Anatomy Chapter 11- Fundamentals of the Nervous System and Nervous Tissue Flashcards
Nervous System Functions
- Sensory Input- Monitor changes that occur inside and outside the body
- Integration- process and interpret information
- Motor output- response is carried out
Components of the Nervous System
- Central Nervous System
- Peripheral Nervous System
Central Nervous System
Brain and Spinal Cord
Function- Responsible of interpreting sensory input and deciding motor output
Peripheral Nervous System
Nerves that extend from the CNS to the rest of the body
Function- info can be sent between the CNS to the rest of the body
Neurons
nerve cells that can respond to stimuli & transmit electrical signals
Highly specialized
Neuroglia
Glial cells
Provide support and maintenance to neurons
Astrocytes
Most abundant, support and protect neurons in the CNS
Functions of Astrocytes
- Provide nutrient supply for neuron cells
- Allows migration of young neurons
- “Clean up” outside neuron cells
Microglial Cells
CNS
1. Contact nearby neuron cells to monitor neuron health
2. Migrate toward injured neurons and transform into a macrophage and phagocytize the neuron
Ependymal Cells
CNS
Usually have cilia
Function- Lines central cavities of the CNS to circulate cerebrospinal fluid within cavities
Satallite cells
PNS
Support and protect cells
Oligodendrocytes and Schwann Cells
CNS and PNS, respectively
Function- Myelin sheat creates an insulating covering for neurons
Neurons
Cells of the nervous system specialized to generate or transmit electrical signals
Nerve impulses
electrical signals
The general structure of a neuron
- Cell body
- Dendrites
- Axons
- Myelin Sheaths
Cell Body of a Neuron
Portion of the cell containing the nucleus
Function- plasma membrane can receive information from the surrounding neurons
Dendrites
Main receptive region of a neuron
Axon
Single, long “nerve fiber” extending from the cell body
The axon is the conducting region of the neuron
Tracts
Bundles of axons in the CNS
Nerves
Bundles of axons in the PNS
Axon terminal
Where neurotransmitters are released to pass the impulse to the next neuron
Myelin Sheaths
Protects and electrically insulate long and/or large nerve fibers to increase speed at which impulses are transmitted
Myelin Sheath Gaps
Region of axon that is “exposed” due to absence of Schwann cell covering
Sensory neuron
Afferent neurons transmit signals from the body to the CNS
Motor neuron
Efferent neuron transmits motor response from the CNS to the rest of the body
Interneuron
Lie between sensory and motor neurons
Resting membrane potential
-70 mV
Leakage channels
Nongated
Allow free low of ions across the channel
Gated proteins
Part of the protein forms a gate that mus the opened before ions can move
Types of gated proteins
- Chemically
- Voltage
- Mechanically
Chemically gated
Only open when a certain chemcial binds to protein
Voltage-gated
Open and close in response to changing membrane potentials
Mechanically gated
Open in response to physical deformation of receptor
Depolarization
Decreases in membrane potential
Inside becomes less negative than resting potential
More likely to send a message (excitation)
Hyperpolarization
Increase in membrane potential
The inside of the membrane becomes more negative than the resting potential
Less likely to send a message
Graded potentials
Occur over short distances
Necessary to initiate an action potential
Graded
Magnitude varies directly with stimulus strength
Action potentials
A very brief reversal of membrane potential
-70 mV to +30 mV
Trigger point
Action potentials originate at the beginning of axon arising from cell body
Activation gate
Voltage-sensitive, opens at depolarization
Inactivation Gate
Blocks chanel to prevent Na+ movement
K+ gate
- All voltage-gated channels are closed at the resting state (-70 mV)
- Depolarization: voltage-gated Na+ channels open at the axon
- Repolarization- Where action potential ends
- Hyperpolarization: excess K+ leaves cell
Refractory Period
A period of time in which a second Action potential cannot be generated at an axon
Absolute Refractory period
Cannot begin an action potential
Importance-
Ensures each action potential is a separate event
Enforces 1 was transmission
Relative refractory period
occurs after the absolute refractory period
only strong stimulus can stimulate an Action potential due to hyperpolarization
Conduction Speed is based on…
Axon Diameter
Degree of Myelination
Axon Diameter
Larger axon = faster conduction
Degree of myelination
More myelination = faster conduction
Types of conduction
- Continuous conduction
- Saltatory conduction
Continuous conduction
Propogation in unmyelinated fibers
Saltatory conduction
Propagation in myelinated fibers
Synapse
Junction between two neurons that sends information from one neuron to thenext
Presynaptic neurons
Conduct impulses toward the synapse
Sending info
Postsynaptic neurons
Conduct signal away from the synapse
receiving info
Synaptic cleft
Fluid filled space
Transmission of action potentials from one neuron to another- chemical synapses
1) Action potential arrives at axon terminal of presynaptic neuron
2) Voltage-gated Ca2+ channels in terminal open in response to AP
3) Synaptic vesicles in axon terminal fuse with membrane in response to Ca2+ influx
4) Neurotransmitter crosses cleft, binds to proteins on postsynaptic neuron
5) Neurotransmitter binds receptors on the postsynaptic neuron membrane (proteins - causes the message to be received)
6) Neurotransmitter in synaptic cleft is disposed of
Neurotransmitter disposal process
- Reuptake- presynaptic neuron or astrocyte takes neurotransmitter
- Degradation- breaking it down by enzymes
- Diffusion- Leaves bc its too far away from postsynaptic neuron
Neurotransmitter disposal process
- Reuptake- presynaptic neuron or astrocyte takes neurotransmitter
- Degradation- breaking it down by enzymes
- Diffusion- Leaves bc its too far away from the postsynaptic neuron
Postsynaptic Potentials
The temporary change in membrane potential of the postsynaptic neuron
Excitatory Postsynaptic potential
Binding of neurotransmitter causes the membrane to depolarize
Temporal summation
The postsynaptic neuron receives multiple EPSPs in rapid-fire order
Spatial summation
Postsynaptic neurons receive multiple EPSPs at the same time
Inhibitory postsynaptic potential
Binding of neurotransmitter causes the membrane to hyperpolarize
Neurotransmitters
Chemical signals produced in the cell body and is transported to the axon terminal
Channel-linked receptors
Mediate fast synaptic transmission
Ligand gated ion channels that opens
G Protein Coupled receptors
- Neurotransmitter binds in the postsynaptic membrane
- G protein activated inside the neuron
- G protein activates adenylate cyclase
- adenylate cyclase produces cyclic AMP
