The Nervous System

Week 12

What is the nervous system responsible for | 4

• Maintaining homeostasis

• Monitoring perceptions, behaviours, memories + senses

• Voluntary + involuntary movements + process

What is the nervous system composed of | 4

Brain, spinal cord, cranial + spinal nerves, specialized cells (neurons, neuroglia)

What is the central nervous system (CNS) | 2

Brain + spinal cord

What is the CNS responsible for | 2

• Process sensory info, thoughts, emotions, memories

• Initiates signals that stimulate muscles + glands

What is the peripheral nervous system (PNS) | 3

• All nervous tissues outside CNS

• Nerves + sensory receptors

• Divided into sensory and motor divisions

What is the sensory (afferent) divisions | 2

• Conveys input into CNS from sensory receptors

• Somatic senses: thermal, pain, proprioceptive, equilibrium

What is the motor (efferent) divisions | 3

• Conveys output from CNS to effectors 

• Muscles + glands

• Divided into somatic + autonomic nervous systems

What is the somatic nervous system 

Conveys output from CNS to skeletal muscle (voluntary)

What is the autonomic nervous system | 4

• Conveys output from CNS to smooth + cardiac muscle, glands (involuntary)

• Sympathetic, parasympathetic + enteric nervous system

What is the sympathetic nervous system

Flight, fight or freeze

What is the parasympathetic nervous system

Rest + digest/low + slow

What is the enteric nervous system | 2

Regulates activity of smooth muscles + glands in digestive tract

What are the 3 process of the nervous system

Sensory (input), integration (processing) + motor (function)

What is the sensory (input) process

Receptors detect internal/external stimuli + relay info into brain + spinal cord via cranial + spinal nerves

What is the integration (processing) process

Information is then processed and analyzed

What is the motor (function) process

Effectors (muscles/glands) are stimulated through cranial + spinal nerves to contract or secrete substances

What are neurons (brain cells) | 2

• Sensing, thinking, controlling, regulating of NS

• Can’t participate in mitosis (when they die, they die)

What are neuroglia | 6

• Support, nourish + protect neurons

• Maintain interstitial fluid

• Make up half of CNS

• Do not generate action potentials

• When neurons die, neuroglia divide to fill space (may become brain tumour, glioma)

• 6 types (4 in CNS, 2 in PNS)

How fast can impulses travel throughout body

0.5-130m/s (1.8-468km/hr)

What three parts make up neurons

Axon, dendrites + cell body

What is the cell body | 2

• Contains nucleus surrounded by cytoplasm

• Has regular cellular organelles

What is a ganglion (ganglia) | 2

• Collection of neuron cell bodies in PNS

• Called nucleus in CNS

What are dendrites | 2

• Receiving or input portion of neuron

• Plasma membranes contain chemical receptor sites

What are nerve fibres

Neuronal processes that emerge from cell body (multiple dendrites and/or one axon)

What are axons | 2

• Moves neuron impulses toward adjacent neuron or effector

• Cylindrical projection joined to cell body by axon hillock

What are axon collaterals

Side branches off axon

What are axon terminals

Axon and collaterals divide into fine tendrils

What is a synapse/synaptic plex

Space between neurons or an effector and neuron for communication

What are neurotransmitters | 2

• Chemicals stored at the end of axon terminals

• When chemical released excites/inhibits another neuron, muscle fibre or gland cell

What is a multipolar neuron

Several dendrites, one axon

What is a bipolar neuron

One main dendrite, one axon

What is a unipolar (pseudounipolar) neuron

Dendrites and axon fuse together to form a continuous process that emerges from cell body

What are sensory (afferent) neurons | 3

• Sensory receptors at dendrites or located proximally adjacent to sensory receptors

• Action potential conveyed into CNS

• Usually unipolar

What are motor (efferent) neurons | 2

• Convey action potentials away from CNS to effectors

• Usually multipolar

What are interneurons (association neurons) | 3

• Found in CNS between sensory + motor neurons

• Process incoming sensory info + activate response via motor neurons

• Usually multipolar

What are astrocytes (CNS) | 4

• Provide strength, protection + support to neurons

• Wrap around capillaries in CNS to create blood-barrier 

• Play a role in learning + memory by forming new synapses

• Maintain homeostasis to promote generation of nerve impulses

What is a blood-brain barrier

Restricts movement of substances between blood and interstitial fluid in brain/CNS

What are oligodendrocytes (CNS)

Forming and maintaining the myelin sheath

What are microglia (CNS)

Phagocytes - remove damaged nervous tissue + cellular debris

What are ependymal cells (CNS) | 2

• Line the ventricles of brain + central canal of spinal cord

• Produce + circulate cerebrospinal fluid (CSF)

What are ventricles

Open space in the brain

What are schwann cells (PNS) | 2

• Encircle PNS axons + forms myelin sheath

• Aids in axon regeneration (only for PNS)

What are satellite cells (PNS) 

Surrounds cell bodies + regulate exchange of materials in interstitial fluid

What is a myelin sheath | 4

• Multilayered lipid + protein covering that surrounds + insulates axon

• Increases speed of nerve impulse conduction

• Produced by schwann cells (PNS) + oligodendrocytes (CNS)

