Lecture 3 Flashcards
Nervous System Organization
Central nervous system: Brain and spinal cord.
Peripheral nervous system: Body.
Peripheral Nervous System
Somatic: controls voluntary muscles with spinal nerves and cranial nerves.
Automatic: consists of autonomic nerves and some cranial nerves that control the function of organs and glands.
Divisions of ANS
Sympathetic: fight or flight system.
Parasympathetic: predominates at times when the energy reserves can be conserved and stored for later use.
Cerebral Spinal Fluid
- surrounds the brain and spinal cord.
- protects the brain.
- helps in the exchange of nutrients and waste products between the brain and blood.
CNS has SIX distinct regions
- ) Spinal Cord
- ) Myencephalon (medulla)
- ) Metencephalon (hindbrain)
- ) Mesencephalon
- ) Diencephalon (forebrain)
- ) Telencephalon (forebrain)
Myencephalon (medulla)
- origin of reticular formation.
- multiple cell groups regulating vital functions.
Metencephalon (hindbrain)
- cerebellum & pons.
- plays a role in attention, arousal, sleep, muscle tone.
Mesencephalon
- important for pain modulation.
- critical in initiation and modulation of movement.
Diencephalon (forebrain)
- thalamus & hypothalamus.
- process and then distribute sensory and motor information.
Telencephalon (forebrain)
- the cerebral hemisphere and the largest region of the brain, and include the external cerebral cortex.
- emotional responses, regulates motivated behavior & learning.
Micro-Neuroanatomy
- There are 85 to 100 billion neurons in the brain.
- Neurons make 100 trillion synapses.
- 1 trillion glial cells.
Neuron
Specialized nerve cells that form the brain, spinal cord, and nerves that transmit electrical signals throughout the body.
Four Principle Types of Glial cells
- ) Oligodendroglia
- ) Microglia
- ) Astrocytes
- ) Schwann cells
Oligodendroglia
- form myelin sheath on multiple axons in the CNS.
- provides energy efficient and fast neural conduction.
Microglia
provide immune function.
Astrocytes
- provide structural support (biggest).
- maintain ionic and chemical environment.
- store nutrients to provide energy for neurons.
Schwann cells
supporting cells of the peripheral nervous system responsible for the formation/reformation of myelin.
Electric Transmission
transmission of information within a single neuron is an electrical process and depends on the semipermeable nature of the cell membrane.
Polarized
means that there is an electrical difference across the cell membrane.
Two Main Ions
Sodium (NA = not allowed)
Potassium (K = keep)
Resting Membrane Potential
- when a neuron is at rest, the inside of the neuron is negative (has more negatively charged ions) relative to the outside of the cell.
- 70mV.
Gated Ion Channels
Most channels are not normally open to allow free passage of ions, but are in a closed configuration that can be opened momentarily by specific stimuli.
Ligand-gated channels
- bind neurotransmitters and open in response to ligand binding.
- ion moves from high to low concentration.
Voltage-gated channels
opened by the application of a small electrical charge to the membrane surrounding the channel.
Local Potentials
small, local changes in ion distribution and electrical potential differences.
Depolarization
- positively charged ions make the inside of the call slightly more positive in a small, localized area of the membrane, bringing the membrane potential a tiny bit closer to the threshold for firing.
- small amounts of Na+ enter cell.
Hyperpolarization
- increase in the negatively charged ion makes the call slightly more negative inside and brings the resting potential farther away from threshold.
- small amounts of Cl- enter or K+ exit cell.
Excitatory postsynaptic potentials (EPS)
- makes the postsynaptic neuron more likely to fire an action potential.
- depolarization.
Inhibitory postsynaptic potentials (IPSPs)
- makes a postsynaptic neuron less likely to generate an action potential.
- hyperpolarization.
Action Potential
- the rapid change in membrane potential that is propagated down the length of the axon.
- the membrane potential must be changed from resting (-70mV) to the threshold for firing (-50mV).
Axon Hillock
the portion of the axon that is adjacent to the cell body where electrical signal is generated.
Five Stages of Action Potential
- ) Resting State: Na+ and K+ channels are closed.
- ) Depolarization: A stimulus opens some Na+ channels.
- ) Depolarization opens most sodium channels, while potassium remains closed.
- ) Falling phase: most Na+ channels become inactivated, blocking Na+ inflow. K+ channels open, making K+ outflow.
- ) Undershoot: Na+ channels close, but some K+ channels are still open. As the K+ channels close and Na+ become unblocked, the membrane returns to resting state.
Saltatory Conduction
The process by which if insulating myelin is present on an axon then the nerve impulses that is conducted will “jump” from gap to gap in the myelin layer.
Node of Ranvier
A small gap between myelinated segments where axonal membrane is exposed; increases speed of impulses.
Axodendritic transmission
- axon to dendrite and spines.
- most common.
Axosomatic transmission
axon to cell body.
Axoaxonic transmission
axon to axon.
Synaptic Cleft
The gaps between neurons, where chemical signals are transmitted.
Synapse
a structure that permits a neuron to pass an electrical or chemical signal to another neuron.
Presynaptic Neuron
release zone, where terminals are.
Postsynaptic Neuron
the neuron on the receiving end of the synapse, where the dendrites are.
Synaptic Factors
Action potential
Probability of release
Heteroreceptors: receptors for other transmitters released at axoaxonic synapses.
Autoreceptors: receptors for the same transmitter released by the neuron.
Terminal autoreceptors
located on axon terminals, and when activated by neurotransmitter, their main function is to inhibit further transmitter release.
Somatodendritic autoreceptors
found on the cell body or dendrites.
when these autoreceptors are activated, they slow the rate of cell firing.
Ionotropic receptors
Ligand-gated ion channel.
Fast response.
Metabolic receptors
Activate other proteins called G proteins.
Slow.
Second Messengers
- Activate protein kinases (enzymes that phosphorylate proteins).
- Given numerous roles of proteins (receptors, enzymes, channels, etc) can lead to several downstream effects.
Tyrosine Kinase Receptors
Enzymes that phosphorylate proteins.
How might drugs affect neurotransmitters?
- A drug can block the reuptake transporter, so the neurotransmitter will stay inside.
Ex: SSRI’s it blocks the reuptake of serotonin.
Nitric Oxide
a gas that performs a type of signaling between neurons.
Endocrine System
- a collection of glands and groups of cells that secrete hormones that regulate growth,development, and homeostasis.
- drugs can alter the secretion of many hormones, causing physiological abnormalities.
