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Nervous System- Chapter 8 (8.4-8.6 Kahoot (Synaptic knobs occur at the…
Nervous System- Chapter 8
8-1
A. The organs of the nervous system are divided into two major groups
Central Nervous System= brain and spinal cord
Peripheral Nervous System= nerves that extend from the brain (cranial nerves) and spinal cord (spinal nerves)
B. General Functions of Nervous System (3 fold function)
Sensory Input Function
a. PNS;
b. Sensory receptors (located at the ends of peripheral neurons) detect changes (i.e. are stimulated) occurring in their surroundings;
c. Once stimulated, sensory receptors transmit a sensory impulse to CNS
d. A sensory impulse is carried on a sensory neuron
Integrative Function
a. CNS (brain and/ or spinal cord)
b. Involves interpretation of an incoming sensory impulse (i.e. decision is made concerning what's going to happen next, based on sensory impulse).
c. Integration occurs in inter neurons
d. A motor impulses begins...
Motor Function
a. PNS;
b.Involves the response of a body part;
c. Motor impulses are carried from the CNS to responsive body parts called effectors;
d. A motor impulse is carried on a motor neuron;
e. Effectors= 2 types:
mucus (that contract)
glands (that secretes a hormone)
C. Levels of Organization of the Nervous System
*Nervous system
Central Nervous system (Brain and Spinal Cord) (Interneurons)
Peripheral Nervous System (Cranial Nerves and Spinal Nerves)
Sensory (Input into the Central Nervous System) (Afferent Neurons)
Motor (Output from the Central Nervous System) (Efferent Neurons)
Somatic (Effectors: Skeletal Muscle) (Conscious Control)
Autonomic (Effectors: Smooth Muscle; Cardiac Muscle; Glands) (Unconscious Control)
Parasympathetic (Homeostasis) (NT. Acetycholine)
Sympathetic (Fight or Flight) (NT. Norepinephrine)
8.2
A. Neuron = the structural and functional unit of the nervous system; a nerve cell.
Neuron Structure
Each neuron is composed of a cell body and many extensions from the cell body called neuron processes or nerve fibers
a. Cell Body = central portion of neuron; contains usual organelles, except centrioles;
*Identify: nucleus, prominent nucleolus and many Nissl Bodies = RER
b. Neurons Process/ Nerve Fibers = extensions from cell body; two types:
Denrites
Many per neuron
Short and Branched
Receptive portion of a neuron
Carry impulses toward cell body
Axon
One per neuron
Long, thin process
Carry impulses away from cell body
Note terminations of axon branch = axonal terminals; synaptic knobs
Axons in the Peripheral Nervous System
a. Large axons are surrounded by a myelin sheath produced by many layers of Schwann Cells (neuroglial cell)
Myelin = Lipoprotein
"myelinated nerve fiber"
Interruptions in the myelin sheath between Schwann cells = Nodes of Ranvier
b. Small axons do not have a myelin sheath
"unmyelinated nerve fibers"
However all axons (in peripheral nervous system) are associated with Schwann Cells
Axons in the Central Nervous System (i.e. in brain and spinal cord)
a. Myelin is produced by an oligodnedrocyte rather than Schwann Cells
b. A bundle of myelinated nerve fibers = "White Matter"
PNS = Nerve
CNS = Tract 1 column
c. This is in contrast to CNS "Gray Matter" = A bundle of cell bodies (or unmyelinated nerve fibers)
PNS = ganglia
CNS = nucleus
Regeneration of Nerve Fibers
Cell body injury = death of neurons
Damage to an axon may allow for regeneration
B. Neuroglial Cells = accessory cells of neurons system from supporting network for neurons; "nerve glue"
PNS = Schwann Cells produces myelin, and satellite nourish neurons
CNS = 4 Types; provides bulk of brain and spinal cord tissue:
a. Oligodnedrocyte
Looks like eyeball
Function: produces myelin
b. Astrocyte
star-shaped
Function: nourishes neurons
c. Miarogia
looks like spider
Function: phagocytosis
d. Ependymal
epithelial-like layer
Function: lines spaces in CNS
brain = ventricles
spinal cord = central canal
Neurons- The General Structure of neurons
"Representative" neuron has
1) a cell body
2) Several branching, sensitive dendrites, which receives information incoming signals
3) An elongate axon, which carries outgoing signals toward
4) One or more synaptic terminals.
