Hemispheric Specialisation Left side V’s Right side
Transcript
Slide 1
Left side Vs Right side
Slide 2
Left workRight play
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Hemispheric Specialisation Left Verbal Analytical (movement and
sensation right side of body, including sight from right Visual
field) Right Non Verbal, Visio Spatial, Music, (movement and
sensation left side of body, including sight from left Visual
field)
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The cross over Left controls Right Right controls Left No one
knows why so dont ask! This diagram is from the back Note sexy
yellow budgie smugglers
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Wake up. Go to sleep.wake up..go to sleep Look over there!
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The Reticular Activating System
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BRAIN STEM Spinal cord is a continuation of the brain stem
(also called hindbrain) Brain stem is a structure that looks like a
stem on which the brain sits. Three anatomical structures comprise
the brain stem: Medulla Cerebellum Pons Copy Figure 4.31 on page
204
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RETICULAR FORMATION Runs up through centre of brain stem,
upward through midbrain to the forebrain (area under the cerebral
cortex) is a structure known as the reticular formation. Through a
microscope it looks like white netting or lacing (reticular means
like a network). Neuroscientists Moruzzi and Magoun (1949)
electrically stimulated reticular formation of cats and they woke
suddenly and remained alert. When severed connections between
reticular formation and remainder of brain the cats fell into a
prolonged coma until they died. Moruzzi and Magoun (1949) thus
proposed the function of the reticular formation was to control
sleeping and waking.
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RETICULAR FORMATION From the influence of these findings, the
reticular formation gradually came to be known as the reticular
activating system. It is now recognised there is more to this
structure than regulating sleep and wakefulness and that other
parts of the brain are also involved in regulating wakefulness.
Exactly what the reticular formation does and how it does it is
still unclear.
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RETICULAR ACTIVATING SYSTEM It is a network of neurons that
extends in many directions from the reticular formation to
different parts of the brain and spinal cord (like a bicycle wheel
hub). Ascending tracts (upward nerve pathways) extend to the
cerebral cortex and descending tracts (downward nerve pathways)
extend to the spinal cord.
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The Reticular Activating System Major functions are to regulate
cortical arousal (alertness) either increasing or decreasing
arousal in response to feedback from upper and lower brain areas.
Helps regulate sleeping and waking anaesthetics operate by
dampening RAS neural activity Less active RAS we go to sleep.
Damage to the RAS leads to permanent coma or a chronic vegetative
state. Plays a major role in selective attention helps decide which
stimuli will enter awareness Steady stream of impulses from RAS
keep cerebral cortex active and alert. Filters incoming sensory
information helps us ignore useless information (weak or familiar
sensory information) Highlights neural information that is of
importance, directing attention to potentially significant events.
E.g. Country driver sees a kangaroo in middle of road.
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RETICULAR ACTIVATING SYSTEM When event occurs that demands our
attention, RAS bombards cortex with stimulation to arouse specific
cortical areas. Information from 2 simultaneous sensory sources
(e.g. Sounds and images) the RAS calls our attention to both and
assists cerebral cortex to focus on the more relevant information.
Brain scanning shows activation when shifting attention between
stimuli Helps regulate cardiovascular system in response to
external stimuli eg. Sympathetic arousal Ascending RAS tracts
connect to central thalamus areas and appears to influence arousal
and attention through the thalamus.
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What should I pay attention to? What will enter my conscious
awareness?
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The Thalamus
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Located in middle of the brain, right on top of the brain stem.
About 3 cm in length, consisting of 2 ovoids (look like 2 little
footballs) Each ovoid in a different hemisphere. Due to location,
sometimes referred to as the gateway from lower part of brain to
the cortex in the upper part. Sensory relay station filters
information from senses and transmits info to cerebral cortex.
Receives input from all major senses, except smell, which has a
direct route to the cortex, bypassing the thalamus. All other
sensory info must pass through thalamus to reach the cortex.
Integrates information from the senses puts the voice with the face
and the handshake Damage can cause sensory problems blindness,
deafness etc. (except smell) or cause the cortex to misinterpret or
not receive sensory info. Some form of analysis or processing of
sensory information is likely to occur in the thalamus (based on
evidence from case studies of brain damaged patients or those with
an abnormal thalamus).
