Lecture Notes: Nervous System Flashcards
central nervous system
- Integration
- Brain
- Spinal Cord
Integration
association of stimuli with output
brain
integration of homeostasis, perception, movement, intellect and emotions
spinal cord
reflexes + transmits information from skin and muscles to brain
peripheral nervous system
- sensory (afferent)- mechanoreceptors linked to the CNS
2. motor (efferent)- CNS controlling effector cells
Voluntary (somatic)
- signals to skeletal muscles in response to stimuli
- reflexes and involuntary
Autonomic
- Involuntary
- Parasympathetic and Sympathetic
Parasympathetic
activities that gain and conserve energy
-slow heart beat, stimulate digestion
Sympathetic
activities that increase expenditure of energy
Neurons
transmission of electrical/chemical signals to conduct messages
- sensory, interneurons, motor
Sensory neurons
stimulated by receptors triggered by environmental stimuli
Interneurons
receive and transmit stimuli from and to other neurons
Motor neurons
transmit impulses from CNS to effector cells
Neuroglial cells
- do not conduct impulses
- support and orient
- protection
- insulation
- maintain ionic environment
- supply nutrients
types of neuroglial cells
- schwann cells (PNS)
- ogliodendrocytes (CNS)
- Astrocytes
Ogliodendrocytes
myelin sheath; electrical insulation
increase speed of impulse propagation
astrocytes
blood-brain barrier at brain capillaries
neurons are excitable cells
- sodium potassium pump maintains a membrane potential
- neurons can change their membrane potential in response to stimuli
- selective opening of gated channels (voltage or chemical)
Action Potentials
- rapid (1-2ms) reversal in membrane potential that propagates throughout a cell membrane without changing it’s magnitude.
- APs are only produced by depolarizing stimuli
- “All or nothing principle” must reach threshold
all or nothing principle
- once a voltage threshold is reached the AP will occur
- amplitude of AP not affected by intensity of stimulus
- systems distinguishes between weak and strong stimuli based on frequency of AP
Resting Phase
- Sodium Potassium Pump
- Leak Potassium channels: always open
- Voltage-gated K+ channels: closed
- Voltage-gated Na+ channels: closed
- large negatively charged molecules remain inside
- membrane potential: about -70 mV
phases of an AP
- depolarization
- threshold
- maximum depolarization
- repolarization
- hyperpolarization
Depolarization
- Voltage-gated K+ channels: closed
- some voltage-gated Na+ channels opened
- –activation gate:open
- –inactivation gate:closed
- influx of sodium, causing membrane potential to decrease ( becomes more positive)`
Threshold
- influx of sodium causes voltage gated sodium channels to open, which then causes a membrane potential threshold to be reached
- more voltage gated sodium channels open and there is more influx of sodium
- rapid reversal in membrane potential (inside more positive than outside.
Maximum depolarization
- voltage gated sodium channels begin to close, influx of sodium decrease
a. activation gate: open
b. inactivation gate: closed - voltage gated potassium channel:open
a) slower than the voltage-gated sodium channel
Repolarization
- Voltage-gated Sodium channels: closed
a. activation gate: open
b. inactivation gate: closed - voltage-gated potassium channels: open
- membrane potential returns to resting stage
Hyperpolarization
- voltage gated sodium channels:closed
a. activation gate: closed
b. inactivation gate: open - voltage gated potassium channels: open
- membrane potential becomes more negative than resting potential
- ends when voltage gated potassium channels close and cell returns to resting potential
Refractory period
- allow AP to travel in one direction
- ensure that depolarization and repolarization are completed before new AP
- prevents prolonged depolarization of the membrane
Absolute (refractory period)
- beginning of depolarization until shortly after repolarization is completed
- once an AP starts
- while voltage gated sodium channels are closed
a. activation gate: open
b. inactivation gate: closed - new AP is not possible
relative (refractory period)
- during hyper polarization
- a stronger-than-threshold depolarizing stimulus is needed to produce an AP
propagation of Action Potential
- strong depolarization of one area, depolarization above threshold in neighboring areas because sodium diffuses inside the axon
- AP is regenerated at each new position along the membrane
- AP moves in only one direction b/c refractory period
speed ( in relation to AP)
increased diameter of axon, less resistance to the diffusion of sodium and increased speed
saltatory conduction
- ions cannot cross the myelinated regions of axon
- ion channels are concentrated at nodes of Ranvier
- AP “jumps” between myelinated regions from one of ranvier to the next
synapse
junction between the pre-synaptic cell and a post synaptic cell
synaptic cleft
space between pre-synaptic membrane and post-synaptic membrane
electrical synapses
- direct transmission via gap junction with connections (protein tunnels)
- fast
- AP can travel in both directions
- no summation of inputs
- do not allow for large numbers of synaptic inputs
- little plasticity
chemical synapses
better at integration of information
transmission at chemical synapses
- neurotransmitter is synthesized and packaged into vesicles at axon terminal
- Ap arrives at presynaptic terminal, depolarization, gated calcium channels open, influx of calcium
- acetylcholine vesicles fuse to membrane ane neurotransmitters are releases into synaptic cleft
- neurotransmitter binds to receptor in postsynaptic membrane
a) depolarization: excitatory, open sodium channels
b) hyperpolarization: inhibitory, open gated potassium or chloride channels) - neurotransmitters are degraded and recycled
summation of post-synaptic
- happens at the axon hillock
- non-insulated and with many ion channels
- input excitatory and inhibitory postsynaptic potentials spread to axon hillock
- combination of input postsynaptic potentials may or may not result in AP at axon hillock
- can occur spatially (simultaneous inputs) or temporally ( sequential inputs)
- mechanism for integration of information
