BIOL 241 Exam 4 Condensed

Peripheral Nervous System Organized into:

• Afferent

  • Going to CNS (Sensory)

• Efferent

  • Going away from CNS (Motor)

CNS Glial Cells (Assholes Owe Everyone Money)

• Astrocytes

  • Maintain blood-brain barrier

• Oligodendrocytes

  • Myelination of CNS axons

• Ependymal cells

  • Help with CSF flow

• Microglia

  • Phagocytes

PNS Glial Cells

• Satellite cells

  • Regulate environment around neurons

• Schwann cells

  • Myelination of PNS axons

Anterograde vs Retrograde

• Anterograde

  • Movement AWAY from cell body (Kinesin)

• Retrograde

  • Movement TOWARDS cell body (Dynein)

Categorization of neurons

1. Structure (relationships of dendrites to the cell body)

   1. Anaxonic neuron (no axon) (only in Brain)

   2. Bipolar neuron (Two axons)

   3. Unipolar neuron (One continuous axon)

   4. Multipolar neuron (>2 dendrite clusters)

2. Function (S.A.M.E principle)(Sensory Afferent, Motor Efferent)

   1. Unipolar neurons

      1. Sensory (afferent)

   2. Bipolar neurons

      1. Sensory (afferent)

   3. Multipolar

      1. Motor (efferent)

Myelin Sheath

• Protein lipoid (70% fat)

• Insulates fibers = myelinated -> rapid impulses

• If non-insulated = non-myelinated -> slow impulses

• Myelin sheath covered areas = white matter

Gated Channels

• Chemically Gated Channel (does not open until a chemical binds to it)(Ach)

• Voltage-gated channel (rely on voltage difference to open)

• Mechanically gated channel (rely on a force being applied to open)

Resting potential

-70mV

• Neurons have more potassium channels than sodium channels

  • Potassium flows out more easily than sodium flows in (creates a larger negative charge inside the cell and positive outside the cell)

  • Cell has a resting "polarity"

• Changes in membrane permeability cause:

  • Graded potentials

  • Action potentials

Graded Potential

• Type of potential that can lead to an action potential (if stimulating)

• Vary in size

• Use chemically-gated channels

Hyperpolarization

• If permeability change sends charge BELOW -70mv (cell get more negative)

• Can happen if positively charged ions leave for a long time

  • Point: inhibits an action potential

Depolarization

• If charge goes ABOVE -70mV

  • i.e. cell get more positive (lose polarity)

• How does this happen?

  • Let positively charged sodium ions enter fast

  • Point: facilitates an action potential

Two type of graded potentials

1. Receptor potential

   1. A 'receptor' is affected (NMJ)

2. Postsynaptic potential

   1. Neurotransmitter -> synapse -> postsynaptic neuron

   2. Graded potentials can be 'additive' to generate AP

Action Potential

• Do not vary in size (all-or-none)

• Use voltage gated channels

• Action potentials do not weaken over distance

• Move down axon in one direction

• Main way neurons send signals

• Main long-distance neural communication

• Main players:

  • Voltage-gated sodium channels (two types)

    • Activation gate (opened to allow ions through)

    • Inactivation gate (close up channel to ions)

  • Voltage-gated potassium channels (one type)

Events leading to an Action Potential

1. Resting state (no ion movement = -70mV)

2. Depolarization  (sodium rushes in, potassium channels remain closed)

   1. Becomes more positive

3. Repolarization (sodium channel closes, potassium channel opens)

   1. Becomes more negative

4. Hyperpolarization (continued outflow of potassium, below -70mV))

Refractory Periods

• Absolute Refractory Period, sodium channels are fully open thus cannot respond to another stimulus.

• Relative Refractory  Period, most sodium channels are resting thus a 2nd stimulus can cause another action potential.

Propagation of APs

• Recap: APs happen in one place then spread

• Spread = propagation

• Two ways to propagate

  1. Continuous (non-myelinated cells) (SLOW)

     • After the Axon Hillock is depolarized, the AP moves down axon by opening the voltage gated sodium channels. As AP moves down each sodium channel is going from -70mV to -55mV, which lets in more sodium each time.

  2. Saltatory (jumping) (Myelin covered cells)

     1. Myelin sheath covered areas do not have channels under them (nodes)

     2. AP jumps from one node to another node (FAST)

Speed of Action Potentials

• Effected by:

  • Myelination

  • Axon diameter

    • Large area = fast flow

    • Large diameter = low resistance

• Group A

  • -large diameter, lots of myelin = FAST

  • Position, balance, delicate touch

• Group B

  • Medium diameter, little myelin = Medium

  • Temperature, touch, pain

• Group C

  • Smallest diameter, non-myelinated = SLOW

Where do Action Potential go?

Synapses

• Presynaptic neuron

  1. AP arrives at axon terminal

  2. Voltage gated calcium channels open and enter axon terminal

  3. Calcium entry causes synaptic vesicles to release neurotransmitter

• Postsynaptic neuron

  1. Neurotransmitter diffuses across the synaptic cleft and binds to receptors on postsynaptic membrane

  2. Ion movement on postsynaptic neuron causes graded potential

  3. Neurotransmitter effects are terminated by reuptake through transport protein, enzymatic degradation, or diffusion away from the synapse.

• In axosomatic synapses

  • Axon terminal to the body of a neuron

• In axodendritic synapses

  • Axon terminal connects to the dendrites of the postsynaptic neuron

• In axoaxonal synapses

  • Axon connects to another axon

Postsynaptic Potentials

• Signals leaving the synapse are graded potentials

• Can be

  • Excitatory

    • Called Excitatory postsynaptic potential (EPSP)

    • If enough build up (reach threshold -55mV) can lead to depolarization and an AP.

