Brain organisation and neurodevelopment Flashcards
What are the 2 components of the CNS?
Spinal cord (ventral horn = somatic, lateral horn = autonomic reflexes) Brain - perception/processing sensory stimuli, executing voluntary motor responses, regulating homeostasis
What are the 2 divisions of the PNS?
Somatic division - communicates with sense organs and voluntary muscles
Autonomic division - communicates involuntarily with internal organs and glands, controlled on the basis of automatic feedback to the sensory division (functionally supported by autonomic ganglia)
What are the 2 components of the somatic division?
Sensory/afferent nerves - arise from sensory surfaces and convey info from body to brain/spinal cord
Motor/efferent nerves - controlling skeletal muscles
What are motor neurons in the somatic division like?
Cell body in CNS single neuron from CNS to effector organs Heavily myelinated axons ACh released at effector Effector organ is skeletal muscle Stimulatory effects
What are the 2 divisions of the autonomic nervous system and what are their neurons like?
Sympathetic - Cell bodies in CNS, two-neuron chains from CNS to effector, lightly myelinated pre-ganglionic axons, non-myelinated post-ganglionic, ACh released at synapse, norepinephrine released at effector, effectors are smooth muscle/glands/cardiac muscle, stimulatory or inhibitory effects depending on NT and receptors on effector organs
Parasympathetic - Two neuron chain, lightly myelinated pre-ganglionic, ACh at synapse with ganglion, non-myelinated post-ganglionic, ACh at effector, effector organs and effect same as for sympathetic
What are the key features of the sympathetic division?
Increases function (fight or flight) Sympathetic chains of autonomic ganglia and nerve fibres from them (pre-ganglionic axons are short) Thoracic and lumbar spinal cord
What are the key features of the parasympathetic division?
Decreases function (energy conservation)
Brain and sacral spinal cord
Ganglia usually located close to target organs
How does the autonomic nervous system produce its effects?
Direct neural stimulation of body organs
Stimulating release of hormones from endocrine glands
What are the earliest stages of the brain’s development?
Initially a neural tube, filled with fluid
Three swellings after a few weeks - forebrain, midbrain and hindbrain
What happens to the brain 50 days after conception?
Forebrain and hindbrain are clearly sub-divided
Forebrain becomes telencephalon (cerebral hemispheres plus deeper structures) and diencephalon (thalamus and hypothalamus)
Hindbrain becomes metencephalon (cerebellum and pons) and myelencephalon (medulla oblongata)
What is the key difference between a human brain and the brains of other mammals?
Cerebral cortex is more highly developed - subcortical, evolutionarily older structures are very similar and perform similar roles
Historically, where has our understanding of brain function come from, and what is an issue with this?
Brain damaged patients - studying their cognitive and behavioural deficits and locating corresponding areas of damage using neuroimaging or post-mortem study
Disconnection between the information of the present deficits and the information of the underlying biological problem (poor medical communication)
What did Dax discover in 1836?
Speech difficulties in patients with frontal lobe damage suggesting a role of this area in controlling speech
What did Aubertin discover?
Patient with front of cranium missing - press spatula against exposed area of frontal lobe and patient stopped talking
What did Broca suggest?
The case of Tan - unable to speak more than a few meaningless syllables but intelligent and able to comprehend language and communicate using gestures
Post mortem showed lesion to back of LEFT frontal lobe, providing evidence for highly localised control of function in the cortex
What did subsequent studies find following on from Broca?
Similar lesions in other patients with similar deficits - area now termed Broca’s area
Left sided in everyone irrespective of dominance, and located adjacent to the part of the motor cortex responsible for vocal cords and mouth movement (convenient location)
How can neuroimaging be used to understand brain function?
Structural - detecting structural abnormalities
Functional - measurement during task performance i.e. measuring areas activated by different aspects of a task
What are some functions of the frontal lobe, and thus what do we see if a stroke occurs here?
