Unit 11

Synapse

The region of contact where a neuron transfers information (a nerve impulse) to another neuron or muscle.

Presynaptic Neuron

First neuron, axon terminal, transfers nerve impulse to next neuron.

Postsynaptic Neuron

Second neuron, dendrite, receives nerve impulse from presynaptic neuron

Synaptic Cleft

Space between pre and postsynaptic neuron,, filled with matrix, helps neurons adhere to each other.

Neurotransmitters

Chemical that an axon terminal releases to cause the transfer of a nerve impulse to another neuron or a muscle fiber, used to communicate with postsynaptic neuron.

Protein Channels

On postsynaptic membrane, allow ions to enter.

Calcium Protein Channels

On sides of axon terminal.

Calcium (Ca2+)

In extracellular fluid

Sodium (Na+)

Mainly in extracellular fluid (which is in the synaptic cleft)

Chlorine (Cl-)

In the extracellular fluid (which is in the synaptic cleft), is the negative ion

Excitatory neurotransmitters

Type of neurotransmitter that WILL continue the nerve impulse to the next neuron or muscle

Inhibitory neurotransmitters

Type of neurotransmitter that will NOT continue the nerve impulse to the next neuron or muscle

Synaptic Transmission

Process by which the nerve impulse in the presynaptic neuron signals the postsynaptic cell so the nerve impulse can continue.

Process of a synapse

Action potential travels down axon to axon terminal, causes calcium protein channels to open, Ca2+ rushes in from extracellular fluid, calcium rushing in triggers synaptic vesicles to fuse to presynaptic membrane, synaptic vesicles open and spill out neurotransmitters into synaptic cleft, neurotransmitters bind to proteins channels on postsynaptic neuron, stimulate protein channels to open to allow in Na+.

If neurotransmitter EXCITATORY(EPSP

Na+ goes into cell, it causes depolarization in the postsynaptic membrane, this causes the neuron to become positive and action potential continues - nerve impulse continues!

If neurotransmitter INHIBITORY (IPSD)

Causes chlorine to rush in, which causes hyperpolarization (away from threshold, opposite), change in membrane potential causes the membrane to be “inhibited”, no action potential triggered.

Reuptake of Neurotransmitter

After the neurotransmitter has done its job in the synaptic cleft, it is taken care of by one of three ways: diffuses into extracellular fluid, an enzyme comes in and decomposes it, or transported back into the synaptic vesicles of the axon terminal. Called REUPTAKE.

Electrical to Chemical to Electrical

The nerve impulse goes from an electrical signal down the axon, to a chemical signal in the synapse, back to an electrical signal down the next neuron.

Dendrites (sensory receptors) gather information by..

detecting changes inside and outside our body.

Monitor external environment

light, sound, five senses

Monitor internal environment

temperature, oxygen, concentration

Convert the information into a…

MESSAGE that travels in the form of a nerve impulse.

Dendrites

Receive information from other neurons or environment and carries the information in the form of a nerve impulse

Axons

Carries nerve impulse to the next neuron or motor (muscle)

Synapse with axons

Axon to dendrite and Axon to muscle

Path of Nerve Impulse

Information is picked up in the dendrite, carried in the form of a nerve impulse through cell body, carried in the form of a nerve impulse through the axon, passed through a synapse to the next neuron,process continues over and over again

Facilitated Diffusion

If atom, molecule, or ion is not permeable for cell membrane, need help getting across, “carriers” help it across, and ions move across mainly in this way.

Gated Channels

Some of these carries are gated, they have a gate which opens telling them when chemicals can come in and out.

Active Transport

Sometimes atoms, molecules, or ions need to move AGAINST the concentration gradient, need energy, ATP, to “push” it against the concentration gradient.

In a resting neuron…

there is no nerve impulse going through it

Na+ inside and outside cell…

high outside the cell, low inside the cell

K+ inside and outside cell…

high inside the cell, low outside the cell

Anions

Negatively charged ions, distributed throughout the inside of the cell.

Resting Membrane Potential

Neurons have electricity running through them at all times, this reading (in a resting neuron) is -70mV.

Difference in Charge Across the Membrane

The reason it is negative is because there is a difference in the amount of Na+ outside the neuron, as opposed to the amount of K+ inside the neuron.

Nerve Impulse

Information in the form of an electrochemical signal that travels through a neuron.

What is an Action Potential

when the changes flip, + on the inside and - on the outside, only happens temporarily, as it flips back to go back to normal.

Nerve Impulse =

Multiple Action Potentials

Depolarization

Sodium channels open up and sodium rushes into neuron cell, the neuron cell now becomes flips charges and becomes positive.

Repolarization

Potassium channels open up and potassium rushes out of neuron cell, the neuron cell now becomes flips charges back to being negative.

Hyperpolarization

Sodium-potassium pump works with ATP (going against concentration gradient) to bring the cell back to normal; 3 sodium get pulled out of the cell and 2 potassium get pulled back into cell

Absolute Refractory Period

Time after action potential in which it is impossible to initiate another action potential (about 1 msec)

Multiple Action Potentials

Rate of action potential generation = Magnitude of the stimulus

As magnitude increases…

firing of action potentials increase.

