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F215 control, genomes and environment
Module 4 – responding to the environment
Learning Outcomes


Discuss why animals need to respond
to their environment.
Outline the organisation of the nervous
system in terms of central and
peripheral systems in humans.
Introductory question

Two reasons why animals need to be
able to respond to their environment
are to move away from danger or to
find food.
 Make a list of at least 5 other reasons
Reasons

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Respond to changes in temperature
or day length to begin breeding
activities
Seeking a mate
Courtship behaviours
Responding to demands from
offspring
Moving to warmer areas to avoid low
temperatures
 etc
Sensitivity

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
All organisms detect changes in their
environment and respond to them 
Sensitivity
Changes are detected in cells and
organisms that bring about responses
 Stimuli
Stimulus is detected by a receptor,
and an effector brings about a
response.
Human Nervous System

There are two main types of cells
involved
 Neurones
▪ which are elongated branched cells
specialised for the conduction of impulses
 Glial cells
▪ cells that support the neurones in a number of
ways
▪ Form insulating sheaths
▪ Provide nutrients to neurones
▪ Control the composition of fluid surrounding the
neurones
Unit 4 revision
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Structure of a neurone – cell body and
nerve fibres
3 types of neurone – motor, sensory
and relay (interneurone)
Schwann cells – form the myelin
sheath, a junction in the myelin sheath
is called node of ranvier
Reflex arc, action potentials
Organisation of the Human NS

There are two main
parts:
 Central nervous
system (CNS) – brain
and spinal cord
 Peripheral nervous
system (PNS) – all
other neurones
Organisation of Human NS
Central Nervous System


Most neurones are intermediate
neurones, with many short dendrites
and many synapses with neighbouring
cells.
The function of the neurones is to
receive and integrate the information
arriving via the synapses

Two types of synapse
 Excitatory
 Inhibitory

Within a neurone the balance
between excitation and inhibition that
is happening at all the synapses will
determine whether or not the neurone
passes on the action potential along
its axon to other neurones.

Brain
 contains a mass of intermediate neurones

Spinal cord
 runs from the base of the brain, through
the neural canal, as far as the first lumbar
vertebrae

Central canal
 contains CSF which nourishes and
maintains electrolyte balance in CNS

White matter
 bundles of motor and sensory neurones,
well myelinated

Grey matter
 cell bodies and unmyelinated axons of
interneurones, many glial cells

Meninges
 3 membranes which surround the brain
and spinal cord
 Help to secrete cerebrospinal fluid

CSF
 Fills all spaces inside the brain and spinal
cord and the space between skull bones
▪ Helps absorb mechanical shocks to the brain
▪ provides nutrients and oxygen to the brain cells
Spinal Cord
showing Neurones in a Reflex Arc
Peripheral Nervous System

Sensory neurones carry action potentials
from receptors towards CNS.
 Cell bodies are in the dorsal root ganglia
 Have long cytoplasmic processes which pick up
information and transmit action potentials
 Action potentials pass along axons to CNS

Motor neurones carry action potentials from
CNS to effectors.
 Cell bodies in spinal cord
 Long axons stretch towards effectors
Nerves
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In PNS, axons and dendrons are
arranged in bundles called nerves.
Axons and dendrons enter and leave
spinal cord in Spinal nerves
 Dorsal root (receptor  spinal cord)
 ventral root (impulse to effectors)

Cranial nerves
 Nerves arising from brain
Human Nervous System
Somatic Motor Pathway

The somatic
nervous system
includes
 All the sensory
neurones
 All motor neurones
that take information
to the skeletal
muscles

Typically all
neurones involved
in the reflex arc
Autonomic nervous System

The autonomic
nervous system
includes
 All motor neurones
supplying internal
organs (viscera)
Learning Outcomes

Outline the organisation and roles of
the autonomic nervous system.
Somatic vs. Autonomic

Somatic nervous system
 Myelinated neurones
 Connections to the effectors
consist of one neurone

Autonomic nervous system
 Unmyelinated neurones
 Connections to the effectors
consist of at least two
neurones
▪ These two neurones connect at
a swelling known as a ganglion
Autonomic Nervous System

