Chapter 12 - Nervous Tissue Flashcards
What is the objective of the nervous and endocrine systems?
To keep controlled conditions within limits that maintain life
Which body system is the smallest and most complex?
The nervous system
What are the two main subdivisions of the nervous system?
- Central nervous system
2. Peripheral nervous system
What is the central nervous system composed of?
Brain and spinal cord
What is the brain?
Part of the CNS
Located in the skull
Contains about 100 billion neurons
What is the spinal cord?
Park of the CNS
Connected to the brain (through foramen magnum of the occipital bone)
Contains about 100 million neurons
What is the function of the central nervous system (CNS)?
Processes incoming sensory information
Source of thoughts, emotions and memories
Stimulates muscles to contract
Stimulates glands to secrete
What does the peripheral nervous system consist of?
Cranial nerves, spinal nerves, ganglia, enteric plexuses, sensory receptors
(All nervous tissue outside of the CNS)
What is a nerve?
Bundle of axons located in the PNS
- Cranial nerves connect the brain to the periphery
- Spinal nerves connect the spinal cord to the periphery
How many cranial nerves do we have?
12 pairs
How many spinal nerves do we have?
21 pairs
What is a ganglion? (glanglia)
Cluster of neuronal cell bodies located in the PNS
What is an enteric plexuses? What is the function?
Extensive networks of neurons located in the walls of organs of the gastrointestinal tract
- regulate the digestive system
What is a sensory receptor?
Refers to a specific structure of the nervous system that monitors changes in the external or internal environment
What are examples of sensory receptors?
Touch receptors in the skin
Photoreceptors in the eye
Olfactory receptors in the nose
What are the 3 divisions of the PNS?
- Somatic nervous system
- Autonomic nervous system
- Enteric nervous system
What does the somatic nervous system (SNS) consist of?
- Sensory neurons - convey information from somatic receptors in the head, body wall, and limbs
- special senses: vision, hearing, taste, smell to CNS - Motor neurons - conduct impulses from the CNS to skeletal muscles ONLY - voluntary
What does the autonomic nervous system (ANS) consist of?
- Sensory neurons - convey information from autonomic sensory receptors in the visceral organs (stomach, lungs) to the CNS
- Motor neurons - conduct nerve impulses from the CNS to smooth muscle, cardiac muscle and glands - INVOLUNTARY
What are the two branches of the motor part of the ANS?
- Sympathetic Division
2. Parasympathetic Division
What is the enteric nervous system (ENS)?
The “brain of the gut”
Involuntary
- monitor chemical changes within the GI tract
What do enteric motor neurons govern?
Contraction of GI tract smooth muscle, secretions of the GI tract organs (acid from stomach) and activity of GI tract endocrine cells (secrete hormones)
What are the functions of the nervous system?
- Sensory
- Integrative
- Motor
What is the sensory function?
Sensory receptors detect internal/external stimuli
- ex. increase in blood pressure
Information is carried to brain and spinal cord
What is the integrative function?
Nervous system processes the sensory information
Analysis and then makes decision “integration”
What is the motor function?
Once sensory information is integrated, nervous system may elicit a motor response by activating effectors
- causes muscles to contract or glands to secrete
What is an effector?
Muscle or gland that elicits a response through cranial or spinal nerves
What is an example of an effector of the SNS, ANS, and ENS?
SNS - skeletal muscle
ANS - smooth muscle, cardiac muscle, glands
ENS - smooth muscle, glands and endocrine glands of GI tract
What two kinds of cells types is nervous tissues made up of?
- Neurons
2. Neuroglia
What does a neuron do in the body?
Nerve Cell.
Connects all regions of the body to the brain & spinal cord
Sensing, thinking, remembering, controlling muscles, regulating glands,
Lost ability to divide (mitosis)
What is electrical excitability?
Ability to respond to a stimulus and convert it into an action potential
What is a stimulus?
Any change in the environment that is strong enough to initiate an action potential
What is an action potential (nerve impulse)?
Electrical signal that travels along the surface of the membrane of a neuron
- due to movement of ions (sodium and potassium)
Which nervous system cells posses electrical excitability?
Neurons.
What are the three parts of a neuron?
- Cell body
- Dendrites
- Axon
What is the cell body?
Contains the nucleus surrounded by cytoplasm (lysosomes, mitochondria, golgi complex, free ribosomes, rER)
Also known as Perikaryon or Soma
What are microtubules?
Assist in moving materials between cell body and axon
What is lipofuscin?
Product of neuronal lysosomes that accumulates as the neuron ages
Does not affect function
What are Nissl bodies?
Prominent clusters of rough endoplasmic reticulum and free ribosomes
- Replace cellular components
(material for growth or regenerate damaged axons)
What are neurofibrils?
Provide cell shape and support (intermediate filaments)
What is a dendrite?
The receiving or input portion of a neuron
Short, tapering, highly branched
Contain numerous receptor sites for binding chemical messengers
Contains Nissl bodies, mitochondria, other organelles
What is an axon?
Long, thin, cylindrical projection
Propagates nerve impulses toward another neuron
What is an axon hillock?
Where the axon joins to the cell body
Cone-shaped elevation
What is the initial segment?
Part of the axon closest to the axon hillock
What is the trigger zone?
Nerve impulses arise at the junction of the axon hillock and the initial segment, then travel along the axon to their destination
What does an axon contain?
Mitochondria
Microtubules
Neurofibrils
* no rough ER, so no protein synthesis
What is axoplasm?
Cytoplasm of an axon
What is the axolemma?
