Nervous tissue

Somatic sensory

Carries sensory information from the skin, skeletal muscles, joints, and special senses to the CNS.

visceral sensory

Carries sensory information from internal organs (viscera) such as the stomach, heart, lungs, and bladder

somatic motor

Controls voluntary movement by sending signals from the CNS to skeletal muscles

visceral motor

Controls involuntary movement by sending signals to:

• Smooth muscle

• Cardiac muscle

• Glands

(Also called the autonomic nervous system

What is the function of dendrites?

Receive incoming signals from other neurons or receptors.

What is the function of the cell body (soma)?

Contains the nucleus and carries out the neuron's metabolic activities.

What is the axon hillock?

The site where action potentials begin if threshold is reached.

What is the function of the axon?

Carries action potentials away from the cell body.

What is the myelin sheath?

insulates the axon and speeds nerve impulse conduction.

What are Nodes of Ranvier?

Gaps in the myelin where electrical impulses can jump from node to node

What is the function of axon terminals (synaptic end bulbs)?

Release neurotransmitters into the synapse.

types of glial cells in CNS

astrocytes, oligodendrocytes, microglia, ependymal cells

types of glial cells in PNS

schwann cells, satellite cells

Astrocytes

Support neurons, help maintain the blood-brain barrier, regulate extracellular ions (especially K+).

oligodendrocytes

Produce myelin in the CNS

microglia

Immune cells of the CNS; remove pathogens and debris

ependymal cells

Line brain ventricles and circulate cerebrospinal fluid (CSF)

Schwann cells

Produce myelin in the PNS.

satellite cells

supportive, non-neuronal cells located exclusively in the PNS

types of neurons

afferent, efferent, interneuron

afferent

Sensory neuron that carries information to the CNS

efferent neuron

Motor neuron that carries commands away from the CNS.

interneuron

Found entirely within the CNS; processes incoming sensory data before coordinating the appropriate motor response.

unipolar neuron

One process; mostly sensory neurons in the PNS.

bipolar neuron

One axon and one dendrite; found in the retina, inner ear, and olfactory epithelium

multipolar neuron

One axon and many dendrites; most common neuron type; usually motor neurons and interneurons

CNS

Brain and spinal cord.

PNS

all nerves outside the CNS

PNS sensory (afferent) division

Carries information to the CNS

PNS (motor) division

Carries commands from the CNS.

somatic nervous system

voluntary control of skeletal muscles

autonomic nervous system

Involuntary control of smooth muscle, cardiac muscle, and glands.

sympathetic division

Fight or flight.

parasympathetic division

Rest and digest.

Action potential

rapid, temporary electrical impulse that travels along a cell membrane

resting membrane potential

-70mV

what is threshold

-55mV

What happens during depolarization?

Voltage-gated Na⁺ channels open, Na⁺ enters the cell.

• Na⁺ rushes into the neuron.

• Membrane potential becomes more positive.

• Voltage rises from -55 mV to about +30 mV.

Peak of action potential?

About +30 mV.

• Na⁺ channels inactivate (close).

• Voltage-gated K⁺ channels open.

What happens during repolarization?

Voltage-gated K⁺ channels open, K⁺ leaves the cell.

• The membrane potential becomes negative again.

• Returns toward -70 mV.

What is hyperpolarization?

K⁺ channels stay open slightly longer, making the membrane more negative than resting.

How is resting potential restored?

Leak channels and the Na⁺/K⁺ pump

What does the sodium-potassium pump do?

Uses ATP to move:

• 3 Na⁺ out

• 2 K⁺ in

Why is the Na⁺/K⁺ pump important?

Maintains ion gradients and resting membrane potential.

What does sodium do during an action potential?

Rushes into the cell causing depolarization.

What does potassium do?

Leaves the cell causing repolarization.

What is a graded potential?

Local change in membrane potential.

• Variable strength

• Can increase or decrease

• Occurs on dendrites/cell body

differences in graded potential and action potential

Graded Potential	Action Potential
Variable strength	All-or-none
Can weaken	Does not weaken
Local	Travels entire axon
Dendrites & soma	Axon

What is saltatory conduction?

Action potential "jumps" from one Node of Ranvier to the next on a myelinated axon

Why is saltatory conduction faster?

Only the nodes depolarize instead of the entire axon.

Absolute refractory period

No second action potential can occur regardless of stimulus.

Relative refractory period

Another action potential is possible, but only with a stronger-than-normal stimulus

What is a neurotransmitter?

Chemical messenger released by neurons to communicate with another cell.

What triggers neurotransmitter release?

Ca²⁺ enters the axon terminal through voltage-gated calcium channels

What neurotransmitter is released at the neuromuscular junction?

Acetylcholine (ACh)

Functions of acetylcholine

• Skeletal muscle contraction

• Parasympathetic nervous system

• Learning and memory

Glutamate

major excitatory neurotransmitter

GABA

major inhibitory neurotransmitter

Glycine

Inhibitory neurotransmitter in the spinal cord.

Dopamine

Movement, motivation, reward

Norepinephrine

Alertness and sympathetic responses

serotonin

Mood, sleep, appetite

What is a cholinergic neuron?

Releases acetylcholine (ACh)

What is an adrenergic neuron?

Releases norepinephrine (NE) (or responds to epinephrine).

Action potential sequence

1. Resting membrane potential = -70 mV

2. Stimulus opens Na⁺ channels

3. Threshold reached (-55 mV)

4. Voltage-gated Na⁺ channels open

5. Na⁺ enters → Depolarization

6. Membrane reaches +30 mV

7. Na⁺ channels inactivate

8. Voltage-gated K⁺ channels open

9. K⁺ leaves → Repolarization

10. K⁺ continues leaving → Hyperpolarization

11. K⁺ channels close

12. Na⁺/K⁺ pump restores resting membrane potential

13. Action potential continues down the axon

14. Ca²⁺ enters the axon terminal → neurotransmitter release

What happens first during an action potential?

A stimulus causes depolarization.

• Ligand-gated or mechanically gated Na⁺ channels open.

• Na⁺ enters the cell.

• If the membrane reaches -55 mV (threshold), an action potential begins

How does the action potential end?

When it reaches the axon terminals, voltage-gated Ca²⁺ channels open, causing neurotransmitters to be released into the synapse

voltage gated channels

open in response to cells membrane potential

ligand gated channel

opens when certain neurotransmitters bind to receptors