Download Transmission of information between neurons

The Biology of Mind (Chapter 2)
 Our nervous system provides us with fundamental information
processing capabilities in relation to internal and external
environments and associated stimuli and metabolic processes
(input, process, output)
 Information is input by means of specialized sense organs
(transducers) – we have three main types of energy transducers:
 Thermal – hot and cold temperature sensation
 Mechanical – touch, pressure, hearing, vestibular
 Chemical – vision, olfactory
 Information processed in brain: sensation, perception, attention,
memory, comparison, decision, emotion
 Output / Response: chemical changes in body, motor and
vocal response
Hard wired parts of the nervous system:
 Predominately brain stem and central core areas
 Functions we either don’t have to learn or which are learned at a
very early age
 Conscious attention is not usually required, e.g., breathing, heart
rate, digestion, sleep, body temperature, etc.
 Regulated by specific areas of the brain and by specific
structures
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Parts of the brain involved in learning:
 Predominately cerebral areas
 Less specific in terms of location of different functions
 If injured when young, some functions can relocate
 Generally the longer an organism’s life span, the larger the
cortical area in order to accommodate learning
 Ability to learn makes an organism flexible in its environment
 Organisms with long life spans and large capacities for learning
are slow to mature
Neuron:
 many different types of neurons but they all have the same basic
components
 soma (cell body)
 dendrites (tree branches)
 axon
 neurons vary in length from less than 1 mm to several feet
 estimates of 10 – 100 billion in the human body
 neurons don’t regenerate very well
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 glial cells hold neurons together – 10 times as many glial cells
as neurons
 axons of some neurons covered with myelin sheathing
 myelin helps protect the neuron
 myelin helps increase the speed of information transfer within a
neuron (up to 200 MPH)
 deterioration of myelin causes multiple sclerosis ( MS )
Transmission of information within neurons:
 Within a neuron, transmission of information is electrical by
means of sodium and potassium ions transferring across the cell
membrane
 This creates a differential charge between the inside and outside
of the neuron

 At rest, sodium Na has been pumped out of the neuron,
leaving the cell negatively charged with K  (potassium) on the
inside (resting voltage potential is about –70 mv)

 When a neuron triggered by another neuron, Na enters the cell
and pushes the voltage up to +40 mv (action potential)
 After they fire, neurons pump the sodium out (at this time they
can not fire again until they recover – refractory period)
 The neuron is returned to a resting potential of –70 mv
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 Neurons either fire or they don’t fire (all or none principle)
Transmission of information between neurons:
 Transmission of information between neurons is chemical by
means of neurotransmitters
 neurotransmitters travel from one neuron (pre-synaptic
membrane), across a synapse, and attach to a neighboring
neuron (post synaptic membrane)
 Neurotransmitters fit into postsynaptic receptor cites like keys
into a lock or key-way
 There are over 75 known neurotransmitters
 Neurons are specific in terms of the neurotransmitters they
manufacture and use
 Neurotransmitters are of 2 basic types: excitatory and
inhibitory
 Pain killing neurotransmitters (inhibitors) and modulators –
endorphins and enkephalins (opiates) kill pain and create
sensations of euphoria
 Relationship between botany and human chemistry (pharmacy)
 Neurons re-uptake their neurotransmitters and reprocess them
future use
 The nervous system achieves graded signals by:
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 Which neurons fire
 How many fire
 How often they fire
Relationship between the brain and nervous system:
 Two divisions within the nervous system:
 central nervous system (CNS)
 peripheral nervous system (PNS)
 CNS consists of the brain and spinal cord
 PNS transmits information between the CNS and the body
 PNS has two main divisions:
 Somatic (connects CNS with voluntary muscles)
 Autonomic (ANS) (connects CNS with involuntary
muscles and glands)
 ANS has two main divisions:
 Sympathetic (excites)
 Parasympathetic (inhibits)
 Sympathetic and parasympathetic systems are antagonistic to
each other and work to balance ANS activity
 Sympathetic is faster to respond
Organization of the Brain:
 Weight = 1.3 kg, Volume = 1.3 litres
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 Consists of huge numbers of neurons (generally non-
myelinated) and glial cells
 Estimates are 100 to 200 billion neurons in the human brain
(100 to 200 trillion synapses)
 Approximately 10 times as may glial cells as neurons
 Glial cells provide structural support and nourishment and
housekeeping functions for neurons
 Tumors within the CNS are frequently caused by glial cells
Functions of the brain:
 Takes in information from body and external environment
 Interprets information and makes decisions
 Controls muscles and motor behaviour
 Regulates vital functions
Main components of the brain:
 Brain stem (central core)
 Limbic system
 Cerebral cortex
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I Brain stem
Cerebellum:
 controls muscles and muscle coordination
 involved in planning, anticipation and has connections to
frontal areas of brain
Medulla and pons:
 controls breathing and respiration
 cross over for afferent and efferent contralateral wiring
Reticular activating system or formation:
 controls sleep / wake cycles and level of arousal
 sensory information filter
Thalamus:
 relays sensory information to specific brain areas
 also involved in sleep regulation
II Limbic system
 controls basic needs, emotions, and drives (motivation) and
involved in establishing memory traces
 Hypothalamus:
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 Controls endocrine system (hormonal system) Via
connections to the pituitary (master endocrine gland) and
affects eating, drinking and sexual behaviour
Amygdala:
 Controls aggression
Hippocampus:
 Important for creating new memory traces, damage causes
emotional change
III Cerebral cortex
 Cortex only the outermost layer of the brain ( a few millimeters)
 Cerebrum is the area below or underneath the cortex
 Cerebral cortex refers to both the cortical layer and the
underlying cerebral areas
 Corpus callosum (made of axons) connects the two halves of the
cerebral cortex
Lobes
Frontal lobe:
 Planning behaviour, personality, not intelligence
Temporal Lobe:
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 Some memory, hearing, speech areas – Broca’s (speech
production), Wernicke’s (speech comprehension)
Parietal Lobe:
 Integration of complex sensory information
Occipital lobe:
 visual cortex
Sensory and motor areas of the brain
 Sensory and motor body maps
Split brain
 We have two somewhat independent brains – the left and right
hemispheres
 A split brain can be created by severing the corpus collosum (an
operation once performed for alleviation of epilepsy – drugs
now a more common procedure)
 Roger Sperry won the Nobel Prize in the early 1970’s for his
work identifying the functions of the 2 hemispheres
For most right handed people:
 Left hemisphere is involved with sequential analytical thought –
language, scientific reasoning, mathematics (arithmetic)
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 Right hemisphere is involved with holistic thinking – spatial
processing (mapping), face recognition, music, art, intuition,
skilled behaviours
Endocrine system
 Affected by CNS and body chemistry
 Slower than CNS
 Communication by means of hormones secreted into the blood
stream
 Pituitary is the master endocrine gland – amongst other things it
regulates body growth.
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