Transcript Chapter 4: The Central Nervous System

CHAPTER 4: THE CENTRAL
NERVOUS SYSTEM AND
CHAPTER 5: THE PERIPHERAL
NERVOUS SYSTEM
THE NERVOUS SYSTEM
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THE CENTRAL NERVOUS SYSTEM
 The
central nervous system (CNS) is one of
the two major branches of the human
nervous system.
 The
CNS is comprised of the brain and spinal
cord.
 The
spinal cord connects the brain to the
second major branch – the peripheral nervous
system (PNS).
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THE SPINAL CORD

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The spinal cord is the cablelike column of nerves that
extends from the bas of the
brain to the lower back
Its major role is to receive
sensory information from the
body and transmit it to the
brain, and receive information
from the brain and relay it to
the body to control muscles,
glands and organs
The spinal cord consists of two
major components, white
matter and grey matter
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THE SPINAL CORD

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White matter is made up solely of axons which run the length
of the spinal cord
An axon is the part of a neuron that sends information away
from the soma (cell body) to other neurons or to cells in
muscles or glands
Axons are covered in a white protective coating known as
myelin and are located mainly in the other layers of the
spinal cord
The grey matter contains cell bodies, together with their axons
and dendrites, and is mainly located in the centre of the spinal
cord
Dendrites are thin extensions of a neuron that receive
information from other neurons and transmit it to the cell
body
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NEURONS


Neurons are cells that are specialised to receive,
process and/or transmit information to other cells
within the body
Neurons can be broadly categorised into 3
categories depending on the primary function
they perform
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SENSORY NEURONS
Sensory Neurons are nerve cells that carry messages
from sensory organs and receptors through nerves in the
PNS, up the tracts in the spinal cord and to the brain.

Sensory neurons generally respond only to a particular
type of stimulus.
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Pressure Receptors – touch, pressure, pain
Temperature Receptors – hot and cold
Pain Receptors – linked to pressure & temp receptors
Taste Receptors
Smell Receptors
Sensory neurons are also known as afferent neurons
because they transmit sensory information along
afferent tracts in the CNS
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SENSORY NEURONS
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MOTOR NEURONS
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Motor Neurons are nerve cells that carry
messages away from the brain and spinal cord
towards muscles, glands and organs that enable
bodily movements or glandular secretions.
Motor neurons are also known as efferent
neurons as they transmit motor activity along
the afferent tracts of the spinal cord
The main distinction between motor neurons
and sensory neurons is the direction of the
nerve impulses and what occurs at their
respective destinations.
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MOTOR NEURONS
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SENSORY AND MOTOR NEURONS

S – Sensory

A – Afferent
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M – Motor
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E – Efferent
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So sensory/afferent neurons carry information
from sensory receptors in the PNS towards the
CNS while motor/efferent neurons carry
information away from the CNS to the muscles
and glands
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INTERNEURONS
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Interneurons perform the important function of making
the connection between motor and sensory neurons.
Interneurons relay messages from one group of neurons
to another group of neurons.
They exist only in the CNS (brain & spinal cord).
Interneurons have a single axon leaving the cell body
and a single dendrite coming into the cell body from a
receptor cell.
Interneurons play an important role in reflexes
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THE PERIPHERAL NERVOUS SYSTEM

The Peripheral Nervous System (PNS) is the
complete network of neurons located outside the
CNS.
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The PNS extends from the top of the head to the
rest of the body.
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The PNS has two main functions:
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To carry information from the sensory organs to the
CNS.
To convey information from the CNS to the muscles,
organs and glands. (up to here)
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THE PERIPHERAL NERVOUS SYSTEM

The PNS can be subdivided into two quite
distinct nervous systems, each of which have
different functions:
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The Somatic Nervous System
The Autonomic Nervous System
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THE SOMATIC NERVOUS SYSTEM


The Somatic Nervous System has both a
sensory function and a motor function.
The Somatic Nervous System, also called the
Skeletal Nervous System, is the network of
neurons that transmits messages from the
sensory receptors to the CNS and controls
voluntary movement of skeletal muscles through
messages sent from the CNS.
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THE SOMATIC NERVOUS SYSTEM

