A-level Biology
Coordination and control in animals
Coordination means to cause the part to function together or in proper order.
Coordination and control in animals is performed by the nervous system and endocrine system.
Difference between nervous and endocrine system
Nervous system Endocrine system
1. Fast acting slow acting
2. It’s effects are localized It’s effects are diffuse
3. Transmission are electrical and Relies on chemical transmission through
Chemical theory cell fibre circulatory system
4. Transmission occur in nerve It occurs in blood
The nervous system.
The nervous system is composed of highly differentiated cells called nerve cells or neurons.
Those that carry impulses from receptors to the control nervous system are called sensory
neurons while those that carry impulses from the CNS to effector are called effector neurons.
,Differences between effector and sensory neuron
Effector neurons Sensory neuron
1. Transmit impulse from CNS Transmit impulse from sense organ or
to the effector receptor to the CNS cell body in the middle of
axon
2. Cell body at the end of the axon Cell body in the middle of axon
3. Cell body located in grey matter of Cell body located in dorsal root ganglion of
spinal cord the spinal chord
Structure of the nerve cell
1. The cytoplasm contains the same organelles as the other body cell; mitochondria, nucleus
cell membrane and ribosome grouped in Nissl’s granules.
2. Along nerve fibre axon extend from the cell body in effector neurons or either sides of
the cell body in sensory neuron to transmits impulses. The axon enclosed within a fatty
myelin sheath which is not part of the neuron but another cell Schwann cell which wraps
itself repeatedly round the axon. The myelin sheath protects the axon, but also insulates
the axon and speeds up transmission of impulse.
Transmission of impulse.
The resting potential of axon
A potential difference is maintained between the inside and outside of undisturbed axon. The
inside being negatively charged [about- 70 ml] with respect to the outside. In this state the
membrane is said to be polarized. The resting membrane potential is maintained by the
sodium / potassium pump using energy derived from ATP and it pumps ions against their
concentration gradient pumping sodium ions are pumped out of the neuron in exchange for
potassium ion (K+). K+ ions and organic ions is higher inside the neuron whereas Na+ and Cl-
ion concentration is higher outside the neuron
The impulse
An impulse or action potential is a temporary and local reversal of the resting membrane
potential, arising when an axon is stimulated. The term used during the electrical change
which occur during the passage of action potential is depolarization, and axon is said to be
depolarized. The action potential is short- lived lasting about a millisecond, after which the
resting membrane potential is restored. Events occurring into axon during the transmission of
action potential are show in the figure below.
, Information is transmitted through the nervous system as a series of impulse which travel as
action potential.
Properties of nerves and impulses
Stimulation
In normal circumstance impulse are set up in nerve cell as a result of excitation of receptor.
But an impulse can be set up in nerve by applying any stimulus which opens the sodium
channels and cause depolarization of the membrane. In general nerve can be stimulate by
mechanical, osmotic, chemical, thermal and electrical stimuli.
All or nothing law
An excitable tissue will only be excited by a stimulus above a certain threshold stimulus
intensity. For any given neuron the amplitude of the action potential is always constant and
increasing the strength or number of stimuli has no effect on this. For this reason, potentials
are described as all or nothing event. The all- or-nothing law states that the response of
excitable unit (axon) is independent of the intensity.
Refractory period.
After an axon has transmitted an impulse, it cannot transmit another one straight way. The
axon has to be recovered first. The membrane has to be repolarized and first.
The period of under which the nerve cannot transmit an impulse following the transmission
of first one is called refractor period and typically lasts about 3 milliseconds. It can be
divided into absolute refractory period during which the axon is totally incapable of
transmitting an impulse, followed by a somewhat longer relative refractory period during
which it’s possible to generate an impulse in the axon provided that the stimulus is stronger
than usual.
The importance of the refractory period, together with transmission speed, it determines the
maximum frequency at which the axons can transmit impulses. For most axons the maximum
frequency is about 500 per second, though some neurons can reach 1000 per second.
