F214: Communication & Homeostasis: Nerves

Notes on nerves matched to the specification.

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  • Created on: 04-12-12 09:51
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4.1.2 Nerves
(a) Outline the roles of sensory receptors in mammals in converting different forms of energy
into the nerve impulses
Specialised cells that can detect changes in our surroundings
They are energy transducers that convert one form of energy to another
Each transducer is adapted to detect changes in a particular form of energy
E.g. change in light levels, pressure on skin
Changes called stimulus
Whatever stimulus sensory receptors convert the energy into a form of electrical energy called a
nerve impulse
Cell Location Initial Energy Form Resulting energy form
Olfactory Receptors Nose: Lining inner Volatile Chemicals Electrical
surface in nasal
Gustatory Cell Taste buds, tongue Soluble Chemicals Electrical
and throat
Pacinian Corpuscule Skin Pressure Electrical
(pressure receptors)
Rod and cone cells Retina of eye Light Electrical
(Light sensitive cells)
Proprioreceptors Muscles Movement (Internal) Electrical)
(Muscle Spindles)
Sound Receptors Inner Ear (Cochlea) Movement (air) Electrical
(Hair cells)
(b) Describe with the aid of diagrams the structure and functions of sensory and motor
Feature Sensory Neurone Motor Neurone
Position of Cell Body Just outside the CNS Inside the CNS
Myelinated? Yes Yes

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Length of dendrites or dendron Long (often single dendron)- Many short dendrites
runs from sensory receptor to
the cell body just outside the
CNS; has dendrites at the end
of axon
Length of Axon Short- runs from just outside Long- runs from inside CNS to
CNS into the CNS effector
Direction of Communication Carries impulses from sensory Carries impulses from CNS to
receptor to CNS effector
Motor Neurone
Transmits action potentials from the CNS system to an
effector such as a muscle or a gland…read more

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Sensory Neurone
Carry impulses via a dendron from sense organs to the brain or
spinal cord
Cell bodies are inside structures called dorsal root ganglia, just
outside spinal cord
Relay Neurone
Relay neurones have their cell bodies and cytoplasmic processes
inseide the brain or spinal cord
Adapted to carry impulses from and to numberous other neurones…read more

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Term Function Structure
Axon Nerve fibre; a single process
extending from the cell body of
a neurone and carrying nerve
impulses away from it
Dendrite Carries nerve impulses from One of the shorter branching
adjacent neurons into the cell processes of the cell body of a
body neurone. All dendrites have
synaptic knobs at the ends,
which are the "connections" to
adjoining nerves
Mixed Nerves Contain both motor and
sensory nerve fibres. Running
to/from a particular region of
the body e.…read more

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Myelin Sheath Protection of the nerve A complex material formed of
fibre protein and phospholipid (fat)
Insulation of the nerve that is laid down as a sheath
fibre around the axons of certain
Increases the rate of
transmission of nerve
Nerve Bundle containing 100s
and 1000s of axons
plus associated
connective tissue and
blood vessels
Neurone Cell specialized to Each neurone has enlarge
transmit electrical portion the cell body containing
nerve impulses and so the nucleus, from the body
carry information from extend…read more

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Sensory Neurone Transmit impulses inwards
from sense organs to CNS
Synapse Reaching a synapse, Minute gap across which nerve
impulses causes the impulses pass from one
release of a neurone to the next, at the end
neurotransmitter, which of a nerve fibre
diffuses across the gap and
triggers an electrical
impulses in the next
(c) Describe and explain how the resting potential is established and maintained;
Resting Potential: the potential difference or voltage across the neurone cell membrane while
the neurone is at rest.…read more

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When a neurone is transmitting an action potential it is said to be at rest.…read more

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At rest the sodium ion channels are kept closed
Sodium potassium pump uses ATP to actively transport Na+ out for every 2 K+ brought into the
A few of these potassium ions diffuse back out as some potassium channels are open
If some of the sodium channels are opened then sodium ions will quickly diffuse down the
gradient into the cell from the surrounding tissue fluid
This causes depolarisation of the membrane
In the generator region of receptor cells the gated channels are opened…read more

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This causes a large influx of sodium ions and the depolarisation reaches +40mV, which is an action
Once this value is reached the neurone will transmit an action potential because many
voltage-gated sodium ion channels open
Action potential is self-perpetuating- once it starts at one point in the neurone, it will continue
along to the end of the neurone
Ionic Movements
An action potential will consist of a set of ionic movements.…read more

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After an action potential the sodium and potassium ions are in the wrong places. The concentrations
of these ions inside and outside the cell must be restored by the action of sodium and potassium
For a short time after each action potential it is impossible to stimulate the cell membrane to reach
another action potential. This is known as refractory period and allows the cell to recover after an
action potential. It also ensures that action potentials are transmitted only in one direction.…read more


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