Functional Anatomy Of The Brain + Cranial nerves Flashcards
What does the frontal lobe do?
Reasoning
Behaviour
Mood
Movement
What is the function of the temporal lobe?
Hearing
Memory (hippocampus)
Semantics
What is the function of the parietal lobe?
Sensory - pain, pressure, temperature
What is the function of the occipital lobe?
Sight
What is the corpus callosum.
Connects the cerebral hemispheres and allows communication between them
What is the amygdala and what does it do?
It is a group of neurons located deep to the medial temporal lobes
Have a primary role in processing and memory of emotional reactions
What is the general role of the limbic system?
Supports a variety of functions including emotion, behaviour and long-term memory
What is the function of the basal ganglia?
Co-ordinates gross, automatic muscle movements and regulates muscle tone
Which brain regions make up the diencephalon?
Epithalamus
Thalamus
Hypothalamus
Subthalamus
What is the function of the epithalamus?
Consists of the
- pineal gland (melatonin secretion - biological clock and sleepiness)
- habenular nuclei (emotional response to olfaction)
What is the function of the thalamus?
Relays sensory information to the cerebral cortex
Includes nuclei involved in voluntary, motor and arousal actions
Anterior nucleus functions in emotions, memory, cognition and awareness
Describe the function of the subthalamus
Contains - subthalamic nuclei - portions of basal substantia nigra - portions of red nucleus Helps control body movements
Describe the function of the hypothalamus
Controls and integrates ANS and pituitary gland activities
Regulates emotional and behavioural patterns
Controls body temperature
Regulates eating and drinking behaviour
What structures make up the midbrain?
Midbrain
Superior colliculus
Inferior colliculus
What is the function of the midbrain?
Relays motor impulses from cerebral cortex to the pons
Relays sensory impulses from the spinal cord to thalamus
What is the function of the superior colliculus?
Co-ordinates movement of the eyeballs in response to visual and other stimuli
What is the function of the inferior colliculus?
Co-ordinates movement of the head and trunk in response to auditory stimuli
What brain parts make up the hindbrain?
Cerebellum
Pons
Medulla oblongata
What is the function of the cerebellum?
Compares intended movements to what is actually happening
- co-ordinates smooth and complex movements
Regulates posture and balance
What is the function of the pons?
Relays impulses from one side of cerebellum to the other, and from medulla to midbrain
Contains nuclei of origin for CNV, VI, VII, and VIII
What is the function of the medulla oblongata?
Relay between brain and spinal cord
Reticula formation functions in consciousness and arousal
Vital centres regulate heart beat, breathing and blood vessel diameter
Other centres co-ordinate vomiting, swallowing, coughing, sneezing and hiccuping
Contains nuclei of origin for CNIX, X, XI and XII
What does the olfactory nerve do?
Sensory - sense of smell
What does the optic nerve do?
Sensory - sight
What does the oculomotor nerve do?
Motor
- eyelid movement
- eyeball movement (medial, superior and interior rectus and inferior oblique)
- pupillary constriction
- accommodation of lens for near vision
What does the trochlear nerve do?
Motor
- eyeball movement (superior oblique)
What does the trigeminal nerve do?
Both sensory and motor
- sensory to the face (opthalamic, maxillary and mandibular)
- motor to the muscles of mastication (masseter, temporal is, pterygoid)
What does the abducens nerve do?
Motor
- movement of eyeball (lateral rectus)
What does the facial nerve do?
Both
- sensory to skin of external ear and anterior tongue
- motor to muscles of facial expression and helps secrete saliva and tears
What does the vestibulocochlear nerve do?
Sensory
- hearing and equilibrium
What does the glossopharyngeal nerve do?
Both sensory and motor
- motor is for swallowing and speech and secretion of saliva
- sensory is to carotid body and sinus and taste for posterior tongue
What does the vagus nerve do?
Both sensory and motor innervation
- swallowing and speech
- parasympathetic innervation
What does the accessory nerve do?
Motor
- movement of head and shoulders (sternocleidomastoid and trapezius)
What does the hypoglossal nerve do?
Motor
- movements of the tongue
What is the function of the primary motor cortex?
Generates nerve impulses that control the execution of movement
What is the function of the posterior parietal cortex?
Transforms visual information into motor commands
Sends this information to premotor and supplementary motor cortex areas
What is the function of the premotor cortex?
Sensory guide of movement
Controls more proximal and trunk muscles
Describe the function of the supplementary motor cortex.
Planning and co-ordination of complex movements
What is the input and output for the striatum of the basal ganglia?
Input - brain regions - motor cortex, premotor cortex
Output - globus palidus internal (inhibitory neurons)
What are the components of the basal ganglia?
