BSC2085 Chapter 12 Quiz Review

Nervous System

Functions of the Nervous System

• Sensory Input

• Integration

• Motor Output

Sensory Input

• Gathering information. Monitoring changes in and outside the body. Sense organs receive information and send stimuli to the brain and spinal cord.

• Ex: Receptors in the skin sense the temperature of the water

Integration

Process and interpret sensory input to determine appropriate response (either negative or positive)

Motor Output

• Response to stimuli. Will send commands to activate a muscle or gland in response to the input.

• On the basis of the sensory input and the integration in the CNS (Central Nervous System), a motor response is formulated and executed.

• Ex: What is the response if the water is too hot? (Hand out of the way).

Central Nervous System (CNS)

Brain and Spinal Cord

Peripheral Nervous System (PNS)

Cranial nerves and spinal nerves

Cells of the Nervous System

• Neurons

• Neuroglia

How many neurons does the brain approximately have?

86 billion neurons

How many glial cells the brain approximately have?

85 billion glial cells

Neurons

Actual nerve cells that transmit signals

Neuroglia

Support system for the neurons

What are the structures in a Neuron?

• Soma (Cell Body)

• Dendrites

• Axon: Axon Hillock (Trigger Zone)

• Axon Terminal

Soma (Cell Body)

Contains organelles except centrioles (no cell division). Metabolic functions.

Dendrites

Receptive: receive stimuli from other neurons. They convey stimuli to the soma by graded potentials.

Axon Hillock

Nerve impulse (action potential) is generated in the trigger zone. Impulse travels down the axon.

Axon

Conducting Area. Will conduct the action potential to the terminal.

Axon Terminal

Secretory area. Terminal branches have knobs containing synaptic vesicles of neurotransmitters.

How many Neuroglia support a Neuron?

About 50

Neuroglia (Glial Cells) Structure in CNS

• Astrocytes

• Microglia

• Ependymal cells

• Oligodendrocytes

Neuroglia (Glial Cells) Structure in PNS

• Schwann cells

• Satellite cells

Oligodendrocytes

Form myelin around neurons in CNS

Ependymal cell

Line brain cavity. Secrete and circulate cerebral spinal fluid (CSF).

Microglia

Phagocytic immune cells. Destroy microorganisms and remove debris.

Astrocytes

Support sand nourish neurons. Form blood brain barrier.

Schwann cells

Form myelin around neurons in PNS.

Satellite cells

Surround soma of neurons in the ganglia for protection and electrical insulation.

Process of Myelination

• Myelin sheath is an insulating layer of material that is mostly lipid.

• Myelinating glia wrap several layers of myelin around the cell membrane of a segment of the axon.

• Schwann cells insulate peripheral nerves while oligodendrocytes insulate the CNS.

• Areas not covered with myelin are called Nodes of Ranvier.

Nodes of Ranvier

Areas not covered with myelin

White matter

Occupied by dense collections of myelinated axons. Appear white in sections of the brain and spinal cord.

Grey matter

Mostly cell bodies, dendrites, neuroglia, and unmyelinated axons. Appear grey in sections of the brain and spinal cord.

Multiple Sclerosis (MS)

Exact cause is unknown, but thought to be an autoimmune disease. Loss of myelination in CNS will disrupt nerve conduction and result in multiple sensory and motor symptoms

• vision loss

• pain

• fatigue

• impaired coordination

• tremor

Which type of glial cells is a part of the blood brain barrier?

Astrocytes

This part of the neuron carries signals away from the cell body:

Axon

Sensory Neuron

Afferent. Detects sensory stimuli and conducts them to CNS.

Interneuron

Integration inside the CNS. Connects incoming sensory input with outgoing motor response.

Motor Neuron

Efferent. Sends motor response away from CNS.

Motor neurons ____ the spinal cord and are called ____.

