6 Nervous Tissue Flashcards
-two categories of cells found in the nervous tissue.
-these require a chemically stable environment.
Neurons and Neuroglia
-have distinctive cell shapes with a membrane capable of generating electrical impulses. They transfer impulses from one ____ to the next via synapses
-have highly irregular shapes with one or more cellular processes extending from the cell body, also have a long lifespan and are generally considered amitotic (do not divide).
-make up only 10% of nervous tissue
Neurons
-the specialized contact areas between two neurons.
-Where the axon terminal meets another cell
synapses
-are the most abundant cells in nervous tissue (over 90%), filling essentially all the space in the nervous system not occupied by neurons and blood vessels. They provide structural, metabolic, and protective support for neurons.
-support, protect, and nourish neighboring neurons both in the CNS and PNS.
Neuroglia
parts of a neuron:
- Cell body or Soma or Perikaryon.
- Axon.
- Dendrites.
Part of a neuron that contains the same organelles found in other cells except for abundant endoplasmic reticulum and polysomes (Nissl substances) and lack of centrioles which are crucial in the process of cell division.
Cell body/Soma/Perikaryon.
*Part of a neuron
Each neuron has an ____
axon
-the area of the cell body where the axon arises
-also called the trigger zone because it is where action potentials are generated.
axon hillock
These are neuronal processes that serve as the receptive region of the neuron.
Dendrites.
Classification of Neurons Based on the Number of Cellular Processes
- Unipolar neurons or Primary sensory neurons.
- Bipolar neurons.
- Multipolar neurons.
These neurons have a single stem process that bifurcates to form processes (peripheral and central). They innervate peripheral tissues bringing somatic and visceral sensory information to the CNS.
Unipolar neurons or Primary sensory neurons
neurons that have two processes. These neurons are sensory neurons located in the retina of the eye, spiral ganglion of the cochlea, vestibular ganglion of the vestibular organ, and olfactory epithelium.
Bipolar neurons
Each neuron has numerous cell processes (one axon and many dendrites). These are the most prevalent type of neurons.
Multipolar neurons
Classification of Neurons Based on Function
- Sensory or afferent neurons.
- Motor or efferent neurons..
- Interneurons or association neurons.
neurons that respond to sensory stimuli and transmit that information to the nervous system, particularly to the CNS.
Sensory or afferent neurons
neurons that transmit signals from the brain or spinal cord to the muscles or glands.
Motor or efferent neurons
sometimes called association neurons, are the most numerous of all neuronal types. Mostly located in the brain and spinal cord, some are found in the autonomic ganglia. They function to distribute sensory information and coordinate motor activity.
Interneurons or association neurons
Classification of Neurons Based on Neurotransmitters
- Cholinergic neurons.
- Serotonergic neurons.
- Adrenergic neurons.
These neurons release acetylcholine. Examples of these are the motor neurons that innervate skeletal muscles.
Cholinergic neurons
These neurons release serotonin (5 hydroxytryptamine). An example would be those neurons in the raphe nucleus of the brain stem.
Serotonergic neurons
These are neurons that release norepinephrine or epinephrine.
Adrenergic neurons
Synapses consists of
presynaptic membrane
synaptic cleft
postsynaptic membrane.
two types of synapses,
electrical synapse
chemical synapse
type of synapse that allows an action potential to pass from one cell to another with virtually no delay.
electrical synapse
type of synapse that is characterized by a synaptic cleft. An electrical signal cannot cross the synaptic cleft, so a chemical substance called a neurotransmitter carries the signal to the postsynaptic cell. The neurotransmitter is stored in the synaptic vesicles.
chemical synapse
The neuroglia of the CNS includes
ependymal cells
astrocytes
oligodendrocytes
microglia.
The neuroglia of the PNS includes
Satellite cells (or amphicytes)
Schwann cells (or neurolemmocytes)
cells that surround neuronal cell bodies in the peripheral ganglia with unknown functions.
Satellite cells or amphicytes
-support the axons of the PNS.
-form myelin sheaths by concentrically wrapping their plasma membrane around the axon (up to 50 or more layers).
-are arranged side by side along the axon.
-forms an internode of the myelin sheath of various lengths (25–1000 μm).
Schwann cells (or neurolemmocytes)
The ____ axons have longer internodes and faster conduction speed. The junction between each internode is the ____
larger
node of Ranvier
-are small neuroglia of the CNS.
-have numerous cell processes that extend to adjacent axons to form myelin sheaths.
-Generally, it myelinates most axons over 1 μm in diameter to speed conduction velocity.
Oligodendrocytes
nerve fibers that innervate the skeletal muscle are heavily myelinated and have the fastest conduction velocity.
Type Aα nerve fibers
are progressively smaller and poorly myelinated.
Type A (β, γ,δ) and B nerve fibers
are not myelinated and have a slow conduction velocity.
Type C
-comprise 10–20% of all neuroglia.
-are the macrophages of the CNS and act as the first line of defense against tissue injury or infection. They also release nitric oxide, which prevents viral replication.
Microglia
-These glial cells are star-shaped cells with numerous long cell processes.
-represent approximately 50% of the glial cell population in the CNS. They provide structural and metabolic support for neurons.
-release neurotrophic factors (e.g., nerve growth factor), which are important for neuronal survival.
-prevent the build-up of potentially neurotoxic substances such as glutamate. They prevent excess accumulation of extracellular glutamate by metabolizing glutamate into glutamine. In addition, they participate in the repair process following tissue injury.
Astrocytes
The close association between the ____ and ____ is important for glucose transport, regulation of the extracellular environment (pH, ion concentration, osmolarity), glutamate metabolism, and maintenance of the endothelial blood-brain barrier.
astrocytes
capillaries
-covers the ventricles and central canal of the CNS. They also line the choroid plexus.
-The ventricles of this and the central canal form a selective barrier between the nervous tissue and CSF.
-these cells line the cerebroventricles.
Ependymal cells
Two structures acting as gatekeepers to the brain’s interior are the
choroid epithelium of the choroid plexus (that acts as the blood–CSF barrier)
capillaries of the nervous tissue (that act as the blood-brain barrier.)
all blood vessels are lined with
endothelial cells
*Blood-CSF Barrier
-are the anatomical basis of the blood–CSF barrier.
-Choroid epithelial cells are sealed together by this that prevents the passage of water-soluble molecules into the CSF.
Tight junction
*Blood-CSF Barrier
cells that play a key role in regulating what can enter and leave the CNS tissue, maintaining an optimal environment for neurons and neuroglia.
choroid epithelial cells
*Blood-CSF Barrier
this relies on carrier proteins to transport essential molecules.
choroid plexus
*Blood-brain Barrier
The plasma membrane is made up of
lipid bilayer
*Blood-brain Barrier
is a vital source of energy in the brain and its transport depends on a specific carrier (GLUT 1) in the capillary endothelial cells.
Glucose
