The Nervous System

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BACK TO MAIN A2 BIOLOGY MENU
The
Nervous
System
Organisation of the nervous system
Sympathetic and parasympathetic systems
Digestion, heart action, pupil diameter
Investigating the human brain
Gross structure of the human brain
Functions of the cerebrum, hypothalamus,
cerebellum and medulla oblongata
Symptoms and possible causes of Alzheimers
disease
Review and test
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Nervous
The
The Organisation of the Nervous System
System
Types of cells
Neurones
Transmit nerve impulses
Help with ionic balance and nutrient supply to
the neurones
Glial cells
e.g. Schwann cells
Organisation
There are 2 main parts to the nervous system
The Central Nervous System brain and spinal cord
The Peripheral Nervous System the neurones that
lie beyond the brain and spinal cord
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Nervous
The
The Organisation of the Nervous System
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The central nervous system - CNS
Most neurones in the CNS are intermediate
neurones, often each with thousands of synaptic
connections
These synaptic connections are of 2 types
Excitatory action potentials in the nerve
depolarise the post synaptic membrane of the
nerve on the other side of the synapse
Inhibitory action potentials in the nerve
hyperpolarise the post synaptic membrane of the
nerve on the other side of the synapse
There are about 200 x 1012 neurones in the brain
and the mix of inhibitory and excitatory synapses
provides an almost infinite framework for
patterns of nervous activity
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Nervous
The
The Organisation of the Nervous System
System
Canal
The spinal cord (SC) runs through the neural
arches of the vertebrae and in its centre is a
canal containing cerebrospinal fluid.
Butterfly shaped area of unmyelinated neurones
(grey)
Myelinated neurones (white)
The brain is a highly specialised area of the SC.
See later
The brain and spinal cord are surrounded by 3
membranes called the meninges
The meninges secrete cerebrospinal fluid. The
fluid supplies oxygen and nutrients and acts as a
shock absorber
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Nervous
The
The Organisation of the Nervous System
System
Types of cells
Neurones
Transmit nerve impulses
dendrites
Node of Ranvier
nucleus
myelin sheath
cell body
axon
synapse
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The
The Organisation of the Nervous System
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The peripheral nervous system
The cell bodies of sensory neurones are lie just
outside the spinal cord in the dorsal root
ganglion (a group of nerve cell bodies)
The cell bodies of motor neurones are in the
spinal cord
Axons and dendrites are arranged in bundles
called nerves
CHECK IT OUT
In the knee jerk reflex, the lower leg swings
forward quickly when an area just below the knee
is tapped. In order for this reflex to occur, a
message travels through a sensory neuron to the
spinal cord, where an interneuron carries it to a
motor neuron, which sends the information to the
leg muscle and causes the movement.
A typical somatic NS reflex arc
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Nervous
The
The Organisation of the Nervous System
System
TS Nerve containing 100s of axons and dendrons
MYELIN SHEATH
AXON
Nearly all the nerves shown are myelinated but a
few are non-myelinated
BACK
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The
The Organisation of the Nervous System
System
NERVOUS SYSTEM
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Nervous
The
The Organisation of the Nervous System
System
The sympathetic nervous system
The cell bodies of its motor neurones lie in
ganglia outside the spinal cord
PUPILS
From these ganglia sympathetic motor axons pass
to all organs of the body, eventually synapsing
with muscles, e.g. cardiac, smooth.
SALIVARY GLANDS
HEART
BRONCHI
The transmitter liberated at these synapses is
usually nor adrenaline it stimulates organ
activity
LIVER
STOMACH/ SMALL INTESTINE
Ach is released at motor endings in sweat glands,
erector muscles and some blood vessels. It too
causes stimulation.
ADRENAL GLAND / KIDNEYS
LARGE INTESTINE
BLADDER / GENITALS
SNS functions are FIGHT OR FLIGHT
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Nervous
The
The Organisation of the Nervous System
System
The Parasympathetic Nervous System
The nerve pathways all begin in the brain, or at
the top or bottom of the SC
EYE
SALIVARY GLANDS
The neurones keep going till right inside the
organ. Here they synapse with a motor neurone
BRONCHI
HEART
The transmitter liberated at these synapses is
acetylcholine and this has an inhibitory effect
on the organ
STOMACH PYLORIC SPHINCTER
PANCREAS
Many parasympathetic axons are part of the vagus
nerve.
