L6 Nervous system structure and resting membrane potential

Nervous system

• Electrical signals, called action potientals in neurons

• Immediate changes

• Fast response

Central nervous system (CNS)

• brain

• spinal cord

Peripheral nervous system (PNS)

• Sensory neurons

• Effector neurons

  • Somatic nervous system

  • Autonomic nervous system

Information flow in the nervous system

Stimulus

perceived by the receptor

Sensory neuron

Carries the sensory information to the CNS

• Sensory information is carried in the form of an electrical signal, called an action potential

CNS

integrated the infromation and determine if a response is needed

Efferent neuron

stimulates muscles or glands

• motor neuron: skeletal muscle

• autonomic neuron: glands, cardiac, and smooth muscle

Effector

organ elicits a response

1. Neurons

handle information ( functional unit of the nervous system)

2. Glial cells

supporting cells of the nervous system

• holds neurons together in specfic ways

• provide the neurons with an optimal enviroment

Structure of the neuron

Cell body

nucleus and organelles

Dendrites

• Processes extending from the cell body

• Receptive part of the neuron

Axon

long process that carries information

Axon hillock or trigger zone

action potential starts

Synaptic terminals

• swellings of the end of the axon

• vesicles with neurontransmitters

Neurotransmitters

chemical signal used for cell-to-cell communication

Sensory neuron

• Carry sensory information

  • body→ CNS

• Cell body outside the CNS

Interneuron

• communication between neurons

• Within the CNS

Motor neuron

• Carry efferent information to an effector

  • CNS→body

• Cell body located in the CNS

Satellite cells (PNS)

Maintain the enviroment of neurons (O2 nutrients)

Schwann cells (PNS)

• Surround axons

• myelination

Ependymal cells (CNS)

monitor and circulates CSF

Oligodendrocytes (CNS)

Myelinate CNS axons

Astrocytes (CNS)

Maintain blood-brain barrier

Microglia ( CNS)

Remove wastes and pathogens

How does a neuron transmit information

1. Recieve information through dendrites

2. Transmit the electrical signal or action potential along the axon

3. Transmit the information to other cells through synapses

How is the electrical signal generated?

Our cells are already electrically charged

• The resting cell is negative inside, relative to the outside

• Uneven distribution of ions across the cell membrane ( difference in the electrical potential between the inside and outside of the cell)

• Na+-K+ ATP pump and different permeabilities of the cell membrane to different ions ( number of the specific ion channels)

Resting membrane potential

RMP (V_rest)= V_m inside - V_m outside

V_{rest~ -70 mV}

V_m: membrane potential

Ways ions cross the cell membrane : Channels

• Selective for certain ions

• Passive transport, no ATP needed

• Ions move down a concentration gradient

• Fast

Leak channels: always open

• K+ leak channels

• Na+ leak channels

Voltage-gated channel: opens with change in the membrane potential (electrical difference across the membrane)

• Voltage-gated Na+ channel

• Voltage-gated K+ channel

Ways ions cross the cell membrane : Ion pumps

Ion pumps

• Selective for certain ions

• Active transport; needs ATP

• Slow

• Creates concentration gradients by moving ions against their gradients

Na+-K+ ATP pump

• Moves 3 Na+ ions out of the cell and 2 K+ ions into the cell

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Resting membrane potential - cell in equilibruim

Assume a cell

• Distribution of ions (Na+ and K+) is the same inside and outside of the cell

• The inside and outside of the cell is electrically neutral

• Na+ and K+ ions are partnered with negatively charged molecules

Na+-K+ ATP pump creates a concentration gradient ( and a small electrical gradient)

1. Concentration gradient

2. Electric gradient

Resting membrane potential - insert a pump

• Na+-K ATP pump on the cell membrane

• Na+-K ATP pump moves 3 Na+ out of the cell and 2 K+ into the cell ( against a concentration gradient)

• Creates a concentration ( chemical) gradient

  • More Na+-→ outside

  • More K+→ inside

• Creates an electric gradient (small)

Resting membrane potential- Role of K+

• The cell membrane has LOTS of K+ leak channels (very permeable)

• K+ diffuses out of the cell down its concentration gradient

• As K+ leaves the cell, it leaves its negative partners behind

The cell becomes more negative than the outside

Resting membrane potential- Role of Na+

• The cell membrane has fewer Na+ leak channels (less permeable)

• Na+ diffuses into cell down its concentration gradient

• As Na+ enters the cellm its the cell a bit less negative