Clusters of rough ER and free ribosomes, known as Nissl Bodies, give a gray color ti areas containing neuron cell bodies and account for the color of gray matter seen in the brain and spinal cord dissections.
A synaptic terminal is part of a synapse, a site where a neuron communicates with another cell.
Structural Classification of neurons
Neurons are classified into three types
1) A multipolar neuron has two or more dendrites and a single axon. These figures are the most common neurons in the Central Nervous System. All of the motor neurons that control skeletal muscles are multipolar
2) In a Unipolar neuron, the dendrites and axon are continuous and the cell body lies off to one side. In unipolar neuron, the action potential begins at the base of the dendrites, and the rest of the process is considered an axon. Most sensory neurons of the peripheral nervous system are unipolar
3) Bipolar Neurons have two processes- one dendrite and one axon- with the cell body between them. Bipolar neurons are rare but occur in special sense organs where they relay information about sight, smell, or hearing from receptor cells to other neurons.
Sensory Neurons- Approximently 10 million sensory neurons in the human body form the afferent divison of the PNS. They receive information from sensory receptors monitoring the external and internal enviornment and then relay information to other neurons in the CNS (spinal cord or brain)
Motor Neuron- Half million motor neurons of the efferent division carry instructions from the CNS to other tissues, organs, or organ systems. The perpherial targets are call effectors because they respond by doing something.
Somatic motor neurons of the somatic nervous system innervate skeletal muscles, whereas the visceral motor neurons of the autonomic nervous system innervate all other effectors, including cardiac muscle, smooth muscle, and glands.
Interneurons- 20 billion interneurons, or association neurons, are located entirely within the brain and the spinal cord. Implies innerconnect other neurons. They are responsible for the distribution of sensory information.
8.1-8.3 Kahoot ?'s
The brain and spinal cord comprise the central nervous system
The part of the peripheral nervous system that brings information to the central nervous system is the afferent division.
Most neurons in the brain are multipolar
The cytoplasmic extensions that, together with the cell body, provide the main receptive surfaces for neurons are the dendrites
The largest and most numerous of the glial cells in the central nervous system are the astrocytes
The myelin sheaths that surrond the acons of some of the neurons in the CNS are formed by oligondendrocytes
Small phagocytic cells that are especially obvious in damaged tissue in the CNS are the microglia
Aggregations of ribosomes in neurons are referred to as nissl bodies
Neurons that have one axon and one dendites with the soma between them are called bipolar
Most neurons lack centroiles. This observation explains why these neurons cannot regenerate
The polarization of a nerve fiber refers to having the potassium ions inside the cell and sodium outside the cell
Saltatory conduction is faster than conduction on an unmyelinated axon
Opening of sodium channels in the membrane of neuron result in depolarization
When a neuron is at rest, which ion passes through its membrane most easily- potassium
The all or none principle states that all stimuli great enough t bring the membrane to threshold will produce identical action potentials
8.4-8.6 Kahoot
Synaptic knobs occur at the ends of the axons
Neurotransmitters are released from synaptic terminals/knobs
Which type of synapse dominates the system- chemical
The ion needed to initiate the release of acetycholine into the synaptic cleft is calcium
Adrenergic synapses release the neurotransmitter norepinephrine
Which of the following lists the parts of a reflex arc in the correct order- receptor, sensory neuron, interneuron, motor neuron, effector
The correct sequence of events is 2,1,6,7,4,3,5
The specialized membranes that protect the spinal cord are termed spinal meninges
Blood vessels servicing the spinal cord are found in the pia mater
The dural sinuses are located in the dura mater
What contains a delicate network of collagen and elastin fibers through which cerebrospinal fluid circulates subarachnoid space
Diffusion across the arachnoid villi returns excess CFS to venous circulation
The projections of gray matter toward the outer surface of the spinal cord are called horns
Masses of myelinated nerve fibers appear white
Axons crossing from one side of the spinal cord to the other within the gray matter are found in the gray commissures
The white matter of the spinal cord contains bundles of axons that share common origins, destinations, and functions
Enlargements of the spinal cord occur in segments of the spinal cord that control the limbs
The entire spinal cord is divided into 31 segments
The horns of the spinal cord contain nerve cell bodies
The posterior horns of the spinal cord contains sensory nucleui
Gray matter in the spinal cord is mostly interneurons
If the dorsal root of a spinal nerve is severed, incoming sensory information would be disrupted