Regulation of Motor Control & Anatomy of Limbic System Flashcards
what are the mature structures of the mammalian forebrain
telencephalon: cerebral cortices, limbic system and basal ganglia
diencephalon: thalamus, hypothalamus, pituitary gland, mammillary bodies
what are the divisions of the limbic system (7)
- right cingulate cortex
- left cingulate cortex
- hippocampus
- amygdala
- mammillary body
- septum
- fornix
what is the limbic system involved in
control of emotion, learning and memory
what is the structure of the hippocampus
3 layer cortical structure
what is the function of the hippocampus
- spatial memory
- transfer of some types of information for long term memories
what are the cells of the hippocampus
- “grid” cells that provide a universal neuronal coordinate system for spatial navigation
- “place” cells are activated only when animal is in a specific place
what is the hippocampus role in explicit memories
what do hippocampal lesions impact
explicit memory
anterograde amnesia –> unable to recall anything
implicit memories and working memory intact
what is the structure of the amygdala
collection of nuclei
what is the function of the amygdala
affective behaviours and other species typical behaviour
what are the neurons in the amygdala
multimodal and respond to more than one sensory modality
multiple bidirectional with hypothalamus, hippocampus, cortices and brain-stem and regulates neural activity associated with emotions
what do lesions of the amygdala cause
- tameness and loss of fear
- indiscriminate dietary behaviour (eat previously rejected foods)
- greatly increased autoerotic, homosexual and heterosexual activity
- tendency to attend to and react to every visual stimulus
- tendency to examine all objects by mouth
what role does the amygdala play in fear response
learned responses such as to avoid specific animals, places and objects that are associated with danger
fear conditioning (pavlovian methods)
what is the fornix structure
bundle of fibres along medial aspect of hemisphere
inter-connections with hippocampi on both sides of the two cerebral hemispheres
what is the the function of the fornix
primarily connects the hippocampus to the mammillary body of the hypothalamus
other fibres connect directly to the anterior nucleus of the thalamus
what is the role of the fornix in emotional processing
malfunctions of fornix signalling have been associated with multiple sclerosis
demyelination of fibre bundles of the fornix has been identified as a functional consequence and symptoms of cognitive dysfunction such as dementia, short term memory impairements and long term learning impairments
alzheimers disease, schizophrenia
what is the structure of the mammillary body
intricately connected with the hippocampal formation, fornix, amygdala and midbrain
what is the primary function of the mammillary body
associated with recollective memory
emotion and goal directed behaviour
what causes significant damage to the mammillary bodies and what does it cause
trauma
stroke
tumours
alcoholism
results in anterograde amnesia and reduced motivation
what is the function of the septum
emotional behaviours, sexual behaviour, aggressive behaviour, modulation of autonomic functions, attention and memory functions
what does septum recieve input from
hippocampus, amygdala, hypothalamus and midbrain
where does the septum project to
hippocampus and dentate gyrus (via the fornix), the thalamus and several hypothalamic nuclei
what do septal lesions induce
rage and overt aggression
what is the structure of the cingulate cortex
reciprocal connections with the limbic (medial dorsal and anterior) thalamic nuclei and with other limbic areas including the subiculum and entorthinal cortex (hippocampal formation)
where do cingulate cortical neurons send axons to
to motor and premotor areas including the striatum, motor and premotor cortex
what is the cingulate cortex involved in
planned motor movements
what do lesions to the cingulate cortex cause
indifference to pain and other sensations that have strong emotional connotations
produce social indifference and apathy
eliminate emotional intonation in speech
personality changes
lesions in posterior cingulate cortex result in diminished ability to perform spatial navigation
what are bilateral anterior cingulate lesions cause
have been done as psychosurgery to alleviate intractable pain and to incapacitate anxiety, obsessive-compulsive behaviour and intractable depression
what is the structure of the basal ganglia
four nuclei
what is the function of the basal ganglia
voluntary movement
what are the outputs and inputs of the basal ganglia
don’t have direct input or output with spinal cord
input from the cortex and output to the midbrain
another output pathways via the thalamus projects to the frontal, premotor and motor cortices
what is the neural basis of parkinson’s disease
loss of dopamine leads to increased output of the basal ganglia
overactivity of the indirect pathway results in hypokinetic disorders (impaired initiation of movement and reduced voluntary movement)
what are the surgical interventions of parkinson’s disease
- lesions of the subthalamic nucleus reduces symptoms by eliminating the excessive output from the internal segment of the globus pallidus
- lesions of the internal segment of globus pallidus prevents abnormal output and partially restores voluntary movement
where does control of motor activity come from
feedback through sensory input and through prediction from previous activity
what is the hierarchy of motor control
higher animals have additional control from higher centres in brain (encephalization)
spinal cord “expects” input from higher centres –> spinal shock occurs when cut
how does the hierarchy system of motor control work
- sensory input coming in/being processed at higher centres
- higher centres regulate lower centres –> tonic inhibitory effect
- lesions at higher centres –> loss of integrated function, abnormal responses
what is the first step in the hierarchy of motor control
- sensory input goes to limbic system (motivation)
- basal ganglia (initiation of movement)
- cerebellum (coordination of movement)
- motor cortex (refines action)
- movement (spinal cord)
what are the descending pathways in the control of motor responses
- pyramidal tract
- extrapyramidal tract
what is the pyramidal tract
motor neurons that originate in the frontal cortex and terminate in the spinal cord (corticospinal) or brain stem (corticobulbar)
what is the extrapyramidal tract
located in the pons and medulla of the midbrain and involved in involuntary movements
what is pyramidal tract syndrome
characterized by spasticity and paralysis
what is the extrapyramidal tract syndrome
characterized by involuntary movements, muscular rigidity and immobility without paralysis
what are the upper motor neurons in the pyramidal and extrapyramidal tracts
extrapyramidal: reticulo-spinal, vestibulo-spinal, rubro-spinal, tecto-spinal
pyramidal: cortico-spinal
what are the tracts shown
what is the corticospinal tract
starts in cortex
required for fine, skilled movement
fibres terminate on inter-neurones in the spinal cord
what is the reticulospinal tract
“old” tract
basic instincts (startle reaction), postural, initiates locomotion
what is the rubrospinal tract
acts mainly on flexors, postural (where nuclei reside)
what is the tectospinal tract
input from vision and hearing
acts on cervical vertebrae
orientates head
what is the species variation in the tracts
humans: lots of pyramidal
horses: lots of extrapyramidal
dogs: lots of extra and less pyramidal than horses
what are effects of lesions in the descending tracts
lead to hyperactivity in extensor muscles
this is because descending tracts are inhibitory
what are the effects of lesions shown here
- decorticate: spastic
- decerebrate: rigid
- spinal: flaccid
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