Transcript So it is the number of action potentials per second

Figure 48.1 Overview of a vertebrate nervous system
Figure 48.2 Structure of a vertebrate neuron
Figure 48.2x Neurons
Figure 48.3 The knee-jerk reflex
Supporting Cells or Glial Cells of the Nervous System
Types of Glial Cells
1.
Radial Glial Cells: form tracks by which the neurons can
migrate throughout the developing embryo
2.
Astrocytes: these are in the CNS and provide nutritional
support for mature neurons; they also form tight junctions
between capillaries in the brain forming a blood-brain
barrier.
3.
Oligodendrocytes (in CNS) and Schwann cells (in PNS)
form myelin sheaths around axons.
•Myelin is mostly lipid and is nonconductive
•In multiple sclerosis this myelin sheath is degrading and
nerve impulse transmission is disrupted.
Figure 48.5 Schwann cells
Figure 48.6 Measuring membrane potentials
So we say that the RESTING POTENTIAL of a neuron is -70 mV.
It exists because of differences in the ion composition in the
intracellular and extracellular environment.
Figure 48.7 The basis of the membrane potential
How Does A Cell Maintain It’s Membrane Potential
1. There is a great tendency for K+ to diffuse out of the cell.
2. As this occurs, there is a greater and greater negative charge
within the cell due to the loss of K+ and the anions left inside.
3. This buildup of negative charge creates a charge gradient for
cations (potassium) to flow back in.
4. Eventually potassium would be entering the neuron at the same
rate it is leaving.
5. Sodium is also moving across the membrane. There is a higher
concentration outside the cell than inside so sodium moves into
the cell.
6. This also would eventually end up at equilibrium such that the
concentration gradient for sodium would also disappear.
7. To avoid reaching this equilibrium and then have no net
tendency for either ion to flow in or out, there is the sodium
potassium pump that pumps sodium out of the cell and
potassium into the cell.
8. In this way, the concentration gradients are established for ions
to flow.
9. Ions flow across this membrane during nerve impulse
conduction.
How Neurons Work
Figure 48.8 Graded potentials and the action potential in a neuron
Figure 48.9 The role of voltage-gated ion channels in the action potential (Layer 1)
Figure 48.9 The role of voltage-gated ion channels in the action potential (Layer 2)
Figure 48.9 The role of voltage-gated ion channels in the action potential (Layer 3)
Figure 48.9 The role of voltage-gated ion channels in the action potential (Layer 4)
Figure 48.9 The role of voltage-gated ion channels in the action potential (Layer 5)
Refractory Period
Both gates, the activation and inactivation gates, are closed and so
no stimulus can cause a depolarization and thus action
potential.
Strong vs. weak stimuli
Strong stimuli set off action potentials with great frequency and
the nerve depolarizes as fast as the refractory period will
allow.
Weak stimuli do not generate as frequent of action potentials.
So it is the number of action potentials per second that indicate
the intensity of the stimulus.
Figure 48.10 Propagation of the action potential
1.
Sodium ions enter the neuron’s axon.
2.
The sodium ions then flow inside the axon
and depolarize an adjacent region.
3.
The action potential cannot flow in the
reverse direction because that area is
repolarizing and cannot generate an action
potential. Both activation and inactivation
gates for sodium are closed.
4.
This process occurs in unmyelinated axons.
These can be found in humans, squids,
lobsters.
5.
Myelinated axons in many vertebrates,
including humans, speed up conduction by
saltatory conduction.
Figure 48.11 Saltatory conduction
Figure 48.12 A chemical synapse
Mouse Party: Drug Interactions
Figure 48.13 Integration of multiple synaptic inputs
EPSP: when the voltage is brought closer to the threshold
IPSP: when voltage is made more negative and thus farther from the threshold.
Table 48.1 The Major Known Neurotransmitters
Neurotransmitters
1. Acetylcholine
a) Receptor for this NT determines whether it is excitatory or
inhibitory. Between a neuron and a muscle cell it is excitatory but
the receptors on cardiac muscle cells generate an inhibitory
responses to reduce strength of contraction and rate of heart beat.
2. Epinephrine and norepinephrine
a) can be both excitatory or inhibitory
3. Dopamine
a) lack of dopamine is implicated in Parkinson’s disease
b) some hallucinogenic drugs act on dopamine receptors
4. Serotonin
a) sleeeeeeep disorders as well as hallucinogenic effects
5. Gama aminobutyric acid or GABA
6. Endorphins
Figure 48.15 Diversity in nervous systems
Figure 48.16 The nervous system of a vertebrate
Brain and spinal cord have a fluidfilled space called the ventricles
and central canal, respectively.
These cavities are filled with
cerebrospinal fluid
White Matter: myelinated axons in
the CNS
Gray Matter: unmyelinated axons,
dendrites and nuclei.
Figure 48.17 Functional hierarchy of the peripheral nervous system
Figure 48.18 The main roles of the parasympathetic and sympathetic nerves in
regulating internal
body functions
Figure 48.19 Embryonic development of the brain
The Hindbrain: Medulla and Pons and Cerebellum
1. Part of what is called the brainstem.
2. Develops from the embryonic hindbrain
3. Medulla: control centers for breathing, heart rate, digestion
4. Pons: breathing
5. Both the medulla and pons have nuclei or groups of nerve cells
that send axons to other parts of the brain.
a) Sensory info goes through medulla and pons on its way to
cerebrum.
b) Motor info goes through medulla and pons on its way to
muscles so movement is coordinated.
c) This is where axons from one side of brain cross such that
the right side of brain controls left side of body.
Figure 48.20 The main parts of the human brain
6. Cerebellum
a) coordinates movement with visual and motor senses
b) may be involved in remembering motor responses
c) received info about positions of joints and length of muscles
during movement, and coordinates this with visual input.
d) balance; hand-eye coordination
Midbrain
1. From the embryonic midbrain
2. Reticular Activating System is major component
a) lots of nuclei
b) regulates sleep, alertness
c) receives input from all sorts of sensory neurons and filters it
before sending it to cerebral cortex.
Figure 48.21 The reticular formation
Forebrain: Cerebrum, Epithalamus, Thalamus and Hypothalamus
1. Epithalamus
a) produces cerebrospinal fluid
b) associated with it is the pineal gland which is involved in
regulating bio. rhythms such as reproduction, biol. clocks. The
main hormone produced by the pineal gland is melatonin
2. Thalamus
a) sensory input center and then sends signals on to the
cerebrum
b) motor relay center for signals coming from the cerebrum.
3. Hypothalamus
4. Cerebrum
a) Right and left cerebral hemispheres
b) connected by the corpus callosum (white myelinated fibers)
c) outer area is gray matter
Figure 48.20x1 Cerebral cortex, gray and white matter
Figure 48.24 Structure and functional areas of the cerebrum
Figure 48.25 Primary motor and somatosensory areas of the human cerebral cortex
Figure 48.26 Mapping language areas of the cerebral cortex
Figure 48.27 The limbic system