Therefore the Somatic Nervous System allows
you to –
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Feel any sensations from your external environment.
Make any voluntary movements or actions to respond to
your external environment.
Paraplegics and Quadriplegics have had their
spinal cord severed at a certain point allowing no
neural information to pass through the somatic
nervous system below the severed cord.
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THE AUTONOMIC NERVOUS SYSTEM
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The Autonomic Nervous System (ANS) is a
network of neurons that connects the CNS to all
the body’s internal muscles, organs and glands.
When you are suddenly frightened – your heart
rate and breathing rate increases, your pupils
dilate and goosebumbs appear. The Autonomic
Nervous System is responsible for all of these
events occurring.
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THE AUTONOMIC NERVOUS SYSTEM
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The term autonomic means automatic,
independent or self governing.
Regardless of our awareness or alertness, the
ANS keeps the vital organs and systems of our
body functioning, thus maintaining our survival.
This occurs automatically without our conscious
control.
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THE AUTONOMIC NERVOUS SYSTEM
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The ANS modulates (modifies or changes) the
activity of visceral muscles, organs and glands.
The ANS receives constant neural activity from
the CNS by either increasing or decreasing
messages to bring about changes in the body.
While most of the actions controlled by the ANS
are not within our control, there are a few
responses of the ANS that we can voluntarily
control – blinking, heart rate and breathing rate.
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THE AUTONOMIC NERVOUS SYSTEM
 In
India, it has been reported that Yogis
(Hindu holy men) can change their heart
rate from 75 bpm, to 300 bpm or 50 bpm.
 People
who aren’t Yogis can also learn to
control various autonomic responses using
a technique called Biofeedback
Training.
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DIVISIONS OF THE ANS
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Most muscles, organs and glands receive
messages from two sets of neurons from two
distinct divisions of the ANS.
The Sympathetic division is responsible for
increasing the activity of muscles, glands and
organs in times of vigorous activity, stress or
threat.
The Parasympathetic branch is responsible for
decreasing the activity of muscles, glands and
organs and keeping the body functioning at a
normal rate.
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DIVISIONS OF THE ANS
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When you play a game or sport, the sympathetic
nervous system speeds up your heart rate,
increases metabolism and induces sweating in
order for you to perform to your maximum.
When you stop playing, the parasympathetic
nervous system slows your heart and breathing
rate, to help the body return to its normal state.
While the sympathetic and parasympathetic
nervous systems are both active at the same
time, one system usually predominates over the
other at any given time.
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THE SYMPATHETIC NERVOUS SYSTEM
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The sympathetic nervous system originates in
the spinal cord, and enhances survival by
providing an immediate response, in a split
second, to any kind of emergency.
In an emergency situation, the sympathetic
nervous system sends a message to the adrenal
glands to secrete the hormones adrenalin and
noradrenalin.
These hormones are released into the
bloodstream and activate muscles organs and
glands for preparation of the potential
emergency.
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THE SYMPATHETIC NERVOUS SYSTEM
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The results of these hormones include:
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Increased heart rate and blood pressure,
Increased breathing rate,
Increased pupil size,
Increased sweat production,
Decreased digestion,
Heightened senses (ie: goosebumps, see p136)
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THE PARASYMPATHETIC NERVOUS
SYSTEM
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The parasympathetic nervous system has the
effect of counterbalancing the activities of the
sympathetic nervous system.
The parasympathetic nervous system has three
main functions:
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It keeps the systems of the body functioning efficiently.
It helps maintain a constant internal environment.
It restores the body to a state of calm after vigorous or
strenuous activity.
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THE AUTONOMIC NERVOUS SYSTEM
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THE BRAIN
 The
human brain is encased in a hard
protective skull and weighs about 1.5kg.
 It
has the consistency of firm jelly and is
covered by a strong plastic like membrane.
 The
brain contains over one billion neurons
and over one trillion synaptic connections.
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THE BRAIN
 Neuropsychologists
often describe the
brain as having three
main regions:
 The
Hindbrain,
 The Midbrain,
 The Forebrain
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THE CEREBRAL CORTEX
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The cerebral cortex is one of the most easily recognised parts
of the brain
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It is recognisable as the folded outer layer or covering of the
cerebral hemispheres of the brain
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The cerebral cortex is largely involved with:
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information-processing activities,
language,
speech,
learning,
memory,
thinking,
problem solving
the control of sensory and motor abilities.
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THE CEREBRAL CORTEX
 It
is believed that the size of a species’ cerebral
cortex is linked to intellectual ability.
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THE CEREBRAL CORTEX
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In terms of function, the cerebral cortex has three
main parts:
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The various sensory areas (which receives
information about vision, smell and sound)
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The motor cortex (which transmits information
about bodily movements)
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The association cortex (which integrates
sensory and motor information)
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CEREBRAL HEMISPHERES
 The
cerebral cortex is described as having
two halves.
 The
cerebral hemispheres are two almost
symmetrical brain structures that appear to
be separated by a deep groove (known as the
longitudinal fissure).
 These
hemispheres appear to be separated
completely, but they are joined in the
midbrain by a structure called the corpus
callosum.
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CEREBRAL HEMISPHERES
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CEREBRAL HEMISPHERES
 The
cerebral hemispheres is described as
having inverted functions.
 This
means that sensory and motor
information in the right side of the body is
controlled by the left cerebral hemisphere.
 Sensory
and motor information in the left
side of the body is controlled by the right
cerebral hemisphere.
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CORPUS CALLOSUM
 The
corpus callosum is a strand, or ‘bridge’,
of nerve tissue that connects the left and
right cerebral hemispheres and serves as the
main communication pathway between them.
 Its
function is one of a ‘cross-over’ station for
neural messages between the two cerebral
hemispheres.
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CORPUS CALLOSUM
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FOUR LOBES OF THE CEREBRAL CORTEX
 The
cerebral cortex covering each hemisphere
can be divided into four anatomical regions.
 These
cortical lobes are called:
 The
frontal lobes
 The parietal lobes
 The occipital lobes
 The temporal lobes
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FOUR LOBES OF THE CEREBRAL
CORTEX
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FOUR LOBES OF THE CEREBRAL
CORTEX
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Each cortical lobe has areas that specialise in
receiving and processing sensory or motor
information.
There are also association areas that integrate
sensory, motor and other information for complex
mental processes.
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FOUR LOBES OF THE CEREBRAL
CORTEX
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THE FRONTAL LOBE
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THE FRONTAL LOBE
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The frontal lobe is the largest of all lobes and
occupies the front half of the brain.
The primary motor cortex is located at the rear
of the frontal lobes. The PMC controls voluntary
movements.
Stimulation in the left hemisphere of the PMC
will trigger movements of body parts in the right
side of the body and vice versa.
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THE PRIMARY MOTOR CORTEX
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THE PRIMARY MOTOR CORTEX
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The primary motor cortex is mapped so that a
specific area of the cortex controls a specific part
of parts of the body
The amount of area in the cortex devoted to a
specific part demonstrates the amount of finesse
or control given to movement in that part of the
body
Areas with great precision such as fingers are
allocated a much greater cortex area than parts
which have less control such as toes
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THE FRONTAL LOBE
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In the forward section of the frontal lobes
is the association area responsible for
higher mental functions such as judging,
planning and initiative.
The frontal lobes are also involved with
expression of characteristics such as
personality and emotional behviour.