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The Thalamus Closely connected to the RAS and thus also very
involved in arousal & attention does the shifting and filtering
Streams or bursts of information are channelled from RAS through
thalamus Also controls sleeping and waking arousal through
connection to reticular formation and nerve pathways of the RAS.
Damage resulting in lower arousal, lethargy or coma. Info from
cerebral cortex also travels through thalamus to lower brain
structures, spinal cord and out to peripheral nervous system. E.g.
Thalamus has neurons that relay messages between motor cortex and
movement control centres in brain stem (such as cerebellum).
Involved in consciousness sleep-wake, attention, blocks info to the
brain while sleeping Also involved in emotional responses
(interpretations) to stimuli Also linked to disorders like
Narcolepsy, Depression and Schizophrenia (misinterpreting or not
noticing some stimuli)
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The Thalamus Plays a role in attention by actively filtering
vast amounts of incoming info that needs to be attended to,
highlighting and giving weight to some inputs and less to others.
LaBerge and Buchsbaum (1990) one condition participants attend to a
single letters presence or absence, in the other condition
participants had to look out for same letter embedded among other
letters. Greater PET activation of a specific area of thalamus was
shown in 2 nd condition, even when accounting for stimulus
complexity.
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Neural information super Freeway
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The Spinal cord linking the CNS to the PNS Spinal cord is
cablelike column of nerve fibres extending from base of brain to
lower back, encased in a series of bones called vertebrae that
extend further than actual cord. Major function of spinal cord is
to receive sensory info from body (via PNS) and transmit them to
the brain, then to receive info. from brain and relay it to the
body (via PNS) to control muscles, blands and internal organs.
Spinal cord is the super highway for all information / messages
coming to (afferent - sensory) and leaving (efferent - motor) the
brain. There are separate pathways for information / messages
coming to and leaving the brain these are called tracts Damage to
spinal cord causes brain to lose both sensory input from the body
as well as body control. Severity of feeling loss and paralysis
depends on location of spinal cord damage (higher up spine the
greater number of nerve connections between brain and body are
severed).
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The Spinal Cord The spine contains two types of matter White
Matter = Myelinated axons solely that run length of spinal cord
uninterrupted and are bundled together (part of neuron that sends
information away from cell body or soma) Myelin is a protective
coating that helps speed up transmission of information
Interconnected axons in CNS are referred to as tracts, circuits or
pathways. Spinal cord has ascending tracts for somatosensory
information and descending tracts for motor information. Grey
matter contains neuron bodies (cell bodies, axons and dendrites),
mainly located near the centre of the spinal cord.
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The Spinal Cord Adult spinal cord is only about 43 to 45 cm
long but vertebrae extend for about 60 cm.
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The Spinal cord - levels Four Sections of Cord Cheese
(cervical) Tastes (thoracic) Like (lumbar) Shit (sacral) These
sections of the spinal cord are named by the groups of nerves that
enter and exit the spinal cord at each section Cervical 8 pairs of
nerves enter and exit Thoracic 12 pairs of nerves enter and exit
Lumbar 5 pairs enter and exit Sacral 5 pairs enter and exit Nerves
at each level send / receive information to / from different parts
of the body (see handout) The spinal cord only goes to the base of
the thoracic vertebrae. Nerves radiate laterally from the spinal
cord above this, and continue vertically inside the vertebrae below
the thoracic this bundle of nerves is known as the cauda equina or
horses tail
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The Spinal Cord Cervical nerves each level contributes to
different motor functions of neck, shoulders and arms. Thoracic
nerves Radiate to muscles in chest (pectoral muscles). Also links
to visceral muscles which are connected to large internal organs in
chest cavity (e.g. lungs). Thus involved in actions such as
breathing and coughing. Lumbar nerves Leg muscles Sacral nerves
Bowel, bladder and sexual function Spinal cord only extends to last
bone of thoracic vertebrae. Nerves below thoracic section form a
bundle running vertically inside vertebrae. This large section of
nerves is known as the cauda equina (horse tail).
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The Spinal cord - levels
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The Spinal Reflex 1730 English scientist Stephen Hales
demonstrated spinal cord responsible for limb reflex movements.
