Organization of The Nervous System Flashcards
Neural Circuits: Definition of Cellular Connectionism
Individual neurons are the signaling units of the brain; they are generally arranged in functional groups, and connect to one another in a precise fashion
Neural Circuits: Principles
Dynamic Polarization
Unidirectional flow of electrical signals within neurons
Neural Circuits: Principles
Connectional Specificity
Each cell makes SPECIFIC connections
Neural Circuits: what are the 3 basic constituents of a neural circuit?
Sensory (input), interneurons, motor neurons (output)
Myotactic Spinal Reflex (Knee Jerk Reflex) Steps
1) Hammer tap stretches the patellar ligament, which, in turn, stretches sensory receptors in the quadriceps femoris
2) In the spinal cord, the sensory neuron synapses with and excites the motor neuron to the quadriceps femoris. the sensory neuron also synapses with and excites an interneuron. the interneuron synapses with and inhibits the motor neuron to the knee flexor muscles (hamstrings)
3) The motor neuron conducts action potential to synapses on quadriceps femoris, causing contraction. The knee flexor muscles relax because the activity of their motor neurons is inhibited.
4) This produces knee extension.
Neural Circuits: Pattern of Connections
Divergence
One neuron activates many target cells.
This is common in the input stages of the nervous system
Neural Circuits: Pattern of Connections
Convergence
One neuron recieves input from many cells.
This is common in the output stages of the nervous system
Neural Circuits: Inhibition
Feed Forward
Enhances the effect of the active pathway by supressing the activity of other, opposing pathways.
Example: Myotactic reflex
Neural Circuits: Inhibition
Feedback
This is a self-regulating mechanism. The effect is to dampen activity within the stimulated pathway and prevent it from exceeding a certain critical maximum
Anatomical divisions of the Neural System: CNS
Brain, Spinal Cord
Anatomical divisions of the Neural System: PNS
Ganglia, Nerves (nerves are composed of AXONS within their connective tissue sheaths)
Anatomical divisions of the Nervous System: Combined
PNS contains sensory (afferent) neurons that receive and transmit information from the environment to the CNS
Information is processed in the CNS (brain and spinal cord)
PNS - motor (efferent) neurons receive and transmit information from the CNS to the periphery
Functional Systems of the Nervous System: 5 organizing principles
1) Each functional system involves several brain regions that carry out different types of information processing.
2) Identifiable pathways link the components of a functional system.
3) Each part of the brain projects in an orderly fashion onto the next, thereby creating topographical maps 9homunculus)
4) Functional systems are hierarchically organized
5) Functional systems on one side of the brain control the other side of the body
General Functional Systems: Sensory
Acquire and process information from the environment (either internal or external)
General Functional Systems: Motor
Respond to information from the environment by generating movements and other behavior
General Functional Systems: Association (aka Modulatory)
These areas lie between the relatively well -defined input and output systems.
They mediate the most complex and least well-characterized brain functions, loosely referred to as Cognition.
Interpretation and integration of signals
General Functional Systems: Association (aka Modulatory)
What is Cognition?
Cognition refers to the ability to attend to external stimuli or internal motivation; to identify the significance of such stimuli, and to make appropriate responses.
Components of the CNS: Brain
Overall Structure
The brain is the rostral part of the CNS (towards the nose)
It is bilateral and essentially symmetrical; has 7 main parts.
Components of the CNS Preview: Brain - Forebrain
Part: Telencephalon (cerebrum)
What parts does this include?
Cerebral cortex, basal ganglia (deep to cortex), hippocampus (related to memory), and amygdaloid (related to emotion and drive related behaviors.)
Components of the CNS Preview: Brain - Forebrain
Part: Telencephalon (cerebrum)
Where is it located?
Largest and most superior part of the brain.
Components of the CNS Preview: Brain - Forebrain
Part: Telencephalon (cerebrum)
What is its function?
Perceptual (sensory), motor, and cognitive functions
Components of the CNS Preview: Brain - Forebrain
Part: Diencephalon
What parts does this include?
Thalamus, hypothalamus (there are other parts but these are our focus.
Components of the CNS Preview: Brain - Forebrain
Part: Diencephalon
Where is it located?
Surrounded by the cerebral hemispheres superior to the midbrain
Underlying cerebral cortex is the basal ganglia; spinal cord comes down below, and between the brain stem and the basal ganglia/cerebral cortex is the thalamus.
Components of the CNS Preview: Brain - Forebrain
Part: Diencephalon
What is its function?
Processes most of the information reaching the cortex (all sensory goes through the thalamus except olfactory)
The hypothalamus regulates autonomic and endocrine function.
Components of the CNS Preview: Midbrain
Where is it located?
Inferior to the diencephalon and superior to the pons.
Components of the CNS Preview: Midbrain
What is its function?
Controls sensory and motor functions such as eye movement, and the coordination of audio and visual reflexes
Components of the CNS Preview
What parts of the brain make up the brainstem?
What comes from the brainstem?
Midbrain, Pons, and Medulla
Cranial nerves; all pathways to the brain must pass through the brainstem.
Components of the CNS Preview: Brain - Hindbrain
Part: Cerebellum
Where is it located?
