CNN Notes Sensory Second Lecture PDF

SENSORY CONTINUED Cerebral Cortex  Features of the Brain Post Central Gyrus Somatic sensory area I & II Functions (by elimination) – Unable to localize discretely the different sensations in the body – Unable to judge critical degrees of pressure – Unable to j...

SENSORY CONTINUED Cerebral Cortex  Features of the Brain Post Central Gyrus Somatic sensory area I & II Functions (by elimination) – Unable to localize discretely the different sensations in the body – Unable to judge critical degrees of pressure – Unable to judge weight of objects – Unable to judge shapes or form of objects (astereognosisis) – Unable to judge teaxture of materials Somatic Association Areas – Helps in deciphering messages – When removed leads to loss of form of the body (forget your opposite side (amporphosynthesis) Tracts  Sensory Representation on the cortex Representation is upside down No. of receptors corresponds to site of the receiving area Homonculus Cross Section of Cord  Dorsal Columns (Leminiscal System) Fine Touch Proprioception Vibration – Ipsilateral Transmission – Cross over is at the level of the medulla – Pass through the Thalamus – Project onto sensory cortex Dorsal Pathway  Spinothalamic tract Originates in the spinal cord. It transmits information to the thalamus about pain, temperature, itch and crude touch sexual tickle and itch The pathway decussates at the level of the spinal cord, rather than in the brainstem Lateral: Pain & Temp Ventral: Crude Touch Spinothalamic tract Spinothalamics Transmission: Spinothalamic (Anterolateral) Transmission: Dorsal Columns  Sensation Touch: Skin, Lips – Transmission dorsal Columns (fine) Precise touch Gradations of sensation – Ventral Spinothalamics (crude) – Only extensive cord lesions interrupt touch Proprioception: Joints – Dorsal Columns – Most to the the cerebellum – Destruction: Ataxia  Pain and Temperature Temperature – 2 Types of receptors – Those below body temperature – Those above body temperature – Conduction by lateral Spinothalamics – Sense organ is sub-epithelial – Mild adaptation occurs but not above 40oC and below 20oC – Above 45oC tissue damage and pain replaces temperature  Pain – 2 types – Sharp and sudden: Transmitted by Aδ fibres – Slow and dull Transmitted by C fibres – Associated with emotional components pain pathway connected to thalamus  Fast Aδ Pain Slow C Rapid onset: Acute, Slow onset increasing sharp electric steadily: Burning, Mainly superficial gnawing chronic Superficial and deep Eg. Needle stick Eg Knife injury Abdominal Pain Electric Shock Muscle strain Pain receptors: Free nerve endings, superficial and deep in tissues like periosteum, joint surfaces capsules of viscera Deeper tissue do not have an extensive supply but marked tissue damage leads to recruitment of losts of receptors  Features of Pain Pain: protective mechanism for the body which occurs when tissue is being damaged. Eg: Pressure Sores Sitting for a long time Chemicals Pain receptors adapt Responsible for pain very little – Bradykinin Prolonged stimulation – Histamin may cause increase – K+ excitation – Proteolytic enzymes Tissue ischemia eg BP – Acids cuff – Protagladins Muscle Spasms  Pain Continued Superficial Pain Visceral Pain – localised – May be referred Deep/Visceral Pain – Sensitive to – Poorly localised distention – Nauseating – Lots of receptors have to be – Associated with stimulated sweating – Involves contraction – Associated with of adjacent muscle changes in BP (autonomic – Caused by spasms symptoms as – Caused by chemical afferents go to the stimuli CNS via ANS) – Caused by ischemia Pathway: FAST Sensory Cortex Thalamus Reticular Formation Brain Stem Neo Spinothalamics Crossover Contra-lateral Dorsal Horn Spinal Nerves Receptor Pathway: SLOW Sensory Reticular nuclei in Brain Stem Cortex Tectal area of the Mid Brain Periaqueductal area of the aqueduct of Sylvius Thalamus 10%-25% Brain Stem Paleo-Spinothalamics Crossover Contra-lateral Dorsal Horn Laminar II &II Relay Neuron to Laminar V Neurotransmitter is Substance P. Slow to build up. Slow to be Spinal Nerves destroyed: Hence slow onset of pain, increased intensity and Receptor long lasting effect.  Pain Control I Degrees of pain Subjective Brain able to control pain input Local Suppression – Stimulate large sensory from peripheral tactile receptor – Depress Transmission of pain signals from the same area of the body Lateral Inhibition ⌃ ⌃ ⌃ ⌃ – Acupuncture Pre or Post Synaptic – Liniment inhibition – Child blowing or ⌃ rubbing  Pain Control II OPIATE SYSTEM OF THE BRAIN Morphine-like substances which reduce the pain (receptors) Naturally occurring substances with morphine like effect Area of action- – Peri-aqueductal nucleus – Peri-aqueductal grey area – Dorsal horn of spinal cord Opiates : endorphins, dynorphnis, enkephalin  Brain’s analgesic Major Component system Peri-aqueductal gray area (Pons Mid Brain) Raphe Magnus Nucleus (lower Pons and upper medulla) Dorsolateral Horn (pain inhibiting complex in the dorsal horn) Pain fibres Pain Inhibition  Brain insensitive but More Pain not Referred Pain – Venous sinuses Pain in a part of the – Tentorium body considerably – Meninges removed from the Causes (Inside) issue causing the pain – Inflammation – Low CSF HEADACHE – Migraine Usually referred pain – Alcohol from the the deep – Constipation structures Causes (outside) – Inside cranium – Muscular spasms – Outside cranium – Nasal Sinuses – Eye Disorders  Dermatomes The dermatomes are somatic or musculo- cutaneous areas served by fibers from specific spinal nerves Or A skin area innervated by the sensory fibers of a single nerve root is known as a dermatome