Dorsal striatum - caudate nucleus and Putamen Substantia nigra Globus palidus - internal and external Subthalamic nuclei Thalamus
What is the input and output for the globus palidus internal of the basal ganglia?
Input - inhibitory neurons of the striatum
Output - stops inhibiting the thalamus
What is the input and output for the substantia nigra of the basal ganglia?
Input - excitatory neurons of the subthalamic nucleus
Output - dopaminergic neurons that excite the inhibitory messages the striatum is sending to the globus palidus internal
What is the input and output for the subthalamic nucleus of the basal ganglia?
Input - excitatory neurons from the motor cortex and inhibitory neurons from the substantia nigra
Output - excitatory neurons to the substantia nigra
What is the substrate for dopamine synthesis?
Tyrosine
In the cytoplasm a of the dopaminergic neuron, what is tyrosine converted to?
DOPA via the action of tyrosine hydroxylase
How is DOPA converted to dopamine?
DOPA-decarboxylase
How is dopamine transported into storage vesicles?
Active transport carried out by the vesicular transporter mechanism
What is dopamine re-uptake 1?
When dopamine is released into the synaptic cleft and is then actively transported back into the neuronal terminal (this happens to 50% of dopamine in cleft)
What happens to the dopamine in the neuronal terminal that isn’t transporterd into vesicles for storage and release?
It’s broken down by the mitochondrial enzyme monoamine oxidase
What is re-uptake 2?
When some of the dopamine (10%) in the synaptic cleft is actively transported into the effector cell
How is dopamine inactivated in the effector cell?
Inactivated by the enzyme catchol-o-methytransferase (COMT)
What happens the the 40% of dopamine still left in the synaptic cleft?
Diffuses into the circulation and is broken down by monoamine oxidase and COMT in the liver
What are the end products of dopamine metabolism?
Organic acids and alcohol
- excreted in the urine
What is the precursor molecule for tyrosine, and what enzyme catalyses the reaction?
L-Phenylalanine
- phenylalanine hydroxylase
What are the four main dopaminergic pathways in the brain?
Nigrostriatal pathway
Mesolimbic pathway
Mesocortical pathway
Tuberhypophyseal system
What is the name of the bundle of monoamine containing fibres that the nigrostriatal, mesolimbic and mesocortical system travel in?
Medial forebrain bundle
Where are the cell bodies found in the nigrostriatal pathway?
In the substantia nigra
Where are the cell bodies for the dopaminergic neurons in the mesolimbic pathway?
In the midbrain ventral tegmental area (VTA) adjacent to the substantia nigra
Where do the neurons in the mesolimbic pathway project to?
Parts of the limbic system
- especially the nucleus accumbens and amygdaloid nucleus
Where are the cell bodies of the neurons in the mesocortical pathway found?
In the midbrain ventral tegmental area (VTA)
Where do the neurons of the mesocortical pathway project to?
Frontal cortex
Where do the neurons of the tuberohypopyseal system start and terminate?
Run from the ventral hypothalamus to the median eminence and pituitary glands
What is the function of the tuberohypopyseal system of dopamine action?
Controls secretions of the pituitary gland
Which dopamine receptors are in the D1 receptor family?
D1 and D5
Which dopamine receptors are in the D2 receptor family?
D2, 3 and 4
Which areas are D1 receptors found in?
Striatum
Limbic system
Thalamus
Hypothalamus
Which areas of the brain are D2 receptors found in?
Striatum Limbic system Thalamus Hypothalamus Pituitary gland
What are the function of D2 receptors?
Inhibitory autoreceptors
What are the effects in the periphery that dopamine receptors (D1) exert?
Renal vasodilation
Increased myocardial contractility
What is the function of dopamine in the nigrostriatal system?
Excites the inhibitory messages being sent to the globus palidus.
Fine tunes motor movements
What is the function of dopamine in the mesolimbic and mesocortical systems?
Mediates the pleasure system in the brain (reward pathway)
Allows motivational and emotional responses
What is the function of dopamine in the tuberohypopyseal system?
Acts on lactotrophs in the pituitary gland to inhibit release of prolactin.
Where do neurons of the noradrenergic system arise from?
Neurons of the locus coeruleus
- on one each side of the pons
List the places in the brain that the neurons from the locus coeruleus (noradrenergic neurons) innervates?
All the cerebral cortex Thalamus Hypothalamus Olfactory bulb Cerebellum Midbrain Spinal cord
What is the function of the noradrenergic system?
Regulates attention, arousal, sleep-wake cycles, leaning, memory, anxiety, pain, mood and brain metabolism
Where do the serotonin-containing neurons originate?
The nine-rap he nuclei
Where do the more caudal (medulla) of the nine raphe nuclei project?
