Download Notes – Neurons and the nervous system

Neurons and the
Nervous System
What is the nervous system?
 It coordinates a range of operations in our
everyday lives. It receives and analyses sensory
information from the sensory receptors of our
bodies, processes information, and responds in
various ways to that information.
What is the nervous system
made of?
 Nerve cells or neurons
Let’s play, “Which part are
we talking about?”
 Small branching projections distributed
throughout the cell body which convey nerve
impulses toward the cell body
 DENDRITES
Let’s play, “Which part are
we talking about?”
 The space between two neurons
 The synaptic cleft
Let’s play, “Which part are
we talking about?”
 Branch off from the axon and convey nerve
impulses to the synaptic cleft (space between 2
neurons)
 Nerve endings or axon terminal
Let’s play, “Which part are
we talking about?”
 Contains the nucleus which holds the dna of the
cell and produces proteins necessary for the
proper functioning of the cell
 The cell body
Let’s play, “Which part are
we talking about?”
 Gel-like substance that holds all of the major
organelles of the cell
 Cytoplasm
 Separates the interior of the neuron from the
outside world and contains features that allow
nerve impulses to be transported from one nerve
to the next.
 Cell membrane
Let’s play, “Which part are
we talking about?”
 Located along the axon and allows nerve
impulses to travel more quickly along the axon by
insulating it.
 Myelin sheath
 Ex. MS, and toddlers
Let’s play, “Which part are
we talking about?”
 Which parts are a part of the synapse?
 The synaptic cleft, the pre-synaptic neuron and
the post-synaptic neuron
The Nervous System is
Divided into 2 Parts
 CNS:
 Central nervous system
 Coordinates the activity of all parts of the body
 PNS:
 Peripheral nervous system
 Connects the central nervous system to the limbs
and organs
How do we process and
respond to information from
the outside world?
 Sensory neurons, which are part of the PNS, detect
changes in the world around us and then transmit that
information to neurons in the CNS (brain and spinal cord),
where the information gets processed and integrated with
information sent from other neurons.
 Once processed, our CNS sends messages back to the
PNS via motor neurons which tell our muscles or glands to
respond to the sensory information in some way.
 Ex. Picking a book that just fell on the floor.
More on Neural
Communication
 Although neurons can transmit information to
and from the brain as quickly as 200 miles/hour,
our reactions to events are not instantaneous.
 In order to protect us from dangers, reflexes allow
for quicker responses. The physical response
happens before our brain receives the message.
 What part of the body is most involve in reflexes?
 Spinal cord
Why are concussions so
dangerous?
 Neurons are amitotic
 What does that mean?
 They do not undergo mitosis, which is another word
for cell division and replication
 So once a neuron dies, it can never be
regenerated
More on reflexes
Baby reflexes:
baby reflexes (moro reflex)
baby robot arms
Neuronal Communication
Involves both Chemical and
Electrical Messages
 Within a neuron, the message is transmitted
electrically by something called an action
potential
 Between neurons, the message is transmitted
chemically via neurotransmitters through the
synaptic cleft.
Action Potentials
 At rest, the fluid inside a neuron has an excess of
negatively charged ions. i.e. a negative resting
potential
 When a neuron is in its resting state, sodium
channels are blocked, thus keeping excess
positive ions out of the cell.
 When a nearby neuron fires an action potential,
this triggers some of the sodium channels at the
beginning of the axon to open, thus bringing in
positively charged ions into the cell.
 The charge inside that part of the axon then
becomes positive, or depolarized.
More on Action Potentials
 This depolarization then causes the next set of
sodium channels to open, thus depolarizing the
next part of the axon, and this continues like a
domino effect.
 Axons also have channels that pump sodium
back out of the cell, to restore the negative
resting potential so that it becomes ready again
for another action potential.
Strength of an Action
Potential
 A neuron’s action potential is all-or-nothing,
meaning the strength is not affected by how
strong the signal was. No matter how excitatory a
signal is, the neuron will always fire with the same
intensity.
 However, the stronger the stimulus, the more
neurons there are that will fire
 Ex. A slap will trigger more neurons to fire than a tap
 **action potential video
The Synapse
Axon
terminal
Presynaptic
cell
Synaptic cleft
synapse
Post-synaptic
cell
At the Synapse
 When the action potential reaches the axon
terminal, it triggers the release of chemical
messengers, called neurotransmitters, into the
synaptic cleft.
 These neurotransmitters travel across the synaptic
cleft and bind to receptors on the dendrites of
the postsynaptic cell.
 This binding takes place like a key fitting into a
lock.
 *video: neural synapse