Session 3

The Nervous System II:Central NS – Brain

PS111 Brain & Behaviour

Psychobiology

“Things to do with a brain”

Detection & transmission of sensory signals: Specialised receptor cells respond to changes in the envi-

ronment Dozens of different types (e.g., touch, smell, heat...)

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 - CHANGE DETECTION Examples:

Touch Smell Sight

We only sense when things are changing!

“Sensory adaptation” = “getting used to” a specific stimulus

... into the Brain

precisely localised information (e.g., fine touch, proprioception):

axons reach top of spinal cord (medulla)

Sensory neurons from all over the body (except the head) send (myelinated) axons into the spinal cord

poorly localised information (e.g., temperature, pain):

axons synapse immediately with other neurons

Detection & transmission of sensory signals: Detection & transmission of sensory signals:

Neurons transmitting

... 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’:

... into the Brain

eye

brain

thala-mus

opticnerve

retina

visual cortex

At each stage, signals are in-tegrated with signals from functionally

LGNof the

thalamus

Visual Cortex

Retina

Brain

Photoreceptors

Ganglion cells

Bipolar cells

Optic Nerve ‘higher’ levels

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’:

same level

... into the Brain

‘lower’ processing levels

Information Processingfrom functionally lower

levels

from same

functional level

from functionally

higher levels

COMBINED input determines if cell becomes active:

Information Processingfrom functionally lower

levels

from same

functional level

from functionally

higher levels

COMBINED input determines if cell becomes active:

Information Processingfrom functionally lower

levels

from same

functional level

from functionally

higher levels neuron’s own output

COMBINED input determines if cell becomes active:

Information Processing

or no output

from functionally lower levels

from same

functional level

from functionally

higher levels

COMBINED input determines if cell becomes active

(or not):

LGN

Visual Cortex

Retina

Brain

Photoreceptors

Ganglion cells

Bipolar cells

Optic Nerve

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’:

... into the Brain

At each stage, signals are in-tegrated with signals from functionally

‘higher’ levels

same level

‘lower’ processing levels

After that,

it only gets worse…

A lot of information processing

takes place even before

a signal reaches the brain!

Structures of the brain

Where the spinal cord becomes the brain: medulla & pons

Medulla + pons + cerebellum = hindbrain

Brain Stem: Hindbrain & Midbrain

Functions: Contains several nuclei of the autonomic NS

(note: cerebellum not part of brain stem!)

Structures of the brain

Where the spinal cord becomes the brain: medulla & pons

Above the pons: Midbrain (‘mesencephalon’)

Function: combines information from

different senses directs attention

Medulla + pons + cerebellum = hindbrain

Brain Stem: Hindbrain & Midbrain (w/o cerebellum!!)

Above the brain stem: Diencephalon

Functions: Contains several nuclei of the autonomic NS

(note: cerebellum not part of brain stem!)

The forebrain: a) Diencephalon

Thalamus: Massive structure on top of the midbrain, deep in the centre of the brain

Main ‘relay station’ for all incoming sensory signals

Receives downward-going input from higher areas:

MODULATES RELAY OF SENSORY SIGNALS

Hypothalamus: Small structure in front of & below the thalamus;

Directly connected to pituitary gland (‘master gland’ of ES)

Hypothalamus = ‘Gateway’ to ES: NS INFLUENCES ES VIA H-P CONNECTION!

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) hemi-

spheres, each - covered in cerebral cortex (thin layer of neurons)- contains several groups of sub-cortical nuclei (tight cluster

of neurons’ cell bodies)

Structures of the brain

• Grey matter & white matter:- Grey matter: Neurons’ cell bodies, i.e., cortex and sub-

cortical 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

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

Medial view

The forebrain: b) Telencephalon – Limbic System

Several interconnected sub-cortical & cortical structures Connected to

hypothalamus (via septum) olfactory system

Function: memory formation & emotion

Structures of the brain

For-nix

Amyg-dala

Mammil-lary bodies

Hippo-campus

CingulateCortex

“Glass brain” view

Hippo-campus

For-nix

Amyg-dala

Mammil-lary bodies

CingulateCortex

The forebrain: b) Telencephalon – Cortex & Corpus callosum Cerebral cortex: thin layers of neurons covering the

whole hemispherei.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’)

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

Structures of the brain

Signal transmission & interpretation

Things to do with a brain

Vision: retina visual cortex (occipital lobe),

Audition: chochlea auditory cortex (tempo-ral 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!

Sensory signals: receptor cells sensory neurons (spinal thalamus (diencephalon) primary sensory cortexcord )

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 ‘map-ped’ onto somato-sensory cortex

a.k.a “somato-sen-sory homunculus”

Signal transmission & interpretation

Things to do with a brain

retinotopic map: visual sig-nals from neighbouring retinal positions arrive at neigh-bouring positions in the primary visual cortex

But: multiple, differing maps exist for each sense modality!

tonotopic map: auditory signals from adjacent areas of the cochlea arrive at adjacent areas in the primary auditory cortex

Things to do with a brain

Topographic representation: In each sensory area, signals arrive at a position

corresponding to the position of the receptor cell:

Signal transmission & interpretation

R

retina

Left Rightside of the world around you:

Direction of signal transmission: neurons transmit signals only in one direction (from dendrites to

axon terminals), but receive signals from different sources:

Signal transmission & interpretation

Things to do with a brain

- 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!

PrefrontalCortex

Supplementary& Premotor

Cortices

Primary MotorCortex* Somato-sensory

Cortex

Posterior ParietalCortex

final e

xecu

tion sta

ge

pla

nn

ing

&m

on

itorin

g* axons stretch down to spinal cord (‘pyramidal tract’)

Things to do with a brain Finally: Motor output

Cortical motor areas:

Finally: Motor output

Cortical motor areas:

Things to do with a brain

Basal ganglia: modulate movements particularly involved in

selective inhibition of movements

Cerebellum: involved in maintaining

posture & balance timing of movements motor learning

Both receive input from (and send output to!) motor cortex sensory cortex various sub-cortical structures

Final motor signals are send down the spinal cord`

massively interconnected with

Sub-cortical motor areas:

Hindbrain

Midbrain

Forebrain

Spinal Cord

Cerebellum Movement & Posture

Pons

Medulla

Continuation of spinal cord; autonomic nuclei

Tectum Perception & Attention

Tegmentum Motor functions

Cerebral Cortex (cortical lobes)

Perception, Action,Cognition...

Limbic System Emotion & Memory

Basal Ganglia Motor control

Tel-encephalon

Thalamus Central relay station

Hypothalamus Gateway to ES

Di-encephalon

Input Functions, Output Functions

asce

nd

ing

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affe

ren

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descen

din

g (efferent)