Organization and Control of Neural Function

Functions of the Nervous System
Controls skeletal muscle movement
Helps to regulate cardiac and visceral smooth muscle activity
Enables the reception, integration, and perception of sensory information
Provides the substratum necessary for intelligence, anticipation, and judgment
Facilitates adjustment to an ever-changing external environment
Components of the Nervous System
CNS
Consists of the brain and spinal cord, which are protected by the skull and vertebral column
Concentration of computational and control functions
PNS
Found outside the structures of the CNS
Functions as an input-output system for relaying information to the CNS and transmits output messages that control effector organs
Major Cells of the Nervous System
Neurons
Functioning cells
Supporting cells
Protect the nervous system and supply metabolic support
Composition of Neurons
Cell body with cytoplasm-filled process
Dendrites
Axons
Types of Neurons
Afferent or sensory neurons
Carry information to the CNS
Efferent or motor neurons
Carry information from the CNS to the effector organs
Characteristics of Neurons
Neurons: have ability to communicate with other neurons and body cells through electrical signals called impulses
Impulses or action potentials: represent the movement of electrical charge along the axon membrane
Conductance: based on the rapid flow of charged ions through the plasma membrane
Types of Synapses Found in the Nervous System
Electrical synapses
Permit the passage of current-carrying ions through small openings called gap junctions that penetrate the cell junction of adjoining cells and allow current to travel in either direction
Chemical synapses
Involve special presynaptic and postsynaptic membrane structures, separated by a synaptic cleft
Postsynaptic Potential
Excitatory postsynaptic potential (EPSP)
Combination of a neurotransmitter with a receptor site causes partial depolarization of the postsynaptic membrane
Inhibitory postsynaptic potential (IPSP)
Combination of a transmitter with a receptor site is inhibitory in that it causes the local nerve membrane to become hyperpolarized and less excitable
Process of Neurotransmission
Synthesis, storage, and release of a neurotransmitter
Reaction of the neurotransmitter with a receptor
Termination of the receptor action
Principles Underlying the Functioning of the Nervous System
No portion of the nervous system functions independently of the other parts
Newer systems control older systems
Newer systems are more vulnerable to injury
Developmental Organization of the Nervous System
Begins development as a hollow tube
The cephalic portion becomes the brain
The more caudal part becomes the spinal cord
Basic Organizational Pattern of the Body
Longitudinal series of segments
Each repeating the same basic fundamental organizational pattern
A body wall or soma containing the axial skeleton
A neural tube that develops into the nervous system
Development of the Embryonic Neural Tube
On cross section the embryonic neural tube develops into a central canal surrounded by:
Gray matter
The cellular portion of the CNS
White matter
The tract system of the CNS
Further Development of the Nervous System
As the nervous system develops it becomes segmented with:
A repeating pattern of afferent neuron axons forming the dorsal roots of each succeeding segmental nerve
Exiting efferent neurons forming the ventral roots of each succeeding segmental nerve
Arrangement of Nerve Cells in Gray Matter
Arranged longitudinally in cell columns
Afferent sensory neurons are located in the dorsal columns
Efferent motor neurons are located in the ventral columns
Axons of the Cell Column Neurons
Project out into the white matter of the CNS
Form the longitudinal tract systems
Reticular Formation
Rich mixture of neurons and local fibers formed when neurons in the embryonic gray matter migrate out into the inner layer of white matter
Contains the circuitry of most reflexes
In the brain stem, it contains major portions of vital reflexes
The reticular activating system operates in the lateral portions of the reticular formation of the medulla, pons, and especially the midbrain
Horns of the Spinal Cord
Definition: The extensions of the gray matter that form the letter “H”
Dorsal horns: those that extend posteriorly
Contain IA neurons that receive afferent impulses through the dorsal roots and other connecting neurons
Ventral horns: those that extend anteriorly
Contain OA neurons and the efferent LMNs that leave the cord through the ventral roots.
Spinal Nerves
Definition: the peripheral nerves that carry information to and from the spinal cord
Usually, 32 or more pairs of spinal nerves are present
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 2 or more coccygeal
Each pair is named for the segment of the spinal cord from which it exits
Spinal Reflexes
Segmental reflexes
Involve neurons in a single cord segment segmental reflexes
Suprasegmental reflexes
Involve structures in the brain

Types of Spinal Reflexes
Myotatic or Stretch Reflex
Inverse myotatic reflex
Withdrawal reflex


Structure of the Brain
Hindbrain
Includes the medulla oblongata, the pons, and its dorsal outgrowth, the cerebellum
Midbrain
Include two pairs of dorsal enlargements, the superior and inferior colliculi

Structure of the Brain (cont.)
Forebrain
Consists of two hemispheres covered by the cerebral cortex
Contains central masses of gray matter, the basal ganglia, and the rostral end of the neural tube, the diencephalon with its adult derivatives—the thalamus and hypothalamus

Segments of the Brain
Frontal lobe: extends from the frontal pole to the central sulcus (fissure) and is separated from the temporal lobe by the lateral sulcus
Parietal lobe: lies behind the central sulcus (postcentral gyrus) and above the lateral sulcus
Temporal lobe: lies below the lateral sulcus and merges with the parietal and occipital lobes
Occipital lobe: lies posterior to the temporal and parietal lobes and is arbitrarily separated from them
Function of the Autonomic Nervous System
Regulating, adjusting, and coordinating vital visceral functions:
Blood pressure and blood flow
Body temperature
Respiration
Digestion
Metabolism
Elimination
Two Divisions of the ANS
Sympathetic
Maintains vital functions
Responds when there is a critical threat to the integrity – the “fight or flight response”
Parasympathetic
Concerned with conservation of energy
Resource replenishment
Maintenance of organ function during inactivity
Structure of the Outflow of Both Divisions of the ANS
Two-neuron pathway
Preganglionic neuron
Postganglionic neuron

Neurotransmitters
Acetylcholine
Neurotransmitter for preganglionic neurons for both ANS divisions
Neurotransmitter for the postganglionic neurons of the parasympathetic nervous system
Norepinephrine and epinephrine
Neurotransmitters for the sympathetic postganglionic neurons