Med2042 Week 1 - Histology

Front 1

What is the Central Nervous System (CNS)?

Back 1

Brain and spinal cord

Front 2

What is the Peripheral Nervous System (PNS)?

Back 2

Nerve fibres and ganglia (clusters of nerve cell bodies outside the CNS)

Front 3

What are the four primary tissue types?

Back 3

Epithelium
Connective tissue
Muscle tissue
Nervous tissue
- Central nervous system (CNS)
- Peripheral nervous system (PNS)

Front 4

What are the two functional divisions of the nervous system?

Back 4

Somatic parts of CNS and PNS. Excludes innervation of viscera, smooth muscle and glands. (Gr soma = body)

Automomic parts of CNS and PNS
- Efferent (away from CNS) - smooth muscle, heart, glands
- Afferent (towards CNS) - pain and autonomic reflexes

Front 5

What are the 3 components found in all nervous tissue?

Back 5

Nerve cells (neurons)
Supporting cells (glial or neuroglia)
Blood vessels

Front 6

How many neurons are in the human cortex?

Back 6

30-(100?) billion

Front 7

What are neurons able to do?

Back 7

Receive information - signals from external or internal sources
Process and integrate these signals
Conduct nerve impulses (action potentials) to designated target tissues such as other neurons, muscles and glands.

Front 8

What does a typical neuron consist of?

Back 8

Cell body (soma, perikaryon)
Dendrite(s)
One axon

Front 9

What are the different types of neurons? Describe.

Back 9

Mulipolar - more than two processes (most common)
- common in CNS and ANS

Bipolar - one dendrite and one axon
- olfactory epithelium
-retina

Pseudo unipolar - single process that branches close to cell body
- dorsal root ganglia

Front 10

What is the functional characterisation of neurons?

Back 10

Motor (efferent) neurons - control effector organs such as muscle fibres and exocrine and endocrine glands

Sensory (afferent) neurons - receive sesory stimuli from the environment and from within the body

Interneurons - establish relationships between other neurons - form complex functional networks

Front 11

What are features of the neuronal cell body?

Back 11

Axon (Myelin) sheaths
- axons are mylinated by oligodendrocytes (CNS) and Schwann cells (PNS.

Nodes of Ranvier
- Allow for saltatory or discontinuous conduction
- conduction speed determined by
> diameter of axon
> thickness of myelin
- length segments 0.2-1.0mm

Front 12

What do synapses do?

Back 12

- from synapsis Gr. union
- responsible for unidirectional transmission of nerve impulses
Sites where contact occurs between neurons or between neurons and other effector cells (muscle, gland cells)
- most synapses transmit the nerve impulse by releasing neurotransmitters at the axon terminal - these induce the transfer of the nervous impulse
- more than 35 known neurotransmitters - most are amines, amino acids or small peptides
- synapses can excite or inhibit impulse transmission

Front 13

What is the motor end plate?

Back 13

The highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscle's surface, ultimately causing the muscle to contract.

Front 14

Describe neuroglia and where they are found.

Back 14

- 10 times more abundant than neurons in mammalian brain
- surround neuron cell bodies and axonal and dendritic processes
- nervous tissue has no intercellular matrix - glial cells provide a microenvironment suitable for neuronal activity.

CNS
- astrocytes
- oligodendrocytes
- microglia

PNS
- Schwann cells

Front 15

What are the kinds of neuroglia found in the CNS?

Back 15

Astrocytes
Oligodendrocytes
Microglia

Front 16

What are the kinds of neuroglia found in the PNS?

Back 16

Schwann cells

Front 17

Describe oligodendrocytes.

Back 17

- produce the myelin sheath that surrounds axons in the CNS
- can provide myelin to more than one axon (sends out proceses which wrap multiple adjacent axons (50+))
- Cf Schwann cells 1:1

Front 18

Describe astrocytes.

Back 18

- star-shaped cells
- bind neurons to capillaries and to the pia mater - inntermost layer of the meninges

Fibrous astrocytes
- have few long processes
- found in white matter

Protoplasmic astrocytes
- have many short-branched processes
- found in grey matter

- form part of the blood- brain barrier
- influence neuronal survival and activity through release of metabolic substrates and neruoactive molecules (including vasoactive endothelins, opioid precursors called enkephalins)
- communicate with one another via gap junctions (nexus)

Front 19

Describe Microglia.

Back 19

- small elongated cells with short irregular processes
-phagocytic cells derived from bone marrow
- involved in inflammation and repair in CNS
- can act as antigen-presenting cells
- secrete neutral proteases, oxygen radicals and immunoregulatory cytokines

Front 20

Descibe the organisation of white matter in CNS.

Back 20

- white matter forms bulk of deep parts of the brain and the superficial parts of the spinal cord
- aggregates of grey matter such as the basal ganglia (caudate nucleus, putamen, globus pallidus, subthalamic nucleus, nucleus accumbens) and brain stem nuclei (red nucleus, substantia nigra, cranial nerve nuclei) are spread within the cerebral white matter
- The cerebellum is structured in a similar manner as the cerebrum, with a superficial mantle of cerebellar cortex, deep cerebellar white matter (called the "Arbor vitae") and aggregates of grey matter surrounded by deep cerebellar white matter (dentate nucleus, globose nucleus, emboliform nucleus, and fastigial nucleus).
- The fluid-filled cerebral ventricles (lateral ventricles, third ventricle, cerebral aqueduct, fourth ventricle) are also located deep within the cerebral white matter

Front 21

Describe the layering of gray matter in CNS.

Back 21

The standard areas of cortex (isocortex) is characterized as having six distinct layers. From outside inward:

1. Molecular layer
2. External granular layer
3. External pyramidal layer
4. Internal granular layer
5. Internal pyramidal layer
6. Multiform layer.

- input layer 4 - distribute apical and basal directions

Front 22

What are the important parts of the cerebellum?

Back 22

- folia of cerebellum (large mass of brain cells)
- white and gray matter of the cerebellum
- purkinje cell layer

Front 23

What are the parts of the Purkinje cell layer?

Back 23

- Purkinje cells
- Molecular layer (superficial)
- Granular layer (deep)

Front 24

What is the architecture of the PNS?

Back 24

Ganglia
- collections of nerve cell bodies outside the CNS
- also contain glial cells supported by connective tissue
- serve as relay stations - once nerve enters and another leaves each ganglion
- Sensory ganaglia - receive afferent impulses that then go to the CNS
- Autonomic ganglia - present in the autonomic nervous system (for control of smooth muscle, some glands, cardiac rhythm)

Front 25

What is an example of autonomic glangion?

Back 25

Autonomic ganglion gut

Front 26

What is an example of parasympathetic ganglion?

Back 26

Salivary

Front 27

Describe how peripheral nerves exist in the body.

Back 27

- In the PNS, nerve fibres are grouped in bundles to form the nerves
- In addition to axons, Schwann cells and collagen fibrils, peripheral nerves consist of:
> Epineurium - external fibrous coat of dense CT
> Perineurium - surrounds bundles of nerve fibres
> Endoneurium - consists of delicate CT fibres produced by Schwann cells