Unit Four Flashcards
Functions of the Nervous System
- Regulate body activities and maintain homeostasis
- Responsible for perception, behavior, and memories
- Initiate voluntary movements
how many cranial nerves are there?
12 pairs (24)
How many spinal nerves are there?
31 pairs (62)
What are the 3 basic functions of the nervous system?
- Sensory: detects internal and external stimuli via sensory receptors
- Integrative: After receiving sensory info, it integrates and processes the info
- Motor: Information is sent out to make a motor response
What are the two subdivisions of the nervous system?
- Central nervous system: the brain and spinal cord
- Peripheral nervous system: all the nervous tissue outside the central nervous system
What are Ganglia?
Small masses of nervous tissue consisting of neuron cell bodies, located outside the brain and spinal cord
Subdivisions of the Peripheral Nervous System
- Somatic Nervous system
- Autonomic Nervous system
- Enteric Nervous System
What is the somatic nervous system?
All sensory neurons that receive info from receptors from the head, body wall, limbs and special senses and motor neurons that innervate the skeletal muscles only
(It is voluntary)
What is the autonomic nervous system?
Sensory neurons that receive info from receptors in visceral organs (stomach, lungs, etc.) and motor neurons to smooth and cardiac muscles and glands.
(it is involuntary)
What is the enteric nervous system?
All the nerves that control the digestive system
(It is involuntary)
The autonomic nervous system is subdivided into:
- Sympathetic nervous system
- Parasympathetic nervous system
What is the sympathetic nervous system?
Sends the effectors commands for “fight or flight” responses
What is the parasympathetic nervous system?
- Sends the effectors commands for the “rest and digest” responses
- Tells heart to decrease heart rate when trying to sleep
Difference between neurons and neuroglia?
Neurons are nervous cells that possess electrical excitability where neuroglia are cells that support, nourish, and protect neurons
How can action potentials travel?
Due to movement of Sodium and potassium ions
What does the sodium and potassium ions move through
through ion channels in the plasma membrane between the extracellular fluid outside neuron and cytosol inside the neuron
What connects the axon to the cell body?
Axon hillock
Where do nerve impulses arise?
The trigger zone - junction of axon hillock and initial segment
What are axon terminals?
Processes at the distal end of the axon
What are synaptic end bulbs?
Bulb-like structures at the end of axon terminals
What are Synaptic vesicles?
Membrane-enclosed sacs that contain neurotransmitters
What are multipolar neurons?
Neurons with several dendrites and one axon
Where are multipolar neurons found?
In the brain and spinal cord
What are bipolar neurons?
Have one main dendrite and one axon
Where are bipolar neurons found?
In the retina and the inner ear
What are unipolar neurons?
Where the dendrite and axon are combines forming one projection from the cell body
Where are unipolar neurons found?
In ganglia of spinal or cranial nerves
What are neuroglia?
Cells that support and nourish neurons
Difference between neuron and neuroglia?
Neuroglia cannot propagate an action potential and are able to undergo cell division to replace injured or diseased neuroglia cells
What are the 4 types of CNS neuroglia?
- Astrocytes
- Oligodendrocytes
- Microglia
- Ependymal Cells
What are the largest and most numerous of the neuroglia?
Astrocytes
Function of astrocytes?
Neuroglia that support neurons, protect, and maintain appropriate chemical environment for nerve impulses
What do astrocytes regulate?
K (potassium) and Na (sodium) ions and uptake of excess neurotransmitter
What do oligodendrocytes do?
Form and maintain the multilayered lipid and protein myelin sheath (covering around the axon)
What does the myelin sheath do?
Insulate the axon - increases the speed of the action potential conduction
What do microglia do?
Phagocytes that remove cellular debris, microbes and damaged nervous tissue
What do ependymal cells do?
Produce and circulate cerebrospinal fluid
Where are ependymal cells located?
They line the ventricles in the brain and the central canal of the spinal cord
Types of neuroglia in the peripheral nervous system?
Schwann cells and satellite cells
What do Schwann cells do?
Form myelin sheaths and participate in axon regeneration
What do satellite cells do?
Provide support and regulate the exchanges of material between the cell bodies and interstitial fluid
Myelinated vs unmyelinated neurons
Myelinated neurons have myelin sheath and conduct action potential much faster
What is neurolemma in the peripheral nervous system?
Cytoplasm and nucleus of the Schwann cell that forms the outermost layer
What are nodes of Ranvier?
Gaps in the myelin sheath along the axon
Does the central nervous system have neurolemma?
No - because the nucleus and cell body of the oligodendrocytes do not wrap around the axon
Why do axons in the CNS display little regrowth after injury?
Because there is no neurolemma
What is “white matter”
Nervous tissue that is myelinated (due to white color of myelin)
What is “gray matter”
Nervous tissue that is unmyelinated
White matter and gray matter: spinal cord versus brain
Spinal cord: White matter surrounds an inner “H” shaped core of gray matter
Brain: thin shell of gray matter surrounds the core of white matter
Types of ion channels
- Leakage channels
- voltage-gated channels
- ligand-gated channel
- mechanically-gated channel
What are leakage channels?
Randomly alternate between open and closed
Most common: K+ leakage channels
What are voltage-gated channels?
Gates open in response to a change in the membrane potential or voltage
What ion channel participates in the generation and conduction of action potentials?
