The Neuron is the basic unit of the nervous system. Commonly referred to as a “nerve.”

Nervous System

**Axon terminals

**Nodes of Ranvier

**Schwann cells

**axon

**Dendrites

**Cell body

**Nucleus

The neurons connect the brain to the entire body and its parts. But the neurons do not touch each other!

**Synaptic cleft or gap is the gap between neurons

• Substance• P

Pain• Substance• P

Receptor• Substance• P

Receptor

Messages are sent from one neuron to the next via chemicals called Neurotransmitters. In this case, the message of pain is being transmitted by a neurotransmitter called “Substance P” **A Neurotransmitter is a chemical released by 1 neuron that has an effect on another neuron

Each Neuron has specific receptors for each neurotransmitter, which then relay the message through the axon of the neuron toward the axon terminal.

*During a nerve impulse, there is a reversal of polarity in the axon

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The Dendrites are the receiving end of the neuron and the axon terminal is the sending end

Dendrite(s)Receives information, carries to cell body

Cell body contains nucleus

***Axon is cell extension (conducts action potential)Transmits information away from cell body to the axon terminal

Cell has only 1 axon

If the message is being sent to a muscle to contract, the last axon terminal will end at a motor end plate of the target muscle/muscles. That message will stimulate the muscle to contract… This happens in a millisecond. That’s fast!

*Axons are covered with a lipid layer called the myelin sheath

***Myelin sheath increases the speed of nerve impulses or action potential

◦ Resting cell membrane is more permeable to potassium ions than sodium ions

◦ More positive charges leave the cell than enter it

◦ ***Sodium ions are more concentrated outside the cell

◦ *Potassium ions are more concentrated inside the cell

◦ *The inside of the cell is negatively charged◦ The outside of the cell is positively charged

**Resting Potential

*Visual information is processed by the occipital lobe in the brain

**Cerebral cortex is the outer layer of the cerebrum

*Cerebellum smoothes and coordinates movements like walking and running

*The brain stem connects the cerebral hemisphere with the cerebellum

***Brain

**Diencephalon*Contain important relay centersMade up of the thalamus and hypothalamus

Like an interstate, it carries information back and forth

The outer ◦ Composed of a white matter (insulates)

The inner◦ Composed of **gray matter made up of

Dendrites, axons, cell bodies but **does not include motor neurons

**Spinal Cord

1. The Central Nervous System (CNS) a) Brain (includes cranial neurons-so that lobes of

the brain can talk to each other)

b) Spinal Cord (includes spinal neurons, which relay

messages from the body’s extremities and internal organs to the spinal cord)

There are three parts to the nervous system:

*The Central Nervous System (CNS) *Is made up of the Brain and the spinal

cord

There are three parts to the nervous system

*This connects the brain and spinal cord to the rest of the body

**Sensory receptor is a neuron that detects stimuli

* Two principal components of the peripheral nervous system are :1. *Sensory2. *Motor **Includes Spinal Nerves (spinal cord =

CNS)

2. ***The Peripheral Nervous System (PNS)

*Somatic Nervous system ◦part of the PNS◦*Contains neurons that control skeletal

muscle **Afferent Neurons

◦ Collect information from the body and transmit it toward the CNS

◦ Includes neurons in the ear, **eyes (optic nerve) Efferent Neurons

◦ Transmit information away from the CNS. **Included in the PNS:

◦ Somatic system◦ Autonomic system◦ Sensory system

Involuntary muscle contractions in digestive and cardiovascular systems.

This happens ”automatically!” You do not have to think about it. **A spinal reflex is an example of an

involuntary movement

3. **Autonomic Nervous System

Autonomic nervous system has two parts:1. *Sympathetic division

*In times of stress it is the sympathetic nervous system is activated

2. Parasympathetic division

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SENSORY SYSTEM Sense organs

Eyes, ears, nose, mouth, and skin

**HEARING AND BALANCEAuditory canal

Connect to external ear with tympanic membrane (eardrum)

**Tympanic membrane**Vibrates in response to sound

waves Eustachian tube

Opening to throatEqualizes pressure on both sides of

the tympanic membrane

*CochleaInner ear

*Coiled tube essential to hearing

**Contain hair cells are important for hearing and balance

*Semicircular canals*Essential for balance

**AUDITORY INFORMATION

**Travels to the brain stem thalamus cerebral cortex

VISION Retina

Light sensitive inner layer of eye Receives image formed by lens Transmits them through optic nerve to the brain

Pupil Opening at center of iris Controls amount of light that enters the eye

Iris Colored circular part of eye

Lens Convex transparent structure in the eye that focuses light

on retina Rods

Detects dim light Plays major role in non-color and night vision

Cones Distinguishes color Sensitive to bright light

*Photoreceptors in the retina convert light energy to electrical signals

TASTE AND SMELL Pressure and Temperature