• Myelination increase from birth to maturity

• Plasma membrane forms many inner layers

Explain how myelination helps us learn things | 5

More practice + more coordination = new synapses = more myelin sheath = more myelination = real speed bitch

What is schwann cell myelination

Wraps segment of axon by spiralling around it

What is neurolemma | 2

• Outer layer of schwann cell

• Aids in regeneration of axon if damaged

What are nodes of ranvier

Gaps in myelin sheath

What is oligodendrocyte myelination | 4

• Wraps around CNS axons

• No neurolemma - no axon regrowth if damaged

• Nodes of ranvier - present but fewer than PNS

• One oligodendrocyte can warp around multiple axons

What is a nerve

Bundle of axons in PNS

What is white matter | 2

• Composed of mainly myelinated axons

• In spinal cord it surrounds gray matter

What is gray matter | 2

• Contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals + neuroglia

• Covers surface of brain

What are graded potentials

Short distance communication (goes to sensory nerves)

What is action potential

Long distance communication (nerve impulse)

What are ion channels | 4

• In plasma membrane + allow specific ions into cell (move down electrochemical gradient)

• High concentration to low, negative to positive, positive to negative

• As ions move across membrane, they create flow of electric current that can change membrane potential

• 4 types of ion channels in neurons

What are leak channels | 2

• Randomly alternate between open + closed

• K+ usually more prevalent (leakier) than Na+ (membrane more permeable to K+ than Na+)

What are ligand-gated channels | 2

• Opens + closes in response to chemical (ligand) stimulus

• Neurotransmitters, hormones, ions

What are mechnically-gated channels | 2

• Opens + closes in response to mechanical stimulation

• Vibration, touch, pressure, tissue stretching

What are voltage gated channels

Opens in response to change in membrane potential

What is resting membrane potential | 3

• Only ions adjacent to membrane are responsible for potential energy

• Greater difference in charge, greater membrane potential

• Considered to be in polarized state (charged, ready to initiate impulse)

How does graded potential work | 4

• Slight deviation from resting membrane potential

• More polarized = hyperpolarizing (more -ve)

• Less polarized = depolarizing (less -ve)

• Usually die out quickly as charge is lost across membrane

How does action potential work | 3

• Depolarizing phase

• Repolarizing phase

• After-hyperpolarizing phase (doesn’t always occur)

What is a subthreshold stimulus

A weak stimulus that does not bring membrane potential to threshold + will not initiate an action potential

What is the depolarizing phase | 3

• When stimulus causes membrane potential of axon to reach -55mV

• Voltage gated Na+ channels (fast) open into cells to +30mV

• Na+/K+ pumps Na+ out of cell, maintaining low concentration of Na+ in cell

What is the repolarizing phase | 3

• Voltage gated K+ open while Na+ channels close

• Causes membrane potential to drop to -70mV

• No plateau phase

Why no plateau phase for neurons | 2

• Don’t need to contract/alternate/relax atria or ventricles

• Needs to be very quick

What is propagation of action potentials | 5

• Action potential travels from axon towards axon terminals

• Mode of conduction is called propagation (positive feedback)

• Propagate quicker on myelinated axons due to myelin sheath + nodes of ranvier

• Travel quicker in large diameter axon

• Slower in cooler environments

What is a presynaptic neuron

Neuron carrying impulse towards synapse

What is a postsynaptic cell/neuron

Neuron receives impulse + carries it away from synapse (can also be effector that responds to synapse)

What is an electrical synapse | 3

• Action potentials are conducted cell to cell via gap junctions

• Transmission is quicker than chemical (neurotransmitter)

• Action potential can continue to propagate/trigger another action potential w/o release + stimulation of neurotransmitter

What is a gap junction

Open tunnels between two adjacent cells that allow for movement of ions/fluid

What is a chemical synapse | 5

• Presynaptic neuron releases neurotransmitter from axon terminals

• This diffuses into synaptic cleft

• Binds to receptors in plasma membrane of postsynaptic neuron

• Binding produces graded potential called postsynaptic potential

• Postsynaptic potential depolarizes initiates action potential

What is a synaptic cleft

Small space between two neurons that is filled w/interstitial fluid

Where can neurotransmitters be found

Distal ends of neuron + secreted into blood stream

What if they don’t have any neurotransmitter (can’t communicate with other neuron)

Anything left in synaptic cleft gets snatched + used if neuron doesn’t take all

What’s important to note about neurotransmitters

Same neurotransmitter can have a different response in different part of body

What is an agonist

Enhances neurotransmitter effects

What is an antagonist

Blocks the actions of the neurotransmitter

Ventolin (salbutamol) | 3

• Beta2 agonist

• Beat2 receptors in bronchi cause bronchodilation

• Medication binds to beta2 receptors + promotes bronchodilation

Narcan (naloxone) | 3

• Opioid antagonist

• Opioids (narcotics) bind to opioid receptors + cause many effects

• Naloxone binds to receptors (kicking off) the narcotic, decreasing effects