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MD4001 > From Cells to Cortex > Flashcards

From Cells to Cortex Flashcards

1
Q

Draw a neuron, including its main components.

A

Refer to slide 9 in lecture “From Cells to Cortex”

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2
Q

What is the main function of axons ?

A

Direct unitary digital output away from the cell (dendritic spines are principal axon target)

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3
Q

What is the main function of dendrites ?

A

Direct stimulus towards the cell body

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4
Q

What is the main function fo the axon hillock ?

A

“This is the region where the plasma membrane generates nerve impulses”

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5
Q

What are the main features of nervous transmission ?

A
  • Vectorial impulse transmission/propagation
  • Dissociative secretion/synapse formation
  • Chemical transmission (chemical NTs secreted by secretory cell)
  • Can be inhibitory or excitatory
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6
Q

What are the main types of neurons ? Which is the most common in the CNS ?

A
  • Unipolar
  • Bipolar
  • Multipolar (most common in CNS)
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7
Q

Draw a unipolar, bipolar, and multipolar neuron.

A

Refer to Google.

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8
Q

What is a unipolar neuron ?

A

AKA Pseudo-unipolar, cell body gives off a single axonal process resulting from the fusion of two polar processes during development. The process divides into a peripheral axon branch extending outward as a peripheral afferent (sensory) nerve fiber, and a central axon branch that enters into synaptic contact with neurons in the spinal cord or brainstem. Peripheral process collecting the sensory impulse is an axon structurally due to myelin, but a dendrite functionally, as it transports APs towards cell body. The cell body of these neurons “is located in a DRG”

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9
Q

What is a bipolar neuron ?

A

“Two branches leave the cell body of a Bipolar Neuron. Dendritic tree (often with receptors) emerges from one end of the cell body, while the axon emerges from the opposite end, going into the CNS. Bipolar neurons are often sensory neurons associated with special sense organs including ear, eye, nose”

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10
Q

What is a multipolar neuron ? Give examples.

A

“a neuron with several processes, usually an axon (can be short, or long) and three or more dendrites”

E.G.
Interneurons (for local processing, can be inhibitory or excitatory, has short axon)

Pyramidal cell (sends info from cerebral cortex, has long axon)

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11
Q

Identify the main features of unmyelinated axons.

A
  • PNS: Schwann cells ‘envelope’ unmyelinated axons contacting 1 or more axons (i.e. embedded in Schwann Cytoplasm)
  • CNS: Unmyelinated axons are not associated with glial cells

• Unmyelinated axons have ‘continuous conduction’ of action potentials due to passive current flow (low conduction)

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12
Q

Give examples of unmyelinated axons.

A

Examples of unmyelinated axons are sensory fibres carrying pain, temperature, itch

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13
Q

Identify a common pathology due to a defect in myelin, and state its main features.

A

Multiple Sclerosis:

  • Immune attack causing degeneration of myelin (phasic but progressive demyelinating disease)
  • Effects from this include:

Inflammation (T cell/macrophage mediated)
Crosstalk (paraesthesia)
Conduction block (slowing of propagation)
Some re-myelination
Permanent loss (due to cell death/axonal loss)

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14
Q

Distinguish between white and grey matter.

A

WHITE MATTER- Collections of nerve fibres many of which are coated with insulating fatty myelin (largely just cell processes)

GREY MATTER- Contains neuron cell bodies, processes, synapses, dendritic spines, axon endbulbs, Glial cells (contains very little myelin)

In spinal cord, white matter on the outside with grey matter on the inside
In cerebral hemispheres, grey matter is on the outside while white matter is on the inside. However, there are some grey matter structures deep in the brain include basal ganglia, thalamus and hypothalamus.

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15
Q

Identify the main Glial cells of the CNS.

A
  • Oligodendrocytes (myelination)
  • Astrocytes
  • Microglia
  • Ependyma (lining cells of the CNS cavities)
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16
Q

Identify the main Glial cells of the PNS.

