Download Bosma Lab Bosma Lab

Zool448
7 January 2003
Bosma Lab
Early motor neuron development
The hindbrain is the
site of the cranial
nerves, some of which
(trigeminal, facial)
include motor neurons
innervating a unique
type of muscle
(different origin than
other body muscles).
Bosma Lab
How do we identify the neurons?
We inject the targets of the
neurons with a red dextran dye,
and wait for the dye to get
transported up to the somas, in
the CNS. Then we use an
intracellular Ca2+-indicating
dye to examine the physiology
of these developing neurons.
open
dextran
1
Zool448
7 January 2003
Bosma Lab
We are sure we have the right cells
We can fix the tissue,
and look at the
dextran signal (red),
and counter-stain
with an antibody that
is specific to motor
neurons (green).
Bosma Lab
The activity changes over time
Activity is recorded from
individual cells, and each
cell’s activity is plotted in a
different color on these
graphs. At E11.0, the cells
are active, but each is
independent. Twelve hours
later, at E11.5, all the cells
are active synchronously.
2
Zool448
7 January 2003
Zebra
Finch
Female
Male
3
Zool448
7 January 2003
Sample zebra finch song
kHz
8
0
500 ms
The Song System (simplified)
HVc
Song
Production
Auditory input
LMAN
RA
Learning
X
DLM
VTA
s
IIt
nX
Respiration
Syrinx (vocal organ)
4
Zool448
7 January 2003
HVc
L-MAN
RA
Area X
DLM
Luo et al., 2001
Luo et al., 2001
5
Zool448
7 January 2003
Basic properties of neurons
Neurons are a specialized cell type
Neurons have the components
common to most cells: they have
a nucleus which contains DNA,
and where genes are transcribed;
they have a cytoplasm in which
most translation and protein
synthesis begins; they have a
plasma membrane that surrounds
the entire cells; they have an
elaborate cytoskeleton to support
the cell and carry out transport
functions.
Basic properties of neurons
Neurons are unique in several ways
They have a cell body (called the soma),
where the nucleus is.
They have cellular processes, called
dendrites and axons. These processes
can be very elaborate, and the axons may
be very long.
The general function of dendrites is to
receive information from other neurons.
Dendrites
Soma
Axon
The general function of axons is to
transmit information to other cells, such
as neurons or muscles.
6
Zool448
7 January 2003
Basic properties of neurons
Types of neurons
We will concentrate on three different types of neurons:
1. Sensory neurons, that receive information from the
outside world. This will include tactile and visual
information.
2. Motor neurons, that cause muscle contraction in the
periphery of the body.
3. Interneurons, which receive (and often modify)
information from neurons, then pass it on to other neurons.
Basic properties of neurons
Types of neurons
7
Zool448
7 January 2003
Basic properties of neurons
Neurons are organized into groups
Neurons are usually localized into groups of cell bodies,
which underlie the functions of the nervous system. The
nervous system is divided into the central nervous system
(CNS; brain and spinal cord), and the peripheral nervous
system (PNS). In the CNS, a group of cells is usually
called a nucleus. Different parts of the brain contain
specific nuclei; each nucleus is related to specific modalities
(senses) or functions.
Groups of cells located in the PNS are usually called
ganglia; these would include the sympathetic ganglia, which
perform autonomic functions, and sensory ganglia. The
PNS also includes the peripheral nerves.
Neurons make up
nervous systems
Invertebrates
Hydra – nerve net
Starfish – radial nervous
system (symmetric) with
ganglia
Leech – bilaterally
symmetric nervous system
with ganglia
Grasshopper – bilaterally
symmetric with ganglia
gathered towards the head
8
Zool448
7 January 2003
Neurons make up nervous systems
Vertebrates have a dorsal CNS
Animals classified as
higher on the evolutionary
tree have a tendency
towards cephalization, a
larger and more prominent
head.
A major change as animals
evolved is an increase in
the convolutions and
complexity of the cortex.
The axes of the CNS
Rostral-caudal, anterior-posterior
Rostral is defined as being towards the nose, while caudal
is defined as being towards the tail.
Dorsal means towards the back, ventral means towards the
front. In lower animals, the axis of the brain is the same as
the body axis.
Rostral = nose
Caudal = tail
Dorsal = back
Ventral = front
9
Zool448
7 January 2003
The axes of the CNS
Rostral-caudal, anterior-posterior
In higher animals, the axis
of the rostral CNS bends,
and is curved almost 110o
from the spinal cord axis:
thus, by convention, the
rostral CNS axis
nomenclature differs from
that in the spinal cord.
