Nerve Cells and Nerve Impulses

What are neurons

cells that receive information and transmit it to other cells

What are the parts of a neuron

Dendrites - receive information from previous neuron

Cell body - processes said information

Axon - Carries the information from the cell body to the axon terminals

Axon terminals - passes on the information to the next cell

Myelin sheath - a fatty substance that covers the axons and speeds up the propagation of information

Nodes of Ranvier - interruptions in the myelin sheath of the axon

What are the 3 types of neurons

Motor neurons - soma in the spine
- receives excitation from other cell
- conducts impulses to muscles or glands

Sensory neuron - is specialized at one end to be very sensitive to a specific type of stimulation

Inter neurons - connects the sensory and the motor neurons

what are dendritic spines

they are short outgrowths that increase the surface area available for synapses

In people with schizophrenia, they often have a lot of dendritic spines, this can lead to them experiencing things that don’t exist, as they often have impulses that don’t exist.

What are the 2 directions in which a neuron can be labeled

Afferent neuron- brings info into a structure

Efferent neuron - brings info out of a structure

What are glial cells

cells in the nervous system, that don’t carry impulses as far as neurons do.

Astrocytes

star shaped glial cells that wrap around the synapses, and helps in passing chemicals back and forth between neurons and the blood

Microglia

they help in removing waste materials, pathogens, and dead or dying neurons from the brain

Oligodendrocytes

help in building the myelin sheath that surrounds the neurons in the CNS

Schwann cells

helps in building the myelin sheath in the PNS

Radial Glia

guide the migration of neurons during embryonic development. They later differentiate into the other neural cells when development is complete

What is the blood brain barrier

mechanism that excludes most chemicals from the brain

What are the 3 cells that make up the bbb?

Endothelial cells

Pericytes

Astrocytes

What are the 3 mechanisms used in the bbb

• Physical → the endothelial cells are held tgt by tight jns that act as physical barrier

• Transport → They control the movement of anything with the help of certain transporters
  → There are 2 types of transporters efflux transporters [use cellular energy to move things that have passively diffused against their conc gradient, usually located on the blood side of the bbb] and
  → nutrient transporters [facilitate the transport of nutrients(glucose) and amino acids, down their conc gradient and into the brain]

• Metabolic → the barrier contains a bunch of enzymes that metabolize and inactivate a bunch of neurotransmitters, drugs and toxins, preventing them from entering the brain

Why is the bbb not used for other organs also

It is such a good defense that it does not allow for the transport of neccesary materials [glucose and amino acids].

The brain has special transport mechanisms for these materials that are not found in the other parts of the body.

What are the circumventricular organs

They are the organs that are around the midline of the ventricular system and do not have the bbb

eg. the pituitary gland in the brain needs access to blood to monitor hormone levels, and thus has access

How can you make drugs cross the bbb

make them lipid soluble

deliver them direct to the cerebral spinal fluid

use vasoactive compounds

repress the efflux transporters to prevent the drug from being put back into the blood

hack the nutrient transporters to move the drugs

What provides energy for the brain

Glucose, and large amounts of it cross the bbb

Thought the brain is only 2% of the body’s weight it uses 20% of the O2 and 25% of the glucose

What vitamin is needed for the brain to actually use glucose

Vitamin B1, thiamine

Local neuons

neurons without an axon

Electrical gradient

the difference between the levels electrical charges in and out the cell [-70mV at rest, called resting potential]

cellular conditions at rest

Na+ is more outside the cell and is in more quantity making the outside relatively +ve

K+ is more inside the cell and is in less quantity making the inside relatively -ve

Na+ channels are closed

K+ channels are closed

NaK [3 Na out and 2 K in] pump is active and moves ions that have passively diffused against their conc gradients

Voltage gated channels

channels that need the cell membrane to reach a certain voltage to open

Ligand gated channels

Are triggered when a certain chemical attaches to them

Mechanically gated channels

open in response to physical forces [change in length or pressure]

Graded potential

a membrane potential that varies in magnitude based on the intensity of the stimulus

causes the membrane to move away from resting potential

List the 3 phases of this graph and their respective voltages

Rest = -70mV

Threshold = -55mV

Peak = 30mV

Hyperpolarization = below -70mV

All about the action potential

Transcript in the ppt

Hyperpolarization

increased polarization of the membrane

depolarization

reduced polarization

threshold

minimum polarization for all or none action potential

All or nothing law

principle that amplitude and the velocity of an action potential are independent of the stimulus that initiated it

every depolarization post threshold produces the same resulting action potential

Propogation

transmission of an action potential down an axon

Saltatory conduction

the jumping of potentials from node to node

Absolute refractory period

membrane is unable to produce another action potential

Relative refractory period

period after arp, where the membrane requires a stronger than usual stimulus for an action potential

local anesthetic

drug that attaches to na channels preventing propogation of action potentials