Nervous system chapter videos Flashcards
What are the two structural divisions of the nervous system?
- Central Nervous system
- Peripheral nervous system
How are they functionally organized?
Sensory
Somatic sensory: skin, ears, etc,
Visceral blood: vessels or organs
Motor
Somatic Motor: going towards muscles
Autonomic: going to involuntary organs ex, heart
What are the two types of cells in the nervous tissue?
Nerouns
- A basic structural unit of the nervous system
- excitable cells that transmit electrical system
Glial cells
- Nonexcitable cells that primarily support and protect neurons
What are the special characteristics of the neuron?
- Live long 100 years or more
- Amitotic (don’t divide)
- High metabolic rate (depends on a continuous supply of oxygen and glucose)
- Plasma membrane
What is the function of the plasma membrane
- Used for electrical signaling (excitable and conductivity)
- Cell-to-cell interactions during the development
- Secretion
Components of the neuron
(Cell body)
- Enclosed by plasma membrane
- Contains cytoplasm surrounding the nucleus
- Neurons control center
- Conducts electrical signal to axon
- Perikaryon, cytoplasm within the cell
Components of the neuron
(Dendrites)
- Short process branching off the cell body
- May have one or many
- Receive input and transfer it to the cell body
- More dendrites = more input possible
Components of the neuron
(Axon)
- longer process emanating from the cell body
- makes contact with other neurons, muscle cells, or glands
- first part, a triangular region, axon hillock
- cytoplasm here termed axoplasm
- plasma membrane here termed axolemma
- gives rise to side branches, axon collaterals
- at extreme tips, expanded regions, synaptic knobs
- knobs containing numerous synaptic vesicles
- contain neurotransmitter
What are the different types of neurons?
Multipolar Neuron - Multiple nerve processes extend directly from the cell body: typically many dendrites and one axon
Bipolar Neuron - Two nerve cell processes extend directly from the cell body; one dendrite and one axon
Unipolar Neuron - A single short cell process extends directly from the cell and looks like a T as a result of the fusion of two processes into one long axon
Anaxonic Neuron - Nerve cell processes are only dendrites; no axon present
What is Bidirectional axonal transport?
- Bidirectional axonal transport
- Axons dependent on cell body
- for newly synthesized materials
- for breakdown of used materials
- Anterograde transport
- movement of materials from cell body to synaptic knobs
- Retrograde transport
- movement of materials from synaptic knobs to cell body
Where do sensory neurons send signals to?
Spinal cord
Where do motor neurons send signals to?
Receive information and send it to the infector like a muscle.
What is the function of interneurons?
They do the integration
What is a nerve?
- A bundle of axons
- Epineurum surronds the nerve
- Perinerium surrounds the facile
- Endonerium surrounds bundles of axons
- contains both motor or sensory neruns
What are the classifications of nerves?
Cranial Nerves
- extend from the brain
Spinal Nerves
- extend from the spinal cord
Sensory nerves
- Contain only sensory nerves
Motor nerves
- Contain only motor nerves
Mixed nerves
- Contain both sensory and motor nerves
- most named nerve in this category
- individual neurons transmitting one type of information
What is a synapse?
A junction that mediates information transfer from one neuron:
- To another neuron, or
- To an effector cell
What is a Presynaptic neuron?
Presynaptic neuron-conducts impulses toward the synapse
What is a Postsynaptic neuron?
Postsynaptic neuron—transmits impulses away from the synapse.
What is an Electrical synapse?
- Much less common
- Presynaptic and postsynaptic neuron physically bound together
- Gap junctions present
- No delay in passing electrical signal
- In limited regions of brain and eyes
What is Chemical synapse
- Most common
- Composed of presynaptic neuron, signal producer
- Composed of postsynaptic neuron, signal receiver
- Between axon and any portion of the postsynaptic neuron
- most commonly with a dendrite
- Knob almost touches the postsynaptic neuron
- narrow fluid filled gap, the synaptic cleft
Chemical synapses transmit signals from one neuron to another using neurotransmitters. Steps
- Action potential arrives at the axon terminal.
- Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal.
- ca2+ entry causes neurotransmitter - contains synaptic vesicles that release their contents through exocytosis.
- Neurotransmitter
dilutes across the synaptic deft and binds to specific receptors on the
postsynaptic membrane.
What is Astrocytes?
- Most abundant, versatile, and highly branched glial cells
- Cling to neurons, synaptic endings, and capillaries
- Support and brace neurons
- Help determine capillary permeability
- Guide migration of young neurons
- Control the chemical environment
- Participate in information processing in the brain
Microglia
- Small, ovoid cells with thorny processes
- Migrate toward injured neurons
- Phagocytize microorganisms and neuronal debris
Ependymal Cells
- Range in shape from squamous to columnar
- May be ciliated
- Line the central cavities of the brain and spinal column
— Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities
What two types of glial cells do the peripheral nervous system have?
