Transcript The Nervous System: Overall Organisation

PS111 Brain & Behaviour
Psychobiology
Session 3
The Nervous System II:
Central NS – Brain
“Things to do with a brain”
... into the Brain

Detection & transmission of sensory signals:

Specialised receptor cells respond to changes in the environment
 Dozens of different types (e.g., touch, smell, heat...)
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
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Not just five! (5 different types for sight alone, muscle
spindles discussed last week…)
Mostly not neurons, but directly connected to a sensory
neuron
Interlude 

Examples:
 Touch
 Smell
 Sight
We only sense when things are changing!

“Sensory adaptation” = “getting used to” a specific
stimulus
... into the Brain

Detection & transmission of sensory signals:


Sensory neurons from all over the body (except the head)
send (myelinated) axons into the spinal cord
Neurons transmitting

precisely localised
information

poorly localised
information
(e.g., fine touch,
proprioception):
(e.g., temperature,
pain):
axons reach top
of spinal cord
(medulla)
axons synapse
immediately with
other neurons
... into the Brain


Sensory neurons from the head send axons directly into the
brain via cranial nerves (e.g., the optic nerve)
All signals transmitted via several ‘relay stations’:
retina
brain
thalamus
visual
cortex
eye
... into the Brain


Sensory neurons from the head send axons directly into the
brain via cranial nerves (e.g., the optic nerve)
All signals transmitted via several ‘relay stations’:
Photoreceptors

Bipolar cells
Retina
Ganglion cells
At each stage, signals are integrated with signals from
functionally

Optic
Nerve
LGN
of the
thalamus
Brain
Visual
Cortex


‘lower’ processing levels
same level
‘higher’ levels
Information Processing
from functionally lower levels
from same
functional
level
from
functionally
higher levels
Information Processing
from functionally lower levels
from same
functional
level
from
functionally
higher levels
Information Processing
from functionally lower levels
from same
functional
level
from
functionally
higher levels
neuron’s own output
Information Processing
from functionally lower levels
from same
functional
level
from
functionally
higher levels
or no output
... into the Brain


Sensory neurons from the head send axons directly into the
brain via cranial nerves (e.g., the optic nerve)
All signals transmitted via several ‘relay stations’:
Photoreceptors

A lot of information processing
Bipolar
cells
takes place even
before
Retina
a signal reaches
the brain!
Ganglion cells
At each stage, signals are integrated with signals from
functionally

Optic
Nerve
LGN
Brain


‘lower’ processing levels
same level
‘higher’ levels
After that,
it only gets worse…
Visual
Cortex
Structures of the brain

Functions: Contains several nuclei of the autonomic NS
Structures of the brain

Functions: Contains several nuclei of the autonomic NS
Structures of the brain

The forebrain: a) Diencephalon
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Thalamus: Massive structure on top of the midbrain, deep
in the centre of the brain
 Main ‘relay station’ for all
incoming sensory signals


Hypothalamus: Small structure in
front of & below the thalamus;


Receives downward-going input
from higher areas:
Directly connected to pituitary
gland (‘master gland’ of ES)
Hypothalamus = ‘Gateway’ to ES:
Structures of the brain

The forebrain: b) Telencephalon – Cerebral hemispheres


From diencephalon, incoming signals go up to cerebrum
Divided into two highly similar (but not identical) hemispheres, each
- covered in cerebral cortex (thin layer of neurons)
- contains several groups of sub-cortical nuclei (tight cluster
of neurons’ cell bodies)
• Grey matter & white matter:
- Grey matter: Neurons’ cell bodies, i.e., cortex and subcortical nuclei
- White matter: Neurons’ myelinated axons
• Functional organisation: each hemispheres mainly
• receives input from contralateral side of the body
• sends output to contralateral side of the body
Structures of the brain

The forebrain: b) Telencephalon – Basal Ganglia


group of nuclei surrounding thalamus
involved in motor control

globus pallidus + putamen +
caudate


(putamen + caudate =
“corpus striatum”)
Amygdala closely connected
to BG
(sometimes listed as part of BG)

But functionally part of the limbic system:
Structures of the brain

The forebrain: b) Telencephalon – Limbic System
“Glass brain” view
Cingulate
Cortex
Amygdala
Mammillary bodies


Medial view
Fornix
Cingulate
Cortex
Fornix
Mammillary bodies
Hippocampus
Amygdala
Hippocampus
Several interconnected sub-cortical & cortical structures

