Brain Pathways Flashcards
What is the PNS divided into?
Somatic and autonomic
Somatic; LMN, sensory fibres
Autonomic; sympathetic and parasympathetic; smooth muscle and glands
What is the diencephalon?
Thalamus and hypothalamus
What does the lateral (sylvian) fissure separate?
The frontal/parietal lobes from the temporal lobe
What is the function of the superior termporal gyrus?
Primary auditory cortex
What is the function of the cingulate gyrus?
Involved in emotion and memory
What is the function of the corpus callosum?
White matter that connects left and right hemisphere
What makes up the basal ganglia?
Caudate nucleus Putamen Globus pallidus Substantia nigra Subthalamic nucleus
What is the telencephalon?
Cortex
Basal ganglia
Limbic system
What is the metencephalon?
Cerebellum
Pons
What is the myelencephalon?
Medulla
What is the mesencephalon?
Midbrain
What is the basic function of the thalamus?
Relay station that sends information from the body to the cortex; specifically the post-central gyrus of the parietal lobe; somatosensory cortex
It also relays vision, auditory information and balance
What is special about olfactory information?
Does not pass through the thalamus
What do cortical projections to the thalamus play a role in?
Selective attention
What are the main functions of the frontal lobe?
Reasoning Movement Speech (brocas area) Personality Emotional behaviour
What are the main functions of the parietal lobe?
Somatosensory processing
Integrating visual and motor signals
What are the main functions of the temporal lobe?
Higher level visual perception
Auditory perception
Language
Memory
How many cortical layers make up the laminar structure of the neocortex?
6
At what layer does sensory information from the thalamus reach the cortex?
Layer 4
Aside from sensory information, what layer does information from other regions of the cortex reside in?
2,4 and 5
From what layer of the neocortex do outputs to the brainstem and spinal cord originate from?
5
From what layer do outputs back to the thalamus originate from?
6
From what layer do cortical-cortical projections arise from?
Superficial layers 2 and 3
What is special about the primary visual cortex in terms of the laminar structure?
Has a large layer 4 (input layer)
Small layer 5 (output to spinal cord and brainstem)
What is special about the laminar structure of the primary motor cortex?
Very small layer 4; sensory input
Large layer 5; motor information to spinal cord
What are some key brodmann areas?
Area 6; supplementary and premotor area. Planning of movement Area 4; primary motor cortex Somatosensory cortex; 3, 1 and 2 Posterior parietal cortex; areas 5 and 7 Visual cortex; areas 17, 18, 19 Primary visual cortex; area 17 Auditory cortex; areas 41,42
What is the function of the polymodal association cortex?
For example, posterior parietal cortex
Involved in high level sensory representations for example representing the space around us
What if the function of the prefrontal cortex?
Higher level planning and decision making
What are the dorsal and ventral visual streams?
2 major hierarchal pathways that visual information can follow:
Dorsally; Posterior parietal cortex
Ventrally; inferotemporal cortex
What is the role of the dorsal stream/ posterior parietal cortex?
Spatial perception
Damage in this region causes spatial neglect
What is the role of the ventral stream/ inferotemporal (IT) cortex?
Object recognition Semantic memory (what objects are, people, words and facts)
What is the role of the lateral prefrontal cortex?
Executive function
Planning
Working memory
What is the role of the ventromedial/ orbitofrontal cortex?
Social cognition
Decision making
Substantially damaged in phineus gage
What is the role of the anterior cingulate cortex?
Reward based learning
Social cognition
What is working memory?
Holds things in mind whilst you are thinking about something
What role does the lateral PFC play in working memory?
Densely interconnected with different cortex regions
Thought to provide a transient buffer linking memory representations stored in separate cortical regions
Where is the hippocampus located?
Deep within the medial temporal lobe next to the lateral ventricle
What cortical regions of the medial temporal lobe surrounds the hippocampus?
Entorhinal cortex
Rhinal sulcus
Perirhinal cortex
Parahippocampal cortex
What layers of tissue forms the hippocampus along the rostral/caudal section of the brain?
CA3 and CA1
Dentate gyrus
What is the flow of information between processing in the MTL for memory?
