Nervous Tissue Flashcards
Nervous Tissue
- specialized to send and receive electrical signals through the body
- allows the nervous system to communicate with and control the body via their interconnections
- one key feature is that this tissue can generate and propagate electrical signals called action potentials
- contains two basic cell types: neurons (functional unit), glial cells (support)
Central Nervous System (CNS)
- nervous tissue present in the dorsal body cavity
- consists of brain and spinal cord
- it processes incoming stimuli from the internal and external environment and determines the appropriate response; it then sends signals through the body (via PNS) for a response
- much wider range of glial cells in this system to support the neurons
Peripheral Nervous System (PNS)
- nervous tissue found throughout the body outside of the dorsal body cavity
- responsible for collecting information from the external and internal environments and sending it to the CNS (afferent signals)
- transports information from the CNS to the appropriate muscle, gland, etc. in the body for the appropriate response (efferent signals)
- nervous tissue is found in nerves and ganglia (clusters of cell bodies)
- only two types of glial cells here because of the different packaging of the neurons
Neuron
- the functional unit/cell in nervous tissue
- sends and receives electrical signals within the body allowing the parts to be interconnected and function
- often highly specialized in their role: excitable (respond to a stimulus), conduct electricity (AP) and secrete NTs
- the shape and size of these cells are highly variable
- limited ability to undergo mitosis
Soma (Perikaryon)
- the cell body of a neuron
- holds the nucleus and the organelles within its neuroplasm (cytoplasm)
- contains many processes – dendrites, axons
- processes the incoming information from the dendrites and sends the signal along the axon in warranted
What part of the neuron houses the mitochondria?
Axon
Chromatophilic Substance (Nissl Substance/Bodies)
- the distinctive (basophilic) rough ER within the soma
- allows the neuron to produce NTs and maintain the cell
Dendrite
- extension of the neuron cell body that picks up information (stimuli at synapses or dendritic spines) and transfers it to the cell body
- neurons contain many dendrites to receive both excitatory and inhibitory signals
- vary in shape but are often short and highly branched
Axon
- extension of the neuron cell body that allows the neuron to communicate via synapses with other neurons or tissues within the body (muscles or glands)
- creates an AP which allows for communication
- able to interact with other axons to modify the signal being sent
- typically neuron only has one
- branches at the terminal end of the neuron – terminal arborization
- due to its distance from the soma, it has its own terminology – axolemma for neurolemma (cell membrane), axoplasm for neuroplasm (cytoplasm)
What is an axon’s cell membrane called?
Axolemma
What is an axon’s cytoplasm called?
Axoplasm
Axon Hillock
- the triangular area between the soma and the axon
- it summates the electrical signal (AP) and triggers the AP down the axon if the threshold is met
Synaptic Knob (Terminal Bouton)
- the rounded dilation found at the end of the axonal terminal branches
- in chemical synapses, this area stores NTs and releases them when the neuron is ready to send a signal with another structure
- in electrical synapses, gap junctions provide direct transmission of the ion to propagate the electrical signal
Multipolar Neuron
- a neuron that has multiple dendrites and one axon
- most common type of structural classification
- this is seen in motor (efferent) neurons, and some sensory and interneurons too
Unipolar / Pseudounipolar Neuron
- a neuron that does not have any true dendrites but does have two axons
- one axon travels to the CNS while the other axon travels toward a peripheral location
- common with sensory (afferent) neurons
Bipolar Neuron
- a neuron that has one dendrite and one axon
- this type is found in sensory roles such as the retina, inner ear, and olfactory membrane
Sensory Neurons (Afferent Neurons)
- type of neuron that picks up signals from the internal and external environment, and transmits that information to the CNS
- divided into two groups: somatic (conscious input from skin, MSK system, special senses) and visceral (sensory information from internal organs and cardiovascular structures)
Motor Neuron (Efferent Neuron)
- type of neuron that takes information from the CNS and distributes it through the body for a response (muscle and glands)
- can be divided into two groups: somatic (conscious or voluntary control of skeletal muscle), and autonomic (unconscious control of internal organs and glands)
Interneuron
- type of neuron that is present in the CNS
