BASIC PSYCHOLOGY
THE HUMAN NERVOUS SYSTEM
THE STRUCTURE OF THE NUERON
• Dendrites – extension of the soma, connection to other neurons
• Soma – cell body, receives messages from other neurons, controls all metabolic activities
• Axon hillock – messages are summed, initiates an impulse
• Axon – impulses run along the axon
• Myelin sheath – white fatty sheath that insulates the axon
• Nodes of Ranvier – separate myelin sheaths
• Axon terminals/telendrion
• Bouton terminals – connects to a dendrite of a following neuron, filled with neuro
transmitters
• The synapse – synaptic cleft, gap between boutons and dendrites
Types of neurons
• Sensory (afferent) neurons – carry info from senses to spinal cord and brain
• Motor (efferent) neurons- conduct messages from spinal cord/brain to muscles and glands
Axons grouped together:
• Nerve tract – spinal cord and brain
• Nerve – other parts of the body
IMPULSE CONDUCTION IN THE NEURON
Stimuli – received by sensory organs – stimulates neuron – generates a nerve impulse = impulse
conduction
1. Electrical – inside the neuron
2. Chemical – inside the synapse
• Fluid inside & outside the neuron
• Fluid contains ions (positive and negative)
Unevenly distributed
Creates a potential difference
Neuron is electrically charged
Impulse conduction
• Condition of readiness in the neuron (resting membrane potential – inactive but polarised
state)
• Ions
- inside
+ outside
• Soma receives information – form of changing potentials across the membrane)
• Potentials propagate towards the axon hillock (summed)
, • Reaches a particular level (exceed the resting potential – threshold)
• Action potential is triggered
• Axon is polarised, high concentrations of:
+ charged sodium ions on the outside
+ charged potassium ions on the inside
- charged proteins and nucleic acids
(negative is more than positive)
• When an action potential is triggered
Membrane becomes permeable to sodium (moves from outside to inside)
The outside and inside even out
Membrane is depolarised
Membrane becomes permeable to potassium (moves from inside to outside)
Outside becomes +, inside becomes –
Membrane repolarises – potential difference – more potassium outside than there is inside
Hyperpolarised
Returns to resting membrane potential
Refractory period – returns sodium & potassium to original state
Absolut refractory period – does not receive stimuli
Relative refractory period – very strong stimuli only
Characteristics of impulse conduction
• Impulse is initiated at the axon hillock
• Rapidly conducted along the axon
• Towards axon terminals (when a segment finishes conducting it enters a refractory period)
• Moves towards telondendria
Impulses are ALWAYS of the same magnitude – increase in frequency
Kinds of conduction
• Myelinated axons – impulse jumps from node to node (salutatory conduction)
• Un-myelinated axons – impulse propagates smoothly (action potential conduction)
IMPULSE CONDUCTION IN THE SYNAPSE
Communication between different neurons – primarily chemical
The synapse
• Membrane f axon terminal - presynaptic membrane
• Membrane of dendrite/soma – postsynaptic membrane
• The gap – synaptic cleft
Axon potential reaches the tips of axon terminal – chemicals released into synaptic cleft
• Allows contact to take place across it
• Chemicals – neurotransmitters
• Alter activity in neurons
,Neuron fires – action potential conducted to axon terminals – vesicles (with neurotransmitters)
move closer – attach to presynaptic membrane
Neurotransmitters pass into synaptic cleft – mix with fluid – combine with receptors of postsynaptic
membrane – attach to receptors on dendrites/soma
Each neuron releases the same chemical from all branches of axon
Postsynaptic Potentials
• Excites – stimulate the next neuron to fire an impulse (postsynaptic potential)
• Inhibits – stops the impulse firing
• What happens to neurotransmitters:
1. Reabsorbed by neuron that released it (re-uptake)
2. Diffuse away/broken up by enzymes
3. Bounce around and then return to the postsynaptic receptor
• Postsynaptic potential is NOT an all or nothing event – it is a graded potential
• Potentials generated on postsynaptic membrane become weaker as they travel along the
dendrites/across soma
• Process involves:
1. Spatial summation – postsynaptic potential is reinforced by action potentials from the
terminals of several axons reaching the same synapse at the same time. more of the
neurotransmitter is released
2. Temporal summation – the same axon discharges repeatedly
The nature of neurotransmitters