  • Inhibitory

    • Called inhibitory postsynaptic potential (IPSP)

    • Leads to hyperpolarization (away from an AP)

• EPSP and IPSP can be 'additive'

  • Summate

    • By time

    • By area

  • Spatial summation: 2 simultaneous stimuli at different locations cause EPSPs that add together

    • Can also cause changes in membrane potential that cancel each other out. (Excitatory +, Inhibitory -)

  • Temporal summation: 2 excitatory stimuli close in time cause EPSPs that add together

Neurotransmitters

• Acetylcholine

  • Type of receptor: Cholinergic

  • Sometimes excitatory (generates an AP)

  • Sometimes inhibitory (blocks an AP)

• Norepinephrine

  • Type of receptor: adrenergic

  • Typically excitatory

Frontal lobe

Personality traits

Precentral gyrus

Primary Motor Cortex

Postcentral gyrus

Primary somatosensory cortex

Parietal lobe

Size and texture differentiation

Occipital lobe

Visual Cortex

Cerebellum

Fine motor movements

Purkinje Cells

Wernicke’s Area

Speech comprehension

Broca’s Area

Speech muscle control

Thalamus

Sensory relay station

Hypothalamus

Temperature regulation

Hormone regulation (regulate pituitary)

H₂O balance

Pituitary Gland

Controls glands via hormones

Controlled by Hypthalamus

Pons

Respiratory centers

Midbrain

• Superior colliculus (visual reflex)

• Inferior colliculus (auditory reflex)

Medulla Oblongata

Respiratory Centers

Cardiovascular centers

Ventricles of the brain

CSF moves through ventricles

Cranial Meninges

• Protect the brain from cranial trauma

• Three layers

  • Dura mater (Outermost)

  • Arachnoid mater (middle)

  • Pia mater (innermost, lines cerebral cortex)

Dura folds

• Folded inner layer of dura mater

• Stabilize and support the brain

• Three largest dura folds:

  • Falx cerebri (separates the hemispheres of the cerebrum)

  • Tentorium cerebelli (separates the cerebellum from cerebrum)

  • Falx cerebelli (separates the two hemispheres of the cerebellum)

Cerebrospinal Fluid (CSF)

• Surround CNS

• Functions:

  • Cushions delicate neural structures

  • Supports brain

  • Transports nutrients, chemical messengers, waste

• Is made by the choroid plexus (circulated by ependymal cells)

  1. Flow through ventricles

  2. To central canal of spinal cord

  3. Into subarachnoid granulations

  4. Arachnoid granulation absorb CSF into venus circulation

• Brainstem checks CSF for CO₂ and pH

Diencephalon

• Integrated sensory information and motor commands

• Thalamus, Hypothalamus, Epithalamus

Basal Nuclei

• Are masses of gray matter encapsulated by white matter

• Are responsible for subconscious activities

• Found in the cerebrum

Cranial nerves (orange orangutans on tree trunk are feeling very good vibrations AH!)

• Orange - Olfactory (1): Smell

• Orangutans - Optic (2): Vision

• On - Oculomotor (3): Eye movements

• Tree - Trochlear (4): Superior oblique eye muscle

• Trunks - Trigeminal (5): Face sensation and chewing

• Are - Abducens (6): lateral rectus

• Feeling - Facial (7): Motor face, saliva, taste

• Very - Vestibulocochlear (8): sound, rotation, gravity

• Good - Glossopharyngeal (9): taste, parotid gland

• Vibrations - Vagus (10): larynx/pharynx muscles, parasympathetic to thoracic and abdominal viscera

• AH! - Accessory (11): Sternocleidomastoid and trapezius

  • Hypoglossal nerve (12): tongue, swallowing

Autonomic Nervous System

• Motor neurons innervate organs

  • Can be stimulatory or inhibitory

• Subconscious control

• Sympathetic (fight or flight)

  • Norepinephrine (NE) neurotransmitter

• Parasympathetic (sit and digest)

  • ACh neurotransmitter

Receptor for Neurotransmitters

• Cholinergic (binds ACh)

  • Nicotinic

    • All postganglionic neurons (sympathetic and parasympathetic) + NMJ

    • Stimulatory (depolarizing)

  • Muscarinic (binds ACh)

    • Organ cells (heart, intestine)

    • Inhibitory or excitatory

    • Speeds up heart

    • Slows down intestines

• Adrenergic Receptors (binds NE)

  • Alpha

    • Alpha 1: blood vessel constriction

    • Alpha 2: pupil dilation

  • Beta:

    • Beta 1: heart (1 heart)

    • Beta 2: lungs (2 lungs)

Position of ganglia differs

• Parasympathetic

  • Close to target organ

• Sympathetic

  • Close to spinal cord

Dual Innervation

Both division at once: Autonomic plexuses (nerve network)

Sympathetic postganglionic fibers

 AND

parasympathetic preganglionic fibers

• Ex. Cardiac Plexus, Celiac Plexus

• You have more control by having both branches innervate a structure.

• Ex. Heart Dual Innervation

  • Opposing effects on HR

    • Parasympathetic

      • ACh -> increases hyperpolarization -> slows heart rate

    • Sympathetic

      • NE -> increases depolarization -> increase heart rate

  • Typically both neurotransmitters are dumped out continuously

Purkinje cell

• In cerebellar cortex

• Output neurons

Pyramidal cells

• Cerebral cortex

• Motor output

Schwann cells

Schwann cells wrap around axon to form myelin

Nerve CT Layers

• Epineurium (Entire nerve)

• Perineurium (Each fascicle)

• Endoneurium (individual axon)