Decapitated a frog (thus no brain input) and pinched a leg, the
frogs leg pulled away. Hales concluded sensory receptors in leg had
transmitted message to spinal cord and in turn message looped to
motor neurons to stimulate certain muscles, causing contraction and
pulling away from stimulus. Pain not registered as pain registers
in the brain. Interneuron cells in spinal cord connect between
sensory neurons and motor neurons to create the loop. The same
reflex response occurs in humans to protect from harm and enhance
survival. E.g. Prick finger on rose thorn.
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Neurons building blocks of the Nervous System A neuron is a
cell that sends and receives information in the form of neural
impulses (neural impulses are tiny pulses of electro chemical
energy) Sensory and motor neurons do not share the same tracts to
and from the brain, they follow separate but adjacent paths 31
afferent and 31 efferent tracts in spinal cord (separate train
tunnels) Sensory info is transmitted from senesory receptor cells
in PNS via sensory neurons to the CNS. Sensory information is
afferent information (afferent = coming towards) i.e. Towards CNS
e.g. Hearing a kettle whistle, seeing a bird fly, feeling cold of
an ice cube. Sensory (feeling) neurons afferent (coming towards)
Motor (Moving) neurons efferent (leading out) from CNS Interneurons
connecting neurons that relay messages from sensory neurons to
other interneurons or moto neurons within the CNS (enable the
spinal reflex, sensory communicate with motor)
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Transmission of neural information Motor information from the
brain comes from motor cortex at rear of frontal lobes (except for
spinal reflex) where motor neurons carry messages of movement down
the spinal cord to the skeletal muscles and glands where they
connect to effector cells. Effector cells control action of muscles
by causing them to contract, thus causing movement. They are
located in glands and cause the secretion (release) of hormones to
occur when they are activated by messages from motor neurons.
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Neurons There are many types of neurons about 200 different in
the CNS alone. Can be categorised into 3 types based on their
primary function: sensory, interneurons, motor neurons. Sensory
neurons afferent neurons. Carry messages from sensory organs
through nerves in PNS up tracts in spinal cord to the brain.
Receive info. from both external and internal environment. E.g.
Environment through senses and internally from muscles, organs and
glands. Sensory information known as afferent information. Nerve
tracts in the spinal cord that carry this information carry ONLY
somatosensory information. Sensory neurons are quite different in
structure to motor neurons and DO NOT share the same tracts to and
from the brain. There are 31 afferent tracts and 31 efferent tracts
in the spinal cord. Draw a sensory neuron and a motor neuron (see
page 210) Some sensory info. transmitted to brain from spinal cord.
Some sensory info. directly transmitted to brain from cranial
nerves in face (e.g. From forehead or cheek). Sensory neurons
usually only respond to a particular type of stimulation. E.g.
Neurons in nose to odours detected by chemical energy but not light
(electromagnetic energy) or sound (mechanical energy).
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Transmission of sensory info from the Peripheral Nervous System
Afferent means coming towards in this case coming towards the
Central Nervous System. Information such as change in skin
temperature when holding an ice cube, sound of a kettle whistling,
smell of toast cooking are all examples of sensory
information.
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Interneurons Interneurons connecting neurons located near the
base of the spinal cord. Make connections between sensory and motor
neurons which rarely ever connect directly or to other
interneurons. Exist only in CNS where they are in largest number of
any type of neuron. Can have long axon and short dendrites or short
axon and long dendrites. Draw an interneuron (see page 210)
Slide 32
Transmission of motor information from the brain After the
brain receives sensory stimuli information there is often a
response that requires movement. The motor cortex is the launching
pad for most bodily movements, whether voluntary or involuntary
(except movement initiated by the spinal reflex). Motor neurons are
the neurons that carry messages of movement. They leave the motor
cortex (at the rear of the frontal lobes), travel down the spinal
cord to the skeletal muscles and glands where they connect to
effector cells. The effector cells control the action of muscles by
causing them to contract, thus causing movement. Effector cells
located in glands cause the secretion (release) of hormones to
occur when they are activated by messages from motor neurons.
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Motor Neurons Motor neurons efferent neurons. Carry messages
away from CNS towards muscles, organs and glands, thus enabling
body movements, internal organs to be activated and glandular
secretions to occur. Motor messages are known as efferent messages.
Efferent means leading out from in this case, leading out from the
central nervous system. Physically turning taps when shower is
sensed as too hot are messages transmitted from the motor cortex,
down the spinal cord, out to effector cells located in the muscles
of arms, hands and fingers. Direction of neural impulses and what
happens at destination different to sensory neurons.
