Nervous Tissue Flashcards
What are the Anatomical divisions of the nervous tissue
CNS
- Central nervous system
PNS
- Peripheral nervous system
What consists of the CNS (central nervous system)
and what are they made out of
Brain(cerebellum, and cerebrum), and spinal cord.
All these organs are made of white matter (nerve fibers and neuroglia cells) and gray matter (neurons, nerve fibers and neuroglia cells) and are covered by three meninges.
What consists of the PNS (peripheral nervous system) and what are they made out of
Nerves outside the CNS, and ganglia.
Nerves:Bundles of nerve fibers surrounded by connective tissue sheaths
Nerve Fiber connective tissue sheaths
Epineurium, surrounds nerves; perineurium, surrounds fascicles; endoneurium, surrounds a nerve fiber.
Individual nerve fiber is enveloped by a myelin sheath produced by Schwann cells in the PNS and by oligodendrocytes in the CNS.
Epineurium
Surrounds the whole nerve
Perineurium
Surrounds fascicles of a nerve
Endoneurium
Surrounds individual nerve fiber within a fascicle
How does sensory transmit impulses
Transmit impulses to the CNS
How does motory transmit impulses and how is it divided
Transmit impulses from the CNS to the body; the motor part is divided into somatic and autonomic (sympathetic and parasympathetic) systems.
What are the cell types in the nervous system
Neurons
Neuroglia cells
What is a neuron
A cell body and processes (dendrites and an axon)
Conducts impulses
Cell body of a neuron (perikaryon)
Nucleus, RER (Nissl body), Golgi, lipofuscin granules (increase with age), neurofilaments (10 nm in diameter), and microtubules.
Dendrite
Transmits impulses toward the body, contains organelles like in the body except that Golgi is absent, has arborized terminals which permit a neuron to receive stimuli from many other neurons.
Axon
One axon per neuron, conducts impulses away from the body, originates from the axon hillock, lacks organelles except microtubules and neurofilaments, may have collateral branches, terminates in many branches (telodendrions), which form synapses with dendrites or cell bodies of other neurons or form special contacts with other cell types, such as, muscle cells.
What are the different types of neurons
Discuss their structure and functions
Multipolar
Bipolar
Pseudo-unipolar
Unipolar
What is the structure and function of Unipolar
Possess a single process, rare in vertebrates, present in the developing NT.
What is the structure and function of Bipolar
Possess a single axon and a single dendrite, present in sense organs.
examples: parts of vision, smell, taste, hearing.
What is the structure and function of Multipolar
Possess a single axon and more than one dendrite; the most common type of neuron.
Example: Sympathetic ganglion
What is the structure and function of Pseudo-Unipolar
Possess a single process that branches into an axon and a dendrite, present in spinal and cranial ganglia.
What is a neuroglia
Support, nurture and protect neurons.
Do not conduct impulses or form synapses, function to support and protect neurons.
Types of Neuroglia Cells in the CNS
Astrocytes
Oligodendrocyte
Microglia
Ependymal Cells
Astrocyte
Protoplasmic astrocytes mainly in gray matter and fibrous astrocytes mainly in white matter, feet-like processes surround blood vessels and form a part of the blood-brain barrier.
Oligodendrocyte
Necessary for the survival of neurons, located both in gray and white matter, produce myelin for axons in the CNS.
Microglia
Small, phagocytic, derived from monocytes (mesoderm); condensed, elongated nucleus, which can be confused with endothelial nuclei.
Ependymal Cells
Line the neural tube and ventricles of the brain, associated with formation of the cerebrospinal fluid (CSF), often have cilia, which aid in moving the CSF.
Schwann Cells
Are also neuroglia cells but are located around axons in the PNS. Schwann cells also synthesize myelin sheath, but each Schwann cell produces myelin for only one axon, whereas oligodendrocytes can do so for several axons.
Four phases of myelin formation in peripheral nerve fibers
- Schwann cell surrounding an axon
- Schwann cell’s cell membrane surrounds the axon, the point of attachment is called mesaxon
- The cell membrane rolls around the axon (like a jelly role)
- The myelin sheath consists of many layers of the cell membrane of Schwann cell ( that is why myelin sheath is essentially a lipid layer) and is present within the cytoplasm
What are the different types of nerve fibers
Type A
Type B
Type C
What is the structure and function of Type A
Myelinated, thick, and conduct impulse at 15-100 m/sec;
What is the structure and function of Type B
Moderately myelinated, thinner than type A, conduct impulse at 3-14 m/sec;
What is the structure and function of Type C
Thin, unmyelinated, may or may not be covered by Schwann cell or oligodendrocytes, conduct impulse at 0.2-2 m/sec.
What is the Ganglion and what is its structure and function
Aggregations of neuronal cell bodies outside the CNS. Examples: dorsal root ganglion (sensory) and autonomic (motor).
What is the spinal cord and what is its structure and function
White matter in the periphery, divided into dorsal and ventral columns; gray matter, in the form of an H in the center and is divided into dorsal, ventral (site for alpha-motor neurons) and lateral (site for sympathetic or parasympathetic neurons, depending upon the segment of the spinal cord) horns; central canal lined by ependymal cells.
