The Brain- Lecture 3 Flashcards
Describe the detection and transmission of Sensory signals
Dozens of different, specialised types of receptor cells respond to changes in the environment
Note: most are not neurons, but are directly connected to a sensory neuron
Long, myelinated axon of sensory neurons from all over the body (except the head) enter the spinal cord via the dorsal root of the spinal nerves
Neurons transmitting precisely localised information send axons to the top of the spinal cord
Neurons transmitting poorly localised information synapse immediately with other neurons upon entering the spinal cord
Sensory neurons from the head send axons directly
into the brain via cranial nerves (e.g., optic nerve)
All signals (not just visual!) transmitted via several ‘relay stations’:
At each, integrated with other incoming signals from ‘lower’, ‘higher’, and same-level processing stages
What is Sensory Adaptation?
Interlude: Change Detection (e.g., smell, touch, sight):
we only sense when things are changing!
sensory adaptation = getting used to a specific stimulus
What makes up the Brain Stem?
Hindbrain and the Midbrain.
What is in the Hindbrain?
medulla, pons, cerebellum
Medulla & pons: where the spinal cord enters the brain (Functions: contains several nuclei of the autonomic NS)
Cerebellum (‘little brain’): not part of the brain stem! (Function: balance, motor learning)
What is the function of the Midbrain?
Midbrain (‘mesencephalon’): above the pons (functions include combination of information from different sense modalities; direction of attention
What makes up the Forebrain? (the Diencephalon)
Thalamus: Massive structure on top of the midbrain, deep in the centre of the brain
-Main ‘relay station’ for incoming sensory signals
-Receives downward-going input from higher areas, modulating the relay of sensory signals
Hypothalamus: Small structure in front of & below thalamus;
Directly connected to pituitary gland (‘master gland’ of the ES, controls activity of all
other glands)
‘Gateway’ to ES: NS can influence ES via hypothalamus – pituitary connection!
Describe the Telencephalon
Cerebral hemispheres
From the diencephalon, incoming signals go up to
the cerebrum
Divided into two highly similar (but not identical)
hemispheres
Each covered in cerebral cortex (thin layer of neu-
rons covering each hemisphere), also contains
several groups of sub-cortical nuclei (tight cluster
of neuron’s cell bodies – see below)
Describe Grey and White matter
Grey matter: Cortex & sub-cortical nuclei
White matter: Myelinated axons of neurons
Describe the Basal Ganglia
Group of nuclei surrounding the thalamus
involved in motor control process
Consist of globus pallidus, putamen, & caudate
Putamen & caudate often referred to as corpus stria-
tum (‘striped body’)
Amygdala closely connected to this system, therefore
sometimes described as being part of basal ganglia
o but usually described in the context of the…
Describe the Limbic System
Several interconnected cortical & sub-cortical
areas, playing a crucial role in memory & emotion
Sub-cortical: Almost complete circle formed by fornix & hippocampus, ending in mammillary body & amygdale
Cortical: Cingulate cortex directly above corpus
callosum (evolutionary older, more ‘primitive’
than rest of the cortex)
Connected to hypothalamus (septum) & olfactory system
Describe the Cortex and the Corpus Callosum
Cerebral cortex: thin layers of neurons covering the whole hemisphere, i.e., not just
the outside, but the inner (‘medial’) surface as well
Corpus callosum: thick bundle of axons connecting the two hemispheres
-Virtually all signal transfer between the cortices of the hemispheres done via CC!
-Highly folded, forming gyri (s. gyrus, outward folded areas) and sulci (s. sulcus, in ward folded areas)
-Longitudinal fissure: Largest sulcus, separating left and right hemisphere
-Smaller sulci used to define 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; inter-sensory & sensory-motor
integration
Frontal lobe (at the front): Planning & motor output
What does contralateral mean?
A general processing principle: Everything’s reversed!
Sensory input from the right side of the body (or the right visual field) is processed in
the left half of the brain (and vice versa)
Motor output to the right side of the body is generated in the left half of the brain (and
vice versa)
Terminology: the technical term for “on opposite side” is contralateral
Describe signal transmission and interpretation in sensory signals.
Eventually, sensory signals from the diencephalon are relayed to their appropriate primary sensory cortex (see figure above):
-Visual signals -> visual cortex (occipital lobe)
-Auditory signals -> auditory cortex (temporal lobe),
- Signals from skin, muscles & joints -> somato-sensory cortex (parietal lobe)
What is Action Potential?
All signals are identical (electrical neural activity: “action potential”)
how a signal is interpreted depends entirely on its location.
Describe the different Topographic maps for signal transmission and interpretation.
Inside the specific sensory areas, signals arrive at positions corresponding to the position
of the receptor cells (topographic representation):
somatotopic map: signals from the hand arrive in the hand area of the somatosensory
cortex, which is next to the arm area, which is next to the shoulder area…
retinotopic map: similarly, 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
Note: multiple, differing maps exist for each sense modality
Why is it impossible to view the world Objectively?
Direction of signal transmission (see page 1, also lecture 2):
Neurons transmit signals only in one direction (from the dendrites to cell body [soma] to the end of the axon), but receive signals from different sources:
-Some input comes from earlier (functionally ‘lower’) processing stages (‘bottom up’
or ‘feed-forward’)
-Other input comes from functionally ‘higher’ processing areas (‘top down’ or ‘feedback’)
-Yet other input comes from neighbouring neurons in the same area (‘lateral’)
Combination of feed-forward and feedback signal transmissions means that signals
are never just passively ‘forwarded’ – every ‘input’ is already modified by every-
thing else going on in the brain!
Describe Motor output in Cortical Motor Areas
Cortical motor areas: Located in the frontal cortex, at the boundary to the parietal cortex
-Supplementary motor cortex & premotor cortex: involved in planning, monitoring, &
sensory guidance of movements
-Primary motor cortex: final execution stage – its motor neurons send axons directly
down the spinal cord (the pyramidal tract)
-Cortical motor areas are massively interconnected with two sub-cortical structures, forming complex motor control circuits:
-Basal ganglia: modulate movements, particularly in-volved in selective inhibition of movements
-Cerebellum: involved in maintaining posture & balance, timing of movements, & motor learning
-Both receive input from motor cortex, sensory cortex, and from other sub-cortical structures!
-Motor signals are ultimately sent down the spinal cord
