Lecture 3 - Micro Anatomy and Neural Transmission

Question 1

What is the INPUT ZONE of a neuron?

Answer 1

DENDRITES

The part of a neuron that receives information from other neurons or from specialized sensory structures.

Question 2

What is the INTEGRATION ZONE of a neuron?

Answer 2

SOMA

The part of a neuron that receives information from other neurons or from specialized sensory structures.

Question 3

What is the CONDUCTION ZONE of a neuron?

Answer 3

The part of a neuron— TYPICALLY THE AXON —where the action potential is actively propagated.

Question 4

What is the OUTPUT ZONE of a neuron?

Answer 4

The part of a neuron at which the cell sends information to another cell.

AXON TERMINALS TRANSMIT

Question 5

What are parts of an axon?

Answer 5

Axon collaterals - branches of axons
Axon terminals - transmit info

Question 6

What are dendritic spines?

Answer 6

Small projections on the surface that add more space for synapses

Question 7

What are interneurons?

Answer 7

A nerve cell that receives input from and sends output to other neurons.

– neither a sensory neuron nor a motor neuron.

– Most of the neurons in the brain

Question 8

How do interneurons differ in size from motor and sensory neurons?

Answer 8

The axons of interneurons measure only a few micrometers while motor neurons and sensory neurons may have axons a meter or more in length

Question 9

What are the 3 shape classifications of neurons and what do they specialize in for info processing?

Answer 9

1. MULTIPOLAR NEURONS
   - many dendrites; single axon
   - most common
2. BIPOLAR NEURONS
   - single dendrite; single axon
   - common in sensory systems
3. UNIPOLAR NEURONS
   - single extension, usually called an axon.
   - dendrite-like input zone and integration zone are at one end.
   - axon arises directly from this zone and leads to the output zone with axon terminals.
   - The cell body is located partway along the axon.
   - carry touch and pain signals from the body to the spinal cord.

Question 10

What are the 3 principal components of a synapse?

Answer 10

1. The specialized presynaptic membrane of the axon terminal of the presynaptic (i.e., transmitting) neuron
2. The synaptic cleft, a gap of about 20–40 nanometers (nm; billionths of a meter) that separates the presynaptic and postsynaptic neurons
3. The specialized postsynaptic membrane on the dendrite or cell body of the postsynaptic (i.e., receiving) neuron

Question 11

What are synaptic vesicles, and what do they contain?

Answer 11

Tiny spheres in presynaptic terminals that contain neurotransmitters for neuron communication.

Question 12

How are neurotransmitters released from the presynaptic neuron?

Answer 12

Electrical activity causes vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft.

Question 13

What happens after neurotransmitters enter the synaptic cleft?

Answer 13

They bind to receptors on the postsynaptic membrane, affecting the neuron’s excitation level then detach and diffuse away.

Question 14

What is neuroplasticity?

Answer 14

The ability of neurons to remodel connections—changing synapses, receptors, and dendrite structures—based on activity.

Question 15

Compare and contrast axonal signal transmission and axonal transport.

Answer 15

SIGNAL TRANSMISSION

• Fast along axon membrane
• Purpose: to communicate with other neurons or target cells.
• Involves electrical impulses (action potentials).
• Travels in one direction: from the axon hillock to terminals.

AXONAL TRANSPORT

• Slowly Moves materials (e.g., proteins, enzymes) inside the axon.
• Purpose: to deliver supplies and remove waste.
• Happens in both directions:
  Anterograde (cell body → terminals)
  Retrograde (terminals → cell body)

Question 16

What are the two main functions of an axon?

Answer 16

1. Transmit electrical signals along its outer membrane (fast)
2. Transport substances (like enzymes and proteins) within the axon (slow)

Question 17

What is the function of the axon hillock, and what does it trigger?

Answer 17

The axon hillock integrates incoming signals from dendrites and cell body, then triggers electrical impulses down the axon if threshold is reached.

Question 18

What is anterograde vs. retrograde axonal transport?

Answer 18

ANTEROGRADE: Moves materials from cell body to terminals

RETROGRADE: Returns used materials from terminals to cell body

Question 19

What are the roles of glial cells in the nervous system?

Answer 19

They support neurons by supplying raw materials, chemical signals, and structural components—not just acting as “glue.”