What is the cerebellum and what is its structure and function
Gray matter outside and white matter inside.
Function: Maintaining balance and posture and coordination movements.
Consists of three layers:
Molecular Layer
- mainly cell processes, very few cell nuclei;
Purkinje cells layer
- multipolar neuron, each cell receives thousands of excitatory and inhibitory impulses;
Granular layer
- contains closely packed small granule cells
What are the meninges
Dura mater
Arachnoid
Pia mater
Dura mater
Dense connective tissue that is fused with the periosteum in the brain but free in the spinal cord, thus no epidural space in the brain, thick dense CT lined on both sides by simple squamous epithelium
Arachnoid
Thin membrane lined by simple squamous cells, connected by trabeculae to the pia mater
Pia mater
Thin vascular membrane attached to the nervous tissue(the brain).
Spaces of the meninges
epidural (contains fat)
- only in the spinal cord
subdural
subarachnoid (contains CSF).
Spinal Cord meninges difference from Brain
Dura Mater is separate from the periosteum and its dense connective tissue is lined on both sides by simple squamous epithelium.
What is a synapse
Sites where signals are transmitted from one neuron to another neuron or a muscle cell (neuromuscular).
Types of synapses
Axodendritic
Axosomatic
Axoaxonic (Rare)
Axodendritic
Axon transmit signals to the dendrite of another
Axosomatic
Axon transmit signals to cell body of another
Axoaxonic
Axon transmit signals to another axon
Synaptic Morphology
Axon terminal, presynaptic membrane (contains voltage-gated Ca++ channels), postsynaptic membrane (contains receptors for neurotransmitters), and synaptic cleft.
Types of Neurotransmitter
Acetylcholine
Norepinephrine
Glutamic acid
Gamma-aminobutyric acid
Dopamine
Serotonin
Glycine
Acetylcholine
Released at myoneural junctions, all parasympathetic synapses, and preganglionic sympathetic processes.
Norepinephrine
Released at the postganglionic sympathetic synapses
Glutamic acid, gamma-aminobutyric acid, dopamine, serotonin, and glycine
Mainly released at neuronal synapses in the brain.
Is this statement referring to this flashcard or should it be moved–>Biochemical events associated with impulse transmission are the same as described for the motor end plate.
Nodes of Ranvier
Regions along the length of a nerve fiber, lack myelin sheath, and represent discontinuities between adjacent Schwann cells or oligodendrocytes.
The axolemma at the nodes contains many Na+ pumps and allows jumping of the action potential from one node to the next (Saltatory conduction).
The node of Ranvier is covered only by axolemma (lacks myelin sheath or cytoplasm of SC).
Axolemma and what is it surrounded by
Each axon/dendrite is surrounded by a cell membrane (axolemma), which is surrounded by Schwann cells in the case of peripheral nerve fiber and by Oligodendrocytes in the case of central nerve fibers.
Reflex Arc
Consists of a minimum of two (usually more) neurons.
Parts with example:
Receptor (skin)
Afferent limb (dorsal root of the nerve
Integrating center
- First Neuron (unipolar sensory neuron of the dorsal root ganglion)
- Second Neuron (ventral motor neuron of the spinal cord)
Efferent limb (ventral root of the spinal cord)
Effector (muscle fibers)
Example:
Knee-jerk reflex (two neurons)
Withdrawal reflex (more than two neurons)
- Withdrawal of the finger from a hot surface
Cerebral Cortex
Cells and fibers are arranged in layers, but their number depends on the area of the brain and the species. Large domestic species have only 3-4 layers identified.
Molecular
External Granular
External Pyramidal
Internal Granular
Internal Pyramidal
Fusiform
Note, granule cells are considered as receptor neurons, and pyramidal cells as motor neurons. Pyramidal cells are the dominant neurons.
cerebrum occupies the major part of the brain and consists of ridges (gyri) and grooves (sulci).
Pyramidal Cells (upper motor neurons)
Are the most prominent and important cell type of the cerebrum and form pyramidal tracts, such as, corticobulbar and corticospinal
Parts of the patellar reflex
- Quadriceps muscle is stretched, and a sensory impulse is generated (action potential).
- Sensory impulse is carried via afferent fibers of sensory neurons of dorsal root ganglion.
- The impulse is transmitted to the ventral motor neurons in the ventral horn of spinal cord.
- Motor impulse (axons of ventral motor neurons) stimulates quadriceps muscle.
Molecular layer of the cerebral cortex
Fibers and neuroglia cells
External granular of the cerebral cortex
Granule cells
External pyramidal of the cerebral cortex
Small pyramidal cells
Internal granular of the cerebral cortex
Small granule cells
Internal pyramidal of the cerebral cortex
Large pyramidal
Fusiform of the cerebral cortex
Irregular pyramidal
Blood-Brain Barrier
Un-fenestrated endothelium with tight junctions between endothelial cells and a thick basal lamina surrounded by foot-like processes of astrocyte.
