Brain Systems At Work - 7 Flashcards
How does the eye analyse a visual scene?
Involved what the object is and where it is. First part is to form a visual image. The eye has a vision forming component on the front (lens & corena) which converts image into the retina. Distribution across the retina varies. Some areas have high proportion of cones, giving a higher resolution image.
Picking up the detail of the eye
Cones and rods (specialised cells in the retina) transducer the physical energy of the light into a depolarisation of retinal ganglion cells that results in trains of AP’s in the optic nerve. Rods are sensitive to low light intensity, cones sensitive to high. Light falling onto pigment causes a change in structure, releasing a chemical that changes the conductivity of the membrane. Receptors are normally relatively depolarised, although when light falls onto them they become hyperpolarised.
What is the function of the optic nerve?
Optic nerve fibres from the basal half of the retina across the midline, projecting cotralaterally. At the back of the eye find axons coming from retinal ganglia cells which project back to the lateral geniculate nucleus. Projection works by having a pattern which ensures info about the left side of the visual world ends up in the right visual cortex and vice versa.
What are visual streams?
Visual info goes down a stream to end up at the primal visual cortex. There are two broad streams of visual processing: dorsal and ventral. Streams help identify where objects are and what they might be. Third stream which projects to parietal cortical areas which are crucial in controlling voluntary and involuntary eye movements.
What is involved in eye movements?
The superior collicilus & projection on to that are involved in voluntary and involuntary eye movements. If something distracting happens in your visual environment this will lead to an involuntary eye movement. In voluntary movements that concern cognitive control, cortical areas are important. Supplementary motor areas are important in the planning and execution of movements.
What is the role of the basal ganglia in movement control?
The basal ganglia includes the caudate nucleus, putamen, globus pallidus and the substantia nigra. It is involved in producing eye movements.
How saccades require disinhibition of superior colliculus by pause of firing cells within the substantia nigra
which making the eye movement is associated with a burst of action potentials. As the eye movement comes to be initiated can see the action potentials drop: that drop is occurring just ahead of a burst of action potentials in the substantia nigra and the superior colliculus. Cells in the substantia nigra are chronically active: inhibitory cells (which use GABA as their neurotransmitter) are holding other circuits that if become active will produce an action – this holding allows action to occurs = therefore action is produced by a process of disinhibition. This is an important feature of the way motor action is organised within the brain.
What are cortico-striato-thalmo-cortical (CSTC) loops?
Have additional cortical output to brainstem motor control areas which include the superior colliculus. Three further loops connect cortical areas involved in cognition & emotion within the basal ganglia. Also mediate broader motor actions.
What are the 3 functions of the basal ganglia in relation to motor control?
- initiation and termination of actions - explains symptoms seen in conditions e.g. Parkinson’s. This is where selective degeneration is occurring. A delay in being able to initiate actions is a defining feature of Parkinson’s. There is also a deficit in being able to terminate action.
- selection of actions
- relating actions to reward/reinforcement value = actions that run up from the substantia nigra to the basal ganglia are important in reinforcing reward.
What is involved in muscle contractions?
Acetychloine is released at muscle plate, which binds to nicotinic receptors, opening sodium channels. The muscle membrane becomes depolarised & depolarisation is transmitted along the membrane. Depolarisation directly triggers contraction of the muscle fibre.
What is a motor unit?
Idea by Sherrington, 1920s. Muscle contraction involves mix of recruitment and rate coding. One motor neuron can control many motor fibres.
What are the effects of TMS during a reaching task?
Deliver low amplitude transcortical magnetic stimulation (TMS) to motor cortical hand region. This disrupts neuronal firing.