Voltage-gated channels
What are ligand-gated channels?
Gates open and close in response to a specific channel stimulus
What are mechanically-gated channels?
Gates open of close in response to mechanical stimulation
Where are mechanically-gated channels found?
Receptors in the ears, internal organs or skin
What is a polarized neuron?
A membrane at rest
What is the typical value of a neuron at rest?
-70mv
What ions are abundant in the extracellular fluid?
Sodium ions and chloride
What ions are abundant in the cytosol (inside neuron)?
Potassium
What do sodium-potassium pumps help with?
Maintain resting potential by pumping out sodium as fast as it leaks in and pumping in potassium as fast as it leaks out
What voltage is needed for an action potential to generate?
-55mV
What phase is the neuron in when an action potential is formed?
depolarizing phase
What happens when a neuron reaches threshold?
- Voltage-gated Na+ channels open and Na+ rush into neuron
- Neuron becomes positive +30mV
Is neuron depolarization a positive or negative feedback?
Positive feedback - reaching threshold opens Na+ and as more Na+ channels open more Na+ enters and depolarizes even more
How does repolarizing occur?
K+ channels open slowly, so they open once Na+ close. Causing K+ out of the cell until resting potential (-70mV) is reached and K+ channels close
Are nerve impulses propagating the axon positive or negative feedback?
Positive Feedback
What is continuous conduction?
Commonly seen in unmyelinated neurons - As Na+ slows in one part of the axon it causes opening of Na+ channels in adjacent part of neuron
What is Saltatory conduction?
Happens in myelinated neurons and much faster - Na+ and K+ channels are at the nodes of Ranvier and the action potential “leaps” from node to node
Does a larger diameter of neuron increase or decrease the speed of propagation?
Increases speed
What is the fastest conducting neuron?
A-fibers - thickest in diameter and myelinated
Where are A-fiber neurons location?
- Sensory neurons that relate touch, pressure and thermal sensations
- Motor neurons that innervate skeletal muscles
Where are B-fiber neurons found?
Neurons that transmit impulses from the viscera to the Central Nervous System
What is the slowest conducting neuron?
C-fibers - smallest diameter and are unmyelinated
Where are C-fiber neurons found?
Neurons that conduct sensory impulses for pain
Presynaptic neuron versus postsynaptic neuron
Presynaptic neuron: Neuron sending the signal
Postsynaptic neuron: Neuron receiving the signal
What is a chemical synapse?
When a synapse requires the release of neurotransmitters across the synaptic cleft to transmit the impulse
Steps for chemical synapse:
- Impulse arrives at the synaptic end bulb of presynaptic axon
- Impulse depolarizes the membrane of synaptic end bulb. Opening Ca+ channels and Ca+ from extracellular fluid goes into synaptic end bulb
- Ca+ triggers exocytosis of synaptic vesicles
- Neurotransmitter diffuses across the cleft and attach to receptors
- The channels open causing influx of Na+
- Na+ depolarizes the postsynaptic membrane
- Action potential is triggered when the postsynaptic membrane reaches threshold (-55mV)
Ways the neurotransmitter is remove after chemical synapse.
- Diffusion: diffuse out and away from synaptic cleft
- Enzymatic degradation: They get broken down by enzymes
- Reuptake: They are pumped back into the synaptic end bulbs to be recycles and placed in new synaptic vesicles
What do SSRI’s do?
Fight depression by selectively blocking the reuptake of serotonin
Most common neurotransmitter
ACh - Acetylcholine
Regeneration: Central nervous system versus peripheral nervous system
CNS - little to no repair occurs due to absence of Schwann cells
PNS - replication and repair can occur if the cell body remains intact and Schwann cells remain active
What happens when a PNS axon is damaged
- Chromatolysis (Nissl bodies break up into granular masses)
- Wallerian degeneration (myelin sheath degenerates but the neurolemma remains)
- RNA and proteins synthesizes and macrophages clear damaged old tissue. Schwann cells undergo mitosis and form regeneration tube and new myelin sheath
What causes multiple sclerosis?
Progressive destruction of myelin sheaths of neurons in CNS
What is Multiple Sclerosis?
Autoimmune disease caused by genetics or virus infection, where body’s immune system attacks the myelin sheaths
What causes epilepsy?
Short, recurrent attacks of seizures initiated by millions of electrical discharges of neurons in the brain
What are the strongest of the meninges?
Dura mater
Where are anesthetics injected for an epidural?
The epidural space - between dura mater and vertebral cavity walls
What space contains interstitial fluid?
Subdural space - between arachnoid mater and dura mater
What space contains the cerebrospinal fluid?
subarachnoid space - between arachnoid mater and pia mater
Where is the needle inserted during spinal taps?
subarachnoid space
Where does the spinal cord extend from?
Medulla oblongata
What are the 2 enlargements of the spinal cord?
- Cervical enlargement (around C4 - T1)
- Lumbar enlargement (around T9 - T12)
What is the cauda equina?
Spinal nerves that extend below the conus medularis
How many pairs of spinal nerves are there?
31 Total:
- 8 Cervical
- 12 Thoracic
- 5 Lumbar
- 5 Sacral
- 1 Coccygeal
What does the posterior root contain?
Sensory axons
What does the anterior root contain?
Motor neurons
12-13 spinal cord