Plasma membrane of an axon
What is the direction of flow of information?
Dendrites –> Cell Body –> Axon –> Axon Terminals
What are axon collaterals?
Side braches (typically at a right angle to the axon)
What are axon terminals (telodendria)?
The axon and axon collaterals end by dividing into many fine processes called axon terminals
What is a synapse?
The site of communication between two neurons or between a neuron and an effector cell
What are synaptic end bulbs?
The tips of some axon terminals that swell into bulb-shaped structures
-others exhibit a string of swollen bumps called varicosities
What are synaptic vesicles?
Tiny membrane-enclosed sacs contained in the synaptic end bulbs and varicosities
What is a neurotransmitter? Where is it stored?
A chemical that excites or inhibits another neuron, muscle fibre, or gland cell
Synaptic vesicles
What is slow axonal transport?
Conveys axoplasm in one direction only
-from cell body toward the axon terminal
What is fast axonal transport?
Uses proteins that function as “motors” to move materials along the surfaces of microtubules
- goes in both directions
What is anterograde? Retrograde?
Anterograde - from cell body to axon terminals (forward)
Retrograde - from axon terminals to cell body (backward)
How are neurons classified structurally?
According to the number of processes extending from the cell body
What are the structural classifications of neurons?
- Multipolar neurons
- Bipolar neurons
- Unipolar neurons
What is the structural diversity of neurons?
Diversity in size and shape
Range in diameter from 5 -135 micrometers
Long or short axons
What is a multipolar neuron?
Several dendrites and one axon
- brain, spinal cord, motor neurons
CNS
What is a bipolar neuron?
One main dendrite and one axon
- retina of eye, inner ear, olfactory area of the brain
What is a unipolar neuron?
Dendrites and one axon that are fused together to form a continuous process that emerges from the cell body
- function as sensory receptors (touch, pressure, pain or thermal stimuli)
What is a pseudounipolar neuron?
Unipolar neurons
- begin in the embryo as bipolar neurons
- during development, dendrites and axon fuse together and become a single process
Where is the trigger zone on a unipolar neuron?
Junction of the dendrites and axon
- impluses then propagate toward the synaptic end bulbs
Where are the cell bodies of unipolar neurons located?
In the ganglia of spinal and cranial nerves
in the PNS
What are some examples of unipolar neurons?
Meissner corpuscle - touch receptor
Merkel disc - touch receptor with free nerve endings
Pacinian (lamellated) corpuscle - pressure receptor
Nociceptor - pain receptor
How are neurons classified functionally?
According to the direction in which the nerve impulse (action potential) in conveyed with respect the the CNS
What are the functional classifications of neurons?
- Sensory (afferent) neurons
- Motor (efferent) neurons
- Interneurons (association)
What are sensory neurons?
Either contain sensory receptors at their distal ends (dendrites) or are located just after sensory receptors that are separate cells
- Stimulus –> sensory receptor–> sensory neuron –> (action potential) –> axon –> CNS (through cranial or spinal nerves)
- UNIPOLAR
What are motor neurons?
Convey action potentials away from the CNS to the effectors (muscles and glands) in the PNS through cranial or spinal nerves
-MULTIPOLAR
What are interneurons?
Located in CNS between sensory and motor neurons
Process incoming sensory information from sensory neurons and elicit a motor response
-MULTIPOLAR
How are neuroglia different from neurons?
Smaller than neurons Support, protect and nourish neurons 5-25x more numerous Do not generate action potentials Able to divide 6 types
What are gliomas?
Brain tumors derived from glia (neuroglia)
Highly malignant and grow rapidly
What are the 4 types of neuroglia of the CNS?
- Astrocytes
- Oligodendrocytes
- Microglia
- Ependymal
What are astrocytes?
Neuroglia of the CNS
Star-shaped, largest, most numerous
Have many processes
What are the two types of astrocytes?
- Protoplasmic astrocytes - short branching processes, found in gray matter
- Fibrous astrocytes - long unbranched processes, located in white matter
What are the functions of the astrocytes?
- Contain microfilaments for strength, support neurons
- Processes wrapped around blood capillaries isolate neurons of the CNS from various harmful substances in blood (Blood-brain barrier)
- In the embryo, secrete chemcials that appear to regulate the growth, migration, and interconnection among neurons in the brain
- Maintain proper chemical environment (potassium concentration)
- Role in learning and memory by influencing the formation of neurla synapses
What are oligodendrocytes?
Neuroglia of the CNS
Resemble astrocytes, but smaller and contain fewer processes
What is the function of oligodendrocytes?
Responsible for forming and maintaining the myelin sheath around CNS axons
1 oligodendrocyte can maintain many axons
What is the myelin sheath?
Multi-layered lipid and protein covering around some axons that insulates and increases the speed of nerve impulse conduction
What does myelinated mean?
Axons that have a myelin sheath around them
What are microglia?
Neuroglia of the CNS
Small cells with slender processes that give off numerous spinelike processes
What is the function of microglia?
Function as phagocytes
Remove cellular debris formed during normal development of the nervous system and phagocytize microbes and damaged nervous tissue
What are ependymal cells?
Neuroglia of the CNS
Cuboidal or columnar cells arranged in a single layer that possess microvilli and cilia
Line the ventricles of the brain and central canal of the spinal cord
What is the function of ependymal cells?
Produce, possibly monitor, and assist in the circulation of cerebrospinal fluid
Form blood-cerebrospinal fluid barrier
What are the 2 types of neuroglia of the PNS?
Completely surround axons and cell bodies
- Schwann Cells
- Satellite Cells