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Psych b sensory system
1. Sensory Functions
ā¢ General Sensations
ļ¶Mechanical ā touch, pressure, vibration,
stretch
ļ¶Chemical
ā¢ Special Sensations
ļ¶Vision
ļ¶Hearing
ļ¶Taste
ļ¶Smell
2. Sensory area
in the brain
FF
A
NT
RE
E
Touch stimulus
Receptor
Sensory
modality
Ascending
Sensory pathway
Central Connections
Sensory nerve
3. ā¢ stimulation of a receptor usually
produces only one sensation
ļ¶modality specific
ā¢ But some receptors are stimulated
by more than one sensory modality
ļ¶eg. free nerve endings
13. What happens inside a
receptor?
ā¢ TRANSDUCTION
ļ¶Stimulus energy is converted to action
potentials
ļ Inside the nervous system signals are always action
potentials
ļ Language of the nervous system contains only 1
word: action potentials
ā¢ At the brain opposite happens in order to
feel the sensation
ļ¶PERCEPTION
15. Receptor potentials
ā¢ are graded
ā¢ do not follow all-or-none law
ā¢ amplitude depends on the strength
ā¢
of the stimulus
when reaches the threshold: triggers
the action potentials
28. Adaptation
ā¢ āgetting used toā
ā¢ after a period of time sensory receptors adapt
ļ¶partially or
ļ¶completely
ā¢ different types
ļ¶fast adapting receptors
ļ¶slowly adapting receptors
29. Adaptation
ā¢ after a period of time sensory
ā¢
receptors adapt partially or
completely
different types
ļ¶fast adapting receptors
ļ¶slowly adapting receptors
31. Mechanism of adaptation
ā¢ In the Pacinian corpuscle
ļ¶mechanical deformation is transmitted
throughout the capsule and pressure
redistributes
ļ¶Na+ channels inactivates after some
time
33. ā¢ Rapidly adapting receptors
ļ¶phasic or rate or movement receptors
ļ detect changes in stimulus strength
ļ eg. Pacinian corpuscle, hair end-organ
ā¢ Slowly adapting receptors
ļ¶tonic receptors
ļ detect continuous stimulus strength
ļ eg. muscle spindles, Golgi tendon organ,
baroreceptors, Ruffini endings and Merkelās discs,
pain receptors
34. Sensory area
in the brain
Ascending
Sensory pathway
Central Connections
Sensory nerve
Touch stimulus
Receptor
Sensory
modality
35. Two ascending pathways
ā¢ Dorsal column - medial lemniscus
pathway
fast pathway
ā¢ Spinothalamic pathway
slow pathway
These two pathways come together at the level of thalamus
41. Dorsal column medial lemniscus pathway
sensory cortex
thalamocortical tracts
thalamus
M
ed
ul
la
Medial lemniscus
3rd
order
neuron
cross over
Dorsal column nuclei
2nd order neuron
(cuneate & gracile nucleus)
Dorsal column
Dorsal root
Dorsal root ganglion
1st order neuron
42. dorsal column - medial lemniscus
pathway
ā¢ after entering the spinal cord
ļ¶lateral branch: participates in spinal cord
reflexes
ļ¶medial branch: turns upwards
ā¢ forms the dorsal columns
ā¢ spatial orientation:
ļ¶medial: lower parts of the body
ļ¶lateral: upper part of the body
43. dorsal column - medial lemniscus
pathway
ā¢ synapse in the dorsal column nuclei
ļ¶nucleus cuneatus & nucleus gracilus
ā¢ 2nd order neuron cross over to the
ā¢
ā¢
opposite side and ascends upwards as
medial lemniscus
as this travels along the brain stem fibres
from head and neck are joined (trigeminal)
ends in the thalamus (ventrobasal
complex)
ļ¶ ventral posterolateral nuclei
44. dorsal column - medial lemniscus
pathway
ā¢ spatial orientation in the thalamus
ļ¶medial: upper part of the body
ļ¶lateral: lower part of the body
46. Spinothalamic pathway
sensory cortex
thalamocortical tracts
3rd
order
neuron
thalamus
anterior
lateral
2nd order neuron
Spinothalamic tracts
cross over
Dorsal horn
Dorsal root
Dorsal root ganglion
1st order neuron
47. spinothalamic pathway
ā¢ after entering the spinal cord
ļ¶synapse in the dorsal horn
ā¢ cross over to the opposite side
ā¢ divide in to two tracts
ļ¶lateral spinothalamic tract:
ļ pain and temperature
ļ¶anterior spinothalamic tract
ļ crude touch
52. thalamocortical tracts
ā¢ from the thalamus 3rd order neuron
ā¢
ā¢
ascends up through the internal capsule
up to the sensory cortex
thalamocortical radiation
ļ¶tracts diverge
56. Sensory cortex
ā¢ different areas of the body are represented
in different cortical areas in the sensory
cortex
ā¢ sensory homunculus
ļ¶somatotopic representation
ļ¶not proportionate
ļ¶distorted map
ļ¶upside down map
60. somatosensory cortex
Functions
ā¢ Localisation of somatic sensations
ā¢ to judge critical degree of pressure
ā¢ identify objects by their weight, shape,
form - stereognosis
ā¢ to judge texture of materials
ā¢ localisation of pain & temperature
61. Abnormalities
ā¢ Sensory loss
ā¢ Anaesthesia
ļ¶absence of sensation
ā¢ Paraesthesia
ļ¶abnormal sensation
ā¢ Hemianaesthesia
ļ¶Loss of sensation of one half of the body
ā¢ Astereognosis
62. Localisation of the abnormality
ā¢ Peripheral nerve
ļ¶part of a limb is affected
ā¢ Roots
ļ¶dermatomal pattern of sensory loss
ā¢ spinal cord
ļ¶a sensory level
ā¢ internal capsule
ļ¶one half of the body