Functions
 controls activity of all smooth muscle in
body
 controls rate of beating of cardiac
muscles
 controls activity of exocrine glands
 most activities not under voluntary control
Autonomic Nervous System

Structural
 Cell bodies of motor neurones are outside the
CNS in autonomic ganglia
 Preganglionic neurone carries action potentials
from CNS to the ganglion
Autonomic Nervous System

The ANS is divided into two systems
 Sympathetic nervous system
▪ Most active in times of stress
 Parasympathetic nervous system
▪ Most active in sleep and relaxation

These systems are antagonistic
Sympathetic nervous system


The axon of the preganglionic
neurone passes out ventral root, and
synapses with motor neurone cell
bodies in ganglia close to the spinal
cord
From the ganglia, axons pass to all the
organs within the body forming
synapses with cardiac and smooth
muscle
Transmitter substance

Noradrenaline
 Secreted by postganglionic neurone at
the synapse between neurone and
effector
 “Fight or flight” responses
Effects of action

Examples include:
 Increased heart rate
 Pupil dilation
 Increased ventilation rate

The sympathetic nervous system also
co-ordinates the stress responses
 You will learn about this later
Parasympathetic Nervous
System

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Preganglionic neurones synapses with
the effector neurone inside the target
tissue
Many axons of parasympathetic
neurones form the vagus nerve, which
carries impulses to all the organs in the
thorax and abdomen.
Neurotransmitter

Acetylcholine
 Secreted by postganglionic neurone at
the synapse between neurone and
effector
 Usually has an inhibitory effect
 “rest and digest”
Effects of Action
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Decreased heart rate
Pupil constriction
Decreased ventilation rate
Effects of the ANS
The digestive System

Parasympathetic nervous system stimulates
digestive activity
 Sphincter muscles open
 Smooth muscle involved in peristalsis contracts
 Salivary glands and gastric glands increase their
secretion of saliva and gastric juice

Strong stimulation from the sympathetic
nervous system can:
 Reduce peristalsis
 Cause sphincter muscles to close
Effects of the ANS
the action of the heart
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Cardiac muscle is myogenic
The SAN sets the pace and rhythm for
the rest of the heart muscle
The SAN receives impulses from both
the sympathetic and parasympathetic
nervous systems
 SNS – increases the rate of contraction
 PSNS – decreases the rate of contraction
Effects of the ANS
the pupil in the eye

The iris contains radial and
circular muscles
 Radial muscles contract to
widen the pupil after
stimulation from the
sympathetic nervous system
 Circular muscles contract to
narrow the diameter of the
pupil after stimulation from
the parasympathetic system
Learning Outcomes

Describe, with the aid of diagrams, the
gross structure of the human brain,
and outline the functions of the
cerebrum, cerebellum, medulla
oblongata and hypothalamus.
The Human Brain
The brain unfolded
Functions of cerebrum
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Higher order processes
Cerebral cortex receives sensory
information and processes this
information
Two hemispheres receive information
from different sides of body
The cerebral cortex

The cerebral cortex is subdivided into
areas:
 Primary sensory areas
▪ Receive impulses indirectly from receptors
 Association areas
▪ Process input and integrate other information
▪ Parietal, temporal and occipital lobes
▪ Prefrontal association
 Motor Areas
▪ Send impulses to the effectors
Functions of hypothalamus
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Receives and integrates information
Brings about responses through
Autonomic nervous system or
secretions of the pituitary gland
Control of body temperature and
blood water potential
Control of hormones from endocrine
glands
 Secretions from posterior pituitary gland
 Secretions from anterior pituitary glands
Functions of cerebellum
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Control and co-ordination of
movement and posture
Involved in learning of tasks requiring
carefully co-ordinated movements
Functions of medulla oblongata
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Control of breathing
 Rhythmic patterns of impulses
 Conscious controls of breathing patterns
 CO2 receptor cells in Med. Ob. increase
frequency of nerve impulses

Heart rate and blood pressure
 Impulses from M.Ob. to SAN
 PSNS (vagus nerve) – SAN beats more
slowly
 SNS – SAN beats faster
Learning Outcomes


