Chapter 43: Animal Nervous System
The diffuse arrangement of cells is called a nerve net, is found in cnidarians (jellyfish, hydra, anemones) and ctenophores (comb jellies).
A central nervous system (CNS) includes large numbers of neurons aggregated into clusters called ganglia.
Many sensory cells are sensory neurons, which carry information to the CNS.
Cells in the CNS called interneurons, which pass signals from one neuron to another, perform this integration.
Motor neurons and sensory neurons are bundled together into long strands of nervous tissue called nerves.
All neurons and other components of the nervous system that are outside the CNS are considered part of the peripheral nervous system, or PNS.
A cell body, or soma, contains the nucleus.
A highly branched group of relatively short projections called dendrites.
One or more relatively long projections are called axons.
A difference in charge between any two points creates an electrical potential or voltage.
When an electrical potential exists across a plasma membrane, the separation of charges is called a membrane potential.
The volt (V) is the standard unit of electrical potential, and a millivolt (mV) is 1/1000 of a volt.
When a neuron is not communicating with other cells, the difference in charge across its membrane is called the resting potential.
Neurons are said to have excitable membranes because they can generate action potentials that propagate rapidly along the length of their axons.
The action potential depends on voltage-gated channels-membrane proteins that open and close in response to changes in membrane voltage.
Voltage clamping allows researchers to hold the voltage of a cell’s plasma membrane at any desired value and record the electrical currents that occur at a voltage.
Studying individual ion channels became possible in the 1980s when Erwin Neher and Bert Sakmann perfected a variation of voltage clamping known as patch clamping.
Using this technique, Neher and Sakmann were able to document for the first time the currents that flowed through individual channels.
The opening of Na+ channels exemplifies positive feedback-meaning that the occurrence of an event makes the same event more likely to recur.
Positive feedback is rare in organisms: It cannot be employed as a regulatory mechanism under many circumstances, because often leads to uncon oiled events.
Neurotoxins are poisons that affect neuron function often resulting in convulsions, paralysis, or unconsciousness.
In the central nervous system, these accessory oligodendrocytes.
In the peripheral nervous system, they are Schwann cells.
Oligodendrocytes and Schwann cells are two examples of glia, which are nervous system cells that support neurons.
When oligodendrocytes or Schwann cells wrap around the axon,they form a myelin sheath, which acts as a type of electrical insulation.
Consequently, the cations moving down the membrane are able to spread until they reach a gap in the myelin sheath, called a node of Ranvier.
The autoimmune disease multiple sclerosis (MS) develops when the immune system targets oligodendrocytes, destroying myelin in the CNS.
In the 1920s, Otto Loewi showed that this indirect mechanism involves neurotransmitters.
Such channels, called ligand-gated channels, have a binding site for a specific ligand on the part of the channel protein that faces the synaptic cleft.
Changes in the membrane potential of a postsynaptic cell that makes the cell more likely to produce an action potential are called excitatory postsynaptic potentials (EPSPs).
Changes in the membrane potential of a postsynaptic cell that makes the cell less likely to produce an action potential are called inhibitory postsynaptic potentials (IPSPs).
The additive nature of postsynaptic potentials is termed summation.
The sodium channels that trigger action potentials in a neuron are typically located near the place where the axon emerges from the cell body, a site called the axon hillock.
Anatomical and functional studies indicate that the PNS consists of two divisions with distinct functions:
The afferent division transmits sensory information to the CNS.
The efferent division carries commands from the CNS to the rest of the body.
The two types often have opposite effects on the same organ.
Nerves in the parasympathetic nervous system promote “rest-and-digest” functions that converse or restore energy.
Nerves in the sympathetic nervous system typically prepare organs for stressful “fight-or-flight” situations.
This enteric nervous system interacts with autonomic nerves but can also function independently.
The enteric nervous system plays a major role in regulating digestion, but it may also be important in immune function, mental health, cognition, and memory formation in the CNS.
Each structure of the human brain has distinct functions:
The cerebrum accounts for the bulk of the human brain.
It makes up most of the forebrain, is divided into left and right hemispheres, and is the seat of conscious thought and memory.
The diencephalon is also part of the forebrain.
It relays sensory information to the cerebrum and functions in maintaining homeostasis.
The brainstem connects the brain to the spinal cord and contains the midbrain and parts of the hindbrain.
It is the autonomic center for regulating cardiovascular, digestive, and other involuntary functions.
The cerebellum is a structure in the hindbrain that coordinates complex motor patterns.
In 1953, surgeons treated him for life-threatening seizures by removing a small portion of his temporal lobe and about two 1irds of his hippocampus, a structure at the inner edge of the temporal lobe.
The technique known as optogenetic uses light to control the activity of targeted types of neurons in the brain.
Memory is the retention of learned information.
Learning and memory are thus closely related and are often studied in tandem.
A change in the responsiveness or structure of a synapse is termed synaptic plasticity.
