Neurons- Different Cell Types In Brain And Spinal Cord

Question 1

Neurones

Answer 1

• Specialised for electrical signalling
• Inputs via dendrites
• Action potentials propagate along the axon from the axon hillock
• Mainly formed during development

Question 2

Neuronal communications

Answer 2

Neurons communicate via synapses - 2 types

• Chemical – majority – via neurotransmitters (glutamate, GABA, dopamine, serotonin,
etc.)

• Electrical – less abundant – via direct flow of ions
- enable synchronized electrical activity, e.g. brainstem (breathing) & hypothalamus (hormone secretion)

Question 3

Chemical synaptic transmission

Answer 3

Axon potential depolarises synaptic terminal membrane

This leads to Opening of voltage-gated calcium channels leads to calcium influx

The Calcium influx triggers neurotransmitter release

Question 4

Exciting synapses are

Answer 4

Clustered and concentrated on dendritic spines

Question 5

Spines and neural plasticity

Answer 5

• Neural plasticity
- changes in neuronal/synaptic structure and function in response to neural activity - basis of learning and memory
Stronger carry more current, weaker carry less current

• Spines are dynamic structures – number, size, composition

• Spine remodelling linked to neural activity

• Relevant to disease – e.g. schizophrenia & Alzheimer’s - ↓spine density

Question 6

Neuronal heterogeneity

Answer 6

Neurons differ in their

Size
Morphology
Neurotransmitter content
Electrical properties

Eg neocortex

Question 7

Arborisation of axons and dendtrites

Answer 7

Neurones can branch and give multiple terminals

Question 8

Oligodendrocytes

Answer 8

These are Myelinating cells of the CNS

• Unique to vertebrates

• Myelin insulates axon segments, enables rapid nerve conduction

• Myelin sheath segments interrupted by nodes of Ranvier – saltatory conduction far more faster and efficient

• Provide metabolic support for axons

Question 9

Myelin sheath

Answer 9

Formed by wrapping of axons by oligodendrocyte processes (membranes)

• Highly compacted – 70% lipid, 30% protein

• Myelin specific proteins, e.g. myelin basic protein (MBP) can be used as “markers”

Question 10

Microfilm

Answer 10

These are the Resident immune cells of the CNS

• Originate from yolk sac progenitors
that migrate into CNS

• “Resting” state, highly ramified, motile processes survey environment (2-3 μm/min)

• Upon activation (e.g. by ATP), retract processes, become “amoeboid” & motile

• Proliferate at sites of injury - as they are phagocytic cells

Question 11

Functions of microglia

Answer 11

Immune surveillance

Phagocytosis- debris/microbes

Synaptic plasticity-pruning of spines

Good and bad microglia
Bad- when the microglia become over reactive

Question 12

Astro cytes- type of glia cells

Answer 12

Most numerous cells in CNS

Highly heterogeneous service

Common marker glial fibrillary acidic protein

Question 13

Astrocytes contribute t the blood-brain barrier

Answer 13

Anti-GPAF immunostaining for asrocytes- cell bodies and processes coating capillaries

Dual immunostaoning with second astrocyte. Raker AQP4 reveals more of the vascular network:
GPAF
Aquaporin 4 water channel necessary because of blood brain barrier

Question 14

Atrocities functions

Answer 14

Structural-n define brain micro-architecture

Envelope synapses- tripartite synapse- buffer K+, glutamate

Metabolic support

Neuromuscular coupling- changes in cerbral blood flow in response to neural activity

Proliferate in disease= glossies or astrocytes

Question 15

Specialised astrocytes

Answer 15

Radial glia- important for brain development

Bergmann glia cerebellum

Muller cells

Question 16

Abundance of neuronal cell bodies in nuclei

Answer 16

Axons gathered into tracts

Question 17

Commissures

Answer 17

Tracts that cross midline

Question 18

Grey matter abundant in neural cell bodies and processes- neutrophil contains few cell bodies

Answer 18

White matter contains absence of myelinated tracts and commissures

Question 19

Cell bodies and supporting cells located in ganglia eg dorsal root ganglia

Answer 19

Axons bundles into nerves

Many PNS are enveloped by Schwann cells (myelinating cells of the the PNS- neural crest derived c.f. Oligodendrocytes, derived from CNS- resident neural progenitors

Question 20

Dyes injected into blood penetrate most tissues but not the brain

Answer 20

Dyes injected into the CSF brain stains —> specialised blood-brain barrier

Question 21

Formed by endothelial cell tight junctions, basement membrane (few fenestrations), astrocyte end feet and pericytes (contractile, aid blood flow)

Answer 21

Sensitive to inflammation, hypertension, trauma, ischaemia

Question 22

Circumventricular organs lack normal blood brain barrier

Answer 22

homeostatic and endocrine functions

Question 23

Pineal body

Answer 23

Secrets melatonin hormone into blood

Question 24

Area postrema

Answer 24

A chemoreceptor trigger zone that initiates vomiting in response to chemical changes in the plasma

Question 25

Post pituitary

Answer 25

Secretes hormones into blood

Question 26

Organum vasculosum of the laminate terminalis

Answer 26

Osmoreceptor controlling vasopressin secretion and thirst

Question 27

Subfornical organ

Answer 27

Circulating angiotensin II acts here to increase water intake

Question 28

Ependymal cells

Answer 28

Epithelial like line vertices and central canal of spinal cord Functions: CSF production, flow and absorption Ciliated: facilitates flow Allow solute exchange between nervous tissue and CSF

Question 29

Choroid plexus

Answer 29

From like projections in ventricles Formed from modified ependymal cells- villi form around network of capillaries This leads to highly vascularised with a large surface area Main site CSF production by plasma filtration driven by solute secretion Gap junctions between cells from blood-CSF barrier