Nervous Tissue Flashcards
Functions of the nervous system
-Sensory (input)
-Process (integrate)
-Motor (output)
*fast acting, major controller and integrator of the body
*two things you can output to (muscle and /or gland)
Divisions of the nervous system
CNS (central nervous system)
- Brain and spinal cord
PNS (peripheral nervous system)
-somatic nervous system and autonomic nervous system
afferent (sensory)
nerve fibers that convey impulses to the CNS from sensory receptors in the body
efferent (motor)
conducts impulses from the CNS to effector organs (muscle and glands)
-bring about a motor response
-cell body located in the CNS
central nervous system
-consist of brain and spinal cord
-is the integrating and control center of the nervous system
-interprets sensory input and dictates motor output
-there are no nerves in the CNS all in the PNS
somatic nervous system
-somatic nerve fibers connect impulses from the CNS to the skeletal muscles
-voluntary system (consciously control our skeletal muscles)
autonomic nervous system
-composed of motor nerve fibers that regulate the activity of smooth muscle, cardiac muscle, and glands
-involuntary system (we cannot control this)
-ex: pumping of our heart, movement of food
glial cells
-these are supporting cells located in the CNS, they act as the glue
-these are non-excitable cells
What is the general function of glial cells?
support and maintain neurons
Oligodendrocyte
-composes myelin sheath in CNS, no regeneration
astrocyte
-star shaped cells, in between neurons and blood vessels. Numerous and support and brace neurons anchoring them to blood supply
microglia
-act like white blood cells, when microorganisms are invading they are present, turn into a macrophage
Where are cut fibers permanently damaged?
- in the CNS, they can be saved in the PNS
What are the three basic parts of a neuron?
- body
- Dendrites
- Axon
Neuron general function
-generates and conducts nerve impulses
-contains no centrioles so they are amitotic in nature ( meaning they do not undergo mitosis)
-once destroyed cannot be made again
Structure of a motor neuron contains?
- cell body
- dendrites
- axon
- nissl body
- neurofibrils
- axoplasm
7.axolemma - axon collateral (s)
- telodendrion (terminal branches)
- myelin sheath (Schwann cells)
- node of Ranvier
- neurilemma
*motor neurons are efferent neuron
cell body
the biosynthetic and metabolic center (lots of mitochondria)
dendrites
-short, branching neuron process that serves as a receptor or input region to receive synaptic inputs, from axon or others neurons
axon
long process carrying impulse away from the cell body, the conducting and generating portion of a nerve cell
-made from axon hillocks
Nissl body
-similar to the rough ER, they are protein synthesizers
neurofibrils
-part of the cytoskeleton, maintains shape
-also help transport neurotransmitters
axoplasm
cytoplasm within the axon
axolemma
plasma membrane of axon
axon collateral (s)
right angle branches
-are rare
telodendria (terminal branches)
branching ends of an axon, can have hundreds of these and they hold neurotransmitters
neurotransmitters
chemicals in the brain
myelin sheath (schwann cells)
fatty insulating sheath that surrounds all but the smallest nerve fibers
Schwann cells
-form the myelin sheath, located in the PNS
node of Ranvier
-break in the myelin sheath
neurilemma
outer wrap of myelin sheath
axon terminals
-located at the end of branching ends and contain neurotransmitters
-can make more of these by learning
-bulbous ends
When is an impulse officially called an impulse?
