neuron lect1 -handout

Cognitive & Biopsychological Cognitive & Biopsychological PerspectivesPerspectives

Structure & Functioning of NeuronStructure & Functioning of Neuron

(Neuron 1)(Neuron 1)

Structure & Functioning of Neuron

To provide a basic understanding of:

• The structure of the neuron

• Transmission of the neural impulse along the neuron

NERVOUS SYSTEM

Central Nervous System (CNS)

Peripheral NervousSystem (PNS)

BRAIN SpinalCord

Somatic System(Motor & Sensory)

Voluntary

Autonomic Nervous System (ANS)

Sympathetic

Parasympathetic

Side View

Structure of the

Neuron

Structure of Neuron

The Neuron

• Resting Potential

• Threshold

• Action Potential

• ‘All or none’ law

The Neuron

• Sodium ions (Na+)

• Potassium ions (K+)

• Chloride ions (CL-)

• (Also, Protein ions An-)

Resting Potential

Axon

- - - - - -

- - - - - - -

Distribution of Negative Ions

Axon

CL- CL- CL- CL-

An- CL- An- An-

An- An- CL-

CL- CL- CL- CL-

An- Trapped inside axon

CL- greater concentration outside axon than inside

Distribution of Positive Ions

Axon

Na+ Na+ Na+ Na+ K+

Na+ K+ K+ K+

K+ K+ Na+ K+ K+

Na+ Na+ K+ Na+ Na+

K+ greater concentration inside axon than outside

Na+ greater concentration outside axon than inside

Resting Potential

The resting potential is maintained by:

1. Selectively Permeable Membrane

2. Sodium – Potassium Pump

Resting Potential

Axon

Na+ Na+ Na+ Na+ K+

Na+ K+ K+ K+

K+ K+ Na+ K+ K+

Na+ Na+ K+ Na+ Na+

3 Sodium ions (Na+) pumped out for every 2 Potassium ions (K+) drawn in

Propagation Propagation of the action potential refers to the transmission of the action

potential along the axon.

Propagation

Axon

+

+ + + - - - - -

+ + + - - - - - - +

Propagation

Axon

- - + + + - - - -

- - - + + + - - -

Propagation

Axon

- - - - - + + +

- - - - - - + + +

Saltatory Conduction Saltatory conduction is the transmission of the impulse from node to node

"All or None" law If the threshold is reached the neuron will 'fire' (ie a neural impulse will occur) if it is not reached the neuron will not fire

• Therefore, the size and shape of the action potential are independent of the intensity of the stimulus that initiated it

Refractory Period

For a few milliseconds following a neural impulse the membrane is temporarily unexcitable and the axon cannot be fired again regardless of the strength of the stimulus.

This interval is known as the

Absolute Refractory period

Refractory Period

Following the Absolute Refractory period

• there is a short period of time just before the membrane returns to normal during which the neuron will fire but a stronger than normal stimulus is required

• This period of time is called the

Relative Refractory period

Neuron Plasticity & Age

The structure of the neuron is fairly ‘plastic’, that is the fibres of the

neuron can increase or decrease their branching pattern as a function of

age, experience and chemical influences.

Dendritic Growth

Glia (Neuroglia)

• Glia are the other main component of

the nervous system besides neurons • Occupy about the same total space as

neurons • They do not transmit information

Glia Functions

• Remove waste

• Fill space left by dead neurons (form scar tissue)

• Build the myelin sheath

- Schwann cells (PNS) - Oligodendrocytes (CNS)

Spinal Research Raisman (1997)

• Olfactory cells from the nose (although CNS cells) can regenerate and form functional connections after damage

Spinal Research Raisman (1997)

• Studies using Schwann sheath, found although they provide guidance to a regenerating spinal cord, the cord can not make the connection at the other end into the oligodendrocyte

• Olfactory cells were able to make that connection.

EEG

Electroencephalograph (EEG)Machine that records the electrical activity of the brain via electrodes placed on the surface of the scalp

Electroencephalogram (EEG)Trace or record of the electrical activity of the brain

Brain Waves

References

Carlson, N. (2010). Physiology of Behavior, (10th

ed). London: Allyn & Bacon.

Kalat, J. (2009). Biological Psychology, (10th ed).

Belmont, California: Wadsworth.

Pinel, J.P. (2008). Biopsychology, (7th ed).

London: Allyn & Bacon.