Brain organisation and neurodevelopment

Question 1

What are the 2 components of the CNS?

Answer 1

Spinal cord (ventral horn = somatic, lateral horn = autonomic reflexes)
Brain - perception/processing sensory stimuli, executing voluntary motor responses, regulating homeostasis

Question 2

What are the 2 divisions of the PNS?

Answer 2

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)

Question 3

What are the 2 components of the somatic division?

Answer 3

Sensory/afferent nerves - arise from sensory surfaces and convey info from body to brain/spinal cord
Motor/efferent nerves - controlling skeletal muscles

Question 4

What are motor neurons in the somatic division like?

Answer 4

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

Question 5

What are the 2 divisions of the autonomic nervous system and what are their neurons like?

Answer 5

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

Question 6

What are the key features of the sympathetic division?

Answer 6

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

Question 7

What are the key features of the parasympathetic division?

Answer 7

Decreases function (energy conservation)
Brain and sacral spinal cord
Ganglia usually located close to target organs

Question 8

How does the autonomic nervous system produce its effects?

Answer 8

Direct neural stimulation of body organs

Stimulating release of hormones from endocrine glands

Question 9

What are the earliest stages of the brain’s development?

Answer 9

Initially a neural tube, filled with fluid

Three swellings after a few weeks - forebrain, midbrain and hindbrain

Question 10

What happens to the brain 50 days after conception?

Answer 10

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)

Question 11

What is the key difference between a human brain and the brains of other mammals?

Answer 11

Cerebral cortex is more highly developed - subcortical, evolutionarily older structures are very similar and perform similar roles

Question 12

Historically, where has our understanding of brain function come from, and what is an issue with this?

Answer 12

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)

Question 13

What did Dax discover in 1836?

Answer 13

Speech difficulties in patients with frontal lobe damage suggesting a role of this area in controlling speech

Question 14

What did Aubertin discover?

Answer 14

Patient with front of cranium missing - press spatula against exposed area of frontal lobe and patient stopped talking

Question 15

What did Broca suggest?

Answer 15

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

Question 16

What did subsequent studies find following on from Broca?

Answer 16

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)

Question 17

How can neuroimaging be used to understand brain function?

Answer 17

Structural - detecting structural abnormalities

Functional - measurement during task performance i.e. measuring areas activated by different aspects of a task

Question 18

What are some functions of the frontal lobe, and thus what do we see if a stroke occurs here?

Answer 18

Personality, mood, language etc. (dominant hemisphere)

Personality and behaviour changes, inability to problem solve etc

Question 19

What are some functions of the parietal lobe and potential dysfunction?

Answer 19

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)

Question 20

What is the importance of the temporal lobe?

Answer 20

Memory, language, location of the primary auditory cortex

Recognition deficits i.e. agnosias can result from lesions here

Question 21

What are some key features of the midbrain?

Answer 21

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)

Question 22

What is the function of the cerebellum (metencephalon)?

Answer 22

Coordinates complex somatic motor patterns and adjusts the output of other somatic motor centres in the brain and spinal cord

Question 23

What does the pons do (metencephalon)?

Answer 23

Relays sensory information to cerebellum and thalamus
Subconscious somatic and visceral motor centres
Contains several nuclei from which cranial nerves arise

Question 24

What are 3 roles of the medulla oblongata?

Answer 24

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)

Question 25

How can frontal lobe function be tested?

Answer 25

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

Question 26

What are the 4 brain regions associated with motor control?

Answer 26

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

Question 27

What are the 4 key areas involved in sensory control?

Answer 27

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)

Question 28

What 3 brain areas are involved in higher cognitive functions?

Answer 28

Prefrontal cortex - personality, emotion, mood
Frontal cortex - calculation, reasoning
Temporal cortex - learning, memory and spatial recognition

Question 29

What are the 3 functions of CSF?

Answer 29

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

Question 30

What are ependymal cells?

Answer 30

Cells which line the ventricles, forming a structure called the choroid plexus, within which CSF is made by filtering blood

Question 31

What is the Wada test?

Answer 31

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

Question 32

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?

Answer 32

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