Nervous systems throughout the animal kingdom vary in structure and complexity, as illustrated by the variety of animals shown in Figure 35.1.1. Some organisms, like sea sponges, lack a true nervous system. Others, like jellyfish, lack a true brain and instead have a system of separate but connected nerve cells (neurons) called a “nerve net.” Echinoderms such as sea stars have nerve cells that are bundled into fibers called nerves.
Neurons contain ________, which can receive signals from other neurons.
- Golgi bodies
A(n) ________ neuron has one axon and one dendrite extending directly from the cell body.
Glia that provide myelin for neurons in the brain are called ________.
- Schwann cells
How are neurons similar to other cells? How are they unique?
Neurons contain organelles common to all cells, such as a nucleus and mitochondria. They are unique because they contain dendrites, which can receive signals from other neurons, and axons that can send these signals to other cells.
Multiple sclerosis causes demyelination of axons in the brain and spinal cord. Why is this problematic?
Myelin provides insulation for signals traveling along axons. Without myelin, signal transmission can slow down and degrade over time. This would slow down neuronal communication across the nervous system and affect all downstream functions.
All functions performed by the nervous system—from a simple motor reflex to more advanced functions like making a memory or a decision—require neurons to communicate with one another. While humans use words and body language to communicate, neurons use electrical and chemical signals. Just like a person in a committee, one neuron usually receives and synthesizes messages from multiple other neurons before “making the decision” to send the message on to other neurons.
For a neuron to fire an action potential, its membrane must reach ________.
- the threshold of excitation
- the refractory period
- inhibitory postsynaptic potential
After an action potential, the opening of additional voltage-gated ________ channels and the inactivation of sodium channels, cause the membrane to return to its resting membrane potential.
What is the term for protein channels that connect two neurons at an electrical synapse?
- synaptic vesicles
- voltage-gated ion channels
- gap junction protein
- sodium-potassium exchange pumps
How does myelin aid propagation of an action potential along an axon? How do the nodes of Ranvier help this process?
Myelin prevents the leak of current from the axon. Nodes of Ranvier allow the action potential to be regenerated at specific points along the axon. They also save energy for the cell since voltage-gated ion channels and sodium-potassium transporters are not needed along myelinated portions of the axon.
What are the main steps in chemical neurotransmission?
An action potential travels along an axon until it depolarizes the membrane at an axon terminal. Depolarization of the membrane causes voltage-gated Ca2+ channels to open and Ca2+ to enter the cell. The intracellular calcium influx causes synaptic vesicles containing neurotransmitter to fuse with the presynaptic membrane. The neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane. Depending on the specific neurotransmitter and postsynaptic receptor, this action can cause positive (excitatory postsynaptic potential) or negative (inhibitory postsynaptic potential) ions to enter the cell.
The central nervous system is made up of the brain and spinal cord and is covered with three layers of protective coverings called meninges (from the Greek word for membrane). The outermost layer is the dura mater with the primary function for this thick layer is to protect the brain and spinal cord. The dura mater also contains vein-like structures that carry blood from the brain back to the heart. The middle layer is the web-like arachnoid mater. The last layer is the pia mater.
The ________ lobe contains the visual cortex.
The ________ connects the two cerebral hemispheres.
- limbic system
- corpus callosum
Neurons in the ________ control motor reflexes.
- spinal cord
- parietal lobe
What methods can be used to determine the function of a particular brain region?
To determine the function of a specific brain area, scientists can look at patients who have damage in that brain area and see what symptoms they exhibit. Researchers can disable the brain structure temporarily using transcranial magnetic stimulation. They can disable or remove the area in an animal model. fMRI can be used to correlate specific functions with increased blood flow to brain regions.
What are the main functions of the spinal cord?
The spinal cord transmits sensory information from the body to the brain and motor commands from the brain to the body through its connections with peripheral nerves. It also controls motor reflexes.
The peripheral nervous system (PNS) is the connection between the central nervous system and the rest of the body. The central nervious system (CNS) is like the power plant of the nervous system. It creates the signals that control the functions of the body. The PNS is like the wires that go to individual houses. Without those “wires,” the signals produced by the CNS could not control the body (and the CNS would not be able to receive sensory information from the body either).
Activation of the sympathetic nervous system causes:
- increased blood flow into the skin
- a decreased heart rate
- an increased heart rate
- increased digestion
Where are parasympathetic preganglionic cell bodies located?
- dorsal root ganglia
________ is released by motor nerve endings onto muscle.
What are the main differences between the sympathetic and parasympathetic branches of the autonomic nervous system?
The sympathetic nervous system prepares the body for “fight or flight,” whereas the parasympathetic nervous system allows the body to “rest and digest.” Sympathetic neurons release norepinephrine onto target organs; parasympathetic neurons release acetylcholine. Sympathetic neuron cell bodies are located in sympathetic ganglia. Parasympathetic neuron cell bodies are located in the brainstem and sacral spinal cord. Activation of the sympathetic nervous system increases heart rate and blood pressure and decreases digestion and blood flow to the skin. Activation of the parasympathetic nervous system decreases heart rate and blood pressure and increases digestion and blood flow to the skin.
What are the main functions of the sensory-somatic nervous system?
The sensory-somatic nervous system transmits sensory information from the skin, muscles, and sensory organs to the CNS. It also sends motor commands from the CNS to the muscles, causing them to contract.
A nervous system that functions correctly is a fantastically complex, well-oiled machine—synapses fire appropriately, muscles move when needed, memories are formed and stored, and emotions are well regulated. Unfortunately, each year millions of people in the United States deal with some sort of nervous system disorder.
Parkinson’s disease is a caused by the degeneration of neurons that release ________.
________ medications are often used to treat patients with ADHD.
Strokes are often caused by ________.
- blood clots or burst blood vessels
What are the main symptoms of Alzheimer’s disease?
Symptoms of Alzheimer’s disease include disruptive memory loss, confusion about time or place, difficulties planning or executing tasks, poor judgment, and personality changes.
What are possible treatments for patients with major depression?
Possible treatments for patients with major depression include psychotherapy and prescription medications. MAO inhibitor drugs inhibit the breakdown of certain neurotransmitters (including dopamine, serotonin, norepinephrine) in the synaptic cleft. SSRI medications inhibit the reuptake of serotonin into the presynaptic neuron.