Download Nerves Part 1 Powerpoint

Nervous System Part 1
Nervous System
• The nervous system is one
of the two control
systems of the body
– The other being the
endocrine system
– These two systems have a
lot of interaction!
• Made of neurons and
neuroglia
– Nervous tissue!
Nervous System Organization
Neurons
• There are three
classifications of neurons
– Sensory Neurons
– Interneurons
– Motor Neurons
• Interneurons form the
central nervous system
(CNS)
• Sensory and motor
neurons form the
peripheral nervous system
(PNS)
Neuron Structure
• Neurons have three
general structures:
– Soma (cell body)
– Axon (signal
transmission)
– Dendrite (signal
reception)
• Some neurons look
rather different but all
have these three parts
in some way
Central Nervous System
• Composed of the brain and
spinal cord
• Contains many tracts
(bundles of axons) leading
from one area to another
– These are all interneurons,
signaling each other and
storing information
– This is how we think and
remember!
Peripheral Nervous System
• The PNS consists of organs called
nerves which are sheaths of
neuronal axons covered in
connective tissue
– There are 12 pairs of cranial nerves
and 31 pairs of spinal nerves
• Peripheral nerves sending signals
towards the brain are afferent
nerves, while nerves sending signals
to the body are efferent nerves
– Afferent nerves make up our senses
(chapter 12, not covered in this class)
Cranial & Spinal Nerves
• When a nerve ends at a
particular body part it is said to
innervate that region
• The cranial nerves project out of
the brain and innervate the body
directly from the brain
– Include the optic nerve (eye) and
the vagus nerve (organs)
• The spinal nerves branch out
from the spinal cord and each
innervates a region of the body
– Named for which vertebral gap
they come out of
Cranial vs. Spinal Nerve
• Both afferent and efferent
nerves (sensory and motor
neurons) are bundled in each
cranial and spinal nerve
• The spinal cord contains the
cell bodies (somas) of the
PNS neurons in clusters called
ganglia (sing. ganglion)
– Only the axons stick out into
the rest of the body
– The axon of the neuron can be
regrown if the soma is intact!
Examples of Cranial vs. Spinal Nerve Activities
Action Potentials
• Recall: Sodium inrush
depolarizes a cell
membrane, before
potassium rushes out and
repolarizes the membrane
again
• This brief flicker back and
forth of voltage triggers
adjacent voltage-gated ion
channels to open
• Propagates the action
potential as a wave of ions
rushing across the
membrane
Speed of Conduction
• Action Potentials may be sped
up if there is myelin on the
axon
• Myelin is a dense, fatty material,
with gaps called Nodes of
Ranvier
• Myelin conducts the voltage
from one Node of Ranvier to
the next much more quickly
• Only some neurons (e.g. skeletal
motor neurons) are myelinated
More on Myelin
• Heavily myelinated nervous tissue
appears white, while unmyelinated
tissue appears gray
– White matter vs. Gray matter
• If myelin is stripped off (by, for
example, the immune system)
there are no voltage-gated ion
channels underneath it and the
neuron fails to send signals
– This is the cause and effect of
Multiple Sclerosis, which paralyzes
myelinated neurons while leaving
other neurons intact
Release of Neurotransmitters
• Once the action potential reaches
the end of a neuron, voltagegated calcium channels open and
allow calcium into the neuron
– The neuron attaches to another
neuron or to another organ at a
synapse
• The calcium stimulates the
release of synaptic vesicles into
the synapse
– These vesicles contain
neurotransmitters that have an
effect on the target cell
That’s our show!
• Next class: last new material before exam #2!