Anatomical Terms: Nervous System

• axilla = armpit
• baro = pressure
• cutane = skin
• esthesi = sensation
• extern = outside
• fusi = spindle
• glosso = tongue
• herpes = creeping
• noci = harm
• osmi = a smell, odor
• peripher = outer surface
• phren = diaphragm
• plex, plexus = interwoven
• propri = one’s own
• pudenda = shameful
• ramus = branch
• sciatic = of the hip
• therm = heat
• vag = wondering
• vestibul = a porch

Nerves

• Act as messengers, transmitting and receiving information throughout the body.
• The body contains two main nerve teams: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

Central Nervous System (CNS)

• Functions as the "boss," comprising the brain and spinal cord.
• Responsible for decision-making and issuing commands.

Peripheral Nervous System (PNS)

• Acts as the "delivery team," carrying messages between the body and the CNS.

PNS Divisions

• Sensory Division: Responsible for picking up information related to sensations, such as temperature, pain, and pressure, as well as visceral senses.
• Motor Division: Helps the body move or react, like waving or kicking.

Nerve Job Locations

• Somatic: Controls voluntary movements of body parts like arms and legs ("outside tube").
• Visceral: Controls involuntary functions like heartbeat and digestion ("inside tube").

Sensory System

• General Senses: Feeling temperature or pain anywhere in the body.
• Special Senses: Smell, taste, or sight, each associated with specific organs.

Automatic Nervous System (ANS)

• Operates automatically without conscious control.
• Two Teams:
  • Sympathetic: Action mode, activated when excited, scared, or in need of quick movement.
  • Parasympathetic: Calm mode, activated when relaxing, sleeping, or digesting.

PNS Components

• Sensory Receptors: Detect changes like heat, pain, or sounds and send messages to the brain.
• Nerves & Ganglia: Nerves serve as telephone wires that carry messages, and ganglia are nerve cell body groups that process messages.
• Motor Endings: Connect to muscles and glands, signaling them to move or release substances like sweat or saliva.

Peripheral Sensory Receptors

• Tiny detectors that help you feel and sense things by noticing changes around you and sending messages to your brain.
• Two Main Types:
  • Free Nerve Endings: Simple, spread all over the body, and help you feel touch, pain, pressure, and temperature.
  • Specialized Receptor Cells: Fancy detectors found in certain body parts, like your tongue, eyes, and ears, that primarily help with special senses like taste, sight, hearing, and balance.

Sensory Receptor Classification

• By Function: Whether they help with general feelings or special senses.
• By Structure: Whether they are simple and free or special cells that connect to nerves.

Body Sensors Grouping

• By Location: Where they pick up signals.
• By Detection: What kind of information they sense.

Sensor Locations

• Exteroceptors (Outside Sensors): Near the skin surface, that help you feel things like touch, pressure, pain, and temperature.
• Interoceptors (Inside Sensors): Deep inside the body, in places like the stomach, bladder, and lungs.
• Proprioceptors (Movement Sensors): Live in your muscles, joints, and tendons, that help your brain know where your body parts are and how they are moving.

What Sensors Detect

• Mechanoreceptors (Touch Sensors): Sense pressure, stretching, and vibrations; monitor blood pressure.
• Thermoreceptors (Temperature Sensors): Detect hot or cold.
• Chemoreceptors (Chemical Sensors): Help with smell and taste; check blood chemicals.
• Photoreceptors (Light Sensors): Located in the eyes, and help you see.
• Nociceptors (Pain Sensors): Detect harmful stimuli.

General Sensory Receptors

• Help us feel things like touch, pressure, vibration, stretch, pain, temperature, and body movement.
• Found all over the body and are actually nerve endings that send signals to our brain.
• Two Types:
  • Free Nerve Endings: Simple and spread everywhere.
  • Encapsulated Nerve Endings: Wrapped in a protective covering.
• The same sensor can respond to different types of feelings, and different sensors can react to the same type of touch or pain.

Free Nerve Endings

• Found throughout the body, mostly in skin and underlying tissue.
• Primarily responsible for sensing pain and temperature.
• Some also sense pressure and movement.

