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