Neuroscience and Clinical Semester 1 Week 1: The anatomy of the nervous system

Question 1

What are the two broad classes of cells integrated to form brain tissue?

Answer 1

Neurones - around 100 billion in human brain
Neuroglia cells - outnumber neurones 10:1

Question 2

Specialised features of neurones

Answer 2

• Axon
• Myelin sheath
• Dendrite
• Spines
• Synapse

Question 3

Axon

Answer 3

• output side of the cell
• Arises from a conical shaped thickening on cell body called the ‘axon hillock’, long narrow process that projects from cell body, can travel distances ranging from microns to metres. - Axonal membrane is excitable, specialised for generation and propagation of action potentials.

Question 4

Dendrite

Answer 4

• input side of the cell
• The short processes emanating from the cell body, which receive most of the synaptic contacts from other neurones.
• Highly branched, giving rise to a dense network of processes, the ‘dendritic arbour’ [spines].

Question 5

Spines

Answer 5

• Project from the surface of dendrites
• Receive most of the excitatory input
• Have a neck and head
• Average length = 2 μm
• Contain filaments [actin and α- and β-tubulins]
• Dynamic (change in response to activity)

Question 6

Synapse

Answer 6

Point of specialised contact between two neurones, where chemical signals are transmitted.

Question 7

What features of a neurone are the same as other cells?

Answer 7

• Nucleus: contains DNA
• Rough endoplasmic reticulum: synthesises proteins
• Smooth endoplasmic reticulum: synthesises fats
• Golgi complex: packages products for transport around the cell
• Mitochondria: powerhouse of the cell
• Lysosomes: waste disposal system
• Cytoskeleton: maintains shape and provides ‘rails’ for transport

Question 8

Neuronal classification

Answer 8

Neurones can be classified according to:
- number of processes
- length of axon
- shape of cell body

Question 9

Number of processes

Answer 9

• Bipolar (one dendrite, e.g. purkinje cells)
• Multipolar (more than 1 dendrite, e.g. dopaminergic neurons)

Question 10

Length of axon

Answer 10

• golgi type I neurone (long axon + large - travels to another brain structure, e.g. pyramidal cells)
• golgi type II neurone (short axon - usually stay in structure where cell is located, e.g. spiny stellate cells)

Question 11

Shape of cell body

Answer 11

• Ovoid (circular/spherical, e.g. spiny stellate cells)
• Fusiform (fat in middle, thinner edges, e.g. dopaminergic neurons)
• Triangular (e.g. pyramidal cells)

Question 12

Types of glial cells

Answer 12

CNS:
- Oligodendrocytes
- Astrocytes
- Microglia
PNS:
- Schwann cell

Question 13

Oligodendrocytes

Answer 13

Have extensions that wrap around axons in the CNS. The extensions are rich in myelin (fatty insulating substance) that forms myelin sheaths which increase the speed and efficiency of axonal conduction. Myelinated segments of axon = internodes; unmyelinated = nodes of Ranvier

Question 14

Astrocytes

Answer 14

• Star-shaped
• Communicate with each other through gap junctions.
• Ensheath synapses and dendrites
• Project processes to cell somas (neuron cell body)
• Cover blood vessels in the brain.
• Maintain tight junctions in endothelial cells (which form blood brain barrier)
• Uptake of neurotransmitters (gets rid of them when they’ve done their job)
• Neurovascular coupling

Question 15

Microglia

Answer 15

• Represent the immune system in the brain, as the brain is an immunologically privileged site because of the BBB (immune system )
• Involved in phagocytosis (consuming things that need to be ‘eaten’)

Question 16

Schwann cells

Answer 16

• located in the peripheral nervous system.
• forms the myelin sheath, an insulating layer around nerve fibers.

Question 17

Neuroanatomical directions

Answer 17

• Dorsal (towards the back/top of head) + ventral (towards the chest/bottom of head)
• Anterior/rostral (towards front/nose) + Posterior/caudal (towards bottom/tail)
• Medial (towards middle) + Lateral (away from middle)

Question 18

Planes of section

Answer 18

• Coronal/frontal plane (ear to ear, front and back sections)
• Sagittal plane (vertical plan dividing brain into left and right sections)
• Horizontal plane (upper and lower sections)

Question 19

5 major subdivisions of the brain

Answer 19

FOREBRAIN
- Telencephalon (undergoes greatest growth during development)
- Diencephalon

MIDBRAIN
- Mesencephalon

HINDBRAIN
- Metencephalon
- Myelencephalon

‘Encephalon’ = within the head
Brain stem = hindbrain + midbrain

Question 20

Myelencephalon (medulla oblongata)

Answer 20

• Most posterior division
• Largely composed of tracks that carry signals between brain and body
• Reticular formation - network of around 100 tiny nuclei occupying the central core of the brain stem, from the posterior boundary of the myelencephalon to the anterior boundary of the midbrain. These nuclei are involved in various functions e.g. respiration, sleeping etc.

