Download Chapter 48: Nervous Systems Overview: Command and Control

Chapter 48: Nervous Systems
Overview: Command and Control Center
• The human brain contains an estimated 100 billion nerve cells, or ______________________________
• Each neuron may communicate with thousands of other neurons
Nervous systems consist of circuits of neurons and supporting cells
• All animals except sponges have some type of nervous system
• What distinguishes the nervous systems of different animal groups is how the neurons are organized into circuits
Organization of Nervous Systems
• The simplest animals with nervous systems, the cnidarians have neurons arranged in
______________________________
• Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring
• In relatively simple cephalized animals, such as flatworms, a central nervous system (CNS) is evident
• Annelids and arthropods have segmentally arranged clusters of neurons called
______________________________
• These ganglia connect to the CNS and make up a peripheral nervous system (PNS)
• Nervous systems in molluscs correlate with the animals’ lifestyles
– Sessile molluscs have simple systems
– While more complex molluscs have more sophisticated systems
• In vertebrates the central nervous system consists of a brain and dorsal spinal cord
– The PNS connects to the CNS
Information Processing
• Nervous systems process information in three stages
– Sensory input, integration, and motor output
• Sensory neurons transmit information from sensors that detect external stimuli and internal conditions
• Sensory information is sent to the CNS where interneurons integrate the information
• Motor output leaves the CNS via motor neurons which communicate with
______________________________cells
Neuron Structure
• Most of a neuron’s organelles are located in the cell body
• Most neurons have ______________________________
– Highly branched extensions that receive signals from other neurons
• The ______________________________is typically a much longer extension that transmits signals to other cells
at synapses
– May be covered with a ______________________________
Supporting Cells (Glia)
• Glia are supporting cells that are essential for the structural integrity of the nervous system and for the normal
functioning of neurons
– In the CNS, ______________________________provide structural support for neurons and regulate the
extracellular concentrations of ions and neurotransmitters
– ______________________________ (in the CNS) and Schwann cells (in the PNS) are glia that form the
myelin sheaths around the axons of many vertebrate neurons
Ion pumps and ion channels maintain the resting potential of a neuron
• Across its plasma membrane, every cell has a voltage
– Called a ______________________________
– The inside of a cell is ______________________________relative to the outside
The Resting Potential
• The resting potential is the membrane potential of a neuron that is not transmitting signals
• In all neurons, the resting potential depends on the ionic gradients that exist across the plasma membrane
–
The concentration of Na+ is higher in the extracellular fluid than in the cytosol while the opposite is true
for K+
• A neuron that is not transmitting signals contains many open K+ channels and fewer open Na+ channels in its
plasma membrane
• The diffusion of K+ and Na+ through these channels leads to a separation of charges across the membrane,
producing the resting potential
Action potentials are the signals conducted by axons
• An ______________________________is a brief all-or-none depolarization of a neuron’s plasma membrane
– It is the type of signal that carries information along axons
• When a stimulus depolarizes the membrane the Na+ channels open, allowing Na+ to diffuse into the cell
• As the action potential subsides, K+ channels open, and K+ flows out of the cell
– A ______________________________period follows the action potential during which a second action
potential cannot be initiated
Generation of an action potential
• At the site where the action potential is generated, usually the axon ______________________________an
electrical current depolarizes the neighboring region of the axon membrane
Conduction Speed
• The speed of an action potential increases with the diameter of an axon
• In vertebrates, axons are myelinated, which also causing the speed of an action potential to increase
– Gaps between the myelination are known as ______________________________
Neurons communicate with other cells at synapses
• In an electrical synapse, electrical current flows directly from one cell to another via a gap junction
• The vast majority of synapses are chemical synapses
– When an action potential reaches a terminal, the final result is the release of neurotransmitters into the
synaptic cleft
– Neurotransmitter binding causes the ion channels to open, generating a postsynaptic potential
– After its release, the neurotransmitter
– Diffuses out of the synaptic cleft
– May be taken up by surrounding cells and degraded by enzymes
Neurotransmitters
• The same neurotransmitter can produce different effects in different types of cells
The vertebrate nervous system is regionally specialized
• In all vertebrates, the nervous system shows a high degree of ______________________________and distinct
CNS and PNS components
• The brain provides the integrative power that underlies the complex behavior of vertebrates
• The spinal cord integrates simple responses to certain kinds of stimuli and conveys information to and from the
brain
The Peripheral Nervous System
• The PNS transmits information to and from the CNS
– Plays a large role in regulating a vertebrate’s movement and internal environment
– The cranial nerves originate in the brain and terminate mostly in organs of the head and upper body
– The spinal nerves originate in the spinal cord and extend to parts of the body below the head
– The PNS can be divided into two functional components: the somatic nervous system and the autonomic
nervous system
• The somatic nervous system carries signals to ______________________________
• The autonomic nervous system regulates the internal environment, in an
______________________________manner
– It is divided into the sympathetic, and parasympathetic divisions
– The sympathetic and parasympathetic divisions have antagonistic effects on target organs
– The sympathetic division correlates with the “fight-or-flight” response
• The parasympathetic division promotes a return to self-maintenance functions
Embryonic Development of the Brain
• In all vertebrates the brain develops from three embryonic regions: the forebrain, the midbrain, and the hindbrain
• By the fifth week of human embryonic development five brain regions have formed from the three embryonic
regions
• As a human brain develops further the most profound change occurs in the forebrain, which gives rise to the
______________________________
The Brainstem
• The brainstem consists of three parts: the medulla oblongata, the pons, and the midbrain
• The medulla oblongata contains centers that control several visceral functions
• The pons also participates in visceral functions
• The midbrain contains centers for the receipt and integration of several types of sensory information
The Cerebellum
• The cerebellum is important for coordination and error checking during motor, perceptual, and cognitive
functions
• The cerebellum is also involved in ______________________________and remembering motor skills
The Diencephalon
• The embryonic diencephalon develops into three adult brain regions
– The epithalamus, thalamus, and hypothalamus
• The epithalamus includes the ______________________________, which helps regulate sleep-wake cycles
• The thalamus is the main input center for sensory information going to the cerebrum and the main output center
for motor information leaving the cerebrum
• The hypothalamus regulates ______________________________and basic survival behaviors such as feeding,
fighting, fleeing, and reproducing
The Cerebrum
• The cerebrum has right and left cerebral hemispheres that each consist of cerebral cortex overlying white matter
and basal nuclei
• In humans, the largest and most complex part of the brain is the cerebral cortex, where sensory information is
analyzed, motor commands are issued, and language is generated
• A thick band of axons, the ______________________________provides communication between the right and
left cerebral cortices
The cerebral cortex controls voluntary movement and cognitive functions
• Each side of the cerebral cortex has four lobes
– Frontal, parietal, temporal, and occipital
Information Processing in the Cerebral Cortex
• Specific types of sensory input enter the primary sensory areas
• Adjacent association areas process particular features in the sensory input and integrate information from different
sensory areas
• In the somatosensory cortex and motor cortex neurons are distributed according to the part of the body that
generates sensory input or receives motor input
• Portions of the frontal lobe, Broca’s area and Wernicke’s area are essential for the generation and understanding
of ______________________________
Emotions
• The limbic system is a ring of structures around the brainstem
• This limbic system includes three parts of the cerebral cortex
– The amygdala, hippocampus, and olfactory bulb
• These structures interact with the neocortex to mediate primary emotions and attach emotional “feelings” to
survival-related functions