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Boğaziçi University
SCIENCE 102:
Sensory Systems
Yrd.Doç.Dr. Burak Güçlü
Biomedical Engineering Institute
MECHANICAL
SENSES
CHEMICAL
SENSES
HEARING
VISION
CORTICAL MAPS
Key concepts: Sensory receptor, sense organ, adequate stimulus
A classification of receptors:
a) teleceptors: concerned with events at a distance
b) exteroceptors: concerned with external environment near at hand
c) interoceptors: concerned with internal environment
d) proprioceptors: information about the position of the body in space at any
instant
SENSORY TRANSDUCTION:
Some sensory organs have separate receptor cells and synaptic junctions between
receptors and afferent nerves (e.g. Vision, hearing, equilibrium, taste). In others, the
receptors are specialized ends of nerve fibers (e.g. most cutaneous sense organs).
A nice example: Pacinian corpuscle
Mostly studied tactile receptor, large size, accessible from the mesentery of
carnivores, lamellated capsule, a straight unmyelinated neurite in the middle.
SENSORY MODALITIES:
Generator potential vs. Action potential:
Adaptation:
If constant strength stimulus is maintained,
sometimes the frequency of action potentials
declines over time. Phasic receptors adapt
rapidly, tonic receptors slowly.
Coding:
The action potentials are similar in all nerves.
How do we distinguish information from
different nerves? How do we determine a
strong versus light stimulus?
a) Specific nerves, neurons, and networks
b) Frequency of action potentials
c) Number and type of neurons activated
SKIN:
Meissner corpuscles
Scale bar: 0.5 mm (Bolanowski
et al., 2000)
Pacinian corpuscle
(Bell et al., 1994)
Four tactile-fiber classes:
Tactile pathways in the CNS :
Muscle receptors :
Four-channel model in psychophysics (based on
thresholds):
Cognitive aspects of touch and proprioception:
Stimulus position, movement, direction.
Object texture and weight.
Body position, movement with respect to objects. Different forces
and angles.
Imagery.
Memory.
Sub-modalities are integrated into a complex percept.
Example: wet object, mental rotation
Loss of touch and proprioception:
Trauma, stroke, infection, metabolic (e.g. Diabetic neuropathy),
autoimmune (e.g. Guillain-Barré syndrome).
Local lesions: sensory nerves damaged, motor nerves conserved
Result: No information about the body, needs visual input, living
in a virtual body...
• Can’t detect
displacements/forces and
discriminate weights without
visual input
• Can’t learn new motor skills
• Problems in gait
BRAIN
EXT.
WORLD
Introducing Mind&Brain, A. Gellatly and O. Zarate
Stange case: denial of loss
Mirror drawing: Difficult in
normals due to sensory conflict, easy
for patients with loss of
touch/proprioception
Patients can’t explain what they’re
doing !!
Philosophy:
Awareness of physical existence
by touch and proprioception
Mind-brain fusion (read about
modern theories of
neurophilosophy: Koch,
Churchland et al.)
No special area for mind in the
brain (contrast to brain
surgeon Wilder Penfield)
No hard evidence for mindbrain duality (contrast to
Cartesian philosophy)