Exit from; efferent

What is the resting membrane potential

-70mV

Resting Membrane Potential

• -70mV

• Inside the membrane is more negatively charged

• The membrane is defined as polarized

Causes of Electrical Potential

• Ionic Gradients

• Fixed Negative Charges

• Na-K ATPase Pump

Ionic Gradients

• (difference in concentration)

• ECF has higher concentration of NA+

• ICF has higher concentration of K+

• When a cell membrane is resting, only leakage ion channels allow movement of ions

Fixed Negative Charges

ICF contains negatively charged proteins that cannot move out

Na-K ATPase Pump

Exchanges 3 NA+ ions move them outside, and bring 2 K+ ions inside, thus maintaining a stable resting membrane potential of -70mV

How much ATP is used up by the Na-K ATPase Pump?

70% of the ATP in the nervous system

Which of the following is correct?
A) There are potassium channels open all the time that leak potassium inside the cell

B) There are sodium channels open all the time that leak sodium outside the cell

C) There are potassium channels open all the time that leak potassium outside the cell

C) There are potassium channels open all the time that leak potassium outside the cell

Which of the following is true?

A) RMP is 70 and is due to more potassium inside the cell

B) RMP is -70 and is due to more potassium inside the cell

C) RMP is -70 and is due to more sodium outside the cell

D) RMP is -70 and is due to more sodium inside the cell

B) RMP is -70 and is due to more potassium inside the cell

Types of Neuron Electrical Signaling

• Graded potential

• Action potential

Graded Potential

• short-range, temporary changes in the membrane voltage

• occur at dendrites

• a weak stimulus will open a few NA+ channels and will not travel far, causing only a localized current

• a strong stimulus will open more Na+ channels and may result in action potential

• Size of stimulus determines how many NA+ channels open and consequently the magnitude of the electrical impulse will very, meaning different GRADES of responses.

Action Potential

• Generated at the trigger zone in the axon hillock, when graded potentials are strong enough

• Local potentials must change voltage to -55mV, which is called the threshold potential. Only then will an action potential start.

Phases of Action Potential

• Rest

• Depolarization

• Repolarization

• Hyperpolarization

Rest

Membrane voltage is at -70 mV, then graded potentials increase the voltage to threshold -55 mV at the trigger zone (not resting anymore).

Depolarization

More NA+ gates open in the trigger zone and NA+ enters cell, creating a rapid rise in membrane voltage while will rapidly rise toward +30 mV.

Repolarization

Na+ channels close and K+ gates open and K will exit the cell. Voltage will become negative reaching resting membrane potential (RMP)

Hyperpolarization

K+ gates remain open for a longer period, leading to a more negative voltage than RMP. The membrane voltage returns to its resting value shortly after hyperpolarization. 

Neurotransmitters

• Small molecules made by the body that allow neurons to communicate and “talk” with each other. These molecules are important in the process of chemical synaptic transmission.

• Many brain disorders, such as Parkinson’s disease, Alzheimer’s disease, depression, and Schizophrenia, show alterations in the levels of specific neurotransmitters.

• Ex: adrenaline, dopamine, endorphins.

Gated Membrane Channels

• Voltage-Gated channels

• Ligand-Gated channels

Voltage-Gated Channels

Open when transmembrane voltage changes

Ligand-Gated Channels

• (Chemical)

• In this case, the neurotransmitter acetycholine, binds to a specific location on the extracellular surface of the channel protein, the pore opens to allow select ions through (not sure if this is on quiz/exam, just remember is opened via chemical substrates). 

The Synapse

• A connection between two neurons. It transmits signals between two neurons.

• Presynaptic neuron

• Postsynaptic neuron

• Synaptic cleft

Presynaptic Neuron

Axon bulges to form synaptic bouton (knob) that contains synaptic vesicles which store up a neurotransmitter

Postsynaptic Neuron

has receptors for a specific neurotransmitter. Those receptors are ligand-gated.

Synaptic Cleft

the area between both neurons. Neurotransmitter will cross the cleft from one neuron to the next. Cleft also contains enzymes which break down and degrade neurotransmitters.

Cessation of Signal

• Release of neurotransmitters will stop.

• Reuptake

• D