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Sensory Physiology.docx

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Western University
Physiology 2130

Sensory Physiology Lecture 1 Divisions of the nervous system: 1) Central Nervous System (CNS)- consists of the brain and spinal cord 2) Peripheral Nervous System (PNS) –composed of 2 subsystems -Somatic system- spinal nerves -Visceral System-(autonomic nervous system) parasympathetic and sympathetic Important Terminology: -Anterior: rosteral, ahead of front - Posterior: caudal, behind or towards back - Dorsal: back -Ventral: Front or belly Midline: the center of axis Medial: towards midline/middle Lateral: towards the side Ipsilateral: same side Contralateral: opposite side Planes Through the Brain: -Midsagittal: down the center between the two hemispheres - Horizontal - Coronal: vertical cut (classic brain view) Major Parts of the CNS: 1) Cerebrum- Cerebral Cortex -two cerebral hemispheres divided by the sagittal fissure -concerened with contralateral sensation of movement 2) Cerebellum - also has 2 hemispheres - conserened with ipsilateral motor control 3) Brain Stem - the most primitive part of the brain - concerned with life functions ie) respiration, body temperature 4) Spinal Cord - conduit for information to and from the brain - sensory and motor losses following section Brain Structure Divisions: 1) Forebrain (Prosencephalon) - Telencephalon- cerebral cortex - Diencephalon-thalamus and retina 2) Midbrain (Mesencephalon) - Tectum- superior and inferior colliculus - Tegmentum 3) Hindbrain (Rhombencephalon) - Metaencephalon- cerebral and pons - Myelencephalon-Medulla (TelDieTecTegMeMy) - grey matter in brain where cell bodies are - white matter in brain where axons are The Spinal Cord: -31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal) -each has a pair of nerves (left and right) 1) Dorsal root: responsible for sensory info going IN to the brain 2) Ventral root: responsible for motor commands going OUT to muscles - each segment of the spinal cord receives sensory input from a particular region of the body and supplies motor input to a similar region - on the skin surface, that sensory region is called a dermatome - there are no dermatomes on the face as it id close to the brain, so uses cranial nerves - there are 2 cervical enlargements on the spinal cord at the location of the arms and legs (lumbar enlargement) - we can withdrawl spinal cord fluid a the sacral area without damaging the spinal cord The PNS: 1) Somatic System (voluntary) - spinal nerves - dorsal root ganglia 2) Visceral System (ANS) - the involuntary system - pupil constriction, blood pressure, sweating, crying, salivation Types of neuron/axons: 1) Affrent (in to spinal cord, dorsal root) - carry info to a place - usually refers to bringing sensory info to the CNS 2) Effrent (out from spinal cord, ventral root) - carry info from a place - usually refers to taking motor info from CNS to a motor target Meninges (covering): - 3 meninges covering the brain 1) Dura Mater- hard (outer most layer) 2) Arachnoid- spider (middle layer) 3) Pia Mater- gentle (inner most layer) The Ventricular System: - spaces within the brain that contain CSF (cerebrospinal fluid) are called ventricles - CSF is produced by the choroid plexus - The ventricular system is a series of ventricles and canels that move CSF within the brain and transport out to the subarachnoid space - The ventricular system contains about 150ml of CSF - We produce about 500ml of CSF a day - CSF comes from the center of the brain and moves out Lobes of the brain: 1) Frontal: 2) Parietal: 3) Occipital: 4) Temporal: 5) Central sulcus: Sensory - starting at lecture 3 Fundamental components of the visual system: Eye, retina, optic nerves, optic chiasm, optic tract, lateral geniculate nucleus, primary visual cortex, extrastriate visual cortex Retinal Targets: 1) Lateral geniculate nucleus (LGN) 2) Superior Colliculus- tectum-midbrain 3) Pretectum- controls pupillary constriction 4) Hypothalamus- suprachiasmatic nucleus (SCN)- sycronization of diurnal rythems with day and night cycle Light-The Stimulus for vision: - the electromagnetic spectrum is a continues spectrum of electromagnetic energy, which is energy produced by electric charges that are radiated as waves - the energy in this spectrum can be described by its wavelength- the distance between the peaks of the electromagnetic waves Wavelengths: - extremely short= gamma rays, long= radio waves - humans can perceive wavelengths ranging from 400-700nm Visual Acuity: the capacity of visual system to resolve fine spatial detail -three factors include 1) the stimulus 2) the eye 3) the central visual pathways Snellen Acuity: chart viewed from 20 ft  at 20 ft, viewer can detect 1 deg critical fetures (20/20)  at 20 ft, you can see like normal ppl at 40 ft (20/40)- lower acuity  at 20 ft, you can see like normal ppl at 15 ft (20/15)- higher acuity Legal Blindness: When a persons best corrected vision is 20/200 or worse Anatomy of the eye:  Pupil- hole in center  Iris- the colour of your eye, regulates size of pupil  Cornea- clear sheet in front of the pupil and iris  Sclera- the white of your eye, majority of eyeball  Conjunctiva- inside of eyelid  Extraocular eye muscles- control movement of the eye  Optic nerve- transmits visual info from retina to brain  Lens- transmits and refracts light  Ciliary muscles- a ring of striated smooth muscle in the middle layer that controls accommodation for viewing objects at varying distances  Aqueous humor- between cornea and lens  Vitreous humor- between lens and retina  Retina- light-sensitive layer of tissue, lining the inner surface of the eye  Fovea- responsible for sharp central vision Retinal Cells: 5 types 1) Photoreceptors- light sensitive cells 2) Bipolar cells 3) Ganglion Cells- the output neurons 4) Horizontal cells 5) Amacrine cells Retinal layers: Nuclear layers- where cell bodies are Plexiform layers- where the synapses and axons are 6 layers from bottom of eye to top: 1) ganglion cell layer 2) inner plexiform layer 3) inner nuclear layer 4) outer plexiform layer 5) outer nuclear layer 6) photoreceptor outer segments Retinal Facts: - retina is a sheet of several layers of cells that lies against the posterior wall of the eye - retina is set up backwards to the way you would expect it to be - a pigment epithelium lines the back of the retina, against photoreceptors Photoreceptors: - outer segment- the photosensitive part - inner segment contains cell body - rods and cones are not evenly distributed - nasal retina is larger than temporal retina and contains the blind spot 2 types of photoreceptors: 1) Rods- light sensitive, used during dim conditions (scotopic), 120 mill rods in each retina, found in peripheral vision (outnumber cones 20:1) 2) Cones- colour sensitive, used during day (photopic), fovia containa only cones, 5 mill cones in each retina Blind Spot: between 15 and 20 degrees, receptors are on the back wall of the eye and block ganglion cell axons from leaving the eye. Area devoid of receptors where 1 mill ganglion cell axons leave the eye to form the optic nerve. The brain fills in the blind spot Phototransduction: light into electricity. The photoreceptor outer segment is whe
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