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What 3 structures make up the Brain Stem?
- Midbrain
- Pons
- Medulla Oblongata
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What is the role of the Midbrain?
Links forebrain to hindbrain
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The Substantia Nigra of the Midbrain has what function?
- Connect basal nuclei
- Regulate movement
- (black due to melanin precursor of dopamine)
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The Red Nuclei of the Midbrain has what function?
- Relay descending motor pathways
- (red due to blood and iron)
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The Corpora Quadrigemina of the Midbrain is split into two different functional groups -
- Superior Colliculi - Vision reflexes
- Inferior Colliculi - Auditory reflexes
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The Midbrain's ventral aspect is characterised by what?
Cerebral peduncles which contain large pyrimidal tracts that relay motor signals from the motor cortex to the spine
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What is the function of Periaqueductal Grey Matter of the Midbrain?
- Encircles aqueduct linking 3rd and 4th ventricles
- - Pain supression
- - Links Amygdala
- - Autonomic 'fight or flight' pathways
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What is the Reticular Activating System?
- RAS - Neurons projecting through medulla, pons and midbrain
- ALL SENSES SYNAPSE TO RAS
- 99% filtered out
- Keeps brain awake - inhibited by Hypothalamus
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What is the Pons?
- Origin of CNV CNVI and CNVII
- Conduction tracts
- Contains Pneumotaxic centre
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What is the Medulla?
- Contains ALL ascending sensory nerve tracts and ALL descending motor
- Anterior Surface contains Pyramidal tracts
- Control Centre for a lot of Autonomic reflexes
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Where are the Chemoreceptors and what do they respond to?
- Central - Medulla, stimulated by H+
- Peripheral - Arteries of neck, CO2 and O2, impulses travel via Vagus (CNX) and Glossopharyngeal (CNIX)
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What is the role of the Cardiovascular Centre of the Medulla?
To adjust the force of heart, vessel diameter, blood flow and pressure (vasomotor centre)
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The Cardiovascular Centre recieves input from where?
- Preparation for Exercise - Cerebral Cortex, Limbic System, Hypothalamus
- Anatomical Input - Proprioceptors (joints+muscles), Baroreceptors(blood vessel stretch), Chemoreceptors
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The Cardiovascular Centre outputs to where?
- Sympathetic - Cardiac accelerator nerves
- - Vasomotor nerves for smooth muscle vasoconstriction
- Parasympathetic - Vagus (CNX)
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Explain the process of the Pons and Medullary Deglutition centre
- 1.Bolus of Food voluntarily passes to Oropharynx
- 2. Involuntary: Pharynx signals Deglutition centre in Medulla and Lower Pons
- 3. Returning Impulses cause soft palate and uvula to close of nasopharynx and epiglottis to close off larynx
- 4. Oesophageal sphincter relaxes, bolus moves into oesophagus
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Explain the process of the Medullary Vomiting centre
- 1. Stimuli send impulses to medullary vomiting centre
- 2. Co-ordinated motor impulses sent to contract diaphragm and abdominal muscles and relax cardiac sphincter
- 3. Soft palate closes off nasal passages
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Explain the process of the Medullary Sneezing Centre and Couging centres
- Sneeze - Stimuli -> medulla ->CNV-> uvula depresses, abdominal muscles contract
- Cough - Stimuli-> medulla -> CNX -> glottis closes, respiratory musculature contracts. Can be cortically controlled
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What are the basic concepts of Motor Control?
- Primary Motor Cortex - Conscious initiation
- Actual Control - Cerebellum and Basal Nuclei
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What are the 3 sections of the Cerebellum and their associated roles?
- Anterior and Posterior Lobes - Subconscious Body Movement
- Flocculondular Lobe - Vestibular equilibrium and balance
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What is the Stretch Reflex?
- Spinal Reflex
- Ensures muscle length
- eg. No knee buckling
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What is the Golgi Tendon Reflex?
- Spinal Reflex
- Opposite to Stretch Reflex - relax and lengthen in response to tension
- Allows smoooth muscle action and prevents tears
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What is the Flexor or Withdrawal Reflex?
- Spinal Reflex
- Withdrawal from painful stimuli
- Can be cortically overcome
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What is the Crossed Extensor Reflex?
- Spinal Reflex
- Accompanies Flexor
- Maintains balance when bearing weight
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What are the two Descending Motor Pathways?
- Pyramidal Tracts - Direct and Voluntary
- Extrapyramidal System - Reflexive and indirect, multineuronal
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What are the Reticulospinal Tracts?
- Originate Reticular Formation of Pons and Medulla
- - Locomotion of Limbs
- - Postural control
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What is an oversimplification of Motor Control?
1. Motor Cortex " what do I want to do?"
2. Precommand Areas Cerebellum and Basal Nuclei take over and determine timing and patterns - 3. Via thalamus, returns information to Motor Cortex
- 4. Motor Cortex initiates or terminates action
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