Phys module 2

Afferent neurons (sensory)

carry info TO CNS

Interneurons

completely inside the CNS

Efferent Neurons (motor)

Carry info AWAY from CNS

Glial cells

support and protect neurons

Astrocytes

form blood brain barrier

Ependymal cells

line brain ventricles and spinal canal

Microglia

immune defense cells

Oligodendrocytes

make myelin in CNS

Schwann cells

make myelin in PNS

cell body (soma)

nucleus, control cell activity

dendrites

recieves info, carry signal toward cell body

Axon

send info away from cell body

Axon hillock

where action potential begins

Axon terminals

releases neurotransmitters

myelin sheath

fatty insulation around axon- makes signals travel faster

Node of ranvier

gaps between myelin sections- signal jumps

Membrane potentials (Vm)

difference in charge between inside and outside of cell

Resting membrane potential

-70 mV- inside is more negative than outside

graded potentials

small changes in membrane potential

action potential

electrical signal of a neuron- happens only if threshold is reached

resting potential -70mV

inside of cell more negative

K equilibrium potential

-94 mV

Na equilibrium potential

+60 mV

Resting mV

-70mV

EPSP (Excitatory Postsynaptic Potential)

more positive, closer to threshold- Na enters cell

IPSP (Inhibitory Postsynaptic Potential)

more negative, further from threshold, Cl enters the cell

Action Potential

Occurs when threshold is reached.

Step 1: Depolarization

Voltage-gated sodium channels open.

Na⁺ rushes into cell.

Membrane changes:

-70 mV → +30 mV

Step 2: Repolarization

Sodium channels close.

Potassium channels open.

K⁺ leaves cell.

Membrane becomes negative again.

Step 3: Hyperpolarization

Potassium channels stay open too long.

Membrane becomes more negative than resting level.

Near:

-94 mV

Step 4: Return to Rest

Leak channels and sodium-potassium pumps restore:

-70 mV

Sodium IN

Depolarization

Potassium OUT

Repolarization

Refractory Periods

After an action potential

Absolute Refractory Period

No second action potential possible

Reason: Sodium channels inactive

Relative Refractory Period

Action potential possible

BUT Needs a stronger stimulus

After release, neurotransmitters can:

1. Diffuse away

2. Be broken down by enzymes

3. Be reabsorbed (reuptake)

Acetylcholine (ACh)

• Skeletal muscle contraction

• CNS communication

Catecholamines

Examples:

• Dopamine

• Epinephrine

• Norepinephrine

• Mood

• Alertness

• Stress response

Serotonin

• Sleep

• Emotions

• Mood

Glutamate

Main excitatory neurotransmitter.

GABA

Main inhibitory neurotransmitter.

Central Nervous System (CNS)

• Brain

• Spinal cord

Peripheral Nervous System (PNS)

All nerves outside CNS.

Forebrain ,Cerebrum

• Thinking

• Learning

• Memory

• Voluntary movement

Frontal

• Personality

• Planning

• Movement

• Speech

Parietal

• Touch sensations

• Understanding language

Temporal

• Hearing

• Memory

Occipital

Vision

Insula

• Memory

• Integration

Superior Colliculi

Visual reflexes

Inferior Colliculi

Auditory reflexes

Pons

Connects brain regions

Cerebellum

Balance and coordination

Medulla Oblongata

• Breathing

• Heart rate

• Blood pressure

Sympathetic Division

"Fight or Flight"

Parasympathetic Division

"Rest and Digest"

Photoreceptors

Light

Chemoreceptors

Chemicals

Thermoreceptors

Temperature

Mechanoreceptors

Pressure/stretch

Nociceptors

Pain