Question 21

Nuclei in the myelencephalon

Answer 21

Nuclei that control:
- Dorsal (inspiration/breathing in) and Ventral (rhythm) respiratory groups
- Hypoglossal nucleus -> tongue musculature
- Nucleus ambiguus -> blood pressure and heart rate
Part of the autonomic nervous system
Nucleus ambiguus gives rise to part of the vagus nerve.
Vagus nerve is part of the parasympathetic nervous system which controls heart muscle, smooth muscle (e.g. blood vessels) and glands (e.g. adrenal glands)

Question 22

Metencephalon: Pons

Answer 22

• contains nuclei which are involved in sleep + arousal
• e.g. locus coeruleus - provides noradrenaline (neurotransmitter) to rest of brain, which is involved in level of alertness

Question 23

Metencephalon: Cerebellum

Answer 23

Cerebellum - ‘little brain’
- integrates sensory information and uses this to modify motor output
- Coordinates and smoothes movements
- Damage = jerky/exaggerated movements, poor coordination (alcohol ‘turns off’ the cerebellum)

Question 24

Mesencephalon: tectum

Answer 24

Tectum:
- Dorsal surface of midbrain
- Composed of two pairs of bumps: Inferior colliculi (posterior pair) and superior colliculi (anterior pair)
- Inferior - part of auditory system
- Superior - visual-motor function (e.g. rapid eye movements)

Question 25

Mesencephalon: Tegmentum

Answer 25

3 major structures: - Periaqueductal grey = involved in species-typical behaviours E.g. female rat posture during mating - lordosis Stimulating aqueductal grey resulted in greater arching - Red nucleus = part of motor system, particularly involved in bilateral movements of the arm, muscles in shoulder and upper arm - Substantia nigra = also part of motor system - death of the neurons in this area is associated with Parkinson’s disease

Question 26

Diencephalon: Thalamus

Answer 26

- Two lobes joined by massa intermedia - Divided into nuclei - Sensory relay nuclei = transfer sensory information from receptors to cortex - Other nuclei = unknown function but mainly project to cortex

Question 27

Diencephalon: Hypothalamus

Answer 27

- Regulates autonomic and glandular aspects of responses related to survival e.g. eating, sleeping and homeostasis - Regulates release of hormones from pituitary gland - Contains many nuclei e.g. Suprachiasmatic nucleus - circadian rhythms (24 hr rhythms). Tested on rats, removed suprachiasmatic nucleus and activity is constant between night and day, no circadian rhythms - Optic chiasm - where optic nerves from each eye come together - Mammillary bodies - spherical nuclei behind pituitary

Question 28

Telencephalon

Answer 28

- Largest division of the human brain - Mediates complex cognitive processes - Consists of the limbic system, basal ganglia and cerebral cortex

Question 29

What are the 4 lobes of the cerebral cortex?

Answer 29

- Frontal - Parietal - Temporal - Occipital

Question 30

What are the two types of areas in the cerebral cortex?

Answer 30

Primary receiving areas and association cortices

Question 31

Which lobe contains the primary visual cortex?

Answer 31

Occipital lobe

Question 32

Which lobe contains the primary auditory cortex?

Answer 32

Temporal lobe

Question 33

Which lobe contains the primary somatosensory cortex?

Answer 33

Parietal lobe

Question 34

Which lobe contains the primary motor cortex?

Answer 34

Frontal lobe - stimulation causes muscular movement

Question 35

What is the function of association cortices?

Answer 35

- Primary sensory and motor areas send information to the association cortex - They accomplish what is done between sensation and action (e.g., perceiving, learning/remembering, planning)

Question 36

How do scientists figure out the function of brain areas?

Answer 36

By studying the effect of damage to those areas

Question 37

What happens when there is damage to the visual areas?

Answer 37

Damage to the primary visual cortex (V1) = Blindness Damage to the visual association cortex = more complex deficits - Visual agnosia (failure to recognize what you see)

Question 38

What is the area rostral to (in front of) the motor association cortex called?

Answer 38

Prefrontal cortex: involved in planning and emotional behaviour - Phineas Gage

Question 39

What is the cerebral cortex made up of?

Answer 39

- 90% = neocortex (the lobes) - 10% = allocortex which includes hippocampus (part of the limbic system) etc.

Question 40

Which parts of the brain are in the limbic system?

Answer 40

Hypothalamus, hippocampus, amygdala, cingulate cortex, septum, mammillary bodies

Question 41

What functions are associated with the limbic system?

Answer 41

Regulating motivated behavior, memory (hippocampus), motivated behaviors (hypothalamus), emotion (amygdala)

Question 42

Which parts of the brain are in the basal ganglia?

Answer 42

Amygdala, caudate nucleus, putamen, globus pallidus, substantia nigra (diencephalon), subthalamic nucleus (diencephalon)

Question 43

What functions are associated with the basal ganglia?

Answer 43

Performance of voluntary motor responses, decision making, associated with Parkinson's disease