• Whether a neuron has excitatory/inhibitory effects depends on:
1. Nature of the neurotransmitter
2. Place where it acts
3. Quantity of neurotransmitter in relation to the enzyme that destroys it
4. The amount of inhibitory neurotransmitters in relation to excitatory ones at a synapse
• Identifying characteristics
1. Chemicals that are present in or synthesised by neurons
2. When the neuron is active a chemical is released and produces a response in a target
cell
3. There is a mechanism for removing the neurotransmitter from the synaptic cleft once its
work is done
• Most common neurotransmitters
1. Acetylcholine (Ach)
Released – brain, spinal cord, parasympathetic nerves
Causes, skeletal muscles to contract
Related to memory
Supports normal wakeful behaviour and mental alertness
Alzheimer’s disease
2. Adrenaline (epinephrine)
Released – sympathetic nerves, adrenal glands
Increases – heart rate, contraction of blood vessels, skeletal muscle and heart muscles
, Speeds up – metabolism, glucose into the blood
3. Noradrenaline (NA)/Norepinephrine (NE)
Released – brain cells, sympathetic system, adrenal glands
Lack – depression
Excess - mania
4. Dopamine (DA)
Associated – good mental health
Excess – schizophrenia
Control of motor behaviour
Lack – muscle rigidity & tremor (parkinsons)
5. Serotonin
Brain, digestive tract, blood
Regulate sleep wake cycle & temperature
Seasonal depression
Several antidepressants modulate seratonin
6. Gamma-aminobytyric acid (GABA)
Main inhibitory neurotransmitter
Regulates excitability, controls muscle tone, helps manage aggression and appetite
7. Endorphin
Experience of pleasure
Suppression of pain
Produced during “feel-good” activities
The effects of drugs on synaptic processes
• Agonists – similar effect to neurotransmitters (pain killers)
• Antagonists – block the action of some neurotransmitters (sedatives)
STRUCTURE AND FUNCTION
Main parts
• Central nervous system – brain & spinal cord
• Peripheral nervous system - neurons & organs.
2 parts
1. Somatic nervous system
2. Autonomic nervous system
Central nervous system
• Brain & spinal cord
• Protected by:
Bones
3 strong membranes
1. Dura matter (outer), very strong and thick
2. Arachnoid (middle) thick but more flexible
3. Pia mater (inner) soft and flexible
• Both are made of identical halves
THE HUMAN NERVOUS SYSTEM
THE STRUCTURE OF THE NUERON
• Dendrites – extension of the soma, connection to other neurons
• Soma – cell body, receives messages from other neurons, controls all metabolic activities
• Axon hillock – messages are summed, initiates an impulse
• Axon – impulses run along the axon
• Myelin sheath – white fatty sheath that insulates the axon
• Nodes of Ranvier – separate myelin sheaths
• Axon terminals/telendrion
• Bouton terminals – connects to a dendrite of a following neuron, filled with neuro
transmitters
• The synapse – synaptic cleft, gap between boutons and dendrites
Types of neurons
• Sensory (afferent) neurons – carry info from senses to spinal cord and brain
• Motor (efferent) neurons- conduct messages from spinal cord/brain to muscles and glands
Axons grouped together:
• Nerve tract – spinal cord and brain
• Nerve – other parts of the body
IMPULSE CONDUCTION IN THE NEURON
Stimuli – received by sensory organs – stimulates neuron – generates a nerve impulse = impulse
conduction
1. Electrical – inside the neuron
2. Chemical – inside the synapse
• Fluid inside & outside the neuron
• Fluid contains ions (positive and negative)
Unevenly distributed
Creates a potential difference
Neuron is electrically charged
Impulse conduction
• Condition of readiness in the neuron (resting membrane potential – inactive but polarised
state)
• Ions
- inside
+ outside
• Soma receives information – form of changing potentials across the membrane)
• Potentials propagate towards the axon hillock (summed)
, • Reaches a particular level (exceed the resting potential – threshold)
• Action potential is triggered
• Axon is polarised, high concentrations of:
+ charged sodium ions on the outside
+ charged potassium ions on the inside
- charged proteins and nucleic acids
(negative is more than positive)
• When an action potential is triggered
Membrane becomes permeable to sodium (moves from outside to inside)
The outside and inside even out
Membrane is depolarised
Membrane becomes permeable to potassium (moves from inside to outside)
Outside becomes +, inside becomes –
Membrane repolarises – potential difference – more potassium outside than there is inside
Hyperpolarised
Returns to resting membrane potential