- it receives, processes, links, and communicates with other neurons in the body, creating functional networks called circuits
- most neurons in the body are this type of neuron
- structurally classified as either anaxonic (no axon) or multipolar
Synapse
- where one neuron meets another neuron or the intended signal target (effector cell)
- a uni-directional signal is transferred between the two parts – a presynaptic neuron to a postsynaptic structure
- two types of synapses: electrical and chemical
Electrical Synapse
- presynaptic neuron touches the postsynaptic neuron or structure and transfers the electrical signal directly
- this type of synapse is located in the heart – ions pass through the gap junctions continuing the electrical signal from the presynaptic to the postsynaptic
Chemical Synapse
- presynaptic neuron does not touch the postsynaptic neuron or structure; instead there is a synaptic cleft between the two structures
- to transfer the signal, the presynaptic neuron releases NTs
- Ex. neuromuscular junction (neuron -> muscle fiber)
Neuromuscular Junction
- example of a chemical synapse
- neuron meets up with a myocyte
- AP of the neuron is passed from the nervous system onto the muscular system
- signal changes from electrical (ions) to chemical (NT) at the synapse
Presynaptic Axon Terminal
- component of neuromuscular junction
- the terminal end of the neuron’s axon, the synaptic knob
- NTs are located in the synaptic knob and are released when triggered to pass the AP to the muscle
- glial cells called neurolemmocytes surround this area and help maintain it
What cells surround the Presynaptic Axon Terminal?
Neurolemmocytes
Synaptic Cleft
- component of neuromuscular junction
- the space between the neuron and the myocyte
- NTs released from the neuron pass through this gap and bind to receptors on the myocyte
Motor Endplate (Postsynaptic Cell Membrane)
- component of neuromuscular junction
- part of the myocyte that contains receptors for the NTs released from the neuron
- the NTs bind to the receptors, causing the muscle tissue to respond – can be excitatory or inhibitory
Glial Cell
- located in both the CNS and PNS
- cells that provide a supportive role in the nervous tissue, taking place of connective tissue proper, including protecting and insulating the neurons
- also help ensure an optimal working environment for neurons
- undergo mitosis and create the majority of the nervous tissue
Oligodendrocyte
- the myelinating cell of the CNS
- type of glial cell
- has many processes that surround multiple neuron axons – can myelinate many axons at once
- covers axons with myelin (lipid and protein membrane) which helps insulate the axon and speed up the signal transmission
- contributes to the white matter of the brain
- under the microscope they appear as small cells with rounded condensed nuclei and unstained cytoplasm
Gray Matter
- present in the brain and spinal cord (CNS)
- refers to the neuron cell bodies, dendrites, synapses and the glial cell bodies
- in the spinal cord, this is the inner aspect of the cord (appears as a butterfly pattern)
- in the brain, this is the outer, external surface that is present deep within the brain in areas called cerebral nuclei
- appears grayish in color to the naked eye
White Matter
- present in the brain and spinal cord (CNS)
- refers to the myelinated axons (lipids and proteins); also contains astrocytes and microglial cells
- in the spinal cord, this is more superficial
- in the brain, this is located deeper
- appears white in color to the naked eye
Astrocyte
- present in the CNS
- contains many processes coming from the central cell body; enlarged terminal ends surround capillaries of the blood-brain barrier
- helps during the embryonic development of the CNS, associates with/covers synapses, and assists in the blood-brain barrier and interstitial fluid composition
- these cells fill in areas of damaged brain tissue like connective tissue did in the skin creating scar tissue
- communicate via gap junctions/electrical synapses to allow them to carry out their role
-Histology: star-shaped
Ependymal Cell
- cell that is present in the cavities inside the brain (ventricles) and spinal cord (central canal)
- part of the choroid plexus that aids with the production and circulation of cerebrospinal fluid (CSF supplies needed substances such as ions to the brain and spinal cord neurons)
- apical surface might have cilia or microvilli which aid in CSF movement and absoprtion
- Histology: cuboidal or columnar shaped
Microglial Cell
- a macrophage found within the CNS
- helps with the immune response
- contains many cell bodies at the center with numerous branches shooting outwards
- while it moves throughout tissue, it removes damage or inactive synapses as well as foreign invaders
- originates from myocytes
- only glial cells that migrate
What cell do Microglial cells originate from?
