Nervous system
Nervous coordination of effectors+receptors
Central nervous system (CNS) Peripheral nervous system (PNS)
brain cranial nerves: receptors+effectors
spinal cord @head+neck <> brain
(eg. optic nerves, auditory nerves)
spinal nerves: receptors+effectors @rest of
body <> spinal cord
(eg. sciatic nerve
Neurones (nerve cells)
Nerves: bundles of nerve fibres of neurones wrapped in connective tissues w blood vessels
Structure of neurones
1) Cell body: nucleus, cytoplasm,
organelles (mitochondria, RER)
2) Nerve fibres (extend from cytoplasm
of cell body)
a) Dendrons (branch into
dendrites): receive info from
receptors/other neurones,
transmit nerve impulses >>>
TOWARDS cell body
b) Axons (branch into branches w
synaptic knobs): transmit nerve
impulses AWAY from cell body
^motor neurone c) Myelin sheath (lipid covering):
(v short dendrons, 1 long axon) - layers of cell
membranes+lipids: insulate
nerve fibres, prevent
transmission of nerve
impulses to surroundings
- rapid/efficient propagation
of action potentials, speed
up transmission of nerve
impulses
, Types of neurones
Sensory neurone Interneurone Motor neurone
Nerve impulse transmission: Nerve impulse transmission: Nerve impulse transmission:
From receptors to CNS From sensory neurone to From CNS to effectors
motor neurone/ other
1 long dendron (connected interneurones V short dendrons, 1 long
to receptors), 1 short axon axon (connected to
Short dendrons, short axons effectors)
Cell body OUTSIDE CNS (both connected to other
neurones) Cell body INSIDE CNS
Cell body INSIDE CNS
Synaptic transmission of nerve impulses
1. A nerve impulse arrives at synaptic knob at end of axon
2. Synaptic vesicles containing neurotransmitters fuse w presynaptic membrane of
axon, releasing neurotransmitters into synaptic cleft <simple exocytosis>
3. Neurotransmitters diffuse across synaptic cleft
4. Neurotransmitters bind to specific protein receptors on postsynaptic membrane of
dendron/cell body of the next neurone
5. This binding of neurotransmitters to receptors stimulates the dendron/cell body of
the next neurone to generate a nerve impulse
6. (neurotransmitter finally broken down by an enzyme)
Importance of synapses
1. Synaptic vesicles containing neurotransmitters only present @endings of axons
- Allow nerve impulses to travel in ONE direction only: from axon of one
neurone to dendron of the next neurone
2. Form synapses w >1 other neurone
- Allow 1 neurone to communicate w many other neurones
- Complex network of neurones > enable nervous system to achieve
coordination that involves many receptors+effectors
Nervous coordination of effectors+receptors
Central nervous system (CNS) Peripheral nervous system (PNS)
brain cranial nerves: receptors+effectors
spinal cord @head+neck <> brain
(eg. optic nerves, auditory nerves)
spinal nerves: receptors+effectors @rest of
body <> spinal cord
(eg. sciatic nerve
Neurones (nerve cells)
Nerves: bundles of nerve fibres of neurones wrapped in connective tissues w blood vessels
Structure of neurones
1) Cell body: nucleus, cytoplasm,
organelles (mitochondria, RER)
2) Nerve fibres (extend from cytoplasm
of cell body)
a) Dendrons (branch into
dendrites): receive info from
receptors/other neurones,
transmit nerve impulses >>>
TOWARDS cell body
b) Axons (branch into branches w
synaptic knobs): transmit nerve
impulses AWAY from cell body
^motor neurone c) Myelin sheath (lipid covering):
(v short dendrons, 1 long axon) - layers of cell
membranes+lipids: insulate
nerve fibres, prevent
transmission of nerve
impulses to surroundings
- rapid/efficient propagation
of action potentials, speed
up transmission of nerve
impulses
, Types of neurones
Sensory neurone Interneurone Motor neurone
Nerve impulse transmission: Nerve impulse transmission: Nerve impulse transmission:
From receptors to CNS From sensory neurone to From CNS to effectors
motor neurone/ other
1 long dendron (connected interneurones V short dendrons, 1 long
to receptors), 1 short axon axon (connected to
Short dendrons, short axons effectors)
Cell body OUTSIDE CNS (both connected to other
neurones) Cell body INSIDE CNS
Cell body INSIDE CNS
Synaptic transmission of nerve impulses
1. A nerve impulse arrives at synaptic knob at end of axon
2. Synaptic vesicles containing neurotransmitters fuse w presynaptic membrane of
axon, releasing neurotransmitters into synaptic cleft <simple exocytosis>
3. Neurotransmitters diffuse across synaptic cleft
4. Neurotransmitters bind to specific protein receptors on postsynaptic membrane of
dendron/cell body of the next neurone
5. This binding of neurotransmitters to receptors stimulates the dendron/cell body of
the next neurone to generate a nerve impulse
6. (neurotransmitter finally broken down by an enzyme)
Importance of synapses
1. Synaptic vesicles containing neurotransmitters only present @endings of axons
- Allow nerve impulses to travel in ONE direction only: from axon of one
neurone to dendron of the next neurone
2. Form synapses w >1 other neurone
- Allow 1 neurone to communicate w many other neurones
- Complex network of neurones > enable nervous system to achieve
coordination that involves many receptors+effectors