Describe the role of the brain and
nervous system in the coordination of
muscular movement.
Describe how coordinated movement
requires the action of skeletal muscles
about joints, with reference to the
movement of the elbow joint.
Muscular movement
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
Muscles use energy to contract
There are three types of muscle in the
body
 Cardiac muscle
 Smooth muscle
 Skeletal (voluntary) muscle

Muscles only exert a force when they
contract
Action of muscles
A joint is a place where two or more bones
meet.
 Synovial joints are adapted to allow smooth
movement between the bones
 The elbow is a hinge joint, allowing
movement in one plane
 Two antagonistic muscles act across the
elbow

 The biceps contract to flex the arm
 The triceps contract to extend the arm
Movement of the elbow joint

The contraction of
the triceps muscle
lowers the arm
 extension
Movement of the elbow joint

The contractions of
the biceps and
brachialis muscles
raises the lower arm
 flexion
Movement of the elbow joint

In some movements, both the muscles
contract to some degree.
 For example, the triceps may contract to
act as a steadying force ensuring that the
contraction caused by the biceps
produces a controlled and steady
movement
Keywords

Structure of striated muscle
 Fibres
 Syncitium
 Sarcolemma
 Myofibrils
 Sarcoplasmic reticulum
 T-tubules
Structure of a muscle
Structure of skeletal muscle
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Each fibre is a large, multinucleated cell
(syncitium)
The sarcolemma is the plasma membrane
surrounding the cell.
Fibres contain myofibrils
Contains a large number of mitochondria
Sarcoplasmic reticulum – the cisternae lie
just beneath surfaces of the fibrils
T-Tubules are channels formed by the
sarcolemma, and lie at right angles to the
cisternae of the sarcoplasmic reticulum
Ultrastructure of a muscle fibre
Structure of the myofibril

Each myofibril is made up of filaments
 Thick filaments = myosin
 Thin filaments = actin

Different parts of the stripes have their own letters
 A band
▪ broad, dark bands
▪ H Band represents lighter areas where only myosin present
 I bands
▪ lighter areas
 Z line
▪ thin, dark line in the centre of each I band
 M line
▪ line that runs down centre of the A band
Structure of a myofibril
The Sarcomere

The sarcomere is the part of a myofibril
between two Z lines
Myosin (fibrous)
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Myosin molecules lying side by side
form thick filaments
The molecules are arranged in
bundles with half the heads at one
end and half at the other
The m-line is the place where the
“tails” meet
Actin (globular)
Actin molecules link to form chains, two
chains lie side by side and twist around
each other
 The chains are anchored in the z lines
 There are two other proteins

 Tropomyosin which lies in the grove between 2
chains of actin molecules
 Troponin, which binds to the actin chains at
regular intervals.
Learning Outcomes

Explain, with the aid of diagrams and
photographs, the sliding filament
model of muscular contraction.
Muscle contraction

Muscles cause movement by
contracting
 The sarcomeres in each myofibril get
shorter as the Z lines are pulled closer
together
▪ Sliding filament theory of muscle contraction
 Energy comes from the ATP attached to
the myosin heads (which act as ATPases)
Sliding filament model of
muscle contraction

At rest, tropomyosin and troponin are sitting
in a position in the actin filament that
prevents myosin from binding
Sliding filament model of
muscle contraction

When a muscle contracts
 Troponin and tropomyosin molecules change shape
 Binding sites for the myosin are exposed on the actin
 Myosin binds to actin forming a cross bridge
Sliding filament model of
muscle contraction
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Myosin head tilts, pulling the actin filaments towards
the centre of the sarcomere – the is the power
stroke
Myosin heads hydrolyse ATP, providing enough
energy to break the cross bridge
Myosin heads tip back and bind again to exposed
binding sites on the actin
Sliding filament model of
muscle contraction

As the actin has moved along
 Heads bind to a different part of the actin
filament

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Myosin heads tilt again, pulling the
actin filaments further along.
This goes on and on as long as the
muscle has a supply of ATP.
Learning Outcomes

Compare and contrast the action of
synapses and neuromuscular
junctions.
Neuromuscular Junction