Possibly the best case to support this, is
that of the case of Phineas Gage.
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Box 4.1 – Case study: damage to the
frontal lobes of Phineas Gage
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BROCA’S AREA
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Broca’s area is located in the frontal lobe of the left hemisphere
and is thought to be responsible for articulate speech.
In particular, Broca’s area is involved with the movement of the
muscles required to speak (ie coordination of lips, jaw, tongue
and vocal cords).
Broca’s area is also concerned with the meaning of words, the
structure of sentences and specific parts of speech.
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BROCA’S AREA
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THE PARIETAL LOBE
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THE PARIETAL LOBE
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The parietal lobes receive information about touch,
pressure, temperature, muscle movement and
position.
These are known as somatosensory functions. The
somatosensory cortex is located in the parietal lobe
behind the PMC.
The parietal love also contains association areas
which integrate information from within the lobe and
other structures and areas of the brain – for example
one of these functions enables us to sense our
position in space, to do this we need to integrate
information from our body’s limbs with information
from our visual and auditory receptors from the
temporal and occipital lobes
Other functions of the parietal lobe include attention49
and spatial reasoning – determining where an object
is located in the environment
THE SOMATOSENSORY CORTEX
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THE PARIETAL LOBE
This man is called the
‘homunculus’. What
does he tell us?
 There is a sensory and
a motor homunculus.
How are they
different? How are
they similar?
 Box 4.2 - Phantom
Limbs pg. 189