• no action potentials

Question 20

What are the names of the four types of glial cells?

Answer 20

1. Oligodendrocytes (CNS)
2. Schwann Cells (PNS)
3. Astrocytes
4. Microglial Cells

Question 21

What is the function of myelin and the nodes of Ranvier?

Answer 21

Myelin speeds up signal transmission by insulating the axon; signals jump between nodes of Ranvier for faster conduction.

Question 22

Which glial cells form myelin, and how do they differ?

Answer 22

OLIGODENDROCYTES (CNS): myelinate multiple axons

SCHWAN CELLS (PNS): myelinate one segment of one axon

Question 23

What do astrocytes and microglial cells do?

Answer 23

ASTROCYTES: Support neurons and blood vessels; help regulate the brain’s blood and ionic environment

MICROGLIA: Act as the brain’s immune defense, removing waste and responding to injury

Question 24

What does it mean when a neuron is polarized?

Answer 24

There is a difference in electrical charge between the inside and outside of the cell, particularly more negative inside.

Question 25

Where are ions in cells dissolved?

Answer 25

In the intracellular fluid (cytoplasm) and extracellular fluid between cells outside of the cell membrane.

Question 26

What is the resting potential of a neuron?

Answer 26

–50 to –80 millivolts (mV) (negative sign indicates that the cell’s interior is more -)

Question 27

How does a negative membrane potential come about?

Answer 27

The cell membrane is selectively permeable, especially to potassium ions (K+), but not to sodium ions (Na+). Many K+ channels are always open, allowing K+ to move freely across the membrane. Sodium-potassium pumps actively transport 3 Na+ ions out and 2 K+ ions into the cell, leading to a higher K+ concentration inside the cell. K+ ions diffuse out of the cell down their concentration gradient. This outward movement of K+ leaves behind negatively charged ions inside the cell, creating a negative charge. Electrostatic pressure attracts K+ ions back into the cell, due to the negative internal environment. The balance between the diffusion (outward movement) and electrostatic pressure (inward pull) creates the equilibrium potential, resulting in a negative resting membrane potential (around –65 mV).

Question 28

What special properties of the cell membrane and two forces drive ions across it in neurons?

Answer 28

SELECTIVE PERMEABILITY: Allows certain ions (mainly K+) to pass while blocking others (like Na+). ION CHANNELS: Specific for K+, some of which remain open constantly. SODIUM-POTASSIUM PUMP: (Active transport. Uses ATP). Maintains ion concentration gradients (3 Na+ out, 2 K+ in). Two forces that drive ions across the membrane: 1. DIFFUSION: Movement of K+ ions from high to low concentration ELECTROSTATIC PRESSURE: Attraction between opposite charges (K+ pulled back in due to negative interior).

Question 29

What are pyramidal cells?

Answer 29

A highly polarized multipolar neuron found in the cerebral cortex, serving as the main excitatory neuron.

Question 30

What are Stellate Cells?

Answer 30

A type of inhibitory interneuron involved in local processing and modulation of signals. Multipolar. In cortical stellate cells, they may be considered non-pyramidal and non-polarized in the directional sense (unlike pyramidal cells which have clear apical-basal polarity).

Question 31

What 3 Fibre Types compose the cytoskeleton of axons?

Answer 31

Microtubule - Transport Neurofilament - Structure Microfilament - Shape

Question 32

In a healthy brain, what does tau do?

Answer 32

Tau is a protein that connects adjacent microtubules and holds them in place, but any disruption to its integrity tends to cause behavioural dysfunction.

Question 33

How does tau phosphorylation lead to cell death?

Answer 33

Phosphate molecules are added to tau tau removes and microtubules disconnect, so axons fall apart Interference damages cell transport and communications in our brain, leading to neuro dysfunction. Neurofibrillary tangles reflect a loss of neuron cell bodies and axons -- a thinning of grey matter

Question 34

What is electrostatic pressure?

Answer 34

The inclination of charged molecules or ions to move toward areas with the opposite charge.

Question 35

What is the equilibrium potential?

Answer 35

The point at which the movement of ions across the cell membrane is balanced, as the electrostatic pressure pulling ions in one direction is balanced by the diffusion force pushing them in the opposite direction.