- Satilite cells - wrap around the cell body
- Shwan cells - wrap around the axon
What are Oligodendrocytes?
- Branched cells
- Processes wrap CNS nerve fibers, forming insulating myelin sheaths
If a person suffers from meningitis (an inflammation of the coverings around the brain), which type of glial cell usually replicates in response to the infection?
Microglia are going to phagocytize the infection.
Which specific type of glial cell ensheathes axons in the PNS?
Neurolemmocytes (Schwann cells)
What is the function of myelin shealth
The segmented protein-lipoid sheath around most long or large-diameter axons
* It functions to:
- Protect and electrically insulate the axon
- Increase speed of nerve impulse transmission
Process of the formation of myelin sheath
Schwann cells wraps many times around the axon
- Myelin sheath-concentric layers of Schwann cell membrane
Neurilemma-peripheral bulge of
Schwann cell cytoplasm
* Nodes of Ranvier
- Myelin sheath gaps between adjacent Schwann cells
- Sites where axon collaterals can emerge
Unmyelinated axons
- Associated with neurolemmocytes
- No myelin sheath covers them
- Axon in depressed portion of neurolemmocyte
- Not wrapped in repeated layers
- In CNS,
- unmyelinated axons not associated with oligodendrocytes
What is the function of the myelin sheath?
The myelin sheath provides a protective insulating covering around the axon. It prevents the passage of ions through the axonal membrane and allows for faster action potential propagation.
Axon Regeneration process
- Trauma severs axon.
- The proximal portion of each severed axon seals off and swells. The distal portion of axon and myelin sheath disintegrate; the neurilemma survives.
- Neurilemma and endoneurium form a regeneration tube.
- Axon regenerates, and remyelination occurs.
- Innervation to effector is restored.
Axon Regeneration
Factors influencing axon regeneration
- PNS axons
* vulnerable to cuts, trauma
- Regeneration possible if
* cell body intact
* enough neurilemma remains
- Regeneration success more likely if
* amount of damage less extensive
* smaller distance between site of damage and structure it innervates
Role of Membrane lon Channels
- Proteins serve as membrane ion channels
- Two main types of ion channels
1. Leakage (nongated) channels-always open
2. Gated channels (three types): - Chemically gated (ligand-gated) channels open with the binding of a specific neurotransmitter
- Voltage-gated channels—open and close in response to changes in membrane potential
- Mechanically gated channels open and close in response to the physical deformation of receptors
Pumps
- Type of transport protein
- Move substances against a concentration gradient
- Require energy
- e.g., sodium-potassium and calcium pumps in plasma membrane
Channels
Move substances down a concentration gradient
- Leak channels
* always open for continuous diffusion
*, e.g., sodium ion and potassium ion channels
What is the purpose of chemically gated channels
Chemically gated channels
* Only open when ligand binds to it.
* normally closed
* allow specific type of ion to diffuse when open
* e.g., chemically gated K* channels
What are the Functions of voltage-gated channels?
Voltage-gated channels
* normally closed
* open in response to changes in electrical charge across membrane
* allow specific type of ion to diffuse
* e.g., voltage gated Nat channels
Where are the channels located on neuron cells?
Chemically gated channels are located on dendrites or cell bodies
Voltage-gated channels are found on axons. Also, between myelin sheath.
Calcium channels found at the terminal
What is the difference between a chemically gated channel and a voltage-gated channel in terms of how they function?
Chemically gated channels open in response to the binding of a neurotransmitter.
Distribution of substances inside and outside neuron
Essential for neuron function
- More prevalent within cytosol
* negatively charged phosphate ions (e.g., in ATP)
* negatively charged proteins
* K+
- More prevalent in interstitial fluid
* Nat
* Cl
Movement of substances and membrane potentials
- Ions able to pass through membranes by transporting proteins
- Phosphate-containing molecules and proteins
- generally restricted from crossing
- Net movement dependent on the electrochemical gradient
- combination of the electrical and chemical gradient
What is an electric gradient charge starting point?
Inside relatively negative
outside relatively positive
Chemical concentration gradient
unequal distribution between two areas
* each substance with own chemical concentration gradient
* e.g., Kt with a higher concentration inside the neuron
* e.g., Nat with a higher concentration outside the neuron
What is an electrical gradient? What is a chemical gradient?
An electrical gradient is a difference in electrical charge between two areas.
A chemical gradient is an unequal distribution of a substance between two areas.
Neuron Function
- Neurons are highly irritable
- Respond to adequate stimulus by generating an action potential (nerve impulse)
- Impulse is always the same regardless of stimulus