Types of Free Nerve Endings

• Pain & Temperature Sensors (Nociceptors & Thermoreceptors): Tell you when something hurts or when it’s too hot or cold; cause emotional reactions.
• Itch Receptors: Located in the skin, and make you feel itchy.
• Light Touch Sensors (Merkel Discs & Hair Follicle Receptors):
  • Merkel Discs: Located in the top layer of skin, and help you feel light touches for a long time.
  • Hair Follicle Receptors: Wrap around hair roots and sense when your hair moves, reacts quickly and then stop noticing the touch.

Encapsulated Nerve Endings

• Touch sensors wrapped in a protective covering.
• Respond to pressure, stretch, or movement.

Types of Encapsulated Nerve Endings

• Tactile Corpuscles (Meissner’s Corpuscles) - Light Touch: Located in soft, sensitive, and hairless skin areas.
• Lamellar Corpuscles (Pacinian Corpuscles) - Deep Pressure & Vibration: Located deep under the skin and in connective tissues, they feel strong pressure and vibrations, but only when they first start.
• Bulbous Corpuscles (Ruffini Endings) - Continuous Pressure: Feel constant pressure.
• Proprioceptors - Body Position & Movement: Help you know where your body parts are, even with your eyes closed and found in muscles, tendons, and joints.

Proprioceptors

• Muscle Spindles: Detect muscle stretch and tell your body how tight or loose a muscle is.
• Tendon Organs: Tell your body when a tendon is stretched too much, preventing injury.
• Joint Kinesthetic Receptors: Help you sense movement in your joints, so you know if your knee is bending or straightening.

Touch Sensors Importance

• Help you feel different types of touches, keep track of your movements, and protect you from harm.

Muscle Knowledge of Stretching

• Muscles stretch when the opposite muscle tightens or when you start to lose balance.
• Muscle spindles inside the muscle act like stretch detectors.

Body Reaction to Stretching

• Quick Reaction: Spinal cord tells the muscle to tighten and stop stretching too much.
• Muscle Tone Control: Cerebellum helps keep muscles tight enough so they don’t stretch too much but stay flexible.

Gamma Motor Neurons

• Act like volume knobs, adjusting how sensitive the muscle spindles are.

Tendon Organs

• They are safety monitors inside your tendons.
• If a muscle pulls too hard on a tendon, these sensors tell the brain that it’s too much.

Joint sensors

• Lamellar Corpuscles: Detect quick movements.
• Bulbous Corpuscles: Sense slow, steady stretching.
• Free Nerve Endings: Might sense pain if a joint is overstretched.
• Tendon-like Sensors: Scientists aren’t sure what they do yet.

Hilton’s Law

• States that if a nerve helps a muscle move a joint, it also helps that joint feel things.

Cranial Nerves

• Twelve special nerves that connect directly to your brain.
• Control important functions like sight, hearing, smell, facial movement, and swallowing.

12 Cranial Nerves & Phrase to Remember Their Names In Order

• To remember their names in order, you can use this fun phrase: “Oh, Oh, Oh, To Touch And Feel Very Good Velvet, AH!"
  • Olfactory (I): Smell
  • Optic (II): Vision
  • Oculomotor (III): Eye movement
  • Trochlear (IV): Eye movement
  • Trigeminal (V): Facial sensation and chewing
  • Abducens (VI): Eye movement
  • Facial (VII): Facial expression and taste
  • Vestibulocochlear (VIII): Hearing and balance
  • Glossopharyngeal (IX): Swallowing and taste
  • Vagus (X): Controls heart, stomach, and voice box
  • Accessory (XI): Moves shoulders and neck
  • Hypoglossal (XII): Tongue movement

Cranial Nerves Control

• Sensing: Functions related to smell, vision, and hearing.
• Movement: Muscle movement in the eyes, neck, and tongue.
• Both: Functions with both sensing and movement.

Spinal Nerves

• Thirty-one pairs of nerves that send messages between the brain and body.
• Emerge from the spinal cord and are named based on exit location from the vertebral column.

Groupings

• 8 pairs of cervical nerves (neck area)
• 12 pairs of thoracic nerves (upper back)
• 5 pairs of lumbar nerves (lower back)
• 5 pairs of sacral nerves (pelvis)
• 1 pair of coccygeal nerves (tailbone)

Spinal Nerves Connection

• Dorsal Root (Back Side): Carries sensory messages into the spinal cord.
• Ventral Root (Front Side): Sends motor messages out to muscles.

Dividing Spinal Nerves

• Dorsal Ramus (Back Branch): Serves the skin and muscles of the back.
• Ventral Ramus (Front Branch): Serves the front of the body and limbs.