LARGE INTESTINE, ANAL SPHINCTER
BLADDER
PNS functions are REST AND DIGEST
GENITALS
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Nervous
The
The Organisation of the Nervous System
System
Layout of motor pathways in the autonomic nervous
system
Cranial parasympathetic fibres
Ach
Ach
GANGLION
NA
Ach
GANGLION
Preganglionic neurone
Motor neurone
NA
Ach
Sacral parasympathetic fibres
GANGLION
Ach
Ach
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The
The Organisation of the Nervous System
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Some sympathetic and parasympathetic effects










Effect of sympathetic stimulation
Effect of parasympathetic stimulation
Organ
Increase rate and force of contraction
Reduces rate and force of contraction
Heart
Constricts
Eye
pupil
Dilates
Relax lens thinner for distant vision
ciliary muscles
Contract lens thicker for near vision
Digestive system
glands
Little or no effect
Stimulates secretion
sphincter muscles
Contraction
Relaxation
Small increase in glycogen production
liver
Release of glucose into blood
Little effect, except to increase sweating on
palms of hands
Increases sweating
Skin
sweat glands
Contract, making hairs stand on end
erector muscles
No effect
vasoconstriction
arterioles
No effect
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Nervous
The
Sympathetic and parasympathetic action
System
Effect on the digestive system
Salivary glands produce more saliva
Reduced blood supply to gastric and salivary
glands
Peristaltic muscles contract more frequently
Reduces peristalsis
Sphincter muscles relax
Sphincter muscles close
Gastric glands secrete more juice
PARASYMATHETIC STIMULATES DIGESTION
SYMATHETIC WEAKLY SUPPRESSES DIGESTION
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The
Sympathetic and parasympathetic action
System
The action of the heart
Ach
Ach
NA
NA
PARASYMPATHETIC REDUCES THE RATE AND FORCE OF
CONTRACTION
SYMPATHETIC INCREASES THE RATE AND FORCE OF
CONTRACTION
Ach release from the vagus nerve
NA release from sympathetic nerves
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The
Sympathetic and parasympathetic action
System
Pupil dilation and constriction
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The
Sympathetic and parasympathetic action
System
Pupil dilation and constriction
The SNS is stimulating the radial muscles to
contract, widening the pupil.
The pupil is the dark space in the centre of the
iris
The iris contains circular and radial muscles and
their activity can change pupil diameter
Causes
Dim light
Excitement
Fear
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Nervous
The
Sympathetic and parasympathetic action
System
Pupil dilation and constriction
CLICK TO DILATE
PUPIL CONSTRICTED
The PSNS is stimulating the circular muscles to
contract, narrowing the pupil diameter
The pupil is the dark space in the centre of the
iris
The iris contains circular and radial muscles and
their activity can change pupil diameter
Cause
Very bright light
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Nervous
The
The Brain
System
The study of the brain - introduction
Difficulties arise because of the enormous number
of cells and the huge numbers of connections
Thus research often focuses on the function of
groups of cells and how they connect to other
groups
Post-mortem examination of brain tissue from
patients with mental disorders was for a long
time the only way that brain function could be
studied
Pierre Broca (France, 1861) for example studied
the brain of a patient who could not speak or
write but could understand language that he read
or heard
He found that a small area at the front left side
was damaged. Discovery of similar damage in
other patients led to this being called Brocas
area.
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The
The Brain
System
The study of the brain methods used
Studies of the brains of people with brain
illnesses
before or after death,
either by using post-mortem brain slices or new
scanning methods on living patients.
Investigating areas of brain activity in healthy
people
using new scanning
techniques
CAT scanning
Computer assisted tomography
PET scanning
Positron emission tomography
MRI scanning
Magnetic resonance imaging
Studying the effect of particular drugs on the
brain.