A
  • Schwann cells (myelination)

* Satellite cells (support cells in ganglia)

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17
Q

Describe the structure of Astrocytes, and list their main functions.

A

STRUCTURE
Fibrous in white matter, Protoplasmic in grey matter

FUNCTIONS:
• Control water distribution
• Potassium buffering
• ROS scavenging (ROS stands for reactive oxygen species)
• Define architecture
• Regulate migration/pruning/synaptogenesis
• Help maintain but do not make up the BBB
• Present in CNS scar tissue

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18
Q

What are the main components of the BBB ?

A

Endothelial cells and their tight junctions

but integrity is highly dependent on astrocyte end feet

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19
Q

What are the main functions of the microglial cells ?

A

Resident macrophages of the CNS:
• Phagocytosis and antigen presentation (immune response)
• Synaptic pruning (“synapse elimination including both axon and dendrite death”)

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20
Q

What type of cells are ependymal cells ?

A

Ciliated cuboidal epithelial cells

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21
Q

What are the main functions of ependymal cells ?

A

Line ventricle (in single layer) as part of plexus and secrete (also reabsorb) CSF

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22
Q

Where is CSF produced ?

A

CSF (cerebrospinal fluid) – clear, cell-free fluid produced in specialised ependyma on choroid plexus

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23
Q

Where in the brain can we find choroid plexus ?

A

In lateral, third and fourth ventricles

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24
Q

Identify the lobes of the brain, explaining where each one is.

A

Frontal (anterior aspect)
Parietal (posterior to frontal)
Occipital (posterior to paietal and temporal)
Temporal (inferior to parietal)

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25
Q

Define lamination in the context of the brain.

A

Lamination means layer-like arrangement.

  • Most cerebral cortex is 6 layered neocortex (e.g. visual and motor cortex)
  • Some of it is 3 layered paleocortex (e.g. prepyriform cortex)
  • Some is 4 layered archicortex (e.g. hippocampus)
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26
Q

Identify the main layers of neocortex.

A

From superficial to innermost:

  • Molecular layer (I) (contains mainly neuronal processes)
  • External granular layer (II)
  • External pyramidal layer (III)
  • Internal granular layer (IV)
  • Internal pyramidal layer (V)
  • Multiform layer (VI) (contains output neurons of varying shapes and sizes)
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27
Q

Describe the main features of the Granular layers of cerebral cortex.

A
  • Stellate/Granular neurons
  • Shorter axons and smaller dendritic trees and remain within the cortex.
  • They are the main interneurons.
  • Responsible for local processing
  • External granular layers take input from other local areas in cerebral cortex
  • Internal granular layers take input from places much more distant, from the thalamus
28
Q

Describe the main features of Pyramidal layers of cerebral cortex.

A
  • Pyramidal neurons
  • Characteristic triangular structure (of these neurons), typically with one apical dendrite and abundant dendritic trees coming from the cell body.
  • The axons of the pyramidal cells project from the cortex to other regions of the CNS, making them the main output cells of the cortex.
  • External pyramidal layers take output to other parts of cerebral cortex
  • Internal pyramidal layers take output to more distant places in body through the the brain stem and spinal cord (e.g. to head)
29
Q

Are the layers of neocortex of similar thickness throughout the brain ? Give an example.

A

No, layers vary in thickness (function) from region to region.

In striate cortex (primary visual), layer IV is well developed, which makes a striped appearance)

Interneurons (IV) are more numerous in sensory cortex

Pyramidal output (V) is more marked in motor cortex

30
Q

Define functional specialisaiton in the context of the brain.

A

“Functional specialization suggests that different areas in the brain are specialized for different functions”

31
Q

Define Brodmann areas.

A

“Regions of the cerebral cortex distinguished on the basis of histologic differences and presumed differences in function”

32
Q

Identify ways to map the brain other than based on histology (i.e. Broadmann areas).

