Lecture notes
Class Notes for Neuronal Communication A Level Biology A OCR
- Module
- Neuronal Communication
- Institution
- OCR
My class notes for neuronal communication
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Neural Communication- Coordination
- Neurones
- Sensory Receptors
- Nervous Transmission
- Synapses
- Organisation of the Nervous System
- Structure and Function of the Brain
- Reflexes
- Voluntary and Involuntary Muscles
- Sliding Filament Model
,Coordination
To survive, organisms need to respond to changes in their internal and external
environments. Examples of these changeable environments include:
Internal Environment External Environment
Blood glucose concentration Humidity
Internal temperature External temperature
Water potential Light intensity
Cell pH New or sudden sound
Animals and plants respond to changes in different way.
Animals react though electrical responses (via neurones) and through chemical responses
(via hormones).
Plants react through several chemical responses, including plant hormones. These must be
coordinated to produce the required response in an organism.
Why is coordination needed?
- Needed to coordinate the function of different cells and systems to operate
effectively.
- Except for the heart (which can continue to beat if placed in the right bathing
solution), few body systems can work in isolation.
- For example:
o Red blood cells (RBCs) transport oxygen effectively but don’t have a nucleus.
Therefore, they rely on haematopoietic cells to produce new RBCs.
o Muscle cells must constantly respire so they can contract. To do this, they
need oxygen which is supplied by RBCs.
o In plants, flowering needs to coordinate with the seasons, and pollinators
must coordinate with the plants. In temperate climates, light sensitive
chemicals enable plants to coordinate the development of flower buds with
the lengthening days that signal the approach of spring and summer.
Homeostasis
Homeostasis – the coordination of the function of organs to maintain a relatively constant
internal environment.
For example, the exocrine pancreas (secretes pancreatic juice into the duodenum through
the pancreatic duct), duodenum (first section of the small intestine) and ileum (final section
of the small intestine) along with the endocrine pancreas (secretes hormones such as
insulin) and liver to maintain a constant blood glucose concentration.
,Cell Signalling
Neural and hormonal systems coordinate the activities of whole organisms. This relies on
communication at a cellular level through cell signalling.
This occurs through one cell releasing a chemical which affects another cell, known as the
target cell. Through this, cell can:
- Transfer signals locally, for example, between neurones at synapses. Here, the signal
used is a neurotransmitter.
- Transfer signals across large distances, using hormones. For example, the cells of the
pituitary gland excrete antidiuretic hormone (ADH) which acts on cells in the kidneys
to maintain water balance in the body.
Coordination in plants
Plants don’t have a nervous system.
To survive, they still need to respond to internal and external changes.
For example, plant stems grow towards a light source to maximise their rate of
photosynthesis. This is achieved by using plants hormones.
Neurones
Neurones transmit electrical impulses rapidly around the body so that the organism can
respond to changes in its internal and external environment.
There are several types of neurones in mammals.
Sensory receptors are cells or organs which are energy transducers – they convert energy
from one form to another.
A change in energy levels is called a stimulus. This is converted into a nerve impulse
(electrical energy).
Structure of a neurone
Mammalian neurones have several key features:
- Cell body:
o Contains the nucleus surrounded by the cytoplasm.
o Large amounts of endoplasmic reticulum and mitochondria in the cytoplasm.
These are involved in the production of neurotransmitters.
o Neurotransmitters are the chemicals that pass signals from one neurone to
the next.
- Dendrons:
o Short extensions which come from the cell body.
o Divide into smaller and smaller branches called dendrites.
, o Responsible for transmitting electrical impulses towards the cell body.
- Dendrites
o Very small extensions of the dendron.
o Receive impulses from other cells at synapses.
o Transmits impulses to the dendron an then the cell body.
- Axons:
o Singular, elongated nerve fibres that transmit impulses away from the cell
body.
o Can be very long e.g. those that transmit impulses from the tips of the toes to
the spinal cord.
o The fibre is cylindrical in shape consisting of a very narrow region of
cytoplasm (in most cases approx. 1µm) surrounded by a plasma membrane.
- Axon terminals:
o Very small branches at the end of an axon.
- Myelin sheath:
o Forms covering of axon in myelinated neurones
o Made of plasma membranes called Schwann cells
o Rich in a lipid known as myelin
- Schwann Cells
o Surround an axon by wrapping around it many times.
o Protects the axon and provides electrical insulation.
o Grows around the axon – each layer provides to plasma membrane layers.
o May grow up to 20 layers of phospholipid bilayer.
o Involved in phagocytosis of damaged axons to stimulate nerve regeneration.
- Nodes of Ranvier
o Gaps between adjacent Schwann cells.
o Occur every 2-3µm and occur every 1-3mm.
o Electrical impulse jumps from one node to the next – makes transmission
faster.
Types of neurone
There are 3 different types:
- Sensory Neurones
o Transmit impulses from a sensory receptor cell to a relay neurone, motor
neurone or the brain.
o Have one dendron and one axon.
- Relay Neurones:
o Transmit impulses between neurones.
o Have short axons and dendrons.
- Motor Neurones:
o Transmit impulses from a sensory/relay neurone to an effector e.g. a muscle
or gland.
o One long axon and many short dendrites.
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