Trials with
various molecules have provided much information
about the structures and functions of molecules
found in normal brains
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Nervous
The
The Brain - Structure
System
EXTERNAL STRUCTURE
PARIETAL LOBE
FRONTAL LOBE
OCCIPITALLOBE
TEMPORALLOBE
CEREBELLUM
MEDULLA OBLONGATA
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The
The Brain - Structure
System
VERTICAL SECTION THROUGH THE HUMAN BRAIN
VENTRICLES CONTAINING CEREBROSPINAL FLUID - CSF
PARIETAL LOBE
FRONTAL LOBE
OCCIPITAL LOBE
THALAMUS
CEREBELLUM
MEDULLA OBLONGATA
HYPOTHALAMUS
PITUITARY GLAND
SPINAL CORD
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The
The Brain - Function
System
THE MAJOR PARTS OF THE BRAIN
The cerebrum contains the right and left cerebral
hemispheres linked by the corpus callosum
Part of brain Function
Cerebrum
Hypothalamus
Cerebellum
Medulla oblongata
Thinking, language, planning, emotions, memory
The surface of each cerebral hemisphere is
covered by a highly folded tissue called the
cerebral cortex
Control of the autonomic nervous system and some
endocrine glands
Lobes in the cerebral cortex frontal, parietal,
temporal, occipital.
Control and coordination of movement and posture
The thalamus and hypothalamus lie below the
cerebrum. The hypothalamus is closely associated
with the pituitary gland
Control of breathing movements, heart rate,
action of smooth muscle in the gut
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Nervous
The
The Brain - Function
System
The Cerebrum
Both cerebral hemispheres receive sensory
information from the eyes, ears, skin etc.
Areas first receiving this information are called
primary sensory areas
Areas which then process and integrate this
information are called association areas.
There are 3 main association areas making up a
large part of the cortex. They involve
co-ordination such as body position analysis,
planning actions and movements, and also creating
emotions and memory
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The
The Brain - Function
System
The Cerebrum
PET scanning of the brain shows that different
regions are involved in different stages of a
task. E.g. communicating with words
In the mid 1800s Paul Broca discovered that 1
small area of the brain was involved in the
production of language, speech or writing
In 1876 Carl Wernicke reported a different are
responsible for the understanding of language
Although the right and left cerebral hemispheres
communicate constantly through the corpus
callosum, there is an asymmetrical distribution
of sites for language and 3D processing
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The
System
Dr Paul Broca
Carl Wernicke
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The
The Brain - Function
System
The right and left cerebral hemispheres
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The
The Brain - Function
System
Functions of the hypothalamus
cerebral cortex
right thalamus
left thalamus
cerebellum
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The
The Brain - Function
System
Pituitary Hormones
Nerve cells in the hypothalamus synthesise
oxytocin and antidiuretic hormone (ADH).
HYPOTHALAMUS
These travel along axons to the posterior
pituitary.
They are released from nerve endings into the
blood when the nerves are active.
Nerve cells in the hypothalamus synthesise and
release hormones into the blood stream. This is
called neurosecretion.
ANTERIOR PITUITARY
POSTERIOR PITUITARY
The hormones (called releasing hormones) travel
to the anterior pituitary where they stimulate
further hormone release into the blood (see next
table)
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The
The Brain - Function
System
Pituitary Hormones
Action of hypothalamus Effect on Pituitary Result





Release of thyroxine from thyroid gland which
increases metabolic rate
Secretion of thyrotropin releasing hormone
Release of thyroid stimulating hormone from the
anterior pituitary
Secretion of growth hormone releasing hormone
Release of growth hormone from the anterior
pituitary
Growth of cells and tissues
FSH Follicle growth in ovaries. Sperm
production in the testes. LH Ovulation and
secretion of oestrogen progesterone and
testosterone.
Release of LH and FSH hormone from the anterior
pituitary
Secretion of gonadotrophin releasing hormone
Production of antidiuretic hormone (ADH)
ADH is released from nerve endings in the
posterior pituitary
Water retention by the kidney
Uterus contraction during birth. Milk ejection
during breast feeding
Oxytocin is released from nerve endings in the
posterior pituitary
Production of oxytocin
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Nervous
The
The Brain - Function
System
Functions of the cerebellum
Coordination of movement and posture
Does this by smoothing the action of movements
initiated by the motor cortex
Involved in coordinated task learning e.g.
riding a bicycle, catching a ball
Medulla oblongata
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The
The Brain - Function
System
Functions of medulla oblongata
Breathing Controls diaphragm and intercostals
via the vagus nerve
If blood CO2 changes the medulla can modify the
speed and depth of breathing
CO2 levels are monitored by receptors in the
medulla itself, and also by receptors in the
walls of the carotid arteries and aorta.
