2.1 Histology of Nervous Tissue Flashcards
Central Nervous System
Brain and Spinal Cord; contains 85 billlion neurons
Peripheral Nervous System
All nerves outside CNS; include nerves, ganglia, enteric plexuses, and sensory receptors
Nerve
A bundle of 100-1000 axons + associated connective tissue and blood vessels
Pairs of Cranial Nerves;
Spinal nerves?
12;
31
Ganglia
small masses of nervous tissue located outside the CNS; consists primarily of neuron cell bodies
Enteric plexuses
network of neurons located in the GI walls
Sensory receptor
monitors changes in external and internal env
PNS is divided into:
Somatic nervous system (SNS)
Autonomic nervous system (ANS)
Enteric nervous system (ENS)
SNS consists of:
sensory neurons - convey info to CNS from somatic receptors
motor neurons - conduct impulses for CNS to skeletal muscles only
ANS consists of
sensory nueron - convey info to CNS from autonomic sensory receptors
motor nuerons - conduct nerve impulses from CNS to smooth muscle, cardiac muscle, and glands
Note: it is usually involuntary
Motor part of ANS
Sympathetic division
Parasympathetic division
Functions of the nervous system
Sensory: detect internal stimuli
Integrative: process sensory info
Motor: may elicit appropriate response by activating effectors
Two types of cells in nervous tisse
Neurons and Neuroglia
Neuroglia
support, nourish, and protects neurons, and maintains the interstitial fluid that bathes them
smaller than neurons, but greatly outnumber them
Electrical Excitability
The ability to respond to a stimulus and convert it into an action potential
Stimulus
any change in the env that is strong enough to start an action potential
Action Potential / Nerve Impulse
electrical signal; propagates along the surface of the neuron membrane;
travels rapidly at constant strength
Parts of a nueron
Cell body, dendrites, and an axon
Cell body / Perikaryon / Soma
contains a nucleus surrounded by cytoplasm that includes typical cellular organelles
Nissl bodies
sites of protein synthesis
used to replace cellular components of neurons and to regenerate damaged axon
neurofibrils
provide cell shape and support
made of bundles of intermediate filaments
Microtubules
moves materials between cell body and axon
Lipofuscin
A product of neuronal lysosomes that accumulates as the neuron ages, but does not harm the neuron
Nerve fiberPikac
general term for any neural extension that emerges from a its cell body
Two kinds of processes: an axon or many dendrites
Dendrites
receiving or input portions of a neuron
its plasma membrane contains many receptor sites for binding chemical messengers
usually short, tapering, and highly branches
Axon
propagates nerve impulses towards another neuron, muscle fiber, or gland cell
contains mitochondira, microtubules, neurofibrils, but no Rough ER so no protein synthesis
Axon hillock
cone-shaped elevation where the axon joins the cell body
Initial segment
part of the axon closest to the axon hillock
Trigger zone
area where the nerve impulses arise at the junction of the axon hillock and the initial segme3nt
Axoplasm and Axolemma
Cytoplasm of an axon;
Plasma membrane of axon
Axon collaterals
side branches along the length of an axon
axon terminal / axon telodendria
fine processes in which the axon and its collaterals divide into and end
synapse
site of communication between two neurons or between a neuron and an effector cell
slow axonal transport
supplies new axoplasm to developing or regenerating axons; replenishes axoplasm in growing and mature axons
conveys axoplams in one direction only; moves materials about 1-5 mm per day
Fast axonal transport
moves membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled
moves materials in both directions (200-400mm per day)
uses proteins that function as “motors”
Neuron classification acc. to structure
Multipolar neurons: several dendrites, one axon
Bipolar Neurons: one main dendrite, one axon
Unipolar neurons: dendrites and one axon are fused together; more appropriately called pseudounipolar neurons
Neuron classification acc. to function
Sensory (Afferent)
Motor (Efferent)
Interneurons
Sensory / Afferent neurons
either contain sensory receptors at their distal ends OR are located just after sensory receptors that are separate cells;
most are unipolar in structure
Motor / Efferent neurons
convey action potentials AWAY from the CNS to effectors
Multipolar in structure
Interneurons / Association neurons
mainly located within the CNS between sensory and motor neurons
most are multipolar in structure
Types of neuroglia
CNS: astrocytes, oligodendrocytes, microglia, and ependymal cells
PNS: Schwann cells and satellite cells
Astrocytes
star-shaped cells that have many processes and are the largest and most numerous of all neuroglia
Function of astrocytes
Functions:
support neurons
maintain the unique selective permeability of the endothelial cells (blood-brain barrier)
regulate the growth, migration, and interconnection among neurons in the brain
maintain chemical env for generation of nerve impulses
influences formation of neural synapse
Oligodendrocytes
look like astrocytes but are smaller and have fewer processes
forms and maintains the myelin sheath around CNS axons
Myelin sheath
multilayered lipid and protein covering around axons that insulate them and increase the speed of nerve impulse conduction
Microglial cell / Microglia
small cells with spine-like projections function as phagocytes that remove cellular debris , damaged nervous tissue, or microbes
Ependymal cells
produce, monitor and assist the circulation of cerebrospinal fluid
single layer of columnar or cuboidal cells that possess microvilli and cilia
Schwann cells
form the myelin sheath around axons; one cell can only myelinate one axon
participate in axon regeneration, easier to do in PNS than CNS
Satellite cells
provide structural support
regulate the exchanges of material between neuronal cell bodies and interstitial fluid
ganglion
cluster of neuronal cells bodies in the PNS
nucleus
cluster of neuronal cells bodies in the CNS
nerve
bundle of axons located in the PNS
tract
bundle of axons located in the CNS
White matter
composed primarily of myelinated axons
gray matter
contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals and neuroglia