Unimodal/ polymodal association areas (frontal, temporal and parietal)
These relay to the parahippocampal and perirhinal cortex
These relay to the entorhinal cortex
The entorhinal cortex relays to the hippocampus
The hippocampus will then finally relay to the subcortical areas via the fornix
All of these connections are bidirectional; information flows both in and out
Describe the trisynaptic circuit of the hippocampus
The entorhinal cortex initially sends projections to the dentate gyrus (perforant pathway)
These projections make synaptic connections with the dentate granule cells
These granules send projections to CA3 via mossy fibre
The CA3 neurons then project to CA1 via Schaffer collateral pathway
CA1 then sends projections back to the EC either directly or via subiculum
What are some of the first cells to show pathological changes in AD?
Layer 2 entorhinal stellate neurones that provide the main input to the dentate gyrus and CA3
How do the CA3 neurons form an autoassociative network?
The neurons from CA3 not only project to CA1 via schaffer collateral pathway but also loop back to project onto their own dendrites (recurrent collaterals)
Why is the autoassociative network of CA3 important?
The neurons can change in strength, there is a simple form of learning
It also allows for pattern completion (this is to do with synaptic plasticity and learning)
What is the role of the fornix?
Connects the hippocampus to the anterior nucleus of thalamus, mamillary bodies, cingulate gyrus and hypothalamus (diencephalon)
What is the papez circuit?
Subcortical projections of the hippocampus via the fornix Fornix to: - Mamillary bodies - Hypothalamus (emotional expression) - Anterior nucleus of thalamus - Cingulate cortex (emotional experience) - Neocortex (emotional colouring) - Back to hippocampus Damage can cause memory impairment
What is the limbic system?
Group of structures involved in emotion and memory
What is involved in the limbic system?
Fornix (carries info from hippocampus to mamillary bodies)
Mamillary body (memory, connections with amygdala and hippocampus
Septal nucleus (pleasure, reward and reinforcement)
Hypothalamus (hormonal influence via anterior pituitary)
Amygdala (fearful and anxious emotions)
Hippocampus (memory)
Parahippocampal gyrus (memory)
Cingulate cortex - above corpus callosum (emotion and memory)
What motor loops are present between the basal ganglia and the cortex?
Motor area to basal ganglia and back
Motor area to cerebellum then into the basal ganglia
Describe the direct pathway in the basal ganglia
Facilitates movement (inhibition of inhibition) Neurons from striatum sends inhibitory neurons to the internal segment of globus pallidus allowing movement via thalamus
Describe the indirect pathway of the basal ganglia
Inhibits movement (via STN) Inhibitory signals sent from striatum to external globus pallidus This prevents GPe from inhibiting the STN which allows the STN to increase output to GPi - and therefore inhibits the thalamus and consequentially movement
Describe the hyperdirect pathway of the basal ganglia
Inhibits movement (supresses unwanted movement) Cortical outputs contact STN directly. This then projects to GPi; inhibits thalamus
What type of neurons make up the striatum and globus pallidus?
Inhibitory
At a cellular level, what is the striatum made up from?
Medium spiny neuron (MSN)
Describe the inputs to medium spiny neurons (MSN)
Excitatory via glutamate from cortex and thalamus
Inhibitory via GABAergic interneurons
Excitatory or inhibitory via dopaminergic neurons from pars compacta of substantia nigra
What is the overarching output of medium spiny neurons?
Inhibitory
What makes up the pars reticulata of the substantia nigra?
GABA inhibitory neurons
Describe the excitatory pathway of the direct pathway in respect to dopamine
Direct pathway expresses D1 receptors
These are Gs linked and triggers an intracellular cascade that ultimately leads to an increased excitability of the neuron
Describe the inhibitory pathway of the the indirect pathway in respect to dopamine
Expression of D2 receptors
These inhibit the cAMP pathway which ultimately leads to a decreased excitability of the cell
Why does dopamine have an overall effect of facilitating movement in the basal ganglia?
It activates the direct pathway; increases excitability of neuron
Inhibits the inhibitory pathway; causes overall decrease in excitability of the cell
What are betz cells?
Neurons present in layer 5 of the primary motor cortex
Cell bodies whose axons run down to the corticospinal tract
What is the difference between the anterior and lateral corticospinal tract?
Anterior; proximal musculature; decussation at level of LMN
Lateral; distal musculature; decussation at pyramids
Describe an UMN lesion
Weakness or paralysis
Hyperactive reflexes
Decreased motor control
Spastic muscle tone
Where do LMNs leave the spinal cord?
Alpha motor neurons leave the ventral (anterior) root of the spinal cord to innervate muscle
What is a motor unit?
An alpha motor neuron and all of the muscle fibres that it innervates