Refractory period – returns sodium & potassium to original state
Absolut refractory period – does not receive stimuli
Relative refractory period – very strong stimuli only
Characteristics of impulse conduction
• Impulse is initiated at the axon hillock
• Rapidly conducted along the axon
• Towards axon terminals (when a segment finishes conducting it enters a refractory period)
• Moves towards telondendria
Impulses are ALWAYS of the same magnitude – increase in frequency
Kinds of conduction
• Myelinated axons – impulse jumps from node to node (salutatory conduction)
• Un-myelinated axons – impulse propagates smoothly (action potential conduction)
IMPULSE CONDUCTION IN THE SYNAPSE
Communication between different neurons – primarily chemical
The synapse
• Membrane f axon terminal - presynaptic membrane
• Membrane of dendrite/soma – postsynaptic membrane
• The gap – synaptic cleft
Axon potential reaches the tips of axon terminal – chemicals released into synaptic cleft
• Allows contact to take place across it
• Chemicals – neurotransmitters
• Alter activity in neurons
,Neuron fires – action potential conducted to axon terminals – vesicles (with neurotransmitters)
move closer – attach to presynaptic membrane
Neurotransmitters pass into synaptic cleft – mix with fluid – combine with receptors of postsynaptic
membrane – attach to receptors on dendrites/soma
Each neuron releases the same chemical from all branches of axon
Postsynaptic Potentials
• Excites – stimulate the next neuron to fire an impulse (postsynaptic potential)
• Inhibits – stops the impulse firing
• What happens to neurotransmitters:
1. Reabsorbed by neuron that released it (re-uptake)
2. Diffuse away/broken up by enzymes
3. Bounce around and then return to the postsynaptic receptor
• Postsynaptic potential is NOT an all or nothing event – it is a graded potential
• Potentials generated on postsynaptic membrane become weaker as they travel along the
dendrites/across soma
• Process involves:
1. Spatial summation – postsynaptic potential is reinforced by action potentials from the
terminals of several axons reaching the same synapse at the same time. more of the
neurotransmitter is released
2. Temporal summation – the same axon discharges repeatedly
The nature of neurotransmitters
• Whether a neuron has excitatory/inhibitory effects depends on:
1. Nature of the neurotransmitter
2. Place where it acts
3. Quantity of neurotransmitter in relation to the enzyme that destroys it
4. The amount of inhibitory neurotransmitters in relation to excitatory ones at a synapse
• Identifying characteristics
1. Chemicals that are present in or synthesised by neurons
2. When the neuron is active a chemical is released and produces a response in a target
cell
3. There is a mechanism for removing the neurotransmitter from the synaptic cleft once its
work is done
• Most common neurotransmitters
1. Acetylcholine (Ach)
Released – brain, spinal cord, parasympathetic nerves
Causes, skeletal muscles to contract
Related to memory
Supports normal wakeful behaviour and mental alertness
Alzheimer’s disease
2. Adrenaline (epinephrine)
Released – sympathetic nerves, adrenal glands
Increases – heart rate, contraction of blood vessels, skeletal muscle and heart muscles
, Speeds up – metabolism, glucose into the blood
3. Noradrenaline (NA)/Norepinephrine (NE)
Released – brain cells, sympathetic system, adrenal glands
Lack – depression
Excess - mania
4. Dopamine (DA)
Associated – good mental health
Excess – schizophrenia
Control of motor behaviour
Lack – muscle rigidity & tremor (parkinsons)
5. Serotonin
Brain, digestive tract, blood
Regulate sleep wake cycle & temperature
Seasonal depression
Several antidepressants modulate seratonin
6. Gamma-aminobytyric acid (GABA)
Main inhibitory neurotransmitter
Regulates excitability, controls muscle tone, helps manage aggression and appetite
7. Endorphin
Experience of pleasure
Suppression of pain
Produced during “feel-good” activities
The effects of drugs on synaptic processes
• Agonists – similar effect to neurotransmitters (pain killers)
• Antagonists – block the action of some neurotransmitters (sedatives)
STRUCTURE AND FUNCTION
Main parts
• Central nervous system – brain & spinal cord
• Peripheral nervous system - neurons & organs.
2 parts
1. Somatic nervous system
2. Autonomic nervous system
Central nervous system
• Brain & spinal cord
• Protected by:
Bones
3 strong membranes
1. Dura matter (outer), very strong and thick
2. Arachnoid (middle) thick but more flexible
3. Pia mater (inner) soft and flexible
• Both are made of identical halves