A

Disease/damage effects
fMRI
PET
Electrical stimulation (during surgery)

33
Q

What is Broadmann area 4? What is its location ?

A

Area 4- Primary motor cortex (in precentral gyrus of the frontal lobe)

34
Q

Label the main Broadmann areas on a brain.

A

Refer to slide 34 in lecture “From Cells to Cortex”

MUST IDENTIFY:

  • Wernicke’s area (39-40)
  • Broca’s area (44-45)
  • Primary auditory cortex (22)
  • Primary motor cortex (4)
  • Primary visual cortex (17)
  • Visual association cortex (18, 19, 20, 37)
  • Primary somatosensory cortex (1, 2, 3)
35
Q

Where in the brain is the visual cortex located ? Identify the main Broadmann areas in the visual cortex, stating the role of each.

A

Visual Cortex is in occipital lobe

Areas 17, 18, 19, 20, 37. First point of entry of sensory input. Higher order processing occurs in association visual cortex, i.e. areas 18, 19, 20, 37

-Area 17- Primary visual cortex (AKA V1)

  • Area 18- Depth, binocular, patterns
  • Area 19- Motion
  • Area 20- Object, Recognition
  • Area 37- Facial recognition (Fusiform face area)
36
Q

Describe the consequence of damage in Broadmann area 37.

A

Area 37 is responsible for facial recognition, so damage results in Prosopagnosia

37
Q

Describe the processing of information in the visual cortex.

A

From the primary visual cortex, the reassembled visual information is separated again into new streams and relayed to specialized visual association areas. There are two distinct streams: the ventral pathway, which is involved in color and shape perception, and the dorsal pathway, which is involved in motion and spatial analysis

The two streams, although distinct, are highly integrated:

1) VENTRAL PATHWAY- Vision perception
-Concerned with the “what” of the visual inputs.
-Anatomically, the ventral stream projects to the temporal lobe (including infero-temporal cortex)
-In this stream:
• Distinguishes spatial patterns, objects and faces (also processes colors and shapes)
• Stores visual memory
• Recognises significance of objects and faces

2) DORSAL PATHWAY- Vision for action
-Concerned with the “where” and “how” of visual inputs.
-Anatomically, the dorsal stream projects mainly to the parietal lobe.
-In this stream:
• Integrates motion vs object locations (to facilitate navigation through that space)
• Coordinates visual guided action for skilled
movements (i.e. manipulation of objects and facilitation of eye-hand coordination)
• Guides visual attention

38
Q

Describe the possible consequences of damage in the ventral pathway (which follow primary visual cortex).

A

Ventral- A lesion here will lead to problems in visual orientation, discrimination of shapes, and recognition of objects and faces, as well as deficits in attention to visual cues.

39
Q

How are the visual field and area of primary cortex activated linked ?

A

The top of the visual field is in lower part of the primary visual cortex, and vice versa.

40
Q

What is the function of the primary motor cortex ?

A

Responsible formore direct control of motor activity than other motor areas: Force, direction, and speed of muscle contraction (basic information has already been processed by association areas)

41
Q

Define Somatotopy in the context of the motor cortex.

A
  • The neurons in the primary motor cortex are clustered in functional areas representing the various muscle groups they influence.
  • A graphic representation of this somatotopy on the cortex results in a motor homunculus. The size of body parts of the homunculus represents the size of the neuron pool supplying the musculature of that part of the body.
  • Certain body parts have enlarged representation, such as motor and sensory hand and face (sensory homunculus also exists)
42
Q

State the location of the neurons for legs, hands, and face in the primary motor cortex.

A

“The leg area is located close to the midline, in interior sections of the motor area folding into the medial longitudinal fissure

The lateral, convex side of the primary motor cortex includes the face

The arm and hand motor area is the largest, and occupies the part of precentral gyrus between the leg and face area.”