Nerve Plexuses

• Tangled highways of nerves formed by some ventral rami to help different body parts work together.

Back Nerves (Dorsal Rami)

• Follow a simple pattern.
  • Connects to back muscles
  • Serves a specific horizontal strip of skin.

Front Nerves (Ventral Rami)

• Thoracic and abdominal wall have a clear nerve pattern but only in the thorax (chest area). Intercostal Nerves:
  • Control the muscles between your ribs.
  • Send signals to the skin on your chest and sides.
  • Help the abdominal muscles below the ribcage.

Subcostal Nerve

• The last intercostal nerve (under the 12th rib)

Nerve Plexus

• A tangled net of nerves where some nerves mix and match to work together.
• Locations: Neck (Cervical Plexus), Shoulders & Arms (Brachial Plexus), Lower Back (Lumbar Plexus), Hips & Legs (Sacral Plexus)

Cervical Plexus (Nerves in the Neck)

• A nerve network under a muscle in your neck that comes from the first four spinal nerves in your neck.
• Skin Sensors
• Muscle Movers
• Phrenic nerve controls your diaphragm, the muscle that helps you breathe.

Brachial Plexus (Nerves for Arms & Hands)

• Complex nerve network that controls your arms and hands, that starts in the neck, runs under your collarbone, and stretches into your armpit.
• Roots (big branches from the spine)
• Trunks (three major bundles)
• Divisions (splitting into front and back parts)
• Cords (final groups of nerve fibers)
• Front Nerves (Yellow in Diagrams): Help you bend your arms and fingers.
• Back Nerves (Green in Diagrams): Help you straighten your arms and fingers.

Nerves to Remember "Really Tired? Drink Coffee!"

• Musculocutaneous Nerve: Bends your elbow.
• Median Nerve: Moves your fingers (except pinky).
• Ulnar Nerve: Moves your pinky and ring finger (also the funny bone nerve!).
• Axillary Nerve: Helps lift your arm.
• Radial Nerve: Straightens your arm and wrist.

Nerve Networks

• Functions:
  • Keep your limbs moving and feeling things.
  • Make sure no single nerve injury causes full paralysis.
  • Help your body bend, straighten, and grip things without you even thinking about it.

Lumbar Plexus (Nerves of the Lower Body)

• Group of nerves in your lower back that help your legs move and feel things.
• Femoral Nerve: Helps you straighten your leg and feel things in the front of your thigh and lower leg.
• Obturator Nerve: Helps you move your inner thigh muscles.

Sacral Plexus (Nerves for Your Legs & Pelvis)

• Nerve group below the lumbar plexus that helps ensures your butt, legs, and pelvis work properly.
• Sciatic Nerve: The biggest and longest nerve in your whole body:
• Tibial Nerve
• Common Fibular Nerve

Sciatic Nerve

• The largest and longest nerve in the body, which extends from the lower back down the legs.
• Composed of two nerves (the tibial and common fibular nerves) wrapped together.

Tibial Nerve

• One of the two branches of the sciatic nerve.
• Runs behind the knee and down the back of your calf.
• Then splits into the medial and lateral plantar nerves.
• Functions as a power cable for the muscles in the back of your lower leg and the bottom of your foot.

Common Fibular Nerve

• Also known as the peroneal nerve, the other branch of the sciatic nerve.
• Runs around the outside of your knee near the fibula.
• Divides into the superficial and deep fibular nerves.
• Crucial for lifting your foot during walking to prevent tripping.

Sacral Plexus Extra Nerves

• Gluteal nerves: Move the gluteal (butt) muscles.
• Pudendal nerve: Controls pelvic area muscles; sometimes numbed during childbirth or surgery.

Dermatome

• An area of skin that gets its feeling from a single spinal nerve.
• In the trunk (chest & back), dermatomes are like horizontal stripes.
• The lumbar nerves (from the lower back) control the front of your leg.
• The sacral nerves (from the tailbone area) control the back of your leg.

Disorders of the Peripheral Nervous System

• Shingles (Herpes Zoster): Virus wakes up in nerves, showing up as a painful, bumpy rash on your skin.
• Migraines: Happen because of a problem with a nerve in your brain called the trigeminal nerve.
• Peripheral Neuropathy: This can happen from getting hurt, using a body part too much, or from illnesses like diabetes.