Name 3 visceral stimuli that act as afferent inputs into the nervous system.

• Blood Pressure
• Visceral Pain
• Osmolarity

There is the somatic/general sensory and special sensory.Their actions are mediated through the somatic nervous system.

General Sensory

- Pain/Touch/Temperature - Proprioception - Balance

Special Sensory

- Hearing - Vision - Olfaction - Gustation

What are the two types of cells of the nervous system?

Neurons

Glial Cells / Neuroglia

What are the divisions of Glial cells in the nervous system?

Macroglia

Microglia

What are the functions of Macroglia?

Macroglia are phagocytes that are mobilized in injury, inflammation and disease. They originate from macrophages outside the nervous system and are embryologically unrelated to other cells in the nervous system.

What types of microglia are there?

• Astrocytes
• Oligodendrocytes
• Schwann cells

Describe what Schwann Cells do and how they achieve it.

Schwann Cells myelinate a single internode of a single axon in the peripheral nervous system. It does this by wrapping its' processes around a segment of an axon to form a myelin sheath around that segment.

Describe what Oligodendrocytes do.

Oligodendrocytes provide the myelin sheath for many (average of 15) internode of several axons in the central nervous system.

What are the differences between Oligodendrocytes and Schwann Cells?

Schwann Cells are in the PNS whereas Oligodendrocytes are present in the CNS.

Scwann Cells only myelinate 1 internode of an axon whereas Oligodendrocytes myelinate an average of 15 axonal internodes.

Last but not least, the chemical makeup of the Myelin produced by Schwann Cells and Oligodendrocytes differ slightly.

Describe the rough structure of an astrocyte.

An astrocytes is a glial cell which has a star shaped cell body with processes projection out from it that terminate in an end foor.

List the 4 functions of Astrocytes.

1. Provide nutrition to nervous tissue (brain and spinal cord)

2. End feet on capillaries causes the endothelium to form tight junctions, thus maintaining the blood brain barrier.

3. Absorbs K⁺ after these ions are released. Thus preventing neighbouring neurons from being excited and interfering with signalling.

4. Uptake of neurotransmitter after release.

What is the role of myelin?

Myelin insulates the axons of neurons. It helps to improve the conduction / propogation velocity of action potentials down an axon.

A - Axon

B - Soma / Cell Body

C - Presynaptic Terminals

D - Dendrites

What are the morphological variants of the neuron?

Unipolar, Psuedo-unipolar, Bipolar, Multipolar.

Name an example of Unipolar, Psuedo unipolar, Bipolar and Multipolar neuron as found in vertebrates.

Unipolar Autonomic Nervous System (but normally found in invertebrates)

Bipolar Retinal Cells, Olfactory Epithelium

Psuedo-Unipolar Pain/Touch/Proprioceptive of the Dorsal Root Ganglion

Multipolar Spinal Motor Nerves, Pyramidal neurons of the hippocampus, Purkinje fibers of the cerebellum

Where does signalling between Neurons occur?

Signalling occurs at the synapse, between the pre-synaptic nerve terminals and the post synaptic element (normally a dendrite or a soma however it may also end at a pre-synaptic terminal - presynaptic inhibition).

Apical, Basal

What are the three type of synaptic junctions and what is their nature?

1. Axosomatic

From axon to cell body. Inhibitory.

2. Axodendritic

From axon to dendrite. Excitatory.

3. Axoaxonic

From axon to presynaptic terminal. Inhibition of presynaptic release.

What determines our perception of afferent information/action potentials?

What is the typical resting membrane cell potential of a neuron?

-65 mV on the inside compared to the outside of a cell.

What 2 factors lead to the existance of the resting membrane potential?

(1) The unequal distribution of cations Na⁺/ K⁺ and negatively charged AAs/proteins on either side of the membrane.

(2) The selective permeability of the cell membrane to K⁺.

What does the Na⁺-K⁺ ATPase do? :o

It pumps 3 Na⁺ out to 2 K⁺ in (Sods get out), thus maintaining the resting membrane potential. Keeps intracellular potassium high and sodium low.

What types of potentials can be created in the nervous system?

Long range action potentials and Graded potentials which have a short range (synaptic and graded receptor potentials).

What are the 4 functions of ion channels?

1) Open and close in response to stimulus, allowing the inflow of ions -> AP generation -> for us to perceive the stimulus. 

2) Selectivity - to be selective for specific ions, hence ensuring we perceive the CORRECT stimulus.

3) Ion Transport - Otherwise ions would not be able to pass through the HYDROPHOBIC membrane - 10^8 ions transported per second, allow for rapid excitation of membrane.

4) Generate Membrane potential - K+ channel on cell membrane is leaky therefore efflux of K+ down its' concentration gradient (set up by Na+ K+ pump) leads to buildup of -ve charge inside the cell.

Describe the structure of a voltage gated Na⁺ Channel.

4 domains, each with 6 membrane spanning regions (S1 - S6) composed of hydrophobic alpha helices. S4 is believed to be the voltage sensor.

Describe how the voltage gated Na⁺ channel works.

How are the 3 different ways in which ion channels open/close?

Local conformational change

Generalized conformational change

Blocking particle

Name 3 forms of gating of ion channels.

Ligand Gating

Voltage gating

Mechanical Gating

How do ligand gated channels enter the refractory period?

They exhibit signs of desensitization after prolonged exposure to the ligand.

Where do voltage gated channels gain the energy to change from their closed to open configuration?

From the movement of the voltage sensor through the electric field which generates free energy.

How do voltage gated channels enter their refractory period?

It goes through an additional state (1 open/activated, 1 closed/neutral and 1 inactivated phase).

Describe the Na⁺ ion channel's phases.

1. Rest - Inactivation gate open, activation gate closed

2. Activation - Both gates open

3. Inactivation - Inactivation gate closed, activation gate open.

Where does the energy to undergo a conformation change in mechanically gated channels come from?

Cytoskeleton-cell membrane interactions.

What are the two forms of synaptic transmission?

Chemical

Electrical

Highlight 4 characteristics of electrical neurotransmission

Virtually instantaneous; no delay

Relies on changes in membrane pt

Cytoplasmic continuity

Gap junctions - connexons/connexins

Highlight 4 features of chemical neurotransmission.

Some delay, at least 0.3 ms (normally 1 - 5)

Synaptic cleft + neurotransmitter in active zones

No cytoplasmic continuity

Amplification, quanta release of NT

Unidirectional transmission