Personality, mood, language etc. (dominant hemisphere)
Personality and behaviour changes, inability to problem solve etc
What are some functions of the parietal lobe and potential dysfunction?
Control of language, calculation (dominant hemisphere) Visuospatial functions (non-dominant hemisphere) Attention deficits such as contralateral hemispatial neglect syndrome (no attention paid to side of body opposite to side of lesion)
What is the importance of the temporal lobe?
Memory, language, location of the primary auditory cortex
Recognition deficits i.e. agnosias can result from lesions here
What are some key features of the midbrain?
Responsible for processing visual (superior colliculi) and auditory data (inferior colliculi), generating reflexive somatic motor responses and maintaining consciousness
Smaller and structurally simpler than forebrain and hindbrain - Tectum (the colliculi), substantia nigra (motor system, parkinsons when damaged), and red nucleus (motor centre that communicates with motor neurons in spinal cord)
Several cranial nerves arise from the midbrain (rest come from brainstem)
What is the function of the cerebellum (metencephalon)?
Coordinates complex somatic motor patterns and adjusts the output of other somatic motor centres in the brain and spinal cord
What does the pons do (metencephalon)?
Relays sensory information to cerebellum and thalamus
Subconscious somatic and visceral motor centres
Contains several nuclei from which cranial nerves arise
What are 3 roles of the medulla oblongata?
Relays sensory info to thalamus
Nuclei of cranial nerves 11 and 12 are found here (control of neck and tongue muscles respectively)
Autonomic centres for regulation of visceral functions e.g. cardiovascular and respiratory activities (so lesions here are often fatal)
How can frontal lobe function be tested?
1) Wisconsin card sort task - have to match a card to a category which is never explicitly stated, need to figure out what rule is being used based on correct/incorrect feedback
2) Tower of Hanoi/London - need to move stack of rings to a different pole, but can only move one at a time and larger rings must never be on top of smaller ones; requires executive function and strategic planning so perform poorly with frontal lobe damage
What are the 4 brain regions associated with motor control?
Primary motor cortex (precentral gyrus - motor homunculus map is here) - motor output to muscles
Supplementary motor cortex - motor planning
Basal ganglia - motor patterns
Cerebellum - motor coordination
What are the 4 key areas involved in sensory control?
Primary somatosensory cortex and association cortex (info arrives, and info processed respectively) - parietal, postcentral gyrus
Primary auditory and auditory association cortex (temporal)
Primary visual and visual association cortex (occipital)
Primary olfactory and olfactory association cortex (beneath temporal lobe)
What 3 brain areas are involved in higher cognitive functions?
Prefrontal cortex - personality, emotion, mood
Frontal cortex - calculation, reasoning
Temporal cortex - learning, memory and spatial recognition
What are the 3 functions of CSF?
Protection and cushioning
Buoyancy and reduction in weight –> reduction in pressure on base of brain
Chemical stability - e.g. helps maintain low extracellular potassium for synaptic transmission
What are ependymal cells?
Cells which line the ventricles, forming a structure called the choroid plexus, within which CSF is made by filtering blood
What is the Wada test?
It is a test to determine where your brain controls language and memory functions
One side of the brain is put to sleep - Once the doctors are sure one side of your brain is asleep, the neuropsychologist tests your ability to speak and remember. They will show you words, objects, and pictures on a card.
The awake side of the brain tries to recognize and remember what it sees.
After just a few minutes, the medicine wears off. The side that was asleep starts to wake up.
Once both sides of your brain are fully awake, the neuropsychologist will ask you what was shown. If you don’t remember what you saw, items are shown one at a time and asked whether you saw each one before.
The same is done on the other side too
In addition to looking at behavioural deficits and also using functional mri to assess brain activity, what is one final way in which we can study brain function?
Animal models - look at neuronal and neurochemical activity, effects of drugs etc. in experimental animals
Subcortical functions can be studied using lower mammals e.g. rodents, while cortical function generally requires higher mammals such as cats or primates