Posterior to the Pons
Components of the CNS Preview: Brain - Hindbrain
Part: Cerebellum
What is its function?
Modulates the force and range of movement and is involved in the learning of motor skills.
Components of the CNS Preview: Brain - Hindbrain
Part: Pons
Where is it located?
Inferior to the midbrain, superior to the medulla.
Components of the CNS Preview: Brain - Hindbrain
Part: Pons
What is its function?
Relays information about movement and sensation from the cerebral cortex to the cerebellum.
Involved in respiration, taste, and sleep.
Components of the CNS Preview: Brain - Hindbrain
Part: Medulla
Where is it located?
Most inferior part, beneath the pons, superior to the spinal cord.
Components of the CNS Preview: Brain - Hindbrain
Part: Medulla
What is its function?
Responsible for several vital autonomic functions.
Components of the CNS: Spinal Cord
Location, function
It is the most caudal (towards the tail) Part of the CNS
Function: receives and processes sensory information from the extremities, trunk, and viscera and controls movement of the extremities, trunk and viscera.
Classification of groups of Neurons: Gray Matter
Definition
Gray Matter contains NEURONAL CELL BODIES, dendrites, unmyelinated axons, and glial cells. Types of cells vary by region.
Classification of groups of Neurons: Gray Matter
Gray Matter in the Brain
Occupies the superficial outer layer and some deeper regions. Constitutes the cortex and the nuclei (aka basal ganglia) respectively.
Cell bodies are arranged in layers that may be called a layer, lamina, or striatum. (there are 6 layers in the cerebral cortex)
Classification of groups of Neurons: Gray Matter
Gray Matter in the Spinal Cord
Occupies the central H shaped region.
Constitutes the nuclei of the dorsal and ventral horns.
Longitudinal groups of functionally related cell bodies may be called columns and/or Rexed’s lamina
Classification of groups of Neurons: White Matter
Definition
Contains myelinated axons and oligodendrocytes
Functionally related axons constitute the lemnisci, funiculi, fasciculi, and tracts (these are all terms used to designate white matter)
Classification of groups of Neurons: White Matter
White Matter in the Brain
Occupies the deeper regions (deep tot he cortex)
Classification of groups of Neurons: White Matter
White Matter in the Spinal Cord
Occupies the peripheral region
Surface Coverings: Meninges
Function
Encase the brain and the spinal cord
Surface Coverings: Meninges
Dura Mater
It is the outermost layer
It is a sheath of dense CT
It is continuous with the periosteum in the skull, but separated from the vertebrae in the spine by the epidural space.
It is separated from the arachnoid mater by the subdural space.
Surface Coverings: Meninges
Arachnoid Mater
It is the middle layer
It is a cellular layer in contact with the dura mater and a system of trabeculae connected to the pia mater.
the cavities between the trabeculae form the subarachnoid space and are filled with CSF
Surface Coverings: Meninges
Pia Mater
Innermost layer
Sheath of loose CT lying directly on the surface of the nervous tissue (can’t really be pulled away from nervous tissue except at specializations such as denticulate ligament and filum terminale).
Functional Subdivisions of the PNS: Somatic
Composed of neural elements associated with the body wall and extremities (i.e. skin, skeletal muscles, and joints)
Functional Subdivisions of the PNS: Autonomic
Composed of neural elements associated with the internal organs or viscera (i.e. cardiac muscle, smooth muscle, glandular epithelium.
Functional Subdivisions of the PNS: Somatic AND Autonomic
Functional Features
BOTH systems transmit afferent and efferent information
These systems are ANATOMICALLY distinct from the CNS, but they are functionally intertwined with it.
Components of the PNS: Components
What are the components of the PNS?
Ganglia and Nerves
Components of the PNS: Ganglia
What are ganglia?
Ovoid structures containing neuronal cell bodies and glial cells, supported by connective tissue.
Examples of ganglia: dorsal root ganglia, paravertebral ganglia, prevertebral ganglia, ternimal ganglia
Components of the PNS: Ganglia
Sensory (Somatic and Visceral)
Associated with the dorsal roots of the spinal nerves and cranial nerves 5,7,8,9,10
Contain the cell bodies of pseudounipolar neurons
Components of the PNS: Ganglia
Motor (Visceral)
These are the sympathetic/parasympathetic ganglia (paravertebral, prevertebral, terminal)
Components of the PNS: Nerves
What is a nerve?
A collection of axons with associated Schwann cells with connective tissue coverings
Components of the PNS: Nerves
How are nerves classified?
They are classified according to the functional components of their neurons.
Spinal nerves - 31 pairs that can contain GSE, GVE, GSA, and GVA neurons
Cranial Nerves - 12 pairs that can contain GSE, GVE, SVE, GSA, GVA, SSA, SVA neurons
Components of the PNS: Surface coverings of Nerves
Epineurim
Sheath of dense CT that surrounds the ENTIRE nerve
There is a rich vascular supply within the CT sheaths
Components of the PNS: Surface coverings of Nerves
Perineurium
Sheath of dense CT that surrounds bundles of nerve fibers (myelinated axons) called FASCICLES
Components of the PNS: Surface coverings of Nerves
Endoneurium
Delicate layer of loose CT that surrounds individual nerve fibers