The spinal cord
- modulate pain-related sensory signals
Where do the more rostal (those in the pons and midbrain) of the nine raphe nuclei innervate?
Most of the brain, in the same diffuse way as the locus coeruleus neurons
When do serotonin neurons fire the most rapidly?
Fires the most during wakefulness (when aroused and active)
- most quiet during sleep
- so involved in the sleep-wake cycles
Describe the reticular activating system.
Includes the raphe nuclei and the locus coeruleus
Included the reticular core of the brainstem in the processes that arouse and awaken the forebrain
Define Parkinson’s disease.
Progressive degenerative disorder of the basal ganglia that results in variable combinations of tremor, rigidity and bradykinesia
What is the pathology that causes Parkinson’s?
Dopamine depletion resulting from a degeneration of the dopamine nigrostriatal system
What are some other reasons (apart from dopamine depletion) that can causes Parkinsonism.
Postencephalitic syndrome
Side effects of anti-psychotic drugs (block dopamine receptors)
Toxic reaction to a chemical agent
Outcome of severe CO poisoning
What are the pathological processes that destroy the nigrostriatal system.
Oxidative stress
Apoptosis
Mitochondrial disorders
Auto-oxidation of dopamine may injure the neurons
Describe what happens in alpha-synuclein mutations to cause Parkinson’s.
Alpha-synucleins are a member of a family of proteins found mostly in the substatia nigra
Mutations cause an autosomal dominant form of the disease
- mutation can cause this protein to form Lewy bodies (eosinophilic cytoplasm inclusions found in surviving neurons)
Name the two mutations associated with Parkinson’s disease.
Alpha-synuclein mutations
Parkin mutations - autosomal recessive early onset form of Parkinson’s
What are the main symptoms of Parkinson’s disease.
Tremor Rigidity Bradykinesia Falls Fluctuations in motor function Neuropsychologist disorders Sleep disorders
Describe the tremors associated with Parkinson’s disease.
Affects distal segments of limbs - hands, feet, head, neck, face, lips and tongue Rhythmic flexion and contraction Usually unilateral Occurs when limb is supported/at rest Disappears in movement or when sleeping
Describe the rigidity associated with Parkinson’s disease.
Resistance to movement of flexors and extensors
Most evident during passive joint movements
- cogwheel rigidity
- requires lots of energy to perform
Flexion contraction occur due to rigidity
Starts unilateral - becomes bilateral
What is bradykinesia?
Slowness in initiating and performing movements
Difficulty with sudden, unexpected stopping of voluntary movements
Unconscious movements occur in a series of disconnected steps - not in a smooth manner
Describe problems bradykinesia causes.
Difficulty initiating walking and turning
Feet may freeze in place while walking
Lean forward when walking to maintain centre of gravity
Small, shuffling steps without swinging arms
Describe some of the later stage Parkinson symptoms.
Loss of postural reflexes
Voluntary/emotional face movements become limited - mask like face
Loss of blinking reflex
Tongue, palate and throat muscles become rigid = drooling
Speech becomes slow and monotonous - no modulation and poorly articulated
Excessive sweating, sebaceous gland secretion and salivation - due to basil ganglia involvement with ANS
- also causes lacrimation, dysphagia , orthostatic hypertension, thermal regulation, constipation, impotence and urinary incontinence
What are the later stage cognitive problems of Parkinson’s?
Cognitive dysfunction occurs in 20-30% of people
Deficits in executive function disappear first
- difficulty planning, starting and carrying out tasks
Dementia
Slower rate of decline than in Alzheimer’s
How does L-DOPA medication help people with Parkinson’s?
L-DOPA is a precursor to dopamine
Administering more substrate will increase the amount of dopamine being synthesised in the remaining 20% of healthy dopaminergic neurons
What is the disadvantage of L-DOPA?
It only manages symptoms - doesn’t fix the destroyed nigrostriatal pathway
Only works while it is present in the body
Only works if there are enough healthy neurons left to convert it into dopamine
- doesn’t work in late stage Parksinon’s because the degeneration has progressed too far
Which drugs is often co-administered with Levodopa, and why.
Carbidopa - a DOPA decarboxylase inhibitor
- can’t cross the blood brain barrier
- reduces nausea and vomiting often found with L-DOPA administration
Why is levodopa given to patients rather than dopamine?
Dopamine can’t cross the blood brain barrier, so would remain in the periphery
Why are such large amount of levodopa given to patients?
Because a lot is converted to dopamine in the periphery before it can enter the brain
Describe the mechanism of action of cabidopa.
Inhibits dopa decarboxylase, so prevents peripheral conversion of levodopa to dopamine
Lowers levodopa dose needed by 5-fold
Decreases severity of side effects - vomiting and nausea