Schwann Cells

In PNS and wraps around axons

Oligondendrocytes

In CNS and wraps around axons

Nodes of Ranvier

breaks between individual cells

Myelin sheets make up…

Schwann cells and Oligondendrocytes

Saltatory Conduction

Speed of action potential is increased because the action potential jumps from node to node, cuts down on the number of action potentials has to do to get to end of axon.

Neuroglia

Neurons and neuroglia are intimately related, these make up nerve tissue.

Neuroglia functions

Maintain homeostasis, provide support and protection for neurons, form myelin (IMPORTANT!) for fast nerve impulses

Neuroglia in CNS

Astrocytes, Oligodendrocytes, Microglia

Neuroglia in PNS

Schwann Cells

Astrocytes

Structural support, communication between neurons

Oligodendrocytes

Wrap around axons

Microglia

Immune protection (fight off infection)

Schwann Cells

Wrap around axons (with myelin), make it so the speed of the nerve impulse goes FAST

Neurons

You are born with the number of neurons that you will have throughout your life, no cell division, if you lose them, you lose them for good (Alzheimer’s disease)

Neuroglial cells

Do divide and make more, go through cell division.

Regeneration of Neurons

Neurons in the Peripheral Nervous System CAN REGENERATE, injury to the cell body usually kills the neuron, as these cells do not go through mitosis, a damaged peripheral axon may regenerate, PNS – does (sometimes) regenerate, CNS – does not

The nervous system is the body’s…

information gatherer, storage center, and control system .

Main functions of Nervous System

Collect info about the body’s external/internal state from our senses, transfer this information to the brain to analyze, send impulses out to initiate appropriate motor responses to meet the body’s needs.

Central Nervous System (CNS) has..

The brain and spinal cord and this allows it to process info

Peripheral Nervous System (PNS) has…

Cranial nerves and spinal nerves and this allows it to receive information from environment (senses) and respond to environment (motor movements)

Two Subdivisions of the Peripheral Nervous System

Somatic and Autonomic Nervous System

Somatic Nervous System

Nerves that connect the CNS to the skin and skeletal muscles, controls, CONSICOUS actions, voluntary, made up of spinal nerves, have sensory neurons and motor neurons, 13 pairs of spinal nerves, which originate from the spinal cord.

Autonomic Nervous System

Nerves that connect the CNS to organs such as the heart, stomach, intestines, and various glands, controls SUBCONSCIOUS actions, involuntary.

Types of Spinal Nerves

Sensory and motor neurons

Sensory Neurons

Get messages from the senses, up the spinal column, to the brain.

Motor Neurons

Get messages from the brain, down the spinal column, to the muscles.

Example of Autonomic Nervous System

Breathing faster when stressed

Example of Somatic Nervous System

Sending a message to move a muscle.

Divisions of the Autonomic Nervous System

Sympathetic and Parasympathetic

Sympathetic

“Fight or Flight”, respond to stress, prepares body the body for energy-expending, stressful, or emergency situations, increase in everything (heart rate, breathing, etc.)

Parasympathetic

“Rest and digest”, bring body back down from stressful situations, this system is active during ordinary, restful situations, keeps everything at normal levels.

Neuron

The name for a nerve cell and a unique type of cell found in the brain and body.

Nerve Impulse

Electrical message that travels down a neuron, this is how messages are transmitted to and from the brain.

Cell body (soma)

Spherical part of cell, main control center, contains Nucleus

Dendrites

Branches coming off of the cell body

Axon

The long, hair-like extension

Axon Terminal

End of Axon

Synaptic Vesicles

In the axon terminal and small bubbles that contain neurotransmitters

How are neurons connected?

One is connected to another, which is connected to another, so on and so forth until it reaches an end.

Synapse

Point of contact with another neuron or muscle

How many neurons are in the human brain and spinal cord?

8 billion in brain and 1 billion in spinal cord

Longest axon in the world..

15 feet, found in a giraffe

Which neurons are bigger, CNS or PNS?

PNS neruons

Unipolar

One branch (dendrite and axon combined)

Bipolar

Two branches (dendrite, axon separate)

Multipolar

Many branches, dendrites, only one axon and most neurons in the brain

Classifications of Neurons

Number of units arising from cell body, all of them have one axon, the only difference is the number of denrites.

Sensory Neurons or..

Afferent

Sensory (Afferent) Neurons

Lie in PNS (outside of spinal cord and brain), unipolar, dendrites are sensory receptors

Interneurons

Lie within CNS (brain and spinal cord), multipolar, connect one neuron to another neuron, and most neurons of the body

Motor Neurons or..

Efferent

Motor (Efferent) Neurons

Lie in PNS (outside brain and spinal cord), connect to muscles or glands, multipolar

On the action potential graph, where does an action potential occur?

2; depolarization

On the action potential graph, where are the absolute refractory periods?

4 and 5; hyperpolarization and resting membrane

Are nodes of ranvier myleniated?

No