Nervous System Notes

Levels of Organization

• Organ System: Two or more organs working together to perform a specific bodily function (e.g., the digestive system).
• Organ: A structure typically composed of several tissue types that form a functional unit (e.g., the stomach).
• Tissue: A group of similar cells that perform a specific function (e.g., epithelial tissue).
• Cell: The smallest unit of life (e.g., red blood cell, epithelial cell, nerve cell).

Functions of the Nervous System

• Control all body activities.
• Respond and adapt to changes that happen both inside and outside the body (e.g., pain, temperature, pregnancy).

Neurons

• The cells of the nervous system (NS).

  • Dendrites: Receive information.
  • Body (soma): Processes information; contains the nucleus and other organelles.
  • Axon: Conducts signals.
  • Myelin sheath: Serves as insulation for the axon.
  • Axon terminals: Transmit signals to other neurons or other cells.

• Neurons Use Electricity to Transmit Signals

• Details on Neuron Components:

  • Dendrites: Extensions that pick up messages and send them to the cell body.
  • Axon: Conducts nerve impulses away from the cell body to other neurons.
  • Myelin Sheath: Covers and protects the axon.

• Axon Length:

  • Varies depending on the location; some extend from the spinal cord to the toes (about 1 meter long).

• Nerves:

  • Axons of neurons bundled together.

• Axon Terminals:

  • Send signals to other neurons or other types of cells.

Nerves

• Definition: Bundle of axons.
• Many neurons bundled together inside a connective tissue sheath.
  • Includes the axon of one neuron, myelin sheath, and unsheathed nodes.
• Components: Brain, spinal cord, nerves.

Anatomical Divisions of the Nervous System

Central Nervous System (CNS)

• Comprises the brain and spinal cord.
• Controls the body.

Peripheral Nervous System (PNS)

• Contains all the nerves that branch off the brain and spinal cord.
• Picks up sensory stimuli and transmits signals from the CNS to muscles and glands.

Central Nervous System (CNS) Breakdown

• Brain
• Spinal Cord

Peripheral Nervous System (PNS) Breakdown

• Cranial Nerves
• Spinal Nerves
• Ganglia: Outside CNS.

Central Nervous System (CNS) - Brain Regions

• Cerebrum
• Cerebellum
• Brain Stem
• The brain is divided into specialized regions that may or may not interact with each other to produce a given action.

Central Nervous System (CNS) - Lobes and Functions

• Frontal Lobe:
  • Speech & language.
  • Problem-solving.
  • Social behavior.
  • Taste.
  • Movement.
  • Personality.
  • Judgement.
  • Decision making.
  • Development ends at approximately age 25.
• Parietal Lobe:
  • Pain.
  • Touch.
  • Pressure.
  • Development ends at approximately age 14-16.
• Temporal Lobe:
  • Hearing and listening.
  • Development ends at approximately age 11-13.
• Occipital Lobe:
  • Vision.
  • Development ends at approximately age 6.

Central Nervous System (CNS) - Lobe Details

• Frontal Lobe: Governs muscle movement, motor skills, and cognitive functions; finishes developing after the teenage years.
• Occipital Lobe: Processes visual cues.
• Parietal Lobe: Responsible for touch, pain, taste, and pressure.
• Temporal Lobe: Helps sort out auditory information.

Peripheral Nervous System (PNS)

Somatic Nervous System (Motor NS)

• Controls skeletal muscle
• Relays signals from joints and skin

Autonomic Nervous System

• Controls internal organs and glands
• Relays signals about internal organs

Parasympathetic Division

• Encourages housekeeping tasks (digestion, breathing, etc.)

Sympathetic Division

• Prepares the body for fight or flight (stress)

Peripheral Nervous System (PNS) - Autonomic NS

Parasympathetic

• Active during times of rest and normal conditions.
• Decreases heart rate and stimulates digestion.
• Helps you rest and digest.

Sympathetic

• Prepares the body for stressful or energetic activity.

• Supplies more blood to the brain, heart, and muscles by reducing blood flow to the skin and digestive system.

• The sympathetic and parasympathetic divisions of the nervous system have opposite functions in regulating other organs.

Peripheral Nervous System (PNS) - Sympathetic vs. Parasympathetic Effects

Eyes

• Sympathetic: Widens pupils
• Parasympathetic: Narrows pupils

Salivary Glands

• Sympathetic: Decreases salivation
• Parasympathetic: Increases salivation

Heart

• Sympathetic: Increases heart rate
• Parasympathetic: Decreases heart rate

Airways

• Sympathetic: Widens airways
• Parasympathetic: Constricts airways

Stomach

• Sympathetic: Slows secretions and movements
• Parasympathetic: Increases secretions and movements

Liver, Pancreas

• Sympathetic: Slows secretions to digestive tract
• Parasympathetic: Increases secretions to digestive tract

Adrenal Gland

• Sympathetic: Increases secretion
• Parasympathetic: Decreases secretion

Small Intestine, Large Intestine

• Sympathetic: Slows secretions and movements
• Parasympathetic: Increases secretions and movements

Bladder

• Sympathetic: Inhibits urination
• Parasympathetic: Stimulates urination

Genitals

• Sympathetic: Promotes ejaculation
• Parasympathetic: Promotes erection, lubrication

The Nervous System - Summary

Central Nervous System (CNS)

• Brain
• Spinal Cord

Peripheral Nervous System (PNS)

• Motor and Sensory Neurons (nerves)

Somatic Nervous System

• Voluntary movements via skeletal muscles

Autonomic Nervous System

• Organs, smooth muscles

#### Sympathetic