate
- depolarisation is transmitted along the membrane - Depolarisation + sodium influx releases stored calcium ions within the muscle fibre
What is a motor unit?
- initially thought by Sherrington 1920’s
- consists of the motor neuron + set of muscle fibres which it innervates
What are the two different ways muscle contraction can happen?
- Recruitment
- of additional motor units - Rate coding
- increasing the degree of contraction of the motor unit by increasing the firing frq of the motor neurons
When is the supplemetary motor highly active?
- just before a movement is made
- actual movement is taken care of by the motor cortex
What was found when low amplitude transcortical magnetic stimulation (TMS) was delivered to the motor cortical hand region at different points?
- muscles involved in grasps become more sensitive in late stages
- probably additive effect with increased sensitivity of cortical cells to tactile input
What receptors do taste buds in the tongue contain?
- salt
- sour = ionotrophic - NA + H
- sweet
- bitter
- umami = metabotrophic
What is the pathway of a flavour?
- substance bind to receptor
- Information projected to hindbrain
- nucleus of the solitary tract
- then thalamus - Then to cortical areas
- including the insula
What key structures are included in the ‘reward’ and ‘reinforcement’ system that “brings us back for more”?
- ventral tegmentum
- nucleus accumbens
