General Biology II: Nervous System & Action Potentials

Cnidarians

Known as the simplest animals with nervous system with no central control and just nerve net (still have neurons though)

Echinoderms (sea star)

These have some sort simple control with the nerve ring signaling muscles (neurons)

Bilateria

With lots of variation with simple CNS, brain, eyespot, ladder type nervous system and a more complex brain/ganglia

Vertebrates

Contains a CNS and PNS

Central Nervous System (CNS)

Brain and spinal cord

Peripheral nervous system (PNS)

Nerves and Ganglia

Glial Cells

These type of cells provide support for the CNS

Microglia

Scavenge dead cell & protect brain from microorganisms

Astrocytes

Help with blood & nutrient flow to neurons which will form that blood brain barrier

Ependymal

These help produce, move and support cerebrospinal fluid

Oligodendrocytes

Part of the CNS that can myelinate several axons

Schwaan Cells

Only glial cell part of PNS where can myelinate one axon

Myelin

Insulation that prevents loss of signal down the axon

Radial Glial

Form tracks in developing embryo which leads to glial cell types in adults that may aid in synaptic plasticity in adults

Brain

Central control organ that contains ventricles, grey matter that surrounds white mater and cerebrospinal fluid

Spinal cord

The link between brain and the rest of the nerve system that has a small central canal with fluid, grey matter surrounding canal, and white matter will surround grey. This will transport impulse from brain to brain and is in charge of reflex actions (knee jerk reaction)

Interneurons

Relayed to neuron and talks to PNS

Sensory Receptors

Will transmit info to and from CNS that can detect either visual or auditory stimuli

Cranial Nerve

Hind part of brain → head and upper body

Spinal Nerve

Origin in spinal cord in the entire body

Afferent (Visceral or Somatic) → Interneurons to CNS → Efferent → Autonomic (Parasympathetic, sympathetic, enteric) or motor system (Skeletal muscle)

SEQ how PNS sends signals

Afferent

These act as receptors, NOT EFFECTORS can either be visceral or somatic

Visceral

The input for afferent that you are not aware of

Somatic

The input where you are aware

Motor System

This system are efferent neurons that help with skeletal muscle and are voluntary/reflexes with NO receptors

Autonomic nervous system

Efferent neurons that involves glands, heart, smooth muscle, and control what we are not aware of

Enteric

Digestive → helps maintain pH for small intestine and moving food in digestion

Parasympathetic

Rest & Digest (can help with giving more blood flow as digesting/slows breathing & heart rate)

Sympathetic

Fight or Flight (increases heart rate & breathing)

Forebrain, midbrain, hindbrain

What are the 3 main regions of the brain?

Grey Matter

This is contained in cell bodies and dendrites in the brain structure

Corpus Callosum

Thick band of axons that allow for communication between sides

Cerebrum

Two central hemispheres + their cortices (grey and white matter) that is involved in voluntary movement, learning, emotion, memory, sensory which is developed from the neural tube

Cerebral Cortex

Outer grey matter layer

Cerebellum

Coordination of movement/balance, which helps remembering learning skills

Thalamus

Your main input area that routes info to correct area of cerebrum

Midbrain

This will receive, integrates, routes sensory info

Pons

Respiratory and sleep centers

Medulla

Involved in respiration, heartbeat, blood pressure, swallowing, coughing and vomiting

Brain Stem

Involved in regulation of the body mostly, and seperated into 3 portions: Midbrain, Pons, and Medulla

Neuron

Your nerve cell that conducts messages as electrical signals → signal is unidirectional

Cell Body

Contains organelles in neurons

Dendrites

Will receive stimulus and send to cell

Axon

Transmits stimulus to effector (muscle gland) or another nerve

Axon Hillock

Signals generated here, base of axon

Synaptic Terminals

At end of branches of neurons

Ion Channels

These use faciliated diffusion which will move down the concetration gradient

Will be closed until opened by a key → that key is change in voltage

What does it mean when ion channels are gated → voltage gated by that meaning?

Sodium Potassium Pump

This will be aganist the concentration gradient or ignores it by using ATP→ 3 Na⁺ out and 2 K⁺ in

Resting Potential

Non-stimulated cell is at rest → at -70mV and ion channels are closed → but K⁺ channels are always slightly opened due to leaking and pump is opened.

Changing the voltage or cross the signal threshold → a stimulus that can either be sound, sight, or touch

How can we use the resting potential to send a signal?

Depolarization

When most Na⁺ channels are opened which will reach threshold (-55mV)

Rising Phase

Many Na⁺ channels are opened where they spike to 35mV to action potential

Falling Phase

Many K⁺ channels are opened and are flowed out

Refractory Period

Wait period for the Na⁺ channels to reset

Hyperpolarization/Undershoot

When some K⁺ channels remain open and it makes it harder to send a signal, where the channels will close and get back to Resting Potential

Unmyelinated axons (gray matter) glial

These undergo continuous conduction

Saltatory propagation

Jumping conduction of signal

Nodes of ranvier

These are your unmyelinated segments (no myelin) where impulse will jump from node to node

Platyhelminthes

Simple CNS, brain, eyespot, ladder type nervous system

Annelid/arthropods

More complex that contains a brain/ganglia