Chapter 8 - Neurons: Cellular and Network Properties
The nervous system can be divided into the central nervous system (CNS) and the
peripheral nervous system (PNS). The peripheral nervous system can be divided into the
afferent (sensory) and efferent (motor) actions. The efferent actions can be divided into
somatic (voluntary) and autonomic (involuntary). Lastly, the autonomic nervous system
consists of the sympathetic (action) and the parasympathetic (rest) nervous system.
Neurons contain dendrites (which receive incoming signals) and axons (which carry outgoing
information). The shape, number and length of axons and dendrites vary from one neuron to
the next.
Sensory neurons carry information about temperature, pressure, light and other stimuli from
sensory receptors to the CNS. Interneurons are located inside the CNS, they come in a
variety of forms but often have quite complex branching processes that allow them to
communicate with many other neurons. Efferent neurons have enlarged endings called axon
terminals, which store and release neurotransmitters.
,The region where an axon terminal meets its target cell is called a synapse. The neuron
which delivers a signal to the synapse is known as the presynaptic cell, the cell which
receives the signal is called postsynaptic cell. The narrow space between these two cells is
called the synaptic cleft.
There are different kind of glial cells:
- CNS
- Ependymal cells → Create barrier between compartments and is the source
of neural stem cells.
- Astrocytes → Provides neurons with metabolic substrates for ATP production
and is part of the blood-brain barrier.
- Microglia → Specialized immune cells that reside permanently in the CNS.
When they are activated, they remove damaged cells and foreign invaders.
- Oligodendrocytes → Support and insulate axons by forming myelin, this is a
substance which is composed of multiple concentric layers of phospholipid
membrane.
- PNS
- Schwann cells → Support and insulate axons by forming myelin, this is a
substance which is composed of multiple concentric layers of phospholipid
membrane.
- Satellite cells → Forms a supportive capsule around nerve bodies located in
the ganglia.
Entrance of Na+ into a cell causes depolarization (cells become more positive).
Entrance of K+ into a cell, causes hyperpolarization (cells become more negative).
Graded potentials are depolarizations or hyperpolarizations whose strength is directly
proportional to the strength of the triggering event. Graded potentials lose strength as they
move through the cell.
,Action potentials are rapid electrical signals that travel undiminished in amplitude down the
axon from the cell body to the axon terminal. They begin in the trigger zone if a single
graded potential or the sum of multiple graded potentials exceeds the threshold voltage.
Depolarizing graded potentials make the neuron more likely to fire an action potential.
Hyperpolarizing graded potentials make the neuron less likely to fire an action potential.
During the absolute refractory period, a second action potential cannot be triggered, no
matter how large the stimulus is.
During the relative refractory period, a higher-than-normal graded potential is required to
trigger an action potential.
Spatial summation is the summation of simultaneous graded potentials from different
neurons. Temporal summation is the summation of graded potentials that closely follow each
other.
, Chapter 9 - The central Nervous System
The CNS consist of seven divisions:
- Cerebrum → Composed of two hemispheres, connected via the corpus callosum.
- Diencephalon → Contains the thalamus, hypothalamus, pituitary and pineal glands.
The thalamus receives a lot of sensory information.
- Midbrain → Control eye movement and relays signals for auditory and visual
reflexes.
- Cerebellum (kleine hersenen) → Process sensory information and coordinate the
execution of movement.
- Pons → Coordination of the control of breathing (along with the medulla).
- Medulla oblongata → Transition from the spinal cord into the brain. Contains the
control centers for many involuntary functions.
- Spinal cord
The cerebrum and diencephalon are developed from the forebrain. The cerebellum, pons
and medulla oblongata are divisions of the hindbrain. The fully developed cerebrum covers
the diencephalon and the midbrain. Therefore, only the cerebrum, cerebellum, pons, medulla
oblongata and spinal cord are visible.
The tissues of the CNS are divided into gray and white matter. The gray matter consists of
unmyelinated nerve cell bodies, dendrites and axons. The white matter is mostly myelinated
axons and contains very few cell bodies.