Rostral = nose
Caudal = back of head
Dorsal = top of skull
Ventral = jaw
The axes of the CNS
Medial-lateral
Medial means
towards the midline
of the brain or animal,
while lateral is to the
side.
10
Zool448
7 January 2003
The planes of section
The major types of brain sections are shown:
Horizontal sections move from the top of the head to the bottom.
Coronal sections move from the front of the head to the back
(seen as if wearing a crown).
Sagittal sections begin in the midline of the brain and give a side
view of the brain; parasagittal sections are off-midline.
Divisions of the CNS
Spinal cord – most caudal
The spinal cord receives
sensory information from the
trunk and limbs of the body,
and controls the motor
neurons to that portion of the
body.
It is divided into four major
segments, and contains the 31
pairs of spinal nerves, each of
which carries the sensory
information from a particular
area as well as the motor
output for that area.
Spinal cord
11
Zool448
7 January 2003
Divisions of the CNS
The brain stem contains three parts
The brain stem is made up
of the medulla, pons and
midbrain. It contains the
cranial nerves (except
olfactory), receiving
sensation from the face and
special senses. They control
the motor components of the
face and neck. There are
also projection neurons that
extend throughout the brain
from the reticular formation
that control awareness.
Brain
stem
Midbrain
Pons
Medulla
Divisions of the CNS
The cerebellum coordinates motor skills
The cerebellum receives
vestibular information,
posture and sensory
information from the body,
and coordinates that
information with visual
inputs to allow the fine
tuning of posture and body
position, and the learning of
motor tasks.
Cerebellum
12
Zool448
7 January 2003
Divisions of the CNS
The diencephalon contains two parts
The diencephalon contains
two major parts. The
thalamus is a major relay
center for visual, auditory
and vestibular information to
the cortex.
Diencephalon
The hypothalamus controls
reproduction and endocrine
systems as well as the
circadian clock and general
body homeostasis.
Thalamus
Hypothalamus
Divisions of the CNS
The cerebral hemispheres
The cerebral hemispheres
are made up of the cerebral
cortex on the surface of the
brain, which is involved in
cognition and planning of
motor activities. The three
deeper structures are the
basal ganglia controlling
fine movement, the
amygdala controlling
emotion and behavior, while
the hippocampus is
concerned with memory.
Basal ganglia
Cerebral
hemispheres
13
Zool448
7 January 2003
Divisions of the CNS
The cerebral hemispheres
The cerebral cortex is divided into lobes: the frontal lobe plans
actions, the parietal lobe is concerned with representation of
the body, the occipital lobe is where vision is mediated, and the
temporal lobe is concerned with audition and some aspects of
learning.
Neurons mediate brain functions
Neurons signal extremely rapidly
Because of neuron signaling speed, we can act and move
quickly. The mechanism of rapid signaling is via electrical
impulses called action potentials, which are caused by the
opening and closing of ion channel proteins localized in the
plasma membrane.
Neurons convert this electrical signal into a chemical signal
at the synapse, where information is passed to the next cell.
The receiving cell (the post-synaptic cell) has specialized
receptor proteins for responding to the chemical signal
from the first cell cell (pre-synaptic cell). Via this
signaling, the post-synaptic cell can then fire action
potentials.
14
Zool448
7 January 2003
When would this be used?
The knee-jerk response
This reflex includes four neurons, two (opposing) muscles
and a stimulus (hammer). The sensory neuron stretch
receptor in the muscle transduces the input (feels the thwack
of the hammer), and signals to two neurons.
When would this be used?
The knee-jerk response – part 1
The motor neuron causes the quadriceps to contract.
15
Zool448
7 January 2003
When would this be used?
The knee-jerk response
The motor neuron causes the quadriceps to contract.
When would this be used?
The knee-jerk response – part 2
The motor neuron causes the quadriceps to contract. An
interneuron inverts the signal, and causes the opposing
muscle to relax.
Figure 6-6
16
Zool448
7 January 2003
Information is passed along
What is that motor
neuron experiencing?
The sensory neuron sends
a chemical signal at the
synapse (in the form of
neurotransmitter) to the
motor neuron. This is
converted to an electrical
signal that is sent to the
muscle, through another
synapse.
Figure 6-1
Neurons are complex
Motor neurons are large
and complex cells, with
many dendritic branches
to receive the inputs from
other cells, and axons to
send the information
from the motor neuron.
Figure 1-3
17
Zool448
7 January 2003
Example: sensory neuron
Signaling is directional and proportional to the stimulus
Example: sensory neuron
Signaling is directional and proportional to the stimulus
18