Connected to

hypothalamus (via septum)

olfactory system
Function: memory formation & emotion
Structures of the brain

The forebrain: b) Telencephalon – Cortex & Corpus
callosum

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Cerebral cortex: thin layers of neurons covering the
whole hemisphere
i.e, not just outside, but inner (‘medial’) surface as well!
Corpus callosum: thick bundle of axons connecting the
two hemispheres
Note: virtually all signal transfer between hemispheres
done via CC!
Structures of the brain

The forebrain: b) Telencephalon – Cerebral Cortex

Highly folded

Gyrus: outward folded (pl. ‘gyri’)

Sulcus: inward folded (pl. ‘sulci’)
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Longitudinal fissure:
Largest sulcus, separates
left & right hemisphere
Smaller sulci: boundaries
of cerebral lobes:
Occipital lobe (at the back): Visual perception
Temporal lobe (at the sides): Auditory perception
Parietal lobe (at the top): Somatosensory perception;
intersensory & sensory-motor integration
Frontal lobe (at the front): Planning & motor output
Things to do with a brain
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Signal transmission & interpretation
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Sensory signals: receptor cells  sensory neurons  (spinal
cord ) thalamus (diencephalon)  primary sensory cortex
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Vision: retina  visual
cortex (occipital lobe),
Audition: chochlea 
auditory cortex (temporal lobe),
Touch, proprioception,
etc.: skin, muscles,
joints  somatosensory
cortex (parietal lobe)
NOTE: All signals are identical (a neuron becoming electrically
active)

Signal interpretation depends entirely on the location in the
brain where it arrives!
Things to do with a brain

Signal transmission & interpretation

Topographic representation:

In each sensory area, signals arrive at a position
corresponding to the position of the receptor cell:
 Somatotopic map:
 Signals from the
hand arrive in “hand
area”, which is next
to “arm area”, which
is next to “shoulder
area”…
 Body shape ‘mapped’ onto somatosensory cortex
 a.k.a “somato-sensory homunculus”
Things to do with a brain

Signal transmission & interpretation

Topographic representation:

In each sensory area, signals arrive at a position
corresponding to the position of the receptor cell:
Left
Right
side of the world around you:

R

retina

retinotopic map: visual signals from neighbouring retinal
positions arrive at neighbouring positions in the
primary visual cortex
tonotopic map: auditory
signals from adjacent areas of
the cochlea arrive at adjacent
areas in the primary auditory
cortex
But: multiple, differing maps exist for each sense
modality!
Things to do with a brain

Signal transmission & interpretation

Direction of signal transmission: neurons
 transmit signals only in one direction (from dendrites to
axon terminals), but
 receive signals from different sources:
- earlier or ‘lower’ processing stages
(‘bottom up’ or ‘feed-forward’)
- neighbouring neurons in the same
area (‘lateral’)
- subsequent or ‘higher’ processing
areas (‘top down’ or ‘feedback’)

Combination of feed-forward & feed-back
signal loops:

information is not just passively
‘forwarded’,

but modified by everything else
going on in the brain!
Things to do with a brain
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Finally: Motor output

Cortical motor areas:
Supplementary
& Premotor
Cortices
* axons stretch down to spinal cord
(‘pyramidal tract’)
planning &
monitoring
Prefrontal
Cortex
Primary Motor
Cortex*
Somato-sensory
Cortex
Posterior Parietal
Cortex
Things to do with a brain
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Finally: Motor output
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Cortical motor areas:
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massively interconnected with
Sub-cortical motor areas:
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Basal ganglia:
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modulate movements
particularly involved in
selective inhibition of
movements
Cerebellum:
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involved in maintaining
posture & balance
timing of movements
motor learning
Both receive input from (and send output to!)
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motor cortex
sensory cortex
various sub-cortical structures
Final motor signals are send down the spinal cord`
Telencephalon
descending
(afferent)
Forebrain
(efferent)
ascending
Midbrain
Hindbrain
Diencephalon
Cerebral Cortex
(cortical lobes)
Perception, Action,
Cognition...
Limbic System
Emotion & Memory
Basal Ganglia
Motor control
Thalamus
Central relay station
Hypothalamus
Gateway to ES
Tectum
Perception & Attention
Tegmentum
Motor functions
Cerebellum
Movement & Posture
Pons
Continuation of spinal
cord; autonomic nuclei
Medulla
Spinal Cord
Input Functions, Output Functions