Exam 5 part 2: Neuronal Physiology

Threshold potential

• V_m to open Na⁺ channels

• Stimulus (changing green line)

  • Was GP (depolarization)

    • Stimulatory stimulus

  • Now Na⁺ influx

Sub-threshold potential

No Action potential

Action potential amplitude

• independent of original GP

• analogy to gun + trigger

• no change in size (not equal to GP trait)

What is a limitation for AP

Distance

AP propagation

• no AP movement

• AP, triggers AP₂, etc

AP propagation: increase in distance (AP₂₀₀, AP_200k)

• no change in size (no decrease)

• problem solved

AP propagation: unidirectional (speed)

• how does it not go backwards?

1) Hyper-polarized

2) Na⁺ inactivated

• Those 2 prevent backwards AP

AP propagation: impacts of myelin

1) Aids GP and block AP

2) Increase in conduction velocity (GP faster than multiple AP)

3) Saltatory conduction (bad name!)

Why does myelin aid GP and block AP

• less of a distance problem

  • b/c AP takes 1-2 ms → lots of sections to cover

impacts of myelin: Saltatory conduction

• APs only at nodes

• “jump” via GP under myelin

  • (More so burrowing*

Basis: synapse- postsynaptic neuron: two types of input (likelihood of AP occuring)

EPSP: excitatory (stimulatory) = depolarizing

IPSP: inhibitory = hyperpolarizing

• psp = pre synaptic potential

Post synaptic neuron: two types of summations

1) Temporal

• same pre-synaptic impacting post-synaptic close in time

2) Spatial

• different pre’s, at same time (close in space)

Increase in # of synapses

increased combos of summations = very quickly a highly complex system

Synapse strength: Presynaptic factors

1) Ca²⁺ availability in IF (needed for exocytosis of NT)

• typically non-existent in cell’s cytosol

2) NT availability (messenger)

3) Receptor availability

• Receptors pre-synaptic needed to active

4) V_m (impacts Ca⁺ entry)

• Voltage-gated channels

Postsynpatic factors

• Receptor availability

• V_m (impacts reaching TP)

• Other presynaptic inputs

  • ex/ summation

Brainstem

Basic life functions

• medulla, pons, midbrain

• Functions

  • Respiration

  • circulation

  • digestion (swallowing)

Cerebellum

“muscle memory”

Functions:

• balance/coordination

• muscle tone

Diencephalon

1) Thalamus

2) Hypothalamus

Thamalus

Major relay station

• motor control

• sensation (very crude)

  • Vision (movement, not color)

  • Sound (loud noises)

Hypothalamus

• homeostatic regulation

• links the NS and endocrine system