Lecture 8 Neurons

Question 1

Interneurons aka relay neurons

Answer 1

Found exclusively within the spinal cord
And brain. Stimulated by signals from sensory/interneurons or both.

Highly diverse in structure and function

Aka association neurons or relay neurons

Question 2

Sensory neurons

Answer 2

Run from various types of stimuli receptors e.g.
touch taste sound vision odour
Run to spinal cord and brain

Question 3

Motor

Answer 3

Transmit impulses from CNS to muscle and glands that carry out a response

Motor end plates (axon terminals) on muscle fibres

Many are stimulated by interneurons although some directly stimulated by sensory neurones

Question 4

Pain perception

Answer 4

Cell bodies of sensory neurons leading to spinal cord are located in clusters called ganglia
Next to spinal cord
axons usually terminate at interneurons

E.g. skin>sensory neuron>interneuron>motor neuron >effector (muscle in this case)

Question 5

How fast does info travel in the nervous system?

Answer 5

Diff speeds depending on diff types of neuron
Can be as slow as 0.5m/s or as fast as 120m/s

Question 6

Spinal cord

Answer 6

31 pairs of spinal nerves along the spinal cord. They are “mixed” nerves because each has a sensory and a motor axon. However within spinal column:

All sensory axons pass into dorsal root ganglion where cell bodies are located and then into spinal cord

All motor axons pass into the ventral roots before uniting with the sensory axons to form mixed nerves

Question 7

Glial cells

Answer 7

Support cells that surround neurons and provide support/insulation. Most abundant cell type in cns.

PNS:
Schwann cells- myelinate axons and participate in repair process after injury

Satellite cells- surround neuron cell bodies, regulate O2 CO2, nutrient and neurotransmitter levels around neurons in ganglia

CNS

Oligodendrocyte
- myelinate CNS axons
- provide structure

Astrocytes
- maintain blood-brain barrier
- provide structure
-regulate ion nutrient and dissolved gas conc.
- absorb/recycle neurotransmitters
- form scar tissue after injury

Microglia
-remove cell debris, waste and pathogens by phagocytosis

Ependymal cells
- line ventricles (brain) and central canal (spinal cord)
- assist in producing, monitoring and circulating cerebrospinal fluid

Question 8

Brain structure

Answer 8

Motor cortex
Somatosensory cortex
Auditory cortex
Visual cortex

Question 9

Roles of different parts of the brain

Answer 9

Movement control - motor
Sense environment/danger
Process: see/hear/smell/taste/feel
Encode memories
Regulate sleep and feeding
Regulate autonomic physiology
Controls personality and behaviour

Question 10

Neurotransmission

Answer 10

Sodium potassium pump
Potassium channel
Sodium channel

Question 11

Resting potential

Answer 11

All cells have this. An electrical charge across the plasma membrane w/interior of cell neg charged compared to exterior.

Size of resting potential varies but in excitable cells (neurons) it’s about -70 millivolts (mv)

Re sting potential arises from 2 activities

1) Na+/K+ pump pushes only 2 K+ ions into the cell for every 3Na+ it pumps out

2) some k+ channels leak allowing slow facilitated diffusion of K+ out of cell

Question 12

Depolarisation

Answer 12

Certain external stimuli reduce charge across plasma membrane

Mechanical stimuli (e.g stretching, sound waves) activate mechanically-gated Na+ channels

Certain neurotransmitters (e.g. acetylcholine) open ligand gated Na+ channels

In each case facilitated diffusion of Na+ into the cell reduces resting potential at that spot on the cell creating excitatory postsynaptic potential or EPSP.

If potential is reduced to a threshold voltage an action potential is generated in the cell

Question 13

Action potential - all or none

Answer 13

In a resting neuron the intetior of the axon membrane is neg charged compared to exterior. As action potential passes polarity is reversed (Na+ enters through voltage gated channels) the sodium channels then inactivate and outflow of K+ ions quickly restores normal polarity

Question 14

Myelinated neurons

Answer 14

Axons of many neurons have a myelin sheath

Voltage gated Na+ channels are confined to nodes of Ranvier

Inrush of Na+ at one node creates enough depolarization to reach the threshold of the next

So action potential “jumps” from one node to the next.

This process is much faster than is possible in non myelinated neurons

Question 15

Multiple schlerosis

Answer 15

Inflammatory demyelinating disease
Unknown cause- thought to be due to a spectrum of diseases combined

Causes oligodendrocyte loss

Leads to disorganised functioning and slowing of signals

Question 16

History of neuroscience

Answer 16

1873 C. Golgi invents silver staining method for nerves that turns a small no. of them black throughout their structure

S.R. Cajal produced evidence for discrete nerve cells realising that golgis stain reveals the entire cell

W. Waldeyer argues nervous system composed of individual discrete cells

C. Sherrington 1897 coined term synapse

1911-1928 E.D. Adrian and K. Lucas formulate all or nothing theory of nerve firing

A. hodgkin and A. Huxley 1952 : Hodgkin Huxley Model - nerve impulses propagated by Na+ ions flooding into nerve cell turning internal solution from neg to pos charged. Followed by second phase of K+ ions moving out of cell to return internal solution back to normal resting potential

Question 17

More recent neuroscientists

Answer 17

Rita Levi-Montalcini
1986: nerve growth factors

Linda B. Buck
2004: discovered odorant receptors and the organisation of the olfactory system

Question 18

2014 Place and Grid cells (Brains GPS)

Answer 18

Edvard Moser, John O’Keefe and May-Britt Moser

Place cells fire as a rat travels through a tunnel