Myocytes
What cell surrounds a neuron cell body in the PNS?
Satellite Cell
Satellite Cell
- a glial cell that is found in the PNS
- multiple of these cells surround a neuron cell body found in ganglia (accumulations of neuron cell bodies of the PNS)
- function in protecting the soma from the surrounding environment and provide insulation
- ganglia are often surrounded by connective tissue making them appear like discrete, bulbous structures to the naked eye
- Histology: appear like squamous or cuboidal cells around the soma
Neurolemmocyte (Schwann Cell)
- the myelinating cell of the PNS
- protects the neuron’s axon by creating a myelin sheath (lipid and protein) around the motor or sensory axons
- although not all axons in the PNS are myelinated, they have neurolemmocytes associated with them because they cover the axon through the synapse
Neurolemmocyte (Schwann Cell)
- the myelinating cell of the PNS
- can only myelinate one cell axon at a time
- protects the neuron’s axon by creating a myelin sheath (lipid and protein) around the motor or sensory axons
- although not all axons in the PNS are myelinated, they have neurolemmocytes associated with them because they cover the axon through the synapse
Nodes of Ranvier
- gaps in the myelinated axon – often called nodal gaps
- they allow the electrical signal (AP) to pass over the myelination which speeds up the signal transduction because the AP doesn’t have to travel the entire axolemma
Nerve
- a bundle of neurons (can be myelinated or unmyelinated) and their supporting glial cells that travel through the body (PNS)
- different types of nerves in the body based on the type of neurons they hold: sensory only, motor only, or mixed
- the mixed type (contains both sensory and motor neurons) is the most common
Endoneurium
- the deepest connective tissue layer in a nerve
- composed of loose connective tissue surrounding each of the neuron’s axons and associated neurolemmocytes
- separates and insulates the electrical signals traveling along the axons
- also serves as a pathway for capillaries and contains fibroblasts
Perineurium
- it is connective tissue that bundles a group of axons together (fascicle) in a nerve
- fibrocytes join together via tight cellular junctions to create the blood-nerve barrier
- fascicles hold neurons that are going to the same area in the body
Nerve Fascicle
- a bundle of nerve fibers belonging to a nerve in the PNS – essentially it is a group of nerve fibers
- it is enclosed by perineurium, a layer of fascial connective tissue
Epineurium
- the most superficial connective tissue layer within a nerve
- it bundles fascicles within a nerve together and fills in the spaces between them, providing support and protection as the nerve travels throughout the body
Characteristic of the chromatophilic substance found in neurons:
it is the site of mRNA translation for proteins of the axolemma
(this is a region with concentrated rER and other polysomes that are basophilic and help in the production of cytoskeletal proteins and proteins for transport/secretion)
What structure in the choroid plexus is responsible for transporting water directly into the CSF from capillaries?
Ependymal Cells
Term that applies to a collection of neuron cell bodies in the CNS:
Nuclei
(deep within the brain are localized, variously shaped darker areas called cerebral nuclei, each containing large numbers of aggregated somas)
Characteristic of the connective tissue layer that surrounds individual fascicles in a large peripheral nerve:
Important part of the blood-nerve barrier
(groups of axons with their schwann cells and endoneurium are surrounded by the perineurium, consisting of layered squamous fibroblastic cells joined by tight junctions)