CONTROL AND COORDINATION
1. Coordination and control in mammals
1.1 The endocrine system
A hormone is a chemical substance produced by
an endocrine gland and carried in the blood stream
They are cell signalling molecules - transmit information
around the body – slower compared to nerve impulse
A gland is a group of cells that produces and releases one
or more substances
Hormones such as insulin, glucagon and ADH are peptides
or small proteins
o They are water-soluble and so cannot cross the phospholipid bilayer of cellsurface
membranes
o These hormones bind to receptors on the cell surface membranes of theirtarget
cells, which activates second messengers to transfer the signal throughout the
cytoplasm
Hormones such as testosterone, oestrogen and progesterone are steroid hormones
o They are lipid-soluble and so can cross the phospholipid bilayer
o These hormones bind to receptors in the cytoplasm or nucleus of their target cells
1.2 The nervous system
The human nervous system consists of the:
o Central nervous system (CNS) – the brain and the spinal cord
o Peripheral nervous system (PNS) – all the nerves in the body
Information is sent through the nervous system as nerve impulses – electrical signals pass along
nerve cells known as neurones
, Structure of neurons
Neurones have a long fibre known as an axon
The axon is insulated by a myelin sheath made from fats -
uninsulated sections along its length (called nodes of Ranvier)
o This means that the electrical impulse does not travel
down the whole axon, but jumps from one node to the
next – quick transmission
Their cell bodies contain many extensions called dendrites – can
connect to other neurons and transmit impulse
Three types of neurones
Sensory neurones carry impulses from receptors to
CNS (brain or spinal cord) – body cell branches off in the
middle of the cell
Relay (intermediate) neurones are found entirely within the
CNS and connect sensory and motor neurones
Motor neurones carry impulses from
the CNS to effectors (muscles or glands) – body cell at one
end and many dendrites
Process of electrical impulse travel
The stimulus is detected by a receptor receptor gets depolarised (stronger impulse more
depolarised) sensory neurone sends electrical impulses to the spinal cord (the coordinator)
Electrical impulses are passed on to relay neurone in the spinal cord connects to the motor
neurone and passes the impulses on
The motor neurone carries the impulses to the muscle (the effector) the muscle to carries out
what action is necessary (the response)
Reflex arc
A reflex arc is a pathway along which impulses are transmitted from a receptor to an effector without
involving ‘conscious’ regions of the brain – instead impulse is sent to the spinal card
Carries out a quick action like removing your hand off a hot object
1. Coordination and control in mammals
1.1 The endocrine system
A hormone is a chemical substance produced by
an endocrine gland and carried in the blood stream
They are cell signalling molecules - transmit information
around the body – slower compared to nerve impulse
A gland is a group of cells that produces and releases one
or more substances
Hormones such as insulin, glucagon and ADH are peptides
or small proteins
o They are water-soluble and so cannot cross the phospholipid bilayer of cellsurface
membranes
o These hormones bind to receptors on the cell surface membranes of theirtarget
cells, which activates second messengers to transfer the signal throughout the
cytoplasm
Hormones such as testosterone, oestrogen and progesterone are steroid hormones
o They are lipid-soluble and so can cross the phospholipid bilayer
o These hormones bind to receptors in the cytoplasm or nucleus of their target cells
1.2 The nervous system
The human nervous system consists of the:
o Central nervous system (CNS) – the brain and the spinal cord
o Peripheral nervous system (PNS) – all the nerves in the body
Information is sent through the nervous system as nerve impulses – electrical signals pass along
nerve cells known as neurones
, Structure of neurons
Neurones have a long fibre known as an axon
The axon is insulated by a myelin sheath made from fats -
uninsulated sections along its length (called nodes of Ranvier)
o This means that the electrical impulse does not travel
down the whole axon, but jumps from one node to the
next – quick transmission
Their cell bodies contain many extensions called dendrites – can
connect to other neurons and transmit impulse
Three types of neurones
Sensory neurones carry impulses from receptors to
CNS (brain or spinal cord) – body cell branches off in the
middle of the cell
Relay (intermediate) neurones are found entirely within the
CNS and connect sensory and motor neurones
Motor neurones carry impulses from
the CNS to effectors (muscles or glands) – body cell at one
end and many dendrites
Process of electrical impulse travel
The stimulus is detected by a receptor receptor gets depolarised (stronger impulse more
depolarised) sensory neurone sends electrical impulses to the spinal cord (the coordinator)
Electrical impulses are passed on to relay neurone in the spinal cord connects to the motor
neurone and passes the impulses on
The motor neurone carries the impulses to the muscle (the effector) the muscle to carries out
what action is necessary (the response)
Reflex arc
A reflex arc is a pathway along which impulses are transmitted from a receptor to an effector without
involving ‘conscious’ regions of the brain – instead impulse is sent to the spinal card
Carries out a quick action like removing your hand off a hot object
