Nervous System Flashcards
Nervous System Consists of: (6 Parts)
- Brain
- Spinal Cord
- Nerves
- Ganglia
- Sensory Receptors
- Effector Organs (muscles + glands)
Central Nervous System (CNS)
- The body’s coordinating center for mechanical/chemical actions.
- Made up of the BRAIN and SPINAL CORD
Peripheral Nervous System (PNS)
- All parts of the nervous system that relay info between the central nervous system and other parts of the body.
- Divided into autonomic and somatic nervous system
Somatic Nervous System (voluntary)
- controls skeletal muscles, bones and skin
- sensory nerves (environment -> SNS)
- motor nerves (CNS -> body parts)
Autonomic Nervous System (involuntary)
Controls organs
Divided into:
- Sympathetic Nervous System
- Parasympathetic Nervous System
Parasympathetic (relax)
PNS- Autonomic
- contracts pupils
- stimulates salivation
- contracts bronchi
- slows heart beat
- stimulates digestive activity
- stimulates gall bladder
- contracts bladder
Sympathetic (flight or flight)
PNS- Autonomic
- dilates pupils
- inhibits salivation
- relaxes bronchi
- accelerates heart beat
- inhibits digestive activity
- stimulates glucose release by liver
- relaxes bladder
Types of Nerves Cells
- Glial: non-conducting cells important for structural support and the metabolism of nerve cells.
- Neurons: nerve cells that conduct impulses, they are the functional units of the nervous system.
Sensory Neurons
Neurons that carry impulses (stimuli) from sensory receptors to CNS.
- Known as AFFERENT (towards) neurons
- Ganglia are collections of sensory nerve cell bodies (chemoreceptors, photoreceptors)
Motor Neurons
Neurons that carry impulses from the CNS to effectors (muscles, organs, etc.)
-Known as EFFERENT (away) neurons
Interneurons
Integrates and interprets info and connects to outgoing motor neurons
- Found in brain and spinal cord
- Link sensory neurons to motor neurons
5 Essential Components for Reflex Arc
- Receptor
- Sensory Neuron
- Interneuron (in spinal cord)
- Motor Neuron
- Effector
Resting Potential
Voltage difference across a cell membrane when it is at REST.
- usually = -70mV
Higher conc. of potassium ions (K+) INSIDE, higher conc. of sodium (Na+) OUTSIDE
- “Polarized Membrane”
Action Potential
Nerve Impulse
- all or none occurrence
- triggered by membrane potential reaching threshold potential
- strength of action potential is always the same, stronger stimuli only cause MORE FREQUENT action potentials
Depolarization
Some Na+ channels open, sodium ions move into cell via facilitated diffusion.
K+ channels are closed, so potassium is trapped inside.
Inside of the cell becomes more positive than outside of the cell.
Threshold Potential
Particular membrane potential that a neuron MUST reach to trigger an action potential.
-usually = -50mV
When reached, all Na+ channels open
Repolarization
When membrane potential hits +40mV, Na+ channels shut and K+ channels open slowly so potassium ions can diffuse OUT of the cell slowly.
-restores membrane potential to be more negative again = -70mV
Hyperpolarization
Leaky K+ channels cause too much potassium to leave the cell causing the membrane potential to be TOO negative (-85mV)
Refractory Period
Na+/K+ Pump restores the resting membrane potential back to the resting membrane potential by using ATP (energy) to transport 3 Na+ out and 2 K+ in, against their conc. gradient to reach -70mV
-depolarization cannot occur until resting membrane potential is reached
Refractory period is the time taken to get from the hyperpolarized state back to resting membrane potential.
Propagation of Action Potentials
Depolarization at one point causes the adjacent section to depolarize.
- triggers new action potential at the new site, called WAVE OF DEPOLARIZATION.
- refractory period prohibits the AP to move backwards
- direction of AP always goes from dendrite to axon
Saltatory Conduction
ion channels are concentrated in the nodes of ranvier. Impulses jump from node to node, skipping regions cover by the myelin sheath.
-Depolarization only happens where there is no myeline sheath.
Synapses
- Space between neurons
- Communication between neurons is through chemicals called NEUROTRANSMITTERS.
Presynaptic Neuron
Neuron that carries impulses TO the synapse.
-releases neurotransmitters into the synapse from synaptic knobs or endplates
Voltage gated calcium (Ca+) channels open, calcium causes synaptic vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft (space)
Postsynaptic Neuron
Neuron that carries impulses AWAY from the synapse.
- have receptors for neurotransmitters (NT)
- NT alter permeability of the post synaptic membrane (affects whether there will be an AP or not)
