Neurons and the Nervous System
Neurons
Cells that receive and transmit information within the body
Structure
Basic unit of the nervous system
Axon Hillock: location where the signal is generated
Synaptic Terminals: Branches that form the synapse, synapse = connection between 2 cells
Axon: Long extensions from a cell body to another cell body
Synapse: connection between axon and dendrites (they don't actually touch), releases neurotransmitters from axon to dendrites
Dendrites: Hair like projections off of cell body, receive signals from other neurons
Overall organization: presynaptic cells send information, postsynaptic cells receive information
Cell Body: contains most of the organelles, including the nucleus
Information Processing
Neurons for integration are part of the central nervous system (CNS)
Neurons related to carrying information into CNS are part of peripheral nervous system (PNS)
Neuron structure is directly related to function
Nerves are just bundles of axons
3 Stages
Integration: nervous system processes information, decides on an action. Brain integrates information and considers immediate context and experience. Mostly occurs through internuerons
Motor Output: response to observation, trigger output such as muscle or gland activity, motor neurons
Sensory Input: make and observation about environment, sensory neurons transmit info about stimuli
Neurons that receive a lot of information have highly branched dendrites
Wherever cell fits in the process it will adapt for that
Neuron that transmits a lot of information has highly branched axons
Nervous Systems
Nervous System
Signals Transmitted as Action Potential
Synapses
Response to stimulus leads to change in membrane voltage called an action potential (potassium helps fuel action potential)
All or nothing signal (open or closed)
Change in ion flow depolarizes neighboring regions of axon, triggering action potential in neighboring neurons
Stimulus opens or closes gated ion channels, which alters membrane potential
Signal cascades down axon
Electrical change in membrane
Response depends on type and amount of neurotransmitter, and responsiveness of postsynaptic cells (how many and which receptors they have)
Neurotransmitters released: activate receptors
Neurotransmitters include:
Communication between neurons and between other cells
Received by postsynaptic cells
Released from presynaptic cells
Dopamine: related to things related to pleasure (motivation and desire)
Serotonin: related to mood, sleep, attention and learning, and more
Acetylcholine: related to muscles, memory, and learning
Nervous Systems can be Relatively Simple:
Integrated system for using sensory cells and processing information and making decisions does not appear until Cambrian explosion
Bilaterians
Sensory cells first appeared billions of years ago in eukaryotic organisms
Echinoderms
Cnidarians
Controls gastrovascular cavity
Neurons react independently and lack coordination
Nerve net--> basically a bunch of connected neurons across the body wall
Limited central processing: legs of sea star can communicate with each other, but no central unit to communicate with
Specific routes for information arise
Simple CNS
Cephalization
More Complex CNS
Become more complex and specialized
forms an integration center at a part in the body
Information will be processed and decided on here
clustering of sensory neurons and interneurons at front of body
Nerve cords run throughout body but aren't specialized
Brain and nerve cords
Regional Specialization
Includes Ganglia (clusters of neurons)
Things can work fairly independently (one arm up one arm down)
Different signals coming from different parts of the body
CNS (vertebrates)
Cerebrospinal Fluid
White matter = bundled axons
The notochord derived trait of chordates plays a key role in supporting the CNS
Grey matter = neuron cell bodies
Cerebrospinal fluid also plays a key role in gas exchange--> pH level can indicate whether we need to breathe more
Brain and Spinal Cord (develop from dorsal hollow nerve cord)
flows to brain
supplies CNS with nutrients, removes wastes
Derived from blood plasma
PNS
Important for regulating movement and internal environment
Classification
Transmits information to and from CNS
Efferent Neurons
Afferent Neurons: info that travels to CNS
Motor System
Passes information to other parts of body for reactions
Autonomic nervous System
PNS gives information to muscles, glands, or endocrine cells
Info is transferred to skeletal muscle
takes info from brain and creates movement
Involuntary movement (reflex)
Voluntary movement (walking across room)
Sympathetic Division
Parasympathetic Division
Controls digestive, cardiovascular, excretory, and endocrine organs
Entric System (digestive tract, pancreas, and gallbladder) rest and digest :)
All the processes that the body needs to do to live (mostly involuntary)
Body getting amped up in response to stimuli
Pupils dilate, sweating, lack of saliva, heart accelerates, inhibits emptying of bladder
Fight or Flight response
Basically does the opposite of the Sympathetic division, in almost direct relation (stops sweating, allows emptying of bladder, etc)
Calming responses
Exits CNS at midpoint in spinal cord and creates synapses with ganglia located just outside of spinal cord
Exits CNS at base of brain or spinal cord and creates synapses at in ganglia near or in organs