Motor systems Flashcards
What colour is white matter?
beige
Adult human gross brain anatomy (dont need to know but for scale)
- Human CNS- most complex system known
- 1011 neurones -100,000,000,000, 100 billion
- >1014 synapses- 100,000,000,000,000, 100 trillion
Lateral view of the cerebral cortex in human, cat and rat
nb. relative increase in human cortex that is not primarily motor or sensory cotex

Section of the brain and the homunculus

What do the following allow?
- Action potential
- Synapses
Action potentials: allow rapid signalling within one neurone.
Synapses: allow convergence and divergence of signals between different neurones
What are the layers of organisations of the cells?
Layers
Cell body layers (e.g. pyramidale)
Molecular layers- mainly neurites and synapse
Six layers in cortex
What are the cell types and their subtypes ?
Cell types
- Neurons:
Excitatory / Inhibitory
morphology / location
- Glia
astrocytes
oligodendrocytes (cns)
Schwann cells (pns)
microglia
Neuronal morphology- evolved for fast information transfer
- Where are APs transduced?
- What does the structure of myelinated axons allow?

Nervous systems scales- distances and speed

What types of voltage recordings can be taken?
Where is the energy from?
What does it drive?
- Record membrane potentials, APs, EPSPs, IPSP
- Energy from mitochondria
- Drives ion pumps
What is the cell membrane in referance to conductivity and composition?
Cell membrane is nonconductive lipid membrane bilayer
How do all ions flux?
All ion flux via protein channels- Voltage gated and neurotransmitters-gated
Differential membrane conductance sets up membrane potential

Passive (electrotonic) properties of membranes- signals fade with distance/ capacitance requires energy to change voltage

Passive membrane properties

Simple electrical model of a neuron?

Voltage clamp: determination of ionic basis of action potential
Sir John Carew Eccles, Alan Lloyd Hodgkin and Andrew Fielding Huxley 1963 Nobel Prize in Physiology or Medicine
“for their discoveries concerning the ionic mechanisms involved in excitation and inhibition in the peripheral and central portions of the nerve cell membrane”
Seminal Paper:
A Quantitative Description of Membrane Current and its Application to Conduction and Excitation in Nerve, J. Physiol. (I952) 117, 500-544
A. L. HODGKIN AND A. F. HUXLEY

Voltage-clamp
Whats isolated using the voltage clamp technique?
What does this ensure?
- The currents through the different sets of voltage-gated channels that are responsible for the AP can be isolated using the Voltage-Clamp technique.
- This ensures the membrane voltage is controlled at pre-set values, and the currents that flow can be measured
Whats Patch clamp?
What can it be used to resolve?
- A form of voltage clamp that allows the measurement of the properties of individual ion channels
- It can resolve the ion flow through single multimeric membrane-protein molecules of the order of 1 pico Amp - (1x10-12Amp)
What single channel properties can be measured?
- i - current
- g – conductance
- Open times
- Closed times
- Probabilities
- Voltage-Dependence
Voltage clamp

Saltatory AP transmission in myelinated axons
nb. V-gated sodium channels at Nodes of Ranvier produce AP inward current

At the neuromuscular junction, what determines which muscle is stimulated?
Modality is coded by WHICH axon is activated
WHICH AXON determines which muscle (or another effector) is stimulated

Summary of lecture 11
- CNS functions are localised (eg. motor/sensory)
- Within these areas there is Topological mapping
- Nervous system has had to evolve fast long-distance communication - evolutionary pressure
- Action Potentials in myelinated axons provide fast long-distance signalling from CNS to peripheral muscles
- Modality coded by which axon / Intensity by number APs
Overall organisation of neural structures involved in the control of movement











