-when it gets to the axon
Salatatory conduction
-happens in myelin sheath, when impulses jump across myelin from node to node to help speed up conduction
Functional classification of neurons
-direction in which impulses are conducted
sensory (afferent) neurons
-can be bipolar or unipolar
-transmit impulses from some receptor (skin, sense, organs, viscera) to the CNS
-cell body located in the PNS
bipolar neuron
- 1 dendrite and 1 axon
-this is a sensory neuron
unipolar neuron
A unipolar neuron has one axon which extends into dendrites
-this is a sensory neuron
Association neurons
-an example are interneurons, connector neurons
-most of the neurons in the system are this
-conduct impulses within the CNS
- connect INPUT to an OUTPUT
motor (efferent) neuron
-multipolar
-transmit impulses away from CNS to effector
-the body of a motor neuron is in the CNS
Structural classification of neurons basis
number of processes extending from the cell body
Multipolar neurons
many dendrites with one axon
Nerve description
- bundle of nerve fibers (axons) in PNS
Nerve location and type
Spinal Nerves: located in the spinal cord
Cranial Nerves: arises from the brain
Sensory nerve
conduct impulses towards the CNS (made from sensory neurons)
motor nerve
conduct impulses away from the CNS (made from motor neuron)
mixed neuron
-ALL SPINAL NERVES ARE MIXED
-conducts impulses toward and away from the CNS (made from both sensory and motor neurons)
Epineurium
-connective tissue covering the entire nerve
Perineurium (fascicles)
-connective tissue that divides nerves into smaller bundles of nerves
-made of DFCT
endoneurium
-connective tissue surrounding each nerve fiber which is LFCT
Example of ion channels (3 types of doorways)
- leakage channel (diffusion)
- chemically (ligand) gated channel (based neuron transmitters)
- Voltage gated channel (based on mv)
Physiology of a nerve impulse
- Transmission along a neuron
- Formation of an Action Potential (an impulse)
- Repolarization
A resting neuron
- Polarized (different charge on either side of membrane, positive outside, negative inside)
2.Na and K pump ( 3 sodium out, 2 potassium in)(sodium is in excess outside and potassium excess inside)
- many - ions inside cell (charged proteins to large to exit cell)
*conditions of a resting neuron needs these to be ready for potential
Na and K pumps open and close depending on voltage
Formation of an action potential (an impulse)
- threshold stimulus changes permeability of membrane to Na (Na channel opens) (weakest stimulus capable of getting a response)
- Na rushes into cell–> membrane begins to depolarize (decrease in membrane potential)
- as even more Na rushes in there is a momentary reversal in polarity
- This local event causes the collapse of resting potential in the adjacent area of the membrane
- depolarization spreads like a chain reaction down the length of the membrane to the end of the axon
Impulse
-a wave of depolarization that travels down the neuron
What principle does an action potential follow
-all or nothing principal
goes from -70 mv –> 0 –> +30 mv (closes Na channel and opens K+ channel)
Repolarization
-return to the resting state
1. part of membrane over which impulse has passed begins to repolarize
2. Na channels close
3. K even leaks out to restore a (+) charge outside
4. the Na and K pumps work to reestablish the original distribution of Na and K ions
refractory period
-period following stimulation when no additional actional potential can be made
What contributes to the speed of impulse
- myelin
- thickness of fibers
synapse
transmits impulses between neurons
presynaptic neuron
-1st neuron at a synapse releases neurotransmitters (AXON)
synaptic gap
- neurotransmitter released into a gap
-junction between two neurons
postsynaptic neuron
2nd neuron at a synapse, that receives neurotransmitters (DENDRITES)
neurotransmitter substances description
-chemical messenger released by neurons stored in axon terminals
Which neuron at a synapse releases he neurotransmitter substance
presynaptic neuron
What effect does the neurotransmitter substance have on the postsynaptic neuron?
- excitatory , open Na pump
- inhibitory hard to open Na pump (add to negativity)
excitatory neurotransmitters
-threshold is lowered, neurotransmitter increase membrane permeability to Na+ –> norepinephrine
ex: serotonin, dopamine, noradrenaline
inhibitory neurotransmitters
-threshold is raised, neurotransmitters causes a decrease in membrane permeability Na+–> GABA
what effect does the postsynaptic neuron have on the nerotransmitter
-releases enzyme to destroy neurotransmitters (clears the gap)
why is transmission of an impulse in one direction only
-only axons store and release neurotransmitters
synaptic fatgue
-overstimulation “runs out” of neurotransmitter
What was the first neurotransmitter
acetylcholine