The diffuse arrangement of cells is called a nerve net, is found in cnidarians (jellyfish, hydra, anemones) and ctenophores (comb jellies).
A central nervous system (CNS) includes large numbers of neurons aggregated into clusters called ganglia.
Many sensory cells are sensory neurons, which carry information to the CNS.
Cells in the CNS called interneurons, which pass signals from one neuron to another, perform this integration.
Motor neurons and sensory neurons are bundled together into long strands of nervous tissue called nerves.
All neurons and other components of the nervous system that are outside the CNS are considered part of the peripheral nervous system, or PNS.
A cell body, or soma, contains the nucleus.
A highly branched group of relatively short projections called dendrites.
One or more relatively long projections are called axons.
A difference in charge between any two points creates an electrical potential or voltage.
When an electrical potential exists across a plasma membrane, the separation of charges is called a membrane potential.
The volt (V) is the standard unit of electrical potential, and a millivolt (mV) is 1/1000 of a volt.
When a neuron is not communicating with other cells, the difference in charge across its membrane is called the resting potential.
Neurons are said to have excitable membranes because they can generate action potentials that propagate rapidly along the length of their axons.
The action potential depends on voltage-gated channels-membrane proteins that open and close in response to changes in membrane voltage.
Voltage clamping allows researchers to hold the voltage of a cell’s plasma membrane at any desired value and record the electrical currents that occur at a voltage.
Studying individual ion channels became possible in the 1980s when Erwin Neher and Bert Sakmann perfected a variation of voltage clamping known as patch clamping.
Using this technique, Neher and Sakmann were able to document for the first time the currents that flowed through individual channels.
The opening of Na+ channels exemplifies positive feedback-meaning that the occurrence of an event makes the same event more likely to recur.
Positive feedback is rare in organisms: It cannot be employed as a regulatory mechanism under many circumstances, because often leads to uncon oiled events.
Neurotoxins are poisons that affect neuron function often resulting in convulsions, paralysis, or unconsciousness.
In the central nervous system, these accessory oligodendrocytes.
In the peripheral nervous system, they are Schwann cells.
Oligodendrocytes and Schwann cells are two examples of glia, which are nervous system cells that support neurons.
When oligodendrocytes or Schwann cells wrap around the axon,they form a myelin sheath, which acts as a type of electrical insulation.
Consequently, the cations moving down the membrane are able to spread until they reach a gap in the myelin sheath, called a node of Ranvier.
The autoimmune disease multiple sclerosis (MS) develops when the immune system targets oligodendrocytes, destroying myelin in the CNS.
In the 1920s, Otto Loewi showed that this indirect mechanism involves neurotransmitters.
Such channels, called ligand-gated channels, have a binding site for a specific ligand on the part of the channel protein that faces the synaptic cleft.
Changes in the membrane potential of a postsynaptic cell that makes the cell more likely to produce an action potential are called excitatory postsynaptic potentials (EPSPs).
Changes in the membrane potential of a postsynaptic cell that makes the cell less likely to produce an action potential are called inhibitory postsynaptic potentials (IPSPs).
The additive nature of postsynaptic potentials is termed summation.
The sodium channels that trigger action potentials in a neuron are typically located near the place where the axon emerges from the cell body, a site called the axon hillock.
Anatomical and functional studies indicate that the PNS consists of two divisions with distinct functions:
The afferent division transmits sensory information to the CNS.
The efferent division carries commands from the CNS to the rest of the body.
The two types often have opposite effects on the same organ.
Nerves in the parasympathetic nervous system promote “rest-and-digest” functions that converse or restore energy.
Nerves in the sympathetic nervous system typically prepare organs for stressful “fight-or-flight” situations.
This enteric nervous system interacts with autonomic nerves but can also function independently.
The enteric nervous system plays a major role in regulating digestion, but it may also be important in immune function, mental health, cognition, and memory formation in the CNS.
Each structure of the human brain has distinct functions:
The cerebrum accounts for the bulk of the human brain.
It makes up most of the forebrain, is divided into left and right hemispheres, and is the seat of conscious thought and memory.
The diencephalon is also part of the forebrain.
It relays sensory information to the cerebrum and functions in maintaining homeostasis.
The brainstem connects the brain to the spinal cord and contains the midbrain and parts of the hindbrain.
It is the autonomic center for regulating cardiovascular, digestive, and other involuntary functions.
The cerebellum is a structure in the hindbrain that coordinates complex motor patterns.
In 1953, surgeons treated him for life-threatening seizures by removing a small portion of his temporal lobe and about two 1irds of his hippocampus, a structure at the inner edge of the temporal lobe.
The technique known as optogenetic uses light to control the activity of targeted types of neurons in the brain.
Memory is the retention of learned information.
Learning and memory are thus closely related and are often studied in tandem.
A change in the responsiveness or structure of a synapse is termed synaptic plasticity.