Medulla oblongata
Heart rate and blood pressure Sympathetic and
parasympathetic (vagus) nerves link the medulla
to the SAN
Baroreceptors (pressure receptors) in the carotid
arteries and CO2 receptors monitor levels and
send information to the medulla
High blood pressure or low CO2. Response Vagus
nerve causes the SAN to pulse more slowly
Low blood pressure or high CO2. Response
Sympathetic nerves cause the SAN to pulse faster
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Nervous
The
The Brain - Function
System
Alzheimers disease
First recorded by Alzheimer after studying the
brain of a woman who had died after suffering
dementia in 1906.
Shrinkage of brain tissue. Ventricles enlarge.
short-term memory begins to decline ability to
perform routine tasks also declines.
Emotional outbursts may occur and language is
impaired. Progressively more nerve cells die
with subsequent behaviour changes, such as
wandering and agitation.
( from the front).
The ability to recognize faces and to communicate
is completely lost in the final stages. Patients
lose bowel and bladder control, and eventually
need constant care.
The average length of time from diagnosis to
death is 4 to 8 years, but can take 20
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The
The Brain - Function
System
Alzheimers disease and amyloid plaque formation
In Alzheimer's some of the neurones have bundles
of fibres in them, called tangles.
Between the neurones there are dark-staining
deposits called plaques
The tangles in the neurones are made of a protein
called tau. The plaques contain a peptide called
beta amyloid, Aß
All cell membranes contain a larger protein
called amyloid precursor protein or APP. APP to
Aß conversion is part of the normal activity of
the cell membrane, but the resulting Aß is
removed by the tissue fluid .
Abnormal metabolism of APP may be the cause of
some types of Alzheimers
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The
The Brain - Function
System
Alzheimers
Risk factors
Ageing. Less than 1 in 1000 people lt 65 have
Alzheimer's. 1 in 20 gt 65 has!
A small proportion of sufferers have a genetic
(familial) form
A varied and active life may help avoid
Alzheimers.
Severe blows to the head (especially in the over
50s) may increase the chance of developing the
disease
Smoking and high cholesterol may also be risk
factors for Alzheimers
Future therapy?
A vaccine to break down the ß amyloid plaques?
Trials in mice
An inhibitor of the membrane enzyme that breaks
down APP into Aß?
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Nervous
The
WHAT YOU SHOULD KNOW AT THE END OF THIS UNIT
REVIEW
System
Describe the organisation of the nervous system
with reference to the central and peripheral
systems
Outline the organisation of the autonomic nervous
system into a parasympathetic and a sympathetic
system
Outline the roles of the autonomic nervous system
in controlling the digestive system, heart action
and the size of the pupil in the eye
Describe the gross structure of the human brain
Outline the functions of the cerebrum,
hypothalamus, cerebellum and medulla oblongata
Describe the symptoms and possible causes of
Alzheimers disease as an example of brain
malfunction.
TEST QUESTIONS
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Nervous
TEST
Name ________________
The
System
Name the 2 major parts of the nervous system 2
Q1
The central and peripheral nervous systems
What are the 2 divisions of the peripheral
nervous system? 2
Q2
The somatic and the autonomic nervous systems
Give 2 features of the parasympathetic
stimulation of digestion 2
Q3
Salivary secretion increases, peristaltic
increase, sphincters relax, gastric glands
secrete more
Give 2 features of the sympathetic control of the
heart beat 2
Q4
Increased force and increased rate of contraction
Outline the effect of the PSNS on light entry
into the eye. 2
Q5
Stimulates circular muscles to contract,
narrowing the pupil diameter.
Name 2 cerebrum functions listed in the table you
were given. 2
Q6
Thinking, planning, language, emotions, memory
Q7
What is neurosecretion? 3
Synthesis and release into the blood of hormones
by nerve sells in the hypothalamus
Q8
What are the main function of the cerebellum.
Give 1 example of this function. 2
Coordination / smoothing of movement and posture.
e.g. flying / riding a bike
Q9
The medulla oblongata controls breathing. Name 2
places where CO2 receptors are found 2
In the medulla, in the walls of the carotid
arteries and aorta.
For what reasons have Paul Broca and Carl Wernike
become famous? 2
Q10
Discovered centres for Production of speech,
writing. Understanding of language.
Q11
Give the 2 most obvious anatomical symptoms of
Alzheimers disease 2
Shrinkage of brain tissue, enlargement of the
ventricles, amyloid plaque formation
TOTAL /23