Visual Neurophysiology - 1

Visual Neurophysiology - 1

1. Lobes

   • Occipital Lobe
     • Striate cortex/ visual area (V1) -> receives the main visual input
   • Frontal eye fields
     • Control eye movements
   • Parietal and temporal lobes
     • Analysis of visual information - fuses info. into one image
   • More than 1/3 of correct is associated with vision
   • Lateral Geniculate Nucleus
     • Visual image is transmitted here - then to input area of V1

2. Nervous System

   • CNS
     • Brain and Spinal chord and CSF -> The brain is supported by 3 layers of cranial meninges and floats, completely shockproof, in the cerebral spinal fluid (CSF). CSF provides balanced chemical environment. Its total volume is produced and displaced 3 times a day
   • Peripheral nervous system
     • Neurons and fibres - outside the brain and spinal chord, Affferent = towards the CNS, Efferent = away from the CNS
   • Somatic nervous system
     • The afferent and efferent fibres concerned with input from skin, tendon, joints, voluntary muscles, eyes, tongue and nose
   • Visceral nervous system
     • Controls the smooth muscle e.g. those in the gut - efferent fibres are more commonly classified as being part of the autonomic nervous system
   • Autonomic nervous system
     • Composed of fibres from brain and spinal cord which either inhibit or excite smooth muscle, cardiac muscle and glands - organs can operate without autonomic control but activity is modulated by 2 branches of the ANS - sympathetic and parasympathetic system. These act antagonistically

3. CNS

   • Brainstem
     • Mesencephalon (mid-brain) and rhombencephalon (hind-brain)
       • Mesencephalon - base of forebrain
         • 2 cerebral peduncles - CN III and IV - control eye movements and tectum
           • Tectum = 4 small nodular bodies - two superior and two inferior
       • Rhombencephalon
         • Pons, medulla and cerebellum
           • Cerebellum - behind the pons
             • Contraction of voluntary muscles
             • Co-ordinates action of antagonists and agonists
   • Diencephalon
     • Thalamus
       • Centre of cranial cavity
       • Intermediate relay point for all sensory impulses - not smell
       • Transmission of sensory and motor impulses between power regions of brain and cerebrum
       • Mediates pain
       • Posterior part
         • Pulvinar
           • Receives fibres from retina
           • Part of sub-cortical pathway between eye and brain
         • Lateral Geniculate Nucleus
         • Medial geniculate nucleus
     • Hypothalamus
       • Regulates body fluids
       • Regulates body temperature
       • Regulates hormones
       • Regulates reproductive cycles
       • Make you feel hungry and thirsty
       • Controls sympathetic nervous system - has a direct link with the pituitary gland
   • Cerebrum
     • Largest, most complex part of the brain
     • 2 cerebral hemispheres
       • Grey matter = cerebral cortex
       • 50M neurons and 250M glia cells = connective tissue of CNS
       • Raised ridges = gyri
       • Grooves = sulci
         • Deeper grooves = fissures
           • Longitudinal fissure separates 2 hemispheres
         • Separate major lobes
       • Beneath cortex = white matter = myelinated fibres - transmit impulses to and from thalamus
       • A link is the corpus callosum
         • Large band of fibres
         • Link to corresponding points in each hemisphere in almost all areas of the cerebrum

4. Cerebral lobes

   • Frontal
     • Anterior half = important for explanation of thought
     • Posterior half = motor area -> cells mediate control of the different parts of bod, Broca's area is responsible for the larynx and mouth = speech
   • Parietal
     • Somatosensory activity - touch, pressure, temperature and pain
   • Occipital
     • Vision area - striate cortex/V1 = characterised with stripes
   • Temporal
     • Auditory area and Wernicke's area of sensory integration - all signals from the sense come together
     • Wernicke's area is only in the man