Nervous Tissue

Question 1

What are the 2 parts of the nervous system from an anatomical perspective and from a histological perspective?

Answer 1

Anatomically:
CNS → Brain, Cerebellum, Spinal cord (Gray and white matter)
PNS → Nerve Ganglia, Nerve Fibers

Histologically:
Neurons (Nerve cells)
Neuroglial → Glial cells equivalent to the CT; involved in support, neuron protection, defense and nutrition

Question 2

What is the gray and white matter of the CNS composed of?

Answer 2

Gray matter → Cell bodies of neurons, neuroglia
White matter → Neuronal processes (axons), Neuroglia

Question 3

What is the functional unit of the nervous system?

Answer 3

Neuron

Question 4

What are the 3 main structures of the neuron?

Answer 4

1. Dendrites
   - Receive signals
2. Cell Body
   - Integrates incoming signals from dendrites
   - And outgoing signals to axons
3. Axons
   - Transmits signal to another neuron or effector cell

Question 5

WHat are 2 alternate names for the cell body of a neuron?

Answer 5

Soma
Perikaryon

Question 6

What are the different ultrastructures of the cell of body of a typical neuron?

Answer 6

• Lysosomes
• Lipofuscin Body
• Centrally located nucleus (with a prominent nucleolus)
• Nissl bodies (free RER and free ribosomes) at the entries of the dendrites, but not of the axon!
• Axon Hillock (no Nissl Bodies)
• Mitochondria

*Axon and dendrites have Intermediate filaments (Neurofilaments) and Microtubules

Question 7

What are different types of neurons based on their morphology?
What are multipolar neurons?

Answer 7

• Pyramidal cells (brain cortex)
• Purkinje (Cerebellum)
• Motor Neurons (Spinal cord)
• Pseudo Unipolar (Spinal Ganglia)
• Bipolar (Retina, Olfactory Mucosa)

*Multipolar neurons have more than 2 processes

Question 8

What shapes can take the perikaryons?

Answer 8

• Spherical
• Ovoid
• Angular

Question 9

What are the 3 main structures of the CNS?
Ant their functions?

Answer 9

1. Cerebrum → integration of sensory information (from PNS) + Initiation of voluntary motor responses
2. Cerebellum → Intergation of sensory information (from PNS) + Fine-tuning of voluntary motor responses
3. Spinal Cord:
   - Relay messages from brain to body
   - Pass sensory information from sensory receptors to the brain
   - Coordinate reflexes that are managed by the spinal cord alone (patellar/knee jerk reflex)

Question 10

What is the difference between gray and white matter?
Where is it located in the different CNS sections?

Answer 10

Gray matter → contains neuronal cell bodies and neurglial cells

White matter → contains acons and neurglial cells
- appears white due to the presence of myelin around the axons

Spine = gray inside/white outside
Cerebellum = white inside/gray outside
Cerebrum = white inside/gray outside

Question 11

What is the histology of the cerebrum like?

Answer 11

White + Gray matter

Gray matter:
- 6 layers in the cerebral cortex
- Pyramidal neurons are the most prominent (arranged in parallel with on another + larger than surrounding glial cells)

Question 12

What is the histology of the cerebellum like?

Answer 12

The gray matter has 3 layers:
1. Molecular Layer:
- Sparse neurons
2. Purkinje Layer:
- Very large purkinje neurons
- Dendrites project → molecular layer + Axons project → granular layer
3. Granular Layer:
- Very small, densly packed neurons
- Axons are unmyelinated, project into molecular layer where they synapse with dendrites of purkinje cells

Question 13

What are the different subdivision of the PNS?

Answer 13

Somatic PNS:
- Sensory nerve fibers → CNS (afferent)
- Motor nerve fibers ← CNS (efferent)
Autonomic PNS:
- Controles smooth muscle of the internal organs and glands

*Sensory and Autonomic neurons have their cell bodies in ganglia. Neuron cell bodies of motor neurons are located in the spinal cord

Question 14

Which cells are responsible for axon myelination in the CNS vs PNS?

Answer 14

CNS → Oligodendrocytes
- Multiple axons for 1 oligodendrocyte

PNS → Schwann cells
- 1 Schwann: 1 axon

Functions of myelination → electric insulation + faster condution of nerve impulse
*Myelin makes the white in white matter

Question 15

What are Nodes of Ranvier?

Answer 15

Gaps in the myelin sheath that promote transmission of the action potential

Question 16

What is myelin composed of?

Answer 16

modified cell membrane containing a lipoprotein called myelin

• Phospholipids
• Spingolipids
• Proteins (Myelin Basic protein, MP2, etc.)

Question 17

What can are different possibilities for an axon to synapse on?

Answer 17

1. Axon - Dendrite
2. Axon - Cell body
3. Axon - Axon
   *Synpases can be excitatory or inhibitory
   *Axon starts at Axon Hillock and ends at terminal bouton

Question 18

Which cells compose the neuroglia?

Answer 18

Neuroglial cells provide support, protection and nutrition to neurons

1. Astrocytes:
   - Largest neuroglial cells
   - in white matter of CNS
   - Form/maintain blood-brain barrier
   - Remove ions and neurotransmitters (GABA, Glutamate, etc.)
2. Oligodendrocytes:
   - in gray and white matter of CNS
   - Produce myelin when in white matter
   - Satellite cells around neurons in CNS = oligodendrocytes
3. Microglia:
   - Scattered througout CNS
   - Smallest neuroglial cells, derived from monocytes
   - Darkly stained
   - Function as phagocytes → clear derbis of damaged structures in CNS