BIO 2 Nervous systems and neurons functions

neurons (nervous system)

• basic unit of a nervous system

• They are excitable!

• Can send and receive electrical signals

• Do not commonly divide in adult humans

Glial cells (nervous system)

• “Life support” for neurons

• do not send electrical signals

• actively divide

motor neurons (type of neuron)

control muscles and glands

Sensory neurons (type of neuron)

detect environmental stimuli and translate these into electrical signals

Interneurons (type of neuron)

integrate, store, and process information

Anatomy of a neuron

• Dendrites receive information (finger-like things connected to thing that looks like the palm of a hand)

• Cell body processes info from dendrites (palm-like thing)

An axon conducts electrical signals away from the cell body (arm-like thing)

Signals are communicated to other neurons at synapses

Central Nervous System (CNS)

brain and spinal cord

• Brain

1. Complex processing and responses

2. Memory

3. Thoughts

4. Emotions

• Spinal cord

1. “Interstate” of the nervous system

2. Limited processing

3. Reflexes!

Hindbrain

• regulates automatic functions like breathing and heart rate

• Responsible for many automatic, subconscious processes

• The medulla and pons (brainstem) control breathing rate and pattern, heart rate, and blood pressure

• The cerebellum coordinates routine movements and plays a role in “muscle memory”

Forebrain

• Cerebrum – higher thought, consciousness, memory, and processing

1. Separated into 2 hemispheres (right and left)

2. Each hemisphere consists of 4 lobes

• Hypothalamus – homeostasis and hormones

Frontal lobe (cerebrum)

Higher thought, voluntary muscle movement, and personality

parietal lobe (cerebrum)

Sensory interpretation

occipital lobe (cerebrum)

Visual processing

temporal lobe (cerebrum)

Auditory processing, pattern recognition, and naming

midbrain

transmits sensory and motor information to/from forebrain

Peripheral nervous system (PNS)

carries information to/from CNS to the body; composed of two systems (autonomic and somatic)

Somatic:

• Conscious control (though spinal reflexes are automatic)

• Sends signals to skeletal muscles for movement

Autonomic:

• Involuntary control of glands, smooth muscle, and heart muscle

• Sympathetic nervous system

• Parasympathetic nervous system

Neuron Function

• What makes neurons “excitable”?

1. “Neurons are like batteries.” They hold a charge and can create currents when ions move across their membranes.

2. Diffusion is critical for neuron function and relies primarily on movement of sodium and potassium

Neurons are little batteries

• At rest, the membrane of a neuron is

1. Positive outside

2. Negative inside

• A sodium-potassium pump (uses ATP) and channels (allow diffusion) create this difference

• The difference in charges (from inside to outside) when a neuron is inactive is called the resting potential (-60 millivolts or -60 mV)

• When a neuron is stimulated, the balance briefly goes up and then back down

Key points about resting neurons

1. There is a slight negative charge inside the cell.

2. Potassium (K+) more concentrated inside

3. Sodium (Na+) more concentrated outside

Thus, in a resting neuron, there are gradients of both Na+ and K+. When sodium or potassium channel proteins open, the ions diffuse down their gradients.

If a neuron is excited and becomes less negative inside, it does this by moving

positive ions

If you a resting neuron opened sodium channels in the cell membrane, _______ would _______ the cell by diffusion.

Sodium; enter

Action potential

• Action potentials travel through the axon

• “Signals” that travel down a neuron if neuron is stimulated.

• Action potentials always travel AWAY from the cell body.

• Action potentials rely on diffusion of Na+ and K+ across a

membrane.

1. We call this an action potential because this brief reversal in charge moves down the axon

Sodium and potassium summary

1. Sodium channels open first, allowing sodium to diffuse inward and raising membrane potential.

2. Potassium channels open shortly afterward, and potassium leaves the cell to return voltage back to resting potential.

3. The original Na + and K + concentrations inside and outside the cells are restored by the active transport of the ions by the sodium potassium pump (uses ATP).

How action potential travel

1. Threshold is reached at one point in an axon.

2. Na+ channels open in this area, and more Na+ enters

3. Areas further down the axon reach threshold, and Na+ open.

• This pattern results in a “wave” of voltage changes that moves down an axon toward the synapses.

PREsynaptic (axon)

(“before the synapse”) neuron (the cell body area)

POSTsynaptic (dendrites)

(“after the synapse”) neuron

How messages pass through the synapses

• chemical transmission between neurons

1. Neurotransmitters are released into cleft by the presynaptic neuron

• Axons communicate with dendrites communicate across a gap (synaptic cleft)

If a neurotransmitter opened a sodium channel in a post-synaptic cell, would the neuron be MORE or LESS likely to make an action potential?

More. Voltage would be closer to threshold.

cell body (neuron function)

• cell body “adds up” signals from all dendrites

• If the membrane potential is more positive than a threshold, an action potential is created