A synapse between the membrane of
the axon of a motor neuron and the
sarcolemma of a muscle fibre

The motor neuron axon divides into
several branches, so it can stimulate
different muscle fibres (motor end
plate)
Neuromuscular Junction -
The Motor End Plate
axon
Myelin sheath
mitochondrion
Presynaptic
membrane
sarcolemma
sarcoplasm
vesicle
Synaptic cleft
Postsynaptic
membrane
Myofibril
How a nerve impulse causes
muscle contraction
Events at the motor end plate
Action potential
arrives causing
the uptake of
calcium ions
Ca2+
Events at the motor end plate
Vesicles
containing ACh
fuse with
presynaptic
membrane
Events at the motor end plate
ACh is released,
it diffuses across
the synaptic
cleft.
ACh binds to
receptors on the
sarcolemma
Events at the motor end plate
Sodium channels
open in the
sarcolemma.
Na+ ions move in
through open
channels.
Na+
Membrane is
depolarised, and
action potential
spreads along the
membrane
Events in the muscle fibre
Depolarisation of
sarcolemma
spread down Ttubule
Ca2+ channels
open and Ca2+
diffuse out of
sarcoplasmic
reticulum
Ca2+
Events in the muscle fibre
Ca2+ ions bind to
troponin
Ca2+
Muscle Contraction
sliding-filament hypothesis
1. When the muscle is relaxed, the
binding sites on the actin are
covered by tropomyosin
Muscle Contraction
sliding-filament hypothesis
2. When the membrane of the muscle
is depolarised, calcium ions are
released from the tubes and bind
with the troponin, this displaces
tropomyosin from the binding site
Muscle Contraction
sliding-filament hypothesis
3. The myosin head binds to the actin,
using energy from ATP, this forms an
actomyosin bridge.
Muscle Contraction
sliding-filament hypothesis
4. As the myosin heads attach to the
actin filaments they tilt causing the
actin filaments to slide past.
Muscle Contraction
sliding-filament hypothesis
5. As actin filaments move past, the
myosin heads become detached
and attach to the next binding site.
Troponin reverts to its original shape
and tropomyosin blocks the binding
site on the actin filaments.
Summary of neuromuscular
junction
Learning outcome

Outline the role of ATP in muscular
contraction, and how the supply of
ATP is maintained in muscles.
Maintenance of ATP supply
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
ATP must be regenerated as quickly as
it is used up.
There are three mechanisms by which
the ATP supply is maintained.
 Aerobic Respiration
 Anaerobic respiration
 Creatine phosphate
Energy sources used in muscle
at high power output
ATP from Aerobic respiration


Occurs in muscle cell mitochondria
Dependent on the supply of oxygen
and availability of respiratory substrate
ATP from Anaerobic respiration


Occurs in muscle sarcoplasm
Leads to production of lactic acid
ATP from creatine phosphate
Occurs in muscle cell sarcoplasm
Phosphate group from creatine phosphate
is transferred to ADP to form ATP
 Controlled by the enzyme creatine
phosphotransferase
 Sufficient to support muscle contraction for
2 – 4 seconds
 ATP molecules produced in respiration can
be used to “recharge” the creatine
phosphate


Learning Outcomes

Outline the structural and functional
differences between voluntary,
involuntary and cardiac muscle.
Muscle

There are 3 types of muscle
 Cardiac muscle
 Smooth / involuntary muscle
 Voluntary / skeletal / striated muscle
Cardiac Muscle
Found only in the heart
 Striated
 Cells about 80μm long,
15μm in diameter
 Cells branch and form
connections
 Intercalated discs
separate cells / fibres
from each other
 Gap junctions
 More mitochondria

Smooth Muscle
Non-striated muscle
Individual cells
each with own
nucleus
 Long and thin cells,
lying parallel to
each other
 Contract more
slowly and steadily


Learning Outcomes


State that responses to environmental
stimuli in mammals are coordinated by
nervous and endocrine systems.
Explain how, in mammals, the ‘fight or
flight’ response to environmental
stimuli is coordinated by the nervous
and endocrine systems
Fight or Flight response

The fight-or-flight response is initiated
when we are under stress