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THE TEMPORAL LOBES
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THE TEMPORAL LOBES
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The temporal lobes are primarily associated with
hearing , but also play an important role in
memory, particularly the recognition of faces
The primary auditory cortex is found in each
hemisphere and receives information from the
ears and inner ears
The association cortex of the temporal lobes allow
us to remember and perceive features of our
environment
A severe blow or damage to the temporal lobe
would result in loss of memory (amnesia) or
decreased mental function
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THE PRIMARY AUDITORY CORTEX
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Both cortices of the PAC are linked
together with a slight delay so as
direction of sound can be
determined. Otherwise you would
hear a sound on the left and
recognise it coming from the right
Each PAC has areas which receive
and process different features of
sound
The two main features of sound are
the frequency (pitch) and the
amplitude (loudness)
Sounds with different frequencies
and amplitudes are perceived in
different areas of the cortex
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THE PRIMARY AUDITORY CORTEX
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Each cortex is also specialised to process different
types of sound
The left primary auditory cortex processes verbal
sounds (such as words) while the right primary
auditory cortex processes non-verbal sounds
(such as music)
This does not mean however, that verbal and
non-verbal information is processed exclusively
in each hemisphere – there is integration and
overlap
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WERNICKE’S AREA
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WERNICKE’S AREA
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Wernicke’s area is located in the temporal lobe of the
left hemisphere next to the PAC.
Wernicke’s area is involved with interpreting sounds –
especially human speech and language.
Wernicke’s area is vital not just for understanding
words, but also for locating appropriate words from
memory to express intending meanings when we speak
and write.
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THE OCCIPITAL LOBES
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THE OCCIPITAL LOBES
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The occipital lobes are regions in which visual
information is received and processed.
The primary visual cortex is located at the base of
each lobe and is where information arrives from the
eyes.
The visual association areas receive information from
the PVC and other regions of the brain to form visual
perceptions, to think visually and to remember visual
images.
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THE PRIMARY VISUAL CORTEX

The primary visual cortex is located at the base of each
occipital lobe

Information from visual sensory receptors (photoreceptors)
in the retinas is sent to the PVC
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Each hemisphere receives and processes half of the visual
information –the left half of each eye (which receives
information from the right half of the visual field) sends
info only to the PVC in the left occipital lobe, the right half
of each eye (which receives information from the left half of
the visual field) sends info only to the PVC in the right
occipital lobe
Neurons in the PVC are specialised to respond to different
types of visual information such as orientation, shape,
motion, colour etc.
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THE OCCIPITAL LOBES
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HEMISPHERIC SPECIALISATION
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In general the right and left hemispheres appear to be
identical – but they in fact have some specialised
functions that are not duplicated in the other.
Hemispheric Specialisation refers to the
specialisation and dominance of certain functions by
each hemisphere of the brain.
These differences are most apparent in stroke victims
and people that had suffered damage to one side of the
brain only.
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HEMISPHERIC SPECIALISATION
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LEFT HEMISPHERE FUNCTIONS
 Verbal
functions that require the use or
recognition of words (reading, writing and
speaking) are primarily the responsibilities of
the left hemisphere.
 Analytical
Functions such as logical
thinking and the ability to analyse, organise
and interpret data are also dominated by the
left hemisphere.
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RIGHT HEMISPHERE FUNCTIONS
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Non-verbal Functions are those which do not
require the use or recognition of words and are
primarily the responsibility of the right
hemisphere.
Non-verbal tasks include: producing artwork,
recognising faces and tunes, solving puzzles and
daydreaming.
http://mtsu32.mtsu.edu:11406/hemispheric_domi
nance.as
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RESEARCH ON HEMISPHERIC
SPECIALISATION

Evidence of hemispheric specialisation
comes from three main approaches:
1.
Research involving people with a damaged
brain.
2.
Studying those with split brain surgery.
3.
Research with people whose brain is intact and
undamaged
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THE RETICULAR ACTIVATING SYSTEM
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Running up through the centre of the brain stem is a
structure called the reticular formation
In an early experiment, Moruzzi & Magoun (1949)
electronically stimulated the reticular formation of cats
which caused the animals to awaken suddenly and remain
alert
When they severed the connections between the reticular
formation and the rest of the brain, it caused the cats to fall
into a prolonged coma and remain that way until they died

As a result they concluded that the function of the reticular
formation was to control sleeping and waking

The reticular formation thus became known as the
reticular activating system (RAS)
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THE RETICULAR ACTIVATING SYSTEM
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The RAS is a network of neurons that extends to many
directions from the reticular formation to the brain and
spinal cord
Its ascending tracts extend to parts of the brain while its
descending tracts descend to the spinal cord
The general functions of the RAS are to regulate cortical
arousal, increasing or decreasing depending on feedback
from the brain and spinal cord
It also influences whether we are awake, asleep or drowsy
The RAS also appears to influence attention, and more
specifically our selective attention, by highlighting neural
information which is of importance
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THE RETICULAR ACTIVATING SYSTEM
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THE THALAMUS
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The thalamus is a brain structure located in the middle of
the brain, right on top of the brain stem
Its role is to filter information from all of the senses (except
smell) and transmit or relay that information to the
cerebral cortex
The thalamus appears to also play an important role in
attention and actively filters information from the senses
based on importance
Evidence from individuals with thalamus damage shows
that they have difficulty filtering information; that is,
attending to one input and ignoring others
The thalamus also has a role in regulating arousal through
the RAS
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THE THALAMUS
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