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Cerebral Cortex There is ongoing interaction in the cerebral
cortex between sensory information coming to the brain and motor
information going from the brain because a lot of the sensory
information requires action to be taken in the form of movement.
The close proximity of the somatosensory and motor cortices has
been suggested as an adaptive evolutionary feature of the
brain.
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A Motor Neuron Axon terminals Myelin sheath Axon Terminal
Button synapsesynapse
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STRUCTURE OF A NEURON The soma or cell body is the structure
that determines whether the neuron will be activated and thus
transmit (send) messages to other neurons. A dendrite (from the
Greek work meaning 'tree') is a short, thin, widely branching nerve
fibre that is specialised to detect and receive neural information.
An axon is a single, tube like, fluid-filled extension that
transmits messages from the soma to other cells in the body
including other neurons, muscles, organs and glands. Encased in a
white fatty substance that helps speed un transmission called
myelin sheath. At the end of each axon are branches called axon
terminals. Each axon terminal has a small knob-like swelling at the
tip of it called a terminal button / synaptic knob The synaptic
knob is a small structure like a sac that stores chemicals called
neurotransmitters which assist in the transmission neural
information from one neuron to another
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The Neural Impulse Neurons are capable of only transmitting
information in a specific form, as neural impulses. A neural
impulse (or action potential) is a combination of electrical and
chemical energy (electrochemical energy) that contains the neural
information that travels along the axon. A neural impulse travels
only the length of a neuron and not continuously along the axon.
When impulse is triggered, one section of axon opens up that
triggers the next section to open up and so on passing the impulse
along the axon Between membrane casing of neuron and the neuron is
a small amount of fluid containing particles called ions.
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The Neural Impulse The ions are either positively charged or
negatively charged with different quantities of each in the fluid.
The difference in the charges between the neuron and the
surrounding fluid results in an electrical charge across the cell
membrane. Neuron in resting state there is a very small difference
in electrical charge inside and outside the neuron. The difference
is known as the resting potential. Each neuron requires a minimum
level of stimulation to be activated from its resting potential so
a neural impulse begins. This minimum level to activate a neural
impulse is the neurons threshold.
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The Neural Impulse Resting potential changes when a neuron
receives messages from other neurons. If the electrical charge
reaches the threshold, a neural impulse is activated and begins its
movement down the axon, in sections. At the end of each axon
section is an ion channel. Ion channels are like gates that open
and close to allow ions to flow along the axon. The neural impulse
can only move in one direction. Once triggered, a neural impulse is
self-sustaining continuing to the end of the axon without further
stimulation. No matter how much higher than the threshold, the
neural impulse will occur. Magnitude (intensity) is not important,
there is either a neural impulse or not (i.e. It either fires or
doesnt fire). There is no such thing as a partial impulse. This
rule is called the all or nothing principle. Neural impulse speed
down an axon varies. Fastest is 430 km/h and slowest at 3.5 km/h.
Speed depends on diameter (width) of the axon and whether it has a
myelin sheath. Larger diameter = faster, myelinated axons =
faster.
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An Action Potential
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Synaptic Transmission
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Synaptic transmission The gap between neurons is called the
synapse. When the neural impulse reaches the end of each axon, the
terminal buttons releases chemicals called neurotransmitters A
neurotransmitter is a chemical substance that is manufactured by
the neuron. It contains ions that travel across the synapse to the
receptors on the dendrites of the receiving neuron Sometime the
neurotransmitter triggers or activates a neural impulse on the
connecting neuron. At other times, the neurotransmitter inhibits or
prevents the connecting neuron from firing When the
neurotransmitter has done its job it is either taken back by the
terminal buttons or disposed of
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100 billion neurons 10,000 connections for each neuron
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The Parts of a Neuron Dendrites Cell body (soma) Axon Axon
Terminals Terminal Buttons Synapse DCATBS Dont Confuse All This
Bull Shit! Do CATs Bite Snakes?
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Parts of a neuron story? Denny Dendrite was a prisoner who
lived in a cell with a dead body. He was in jail for murdering his
mother with an axe on her way to the train terminal. He also likes
to collect buttons?
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The Mexican wave!
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The Key in the Lock!
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Stuff to do Hemispheric dominance quiz Handout on lobes Neuron
structure handout Learning activities 4.9, 4.10, 4.12, 4.13