Lecture 4: sensation and perception Flashcards
Senses
the physiological capacities to provide input from the environment to our neurological system
Sensation
the translation from information about the environment into patterns of neural activity
perception
our sensory experience of the environment
Although the senses work very differently, they have some anatomical and processing features in common.
Each sensory system:
Starts with an anatomical structure to collect, filter and amplify environmental information
has specializes receptors to transform the environment information in a neural signal that are passed along specific sensory nerve pathways
These nerves end up in the Thalamus and then go to a primary sensory region of the cortex (except olfactory nerve)
Acuity
how good we can differentiate among stimuli within a sensory modality
acuity depends on:
the anatomical structure to collect the stimulus (dogs can move their ears independently to better capture sound waves)
The number and distribution of the receptors. acuity is best in the centre of the visual field because the fovea is packed with photoreceptors.
our sensory systems (5)
olfaction: smell
gustation: taste
Somatosensation: touch
auditon: hearing
vision: sight
Olfaction (smell)
The olfactory epithelium
odor molecules enter the nasal cavity
These molecules bind to bipolar receptors in the nasal mucosa (=The olfactory epithelium)
Olfaction (smell) in the brain
glomeruli & olfactory cortex (pyriform cortex) & orbitofrontal cortex
The axons of the glomeruli from the olfactory nerve that projects to the primary olfactory cortex (pyriform cortex). from there the signal proceeds to the orbitofrontal cortex.
Shape theory (docking theory) of olfaction
Odor molecules bind to some of the thousand different types of receptors because the shape of the molecule corresponds to the shape of the receptor (like a key fits a lock). The odor depends on which molecule binds to which receptor. however some molecules with similar shapes have very different odors
Vibrational theory
Similarly shapes molecules have different molecular vibrations (at quantum level)
olfaction and behavior
Men rated women as less attractive after smelling real tears:
Brain areas related to sexual arousal (hypothalamus & fusiform gyrus) showed a decreased BOLD response while watching emotionally evocative (erotic) clips after smelling real tears.
Gustation (smell) way to the brain
papillae
on the tongue there are papillae and have taste buds.
food molecules (tastants) pass the tongue via the taste pores to the tase buds. each taste bud contains taste receptor cells.
molecules bind to receptor, the axons form the chorda tympani nerve. together with other nerves, this nerve forms the facial nerve VII and projects to the solitary tract nucleus in the brainstem.
from there the signal goes to the thalamus and the primary gustatory cortex in the insula.
Gustotopic map
neurons in the gustatory cortex are organized meaning that their spatial organization follows a property of the environment or body
gustation research in the thalamus showed:
when researchers recorded the thalamus they saw that neurons respond selectively to one taste (sour, sweet, bitter or umami)
somatosensation (touch)
the perception of all mechanical stimuli that effect the body
- the interpretation of signals that indicate the position of the limbs and head (proprioception
- temperature
- pressure
-touch
-pain
-etc..
somatosensation is caused by…
somatosensory receptors under the skin and at the musculoskeletal junctions (where all the muscle fibers meet)
nociceptors
pain is sensed my the nociceptors (free nerve endings)
somatosensation (touch) signal to brain
via the dorsal root ganglion, the signal travels through the spinal cord to the medulla and the contralateral side of the thalamus. the thalamus sends the signal to the primary somatonsensory cortex (the postcentral sulcus)
somatotopic map
neurons in the primary somatosensory cortex are organized in a somatotopic map.
size of the representation is proportional to the sensitivity of the body part (hands are sensitive and have a relatively large representation in the brain)
Audition (hearing
The peripheral auditory system: the external ear & the middle ear
The external ear: collect and focus sound energy
The middle ear: sound energy hits the eardrum (the tympanic membrane) that is connected to the three tiny bones: mallues, incus and stapes.
Stapes are connected to the cochlea via the oval window
The internal ear
Cochlea consists of three chambers, all filles with fluid
the basilar membrane
the basilar membrane inside the cochlea is embedded with hair cells (the tips of the hair cells are called sterocilia)
tonotopic organization
depending on the frequency of the sound, different hair cells will move. the basilar membrane close to the oval window reacts to high frequencies; the membrane at the end of the cochlea (apex) react to low frequencies.
low tones travel far.
The central auditory system
Signal from hair cells is propagated to the brain via the auditory nerve cell that first projects to the cochlear olivary complex. the signals from the left and right ear come together.
then to the inferior colliculus (orientation towards the sound) and medial geniculate complex.