neural signalling

axon

A long fiber that transmits electrical signals to other cells

-carries them away from cell body

-long and slender, ends in axon terminals

dendrite

DENDRITES DETECT SIGNALS

FUNCTION: receive signals from other neurons or sensory receptors and transmit them to the cell body.

-short, branching extensions

-convert chemical signals into electrical impulses that travel to the cell body

-a single neuron can have thousands of dendrites, forming connections with many other neurons

sensory neuron

intermediate neuron

motor neuron

**their axons can be over a meter long, reaching from your spinal cord to your toes!

speed of nerve impulses

FACTORS:

-myelinated axons

-axon diameter

-temperature

Diameter: larger axons have less resistance to ion flow, allowing impulses to travel faster

Temperature: sodium channel activation is accelerated

giant squid axons

-squid contain giant axons

-escape response when in danger

**500 μm in diameter, and nerve impulse speed of 25m/s

generation of excitatory postsynaptic potential

neuron

A specialized cell in the nervous system that transmits electrical impulses

**transmits info between different parts of body

3 main parts of neuron

1. cell body (soma)

2. axon

3. dendrites

stages of nerve impulse

1. Signal reception: Dendrites receive a signal

2. The cell body processes the signal

3. Conduction: An action potential travels along the axon

4. Transmission: Neurotransmitters are released at the synapse

resting membrane potential

the electrical charge difference across a neuron's membrane when it is NOT transmitting a signal

-70 mV (millivolts) ***negative

-INSIDE is more negative than outside

**"stored energy" waiting to transmit an impulse

**PREPARES for action potentials: the negative charge provides a baseline for rapid depolarization

establishing resting potential

-more positive ions are PUMPED out than brought in

-K⁺ ions leak out through channels (membrane is more permeable to K+)

-large ANIONS inside the cell cannot cross the membrane (- charged)

sodium potassium pump cycle

1. Binding of 3 Na⁺ ions inside the cell

2. ATP hydrolysis and phosphorylation of the pump --> ADP release

3. Release of Na⁺ ions outside the cell

4. Binding of 2 K⁺ ions outside the cell

5. Dephosphorylation and release of K⁺ ions inside

**establishes ion gradient needed for action potential to occur

action potential

A rapid, temporary change in electrical charge that travels along a neuron

ex) When you touch something hot, action potentials travel from your sensory neurons to your brain, alerting you to pull away

action potential stages

1. voltage gated sodium channels open (because threshold potential is reached)

2. sodium ions diffuse into cell

3. depolarization (membrane potential changes from - to +)

**-70 mV to +30 mV

4. voltage gated potassium channels open

5. potassium ions diffuse out of cell

6. repolarization (+ to -)

**+30 mV to -70 mV

7. sodium-potassium pump re-establishes resting potential by actively pumping sodium ions out and potassium ions in

hyperpolarization

too many K⁺ ions leave the neuron

--> membrane potential becomes more negative than the resting potential

--> neuron cannot fire another action potential

REFRACTORY PERIOD

period after an action potential during which a neuron CANNOT fire another action potential

-sodium channels deactivated after action potential

-ensuring one-way transmission

propagation of nerve impulse

action potential in one part of the axon triggers action potential in the next part

nerve impulse

an electrical signal that travels along a neuron, transmitting info

myelin sheath

**Myelin is a multilayer of phospholipids and proteins, which SURROUNDS AXONS

--> acts as an insulating layer for axon, and increases the speed of impulse transmission

--> as high as 100 m/s compared to unmyelinated axons of

0.5-10 ms/s

--> Schwann cells deposit myelin by growing around the axon

**nodes of Ranvier

nodes of Ranvier

-gaps in the myelin sheath

-myelin sheath is not continuous

**nerve impulse jumps from one node ot another

--> SALTATORY CONDUCTION

practical application--> multiple sclerosis

Demyelination leads to slower nerve conduction

synapse

-GAPS between two neurons or a neuron and an effector

-nerve impulses pass from the presynaptic membrane to the postsynaptic membrane

**unidirectionality

**specificity--> neurotransmitters only bind to specific receptors

**plasticity--> synapses can strengthen/weaken over time, crucial for memory

synapse components

-presynaptic membrane

-synaptic cleft (narrow fluid filled gap)

-postsynaptic membrane

types of synapses

-neuron to neuron synapses

-neuromuscular junctions (connect to muscle fibers)

-neuroglandular synapses (neuron to gland)

*also sensory receptor to neuron

neurotransmitter

chemical messengers that transmit signals across synapses

ex) Dopamine: reward, motivation, and movement

ex) serotonin: mood, appetite, sleep

neurotransmitter release stages

1. action potential reaches axon terminal

2. Voltage-gated calcium channels open, allowing calcium ions (Ca²⁺) to enter the neuron

3. Calcium ions trigger the movement of synaptic vesicles toward the presynaptic membrane

4. Synaptic vesicles fuse with the membrane and release neurotransmitters into the synaptic cleft (exocytosis)

5. Neurotransmitters DIFFUSE across the cleft and bind to receptors on the postsynaptic neuron

**electrical signal (action potential) --> chemical signal (neurotransmitter release) --> electrical signal (in the postsynaptic neuron)

depolarization

A reduction in the difference in charge between the inside and outside of a cell membrane

acetylcholine

A neurotransmitter that enables learning and memory and also triggers muscle contraction

EPSP stages

1. neurotransmitter diffuses across synaptic gap

2. binds to receptors in postsynaptic membrane

3. neurotransmitter binds to sodium channel, causing it to open and let sodium ions into the membrane, causing membrane potential to become less negative

4. neurotransmitter is removed by enzyme so sodium channel closes

5. propagation of nerve impulse

threshold potential

The minimum membrane potential that must be reached in order for an action potential to be generated

-55 mV

acetylcholinesterase

the enzyme that breaks down acetylcholine in the synaptic cleft

-prevents continuous stimulation

excitatory postsynaptic potential (EPSP)

A *depolarizing change in the postsynaptic membrane potential* that makes the postsynaptic cell more likely to fire an action potential

**not all neurotransmitter cause this