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Psych b sensory system
1. Sensory Functions
• General Sensations
Mechanical – touch, pressure, vibration,
stretch
Chemical
• Special Sensations
Vision
Hearing
Taste
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. • stimulation of a receptor usually
produces only one sensation
modality specific
• But some receptors are stimulated
by more than one sensory modality
eg. free nerve endings
13. What happens inside a
receptor?
• TRANSDUCTION
Stimulus energy is converted to action
potentials
Inside the nervous system signals are always action
potentials
Language of the nervous system contains only 1
word: action potentials
• At the brain opposite happens in order to
feel the sensation
PERCEPTION
15. Receptor potentials
• are graded
• do not follow all-or-none law
• amplitude depends on the strength
•
of the stimulus
when reaches the threshold: triggers
the action potentials
28. Adaptation
• “getting used to”
• after a period of time sensory receptors adapt
partially or
completely
• different types
fast adapting receptors
slowly adapting receptors
29. Adaptation
• after a period of time sensory
•
receptors adapt partially or
completely
different types
fast adapting receptors
slowly adapting receptors
31. Mechanism of adaptation
• In the Pacinian corpuscle
mechanical deformation is transmitted
throughout the capsule and pressure
redistributes
Na+ channels inactivates after some
time
33. • Rapidly adapting receptors
phasic or rate or movement receptors
detect changes in stimulus strength
eg. Pacinian corpuscle, hair end-organ
• Slowly adapting receptors
tonic receptors
detect continuous stimulus strength
eg. muscle spindles, Golgi tendon organ,
baroreceptors, Ruffini endings and Merkel’s 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
• Dorsal column - medial lemniscus
pathway
fast pathway
• 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
• after entering the spinal cord
lateral branch: participates in spinal cord
reflexes
medial branch: turns upwards
• forms the dorsal columns
• spatial orientation:
medial: lower parts of the body
lateral: upper part of the body
43. dorsal column - medial lemniscus
pathway
• synapse in the dorsal column nuclei
nucleus cuneatus & nucleus gracilus
• 2nd order neuron cross over to the
•
•
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)
ventral posterolateral nuclei
44. dorsal column - medial lemniscus
pathway
• spatial orientation in the thalamus
medial: upper part of the body
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
• after entering the spinal cord
synapse in the dorsal horn
• cross over to the opposite side
• divide in to two tracts
lateral spinothalamic tract:
pain and temperature
anterior spinothalamic tract
crude touch
52. thalamocortical tracts
• from the thalamus 3rd order neuron
•
•
ascends up through the internal capsule
up to the sensory cortex
thalamocortical radiation
tracts diverge
56. Sensory cortex
• different areas of the body are represented
in different cortical areas in the sensory
cortex
• sensory homunculus
somatotopic representation
not proportionate
distorted map
upside down map
60. somatosensory cortex
Functions
• Localisation of somatic sensations
• to judge critical degree of pressure
• identify objects by their weight, shape,
form - stereognosis
• to judge texture of materials
• localisation of pain & temperature
61. Abnormalities
• Sensory loss
• Anaesthesia
absence of sensation
• Paraesthesia
abnormal sensation
• Hemianaesthesia
Loss of sensation of one half of the body
• Astereognosis
62. Localisation of the abnormality
• Peripheral nerve
part of a limb is affected
• Roots
dermatomal pattern of sensory loss
• spinal cord
a sensory level
• internal capsule
one half of the body