Coordination and control in animals
Coordination means to cause the part to function together or in proper order.
Coordination and control in animals is performed by the nervous system and endocrine system.
Difference between nervous and endocrine system
Nervous system Endocrine system
1. Fast acting slow acting
2. It’s effects are localized It’s effects are diffuse
3. Transmission are electrical and Relies on chemical transmission through
Chemical theory cell fibre circulatory system
4. Transmission occur in nerve It occurs in blood
The nervous system.
The nervous system is composed of highly differentiated cells called nerve cells or neurons.
Those that carry impulses from receptors to the control nervous system are called sensory
neurons while those that carry impulses from the CNS to effector are called effector neurons.
,Differences between effector and sensory neuron
Effector neurons Sensory neuron
1. Transmit impulse from CNS Transmit impulse from sense organ or
to the effector receptor to the CNS cell body in the middle of
axon
2. Cell body at the end of the axon Cell body in the middle of axon
3. Cell body located in grey matter of Cell body located in dorsal root ganglion of
spinal cord the spinal chord
Structure of the nerve cell
1. The cytoplasm contains the same organelles as the other body cell; mitochondria, nucleus
cell membrane and ribosome grouped in Nissl’s granules.
2. Along nerve fibre axon extend from the cell body in effector neurons or either sides of
the cell body in sensory neuron to transmits impulses. The axon enclosed within a fatty
myelin sheath which is not part of the neuron but another cell Schwann cell which wraps
itself repeatedly round the axon. The myelin sheath protects the axon, but also insulates
the axon and speeds up transmission of impulse.
Transmission of impulse.
The resting potential of axon
A potential difference is maintained between the inside and outside of undisturbed axon. The
inside being negatively charged [about- 70 ml] with respect to the outside. In this state the
membrane is said to be polarized. The resting membrane potential is maintained by the
sodium / potassium pump using energy derived from ATP and it pumps ions against their
concentration gradient pumping sodium ions are pumped out of the neuron in exchange for
potassium ion (K+). K+ ions and organic ions is higher inside the neuron whereas Na+ and Cl-
ion concentration is higher outside the neuron
The impulse
An impulse or action potential is a temporary and local reversal of the resting membrane
potential, arising when an axon is stimulated. The term used during the electrical change
which occur during the passage of action potential is depolarization, and axon is said to be
depolarized. The action potential is short- lived lasting about a millisecond, after which the
resting membrane potential is restored. Events occurring into axon during the transmission of
action potential are show in the figure below.
, Information is transmitted through the nervous system as a series of impulse which travel as
action potential.
Properties of nerves and impulses
Stimulation
In normal circumstance impulse are set up in nerve cell as a result of excitation of receptor.
But an impulse can be set up in nerve by applying any stimulus which opens the sodium
channels and cause depolarization of the membrane. In general nerve can be stimulate by
mechanical, osmotic, chemical, thermal and electrical stimuli.
All or nothing law
An excitable tissue will only be excited by a stimulus above a certain threshold stimulus
intensity. For any given neuron the amplitude of the action potential is always constant and
increasing the strength or number of stimuli has no effect on this. For this reason, potentials
are described as all or nothing event. The all- or-nothing law states that the response of
excitable unit (axon) is independent of the intensity.
Refractory period.
After an axon has transmitted an impulse, it cannot transmit another one straight way. The
axon has to be recovered first. The membrane has to be repolarized and first.
The period of under which the nerve cannot transmit an impulse following the transmission
of first one is called refractor period and typically lasts about 3 milliseconds. It can be
divided into absolute refractory period during which the axon is totally incapable of
transmitting an impulse, followed by a somewhat longer relative refractory period during
which it’s possible to generate an impulse in the axon provided that the stimulus is stronger
than usual.
The importance of the refractory period, together with transmission speed, it determines the
maximum frequency at which the axons can transmit impulses. For most axons the maximum
frequency is about 500 per second, though some neurons can reach 1000 per second.