43
Q

Identify the main motor association cortex regions. What is their function ?

A

Motor association cortex regions - organisation of complex movements.

1) Supplementary motor area
- For planning complex tasks, especially two hand movements
- Also activated in mental rehearsal of complex movement (without doing it), and in practice-related sequential/repetitive movements

2) Premotor cortex
-Preparation for action - posture and gait
(integration of spatial information and planned movement)

3) Posterior parietal cortex (part of dorsal stream from visual cortex)
- Using visual information to formulate motor commands

44
Q

Which areas will the following activate ?

  • Doing simple movement
  • Doing complex movement
  • Planning without doing complex movement
A
  • Doing simple movement activates primary motor cortex
  • Doing complex movement activates both primary motor cortex and SMA
  • Planning doing complex movement without doing it, activation of SMA (without primary motor cortex)
45
Q

Where are the motor association cortex regions located ?

A

Supplementary Motor Area is located “on the midline surface of the hemisphere just anterior to the primary motor cortex leg representation”

Premotor cortex is “within the frontal lobe, just anterior to primary motor cortex”

Posterior parietal cortex is “posterior to the primary somatosensory cortex”

46
Q

Identify the main types of cerebral cortex specialisations.

A

PRIMARY: principal exit (motor) and entry points (sensory)
ASSOCIATION (majority of cerebral cortex): integration, complex processing of
cognate primary cortex info.

47
Q

What are the main types of association cortex ?

A

UNIMODAL (one type of modality input/output)

POLYMODAL (multiple modal input (e.g. vision and somatic sensation in the dorsal stream))

48
Q

Where is the primary somatosensory cortex located ?

A

“On the postcentral gyrus”

49
Q

Identify some modalities processed by primary somatosensory cortex. Where in the primary somatosensory cortex are these processed ?

A

Different modalities in different regions of primary somatosensory cortex. Higher order of processing occurs the further we go from post-central sulcus, in the parietal lobe:

  • Tactile information/muscle spindle information (deep, and superficial)
  • Size, shape, texture
  • Motion, Direction, Orientation

(+Tactile-sensory aspects of pain)

50
Q

Identify the main association somatosensory cortex areas, and describe their role.

A

1) Parietal lobules (superior and inferior): Awareness/perception in space (orientation), rearrangement of memories, organising grasping reaching movement, number processing (superior parietal lobule gets visual input)

2) Pre-frontal region (AKA frontal association area)
• Contributes to attention
• Morality
• Planning
• Working memory
• Conscious decision making
• Social behavior regulation
51
Q

Describe the consequences to damages in inferior, and superior parietal lobules.

A

Damage inferior parietal lobule: Contralateral neglect (especially right lesions) Either hemisphere - astereognosis (inability to recognize objects by touch)

Damage in superior parietal – problems with visuomotor integration (optic ataxia)

52
Q

Describe the consequences to damages in pre-frontal region.

A

(1) Personality changes
(2) Deficits in planning
(3) Perseveration
(4) Primitive reflexes (suckling reflex)
(5) Abulia (slowness of intellect)

53
Q

Identify the main brain areas for language, and the location and role of each.

A

Broca’s area (located in the inferior frontal gyrus of the frontal lobe, just anterior to the inferior part of the precentral gyrus): links various cortical areas together for the production of language. Language includes spoken, written, and sign language, as well as symbols (signs or words)

Wernicke’s area (located in the superior temporal gyrus and extends around the posterior end of the lateral sulcus into the parietal region): dedicated to the comprehension of both signed and spoken language

Primary auditory area (located deep within the lateral sulcus, on the superior surface of the superior temporal gyrus of the temporal lobe): “Perception of tone and pitch”

BUT multiple areas across the cerebral cortex involved in language in addition to the classical “centres”

54
Q

Explain which hemisphere language is located in.

