lab exam 3 Flashcards
Two divisions of the nervous system
Central nervous system (CNS)
Peripheral nervous system(PNS)
Central Nervous System
Consists of the brain and the spinal cord; located in the dorsal body cavity surrounded by meninges.
Peripheral nervous system
consists
of the all neural structures outside the CNS
including the cranial nerves, spinal nerves,
ganglia and sensory receptors
Composition of nervous tissue
The Nervous System is composed mainly
of Nervous Tissue; connective tissue and
blood vessels are also present.
The nervous tissue is composed of 2 types of cells:
-Neurons
-supporting cells
Neurons
(nerve cells) are conducting cells because they generate electrical signals
supporting cells (neuroglia)
are non-conducting cells because they do not typically generate electrical signals.
cell body (soma or perikaryon)
Contains the nucleus and all
other cytoplasmic organelles
EXCEPT CENTRIOLES
hence, neurons are generally
AMITOTIC
Contains well-developed rough
ER called Nissl Body or
Chromatophilic
substance; prominent nucleoli;
they indicate a neuron is a of a
secretory cell –
neurotransmitter from the axon
terminals. Neurotransmitters
are synthesized in the cell
body hence referred to as the
“BIOSYNTHETIC region” a
neuron
Axon
A single process extending from
the cell body – each neuron can
have only one axon; uniform
diameter; unmyelinated or
myelinated
Generates and transmits action
potentials AWAY from the cell body
hence, known as the
“CONDUCTING region” of a
neuron
Branches at the end into telodendria
which end in bulbous ends called
axon terminals (=synaptic
knobs=boutons) – store and release
neurotransmitter hence the axon
terminals are referred to as the
“secretory region” of a neuron
dendrites
Tapering processes that act as the “RECEPTIVE regions” of a neuron
Receive and convey electrical signals toward the cell body.
two ways to classify neurons
structural and functional
3 structural classifications of neurons
based on the number of processes extending from the cell body of the neuron
multipolar neuron
has at least 3 processes – one axon and at least
2 dendrites; most abundant neuron in the human body
Bipolar neurons
has 2 processes – one axon and one dendrite.
pseudo unipolar neuron
has one short process extending from the
cell body that bifurcates into a central process and a peripheral
process.
Sensory or afferent neuron
transmits impulses from sensory receptors TOWARD the CNS
association neurons or interneurons
located in the
CNS between the sensory
neurons and the motor neurons
– Most of the neurons (99%) in the body are association
neurons.
motor or efferent neuron
transmits
impulses AWAY from the CNS to effector organs = glands, organs
nucleus
a cluster of neuron cell bodies in the
CNS
Ganglion
a cluster of neuron cell bodies in the
PNS
Nerve
a bundle of axons in the PNS
tract
a bundle of axons in the CNS
axolemma
The plasma membrane of an axon is called an
axolemma.
ENDONEURIUM
Each axon is wrapped in a delicate connective
tissue membrane called ENDONEURIUM
A bundle of endoneurium-covered axons is
called a fascicle
Perineurium
Each fascicle is covered by the coarse
connective tissue membrane called the
PERINEURIUM
epineurium
A bundle of perineurium-covered fascicles form
the nerve or a tract which is covered in a tough
connective tissue membrane called the
EPINEURIUM
4 supporting cells inside the CNS
– Astrocytes
– Microglia
– Ependymal cells
– Oligodendrocytes
2 supporting cells are located inside the PNS.
– Schwann cells
– Satellite cells
microglia
Since the specific immune system does not have access to the
CNS; the microglia are phagocytes to engulf/destroy
pathogens and cell debris.
astrocytes
– Most abundant
– Numerous extensions that wrap around neurons
– Involved in forming the BLOOD-BRAIN BARRIER, a selective
barrier that regulate the chemicals environment of the brain
– Regulate brain function
ependymal cells
Ciliated columnar cells that line the ventricles – cavities in the brain that contain cerebrospinal fluid (CSF)
– Currents created by beating of cilia circulate the CSF
Oligodendrocytes
Their extensions myelinate axons of neurons in the CNS
Schwann cells
Schwann cells = neurolemmocytes
– Myelinate axons of neurons in the PNS
satellite cells
Surround cell bodies of neurons to control their
chemical environment
function of myelin sheath
Protection- physical
protection against trauma
1. Electrical insulation - to
prevent interference from
neighboring axons in a nerve
(if in the PNS) or tract (if in
the CNS)
2.) Increase in the rate of
impulse transmission – using
saltatory conduction occurring
only at the nodes of Ranvier
Severed axons in the PNS can regenerate because
When the axon is severed in the PNS, cells of the immune
system clean up the damaged area of cell debris, a process
known as debridement, which sets the stage for regeneration
– The neurilemma of the Schwann cell forms a REGENERATION
TUBE that guides regeneration of the severed axon
severed axon in the CNS fail to regenerate because
The microglia poorly clean up area of damage – debridement is
not complete
– No neurilemma to form a regeneration tube to guide growth of
severed axon
– Presence of growth-inhibiting proteins in the CNS inhibit
regeneration of a severed axon
the resting membrane potential (RMP)
-70mV to -90mV
Neurophysiology
Generation of Action Potential (AP)
1 phase: depolarization phase
entry of sodium ions (Na+) into
axon referred to as sodium influx makes membrane potential less and
less negative
When the Threshold Potential (-55mV) is reached, an action
potential develops when the threshold potential is
reached. AP is an all-or-none phenomenon
Upshoot or spike due to an explosive entry of Sodium ions = a
positive membrane potential is reached +30mV, the peak
2 phase: repolarization phase
2 events occur at the peak:
(i) sodium channels close (Na+ influx halts)
(ii) potassium channels open (K+ efflux begins) and potassium ions
(K+) rush out of the axon referred to as potassium efflux; this results in
reversal of the membrane potential toward a negative membrane potential
3 phase: hyperpolarization
more K+ efflux occurs
past the RMP driving the membrane potential below the RMP
(RMP is restored by the Na+/K+ pump which pumps 3 Na+ out and 2 K+ in
All or none phenomenon
an action potential will be generated if
depolarization reaches a threshold potential
SELF PRPAGATING
once generated by the axon, it is propagated
down the axon to the axonal terminals; a propagated or transmitted
action potential is called a nerve IMPULSE
All action potentials traced have the same shape and the SAME
amplitude (+30mV) irrespective of stimulus strength
All action potentials traced have the same shape and the SAME
amplitude (+30mV) irrespective of stimulus strength. Thus, the
difference between a stronger stimulus that causes the generation of
an action potential and a weaker stimulus that causes the
generation of an action potential is that the stronger stimulus causes
the impulse to be generated at a higher frequency than the weaker
stimulus