Choroid Plexus
Folds of pia mater in the brain ventricles, which consist of a core of connective tissue covered by simple cuboidal ependymal cells; secrete cerebrospinal fluid.
Cerebrospinal Fluid
Fills the ventricles of the brain( 2 lateral, third and fourth), central canal of the spinal cord, and subarachnoid space, produced by the choroid plexus, and reabsorbed by the arachnoid villi into venous sinuses of the brain. Contains less protein than tissue fluid.
Degeneration and Regeneration of Nervous Tissue
Neurons cannot divide, thus cannot be replaced when injured. Nerve fibers regenerate.
Steps:
ia) Degeneration of the nerve fiber distal to the site of injury (Wallerian degeneration),
OR
ib) degeneration of a small part of the fiber proximal to the injury (primary degeneration),
ii) loss of Nissl bodies and lateral migration of the nucleus (chromatolysis),
iii) proliferation of Schwann cells, which form a tube-like structure, branching of the axon
iv) re-growth of fibers by sprouting,
v) growth of a nerve fiber sprout into the tube surrounded by Schwann cells, (Penetration of a branch of an axon into one of the tubes surrounded by Schwann cells (nerve regeneration is successful). )
vi) eventual re-connection of the nerve fiber (axon) with the muscle.
Note, if nerve (axons) fibers fail to connect with the muscle, then they form neuromas (usually found in horses).
Receptors
Peripheral specialized nerve endings of afferent neurons, which respond to environmental changes.
Exteroceptors
Proprioceptor
Exteroceptors
Peripheral specialized nerve endings of afferent neurons, which respond to environmental changes. These are associated with skin.
Non-encapsulated:
1) Free nerve endings in the epidermis, touch, and pain;
2) Merkel’s discs in the skin and buccal cavity, touch.
3) Thermoreceptors in the skin, heat, cold
Encapsulated:
1) Pacinian corpuscle: pressure, a large lamellar body found in the skin, nipples, genitalia, and tendon;
Meissner’s Corpuscle: touch and tactile, found in fingers, lips, nipples, and genitalia.
Pacinian corpuscle
Concentric lamellae of flattened cells (probably modified Schwann cells) separated by thin collagen fibers and tissue fluid. The center contains non-myelinated sensory fiber that responds to deep pressure.
Meissner corpuscle
Ovoid-appearing structure at the junction of the epidermis and dermis, probably specialized Schwann cells surrounded by delicate collagen fibers.
Proprioceptor
Muscle spindle
Golgi Tendon
Muscle Spindle
Stretch receptors within skeletal muscle that apprise the CNS about the sense of motion of muscles, joints, and tendons.
Muscle spindle showing afferent and efferent nerve fibers that make synapses with the intrafusal fibers (modified muscle fibers).
Note two types of intrafusal fibers: one with a small diameter and the other with a dilation filled with nuclei.
Muscle spindles participate in the nervous control of body posture and the coordinate action of opposing muscles.
Parts of a Muscle Spindle
Extrafusal Fibers
Intrafusal Fibers
Extrafusal Fiber
Normal skeletal muscle fibers;
Intrafusal Fibers
Modified skeletal muscle fibers that consist of nuclear bag fibers in the center and nuclear chain fibers in the periphery.
Innervation of Muscle Spindles
Type Ia
Type IIa
Type Ia of Muscle Spindles
Sensory (annulospiral endings) around the center,
Type IIa of Muscle Spindles
Sensory (flower spray endings) on either side of the annulospiral endings, gamma-efferent motor at both ends of the intrafusal fibers.
Golgi Tendon
Function as tension receptors in the tendon, composed of encapsulated collagen fibers that are supplied by type Ib sensory fibers.
It is stimulated when the muscle contracts too strenuously and the tension on the tendon increases.
Impulses from type Ib fibers then inhibit the alpha- efferent motor neuron to the muscle, thus preventing further contraction.
The sequence of events at the synapse
- Presynaptic membrane depolarization indues
- Brief opening of calcium channels
3.Calcium influx promotes exocytosis of synaptic vesicles with - Release of neurotransmitter
- Neurotransmitter reacts with receptors and
- Promotes postsynaptic membrane depolarization
- Membrane retrieval by coated vesicles
The effect of thickness of a fiber
The thicker the fiber, the thicker the myelin sheath, and the faster the conduction of nerve impulse.
Nuclei
Aggregations of nerve cell bodies within the central nervous system; examples: nuclei of cranial nerves.
Satellite Cells
Neuroglia cells associated with cell bodies in the ganglia or nuclei are called satellite cells
Locations of gray matter and white matter in the body
while gray matter (cell bodies of neurons, neuroglia cells and nerve fibers) is outside and white matter (neuroglia cells and nerve fibers) is inside in the brain, the reverse is the case in the spinal cord
Central Canal
Central canal is lined by ependymal neuroglia cells and contains cerebrospinal fluid.
Main functions of the Cerebrum
Memory, attention, perception, cognition, awareness, thought.