The nervous system can be divided into the central nervous system (CNS) and the
peripheral nervous system (PNS). The peripheral nervous system can be divided into the
afferent (sensory) and efferent (motor) actions. The efferent actions can be divided into
somatic (voluntary) and autonomic (involuntary). Lastly, the autonomic nervous system
consists of the sympathetic (action) and the parasympathetic (rest) nervous system.
Neurons contain dendrites (which receive incoming signals) and axons (which carry outgoing
information). The shape, number and length of axons and dendrites vary from one neuron to
the next.
Sensory neurons carry information about temperature, pressure, light and other stimuli from
sensory receptors to the CNS. Interneurons are located inside the CNS, they come in a
variety of forms but often have quite complex branching processes that allow them to
communicate with many other neurons. Efferent neurons have enlarged endings called axon
terminals, which store and release neurotransmitters.
,The region where an axon terminal meets its target cell is called a synapse. The neuron
which delivers a signal to the synapse is known as the presynaptic cell, the cell which
receives the signal is called postsynaptic cell. The narrow space between these two cells is
called the synaptic cleft.
There are different kind of glial cells:
- CNS
- Ependymal cells → Create barrier between compartments and is the source
of neural stem cells.
- Astrocytes → Provides neurons with metabolic substrates for ATP production
and is part of the blood-brain barrier.
- Microglia → Specialized immune cells that reside permanently in the CNS.
When they are activated, they remove damaged cells and foreign invaders.
- Oligodendrocytes → Support and insulate axons by forming myelin, this is a
substance which is composed of multiple concentric layers of phospholipid
membrane.
- PNS
- Schwann cells → Support and insulate axons by forming myelin, this is a
substance which is composed of multiple concentric layers of phospholipid
membrane.
- Satellite cells → Forms a supportive capsule around nerve bodies located in
the ganglia.
Entrance of Na+ into a cell causes depolarization (cells become more positive).
Entrance of K+ into a cell, causes hyperpolarization (cells become more negative).
Graded potentials are depolarizations or hyperpolarizations whose strength is directly
proportional to the strength of the triggering event. Graded potentials lose strength as they
move through the cell.
,Action potentials are rapid electrical signals that travel undiminished in amplitude down the
axon from the cell body to the axon terminal. They begin in the trigger zone if a single
graded potential or the sum of multiple graded potentials exceeds the threshold voltage.
Depolarizing graded potentials make the neuron more likely to fire an action potential.
Hyperpolarizing graded potentials make the neuron less likely to fire an action potential.
During the absolute refractory period, a second action potential cannot be triggered, no
matter how large the stimulus is.
During the relative refractory period, a higher-than-normal graded potential is required to
trigger an action potential.
Spatial summation is the summation of simultaneous graded potentials from different
neurons. Temporal summation is the summation of graded potentials that closely follow each
other.
, Chapter 9 - The central Nervous System
The CNS consist of seven divisions:
- Cerebrum → Composed of two hemispheres, connected via the corpus callosum.
- Diencephalon → Contains the thalamus, hypothalamus, pituitary and pineal glands.
The thalamus receives a lot of sensory information.
- Midbrain → Control eye movement and relays signals for auditory and visual
reflexes.
- Cerebellum (kleine hersenen) → Process sensory information and coordinate the
execution of movement.
- Pons → Coordination of the control of breathing (along with the medulla).
- Medulla oblongata → Transition from the spinal cord into the brain. Contains the
control centers for many involuntary functions.
- Spinal cord
The cerebrum and diencephalon are developed from the forebrain. The cerebellum, pons
and medulla oblongata are divisions of the hindbrain. The fully developed cerebrum covers
the diencephalon and the midbrain. Therefore, only the cerebrum, cerebellum, pons, medulla
oblongata and spinal cord are visible.
The tissues of the CNS are divided into gray and white matter. The gray matter consists of
unmyelinated nerve cell bodies, dendrites and axons. The white matter is mostly myelinated
axons and contains very few cell bodies.