A

In almost all right-handed people (approximately 98%) and most left-handed people (approximately 70%), the main centers for language are in the left hemisphere. The location of the language areas defines the dominant hemisphere: handedness may or may not be correlated with language. The right (or nondominant) hemisphere is thought to contribute more to the melody (prosody), rhythm, emotional expression, and accent in language.

In the dominant hemisphere, there are two major language centers: one for the expression of language, Broca area, and one for the comprehension of language, Wernicke area. These two centers are connected to each other via a subcortical bundle of white matter, the arcuate fasciculus.

BUT hemispheric specialisation can switch sides (Many of the 4% with right sided language control have damaged left hemisphere, so good hemisphere took over from damaged one)

55
Q

Describe effects of damage in the Broca’s area.

A

EXCESSIVE/PRODUCTIVE APHASIA (BROCA’s APHASIA)

  • Sparse, halting language, difficulty with syntax and grammar, word/phrase repetition, and mangled word structure.
  • Comprehension of speech is intact, and often, these patients are very frustrated with their inability to express themselves.
56
Q

Describe effects of damage in the Wernicke’s area.

A

RECEPTIVE/SENSORY APHASIA (WERNICKE’S APHASIA)

  • No difficulty with syntax, grammar, or the structure of words, and their speech appears to be fluent and to retain melody and rhythm.
  • Because these patients cannot understand the language they are hearing (or seeing), the content of their speech is markedly flawed. They might use the wrong word to describe something, create new words (neologisms), or appear to be speaking “gibberish,” almost as though they are speaking an unknown language. Repetition may be impaired. These patients are often not aware of their disability.
57
Q

Define conductive aphasia.

A
  • Damage to the arcuate fasciculus leads to conduction aphasia (so connection between Wernicke (language comprehension) and Broca (language production) areas is lost)
  • Inability to repeat words. Comprehension and the expression of language are intact, but patients cannot transfer the understood word to Broca area to be expressed.
58
Q

Describe the dorsal/ventral dual stream model of language.

A

If listening, info to primary auditory area. Info then goes through Wernicke’s area.
Streams start and diverge at Wernicke’s area.

1) Dorsal stream (sensorimotor) maps acoustic speech
to articulatory networks in frontal lobe (including to Broca’s area)

2) Ventral stream: Word/sound recognition and comprehension in temporal lobe

59
Q

Which brain areas are important in memory ?

A

Widespread cerebral cortex regions involved, including Hippocampus

60
Q

Define split brain.

A

Corpus Callosum, connecting both hemispheres, damaged (“can be used as treatment for severe epilepsy”)

61
Q

State examples of activities each side of the brain is better at.

A
  • Spatial perception, music, drawing are stronger on R hand side
  • Language and calculation are stronger on L hand side
62
Q

Describe experiments to distinguish Split Brainers.

A

Feel the keys experiment: Left hand feels, right cortex recognises, but cannot activate the language centres in the left hemisphere to speak the word keys.

“Touch the finger” test

63
Q

Define brain plasticity. What is the implication of this for stroke patients ?

A

“The ability of the nervous system to adapt to trauma or disease; the ability of nerve cells to grow and form new connections to other neurons”

This explains why stroke patient scan get better.

64
Q

Define long term potentiation.

A

“Repeated presynaptic stimulation of a nerve, that results in the long-lasting increased strength of a synapse, and is thought to be necessary for learning and memory formation”

65
Q

Identify the main ways brain cells and brain regions talk to each other.

A

Commissural fibers- cortex to cortex cross over the midline (e.g. C. Callosum)

Association fibers– cortex to cortex “stay” on the same side (e.g. Arcuate Fasciculus)

Projection fibers– communicate with other structures inside and outside the brain (e.g. Corticospinal tract, and bundles of nerve fibres in internal capsule and corona radiata)

66
Q

What is the main use of DTI ?

A

Diffusion tensor imaging, used “to identify the linkages and structures of white matter tracts in the brain”

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